Method for controlling syngas composition from an engine-based syngas generator - Patents.com

Abstract

The present disclosure provides a process for controlling syngas composition from an internal combustion engine-based syngas generator. Typically, air is used as the oxidant and nitrogen (N2) is used as the diluent, which results in high cost downstream compression and low feedstock conversion efficiency. The present disclosure provides CO2 as a diluent to reduce the N2 concentration in the syngas. In some embodiments, the CO2 diluent can be from biogas processing in combination with methanol, DME, and / or hydrocarbon production, or natural gas processing in combination with Fischer-Tropsch (FT) synthesis and / or other hydrocarbon synthesis.

Description

[Technical field]

[0001] 1. CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. patent application Ser. No. 63 / 153,033, Atty. Dkt. No. 121-93-PROV, by Parvathikar et al., entitled “Method to Control Syngas Composition from an Engine-based Syngas Generator,” filed Jan. 8, 2021, which is incorporated by reference in its entirety.

[0002] (2. Technical Field) The present disclosure provides a process for controlling the syngas composition from an internal combustion engine-based syngas generator. Typically, air is used as the oxidant and nitrogen (N2) is used as the diluent, which results in high cost downstream compression and low feedstock conversion efficiency. The disclosure provides carbon dioxide (CO2) as a diluent to reduce the N2 concentration in the syngas. In some embodiments, the CO2 diluent can be derived from either biogas processing combined with methanol, dimethyl ether (DME) and / or hydrocarbon production, or natural gas processing combined with methanol, DME, or Fischer-Tropsch (FT) synthesis, or other hydrocarbon production. [Background technology]

[0003] (3. Background technology) (3.1. Introduction) The "Background" discussion provided herein is intended to generally indicate the context of the present disclosure. To the extent that it is described in this Background section, the work of the inventors named in the disclosure, as well as aspects of the description that may not have been admitted as prior art at the time of filing, are not admitted, expressly or impliedly, as prior art to the present disclosure.

[0004] Engine-based syngas generators use an internal combustion engine to partially oxidize a feedstock such as methane (CH4) or natural gas to produce syngas using air as the oxidant. Syngas, a mixture of carbon monoxide (CO) and hydrogen (H2), is an intermediate that can be used in the production of various chemicals such as methanol and Fischer-Tropsch (FT) liquids. The engine primarily operates by partial oxidation, which requires oxygen to convert the hydrocarbon feedstock into syngas.

[0005] Previous work has been disclosed to include air, enriched air, or pure oxygen as the feed oxidant. For example, U.S. Patents 9,909,491 and 9,919,776 (Bromberg et al.) disclose an engine that produces hydrogen-rich gas in a reformer for a liquid fuel production system. They suggest a gaseous hydrocarbon fuel, such as natural gas, as a reactant, and an oxidant, such as air, oxygen-enriched air, or oxygen. For operation with enriched air or oxygen as a reactant, Bromberg et al. suggest using nitrogen or water as a diluent. The reference suggests that "it is possible to use a portion of the generated cooled syngas for dilution or to use exhaust gas from the process." Alternatively, the engine may be operated as a closed system using argon as the diluent.

[0006] US Pat. No. 2,391,687 discloses an engine for producing synthesis gas using 90-99% oxygen as a reactant.

[0007] WO 2019 / 067341 (Carpenter et al.) discloses an internal combustion engine reactor for producing synthesis gas and conditions for operating the reactor under fuel-rich conditions.

[0008] In fact, the operation of the engine to produce syngas requires the use of air, or potentially mildly enriched air (typically 35-38 mol% oxygen), as the oxidizer. Nitrogen (N2) in air or enriched air is necessary because it acts as a diluent that provides a stable flame upon ignition as well as a manageable in-cylinder temperature and pressure profile. The need for a diluent limits the use of other oxidizers such as highly enriched air or pure or nearly pure oxygen (O2). The resulting syngas consists of large amounts of nitrogen, typically more than 50%. Separating N2 from syngas is difficult and expensive. A typical solution is to carry N2 through downstream syngas conversion and separate the products after conversion. As a result, not only the syngas but also the N2 must be compressed to achieve the desired operating conditions in the synthesis process following the engine, increasing the capital and operating costs of the system by more than a factor of two. Carrying inert N2 through these stages results in higher compression costs, larger reactor volumes, lower separation efficiencies, and lower carbon conversions. Summary of the Invention

[0009] 4. SUMMARY OF THEINVENTION The present disclosure provides a method for producing synthesis gas comprising reacting a hydrocarbon fuel with an oxygen-enriched feed gas in an internal combustion engine reactor, the feed gas comprising carbon dioxide diluent present in an amount of about 5 to about 50 mol %, and enriched oxygen present in an amount of about 25 to 95 mol %, to produce synthesis gas.

