Co 2 purification by chemical looping

Abstract

The current invention concerns a chemical looping process for the oxidation of impurities in a CO2 feedstock. The process is especially suitable for removing impurities from a pre-combustion CO2 feedstock.

Description

C02purification by chemical loopingTechnical FieldThe present invention is in the field of CO2 purification of CO2 rich streams. In particular, the invention concerns the further purification of the CO2 product of precombustion CO2 capture processes.Introduction

[0001] Carbon capture and storage (CCS) and carbon capture and utilization (CCU) refer to processes wherein a carbon dioxide (CO2) stream is captured from an industrial process. The CO2 is transported to long term storage (CCS) or utilized as starting material in further applications (CCU). The industrial process from which the CO2 is obtained may be the combustion (oxidation) of fossil fuels, waste, or biomass. Combustion may be in the presence of air or in an atmosphere consisting of pure oxygen and CO2 (oxyfuel combustion). Examples of such post-combustion CO2 sources are flue gasses of energy plants, waste gasses of cement production and the like. CO2 may also be obtained by pre-combustion CO2 capture, from energy-containing streams, such as streams originating from the pyrolysis of fossil fuels, waste or biomass, in which fossil fuels, waste or biomass are heated in the presence of no or a substoichiometric amount of oxygen (steam) and converted into syngas, a mixture of mainly CO, CO2 and H2. The primary aim of capturing CO2 in pre-combustion processes is to prevent the CO2 to enter the atmosphere whilst utilizing the energy present in the fossil fuel or biomass. In this way such a combustion process may become 'CO2-neutral'. CO2 removal in post-combustion is an end-of-pipe solution, needing no specific process integration. Instead, the primary aim in pre-combustion processes is to convert the biomass or fossil fuel in useful building blocks. CO2 separation is an integrated part of the process. Separation of CO2 from post-combustion and pre-combustion sources is known in the art. During separation often some minor components (impurities) are in the resulting CO2 stream. The origin of the CO2 stream, either pre-combustion or post-combustion, affects the type and concentration of the impurities. Consequently, for the removal of impurities different technologies need to be considered.

[0002] Carbon dioxide purity is an important criterion in any carbon capture technology due to technical, economic and safety requirements for transportation, storage, and conversion. The influence of the main impurities on the different sections of the CCS / CCU chain are reviewed by Wang et al. ("Carbon recycling - An immense resource and key to a smart climate engineering: A survey of technologies, cost and impurity impact." Renew. Sustain. Energy Rev. 2020, 131, 110010). For example, impurities influence the energy consumption in compressing CO2. It was found that even small amount of impurities led to an increase in compression work. Transportation is also greatly affected by impurities in the CO2 stream in terms of pipeline design and safe operation, not to mention health and environmental issues in case of gas leakage. Moreover, impurities may lead to acidic species causing corrosion issues during transport and storage. A consequence of corrosion is the formation of leaks, where toxic species like sulphides and CO can lead to health and environmental problems.

[0003] The type of impurities in the CO2 stream is influenced by the process employed to obtain the CO2. A summary of the impurities observed downstream of the main CO2 capture technologies, oxyfuelcombustion, pre-combustion, and post-combustion, was performed by Porter et al. ("The range and level of impurities in CO2 streams from different carbon capture sources.” Int. J. Greenh. Gas Control 2015, 36, 161-174). Porter et al. show that the type of impurities in the CO2 stream greatly depends on the capture technology employed. For example, in pre-combustion processes partial oxidation products are produced in significant quantities, which is different to post-combustion capture where complete oxidation occurs. In post-combustion CO2 streams typically some oxygen (O2) is present, whilst O2 is absent in precombustion CO2 streams. In contrary in post-combustion processes CH4and H2 are absent, and CO is only present in very low concentrations (typically much lower than 0.02 mol%), whilst pre-combustion streams typically comprise higher concentrations of these components. The type of purification technique employed depends on the type of impurities present.

[0004] WO 2016 / 145034 provides a process for removing impurities from a post-combustion CO2 stream; after power generation from the combustion of coal. The process relies on an oxygen uncoupling (CLOU) material. WO 2016 / 145034 does not concern impurities removal from a CO2 stream obtained from pre-combustion processes.

