Tailoring non-equilibrium pathways for the selective formation of intermediate compounds

Abstract

Disclosed are processes for selectively converting a feedstock comprising a reactant and an oxidant to a target intermediate by selectively generating a transiently-formed target intermediate in a reaction chamber from the reactant, and actively removing the transiently-formed target intermediate from the reaction chamber, wherein the rate that the target intermediate is removed from the reaction chamber is greater than or equal to the rate that the target intermediate is consumed. Also described are systems comprising a reaction chamber configured to receive a feedstock and selectively generate a transiently-formed target intermediate from the reactant; and a species recovery unit, said recovery unit being operatively coupled to the reaction chamber and configured to actively remove the target intermediate from the reaction chamber, such that a rate that the target intermediate is removed from the reaction chamber is greater than or equal to a rate that the target intermediate is consumed.

Description

[0001] TAILORING NON-EQUILIBRIUM PATHWAYS FOR THE SELECTIVE FORMATION OF INTERMEDIATE COMPOUNDS

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims priority to U.S. Provisional Patent Application No. 63 / 585,408, filed September 26, 2023, which is incorporated herein by reference in its entirety.

[0004] BACKGROUND

[0005] Methane, which constitutes 70-90% of natural gas, is a potent greenhouse gas that is emitted by various sources including agricultural industries, wetlands, coal mining, and oil and gas systems. The flaring of methane alone is anticipated to contribute 22% of global CO2 emissions, emphasizing the urgent need for enabling distributed methane utilization to produce valuable chemicals like methanol. The traditional two-step methane-to-methanol conversion process involves intricate syngas (synthesis gas) production techniques. These techniques result in suboptimal syngas composition, limiting methanol production. Insufficient conversion to methanol not only results in the production of CO2 and methane emissions, which undermines the environmental objectives, but it also hinders the goal of distributed methane utilization aimed at optimal resource utilization. Moreover, the high pressure (> 30 bars), temperature (~ 1000 K), and carbon footprint (~ 400 g CO2 eq / kg MeOH) of this process render it unsuitable for distributed methane utilization.

[0006] Direct methane to methanol (DMtM) conversion in a single-step shows promise by bypassing syngas production. Combining DMtM with renewable energy input under atmospheric conditions enables distributed methane utilization with near-zero carbon footprint. However, over-oxidation of methanol results in a decrease in selectivity to methanol at higher methane conversions, which impedes high methanol yield production. A number of other transiently-formed compounds are similarly hindered by this selectively - conversion limit. Thus, mechanisms for exceeding this barrier would be advantageous for the recovery of a high yield of a targeted compound and the facilitation of, for example, distributed methane utilization.

[0007] SUMMARY

[0008] In various aspects, disclosed herein is a process for selectively converting a feedstock (e.g., a gaseous feedstock) comprising a reactant (e.g., a hydrocarbon) and an oxidant to a target intermediate, the process comprising: selectively generating in a reaction chamber a transiently-formed target intermediate from the reactant; and actively removing the transiently-formed target intermediate from the reaction chamber, wherein a rate that the transiently-formed target intermediate is removed from the reaction chamber is greater than or equal to a rate that the transiently-formed target intermediate is consumed.

[0009] In some aspects, the transiently-formed target intermediate is selectively generated by contacting the feedstock with a plasma (e.g., a nanosecond pulsed plasma) in the reaction chamber under thermal non-equilibrium conditions to produce a vibrationally excited precursor or radical, and wherein the vibrationally excited precursor or radical is selective for forming the transiently-formed target intermediate. In some aspects, the vibrationally excited precursor has a characteristic vibrational temperature greater than a temperature of the reactant. In some aspects, the plasma is generated using a reduced electric field (E / N) of from 1 to 100 Td (e.g., from 1 to 50 Td, from 1 to 40 Td, from 1 to 30 Td, from 1 to 20 Td, or from 1 to 10 Td).

[0010] In some aspects, the reaction chamber further comprises an inert gas (e.g., argon, helium, neon, krypton, and / or xenon).

[0011] In some aspects, the transiently-formed target intermediate is formed from the feedstock without the use of a catalyst. In some aspects, the transiently-formed target intermediate is selectively generated using thermal catalysis.

[0012] In some aspects, the feedstock has a temperature of 500 K or less (e.g., 450 K or less, 400 K or less, 350 K or less, or 300 K or less). In some aspects, the feedstock comprises a gaseous feedstock having a pressure of 5 atm or less (e.g., 4 atm or less, 3 atm or less, 2 atm or less, 1 atm or less, 0.9 atm or less, 0.8 atm or less, 0.7 atm or less, 0.6 atm or less, 0.5 atm or less, 0.4 atm or less, 0.3 atm or less, 0.2 atm or less, or 0.1 atm or less).

[0013] In some aspects, a Damkbhler number of the active removal of the transiently- formed target intermediate is 1.0 or less (e.g., 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, 0.01 or less). In some aspects, a molar selectivity of the transiently-formed target intermediate is 20% or more (e.g., 22% or more, 24% or more, 26% or more, 28% or more, 30% or more, 32% or more, 34% or more, 36% or more, 38% or more, or 40% or more). In some aspects, a conversion of the reactant is 10% or more (e.g., 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, or 70% or more). In some aspects, a yield of the transiently-formed target intermediate is 10% or more (e.g., 12% or more, 14% or more, 16% or more, 18% or more, 20% or more, 22% or more, 24% or more, 26% or more, 28% or more, or 30% or more). In some aspects, the transiently-formed target intermediate is actively removed from the reaction chamber by contacting the transiently-formed target intermediate with a liquid solvent (e.g., water). In some aspects, the process further includes separating the transiently-formed target intermediate from the liquid solvent (e.g., using distillation).

[0014] In some aspects, the transiently-formed target intermediate is actively removed using a solid-phase adsorbent (e.g., a catalyst- adsorbent).

[0015] In some aspects, the feedstock comprises natural gas. In some aspects, the feedstock comprises a tail gas. In some aspects, the feedstock comprises methane as a reactant.

[0016] In some aspects, the oxidant comprises air, oxygen, N2O, and / or CO2. In some aspects, the transiently-formed target intermediate comprises a liquid oxygenate. In some aspects, the transiently-formed target intermediate comprises methanol, ethanol, acetate, formate, or a combination thereof. In some aspects, the transiently-formed target intermediate comprises methanol.

[0017] In some aspects, the process is a continuous process. In some aspects, the process is a semi-continuous process. In some aspects, the process is a batch process.

[0018] Also disclosed herein is a system for the selective conversion of a feedstock (e.g., a gaseous feedstock) comprising a reactant (e.g., a hydrocarbon) and an oxidant to a target intermediate, the system comprising: a reaction chamber configured to receive the feedstock and selectively generate a transiently-formed target intermediate from the reactant; and a species recovery unit, said recovery unit being operatively coupled to the reaction chamber and configured to actively remove the transiently-formed target intermediate from the reaction chamber, wherein a rate that the transiently-formed target intermediate is removed from the reaction chamber is greater than or equal to a rate that the transiently-formed target intermediate is consumed.

[0019] In some aspects, the reaction chamber further comprises one or more electrodes configured to form a plasma (e.g., a nanosecond pulsed plasma), and wherein the transiently-formed target intermediate is selectively generated by contacting the feedstock with the plasma in the reaction chamber under thermal non-equilibrium conditions to produce a vibrationally excited precursor or radical, and wherein the vibrationally excited precursor or radical is selective for forming the transiently-formed target intermediate. In some aspects, the vibrationally excited precursor has a characteristic vibrational temperature greater than a temperature of the reactant. The non-equilibrium plasma can be formed using any method known in the art. For example, a non-equilibrium plasma can be generated using one or more electrodes. Various electrode geometries may be used to tune the shape and stability of the resulting plasma, including, for example, planar, cylindrical, curved, molded, wire, and / or needle configurations. In some aspects, the one or more electrodes comprises at least two electrodes separated by a discharge gap (e.g., from 10pm to 10 cm, from 1 mm to 5 cm, or from 1 mm to 1 cm) and configured to generate the plasma therebetween. In some aspects, the plasma is generated using a reduced electric field (E / N) of from 1 to 100 Td (e.g., from 1 to 50 Td, from 1 to 40 Td, from 1 to 30 Td, from 1 to 20 Td, or from 1 to 10 Td).

[0020] In some aspects, the transiently-formed target intermediate is formed from the feedstock without the use of a catalyst. In some aspects, the transiently-formed target intermediate is selectively generated using thermal catalysis.

[0021] In some aspects, the reaction chamber further comprises an inert gas (e.g., argon, helium, neon, krypton, and / or xenon).

[0022] In some aspects, the feedstock has a temperature of 500 K or less (e.g., 450 K or less, 400 K or less, 350 K or less, or 300 K or less). In some aspects, the feedstock comprises a gaseous feedstock having a pressure of 5 atm or less (e.g., 4 atm or less, 3 atm or less, 2 atm or less, 1 atm or less, 0.9 atm or less, 0.8 atm or less, 0.7 atm or less, 0.6 atm or less, 0.5 atm or less, 0.4 atm or less, 0.3 atm or less, 0.2 atm or less, or 0.1 atm or less).

[0023] In some aspects, a Damkbhler number of the active removal of the transiently- formed target intermediate is 1.0 or less (e.g., 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, 0.01 or less). In some aspects, a molar selectivity of the transiently-formed target intermediate is 20% or more (e.g., 22% or more, 24% or more, 26% or more, 28% or more, 30% or more, 32% or more, 34% or more, 36% or more, 38% or more, or 40% or more). In some aspects, a conversion of the reactant is 10% or more (e.g., 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, or 70% or more). In some aspects, a yield of the transiently-formed target intermediate is 10% or more (e.g., 12% or more, 14% or more, 16% or more, 18% or more, 20% or more, 22% or more, 24% or more, 26% or more, 28% or more, or 30% or more).

[0024] In some aspects, the species recovery unit comprises a liquid solvent stream configured to actively remove the transiently-formed target intermediate from the reaction chamber. In some aspects, the system further includes a separating unit configured to separate the transiently-formed target intermediate from the liquid solvent (e.g., using distillation). In some aspects, the species recovery unit comprises a solid-phase adsorbent (e.g., a catalyst-adsorbent) configured to actively remove the transiently-formed target intermediate from the reaction chamber.

[0025] In some aspects, the feedstock comprises natural gas. In some aspects, the feedstock comprises a tail gas. In some aspects, the feedstock comprises methane. In some aspects, the oxidant comprises air, oxygen, N2O, and / or CO2.

[0026] In some aspects, the transiently-formed target intermediate comprises a liquid oxygenate. In some aspects, the transiently-formed target intermediate comprises methanol, ethanol, acetate, formate, or a combination thereof. In some aspects, the transiently-formed target intermediate comprises methanol.

[0027] In some aspects, the system is configured to operate continuously. In some aspects, the system is configured to operate semi-continuously. In some aspects, the system is configured to operate as a batch process.

[0028] In some aspects, the reactor chamber has an inlet conduit configured to receive a methane-rich source (e.g., from natural gas or shale gas, syngas, coal, and / or biomass). In some aspects, the reactor chamber is operatively coupled to a wellhead.

[0029] Additional advantages of the disclosed subject matter will be set forth in part in the description that follows and the Figures, and in part will be obvious from the description, or can be learned by practice of the aspects described below. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.

[0030] BRIEF DESCRIPTION OF THE FIGURES

[0031] The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects described below.

[0032] Figures 1A-1D - (Fig. 1A) Conventional pathways to convert methane to methanol are constrained by the production and composition of gas. A single-step partial oxidation of methane to methanol can bypass syngas production. (Fig. IB) Energy diagram for DMtM conversion that illustrates how vibrational excitations (i.e., with plasmas) lower the activation energy of methane and enable reactions to proceed at lower gas temperatures. Methanol, being more reactive than methane, gets over-oxidized to undesired byproducts (including CO2) that result in a selectivity - conversion limit. (Fig. 1C) Both traditional thermal catalysis and non-thermal plasmas have a selectivity limit in the DMtM process. As conversion increases, selectivity decreases which constrains the maximum methanol yield. (Fig. ID) methanol in non-equilibrium conditions breaks the selectivity - conversion limit and enables scalable yields of methanol in mild conditions.

[0033] Figures 2A-2C - (Fig. 2A) Plasma was used to activate methane (i.e., vibrationally) in a batch reactor that featured a fixed gaseous composition (CH4:O2:Ar = 2:1:5, 1 atm) and nanosecond pulsed plasma discharges (1 cm gap, 1 kHz repetition frequency). (Fig. 2B) A selectivity - conversion comparison between two different applied voltages (~ 9kV and - lOkV) showing that lower energy per pulse results in higher selectivity toward methanol. A three-step kinetic model is also shown to fit the data shown (Eqs. 5-6). (Fig. 2C) Variation of methanol yield with energy per pulse. Reducing k2 and Io (expressed in min-1) increases the achievable methanol yield for any reactor. Reaction time is normalized with the time required to reach 99% conversion (199% conversion ~ 5 / ( k3+ ki)) and conversion does not scale linearly with time.

