Carbon sequestration process for solution gas co-extracted with oil and bitumen

Abstract

A carbon sequestration process for solution gas including a mixture of hydrocarbons, in gas phase, is provided. The process comprises: pyrolyzing the solution gas at a temperature above of at least about 1073 K in a pyrolysis reactor at a pressure ranging between about 0.9 atm to about 2.5 atm to obtain solid carbon and a gaseous product including at least about 60% H2; burning the gaseous product in a combustion furnace with air to generate heat for the pyrolysis reactor and flue gases; and recovering heat from the flue gases to heat the solution gas before introduction into the pyrolysis reactor.

Description

CARBON SEQUESTRATION PROCESS FOR SOLUTIONGAS CO-EXTRACTED WITH OIL AND BITUMENTECHNICAL FIELD OF THE INVENTION

[0001] The technical field relates to a carbon sequestration process for solution gases co-extracted with oil and bitumen and other hydrocarbon-containing gases and having a low oxygen content. It also relates to a process to value solution gas and other hydrocarbon-containing gases and having a low oxygen content.BACKGROUND

[0002] During oil extraction from crude oil resources, natural gas is extracted simultaneously since often a large quantity of light hydrocarbons in the form of natural gas is found on top of bitumen. Building pipelines and infrastructures to collect the natural gas can be unfeasible, as it would be very expensive, considering the required length to bring the gas closer to processing facilities and the necessity of having pressurised pipelines. Consequently, oil producers flare or vent natural gas as it is the only economical option to dispose of this byproduct. As a result, the greenhouse gases (GHG) emissions at the oil extraction sites are significant. For instance, in Alberta (Canada), in 2023, the volumes of flared solution gas and vented solution gas were 642 and 130.2 millions cubic meters (m3) respectively (https: / / static. aer. ca / prd / documents / sts / ST60B 2023. pdf) .

[0003] To avoid flaring or venting natural gas, many solutions have been developed to either trap or convert natural gas, mainly into carbon monoxide and hydrogen. These fall under the umbrella name of “Gas-to-Liquid technologies”.

[0004] Steam methane reforming (SMR) is the most applied solution so far, especially at the industrial level. SMR is a two-step process consisting of the catalytic oxydation of CH4 into CO and H2 by H2O, followed by the water-gas shift (WGS) reaction that converts CO into CO2 and H2. The overall reaction is strongly endothermic, having a reaction enthalpy of 165 kJ / mol. One main issue connected with this technology is that itproduces CO2 that is typically vented into the atmosphere, if the plant is not outfitted with Carbon Capture and Storage (CCS) technologies to mitigate the emissions. Although this option is widely considered as the lowest-cost option for H2 production during the transition to a H2 economy, the cost of CO2 capture and sequestration associated with distributed H2 production appears to be prohibitive. Furthermore, these industrial processes are endothermic, and the heat is usually supplied by burning a significant amount of natural gas in the first place.

[0005] In order to improve this aspect, one innovative and possible solution is to proceed with an electrically methane reforming (eSMR), able to minimise nonrenewable energy requirements and achieve high decarbonisation levels. The syngas obtained through these processes (CO and H2) can then be converted into liquids such as methanol, Fischer-Tropsch fuels or dimethyl ether. These technologies are effective but possess some disadvantages, such as the fact that a compression of 2 MPa-7 MPa is required, an operation that requires high operative costs (OPEX), and must be scaled down to fit the relatively small volumes of solution gas produced by an average well.

[0006] Due to long-term environmental uncertainties of the CO2 sequestration approach, decarbonising fossil fuels by recovering and sequestering solid carbon instead of gaseous can be a suitable alternative. This possibility, often disregarded in environmental studies, involves the production of turquoise hydrogen, i.e. hydrogen made from the pyrolysis of methane at high temperatures. Methane pyrolysis, also known as methane cracking, is a process that precisely involves the decomposition of CH4 into its components, H2 and solid carbon through a successive series of endothermic reactions. In this way, the formation of gas-phase carbon (CO2) is prevented.

[0007] The major problem with the CP pyrolysis is that CP is one of the most stable molecules. In fact, the primary bond C-H is very strong, with a dissociation energy of 436 kJ / mol’1and a lack of polarity. The rate-limiting step of the reaction is precisely the rupture of the first CH3-H bond. For this reason, the reaction requires an energy input in the form of very high temperature (above 1073 K), or the presence of a catalyst.

[0008] Catalytic pyrolysis involves the use of a metal catalysts, that may be Ni-, Fe- or Co-based. A catalyst reduces the severity of the operation to temperatures around 873 K. However, catalysts are expensive and deactivate with the carbon build-up on the surface. The reactivation techniques include carbon combustion with oxygen or air or gasification with steam or carbon dioxide. All these methods described above though lead to the formation of COx products, which is a relevant drawback considering the clean nature of CH4 pyrolysis. In addition to this, the carbon by-product is destroyed, therefore it cannot be recovered, and a possible contamination of H2 with carbon oxides can occur, which would require an additional purification step.

[0009] In view of the above, there is a need for a new process to value natural gas, such as the one generated during oil extraction, which would be able to overcome or at least minimize some of the above-discussed prior art concerns.BRIEF SUMMARY OF THE INVENTION

[0010] It is therefore an aim of the present invention to address the above mentioned issues.

[0011] According to a general aspect, there is provided a carbon sequestration process for solution gas including a mixture of hydrocarbons, in gas phase. The process comprises: pyrolyzing the solution gas at a temperature above of at least 1073 K in a pyrolysis reactor at a pressure ranging between about 0.9 atm to about 2.5 atm to obtain solid carbon and a gaseous product including at least 50% H2; burning the gaseous product in a combustion furnace with air to generate heat for the pyrolysis reactor and flue gases; and recovering heat from the flue gases to heat the solution gas before introduction into the pyrolysis reactor.