[0010] The present disclosure also provides a system for converting biogas to liquids, demonstrated herein using methanol and / or DME as an example. The system includes: (a) a biogas processing unit for removing a substantial portion of sulfur compounds from the biogas, and optionally removing at least a portion of the carbon dioxide from the biogas to produce a clean biogas stream having a carbon dioxide content of about 1 to about 35 mol %, (b) an air separation unit for producing an oxygen-rich gas stream of about 25 to about 95 mol %, (c) an internal combustion engine reactor fluidly connected to the biogas processing unit and the air separation unit and reacting the clean biogas stream with the oxygen-rich stream to produce a syngas stream, (d) a gas separation unit and a syngas compression unit fluidly connected to the syngas stream from the internal combustion engine reactor to produce a treated syngas stream, and (e) a methanol, DME, and / or hydrocarbon synthesis unit fluidly connected to the treated syngas stream.

[0011] Additionally, the disclosure provides a system for converting natural gas to liquids, demonstrated herein using synthetic crude oil as an example. The system includes: (a) a natural gas fluid stream; (b) an air separation unit producing an oxygen-rich gas stream having about 25 to about 95 mol% oxygen; (c) an internal combustion engine reactor fluidly connected to the natural gas source and the air separation unit and reacting the clean biogas stream with the oxygen-enriched stream to produce a syngas stream; (d) a water-gas shift / gas separation unit and a syngas compression unit fluidly connected to the syngas stream from the internal combustion engine reactor to produce a treated syngas stream and a carbon dioxide-rich stream; (e) the carbon dioxide-rich stream fluidly connected to the internal combustion engine reactor to provide a carbon dioxide-containing diluent stream; and (f) a Fischer-Tropsch (FT) reactor fluidly connected to the treated syngas stream. [Brief description of the drawings]

[0012] [Figure 1]5. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block flow diagram of a biogas-based feedstock providing CO2 diluent for producing methanol, DME, and / or hydrocarbons. [Diagram 2] FIG. 2 is a block flow diagram of FT synthesis from natural gas. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 6. MODE FOR CARRYING OUT THEINVENTION The present disclosure provides a method and system for providing CO2 as a diluent in the feedstock to the engine. As mentioned above, U.S. Patent Nos. 9,909,491 and 9,919,776 disclose the addition of small amounts of other components such as steam, argon, or hydrogen to enable the operation of the engine, and the use of air or enriched air as the oxidant. Previously, the prohibitive cost of air separation limited the use of pure O2 or dilution of O2 with alternative gases. Similarly, emerging feedstocks such as biogas already have significant CO2 concentrations. CO2 has the advantage of being easily separated from syngas and not participating in partial oxidation reactions. However, at high temperatures such as those found in partial oxidation reactions, CO2 can participate in reforming and water-gas shift reactions that change the composition of the syngas. These reactions of CO2 are limited by its short residence time and rapid cooling from peak temperature in the cylinder to lower temperatures. By replacing N2 dilution with CO2 dilution, a more valuable high-quality syngas may be produced. A higher quality syngas allows for cheaper and more efficient downstream conversion of the syngas to other desired products.

[0014] Use of an O2 stream (25-95 mol% or more) to feed a syngas generator. This O2 stream may be supplied from any number of known sources, such as vacuum pressure swing adsorption, pressure swing adsorption, cryogenic separation, pipeline supply, bulk liquid supply, etc. Amounts are referred to as mole fractions (mol percentages, mol%) throughout this disclosure, although one of ordinary skill in the art will recognize that this term may be used interchangeably with volume percentages or vol%. Similarly, the molecular weight of the gas of interest may be used to convert from mol% or vol% to weight percent (wt%).

[0015] Supply of gaseous hydrocarbon streams from various sources such as gas wells, associated gas from oil wells, waste gas streams, biogas from anaerobic digestion processes, biogas from landfills.

[0016] · Feed CO2 streams into the engine system from multiple sources to dilute the total gas feed to the engine pistons.

[0017] The CO2 is already mixed with the fuel, such as in the case of biogas or other potential waste streams.

[0018] · The CO2 separated from the produced syngas prior to conversion can be recycled into the engine feedstock.

[0019] · The CO2 produced in the synthesis gas conversion can be recycled into the engine feedstock.

[0020] · Alternative CO2 sources may also be used to dilute engine feedstock.

[0021] · Start-up of the syngas generator can be envisaged under two circumstances: when CO2 for dilution is available and when it is not.