[0034] Figures 3A-3D - (Fig. 3A) Mechanistic differences between reactant excitation in high E / N (~ 100 Td) and low E / N (~ 10 Td) conditions (E / N estimates in Example 1). More energetic electrons (i.e., high E / N) generate more methyl radicals (CH3) that cause a cascade of unwanted products (e.g., ethane, ethanol, acetaldehyde, etc.) (Table 1). Lower field strength vibrational excitations form methoxy radicals (CH3O) and thereby methanol (Figs. 8A-8B and Figs. 9A-9B) preferentially. M is a neutral and inert gas species. Dotted shapes represent intermediate species. (Fig. 3B) Variation of methanol selectivity with changing field strengths (via discharge variation) with color-coded data points to signify what mechanistic pathway they choose (~ 9 kV applied voltage, 1 million pulses). (Fig. 3C) Energy loss fractions of different internal modes of CH4, O2, and Ar. Similar modes were summed together to show the combined effect. Lower and higher E / N ranges are shown with the mechanistic pathways and experimental results. (Fig. 3D) Optical emission spectroscopy of CH4:O2:Ar = 2:1:5 at 1 atm in both diffused and filamentary discharge modes.

[0035] Figures 4A-4C - (Fig. 4A) A schematic of an active removal process that involves extracting methanol over timescales shorter than it can accumulate within the reactor. The selective vibrational excitation of reactants in this process enables low gas temperatures and the integration of other phases to trap methanol and limit its oxidation to CO2. (Fig. 4B) Increasing methanol yield (> 20%) was measured as purge rates of the reactor were increased (0-85 SCCM) with fixed plasma properties (same as Fig. 2A). Methanol yield is scalable with Damkbhler number, Da = k4tconvection (where tconvection is the ratio of the volume of the reactor to flow rate). The fit curves were obtained by solving the kinetic equations of the modified mechanism. (Fig. 4C) A modified mechanism to accommodate the active removal process.

[0036] Figures 5A-5C - (Fig. 5A) A comparison of the process yields and energy efficiency (q, Materials and Methods of Example 1, Eq. 4) for DMtM conversion. Selective vibrational excitations and active methanol removal can break the selectivity-conversion limit and enable scalable process yields. (Fig. 5B) A comparison of energy-adjusted methanol yield (defined as amount of methanol produced by unit energy input) between this process and industrial scale conversion. This process enables higher yields than state-of-the- art industrial conditions by operating in a state of thermal non-equilibrium. (Fig. 5C) A comparison of carbon intensity between this process and industrial processes showing that this process benefits from zero carbon emission due to renewable energy input.

[0037] Figure 6 shows measurements of product partitioning indicate that methanol is trapped preferentially in aqueous samples if it is purged continuously. The gaseous products were purged through 15 mL of water with up to 85 SCCM flow rate. The properties of the plasma discharge include a 1 cm discharge gap, applied voltage of - 9 kV and repetition frequency of 1 kHz. ,199% Conversion = 5 / ( ki+ ka).

[0038] Figures 7A-7B - (Fig. 7A) A comparison of different inert gases on the methanol yield. (Fig. 7B) Energy cost of methanol production. Argon at a concentration of CH4:O2: Ar = 2:1:5 (by volume) was found to be the most energy efficient in the experiment.

[0039] Figures 8A-8B - (Fig. 8A) GC-FID signal after exposure to a plasma with high E / N (spark, - 100 Td). Other reactor settings are reported in Fig. 3B. (Fig. 8B) GC-FID signal after exposure to a plasma with low E / N (diffused discharge, - 10 Td).

[0040] Figures 9A-9B - (Fig. 9A) GC-TCD signal after exposure to a plasma with high E / N (spark, - 100 Td). Other reactor settings are reported in Fig. 3B. (Fig. 9B) GC-TCD signal after exposure to a plasma with low E / N (diffused discharge, - 10 Td).

[0041] Figure 10 shows intensified CCD images of a point to plane plasma discharge with varying gap distances (-9 kV, 1 kHz) and a fixed gaseous composition of CH4:O2:Ar = 2:1:5. For discharge gaps between 1-5 mm, the exposure time was 100 ps and gain was 200 (max 255). For discharge gaps between 7-10mm, the exposure time was 20 ms and gain was 220 to capture the fainter diffused discharge.

[0042] Figures 11A-11B - (Fig. 11 A) Methanol selectivity lowers as applied voltage increases. This is how changing applied voltage in Fig. 2C showed a difference in yield. (Fig. 1 IB) Discharge current increases with applied voltage. This implies increasing voltage induces a structural transition in the plasma as the discharge becomes more filamentary and less selective to vibrational excitations.

[0043] Figures 12A-12B - (Fig. 12A) Sampling at five different locations in the reactor shows variation in sampling amount across locations. Initial methane refers to the amount of methane sampled from the reactor before the reaction. Final methane refers to the amount of methane sampled after the reaction. (Fig. 12B) The measured variation of methane composition was < 1% across all locations.

[0044] Figure 13 - (Fig. 13 A) “Plasma Off ” refers to the conditions before the chemical reaction (CH4:O2:Ar = 2: 1:5). Turbulent flow generators were present upstream of the reactor and downstream of the mass flow controllers to mix methane, oxygen, and argon thoroughly before they enter the reactor. (Fig. 13B) “Plasma On” refers to the conditions after the chemical reaction (conditions same as Figs. 12A-12B).

[0045] Figures 14A-14B - (Fig. 14A) Methane calibration curve obtained with GC-FID and gas-tight syringes. (Fig. 14B) Methanol calibration curve obtained with GC-FID and a -1 syringe.

[0046] Figure 15 shows Bruker 600 MHz NMR spectrometer was used to obtain ID 1H- NMR spectrum of methanol generated in the plasma reactor (Number of scans: 32 and pulse width: 45°).

[0047] Figures 16A-16C show electron loss fractions of CH4, O2 and Ar with 2:1:5 composition at 300 K and 1 atm. (Fig. 16A) Electron loss fractions of methane. (Fig. 16B) Electron loss fractions of oxygen using. (Fig. 16C) Electron loss fractions of argon. All the curves were obtained using Bolsig+ with settings described in Methods and Materials of Example 1.

[0048] Figures 17A-17B show inter-molecule synergy between vibrational energy levels in CH4-O2 system and their relaxation timescales. (Fig. 17A) Select vibrational levels of methane and oxygen to show vibrational - vibrational (V-V) and vibrational - translational (V-T) relaxations. (Fig. 17B) Characteristic timescales of these relaxation processes.

[0049] Figures 18A-18C show energy per pulse evaluation in the spark discharge regime.

[0050] (Fig. 18A) Voltage waveform for 1 mm discharge gap with initial corona phase (i.e., voltage rise period) and the spark discharge phase. (Fig. 18B) Current waveform showing the corona and spark regime. (Fig. 18C) Variation of energy with time during a pulse to show the energy consumption differences between the corona and spark phases.

[0051] Figure 19 shows peak discharge voltage estimation at longer discharge gaps (> 5 mm). Theoretical evaluation of peak discharge voltage at longer discharge gaps based on the transition voltage between the glow (i.e., diffused discharge) and spark regimes. Error bars shown indicate standard deviation over 1000 measurements.

[0052] Figures 20A-20D show energy per pulse evaluation for longer discharge gaps (diffused discharge). (Fig. 20A) Methanol yield across plasma phases (discharge gap = 1 cm) showed that corona phase produced negligible amounts of methanol. The transition to discharges increased the yield of methanol by lOx. (Fig. 20B) Current waveform of the plasma in corona discharge regime averaged over 100 samples. (Fig. 20C) Current waveform of the plasma in diffused discharge regime (averaged over 100 samples) which is a combination of the discharge peak (conduction current peak) and corona discharge losses. (Fig. 20D) Conduction current (9) for the evaluation of energy per pulse at longer discharge gaps.

[0053] Figure 21 shows a linear voltage profile approximation for longer discharge gaps.

[0054] Voltage waveform corresponding to a discharge gap of 1mm to compare the actual voltage drop curvature (over discharge pulse width) with linear drop approximation.

[0055] Figures 22A-22B show a decrease in deposited energy per pulse with increasing reaction run time. (Fig. 22A) Conduction current at t = 0 (~ 0% conversion) with an energy deposited of ~ 23 pJ / pulse. (Fig. 22B) Conduction current at t ~ 100 min (~ 30% conversion) with an energy deposited of ~ 15 pJ / pulse.

[0056] Figure 23 shows input energy to the nanosecond pulser at 0% conversion, (top) Input voltage waveform from DC supply to the nanosecond pulser at t = 0 (or 0% conversion). The discharge gap was 1 cm at the output side of the pulser, (middle) Input current waveform at the same settings, (bottom) Total energy input as a function of time obtained by integrating the product of voltage and current.

[0057] Figure 24 shows input energy to the nanosecond pulser at 30% conversion.

[0058] (top) Input voltage waveform from DC supply to the nanosecond pulser at ~ 30% conversion. The discharge gap was 1 cm at the output side of the pulser, (middle) Input current waveform at the same settings, (bottom) Total energy input as a function of time obtained by integrating the product of voltage and current.

[0059] Figures 25A-25D show emission spectra of various species in filamentary and diffused discharges. (Fig. 25A) An emission peak of CH3O present in both filamentary and diffused discharges. (Fig. 25B) Emission band of CH (C X). (C) O emission triplet from both filamentary and diffused discharges. (Fig. 25D) Ha peak present only in filamentary discharge. Figure 26 shows methoxy radical (CH3O) emission peak with reaction runtime. A higher voltage (~ 12kV) was applied across 1 cm discharge gap for a minute increase the methoxy radical production, and its emission intensity was studied at various runtimes (i.e., 1 min, 12 min and 25 min) with a diffused discharge (~ 9kV and 1 cm).

[0060] Figure 27 shows a comparison of product selectivities of a feedstock mixture (methane (CH4), carbon dioxide (CO2), and argon (Ar) in a 30:15:55 ratio) at various reduced electric field magnitudes.

[0061] Figure 28 shows the influence of Damkdhler number and feedstock composition on product selectivity.

[0062] Figure 29 shows a graph illustrating the relationship between flow rate and conversion, yield, and selectivity.

[0063] Figure 30 shows liquid oxygenate selectivity for different reactor configurations.

[0064] Figure 31 - (Fig. 31A) A conventional chemical process featuring heat and mass integration. The reactor is heated by combusting a mixture of fresh fuel and recycled fuel gas. A water stream is used to recover heat from the reactor effluent, and is turned to steam by heat exchange with the hot flue gas generated by combustion heating. The reactor products then undergoes separation in a distillation column whose reboiler is heated using the steam generated by recovering process heat. The bottoms stream of the column is the product of the process, while the light stream at the top is assumed to be of little economic value and is used as fuel. (Fig. 31B) An equivalent electrified process uses electric heaters to eliminate combustion heating of the reactor and to produce steam. This leads to eliminating the flue gas stream, but creates a new challenge: the fuel gas (tail gas) stream of remains unused and must be further processed. (Fig. 31C) An overview of a plasma- catalytic approach to convert CH4 and CO2 from the tail gas stream into methanol and other liquid hydrocarbons.

[0065] Figure 32 - Free electrons in plasmas can excite internal modes in molecules and accelerate rate-limiting steps or drive new reaction pathways. Vibrational excitation of CH4 or CO2, in particular, can enable the synthesis of liquid hydrocarbons at lower temperatures, pressures, and with synergistic catalysts.

[0066] Figure 33 shows results of a DOMtM process for a tail gas feedstock.

[0067] DETAILED DESCRIPTION

[0068] The materials, compounds, compositions, articles, and methods described herein may be understood more readily by reference to the following detailed description of specific aspects of the disclosed subject matter and the Examples and Figures included therein.

[0069] Before the present materials, compounds, compositions, and methods are disclosed and described, it is to be understood that the aspects described below are not limited to specific synthetic methods or specific reagents, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0070] Also, throughout this specification, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed matter pertains. The references disclosed are also individually and specifically incorporated by reference herein for the material contained in them that is discussed in the sentence in which the reference is relied upon.

[0071] General Definitions

[0072] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs.

[0073] The term “comprising” and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. Although the terms “comprising” and “including” have been used herein to describe various aspects, the terms “consisting essentially of’ and “consisting of’ can be used in place of “comprising” and “including” to provide for more specific aspects and are also disclosed. Throughout the description and claims of this specification the word “comprise” and other forms of the word, such as “comprising” and “comprises,” means including but not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps.