[0012] In an embodiment, the pyrolysis reactor operates at about atmospheric pressure.

[0013] In an embodiment, the solution gas comprises natural gas. The natural gas can be a co-product extracted simultaneously with oil and bitumen and the process can further comprise recovering the solution gas at an output of a three-phase separator foroil extraction The carbon sequestration process can further comprise splitting the solution gas at the output of the three-phase separator into a first portion for feeding the pyrolysis reactor and a second portion; and burning the second portion with air to generate heat for the pyrolysis reactor.

[0014] In an embodiment, the solution gas comprises a mixture of hydrocarbons, in gas phase wherein the hydrocarbons are from C1 to C8 and / or less than about 5% of oxygenated molecules.

[0015] In an embodiment, the flue gases comprise essentially H2O, N2, CO2 and O2,, which can constitute at least 90 % of the flue gas content. The flue gases can comprise at least about 70% of water, excluding its N2 content.

[0016] In an embodiment, the pyrolyzing of the solution gas is carried out exempt of a metal catalyst. In an embodiment, the pyrolyzing of the solution gas is carried out in the presence of a carbon-based substrate. The carbon-based substrate can comprise solid carbon, coke, charcoal, coal, graphite, or a mixture thereof. The carbon substrate can be supplied as pellets or granules having a diameter ranging from about 0.5 mm to about 20 mm. The carbon-based substrate can be exempt of metallic atoms except for unavoidable impurities. The carbon-based substrate can comprise less than about 15 wt% of an organic binder. The carbon-based substrate can have a superficial area of at least 15 g / m2and / or a porosity of at least 0.5 cm3 / g.

[0017] In an embodiment, the heat recovery from the flue gases to heat the solution gas is carried out in a heat exchanger.

[0018] In an embodiment, the carbon sequestration process is operated continuously for gaseous constituents.

[0019] In an embodiment, the solid carbon is extracted from the pyrolysis reactor intermittently.

[0020] In an embodiment, a purity of the solid carbon is at least about 95 wt%.

[0021] In an embodiment, the gaseous product comprises at least about 60% of H2.

[0022] In an embodiment, the gaseous product comprises less than about 30 %(molar) of carbon.

[0023] The present document refers to several documents, the contents of which are hereby incorporated by reference in their entirety.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Fig. 1 is a flow diagram of a process for sequestering carbon from a solution gas co-extracted with oil and bitumen in accordance with an embodiment;

[0025] Fig. 2 is a flow diagram of a process for sequestering carbon from the solution gas in accordance with another embodiment, wherein a portion of the solution gas is burnt to generate energy for a pyrolysis reactor; and

[0026] Fig. 3 is a graph showing a reaction velocity as a function of time for experimental data versus literature data.

[0027] It will be noted that throughout the appended drawings, like features are identified by like reference numerals.DETAILED DESCRIPTION

[0028] To provide a more concise description, some of the quantitative expressions given herein may be qualified with the term "about". It is understood that whether the term "about" is used explicitly or not, every quantity given herein is meant to refer to an actual given value, and it is also meant to refer to the approximation to such given value that would reasonably be inferred based on the ordinary skill in the art, including approximations due to the experimental and / or measurement conditions for such given value.

[0029] In the above description, an embodiment is an example or implementation of the inventions. The various appearances of “one embodiment,” “an embodiment” or “some embodiments” do not necessarily all refer to the same embodiments.

[0030] It is to be understood that the phraseology and terminology employed herein is not to be construed as limiting and are for descriptive purpose only.

[0031] Furthermore, it is to be understood that the invention can be carried out or practiced in various ways and that the invention can be implemented in embodiments other than the ones outlined in the description above.

[0032] If the specification or claims refer to “an additional” element, that does not preclude there being more than one of the additional element.

[0033] It is to be understood that where the claims or specification refer to “a” or “an” element, such reference is not be construed that there is only one of that element.

[0034] It is to be understood that where the specification states that a component, feature, structure, or characteristic “may”, “might”, “can” or “could” be included, that particular component, feature, structure, or characteristic is not required to be included.

[0035] Where applicable, although state diagrams, flow diagrams or both may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described.

[0036] The descriptions, examples, methods and materials presented in the claims and the specification are not to be construed as limiting but rather as illustrative only.

[0037] Referring to FIG. 1 , there is shown a process 20 for converting natural gas generated during oil extraction. The process 20 is carried out downstream a three- phase separation of the oil extraction process. The three-phase separation is performed in a three-phase separator 22 fed with an hydrocarbon mixture 24, extracted from an oilextraction well, and producing (a) oil 26; (b) a mixture 28 of water and other chemicals (which are transferred for further treatment or to a reservoir); and (c) a solution gas 30.

[0038] Hereinafter, the term “solution gas” is intended to mean, amongst others, the natural gas, which is co-extracted with oil and bitumen, after it is separated from water and oil, in the three-phase separator 22. Solution gases include a mixture of hydrocarbons, in gas phase. In some embodiment, the hydrocarbons are from C1 to C8. The solution gases can include natural gas, which can be co-extracted from the oil and bitumen industry. The solution gas can be sour or not, that can contain with inert molecules (N2, He, Ar), CO2, and / or traces of other oxygenated molecules such as CO and O2 (less than 5% of oxygenated molecules). For instance, in some embodiments, the minimal carbon content of solution gas is about 90 %. The solution gas 30 is typically recovered from the top part of the three-phase separator 22.