[0022] When CO2 is not available, the syngas generator is started under conditions similar to power generation, where the fuel-air mixture is near-stoichiometric to lean, producing a more complete combustion with a CO2 rich exhaust. The CO2 from this exhaust is separated and recycled to begin diluting the feedstock, and the operating parameters are transitioned from start-up conditions to syngas production conditions.

[0023] When CO2 for dilution is available, such as from a biogas fuel feedstock or alternative source, the start-up of the syngas generation system begins with CO2 dilution and adjusts operating parameters to transition from combustion to partial oxidation during start-up.

[0024] · Downstream of the engine, the produced syngas is then conditioned to adjust the syngas composition as needed, such as by (a) incorporating a water-gas shift reactor to convert excess CO2 to CO and adjusting temperature and pressure as needed, and / or (b) separating excess CO2 from the syngas and producing higher concentrations of CO and H2 in the syngas than traditional systems utilizing an internal combustion engine in a syngas generation system.

[0025] The addition of unused H2 from the syngas conversion process or other sources is envisioned as a way to tailor the feedstock properties to balance some of the potential negative effects, such as reduced flame speed, that increased CO2 concentrations in the feedstock can cause.

[0026] In some embodiments, the CO2 diluent can be derived from either biogas processing combined with methanol, dimethyl ether (DME) or hydrocarbon production, or natural gas processing combined with methanol, DME, or Fischer-Tropsch (FT) synthesis or other hydrocarbon production. The hydrocarbons can be lower olefins (C2-C4 olefins), liquid fuels (C5-C20 hydrocarbons), or aromatics. Non-limiting examples include: For liquid fuels, see N. Duyckaerts, M. Bartsch, I.T.Trotus,, N. Pfa:nder, A. Lorke, F. Schu:th, G. Prieto, Angew. Chem. Int. Ed. 2017, 56, 11480-11484 (Co / Al2O3FT catalyst with Pt / ZSM-5 hydrotreating catalyst to form liquid hydrocarbons), J. Kang, K. Cheng, L. Zhang, Q. Zhang, J. Ding, W. Hua, Y. Lou, Q. Zhai, Y. See Wang, Angew. Chem. Int. Ed. 2011, 50, 5200-5203 (Mesoporous zeolite-supported ruthenium nanoparticles for preparing C5-C11 isoparaffins); X. Peng, K. Cheng, J. Kang, B. Gu, X. Yu, Q. Zhang, Y. Wang, Angew. Chem. Int. Ed. 2015, 54, 4553-4556 (Zeolite-supported cobalt nanoparticles for producing C10-C20 hydrocarbons (diesel fuel)).For lower olefins, see Cheng, B. Gu, X. Liu, J. Kang, Q. Zhang, Y. Wang, Angew. Chem. Int. Ed. 2016, 55, 4725-4728 (Zr-Zn binary oxide and zeolite SAPO-34 to form CH3OH, DME, and C2-C4 olefins), F. Jiao, X. Liu, K. Gong, Y. Chen, G. Li, X. Bao, Angew. Chem. Int. Ed. 2018, 57, 4692-4696 (ZnCr to form ethylene) ox mordenite), X. Liu, W. Zhou, Y. Yang, K. Cheng, J. Kang, L. Zhang, G. Zhang, X. Min, Q. Zhang, Y. Wang, Chem. Sci. 2018, 9, 4708-4718 (Zn-doped ZrO2 nanoparticles and zeolite SSZ-13 nanocrystals for the formation of C2-C4 olefins), J. Su, D. Wang, Y. Wang, H. Zhou, C. Liu, S. Liu, C. Wang, W. Yang, Z. Xie, M. He, ChemCatChem 2018, 10, 1536-1541 (Zirconium-doped indium catalyst and SAPO-34 zeolite for the formation of light olefins). For aromatics, see Cheng, W. Zhou, J. Kang, S. He, S. Shi, Q. Zhang, Y. Pan, W. Wen, Y. Wang, Chem 2017, 3, 334-347 and Abstracts in Brosius, R., Claeys, M. Chem 2017, 3, 198-210 (Zn-ZrO2 nanoparticles in zeolites to form aromatics); JL Weber, I. Dugulan, PE de Jongh, KP de Jong, ChemCatChem 2018, 10, 1107-1112 (Iron-based FT catalysts and zeolites for the synthesis of aromatics and olefins); P. Zhang, L. Tan, G. Yang, N. Tsubaki, Chem. Sci. 2017, 8, 7941-7946 (Cr / Zn hybrid zeolite catalysts for the production of xylenes, including paraxylene).