[0074] As used in the specification and claims, the singular form “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a material” includes a plurality of materials, including mixtures thereof.

[0075] As used herein, the terms "may," "optionally," and "may optionally" are used interchangeably and are meant to include cases in which the condition occurs as well as cases in which the condition does not occur. Thus, for example, the statement that a formulation "may include a hydrocarbon" is meant to include cases in which the formulation includes a hydrocarbon as well as cases in which the formulation does not include a hydrocarbon.

[0076] It is understood that throughout this specification the identifiers “first” and “second” are used solely to aid in distinguishing the various components and steps of the disclosed subject matter. The identifiers “first” and “second” are not intended to imply any particular order, amount, preference, or importance to the components or steps modified by these terms.

[0077] By “reduce,” or other forms of the word, such as “reducing” or “reduction,” is meant lowering of an event or characteristic. It is understood that this is typically in relation to some standard or expected value, in other words it is relative, but that it is not always necessary for the standard or relative value to be referred to.

[0078] By “increase” or other forms of the word, such as “increasing,” is meant raising or elevating. It is understood that this is typically in relation to some standard or expected value, in other words it is relative, but that it is not always necessary for the standard or relative value to be referred to.

[0079] Reference will now be made in detail to specific aspects of the disclosed materials, compounds, compositions, articles, and methods, examples of which are illustrated in the accompanying Examples and Figures.

[0080] Methods

[0081] In various aspects, disclosed herein is a process for selectively converting a feedstock (e.g., a gaseous feedstock) comprising a reactant (e.g., a hydrocarbon) and an oxidant to a target intermediate, the process comprising: selectively generating a transiently- formed target intermediate in a reaction chamber from the reactant; and actively removing the transiently-formed target intermediate from the reaction chamber, wherein a rate that the transiently-formed target intermediate is removed from the reaction chamber is greater than or equal to a rate that the transiently-formed target intermediate is consumed.

[0082] As used herein, the term “transiently-formed target intermediate” refers to an intermediate product of an oxidation reaction that can be further oxidized to a more stable product. For example, methane can be oxidized to form methanol, which itself can be further oxidized to a more stable form of carbon dioxide. The term “reactant” as used herein refers to a compound that participates in the chemical reaction that produces another compound, and particularly to a compound that generates the transiently-formed target intermediate. Reactants can include various chemical species, for example, substituted or unsubstituted hydrocarbons such as alkanes, alkenes, cycloalkanes, cycloalkenes, alkyl aromatics, aryl aldehydes, aryl acids, aryl alcohols, or mixtures thereof.

[0083] As used herein, “alkane” means a straight chain or branched aliphatic hydrocarbons. Representative straight chain alkanes include methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, and decane. Representative branched alkanes include isobutane, isopentane, neopentane, 2-methylbutane, 2-methylpentane, 3-methylpentane, 2,2- dimethylbutane, 2,3-dimethylbutane, 3,3-dimethylbutane, 2-methylhexane, 3-methylhexane, 3,3-dimethylhexane, and 3,3-dimethylheptane.

[0084] The term “alkene” means an unsaturated straight or branched hydrocarbons that contain at least one double bond. Representative straight chain and branched alkenes include ethene, propene, butene, 2-butene, isobutene, 1-pentene, 2-pentene, 3-methyl-l- butene, 2-methyl-2-butene, 2,3-dimethyl-2-butene, 1 -hexene, 2-hexene, 3-hexene, 1- heptene, 2-heptene, 3-heptene, 1 -octene, 2-octene, 3-octene, 1 -nonene, 2-nonene, 3-nonene, 1 -decene, 2-decene, 3-decene, and the like.

[0085] The term “cycloalkane,” means a cyclic alkane. Examples of cycloalkanes include cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, and cyclodecane. The term also encompasses bicycloalkanes and tricycloalkanes.

[0086] The term “cycloalkene” means a non-aromatic cyclic hydrocarbon having at least one carbon-carbon double bond in the cyclic system. Non-limiting examples of cycloalkenes include cyclopentene, cyclopentadiene, cyclohexene, cyclohexadiene, cycloheptene, cycloheptadiene, cycloheptatriene, cyclooctene, cyclooctadiene, cyclooctatriene, cyclooctatetraene, cyclononene, cyclononadiene, cyclodecene, cyclodecadiene, and the like.

[0087] The term “alkyl aromatic” embraces an aromatic ring system substituted with an alkyl group. Exemplary alkyl aromatic compounds are alkyl benzenes, such as methyl benzene (toluene), ethyl benzene, propyl benzene, isopropylbenzene (cumene), 1,2- dimethylbenzene (o-xylene), 1,3-dimethylbenzene (m- xylene), 1,4-dimethylbenzene (p- xylene), 1,3,5-trimethylbenzene (mesitylene), 1,2,3-trimethylbenzene (hemimellitene), 1, 2, 4-trimethyl benzene (pseudocumene), 1,2,4,5-tetramethylbenzene (durene), 1, 2,3,5- tetramethylbenzene (isodurene), l-methyl-4-(l-methylethyl)benzene (cymene), butylbenzene, 1,2-diethylbenzene, 1,3-diethylbenzene, 1,4-diethylbenzene, 1,3,5- triethylbenzen, 1,2,3-triethylbenzene, 1,2,4-triethylbenzene, l-methyl-2-ethylbenzene, 1- methyl-3-ethylbenzene, l-methyl-4-ethylbenzene, l-methyl-2-propylbenzene, l-methyl-3- propylbenzene, l-methyl-4-propylbenzene, l-ethyl-2-propylbenzene, l-ethyl-3- propylbenzene, l-ethyl-4-propylbenzene, l-methyl-2-butylbenzene, l-methyl-3- butylbenzene, l-methyl-4-butylbenzene, pentylbenzene, hexylbenzene, heptylbenzene, octylbenzene, nonylbenzene, dodecylbenzene, pentadecylbenzene, hexyltoluene, nonyltoluene, dodecyltoluene, and pentadecyltoluene. Other alkyl aromatics include 1- methylnaphthalene, 2-methylnaphthalene, 1,2-dimethylnaphthalene, 1,4- dimethylnaphthalene, 1,5 -dimethylnaphthalene, 1,6-dimethylnaphthalene 1,7- dimethylnaphthalene, 1,8-dimethylnaphthalene, 1 -ethylnaphthalene, 2,3- dimethylanthracene, 9-ethylanthracene, 2-methylanthracene, 1 -methylanthracene, 9,10- dimethylphenanthrene, and 3-methyl-phenanthrene.

[0088] The term “aryl aldehyde” refers to an aromatic compound substituted with at least one — CHO radical, such as benzaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, and the like.

[0089] An “aryl acid” means aromatic compound substituted with at least one carboxylic acid ( — COOH) radical. Suitable aryl acids include, for example, benzoic acid, o-toluic, m- toluic acid, p-toluic acid, 2-ethylbenzoic acid, 3 -ethylbenzoic acid, 4-ethylbenzoic acid, 4- isopropylbenzoic acid, 4-tertiary butylbenzoic acid, 4-(l-methylpropyl)benzoic acid, and the like. Other aryl acids include those based on naphthalene or anthracene, such as 1- naphthoic acid, and 2-naphthoic acid. In some examples, the aryl acids are substituted with a halogen, for example, 2-chlorobenzoic acid, 3-chlorobenzoic acid, 4-chlorobenzoic acid, 2,3-dibromobenzoic acid, 2,4-di-iodobenzoic acid, 2,6-dibromobenzoic acid, 3,4- dibromobenzoic acid, 3, 5 -dichlorobenzoic acid, 2,3,5-tribromobenzoic acid, 2,4,6- trichlorobenzoic acid, 2,3,4,5,6-pentabromobenzoic acid, and the like.

[0090] The term “aryl alcohol” means an aromatic ring substituted with at least one hydroxyl ( — OH) containing alkyl moiety. Examples of aryl alcohols include benzyl alcohol, 1 -phenylethanol, 2-phenylethanol, and l-phenyl-2-propanol.

[0091] The transiently-formed target intermediate can be selectively generated from the reactant and optionally additional compounds in the feedstock. The term “selectively generated” and the like refers to the controlled chemical synthesis of a target product (e.g., the transiently-formed target intermediate). For example, the selectively generated compound can be formed by providing a directed energy source to a reactant to enter a specific vibrational state preferential for the formation of the target product.

[0092] In some aspects, the feedstock comprises natural gas. The term “natural gas” refers to a multi-component gas obtained from a crude oil well or from a subterranean gas-bearing formation. The composition and pressure of natural gas can vary significantly, however, a typical natural gas stream contains methane (CH4) as a major component, i.e., greater than 50 mol % of the natural gas stream is methane. The natural gas stream can also contain ethane (C2H6), higher molecular weight hydrocarbons (e.g., C3-C20 hydrocarbons), one or more acid gases (e.g., CO2 or H2S), or any combinations thereof. The natural gas can also contain minor amounts of contaminants such as water, nitrogen, iron sulfide, wax, crude oil, or any combinations thereof. The inlet natural gas stream may be substantially purified to remove unwanted compounds prior to utilization, or can be supplied in the form of a raw gas, meaning a gas generated without reformulation. In some aspects, the feedstock comprises methane as the reactant.

[0093] In some aspects, the feedstock comprises a tail gas. As used herein, the term “tail gas” refers to a gaseous product produced during a Fischer-Tropsch reaction. Typically, the tail gas composition includes gases such as hydrogen (H2) (e.g., 10 to 40 % by volume), nitrogen (N2) (e.g., 10 to 30 % by volume), carbon monoxide (CO) (e.g., 0 to 15 % by volume), methane (CH4) (e.g., 20 to 40 % by volume), carbon dioxide (CO2) (e.g., 10 to 30 % by volume), and light hydrocarbons (e.g., 0 to 15 % by volume).

[0094] The disclosed process can use directed energy to selectively excite chemical bonds using free electron collisions to produce a desired target product. For example, the selective excitation can be provided using RF heating, micro waves, lasers, dielectric barrier discharges, arcs, gliding arcs, sparks, DC, inductively coupled plasmas, capacitively coupled plasmas, or any other source. In some aspects, the transiently-formed target intermediate is selectively generated by contacting the feedstock with a plasma (e.g., a nanosecond pulsed plasma) in a reaction chamber under thermal non-equilibrium conditions to produce a vibrationally excited precursor or radical. The vibrationally excited precursor or radical produced therein is selective for forming the transiently-formed target intermediate. Plasmas can be characterized as “thermal” (equilibrium) or “non-thermal” (non-equilibrium) based on the relative temperatures of the electrons, protons and neutrons. Generally, thermal plasma atoms have electrons and nucleus particles at the same temperature and are said to be in thermal equilibrium. Non-equilibrium plasma generally differs from thermal plasma with respect to their roles in plasma chemical kinetics with thermal plasma typically being more powerful and operating at higher temperatures, whereas non-equilibrium plasma is generally safer and more selective for the controlled formation a particular chemical species. In a non-equilibrium state, plasma can induce selective chemical reactions favoring the formation of a high concentration of a targeted product. In various aspects, the plasma comprises a non-equilibrium plasma. Some examples of non-equilibrium plasma discharge include: dielectric barrier discharge, pulsed corona discharge, and gliding arc discharge. In some aspects, the vibrationally excited precursor has a characteristic vibrational temperature greater than a temperature of the reactant.

[0095] The non-equilibrium plasma can be formed using any method known in the art. For example, a non-equilibrium plasma can be generated using one or more electrodes. The electrodes can be arranged in a variety of geometries to tune the shape and stability of the resulting plasma, including, for example, planar, cylindrical, curved, molded, wire, and / or needle configurations. Dielectric materials can also be positioned between electrodes to assist with thermal regulation and the distribution of electrical energy, which can provide stability to the plasma discharge. Non-limiting examples of suitable dielectric materials include polytetrafluoroethylene (PTFE), aluminum oxide (alumina), silicone, natural rubber, synthetic rubber, ceramic, poly etherimide (PEI), quartz such as a dielectric quartz or fused silica, and / or magnesium fluoride.

[0096] Non-equilibrium plasma can be generated using an applied voltage forming an electric field between electrodes. In some aspects, the plasma is generated using a reduced electric field (E / N) of from 1 to 100 Td (e.g., from 1 to 50 Td, from 1 to 40 Td, from 1 to 30 Td, from 1 to 20 Td, or from 1 to 10 Td). The term “reduced electric field” refers to a determined ratio E / N, where E is the electric field and N is the concentration of neutral particles. A physical unit of the reduced electric field E / N is known as the Townsend (Td). 1 Townsend is defined as being equal to 10-21V*m2. The excitation scheme can be tailored based on the conditions of the feedstock. In the case of methane to methanol, lower E / N reactions were shown to increase product selectivity towards methanol. Higher E / N reactions, however, produced methyl radicals that generally favored larger order C2 / C3 hydrocarbons and less oxygenates.