[0039] Still referring to FIG. 1 , the process 20 includes a heat exchanger 32, a pyrolysis reactor 34, and a furnace 36. The pyrolysis reactor 34 is fed with at least a portion of the solution gas 30, which temperature has been increased in the heat exchanger 32, located upstream the pyrolysis reactor 34. The pyrolysis reactor 34 produces solid carbon 38 and a gaseous product 40, which is transferred to the furnace 36. Therefore, the process 20 can be characterized as a gas-to-solid (GTS) process.

[0040] The process 20 is configured to be operated continuously at least for the gaseous constituents, i.e. the solution gas 30, the gaseous product 40, etc. In some implementations, the solid carbon can be withdrawn intermittently from the pyrolysis reactor 34, i.e. a semi-batch process.

[0041] For the continuous process, the flow of solution gas 30 and gaseous product 40 can be characterized as a solution gas stream 30 and a gaseous product stream 40, respectively.

[0042] The pyrolysis reactor 34 operates isothermally at about 0.1 MPa (i.e. at atmospheric pressure), at a temperature of at least 1073 K (800 °C), and pyrolysis (Equation 1 for methane (CH4)) occurs therein.

[0043] CH42H2+ C AH0= 75.6 kJ mol’1(1 )

[0044] More particularly, inside the pyrolysis reactor 34, by intense heating, hydrocarbons are broken down into the constitutive elements: carbon and exhaust gases. For instance, the CH4thermal decomposition can be summarized as a series of dehydrogenations, starting from CH4itself:

[0045] 2 CH4H2+ C2H62 H2+ C2H43 H2+ C2H2 4 H2(g) + 2 C(s)(2)

[0046] It is appreciated that similar reactions occur for other hydrocarbons present in the solution gas 30.

[0047] The pyrolysis reactor 34 operates at a reactor temperature of at least 1073 K to reach a high hydrocarbon conversion (For instance, XCH4> 70 % and, in some implementations, > 90 %). Hydrocarbon conversion is promoted at high temperatures and low pressure. In some embodiments, the reactor temperature is maintained at a temperature of at least 1123 K (850 °C). An almost complete conversion of (>85% and, in some implementations, > 98%) can be achieved at temperatures higher than 1223 K (950 °C). In some implementations, the reactor temperature is maintained below about 1573 K (1200 °C) and, in some embodiments, below about 1373 K (1100 °C).

[0048] At a temperature of 1373 K, the residence time inside the pyrolysis reactor 34 is at least 8 seconds and, in some embodiments, greater than about 15 seconds, for a substantially almost complete conversion, based on experimental determinations. Those experiments confirm the simulations performed with Aspen Plus®.

[0049] In the present description, the solution gas 30 is often characterized by its methane (CH4) content. However, it is appreciated that it can include other hydrocarbons, inert gas molecules and small amounts (<5%) of oxygenated molecules, as well as sulphurated molecules.

[0050] In some embodiments, the solution gas is particularly sour, containing a non- negligible percentage of hydrogen sulphide (H2S). Table 1 below shows an average composition of Alberta natural gas (Kidnay, A.J., Parrish, W.R., & McCartney, D.G.(2019). Fundamentals of Natural Gas Processing, Third Edition (3rd ed.). CRC Press. https: / / doi. orq / 10.1201 / 9780429464942). It is known that H2S can cause some problems, particularly if the gas mixture is mixed with air and burnt.

[0051] Table 1 : Average composition of Alberta natural gas

[0052] It is appreciated that the solution gas composition can vary from the one shown in Table 1 and is not fixed in time but is constantly subjected to variations.

[0053] The pyrolysis reactor output includes two phases: a solid phase, made of carbon 38, and a gaseous phase 40, mainly composed of H2. The solid carbon 38 is separated from the gaseous phase 40, stored or sold, while the gaseous stream 40 proceeds along the plant 20.

[0054] The solid carbon is a high purity carbon (> 95 wt%) and, in some embodiments, greater than 98 wt%. Possible impurities can include, without being limitative, sulfur, hydrogen, and oxygen.

[0055] The gaseous phase 40 is rich in hydrogen, with a hydrogen content above about 60 and, in some embodiment, between about 60% and about 70%. However, hydrogen is not an output of the overall process 20, rather a side stream that is used to create energy for the process 20, as will be described in more detail below. In addition to hydrogen, the gaseous phase 40 can also include N2, CO, CO2, CS2, and H2S, for instance.

[0056] More particularly, the gaseous stream 40 is mixed with air 44, and enters the furnace 36. It is appreciated that the gaseous stream 40 and air 44 can be introduced independently in the furnace 36 or can be mixed before being introduced in the furnace 36. Inside the furnace 36, combustion occurs and energy (Q) is generated. This energy (Q) is supplied to the pyrolysis reactor 34 to maintain the working temperature, i.e. a reactor temperature equal to or above 1073 K. The heat exchanger 32, mounted upstream to the pyrolysis reactor 34, can be used to increase the solution gas temperature before it is introduced into the pyrolysis reactor 34. More particularly, the heat exchanger 32 exploits hot flue gases 42, expelled from the furnace 36, to heat the solution gas feed 30 before it enters the pyrolysis reactor 34.

[0057] The generated energy (Q) can transferred to the pyrolysis reactor as electricity via turbine(s), generators, and the like, or using burner(s).

[0058] In the process and, more particularly, inside the pyrolysis reactor 34, no metal catalyst is used, thereby limiting the issues related to a catalyst cost and its deactivation. More particularly, the process is exempt of metal-containing catalyst such as a carbon-based catalyst including metallic atoms, such as Fe, Ni, and Co, having a catalytic action in the pyrolysis reaction.