[0027] (6.1.Definition) Although the following terms are believed to be well understood to those of skill in the art, the following definitions are provided to facilitate description of the presently disclosed subject matter.

[0028] The term "partial oxidation" should be understood to mean reacting a hydrocarbon with an oxidant at a level lower than the stoichiometric ratio required for complete conversion to carbon dioxide and water.

[0029] Throughout this specification, the terms "about" and / or "approximately" may be used in conjunction with numerical values ​​and / or ranges. The term "about" should be understood to mean a value close to the stated value. For example, "about 40 [units]" may be within ±25% of 40 (e.g., 30 to 50), ±20%, ±15%, ±10%, ±9%, ±8%, ±7%, ±6%, ±5%, ±4%, ±3%, ±2%, ±1%, ±1%, less than ±1%, or any other value or range of values ​​within or below that range. Alternatively, depending on the context, the term "about" may mean ±1 / 2 standard deviation, ±1 standard deviation, or ±2 standard deviations. Furthermore, the phrases "less than about [value]" or "greater than about [value]" should be understood in light of the definition of the term "about" provided herein. The terms "about" and "approximately" may be used interchangeably.

[0030] Throughout this specification, numerical ranges are provided for specific quantities. It is to be understood that these ranges include all subranges therein. Thus, the range "50-80" includes all possible ranges therein (e.g., 51-79, 52-78, 53-77, 54-76, 55-75, 60-70, etc.). Furthermore, all values ​​within a given range may be endpoints of the ranges contained therein (e.g., the range 50-80 includes ranges having endpoints such as 55-80, 50-75, etc.).

[0031] As used herein, the verb "comprise" and its conjugations as used in the specification and claims are used in an open-ended sense meaning to include the items following the word, but not to exclude items not specifically mentioned.

[0032] Throughout this specification, the word "comprises" or variations such as "comprises" or "comprising" will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of other elements, integers, steps, or group of elements, integers or steps. The disclosure may "comprise," "consist," or "consist essentially of" the claimed steps, elements, and / or reagents, as appropriate.

[0033] Moreover, it should be noted that the claims may be drafted to exclude any element, and thus, this statement is intended to serve as a predicate for using exclusive terminology, such as "solely," "only," and the like, in connection with the recitation of claim elements or the use of a "negative" limitation.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs.Preferred methods, devices, and materials are described, but any methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure.All references cited herein are incorporated by reference in their entirety.

[0035] The following examples are intended to further illustrate the present invention, but are not intended to limit its scope.In particular, it should be understood that the present disclosure is not limited to the specific embodiments described, and may of course be modified.It should also be understood that the terms used herein are intended to describe specific embodiments only, and are not intended to be limiting, since the scope of the present disclosure is limited only by the scope of the appended claims. EXAMPLES

[0036] 7. Working Examples 7.1. Example 1: Biogas Feedstock Biogas typically consists of about 65% CH4, about 35% CO2 and some sulfur compounds. Traditional use of biogas involves removal of the sulfur compounds and CO2, resulting in a pipeline-quality CH4 stream (less than 2 mol% CO2) that can be used in an engine using air as the oxidant. In this scenario utilizing the present disclosure, the CO2 in the biogas is used as a diluent instead of N2 in the feed to the engine. This allows the use of enriched air with O2 concentrations of 25-95 mol% provided by commercially available technologies such as membranes and vacuum pressure swing adsorption (VPSA). Because CO2 is relatively inert in the partial oxidation of CH4 and easier to separate from the gas stream than N2, the syngas composition from the engine effluent can be adjusted to the desired concentration by removing the CO2 using one of several methods such as membranes before compression for further synthesis. For example, for methanol synthesis, the CO2 is adjusted to about 8-12 mol%.

[0037] Another example in this case is the optional recycle to the engine feed of the H2-rich stream separated from the reactor exhaust gas using a selective membrane or a pressure swing adsorber (PSA). This has the advantage of increasing the heating value of the feed gas and allowing stable flame propagation even under conditions of high feed CO2 concentration. A block flow diagram of the proposed process is shown in Figure 1.

[0038] 7.2. Example 2: Natural Gas Feedstock In the case of natural gas feedstocks, such as those originating from pipelines or stranded resources, the feedstock typically does not consist of significant amounts of CO2 or other suitable inerts, as is the case with biogas. However, integration with chemical production processes such as FT Liquids allows the opportunity to replace the N2 in the oxidant air with another stream provided by downstream gas separation.

[0039] In the FT process, synthesis gas is converted to synthetic crude oil in a catalytic reactor. The liquid products of the reaction, consisting of C5+ hydrocarbons, are separated from the gaseous products such as H2, CO, CO2, light hydrocarbons, and unreacted feedstock.