[0097] In some aspects, the reaction chamber further comprises an inert gas (e.g., argon, helium, neon, krypton, and / or xenon). The addition of an inert gas and / or the reduction of pressure within the reaction system can extend the vibrational lifetime of the precursor, implying a slower thermal equilibrium process, and thus, greater specific bond breaking to produce a desired product.

[0098] In some aspects, the transiently-formed target intermediate is formed from the feedstock without the use of a catalyst. However, in other aspects, the transiently-formed target intermediate is selectively generated using thermal catalysis. For example, a transition metal catalyst, such as a catalyst comprising manganese, copper, palladium, tungsten, molybdenum, rhenium, iron, platinum, cobalt, silver or any combination thereof, can be used. In some aspects, a combination of non-equilibrium plasma and one or more catalysts can be concurrently used. Using plasma activation and catalysis in tandem can achieve high conversions and selectivities while operating at much milder operating conditions.

[0099] In some aspects, the feedstock has a temperature of 500 K or less (e.g., 450 K or less, 400 K or less, 350 K or less, or 300 K or less). In some aspects, the feedstock comprises a gaseous feedstock having a pressure of 5 atm or less (e.g., 4 atm or less, 3 atm or less, 2 atm or less, 1 atm or less, 0.9 atm or less, 0.8 atm or less, 0.7 atm or less, 0.6 atm or less, 0.5 atm or less, 0.4 atm or less, 0.3 atm or less, 0.2 atm or less, or 0.1 atm or less). Low temperature, low pressure parameters, particularly in the context of volatile compounds, can reduce the total energy demand of the system and further enhance process safety. In addition, low-pressure conditions can increase the vibrational lifetime of molecules, which can further enhance product recovery.

[0100] The term “actively removed” refers to the recovery of a compound shortly after the compound has been formed. The rate of active removal of the compound can be on a timescale that is shorter than the rate of accumulation of the transiently-formed target intermediate. The step of actively removing the target species can occur in the same thermodynamic environment as the formation of the target compound to create a one-pot process.

[0101] In some aspects, the transiently-formed target intermediate is actively removed from the reaction chamber by contacting the transiently-formed target intermediate with a liquid solvent (e.g., water). In some aspects, the process further includes separating the transiently-formed target intermediate from the liquid solvent (e.g., using distillation).

[0102] In some aspects, the transiently-formed target intermediate is actively removed using a solid-phase adsorbent (e.g., a catalyst- adsorbent). As used herein, the term “adsorbent” refers to a material that can adhere gas molecules, ions, or other species within its structure (e.g., removal of CO2 from air). Suitable examples of adsorbent materials include but are not limited to clays, metal-organic framework, activated alumina, silica gel, activated carbon, molecular sieve carbon, zeolites (e.g., molecular sieve zeolites), polymers, resins, and any of these components or others having a gas-adsorbing material supported thereon (e.g., such as the various aspects of sorbents described herein). Certain adsorbent materials may preferentially or selectively adhere particular species, such as the transiently- formed target intermediate. In some aspects, the solid-phase adsorbent is a catalyst-adsorbent. The term “catalyst- adsorbent” refers to a material that has dual catalytic and adsorptive properties. For example, a catalyst-adsorbent surface, upon contact with a molecular species, may catalyze the conversion of the molecular species into one or more products, and may also be capable of adsorbing the molecular species and / or the one or more products. The catalystadsorbent surface may also be capable of adsorbing other molecular species that cannot be reacted catalytically by the catalyst-adsorbent surface.

[0103] In some aspects, a Damkdhler number of the active removal of the transiently- formed target intermediate is 1.0 or less (e.g., 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, 0.01 or less). As used herein, the term “Damkdhler number” refers to a dimensionless number that is used to relate chemical reaction timescale to other phenomena occurring in a reaction system. For example, the Damkdhler number can represent the ratio of chemical kinetic time, representing the time required for a reaction (e.g., the rate of active removal of a species) to take place under the conditions of a particular region of a reactor vessel, to the residence time, representing the average time that flowing gas molecules reside within that particular region. The Damkdhler number can be represented by, Da=k(T)-r; where k(T) is the first order rate constant for the active removal of a particular species evaluated at a temperature of the feedstock and r is the residence time in the reactor vessel (e.g., the ratio of the reactor volume to a flow rate) evaluated at the feedstock temperature.

[0104] In some aspects, a molar selectivity of the transiently-formed target intermediate is 20% or more (e.g., 22% or more, 24% or more, 26% or more, 28% or more, 30% or more, 32% or more, 34% or more, 36% or more, 38% or more, or 40% or more). The term “molar selectivity” or “selectivity” as used herein refers to the quantity of a particular conversion product with reference to the quantity of the reactant consumed and is provided as a ratio of moles of product formed to the moles of reactant consumed.

[0105] In some aspects, a conversion of the reactant is 10% or more (e.g., 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, or 70% or more). The “conversion” refers to the percentage of reactant (e.g. methane) that undergoes a chemical reaction.

[0106] In some aspects, a yield of the transiently-formed target intermediate is 10% or more (e.g., 12% or more, 14% or more, 16% or more, 18% or more, 20% or more, 22% or more, 24% or more, 26% or more, 28% or more, or 30% or more). As used herein, the term “yield,” refers to the empirical yield for a given chemical reaction. Yield is defined as the percent to which a reaction proceeds to produce a given product.

[0107] A number of suitable oxidants can be used in the present methods. Non-limiting examples of suitable oxidants include, air, oxygen gas, and oxygen-enriched air. In some aspects, the oxidant comprises air, oxygen, N2O and / or CO2. In some aspects, the transiently-formed target intermediate comprises a liquid oxygenate. Non-limiting examples of liquid oxygenates include, for examples, methanol, ethanol, n-propanol, isopropanol, methyl ethyl ether, DME, diethyl ether, di-isopropyl ether, formaldehyde, dimethyl carbonate, dimethyl ketone, acetic acid, and mixtures thereof. In some aspects, the transiently-formed target intermediate comprises methanol, ethanol, acetate, formate, or a combination thereof. In some aspects, the transiently-formed target intermediate comprises methanol.

[0108] In some aspects, the process is a continuous process. In some aspects, the process is a semi-continuous process. In some aspects, the process is a batch process.

[0109] Systems

[0110] Also disclosed herein is a system for the selective conversion of a feedstock (e.g., a gaseous feedstock) comprising a reactant (e.g., a hydrocarbon) and an oxidant to a transiently-formed target intermediate, the system comprising: a reaction chamber configured to receive the feedstock and selectively generate a transiently-formed target intermediate from the reactant; and a species recovery unit, said recovery unit being operatively coupled to the reaction chamber and configured to actively remove the transiently-formed target intermediate from the reaction chamber, wherein a rate that the transiently-formed target intermediate is removed from the reaction chamber is greater than or equal to a rate that the transiently-formed target intermediate is consumed.

[0111] The reactants of the present system can include various chemical species, for example, substituted or unsubstituted hydrocarbons such as alkanes, alkenes, cycloalkanes, cycloalkenes, alkyl aromatics, aryl aldehydes, aryl acids, aryl alcohols, or mixtures thereof. For example, in some aspects, the feedstock comprises natural gas. In some aspects, the feedstock comprises methane. In some aspects, the oxidant comprises air, oxygen, N2O and / or CO2. In some aspects, the feedstock comprises a tail gas. In some aspects, the tail gas composition includes gases such as hydrogen (H2) (e.g., 10 to 40 % by volume), nitrogen (N2) (e.g., 10 to 30 % by volume), carbon monoxide (CO) (e.g., 0 to 15 % by volume), methane (CH4) (e.g., 20 to 40 % by volume), carbon dioxide (CO2) (e.g., 10 to 30 % by volume), and / or light hydrocarbons (e.g., 0 to 15 % by volume). As used herein, the term “chamber” refers to any object capable of containing a fluid (e.g., a gas and / or liquid) within its confines for at least a temporary period of time having at least one port for materials to enter and / or exit the chamber.

[0112] In some aspects, the reaction chamber further comprises one or more electrodes configured to form a plasma (e.g., a nanosecond pulsed plasma), and wherein the transiently-formed target intermediate is selectively generated by contacting the feedstock with the plasma in the reaction chamber under thermal non-equilibrium conditions to produce a vibrationally excited precursor or radical, and wherein the vibrationally excited precursor or radical is selective for forming the transiently-formed target intermediate. In some aspects, the vibrationally excited precursor has a characteristic vibrational temperature greater than a temperature of the reactant. In some aspects, the one or more electrodes comprises at least two electrodes separated by a discharge gap (e.g., from 10pm to 10 cm, from 1 mm to 5 cm, or from 1 mm to 1 cm) and configured to generate the plasma therebetween. In some aspects, the plasma is generated using a reduced electric field (E / N) of from 1 to 100 Td (e.g., from 1 to 50 Td, from 1 to 40 Td, from 1 to 30 Td, from 1 to 20 Td, or from 1 to 10 Td).

[0113] In some aspects, the reaction chamber further comprises an inert gas (e.g., argon, helium, neon, krypton, and / or xenon). The addition of an inert gas to the system can extend the vibrational lifetime of the precursor, implying a slower thermal equilibrium process, and thus, greater specific bond breaking to produce a desired product.

[0114] In some aspects, the transiently-formed target intermediate is formed from the feedstock without the use of a catalyst. In some aspects, however, the transiently-formed target intermediate is selectively generated using thermal catalysis. The thermal catalysis reaction can use, for example, a transition metal catalyst, such as a catalyst comprising manganese, copper, palladium, tungsten, molybdenum, rhenium, iron, platinum, cobalt, silver and / or mixtures thereof.

[0115] In some aspects, the feedstock has a temperature of 500 K or less (e.g., 450 K or less, 400 K or less, 350 K or less, or 300 K or less). In some aspects, the feedstock comprises a gaseous feedstock having a pressure of 5 atm or less (e.g., 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, 0.01 or less).

[0116] In some aspects, a Damkbhler number of the active removal of the transiently- formed target intermediate is 1.0 or less (e.g., 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, 0.1 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, 0.01 or less). In some aspects, a molar selectivity of the transiently-formed target intermediate is 20% or more (e.g., 22% or more, 24% or more, 26% or more, 28% or more, 30% or more, 32% or more, 34% or more, 36% or more, 38% or more, or 40% or more). In some aspects, a conversion of the reactant is 10% or more (e.g., 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, or 70% or more). In some aspects, a yield of the transiently-formed target intermediate is 10% or more (e.g., 12% or more, 14% or more, 16% or more, 18% or more, 20% or more, 22% or more, 24% or more, 26% or more, 28% or more, or 30% or more).

[0117] In some aspects, the species recovery unit comprises a liquid solvent stream configured to actively remove the transiently-formed target intermediate from the reaction chamber. In some aspects, the system further includes a separating unit configured to separate the transiently-formed target intermediate from the liquid solvent (e.g., using distillation).

[0118] In some aspects, the species recovery unit comprises a solid-phase adsorbent (e.g., a catalyst-adsorbent) configured to actively remove the transiently-formed target intermediate from the reaction chamber. As discussed above, examples of adsorbent materials include but are not limited to clays, metal organic framework, activated alumina, silica gel, activated carbon, molecular sieve carbon, zeolites (e.g., molecular sieve zeolites), polymers, resins, and any of these components or others having a gas-adsorbing material supported thereon (e.g., such as the various aspects of sorbents described herein). Moreover, certain adsorbent materials may preferentially or selectively adhere a particular species, such as the transiently-formed target intermediate.

[0119] In some aspects, the transiently-formed target intermediate comprises a liquid oxygenate. Non-limiting examples of liquid oxygenates include, for example, methanol, ethanol, n-propanol, isopropanol, methyl ethyl ether, DME, diethyl ether, di-isopropyl ether, formaldehyde, dimethyl carbonate, dimethyl ketone, acetic acid, and mixtures thereof. In some aspects, the transiently-formed target intermediate comprises methanol, ethanol, acetate, formate, or a combination thereof. In some aspects, the transiently-formed target intermediate comprises methanol.

[0120] In some aspects, the system is configured to operate continuously. In some aspects, the system is configured to operate semi-continuously.

[0121] In some aspects, the reactor chamber has an inlet conduit configured to receive a methane-rich source (e.g., from natural gas or shale gas, syngas, coal, and / or biomass). In some aspects, the reactor chamber is operatively coupled to a wellhead. As used herein, the term “wellhead” refers to the equipment and components present at the surface end of a well that can include a Christmas tree and that at least partially provides physical support to the well below the surface end. The term “operatively coupled” as used herein refers to a connection between the reaction chamber and the wellhead, wherein the connection may be through, but is not limited to, one or more tubes or conduits. The connection between the reaction chamber and wellhead can further include controllers, valves, gauges, pumps, filters / purification stages, or any other components found in fluid control and management systems.