[0059] In some implementation, a carbon substrate can be introduced inside the pyrolysis reactor 34 to speed up the pyrolysis reaction and, more particularly, the carbon sequestration reaction, and promote the mass and heat transfer. The carbon substrate is metal free, except for unavoidable impurities. The carbon-based substrate can comprise solid carbon, coke, charcoal, coal, graphite or a mixture thereof. It can be shaped into pellets or a granule form having a diameter ranging from about 0.5 mm to about 20 mm.

[0060] In some embodiments, the carbon-based substrate is supplied to the pyrolysis reactor 34 as pellets of either a spherical, cy I indral or any suitable irregular shape.

[0061] The carbon-based substrate is manufactured from a carbon-based product, such as and without being limitative, carbon, coke, charcoal, coal, graphite or a mixturethereof, in combination with a binder such as an organic binder (e.g. a ligno-cellulosic binder). In some embodiments, the carbon-based substrate comprises less than about 15 wt% of binder, in other embodiments, less than about 10 wt% of binder, and in still other embodiments, less than about 5 wt% of binder.

[0062] In some embodiments, the carbon-based substrate has a superficial area of at least 15 g / m2In some embodiments, the carbon-based substrate has a porosity of at least 0.5 cm3 / g.

[0063] One of the products of the process 20 is solid carbon 38, which can be later used as a reducing agent, in the production of batteries, as carbon black or again in soil amendment and environmental remediation. Solid carbon formation avoids (or at least reduces) CO2 release in the atmosphere, which is generated in high quantities in the case of flaring.

[0064] Another product of the process 20 is a gas stream 40, rich in H2, which is used, in some embodiments, for heat generation. In some embodiments, the gas stream 40 includes less than about 30 % (molar) carbon. Therefore, the material burnt in the process 20 is mostly composed of H2, and thereby generating flue gases 42 composed primarily of H2O. Inside the furnace 36, the gaseous stream 40 is oxidized to produce heat, CO2, SOx, and H2O, wherein water is the major constituent of the flue gases 42 (in addition to N2 and O2 from the air input of the furnace 36). In some implementations, the flue gases 42 contain at least about 70 wt% of water (excluding nitrogen introduced by the air supply). H2O, N2, CO2 and O2 can constitute at least 90 % of the flue gas content. Water contained in the flue gases 42 is sufficiently pure that no or limited wastewater treatment is required. In some implementations, water produced during the process 20 can be reinjected into the oil well (thereby reducing the freshwater consumption of the oil extraction process) or reinjected into the water bodies.

[0065] In an alternative implementation, H2 can be at least partially used for energy / heat generation purposes. However, burning H2 provides a substantially autonomous process from an energetic point of view. H2 produced in situ is suitable forheat generation. Its calorific value is in fact equal to (141 .9 MJ / kg). Furthermore, H2 combustion only produces H2O, and therefore the problem of CO2 formation during power generation is theoretically eliminated as well.

[0066] Examples

[0067] The process 20 was modelled and simulations were carried out wherein the process 20 was operated at atmospheric pressure. In the simulated process, the furnace 36 was modelled through a Gibbs reactor. The energy efficiency (q) of the furnace 36 was 60 % for all the simulations (typically furnace efficiencies are between 58 % and 65%). The NASA-CEA software was used to calculate chemical equilibrium product concentrations from different sets of reactants.

[0068] The furnace was operated at 1573 K and, according to White et al. (C.M. White, R.R. Steeper, A.E. Lutz, “The hydrogen-fueled internal combustion engine: a technical review, International Journal of Hydrogen Energy”, Volume 31 , Issue 10, 2006, Pages 1292-1305, ISSN 0360-3199, https: / / doi.Org / 10.1016 / j.ijhydene.2005.12.001.(https: / / www.sciencedirect.com / science / article / pii / S0360319905003721 )), the fuel equivalence ratio (<t>) must be equal to 0.46, which corresponds to 5.1 mol of air per mol of H2 burnt.

[0069] Example A

[0070] The process shown in FIG. 1 was simulated. The temperature of the pyrolysis reactor 30 was set to equal to 1053 K. At this temperature, the reactor requires 1060 kW. The furnace 36 produces 1236 kW, of which 742 kW can be exploited considering the heat transfer efficiency (q) of 60 %. The outlet temperature (Tout) of the solution gas feed out of the heat exchanger 32 was set to 1023 K. In these conditions, the heat exchanger 32 is theoretically able to exchange 368 kW. The heat balance around the pyrolysis reactor 34 is reported in Equations 3 and 4. The energy contributions (Q) of the furnace 36 and the heat exchanger 32 are enough to sustain the pyrolysis reactor 34, as the difference results in a negative number, meaning that there is theoretically anadditional quantity of energy (Qextra) with respect to the one required to maintain the pyrolysis reactor 34 at isothermal conditions.

[0071] |Qreactor 34| -0.6 * |Qfurnace 36| - |Qheat exchanger 32|=|Qextra| (3)

[0072] 1060 kW - 0.6 * 1236 kW - 368 kW = -50 kW (4)

[0073] The main characteristics of the heat exchanger 32, calculated by Aspen® Plus, are reported in Table 2.