[0040] In a conventional FT process, the CO2 is removed in a solvent wash process, after which an H2-rich stream is recovered from the CO2-free stream and used to upgrade the C5+ crude oil stream.

[0041] This case illustrates how a gas separation process downstream of the synthesis gas conversion (in this case the FT synthesis reactor) can be used to provide CO2 for dilution and improve the overall system efficiency. In this scenario, a separation process such as membrane or PSA extracts an H2-rich stream from the gaseous effluent of the FT synthesis reactor. This produces a CO2- and hydrocarbon-rich waste gas stream (denoted CO2-rich stream) and at least one H2-rich stream.

[0042] The CO2 and light hydrocarbon rich waste gas stream (denoted CO2 rich stream) is recycled back to the engine feedstock, where the CO2 acts as a diluent and other hydrocarbons may undergo partial oxidation, while simultaneously helping to stabilize in-cylinder ignition and combustion. Recycling this portion of the FT synthetic effluent back to the engine may require gas cooling, water removal, additional filtration, and a small amount of purging, as known in a typical recycle setup. Recycling the waste hydrocarbons also increases the overall system efficiency, as it increases the chances that those molecules will be converted into desired products.

[0043] The H2 rich stream may be used in a variety of ways, such as further upgrading crude oil to diesel / naphtha as shown in the diagram, and may be recycled to the syngas between the engine and FT synthesis to increase the H2 / CO ratio of the syngas fed to the FT block, and a small portion of the H2 rich stream may be recycled back to the engine feed for flame stabilization, if desired and depending on the process run being performed.

[0044] As described in Example 1, the composition of the synthesis gas can be adjusted by either water-gas shift, separation, or gas conversion by a combination of the two before compression for synthesis. An example incorporating this aspect of the disclosure is shown in Figure 2. The use of this recycle allows the use of enriched air in the feed to the engine and replaces it with N2 as a diluent. The extent to which the use of N2 for dilution can be reduced depends on the performance of the catalyst and the operating conditions of the FT synthesis. This can affect the CO2 selectivity in the FT reaction and the availability of alternative inert gas streams. [Prior art documents] [Patent documents]

[0045] [Patent Document 1] (8. Prior Literature) Bromberg, L., Green, WH, Sappok, A., Cohn, DR, Jalan, A., “Engine reformer systems for lower cost, smaller scale manufacturing of liquid fuels”, U.S. Patent No. 9,909,491 [Non-patent literature]

[0046] [Non-Patent Document 1] Browne, JB, “A' techno-economic and environmental analysis of a novel technology utilizing an internal combustion engine as a compact, inexpensive micro-reformer for a distributed gas-to-liquids system”, Doctoral Thesis, Columbia University, 2016.

[0047] (9. General Disclosure Statement) The following numbered statements provide a general description of the disclosure and are not intended to limit the scope of the appended claims.

[0048] Description 1: A method for producing synthesis gas comprising reacting a hydrocarbon fuel with an oxygen-rich feed gas in an internal combustion engine reactor, the feed gas comprising a carbon dioxide diluent present at about 5 to about 50 mol % to produce synthesis gas, the oxygen-rich feed gas being present at about 25 to about 95 mol %. The carbon dioxide diluent may be present at about 5 to about 10 mol %, about 10 to about 15 mol %, about 15 to about 20 mol %, about 20 to about 25 mol %, about 25 to about 30 mol %, about 30 to about 35 mol %, about 35 to about 40 mol %, about 40 to about 45 mol %, or about 45 to about 50 mol %. The enriched oxygen may be present at about 25 to about 35 mol%, about 35 to about 45% mol%, about 45 to about 55% mol%, about 55 to about 65% mol%, about 65 to about 75% mol%, about 75 to about 85% mol%, or about 85 to about 95% mol%.

[0049] Statement 2: The method of statement 1, wherein the enriched oxygen feed gas is obtained by vacuum pressure swing adsorption, pressure swing adsorption, cryogenic separation, membrane gas separation, or a combination thereof.

[0050] Statement 3: The method of any of statements 1 or 2, wherein the hydrocarbon fuel is a gaseous hydrocarbon fuel.

[0051] Item 4: The method of item 3, wherein the gaseous hydrocarbon fuel is natural gas.

[0052] Item 5: The method of item 3, wherein the gaseous hydrocarbon fuel is biogas.

[0053] Item 6: The method of item 3, wherein the gaseous hydrocarbon fuel is from a gas well or is associated gas from an oil well.