[0122] Additional advantages of the disclosed subject matter will be set forth in part in the description that follows and the Figures, and in part will be obvious from the description, or can be learned by practice of the aspects described below. The advantages described below will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.

[0123] EXAMPLES

[0124] To further illustrate the principles of the present disclosure, the following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how the compositions, articles, and methods claimed herein are made and evaluated. They are intended to be purely exemplary of the invention and are not intended to limit the scope of what the inventors regard as their disclosure. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperatures, etc.); however, some errors and deviations should be accounted for. Unless indicated otherwise, temperature is °C or is at ambient temperature, and pressure is at or near atmospheric. There are numerous variations and combinations of process conditions that can be used to optimize product quality and performance. Only reasonable and routine experimentation will be required to optimize such process conditions.

[0125] Example 1:

[0126] In this example, a pathway to extend direct methane to methanol (DMtM) conversion to high yields was demonstrated by controlling the excitation of reactant molecules (in this example CH4) and the dynamics of product accumulation (CH3OH) in states of thermal non-equilibrium. The example shows how these environments can overcome fundamental limits that constrain the scalability of DMtM (i.e., the selectivityconversion limit, Figs. 1B-1C) by extending the selective formation of methanol to high degrees of reactant conversion. Vibrational excitations were leveraged to target C-H bonds (30), activate CH4 molecules, and drive their selective conversion using electrical energy (i.e., plasmas) at room temperature and pressure. The study identified pathways to control the energetics of these excitations in plasma environments to form preferential intermediates and suppress the generation of byproducts such as C2 and C3 hydrocarbons. Finally, the non-equilibrium nature of these excitations was leveraged to enable active product extraction in a one-pot reactor and overcome the selectivity-conversion limit. The experiment showed how targeted energy addition (i.e., energy addition into vibrational modes) enables the scalable utilization of methane, along with a record yield of methanol (> 20%) and energy efficiency (> 12%), at room temperature and atmospheric pressure. These targeted excitations can use renewable electrical energy (Fig. 1A) and, unlike other processes, do not rely on catalysts or industrial process heating (31) to form methanol.

[0127] These findings illustrate how targeted vibrational excitations can overcome constraints imposed by thermal processes (i.e., thermal catalysis) that limit the efficient utilization and conversion of feedstocks. Earlier studies have demonstrated how nonequilibrium molecular excitations can increase the kinetics of processes (i.e., by exciting reactants) through the activation of rate-limiting steps (27, 32). These studies, while efficient at converting CH4 at mild conditions, lack selectivity toward desired products or scalability to high yields of methanol. The present example demonstrated that these processes have characteristic timescales that can be adjusted to promote the selective excitation of reactants and removal of desirable products. By tailoring these timescales, the study showed how vibrational excitations offer a unique pathway to break limits that constrain the achievable yield of DMtM conversion along conventional pathways (Fig. ID). In particular, mechanistic insight was provided to uncover where, when, and how electrical energy should be added to excite reactants (i.e., through electron collisions) to limit branching reactions, energy losses, and undesired product conversion.

[0128] Results

[0129] Experiments were performed to study how molecular excitations influence the selectivity toward methanol in a DMtM process as methane conversion increases. A nanosecond pulsed plasma was used to excite reactants and drive conversion at atmospheric pressure in a 100 mL batch reactor (Fig. 2A). The plasma source featured adjustable field strength (9-90 kV / cm, Fig. 3B) and repetition frequency (1 kHz) to control the type (e.g., vibrational, electronic, etc.) and dynamics of excitation. A fixed reactant composition of CH4:O2:Ar = 2:1:5 (by volume) (Fig. 2A) was used to generate a stable and diffuse plasma with optimal energy costs. Reactant and product compositions were measured for different excitation energies and exposure times using gas chromatography. Increasing product selectivity toward methanol was observed as the E / N of the discharge reduced. Higher voltages (or shorter discharge gaps) were found to feature prominent C2 / C3 hydrocarbons and less oxygenates in the GC FID product composition (Fig. 8A). As voltage was lowered (or discharge gaps were increased), product selectivity toward methanol was found to increase (Fig. 8B). Higher E / N increases the production of methyl radicals and the cascade of unwanted hydrocarbon products. Methanol production was validated using NMR as depicted in Figs. 14A-14B. Along with lower C2 / C3 production (lower !<% lower E / N resulted in lower CO2 and CO production which indicates a higher selectivity to methanol. (Figs. 9A-9B).

[0130] A CH4:O2:Ar reactive mixture (2:1:5) was exposed to the plasma source for varying durations (1-10 million pulses) as reactants were consumed and products accumulated. During the exposure to 9 kV discharges, measurements of methanol selectivity were observed to decrease from > 10% at low conversion (~ 2%) to < 5% at higher conversion (> 10%) (Fig. 2B). Adjusting the applied voltage (and energy per pulse) was observed to increase the selectivity toward methanol by 500% and the maximum methanol yield by 200% at the same non-dimensional time (Time / i99% conversion, Figs. 2B-2C). Even with the inherent tunability of the applied electrical energy, the trend of lowering MeOH selectivity with increasing conversion indicates that these excitations are constrained by the same fundamental DMtM selectivity-conversion limit that restricts thermal processes from achieving high yields. These results indicate that, as methanol accumulates in the reaction vessel, the rate of its over-oxidation to CO2 exceeds the rate of its production (Fig. 2C, Time / i99% conversion > 0.05). In other words, previous studies that report high methanol selectivity and low conversion (generally with thermal catalysis, (J0-J7)) or low methanol selectivity and high conversion (generally with plasmas, (JS, 19, 21-27)) can be related based on the residence time of reactants and the energetics of reactant excitations in plasmas.

[0131] A reduced order kinetic model was developed to generalize these trends and identify pathways to high yields of methanol. The model includes pathways to produce methanol (ki), convert methanol to undesirable products (k2), and convert methane directly to undesirable products ( 1 T . The model was fit to time- dependent measurements of methanol yield (Fig. 2C) to uncover characteristic rates and timescales that govern the selectivityconversion limit as methane is excited and methanol accumulates in the reactor. Unlike attempts to explain DMtM yield in thermal processes (28, 33), the falloff characteristics of MeOH yield in the reactor indicate that the scalability of methanol yields depends on the direct conversion of methane to undesirable products. These measurements indicate that the energy and the dynamics of reactant excitations contribute to the limit of methanol yield in the reactor.

[0132] The kinetic model shows that achievable yields in DMtM conversion are constrained by distinct timescales when driven in states of thermal non-equilibrium. Timescales that govern the formation of unwanted products through branching reactions (oc 1 / Io) and the conversion of methanol (oc 1 / k2) limit scalability of these processes. However, the tunability of non- equilibrium excitations offer pathways to control these timescales, operate in a single-pot reactor, and break scaling limits that are not possible in thermal processes.

[0133] Mechanistic insights into selective methane-to-methanol conversion

[0134] Experiments were conducted to showcase how non-equilibrium excitations can be tailored to limit branching reactions and form methanol selectively. DMtM conversion was repeated at varying reduced electric fields (E / N) to adjust the mean kinetic energy of electrons, the activation of CH4, and reaction pathways to form products. A mechanistic understanding of these excitations was obtained by monitoring the product speciation of CH4:O2:Ar = 2:1:5 reactant mixtures following exposure to a fixed number (N = IM pulses) of gaseous discharges. The reduced electric field of these discharges was varied from low (i.e., diffuse) (~ 1-10 Td, 1 Td = 10'17V cm2) to high (i.e., filamentary) (> 100 Td) E / N by adjusting the discharge gap and applied voltage between a pair of W electrodes in a pin-to- pin configuration (Fig. 3A, Table 1).

[0135] The selectivity to methanol was measured to increase from < 1 % at a 1 mm discharge gap (~ 150 Td, filamentary) to > 10% at a 1 cm discharge gap (~ 1-10 Td, diffuse) (N = IM, Fig. 3B). Analysis of product species showed that filamentary discharges generated more CO, CO2 and C2 / C3 hydrocarbons (e.g., ethane, etc.), and liquid oxygenates (e.g., ethanol, acetone and acetaldehyde). In contrast, diffuse discharges (with low E / N) produced methanol selectively with no other significant hydrocarbons detected among the product species. Optical emission spectroscopy (OES) confirmed these trends by showing that filamentary discharges featured molecular bands and atomic lines from radical driven pathways including C2(d3Hg a3Hu), CH ( A2Z+X2H, B2Z+X2H, C2Z+X2H), H„ (n=3 — n =2), and C (XS — 1P°,3P — 3P°) that were suppressed in diffused discharges (Fig. 3D). These differences indicate that tuning the excitation energy changes the reaction mechanism governing methanol formation in a way that can be tuned dynamically depending on how, where, and the timescales over which electrical energy is added to the reactant species (Fig. 10).

[0136] The conversion of CH4 and O2 into products in plasma environments can be lumped into two distinct reaction pathways depending on the presence of notable intermediates (Table 1). A reduced reaction mechanism is described in Fig. 3A where notable intermediates, stable products, and branching reactions are supported by a combination of gas chromatography, optical emission spectroscopy, and sensitivity analysis (34-37). In high E / N conditions, electrons gain enough mean kinetic energy to dissociate CH4 and create reactive radicals including 'CH3 (methyl) and *H (Fig. 3C). These radicals recombine subsequently to generate unwanted branching reactions that form C2 / C3 hydrocarbons, C, and C2 (i.e., increase l<3) (Figs. 3C and 3D). Moreover, ‘CFE interacts with methanol (i.e., increasing the rate of consumption, k2) to form higher oxygenates including ethanol and acetone (Figs. 8A-8B). In low E / N conditions, electron excitations form vibrationally excited methane (CH4V) preferentially. These excitations result in low 'CH3 production, branching reactions, and C2 / C3 hydrocarbon production (Figs. 8A-8B). However, at the same E / N, the dissociation fraction of O2 into O (1D) radical is higher which enables its participation in oxidative reaction pathways (Fig. 3C). Measurements made by OES confirm details of this reduced mechanism by showing the presence of notable intermediates including 'CH (A2E+ - X2H, B2Z+- X2H, C2Z+- X2H), C2(d3Hg - high E / N while only showing *CH ( A2X+ — X2H) and O* (5P — 5S°) at low E / N discharges (Fig. 3D and 25A-25D). Moreover, OES measurements show the presence of a notable intermediate (CH3O*, Fig. 3D) at low E / N conditions. This indicates how vibrational excitations of CH4 can combine with O* to form a preferential intermediate (i.e., CH3O*) that forms methanol selectively without unwanted branching reactions. (Fig. 26).

[0137] The mechanistic insight and accompanying of the present experiments show that molecular excitations can be tailored to promote the formation of desirable products, specifically methanol, in DMtM conversion. However, methanol formation triggers the production of CH2OH (sensitivity coefficient: ~ 93%, (34)), which then undergoes a series of oxidative steps in the presence of *0, *OH, and O2 (Fig. 3A, Table 1), leading to the production of CO and CO2. It is advantageous to control the accumulation and consumption of methanol to limit these cascading oxidative steps and extend high methanol selectivity to high methane conversions.

[0138] Breaking the selectivity-conversion limit in non-equilibrium environments

[0139] Using timescale-controlled experiments, the experiment demonstrated how nonequilibrium excitations enable control over the dynamics of methanol accumulation in DMtM processes. A separate phase (i.e., water) was added to extract methanol dynamically, protect it from over-oxidation in the plasma phase, and extend the process selectivity to higher conversions. The unique nature of vibrationally excited reactants, and low operating temperatures (~ 300 K gas temperature), enable phase extraction to be integrated where conversion takes place. In particular, targeted excitations eliminate pressure and temperature effects that limit phase extraction in thermal processes. To demonstrate this idea and enable tunable product accumulation times (oc timepeakMeOH yield), an integrated pump was used to cycle product streams through water to remove methanol actively (Fig. 4A). As the flow rate was increased, the study observed the rate of methanol consumption decrease, even as conversion increased (Fig. 4B). Measurements showed that this process was able to achieve record methanol yields (> 20%) (with methanol selectivity of - 35% and methane conversion > 50%) compared to other single- step methane conversion processes. This indicates that phase extraction eliminates the selectivity-conversion limit that constrains the yield of methanol in conventional thermal processes.