[0074] Table 2: Characteristics of the heat exchanger 32 evaluated through Aspen® Plus.Tin’ Required cold Tout, Tin hotTout hotCalculated heat exchanger area Average U [K]cold[K] [K] [K] duty [kW] [m2] [ W / m2 / K]403 1023 1573 1195 368 0.55 850

[0075] As a first assumption, to guarantee a high conversion, the pyrolysis reactor temperature was set equal to 1273 K. However, it was observed that the heat produced by the furnace 36 alone, in spite of the additional heat exchanger 32 contribution, was not enough to guarantee the energy autonomy of the pyrolysis reactor 34. By it is meant that the difference (in absolute value) between the heat duty required by the reactor and the heat duty originated by the furnace and the heat exchanger (both considered as the 60 % of the ideal output value produced by Aspen® Plus) was a positive number. Therefore, for the simulated process, the reactor’s temperature was reduced to 1053 K to obtain energy autonomy.

[0076] The composition of the solution gas feed 30 was the one detailed in Table 1 and the pressure of all process streams was 0.1 MPa. The simulated process produced 34.6 kmol / h of solid C and 59.6 kmol / h of H2. Table 3 lists the simulation results. The operative conditions did not allow for a complete conversion, therefore a fraction of the solution gas (2.74 kmol / h) leaves the pyrolysis reactor 32 and is burnt with in the furnace 36.

[0077] Table 3: Mass balances - Example A42 (Flue gas38 (Solid 40 (Gasous 44 (Air stream phase output phase output introduced in output of Stream of reactor 32) of reactor 32) furnace 36) furnace 36)Temperature 1053 1053 298 1573[K]Phase Solid Gas Gas GasMolar flow 34.6 65.3 304.0 328.8[ kmol / h]Composition [% mol]H2 0.91C 1CH4 0.04H2S 0.01N2 0.01 0.79 0.63O2 0.21 0.15H2O 0.20NO 0.001 co 0.01CO2 0.01SO2, SO3 0.004Traces 0.02 0.005

[0078] The main traces in gas stream 40, that contained the gaseous products of the pyrolysis reactor 34, are constituted by COS, and VOC (volatile organic compounds) with a concentration below 1 %. These were no longer present after the combustion. The flue gas stream 42 contained NO, SOx, and NO2 in addition to water, O2, CO2, and N2.

[0079] Since the pyrolysis reactor temperature was lowered to 1053 K to obtain energy autonomy, the conversion of CH4 was not complete (88 %). Part of remained, therefore, in the product stream (stream 40), mainly composed of H2, that fed the furnace 36.

[0080] Example B

[0081] As explained in Example A, the furnace 36 alone is incapable of sustaining the process if a reactor temperature at 1273 K is desired. To guarantee an isothermal operation at 1273 K in the pyrolysis reactor 34 and at the same time the energetic selfsustainability, additional energy has to be recovered from the process itself. In an implementation, the additional energy is obtained by burning a portion of the solution gas feed, as shown in FIG. 2. The process 120 of FIG. 2 is similar to the process of FIG. 1 , except that it includes a splitter 150 mounted upstream to the heat exchanger 132. The solution gas feed 130 is separated in the splitter 150 into two streams: a first portion 130a is directed to the pyrolysis reactor 134 where pyrolysis occurs, and a second portion 130b is directed to an additional burner 152. For the simulated process, the additional burner 152 was modelled as a Gibbs reactor in Aspen® Plus, in which combustion occurs. Before the second portion of the solution gas 130b is introduced into the burner 152, it is mixed with air 154 to sustain its lean combustion. The additional heat developed through the combustion is provided to the pyrolysis reactor 134.

[0082] For the simulated process, the burner 152 was operated at 1573 K and, according to Glaude et al., the fuel equivalence ratio (<t>) must be equal to 0.56, which corresponds to 17 mol of air per mol of H2 burnt.

[0083] The introduction of the burner 152 guarantees the production of an appropriate quantity of energy so that the process is energetically sustained. The correct amount of solution gas that needs to be split from the feed and burnt depends on the quantity of energy required in the pyrolysis reactor 134. Also, as the stream 130a fed to the reactor 134 (stream 2) is lower in quantity, the pyrolysis reactor 134 requires less energy, and the furnace 136 also produces less energy. Therefore, it was necessary to find a trade-off among all these different aspects and sensitivity analyses have been conducted to find the optimal operation point. For the simulated process, 5 kmol / h of the solution gas feed 130b was directed to the burner 152, this corresponds to 16 % of the total feed.

[0084] Thus, the temperature of the pyrolysis reactor 30 was set to equal to 1273 K. As a result of the solution gas split, only 25 kmol / h of solution gas were fed to the pyrolysis reactor 134 instead of 30 kmol / h (Example A). The pyrolysis reactor 134 requires 1156 kW. Considering that 5 kmol / h of solution gas feed were separately fed to the burner 152, 3.855 kmol / h of CP were burned. In the burner 152, the combustion of natural gas took place, producing 450 kW. Of this energy amount, 270 kW can be exploited to sustain the reactor 134. The furnace 136 gave origin to 715 kW, and specifically 429 kW can be used for the reactor 134. The outlet temperature (Tout) of the solution gas feed out of the heat exchanger 132 was set to 1273 K, which corresponds to the operating temperature of the reactor 134. The heat exchanger 132 was theoretically able to exchange 468 kW. The main characteristics of the heat exchanger in this configuration are reported in Table 4.

[0085] Table 4: Characteristics of the heat exchanger 132 evaluated through Aspen® Plus.Tin’ Required cold Tout, Tin hotTout hotCalculated heat exchanger area Average U [K]cold[K] [K] [K] duty [kW] [m2] [ W / m2 / K]403 1273 1573 1423 468 0.94 850

[0086] The energy balance around the reactor 134 is reported in Equations 5 and 6. The energy amount furnished by the furnace 136 and the burner 152 and the heat exchanger 132 was higher than the heat duty requested by the reactor 134 to be operated isothermally at 1273 K, resulting in a temperature of the product stream 140 at the pyrolysis reactor exit equal to 1282 K.