[0054] Item 7: The method of item 3, wherein the gaseous hydrocarbon fuel is a fuel mixture that includes at least a portion of a carbon dioxide diluent.

[0055] Item 8: The method of item 7, wherein the fuel mixture is biogas from a landfill or biogas from an anaerobic digestion process.

[0056] Item 9: The method of any of items 1 to 8, wherein at least a portion of the carbon dioxide diluent is obtained by separation from the synthesis gas downstream of the internal combustion engine reactor prior to the synthesis gas processing step.

[0057] Item 10: The method of any of items 1 to 8, wherein the carbon dioxide diluent is obtained from the product of a synthesis gas processing step.

[0058] Item 11: The method of item 1, wherein the carbon dioxide diluent is obtained from a separate source.

[0059] Item 12: The method of any of items 1 to 11, wherein the feed gas further comprises hydrogen and a hydrocarbon added to increase flame speed.

[0060] Item 13: The method of item 12, wherein the added hydrogen and hydrocarbons are obtained from a synthesis gas conversion system.

[0061] Description 14: The method of any of claims 1 to 13, wherein the internal combustion engine reactor is initially operated at a stoichiometric to lean fuel-oxygen ratio and then transitioned to a rich fuel-oxygen ratio to maximize synthesis gas production.

[0062] Item 15: The method of any of items 1 to 13, wherein carbon dioxide from an internal combustion engine reactor is first flowed in a full oxidation mode to produce carbon dioxide, which is separated and added to the feed gas stream.

[0063] Description 16: The method of any of claims 1 to 15, wherein the synthesis gas is conditioned by a water gas shift reactor to convert excess carbon dioxide to carbon monoxide, to regulate temperature, to regulate pressure, to separate excess carbon dioxide, or a combination thereof.

[0064] Description 17: The method of any of descriptions 1 to 15, wherein the synthesis gas is conditioned by separating excess carbon dioxide or diluent by a membrane, a pressure swing adsorber, a solvent-based separation system, or a combination thereof.

[0065] Item 18: The method of any of items 1 to 17, wherein the synthesis gas is converted to methanol in a methanol synthesis unit.

[0066] Item 19: The method of item 18, wherein the methanol is subsequently converted to dimethyl ether (DME) in a two-stage DME synthesis unit.

[0067] Description 20: The method of any of descriptions 1 to 17, wherein the synthesis gas is converted directly to dimethyl ether (DME) in a single-stage DME synthesis unit.

[0068] Description 21: The method of any of descriptions 1 to 17, wherein the synthesis gas is converted to lower olefins, liquid fuels, or aromatics in a hydrocarbon synthesis unit.

[0069] Item 22: The method of any of items 1 to 17, wherein the synthesis gas is converted to synthetic crude oil in a Fischer-Tropsch (FT) reactor.

[0070] Description 23: A system for converting biogas to methanol, comprising: (a) a biogas processing unit for removing a substantial portion of sulfur compounds from the biogas and, optionally, removing at least a portion of carbon dioxide from the biogas to produce a clean biogas stream having a carbon dioxide content of about 1 to about 35 mol%; (b) an air separation unit for producing an oxygen-rich gas stream having an oxygen content of about 25 to about 95 mol%; (c) an internal combustion engine reactor fluidly connected to the biogas processing unit and the air separation unit and reacting the clean biogas stream with the oxygen-rich stream to produce a syngas stream; (d) a gas separation unit and a syngas compression unit fluidly connected to the syngas stream from the internal combustion engine reactor to produce a treated syngas stream; and (e) a methanol, DME, and / or hydrocarbon synthesis unit fluidly connected to the treated syngas stream. The system for converting biogas to methanol.

[0071] Description 24: The system of description 23, wherein the biogas separation unit produces clean biogas having a carbon dioxide content of about 5 to about 30 mol%. The clean biogas can have a carbon dioxide content of about 5 to about 10 mol%, about 10 to about 15 mol%, about 15 to about 20 mol%, about 20 to about 25 mol%, about 25 to about 30 mol%, or about 30 to about 35 mol%. The air separation unit can produce enriched oxygen with an oxygen content of about 25 to about 35% mol%, about 35 to about 45% mol%, about 45 to about 55% mol%, about 55 to about 65% mol%, about 65 to about 75% mol%, about 75 to about 85% mol%, or about 85 to about 95% mol%.

[0072] Description 25: The system of descriptions 23-24, wherein the gas separation unit is fluidly connected to the internal combustion engine reactor for introducing carbon dioxide as a diluent to the internal combustion engine reactor.