[0140] The scalability of active removal was quantified by introducing an additional rate coefficient (l ) into the kinetic model to describe the phase extraction of methanol (Fig. 4C). This model was fit to the time dependent methanol yield to extract effective rate coefficients (Fig. 4C). These rates indicate that scalable methanol yields are possible if the timescale that governs the removal of methanol (oc 1 / k*) is much shorter than the timescale over which it accumulates (oc 1 / k2). The results demonstrate this scalability, as the Damkdhler number (Da = kAconvection) was decreased from 0.2 to 0.1, the yield of methanol increased by more than 100 %. In fact, the addition of active removal lowers the consumption rate of methanol and increases the time it takes for methanol to accumulate to critical levels in the gas phase (i.e., where consumption > production), k2 - 10'9min'1.

[0141] The results of the study were compared with the yield and energy efficiency (q) of other DMtM processes to assess its potential for the distributed utilization of CFU. The combination of controlling the excitation of reactant molecules, and the dynamics of product accumulation, resulted in more than double the yield and energy efficiency of other approaches that operate in states of thermal non-equilibrium (Fig. 5A). When compared to state-of-the-art multi-step CH4 to methanol conversion processes, the energy-adjusted yield (MeOH Yield / Input Energy) increases from - 24 pgMeon / J (industrial) to - 33 pgMeon / J (Fig. 5B). However, this method offers a pathway to use electrical energy and scalably convert methane to methanol at near room temperature and atmospheric pressure. The use of clean electrical input energy means the process can achieve near zero carbon intensity (i.e., during input energy generation) that is not industrial processes that utilize hydrocarbon process heating (~ 400 gCCE, eq / kgMeOH) (Fig. 5C).

[0142] Discussion

[0143] This work demonstrates pathways to convert CH4 to methanol at mild conditions using electrical energy. These results indicate the timing and way electrical energy is added (i.e., through molecular excitations) and can result in unwanted branching reactions and impose constraints on the methanol yield. Moreover, characterization of plasma excitations of CH4:O2:Ar = 2:1:5 show that processes with distinct conversions and selectivity can be unified based on the way energy is added (i.e., by the energy of excitations and the residence time of reactants). Kinetic models developed in this work detail two significant timescales that can be optimized uniquely in states of thermal non-equilibrium to break fundamental limits that constrain yields in DMtM processes. To optimize the first timescale, the study show how excitations can be tailored to vibrationally excite methane selectively, limit radical production, reduce branching reactions, and form methanol selectively. To optimize the second timescale, the study demonstrated how the non-equilibrium nature of these excitations enabled active phase extraction in reaction zones over timescales that are shorter than methanol can accumulate. Together, these enable yields of methanol in DMtM that are scalable beyond the selectivity-conversion limit and achieve record methanol yields (> 20%) by extending methanol selectivity (~ 35%) to higher methane conversions (> 50%).

[0144] The scalability of tailored vibrational excitations as a pathway for the distributed conversion of CH4 is generalized through characteristic timescales. By varying Da = k4tconvection, the study show how scalable yields of methanol can be achieved at room temperature and atmospheric pressure. The study also quantifies the energy costs of tailored vibrational excitations and compared it with state-of-the-art processes. While the study demonstrated the selective vibrational excitation of CH4 contributes to methanol formation, vibrational- vibrational (V-V) and vibrational-translational (V-T) relaxations at atmospheric pressure quenches its population (V-T CH4 - CH4 ~ 2 ps-atm and V-T CH4 -02 ~ 8 ps-atm). Adding an inert gas like Ar can provide more than 2-fold longer relaxation timescale (i.e., V-T CH4 -Ar ~ 18 ps-atm) (Figs. 17A-17B) while improving the selectivity of products and limiting unwanted bulk heating. In addition, selective vibrational excitations also offer pathways to improve the rate of methanol production (ki) by integrating catalytic surfaces and synergistically activating molecules to target rate limiting steps (i.e., dissociative adsorption of methane). However, the use of conventional transition metal catalysts presents challenges such as sintering, coking (44), and scaling relation limitations (45).

[0145] Even with higher energy costs, utilizing renewable electrical energy through targeted bond excitations has advantages over distributed scales. The use of electrical energy to drive states of thermal non-equilibrium means the process is simple, can operate at mild conditions, does not rely on catalysts, and can be deployed over the scales where methane is produced. These are all distinct from conventional pathways to utilize methane that include pipelines and distribution networks, conversion processes that utilize high temperatures and pressures, or the use of expensive methane oxidants like N2O and NO2. (46). Together, the targeted gas-phase excitation of reactant molecules using electrical energy - from local renewable energy sources (e.g., solar, wind, tidal energies) instead of burning natural gas (Fig. 1A) - offers pathways to rethink the synthesis of value-added products as processes are becoming increasingly electrified.

[0146] Materials and Methods

[0147] Experimental design

[0148] Reactor design: Methane was converted to methanol in 100 ml reactor that was maintained at atmospheric pressure. The reactor was made of quartz to eliminate interfering catalytic reactions (i.e., in stainless steel (47)) and to isolate methanol production through plasma activation. The reactor was operated with varying mixtures of CH4, O2, Ar (Praxair - 99.999% purity). The mixtures were introduced into the reactor using three digital mass flow controllers (Brooks Instrument, Model GF40). The reactor was purged for 10 mins, and the reactor composition was sampled with a gas chromatography (GC) system before plasma was ignited.

[0149] The reactor design was modular, and was used in two different modes: 1) a batch reactor to study how plasma excitations can synthesize methanol selectivity (Figs. 2A-2C and 3A-3D) and 2) a closed-loop system with a peristaltic pump (Control company Model 3389) operated at various flow rates (0.4 - 85 SCCM) to study how to break the selectivityconversion limit and produce high yields of methanol using active removal (Fig. 4A-4C). A 15 ml of deionized cold water (~ 4 °C) was used to capture the methanol (i.e., active removal) that was produced in the gas phase. Stirring was found to be unnecessary due to shock induced transport from the plasma discharge (Figs. 12A-12B and 13A-13B).

[0150] Plasma generation: A pair of tungsten electrodes (1 mm thick, cathode with 20-25° cone half angle, and anode with a flat tip), placed in a point-to-point configuration (Fig. 2A), were used to generate a spark discharge using a high-voltage nanosecond (ns) pulser (Flare from Airity Technologies). The pulser was used in conjunction with a ns pulse waveform generator (Siglent SDG1062X) and a programmable DC power supply (Keysight N5752A) to generate amplified ns voltage pulses (~ 5-10 kV) at a fixed frequency of 1 kHz. The current and voltage signals of the plasma were obtained using a high voltage probe (Tektronix 6015a) and a current probe (Pearson Model 6585) that were recorded on a mixed signal oscilloscope (Tektronix MSO44, 200 MHz bandwidth). The average energy per pulse in these experiments ranged between - 10 pj / pulse (low current - 50 mA at 1 cm discharge gap) and - 60 pj / pulse (high current - 4 A at 1 mm discharge gap) at an applied voltage - 9kV. For shorter discharge gaps (1-3 mm), energy per pulse was estimated by integrating the product of current and voltage from peak voltage to - 1 ps (Figs. 18A-18C). Corona and parasitic losses were subtracted. For a discharge gap of 1 cm, energy per pulse was estimated by extracting conduction current from total current and then integrating the product of conduction current and voltage over the discharge pulse period.

[0151] Analytical detection tools

[0152] Gas chromatography (GC): An Agilent GC 8890 gas chromatography (GC) instrument equipped with a Flame Ionization Detector (FID) was used to measure reactant (CH4) and product (CH3OH) species. A Durabond (DB-1) wax column with a polar substrate was used to support aqueous injections. The column was 250 pm thick and 30 m long and installed in an oven. The GC temperature program was set to 40 C at the time of injection followed by a linear ramp of 5 °C / min to 160 °C (0 min hold time) and a second linear ramp of 10 °C / min to 220 °C (10 mins hold time). Helium was used as the carrier gas with a constant Iml / min flow rate and nitrogen was used as the make-up gas. A split / splitless inlet was used (15:1 split ratio) with an inlet pressure of 11.6 psi and an inlet temperature of 250 °C. An inlet liner containing glass wool was used to ensure uniform vaporization of water. Unknown samples were analyzed with gas injection volumes of 100 pl (using a Hamilton gas-tight 1700 series syringe with a cemented 22 gauge needle and point style 5 with a 1700 series chancy adapter to lower the uncertainty in gaseous injection to -1%) and aqueous injections were 0.4 pl (using an Agilent microliter syringe with a cemented 22 gauge needle and point style AS) to keep the column and the inlet from getting damaged.

[0153] Nuclear magnetic resonance (NMR): A Bruker 600 MHz NMR spectrometer was used to obtain a ID1H-NMR spectrum (Fig. 15) of the reaction products dissolved in a cold aqueous sample (T ~ 4 °C) and validate the presence of methanol in the GC FID traces.

[0154] Samples were prepared by bubbling contents of the 100 ml reactor vessel through a cold 1 ml aqueous sample. Quantitative analysis was performed by spiking the sample with Tetramethylsilane (NMR grade, > 99.9% purity, CAS: 75-76-3 from Millipore Sigma) for referencing and a known amount of Deuterated Chloroform (CDCh) and Deuterated Water (D2O) for quantification of methanol using the quartet signal.

[0155] Optical emission spectroscopy (OES): A Horiba 0.5 m spectrometer (iHR 550) equipped with an EMCCD camera (synapse) was used to record emission spectra (300 - 1000 nm) from the plasma in both filamentary (spark) and diffused modes (Fig. 3D). An 1800 grooves / mm diffraction grating was used with the blaze wavelength and angle of 500 nm and 26 45’ respectively. A biconvex lens with a focal length of 125 mm was used to focus the plasma emissions into the spectrometer’s slit, and it was f / # matched with the spectrometer (f / # = 6.4). To record emission spectra of diffused discharges (~ 9kV and 1 cm discharge gap), a slit width of 100 pm was used with 3 s exposures and 50 CCD accumulations. To record emission spectra of filamentary discharges (~ 9kV and 2 mm discharge gap), a slit width of 50 pm was used with 0.5 s exposures and 50 CCD accumulations.

[0156] Quantification procedure

[0157] Calibration standards were used to quantify the conversion of methane and yield of methanol (based on external calibration method (4S)). For methane, varying sample volumes of 99.999% pure methane gas were collected in a gas tight syringe (10 pl - 200 pl) and injected into a GC FID. The GC output signal was recorded and correlated to the injected sample weight to establish a calibration curve (Fig. 14A). For methanol, liquid samples were injected into a GC inlet at 250 C to maximize gasification (methanol does not exist in a gaseous form at room temperature). DI water was used (20 - 50 mL) to dilute methanol volumes (0.2 - 0.5 pL) into the desired calibration range. An aqueous methanol sample (~ 0.4 pL) was then injected into the GC inlet. The output was again recorded and correlated to the injected sample weight to establish a calibration curve for methanol (Fig. 14B).

[0158] Conversion, yield, and selectivity in the chemical process were quantified using, Methane Conversion

[0159] Initial moles of methane — final moles of methane (1) Initial moles of methane

[0160] Methanol Selectivity

[0161] T otal produced moles of methanol (2)

[0162] Initial moles of methane — Final moles of methane

[0163] Methanol Yield = Methane Conversion x Methanol Selectivity (3) Energy efficiency of the process was quantified according to,

[0164] Energy Efficiency (77)

[0165] Moles of methanol produced x LHVMe0H(4)

[0166] Energy input + Moles of initial methane x LHVMewhere LHV is the lower heating value in J / mol.

[0167] With active removal, the yield of methanol was calculated by only considering the moles of methanol captured in aqueous phase. Measurements showed that the amount of methanol in the gaseous phase was orders of magnitude smaller (Fig. 6).

[0168] Quantifying electron energy loss fractions

[0169] BOLSIG+ (version: l l / 2019)(49) was used to calculate the distribution of electron energy losses to excite internal modes (i.e., states of non-equilibrium) in a CEL Ch: Ar = 2:1:5 mixture and a gas temperature of 300 K. The excitation temperature was set to 2000K to ensure all the super-elastic collisions were considered for E / N < 5 Td. The electron scattering cross-section data for methane, oxygen and argon were obtained from LXCat database (i.e., Morgan database, www.lxcat.net / Morgan) (50).

[0170] The overall energy loss behavior of a gas mixture (CH4, O2, and Ar) was determined by adding up the energy loss coefficients for different processes involving these species. Specifically, the coefficients for elastic and dissociative attachment, vibrational and rotational excitations, dissociative excitations, and ionization processes for each gas were included. For example, dissociation excitations of methane include the energy loss fractions for all the reactions spanning 9-12 eV (reported in LXCat, Morgan database). These loss fractions were added together to calculate a combined energy loss fraction for methane dissociation (Fig. 3B). Complete electron energy loss plots (detailing individual excitation modes) are shown in Figs. 16A-16C.