[0087] |Qreactor 134| -0.6 * |Qfurnace 136| -0.6 * |Qburner152| - |Qheat exchanger 132| — |Qextra| (3)

[0088] 1156 kW- 0.6 * 715 kW- 0.6 * 450 kW- 468 kW = -11 kW (4)

[0089] The composition of the solution gas feed 130 is given in Table 1. The process shown in FIG. 2 produces 30.6 kmol / h of C and 53.6 kmol / h of H2 (Table 5). The CH4 conversion was in this case almost complete: in fact, only 1 % of it remains in the product stream 140 of the pyrolysis reactor 134, that is almost completely made of H2 (95 %).

[0090] Table 5: Mass balances - Example B156 140 142 (Flue154 (Air (Gaseous 138 (Solid (Gasous gas- Input phase phase phase 144 (Air stream of output of output of output of introduced output of burner burner reactor reactor in furnace furnaceStream 152) 152) 132) 132) 136) 136)Temperature 298 1573 1273 1273 298 1573[K]Phase Gas Gas Solid Gas Gas GasMolar flow 65.4 71.14 30.6 56.4 273.6 298.8[ kmol / h]Composition [% mol]H20.95 c 1CH40.01H2S 0.01N2 0.79 0.65 0.01 0.79 0.67O2 0.21 0.10 0.21 0.19H2O 0.15 0.12NO 0.001 0.001CO 0.01CO2 0.09 0.007S02, S03 0.002 0.006T races 0.0070.006

[0091] Similarly to Example A, the main traces in gaseous phase 140 produced by the pyrolysis reactor 132, that contains the products of the pyrolysis, are constituted by COS, HCN, and NH3, all eliminated after the combustion (flue gases 142 in FIG. 2).

[0092] Comparison between Examples A and B

[0093] The most relevant features of Examples A and B are reported in Table 6.

[0094] Table 6: Outline of the main characteristics of Examples A and B.Example ExampleMain aspects A B1. Operative conditions and productivityReactor temperature [K] 1053 1273Pressure [MPa] 0.1 0.1XCH4 88 % 97 %H2 produced [ kmol / h] 59.6 53.5C produced [ kmol / h] 34.6 30.62. Technical aspectsNumber of main units 3 4Energy autonomy Yes Yes3. EmissionsCO2 [ton year1] 1392 2924NO [ton year1] 120 137.5SO2 [ton year1] 550 550SO3 [ton year1] 7 7.22

[0095] The processes 20, 120 reduce in a relevant way the emissions that would otherwise occur if flaring was carried out, as shown in Table 7, which further includes asimulated flaring situation. In the simulated flaring situation, solution gas is burnt entirely to transform into chemical species that are characterised by a lower global warming potential (GWP). More particularly, a 30 kmol / h solution stream with the composition reported in Table 1 , is mixed with air in the proportion proposed for Example B, and fed to a furnace that works at 1573 K to obtain a complete combustion. Table 7 shows that Example A can theoretically reduce emissions by more than 90 %.

[0096] Table 7: Comparison among emissions of Example A, Example B, and in the simulated flaring situationExample A Example B FlaringPollutant species emitted (ton y1) (ton y1) (ton y1)CO2 1392 2924 14 700NO 120 137.5 128.8SO2 550 550 550SO3 7 7.22 5.6

[0097] Experimental results

[0098] A hydrocarbon mixture was prepared from pure gas bottles by sending them one after the other in a 22.5 L tank, previously vacuumed. A pressure transducer (Omega HORWALKCT6854, 0 kPa-200 kPa, output range 0 V-5 V) monitored the pressure during the filling so that the composition of the mix was estimated from the partial pressure of the gases. In order to guarantee reliable results, the mixture over which the tests were conducted was prepared again. The mixture was composed of 92 % of methane and 8 % of nitrogen. This was further checked at the gas chronomatograph (GC), which, over several tests, constantly returned this composition.

[0099] Charcoal, to be used as a carbon substrate, was pretreated in flux (100 mL / min) for 5 h at 1273 K in the oven to eliminate all the volatile compounds adsorbed on its surface.

[0100] 31.74 g of carbon were pretreated for the tests and inserted within a pyrolysis reactor as well as a 0.871 g quartz wool. The size of the pretreated carbon particles ranged between about 0.09 mm to about 1.18 mm. The pretreated carbon was introduced as a carbon-based substrate to include active surfaces, inside the pyrolysis reactor, to accelerate the carbon sequestration reaction and promote thermal and mass transfer. The quartz wool balls acted as a filter and maintained pretreated carbon particle bed in place.

[0101] Also, most of the tests were conducted by pre-heating the gas before its entrance into the pyrolysis reactor. The pre-heating was obtained in a short piece of a pipe, filled with a bed of SiC particles (200 mesh particle size, corresponding to 74 micrometers). A heating tape was rolled up the tube, and connected to a power regulator useful to control the temperature.

[0102] SiC has no catalytic effect on methane pyrolysis. Tests were carried out and no catalytic effect was observed, even at bed temperatures that were greater than 500 °C.

[0103] Table 8 summarizes the operating conditions for the tests A, B, and C, wherein “Mass of C at tO” is the mass of pretreated carbon introduced when the test started, “Mass of quartz wool” is the mass of quartz wool introduced when the test started, “Temperature” is the pyrolysis reactor temperature, “tau” is the residence time of the solution gas inside the pyrolysis reactor, “Estimated porosity” is the calculated porosity of the pretreated carbon bed (assuming the particles as spheres of different diameters), “Flow” is the flow of solution gas flowrate entering the pyrolysis reactor in mL / s , “T pre-heating” is the temperature of the solution gas leaving the pre-heating assembly, and “flow of N2” is the flowrate of N2 in mL / s in mL / min (nitrogen was used as internal standard).