[0073] Description 26: The system of any of descriptions 23 to 25, wherein the methanol, DME, and / or hydrocarbon synthesis unit produces a hydrogen stream, and the hydrogen stream is fluidly connected to an internal combustion engine reactor, a gas separation unit, a syngas compression unit, or a combination thereof.

[0074] Description 27: A system for converting natural gas to synthetic crude oil, comprising: (a) a stream of natural gas fluid; (b) an air separation unit producing an oxygen-rich gas stream having about 25 to about 95 mol% oxygen; (c) an internal combustion engine reactor fluidly connected to a natural gas source and the air separation unit, and reacting a clean biogas stream with an oxygen-enriched stream to produce a syngas stream; (d) a water-gas shift / gas separation unit and a syngas compression unit fluidly connected to the syngas stream from the internal combustion engine reactor to produce a treated syngas stream and a carbon dioxide-rich stream; (e) the carbon dioxide-rich stream is fluidly connected to the internal combustion engine reactor to provide a carbon dioxide-containing diluent stream; and (f) a Fischer-Tropsch (FT) reactor fluidly connected to the treated syngas stream. The air separation unit may produce enriched oxygen with an oxygen content of about 25 to about 35% mol%, about 35 to about 45% mol%, about 45 to about 55% mol%, about 55 to about 65% mol%, about 65 to about 75% mol%, about 75 to about 85% mol%, or about 85 to about 95% mol%.

[0075] Description 28: The system of description 27, wherein the water gas shift / gas separation unit is fluidly connected to the internal combustion engine reactor and introduces carbon dioxide as a diluent to the internal combustion engine reactor.

[0076]

[0031] Item 29: The system of any of items 27-28, wherein a Fischer-Tropsch (FT) reactor, a water gas shift / gas separation unit, a syngas compression unit, or a combination thereof produces a hydrogen stream, and the hydrogen stream is fluidly connected to the feed gas stream for the internal combustion engine reactor.

[0077] Description 30: The system of any of descriptions 27-28, wherein the synthetic crude from the Fischer-Tropsch (FT) reactor is fluidly connected to a crude upgrading unit, the crude upgrading unit producing diesel and / or naphtha.

[0078] It should be understood that the above description is merely representative of exemplary embodiments and examples. For the convenience of the reader, the above description has focused on a limited number of representative examples of all possible embodiments, examples that teach the principles of the present disclosure. This description does not attempt to exhaustively list all possible variations, or combinations of those variations described. The fact that alternative embodiments may not be presented for certain parts of the present disclosure, or that alternative embodiments that are not further described for some parts may be available, should not be considered as a disclaimer of those alternative embodiments. Those skilled in the art will understand that many of these undescribed embodiments involve differences in technology and materials, rather than differences in the application of the principles of the present disclosure. Therefore, the present disclosure is not intended to be limited to less than what is set forth in the claims and their equivalents.

[0079] (Incorporated by reference)

[0080] All references, articles, publications, patents, patent publications, and patent applications cited herein are incorporated by reference in their entirety for all purposes. However, reference to any reference, article, publication, patent, patent publication, or patent application cited herein is not, and should not be construed as, an admission or any form of suggestion that they constitute valid prior art or form part of the common general art in any country in the world. While the present disclosure has been described in conjunction with its detailed description, it should be understood that the foregoing description is for illustrative purposes and not limiting in scope. Other aspects, advantages, and modifications are within the scope of the claims set forth below. All publications, patents, and patent applications cited herein are incorporated by reference herein as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

Claims

1. 1. A method for producing synthesis gas, the method comprising reacting a hydrocarbon fuel with an oxygen-enriched feed gas in an internal combustion engine reactor, the feed gas containing a carbon dioxide diluent present at about 5 to about 50 mol %, and the oxygen-enriched feed gas being present at about 25 to 95 mol %, to produce the synthesis gas.

2. 10. The method of claim 1, wherein the oxygen-enriched feed gas is obtained by vacuum pressure swing adsorption, pressure swing adsorption, cryogenic separation, membrane gas separation, or a combination thereof.

3. The method of claim 1 , wherein the hydrocarbon fuel is a gaseous hydrocarbon fuel.

4. 4. The method of claim 3, wherein the gaseous hydrocarbon fuel is either (a) natural gas, (b) biogas, (c) from a gas well or associated gas from an oil well, or (d) a fuel mixture containing at least a portion of the carbon dioxide diluent, preferably the fuel mixture is biogas from a landfill or biogas from anaerobic digestion.

5. 2. The method of claim 1, wherein the carbon dioxide diluent is (a) obtained by separation from the syngas downstream of the internal combustion engine reactor prior to a syngas processing step, (b) obtained from a product of a syngas processing step, or (c) obtained from another source.