[0171] High-speed imaging

[0172] An ICCD camera (PI-MAX) was used to image the structure of nanosecond pulsed plasma discharges with varying peak currents (Fig. 10). A variable exposure time between 1 ILLS - 25 ms was used with an adjustable gain between 150 - 230 (depending on the intensity of the plasma discharge). The camera was triggered externally using a TTL generator (SRS DG535) and a current probe to enable simultaneous acquisition of the images.

[0173] Kinetic models

[0174] A three-step model kinetic model was used to interpret the tradeoff between the conversion of methane and accumulation of methanol (i.e., the selectivity-conversion limit). This model includes reactions to describe the conversion of (1) methane to methanol (ki), (2) methanol to unwanted products (i.e., CO2) (k2), and (3) methane to unwanted products directly (Io). These reactions were integrated into coupled differential equations (i.e., global kinetic equations with first-order dependence on the reactants) to describe the variation in partial pressure of methane (pci 14) and methanol (pci 13011) and fit to experimental measurements,

[0175] These coupled differential equations were solved analytically to obtain expressions for methane conversion and methanol yield as a function of time.

[0176] With active removal: A four-step kinetic model was used to describe how active removal of methanol can break the selectivity-conversion limit. A fourth reaction was added to the kinetic model to describe this removal process (l ). The system of differential equations for this model includes, where pcH4, pemoHg, and pci 1301 iw are the partial pressures of methane, gas-phase methanol, and aqueous methanol (i.e., methanol in water-phase) respectively. These differential equations were solved for pcH4, pci 1301 ig, and pci 1301 iw as a function of time and compared with experimental measurements (Fig. 4B).

[0177] Statistical analysis Experimental data were acquired for N > 3 trials to estimate random uncertainties (standard deviation). Fitting routines (i.e., MATLAB’s non-linear regression models) were used to estimate confidence intervals in kinetic parameters (i.e., ki- k*). Details on the uncertainties in these parameters is described below.

[0178] Influence of inert gas

[0179] An inert gas was added to the reactor to stabilize the plasma and to lower the reduced electric field (E / N) for initiating a discharge. Together, these enabled higher yields of methanol. Argon was chosen as the inert gas as the methanol yield difference between argon and helium was small (Fig. 7A) and argon is more economic. Various inert gas compositions were also compared to choose a gas composition for the plasma reactor. A composition of 2:1:5 was used throughout the study to minimize energy costs (Fig. 7B).

[0180] Product composition at varying E / N

[0181] Increasing product selectivity toward methanol was observed as the E / N of the discharge reduced. Higher voltages (or shorter discharge gaps) were found to feature prominent C2 / C3 hydrocarbons and less oxygenates in the GC FID product composition (Fig. 8A). As voltage was lowered (or discharge gaps were increased), product selectivity toward methanol was found to increase (Fig. 8B). Higher E / N increases the production of methyl radicals and the cascade of non-methanol hydrocarbon products (Fig. 3C).

[0182] Plasma discharge regimes

[0183] Experiments were performed to visualize the change in plasma structure (i.e., plasma regime) with varying E / N. Varying the applied voltage (Figs. 2A-2C) and the discharge gap (Figs. 3A-D and 11A-11B) were used to study these effects. Images of the plasma structure were recorded with discharge gaps between 1 mm and 1 cm. The plasma transforms from a filamentary discharge at smaller discharge gaps (high peak current - 2-3 A) to a more diffused plasma at higher discharge gaps (smaller peak current - 40 - 200 mA). For filamentary discharges (1mm - 5mm), a shorter exposure time (100 ps) and a gain setting of 200 were used, as the light output was large. For more diffused discharges (7mm - 10mm), a 20 ms exposure time was used with a gain setting of 220.

[0184] Spatial invariance in the reactor

[0185] Nanosecond pulsed plasmas generate shock waves and vortex rings that mix the contents of the reactor (2). Measurements of methane concentration within the reactor indicate this eliminates the need for a stirrer (Fig. 13). In addition, to ensure spatial homogeneity, composition was checked at a few different locations and the uncertainty in the measurements are reported in Figs. 12A-12B. For initial composition mix (when plasma is not present), a premixer was used to make sure the composition entering the reactor is well-mixed beforehand (Fig. 13, left).

[0186] Nuclear magnetic resonance (NMR)

[0187] NMR was used to doubly confirm the presence of methanol in the product samples. As methanol was produced in the gas phase, GC-FID was used to detect and quantify methanol in gas phase. However, as NMR requires liquid samples, gas-phase components were first bubbled through 1 ml water to dissolve soluble products like methanol. Since methanol retention capacity of water is not 100%, the results obtained using NMR were only used to confirm the presence of methanol in GC measurements. However, qNMR yields were of the same order as GC-FID measurements.

[0188] Evaluating electrical energy costs per pulse

[0189] The energy per pulse at discharge gaps < 5 mm (i.e., in the spark regime) was determined initially by integrating the product of current and voltage. However, due to the nanosecond pulser's rise time of approximately 200 ns, a significant portion of the calculated energy was attributed to corona and parasitic losses (Fig. 18C). Much of this energy is not deposited to molecules within the reactor. In particular, corona discharges did not contribute to methane conversion or methanol yield (Fig. 20A). Based on these measurements, corona and parasitic losses were subtracted from the energy per pulse measurements to eliminate limitations of energy deposited by the pulser. Energy deposition toward the spark generation started from the moment when the voltage reached its peak value to approximately one microsecond, after which the deposited energy remained relatively constant (Fig. 18C).

[0190] For longer discharge gaps, plasma generation (diffused discharge) was not possible due to the additional load the voltage probe imposed on the plasma generation circuitry. Consequently, voltage waveforms at these longer discharge gaps could not be obtained which rendered the traditional method of calculating energy by integrating the product of current and voltage unusable.

[0191] As obtaining voltage waveform for discharge gaps > 5 mm was not possible due to capacitive loading by the voltage probe, peak discharge voltage was estimated by fitting the data obtained at shorter discharge gaps using a theoretical glow to spark transition voltage fit from the literature (8) (Fig. 19). The estimated peak discharge voltage of approximately 9 kV at 10 mm confirmed the fit’s validity. With this approach, the transition reduced electric field (E / NGS) was calculated to be approximately 45 Td (based on a number density close to the Loschmidt constant). Notably, this value lies between the reduced electric field of the diffused discharge (-10 Td) and the reduced electric field of the spark discharge (-100 Td) (Figs. 3A-3D).

[0192] The energy deposited during the discharge was calculated by integrating the product of measured voltage and current waveforms over the duration highlighted in Fig. 20D. Later ringing periods reflect parasitic losses in the circuit and deposit negligible energy into the reactant molecules (9). The total measured current (Itotai) encompasses the conduction current (ICOnd), and parasitic currents (Ipara), which include losses due to corona, where Etotai is the total energy per pulse evaluated using the total current, Ecorona is the corona energy losses, and Epiasma is the deposited discharge energy. The energy deposited per pulse was evaluated using the conduction current obtained by subtracting the current corresponding to corona and parasitic losses from the total current. This approach applies to the spark regime as well (Figs. 18A-18C).

[0193] The energy per pulse was evaluated for the diffused discharge using the glow-to- spark transition voltage (Fig. 19). Adding a voltage probe was found to load the circuit down eliminating the discharge (due to added capacitance. This issue was addressed using the theoretical peak discharge voltage predicted at 1 cm (Fig. 19) and taking a linear drop to zero over the plasma discharge period (defined as the pulse width of the discharge peak highlighted in Fig. 20D). This method estimated an upper bound of the energy deposited per pulse (as voltage drop is non-linear with concave upward curvature (Fig. 21) of - 23 p J (Figs. 22A-22B).

[0194] With the increasing conversion in the reactor, the peak current and energy per pulse decreased. The results in Figs. 5A-5C indicate methane conversions close to 80%, which suggests that the energy deposited per pulse would further decrease to around 3-4 pj / pulse (estimated by linear extrapolation based on the drop from 0% to 30% conversion). Further verifying the energy drop, a - 100 pJ / pulse drop was observed on the input side of the nanosecond pulser over 30% conversion (Figs. 23-24). Therefore, an average energy deposited per pulse (i.e., energy per pulse at 50% conversion) was chosen (~ 10 pJ / pulse). This energy is consistent with the upper end of reported values in the literature for diffused discharges (8-10). Moreover, since the calculated energy is an upper bound (based on linear voltage drop, Figs. 20A-20D), it is reasonable to assume an average energy deposited per pulse of 10 pJ for the evaluation of specific energy input (SEI) in Figs. 5A-5C corresponding to datapoints of 1 cm discharge gap. Estimation of E / N ranges

[0195] E / N was estimated for different discharge regimes based on the applied voltage (V) and discharge gap (d), where Vcathode represents cathode voltage drop or cathode fall voltage. N was assumed to be Loschmidt’s constant. Since the cathode voltage drop is - 0.2kV at 1 cm discharge gap, it was neglected (i.e., it is negligible compared to the applied voltage, - 9kV). The mean electric field estimated using this approach for diffused and spark discharges falls in the typical range of electric fields reported in the literature.

[0196] For lower E / N range in Fig. 3C, the upper limit was chosen based on where methane dissociation starts.

[0197] Select reactions in plasma-assisted DMtM conversion

[0198] The DMtM mechanism (Fig. 3A) combines prominent pathways where methane and oxygen are converted into products through plasma-mediated processes. This includes the excitation of reactants (i.e., vibrations) and generation of radicals (i.e., CH3, H etc.). Reactions from the reaction mechanism (Fig. 3A) are summarized in Table 1. These reactions are inferred from sensitivity analyses, stable products from GC chromatograms, and energy loss fractions (Fig. 3C). The presence of notable intermediates (e.g., O, H, CH, CH3O, etc.) were confirmed with OES measurements.

[0199] Table 1. Fist of reactions used in the DMtM mechanism (Fig. 3A).

[0200]

[0201] Table 2. 95% confidence intervals for rate constants in Fig. 2C. Table 3. 95% confidence intervals for rate constants in Fig. 4B.

[0202] Input energy cost

[0203] The total energy input was evaluated by integrating the product of applied voltage and current (Fig. 23) over 20 ps (beyond which energy change flattens). The total energy input at 20 ps was - 390 pJ while the energy deposited during the discharge phase (i.e., when methanol is formed) was - 20 pJ. This discrepancy includes inefficiencies of the voltage amplifier, its energy penalty, corona losses, and parasitic losses.

[0204] The total energy input at 30% conversion was - 295 pJ. This is - 100 pJ lower than the energy cost at 0% conversion. Optical emission spectroscopy on the diffused discharge shows CH3O (emission peak at 419.5 nm (17)) peak proving the presence of methoxy radical at all times of the reaction.

[0205] The effects of various other process parameters on the selective conversion of a feedstock gas to liquid oxygenates were also studied. To assess the influence of reduced electric field on the selectivity of various products, a diffused discharge configuration with a 1 cm gap and a frequency of 1 kHz was employed. The feedstock gas mixture included methane (CH4), carbon dioxide (CO2), and argon (Ar) in a 30:15:55 ratio. As illustrated by Fig. 27, a lower reduced electric field exhibited higher selectivity for each of methanol, hydrogen, and ethanol.

[0206] Next, the influence of Damkbhler number and the feedstock composition on the product selectivity was analyzed. To isolate the impact of flow dynamics on product formation, argon was eliminated from the experimental setup. A gas mixture composed of CH4 and CO2 in a 1:1 ratio was subjected to a diffused discharge process. Remarkably, reducing the Damkbhler number by half achieved a six-fold increase in methanol selectivity within the reactor. Moreover, a reduction in the selectivity of methanol was shown as larger amounts of methane were present in the feedstock gas. Conversion of methane decreased with increasing flow rate, however, both selectivity and yield exhibited noticeable increases at higher flow rates. A summary of these results are illustrated in Fig. 28 and Fig. 29. Finally, various reactor configurations were studied to observe the methanol and ethanol selectivities in batch and tubular flow reactors. The gas composition used for these tests included methane (CH4), carbon dioxide (CO2) and argon (Ar) in 30:15:55 ratio with active removal of liquid oxygenate products like methanol and ethanol. The results of these tests are shown in Fig. 30.

[0207] Example 2:

[0208] In this example, a process for breaking the hydrocarbon cascade in electric process heating is described. It is generally understood that the chemical industry must undergo a profound transformation to achieve decarbonization and mitigate its climate impact. Reducing emissions related to process heating (which account for over 50% of emissions for chemical and petrochemical processes) is essential to this end. The heat and work required by chemical reactions and product separation are still supplied the same way they have been since the start of the Industrial Revolution - by burning fossil fuels or recycled hydrocarbon feedstock, which in turn releases large amounts of carbon dioxide (CO2). Greener processes should - among others - replace combustion heating with clean energy sources. Electric heating using renewable electricity is a promising candidate.