[0104] Table 8 : Operating conditions for the tests A, B, and CTest A Test B Test CStarting time 11 :00 10:10 10:32Ending time 16:20 16:53 15:58Mass of C at 31.74 31.74 31.74 to [g]Mass of 0.871 0.871 0.871 quartz wool [g]Temperature 1000 1000; 950 from 13:45 1000(T) tau (s) 40 40 40Estimated 0.37 0.37 0.37 porosityFlow (mL / s) 0.886 0.886 0.886T pre-heating 222-226 281-282 250[ °C]Flow of N20.073 0.073 0.073[mL / s]Size of carbon 0.09 - 1.18 0.09 - 1.18 0.09 - 1.18[mm]

[0105] As reported in Table 8, the tests were conducted after pre-heating the setup. For test A, the pre-heating was performed by setting the power to 8, causing the temperature at the entrance of the pyrolysis reactor to vary between 220 °C and 226 °C. Once the steady state was reached, the conversion was about 61 % and remained stable.

[0106] For test B, the pre-heating was performed by setting the power to 10, causing the temperature at the entrance of the pyrolysis reactor to vary between 281 °C and 282 °C (about 50 °C higher than for test A). Once the steady state was reached, the conversion was about 61 % and also remained stable. Therefore, the variation of 50 °C of the gas at the entrance of the pyrolysis reactor did not have a significant impact, as long as the gas was pre-heated.

[0107] For test B, at 13:45, the pyrolysis reactor temperature was decreased from 1000°C to 950 °C. The conversion decreased accordingly, reaching 44 % and then remained stable. Therefore, the pyrolysis reaction is temperature sensitive. At 15:44, the flow was increased from 53.4 to 63.4 mL / min. As expected, since the residence timein the pyrolysis reactor slightly decreased, the conversion decreased as well, reaching 41 %.

[0108] For test C, the test was first performed without pre-heating, with the pyrolysis reactor having a temperature set at 1000 °C. A steady conversion of 56 % was reached. At 13:25, the pre-heating power was set to 10 (as for test B), which caused the gas to be heated up to 250 °C, below the 300 °C reached with power 10 in test B. The conversion dropped to 46 %.

[0109] For tests A, B, and C, the selectivities were 100%, meaning that all the hydrocarbons reacted and, more particularly, the methane was converted into hydrogen and carbon.

[0110] FIG. 3 compares the reaction velocity, which is linked to the deactivation of the carbon bed contained in the pyrolysis reactor 32. More particularly, it shows the loss in reaction performance of carbon filling over time on stream (during the reaction). The Y axis is obtained by dividing the reaction rate observed at a certain time by the initial (maximum) reaction rate (assuming that it is proportional to surface area available). FIG. 3 compares the experimental results at 1000 °C with the literature data (Nazim Muradov, Franklyn Smith, Ali T-Raissi, “Catalytic activity of carbons for methane decomposition reaction”, Catalysis Today, Volumes 102-103, 2005, Pages 225-233, ISSN 0920-5861 , https: / / doi.Org / 10.1016 / j.cattod.2005.02.018.) with activated carbon at 850 °C. The reaction velocity remained higher with the experimental results than expected from the literature data.

[0111] After tests A, B, and C, the bed inside the pyrolysis reactor weighted 37.28 grams, rock wool ball included. An additional 1.11 g of carbon was found while cleaning of the pipes. Therefore, 5.779 g of carbon were produced overall over the three days of tests, i.e. tests A, B, and C.

[0112] Two additional tests were carried out, which operating conditions are detailed in Table 9. Another bottle of hydrocarbon mixture was prepared from pure gas bottles, as detailed above. The composition of the mixture was composed of 91 .87 % ofmethane and 8.13 % of nitrogen. This was further checked at the GC, which, reported a composition of 91 .6 % of methane and 8.4 % of nitrogen.

[0113] For test D, the size of the pretreated carbon was between about 0.009 mm to about 0.355 mm and, for test E, between about 1.18 mm to about 1.4 mm.

[0114] Table 9 : Operating conditions for tests D and ETest D Test EStarting time 09:37 08:50Ending time 15:40 15:05Mass of C at tO [g] 21.7 21.7Mass of quartz wool 0.7952 0.7952[g]Temperature (T) 950; 1000 from 1000; 950 from13:00 12:55 tau (s) 40 40; 50 from 11 .35 estimated porosity 0.37 0.37 flow (mL / s) 0.606 0.606T pre-heating [ °C] 185 255 flow of N2 initial [mL / s] 0.053 0.052Size of carbon [mm] 1.4 - 1.18 1.4 - 1.18

[0115] Test D started by setting the pyrolysis reactor temperature at 950 °C. Under these conditions, an average conversion of 36 % was obtained. The pre-heating temperature was slightly lower than for tests B and C, described above, wherein the power was also set to 10, and the carbon particle size was bigger. At 13:00, the pyrolysis reactor temperature was increased to 1000 °C. Once steady state was reached, an average conversion of 49 % was obtained.

[0116] After fixing issues with the pre-heating set-up, test E was carried out. The power was set to 8 and a temperature of 255 °C was reached. At first, the pyrolysis reactor temperature was set to 1000 °C. Under these conditions, an average conversion of 49.85 % was reached, which is consistent with the results of tests A, B, and C. Then, the residence time of the solution gas inside the pyrolysis reactor (tau) was increasedfrom 40 s to 50 s, i.e. a lower hydrocarbon flowrate. As expected, the average conversion slightly decreased to 46 %. Last, the pyrolysis reactor temperature was decreased to 950 °C. Combined with a lower flowrate of hydrocarbons, the conversion dropped to 27%.