6. 2. The method of claim 1, wherein the feed gas further comprises hydrogen and hydrocarbons added to increase flame speed, preferably the added hydrogen and hydrocarbons are obtained from a synthesis gas conversion system.

7. 2. The method of claim 1, wherein the internal combustion engine reactor is initially operated at a stoichiometric to lean fuel-oxygen ratio and then transitioned to a rich fuel-oxygen ratio to maximize the production of the synthesis gas, and preferably carbon dioxide from the internal combustion engine reactor is initially flowed in a full oxidation mode to produce carbon dioxide, which is separated and added to the feed gas stream.

8. 2. The method of claim 1, wherein the synthesis gas is conditioned by (a) a water gas shift reactor to convert excess carbon dioxide to carbon monoxide, adjusting the temperature, adjusting the pressure, separating the excess carbon dioxide, or a combination thereof, or (b) separating the excess carbon dioxide or diluent by a membrane, a pressure swing adsorber, a solvent-based separation system, or a combination thereof.

9. 2. The method according to claim 1, wherein the synthesis gas is converted to methanol in a methanol synthesis unit, preferably the methanol is subsequently converted to dimethyl ether (DME) in a two-stage DME synthesis unit.

10. 2. The method of claim 1, wherein the synthesis gas is directly converted to dimethyl ether (DME) in a single-stage DME synthesis unit.

11. 2. The method of claim 1, wherein the synthesis gas is (a) converted to light olefins, liquid fuels, or aromatics in a hydrocarbon synthesis unit, or (b) converted to synthetic crude oil in a Fischer-Tropsch (FT) reactor.

12. 1. A system for converting biogas to methanol, DME, and / or hydrocarbons, comprising: (a) a biogas processing unit that removes a substantial portion of sulfur compounds from the biogas, and optionally removes at least a portion of the carbon dioxide from the biogas to produce a clean biogas stream having a carbon dioxide content of about 1 to about 35 mol %; (b) an air separation unit producing an oxygen-enriched gas stream having from about 25 to about 95 mol % oxygen; (c) an internal combustion engine reactor fluidly connected to the biogas processing unit and the air separation unit for reacting the clean biogas stream with the oxygen-enriched stream to produce a synthesis gas stream; and (d) a gas separation unit and a syngas compression unit fluidly connected to the syngas stream from the internal combustion engine reactor to produce a treated syngas stream; (e) a methanol, DME, and / or hydrocarbon synthesis unit fluidly connected to the treated synthesis gas stream; and 1. A system for converting biogas to methanol, DME, and / or hydrocarbons, comprising:

13. The system of claim 12, wherein: (a) the biogas separation unit produces clean biogas having a carbon dioxide content of about 5 to about 30 mol%; (b) the gas separation unit is fluidly connected to the internal combustion engine reactor for introducing carbon dioxide as a diluent to the internal combustion engine reactor; or (c) the methanol synthesis unit produces a hydrogen stream, the hydrogen stream being fluidly connected to the internal combustion engine reactor, the gas separation unit, the synthesis gas compression unit, or a combination thereof.

14. 1. A system for converting natural gas into synthetic crude oil, comprising: (a) a natural gas fluid stream; (b) an air separation unit for producing an oxygen-rich gas stream having from about 25 to about 95 mol % oxygen; (c) an internal combustion engine reactor fluidly connected to the natural gas source and the air separation unit, the internal combustion engine reactor reacting the clean biogas stream with the oxygen-enriched stream to produce a synthesis gas stream; and (d) a water-gas shift / gas separation unit and a syngas compression unit fluidly connected to the syngas stream from the internal combustion engine reactor to produce a treated syngas stream and a carbon dioxide rich stream; (e) the carbon dioxide rich stream is fluidly connected to the internal combustion engine reactor to provide a carbon dioxide containing diluent stream; (f) a Fischer-Tropsch (FT) reactor fluidly connected to the treated synthesis gas stream; and A system for converting natural gas into synthetic crude oil, including:

15. The system of claim 14, wherein: (a) the water gas shift / gas separation unit is fluidly connected to the internal combustion engine reactor and introduces carbon dioxide as a diluent for the internal combustion engine reactor; (b) the Fischer-Tropsch (FT) reactor, the water gas shift / gas separation unit, the syngas compression unit, or a combination thereof, produces a hydrogen stream, the hydrogen stream being fluidly connected to a feed gas stream for the internal combustion engine reactor; or (c) the synthetic crude from the Fischer-Tropsch (FT) reactor is fluidly connected to a crude oil upgrading unit, which produces diesel and / or naphtha.

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