[0209] However, current electric heating presents several process technology, design and operation challenges. These are illustrated in Figs. 31A-31C. For example, replacing conventional combustion heating with electric heating results in fuel gas (tail gas) streams exiting the process unused. Recycling such streams, which are typically hydrocarbon mixes with little economic value alone, to generate heat is part of any process integration strategy and is essential to improving process economics. However, the CCh-rich flue gas are difficult to effectively decarbonize as a hydrocarbon cascade, thereby limiting the efficacy of electric heating in commercial processes.

[0210] The present study describes exemplary techniques to break the hydrocarbon cascade by utilizing plasma-assisted catalytic reaction paths and electrified processes in order to convert fuel gas streams into fungible, products. The study uses a multi-scale, closed-loop approach, whereby process modeling and optimization inform and direct experimental developments in reaction engineering, and updated experimental results are used to continuously improve the process model and economics.

[0211] The present study viewed the conversion of tail gas from ethylene crackers to value- added liquid hydrocarbons such as methanol (CH3OH), acetic acid (CH3COOH), and other liquid oxygenates, however, it is understood that the principles described herein can be applied to similar streams from other sources. Tail Gas Conversion Pathways

[0212] The composition of ethylene cracker tail gas streams varies as a function of feedstock. Lighter feeds (e.g., ethane) have higher ethylene yields (as high as 52% by mass). Heavier feeds (butane, naphtha) increase the production of methane. The remainder of the tail gas comprises a mixture of longer-chain linear or branched alkanes and alkenes, and aromatic compounds such as benzene, toluene and xylene.

[0213] The typical pathway for converting lighter tail gas feeds to value-added liquid hydrocarbons involves two steps. First, the tail gas is converted to syngas (a mixture of hydrogen (H2) and carbon monoxide (CO)) using reforming processes ( AH°298 = 206 kJ / mol for steam reforming, AH°298 = 247 kJ / mol for dry reforming). A variety of products can be created from syngas, including olefins and gasoline (via Fischer-Tropsch synthesis), and oxygenates, including methanol and acetic acid. This indirect pathway, while efficient and selective, leads to industrial processes that are energy and capital intensive, and require large reactors operating at demanding conditions (temperatures up to ~400 °C and pressures up to ~40 atm) to achieve appreciable conversion and yields. Moreover, these processes themselves use fossil fuels and emit large amounts of CO2.

[0214] The direct conversion of methane and CO2 in tail gas to liquid hydrocarbons (CH4 + CO2 0.502 + CO, CH4+ 0.502 CH3OH) is an alternative utilization pathway of CH4 that can enable feasible conversion at much lower temperatures (AH°298 = -126.2 kJ / mol for the methanol reaction). The partial oxidation of methane to methanol (DOMtM), in particular, has been demonstrated using a variety of approaches including heterogeneous catalysis where catalysts ranging from Mo, Fe and Cu-based zeolites, and supported noble metals (e.g., Au, Pd, Rh, etc.) have been explored to optimize catalytic stability, CH3OH conversion yield, and reaction rates. However, these catalytic reactions must overcome challeng- ing thermodynamic constraints and typically have low CH4 conversion rates (< 10%), high pressures, and potential volatilization of catalyst surfaces8. For example, in chemical equilibrium, the product selectiv- ity toward methanol peaks at only ~10'6% at ambient pressure. The poor product selectivity toward CH3OH arises from its reactivity, namely a catalytic active site that can oxidize CH4 to CH3OH can further oxidize CH3OH into unwanted products like CO or CO2 before it can desorb from the surface and upon re- adsorption. Beyond thermodynamic conversion, DOMtM also features high activation energy barriers that can constrain CH3OH production rates and require the use of high temperatures and high activity catalysts that can exacerbate the generation of unwanted products.

[0215] Non-Equilibrium Plasma Conversion

[0216] The use of non-equilibrium plasmas allows the processing of gaseous streams at lower temperatures, pressures, kinetic constraints, and capital costs. These environments feature energetic free electrons (i.e., not bound to atoms) that, through collisions, can selectively excite internal modes of molecules (Fig. 32) (e.g., vibrational, electronic, etc.), cause bond scission, and create reactive radicals in the gas-phase. Plasmas are a pathway to activate CO2 and CPU to enable the synthesis of liquid hydrocarbons at realizable thermodynamic conditions in electrified synthetic processes.

[0217] Preliminary experiments were performed on DOMtM at room temperature and pressure using a plasma spark discharge to demonstrate the value of non-equilibrium excitations (Fig. 33). Measurements of reactant conversion, product distributions, and methanol yield were recorded for varying input energy (i.e., number of sparks), electric field strength, and reactant composition. These experiments show that plasmas can (1) convert components of tail gas (i.e., CPU) to value-added liquid hydrocarbons, (2) electrify synthetic processes, and (3) vary value-added product compositions (i.e., methanol, ethanol, acetylene) by adjusting the strength of electric fields. Furthermore, these measurements show that, by tailoring the free electron energy using electric fields, favorable reaction pathways can be tuned in the gas phase.

[0218] In the current state, the data indicate an energy use of -0.01 eV / initial CPU molecule, with a one-pass conversion of up to 40% and a CH3OH selectivity of up to 10% (CH3OH yield > 3%). By comparison, present industrial systems achieve CH3OH yields of ~ 5-15%. However, these systems generally rely on catalysts, go through multiple steps to synthesize desired products, and operate under demanding thermodynamic conditions (pressures on the order of tens of bars, temperatures around 400°C).

[0219] The methods and compositions of the appended claims are not limited in scope by the specific methods and compositions described herein, which are intended as illustrations of a few aspects of the claims and any methods and compositions that are functionally equivalent are within the scope of this disclosure. Various modifications of the methods and compositions in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative methods, compositions, and aspects of these methods and compositions are specifically described, other methods and compositions and combinations of various features of the methods and compositions are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents can be explicitly mentioned herein; however, all other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.

[0220] The following publications as listed below and throughout this document are hereby incorporated by reference in their entirety herein.

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Claims

CLAIMSWhat is claimed is:

1. A process for selectively converting a feedstock comprising a reactant and an oxidant to a target intermediate, the process comprising: selectively generating in a reaction chamber a transiently-formed target intermediate from the reactant; and actively removing the transiently-formed target intermediate from the reaction chamber, wherein a rate that the transiently-formed target intermediate is removed from the reaction chamber is greater than or equal to a rate that the transiently-formed target intermediate is consumed.

2. The process of claim 1, wherein the transiently-formed target intermediate is selectively generated by contacting the feedstock with a plasma in the reaction chamber under thermal non-equilibrium conditions to produce a vibrationally excited precursor or radical, and wherein the vibrationally excited precursor or radical is selective for forming the transiently-formed target intermediate.

3. The process of claim 2, wherein the vibrationally excited precursor has a characteristic vibrational temperature greater than a temperature of the reactant.

4. The process of any one of claims 2-3, wherein the plasma is generated using a reduced electric field (E / N) of from 1 to 100 Td.

5. The process of any one of claims 1-4, wherein the transiently-formed target intermediate is selectively generated using thermal catalysis.

6. The process of any one of claims 1-5, wherein the reaction chamber further comprises an inert gas.

7. The process of any one of claims 1-4 or 6, wherein the transiently-formed target intermediate is formed from the feedstock without using a catalyst.

8. The process of any one of claims 1-7, wherein the feedstock has a temperature of 500 K or less.

9. The process of any one of claims 1-8, wherein the feedstock comprises a gaseous feedstock having a pressure of 5 atm or less.

10. The process of any one of claims 1-9, wherein a Damkohler number of the active removal of the transiently-formed target intermediate is 1.0 or less.

11. The process of any one of claims 1-10, wherein a molar selectivity of the transiently-formed target intermediate is 20% or more.

12. The process of any one of claims 1-11, wherein a conversion of the reactant is 10% or more.

13. The process of any one of claims 1-12, wherein a yield of the transiently-formed target intermediate is 10% or more.

14. The process of any one of claims 1-13, wherein the transiently-formed target intermediate is actively removed from the reaction chamber by contacting the transiently- formed target intermediate with a liquid solvent.

15. The process of claim 14, further comprising separating the transiently-formed target intermediate from the liquid solvent.

16. The process of any one of claims 1-15, wherein the transiently-formed target intermediate is actively removed using a solid-phase adsorbent.

17. The process of any one of claims 1-16, wherein the feedstock comprises natural gas.

18. The process of any one of claims 1-17, wherein the feedstock comprises a tail gas.

19. The process of any one of claims 1-18, wherein the feedstock comprises methane.

20. The process of any one of claims 1-19, wherein the oxidant comprises air, oxygen, N2O and / or CO2.

21. The process of any one of claims 1-20, wherein the transiently-formed target intermediate comprises a liquid oxygenate.

22. The process of any one of claims 1-21, wherein the transiently-formed target intermediate comprises methanol, ethanol, acetate, formate, or a combination thereof.

23. The process of any one of claims 1-22, wherein the transiently-formed target intermediate comprises methanol.

24. The process of any one of claims 1-23, wherein the process is a continuous process.

25. The process of any one of claims 1-24, wherein the process is a semi-continuous process.

26. A system for selective conversion of a feedstock comprising a reactant and an oxidant to a target intermediate, the system comprising: a reaction chamber configured to receive the feedstock and selectively generate a transiently-formed target intermediate from the reactant; and a species recovery unit, the species recovery unit being operatively coupled to the reaction chamber and configured to actively remove the transiently-formed target intermediate from the reaction chamber, wherein a rate that the transiently-formed target intermediate is removed from the reaction chamber is greater than or equal to a rate that the transiently-formed target intermediate is consumed.

27. The system of claim 26, wherein the reaction chamber further comprises one or more electrodes configured to form a plasma, and wherein the transiently-formed target intermediate is selectively generated by contacting the feedstock with the plasma in the reaction chamber under thermal non-equilibrium conditions to produce a vibrationally excited precursor or radical, and wherein the vibrationally excited precursor or radical is selective for forming the transiently-formed target intermediate.

28. The system of claim 27, wherein the vibrationally excited precursor has a characteristic vibrational temperature greater than a temperature of the reactant.

29. The system of any one of claims 27-28, wherein the one or more electrodes comprises at least two electrodes configured to generate the plasma therebetween.

30. The system of any one of claims 27-29, wherein the plasma is generated using a reduced electric field (E / N) of from 1 to 100 Td.

31. The system of any one of claims 26-30, wherein the transiently-formed target intermediate is selectively generated using thermal catalysis.

32. The system of any one of claims 26-31, wherein the reaction chamber further comprises an inert gas.

33. The system of any one of claims 26-30 or 32, wherein the transiently-formed target intermediate is formed from the feedstock without using a catalyst.

34. The system of any one of claims 26-33, wherein the feedstock has a temperature of 500 K or less.

35. The system of any one of claims 26-34, wherein the feedstock comprises a gaseous feedstock having a pressure of 5 atm or less.

36. The system of any one of claims 26-35, wherein a Damkbhler number of the active removal of the transiently-formed target intermediate is 1.0 or less.

37. The system of any one of claims 26-36, wherein a molar selectivity of the transiently-formed target intermediate is 20% or more.

38. The system of any one of claims 26-37, wherein a conversion of the reactant is 10% or more.

39. The system of any one of claims 26-38, wherein a yield of the transiently-formed target intermediate is 10% or more.

40. The system of any one of claims 26-39, wherein the species recovery unit comprises a liquid solvent stream configured to actively remove the transiently-formed target intermediate from the reaction chamber.

41. The system of claim 40, further comprising a separating unit configured to separate the transiently-formed target intermediate from the liquid solvent.

42. The system of any one of claims 26-41, wherein the species recovery unit comprises a solid-phase adsorbent configured to actively remove the transiently-formed target intermediate from the reaction chamber.

43. The system of any one of claims 26-42, wherein the feedstock comprises natural gas.

44. The system of any one of claims 26-43, wherein the feedstock comprises methane.

45. The system of any one of claims 26-44, wherein the oxidant comprises air, oxygen, N2O and / or CO2.

46. The system of any one of claims 26-45, wherein the transiently-formed target intermediate comprises a liquid oxygenate.

47. The system of any one of claims 26-46, wherein the transiently-formed target intermediate comprises methanol, ethanol, acetate, formate, or a combination thereof.

48. The system of any one of claims 26-47, wherein the transiently-formed target intermediate comprises methanol.

49. The system of any one of claims 26-48, configured to operate continuously.

50. The system of any one of claims 26-48, configured to operate semi-continuously.

51. The system of any one of claims 26-50, wherein the reaction chamber has an inlet conduit configured to receive a methane-rich source.

52. The system of any one of claims 26-51, wherein the reaction chamber is operatively coupled to a wellhead.

53. The system of any one of claims 26-51, wherein the feedstock comprises a tail gas.

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