[0117] With the processes 20, 120 described above, energy is produced on-site, only by burning fuel or associated natural gas. After the three-phase separator unit of the oil extraction process, the natural gas (or solution gas) is available at atmospheric pressure or near atmospheric pressure. The processes 20, 120 also operate at atmospheric pressure or near atmospheric pressure, thereby limiting the costs associated to gas compression (in comparison with other industrial processes). In some implementations, the associated gas is sour, i.e. it contains acid sulfur gases (mainly H2S). Since the processes 20, 120 can be carried out without catalyst, the presence of the sulfuric contaminants does not create problems with respect to catalyst deactivation.

[0118] The processes 20, 120 are not affected by contaminants or the composition of the solution gas. Furthermore, the processes 20, 120 do not affect the upstream oil extraction process.

[0119] The process has high conversion (more than about 70%) and selectivity (around 100%) for solid carbon. Thus, more than 70% of methane (CH4) is converted and, of which, about 100% is converted into solid carbon,

[0120] It will be appreciated that the methods described herein may be performed in the described order, or in any suitable order.

[0121] Several alternative embodiments and examples have been described and illustrated herein. The embodiments of the invention described above are intended to be exemplary only. A person of ordinary skill in the art would appreciate the features of the individual embodiments, and the possible combinations and variations of the components. A person of ordinary skill in the art would further appreciate that any of the embodiments could be provided in any combination with the other embodiments disclosed herein. It is understood that the invention may be embodied in other specificforms without departing from the central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein. Accordingly, while the specific embodiments have been illustrated and described, numerous modifications come to mind. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.

Claims

CLAIMS:

1. A carbon sequestration process for solution gas including a mixture of hydrocarbons, in gas phase, the process comprises: pyrolyzing the solution gas at a temperature above of at least about 1073 K in a pyrolysis reactor at a pressure ranging between about 0.9 atm to about 2.5 atm to obtain solid carbon and a gaseous product including at least about 50% H2; burning at least partially the gaseous product in a combustion furnace with air to generate heat for the pyrolysis reactor and flue gases; and recovering heat from the flue gases to heat the solution gas before introduction into the pyrolysis reactor.

2. The carbon sequestration process of claim 1 , wherein the pyrolysis reactor operates at about atmospheric pressure.

3. The carbon sequestration process of claim 1 or claim 2, wherein the solution gas comprises natural gas.

4. The carbon sequestration process of any one of claims 1 to 3, wherein the solution gas comprises a mixture of hydrocarbons, in gas phase wherein the hydrocarbons are from C1 to C8.

5. The carbon sequestration process of anyone of claims 1 to 4, wherein the solution gas comprises less than about 5% of oxygenated molecules.

6. The carbon sequestration process of claim 3, wherein the natural gas is a co-product extracted simultaneously with oil and bitumen and the process further comprises recovering the solution gas at an output of a three-phase separator for oil extraction.

7. The carbon sequestration process of claim 6, further comprising splitting the solution gas at the output of the three-phase separator into a first portion for feeding the pyrolysis reactor and a second portion; and burning the second portion with air to generate heat for the pyrolysis reactor.

8. The carbon sequestration process of any one of claims 1 to 7, further comprising recovering heat from the combustion furnace and transferring the recovered heat to the pyrolysis reactor.

9. The carbon sequestration process of any one of claims 1 to8, wherein the flue gases comprise essentially H2O, N2, CO2 and O2.

10. The carbon sequestration process of claim 9, wherein the flue gases comprise at least about 70% of water, excluding its N2 content.

11. The carbon sequestration process of any one of claims 1 to 10, wherein the pyrolyzing of the solution gas is carried out exempt of a metal catalyst.

12. The carbon sequestration process of any one of claims 1 to 11 , wherein the pyrolyzing of the solution gas is carried out in a presence of a carbonbased substrate.

13. The carbon sequestration process of claim 12, wherein the carbon substrate is supplied as pellets or granules having a diameter ranging from about 0.5 mm to about 20 mm.

14. The carbon sequestration process of one of claims 12 and 13, wherein the carbon-based substrate is exempt of metallic atoms except for unavoidable impurities.

15. The carbon sequestration process of any one of claims 12 to 14, the carbon-based substrate comprises solid carbon, coke, charcoal, coal, graphite, or a mixture thereof.

16. The carbon sequestration process of any one of claims 12 to 15, wherein the carbon-based substrate comprises less than about 15 wt% of an organic binder.

17. The carbon sequestration process of any one of claims 12 to 16, wherein the carbon-based substrate has a superficial area of at least 15 g / m218. The carbon sequestration process of any one of claims 12 to 17, wherein the carbon-based substrate has a porosity of at least 0.5 cm3 / g.

19. The carbon sequestration process of any one of claims 1 to 18, wherein the heat recovery from the flue gases to heat the solution gas is carried out in a heat exchanger.

20. The carbon sequestration process of any one of claims 1 to 19, wherein the carbon sequestration process is operated continuously for gaseous constituents.

21. The carbon sequestration process of any one of claims 1 to 20, wherein the solid carbon is extracted from the pyrolysis reactor intermittently.

22. The carbon sequestration process of any one of claims 1 to 21 , wherein a purity of the solid carbon is at least about 95 wt%.

23. The carbon sequestration process of any one of claims 1 to 22, wherein the gaseous product comprises at least about 60% of H2.

24. The carbon sequestration process of any one of claims 1 to 23, wherein the gaseous product comprises less than about 30 %(molar) of carbon.

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