[0005] A common impurity in pre-combustion CO2 streams is CO, which is typically caused by incomplete pyrolysis and incomplete separation of CO2 from the obtained syngas. The removal of minor to trace amounts of CO from a concentrated CO2 stream is not trivial, because of the similarities in physicochemical properties between CO and CO2. Existing solutions, for example oxycombustion, suffer from the fact that it is difficult or even impossible to remove all traces of H2 / CO while not introducing new impurities, such as oxygen.

[0006] There remains a need in the art for a process to purify a CO2 stream, in particular pre- combustion CO2. There is especially a need for processes that do not introduce new impurities in the CO2 stream.Summary of the invention

[0007] The inventors have surprisingly found that chemical looping can be used to purify a CO2 stream by oxidizing the impurities in such CO2 stream. The process does not introduce new impurities. Moreover, the process can reduce the amount of different type of impurities in one step, and / or convert different kind of difficult to separate impurities to easily separable impurities. In addition, the process can be run with several setups and in different reactor types making it easy to adjust to different needs. Furthermore, the process is able to generate steam which may be integrated in the upstream CO2 capture unit lowering the energy demand. A further advantage of the process is that it requires no critical raw materials but instead relies on affordable metal oxides. The process employs materials that are very robust and do not create breakdown products.

[0008] Hence, the invention concerns a process for the oxidation of impurities in a CO2 feedstock comprising impurities, wherein the CO2 feedstock comprises more than 80 mol% CO2 based on total of the dry CO2 feedstock, wherein the CO2 feedstock and an oxidant are provided to a chemical looping reactor comprising a redox catalyst, and wherein the impurities in the CO2 feedstock are oxidized when the CO2 feedstock is provided to the chemical looping reactor. The CO2 feedstock that underwent the process for the oxidation of impurities is named "treated CO2 feedstock" or alternatively "purified CO2 feedstock". So, the process for the oxidation of impurities in a CO2 feedstock comprising impuritiesdelivers a treated CO2 feedstock or alternatively a purified CO2 feedstock. Preferably the CO2 feedstock and an oxidant are sequentially provided. Preferably the redox catalyst is a metal oxide. In a preferred embodiment, the CO2 feedstock is obtained from a pre-combustion process so preferably the CO2 feedstock is a pre-combustion CO2 feedstock. Preferably the impurities are oxidizable impurities. Oxidizable impurities are impurities that are oxidized by the redox catalyst at a temperature in the range of 100 - 1200°C. Preferably, the impurities are one or more of CO, H2, and CH4, more preferably one or more of CO and H2. CO, H2, and CH4are oxidizable impurities. Preferably, these impurities are oxidized to CO2 and H2O, wherein optionally the H2O is removed from the treated CO2 feedstock in a subsequent step, preferably by condensation. The process for the oxidation of impurities in a CO2 feedstock may alternatively be named a process for increasing the content of CO2 in a CO2 feedstock, wherein the CO2 content is increased compared to the CO2 feedstock prior to the process. The process may also be named a process for purification of a CO2 feedstock.

[0009] In a further preferred embodiment, the invention concerns a process for obtaining a purified CO2 feedstock comprising:I. pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification of biomass, waste and / or fossil fuel,II. separating the CO2 feedstock from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product wherein the CO2 feedstock comprises more than 80 mol% CO2 based on total of the dry CO2 feedstock,III. subjecting the CO2 feedstock to the process for the oxidation of impurities in a CO2 feedstock according to any one of claims 1-13 to deliver the purified CO2 feedstock, andIV. optionally separation of H2O from the purified CO2 feedstock by condensation.

[0010] In the process of the invention, the redox catalyst is sequentially reduced and oxidized in the chemical looping reactor. This process involves the redox pair redox catalyst / reduced redox catalyst, preferably metal oxide / reduced metal oxide. The metal oxide may be written as a molecular formula so as MexOy wherein the subscripts x and y indicate the number of metal atoms and oxygen atoms in the metal oxide. In case the metal oxide is reduced, the ratio of Me to O is higher and therefore the number of oxygen atoms is lower with an amount 6, so the reduced metal oxide may be written as MexOv-s. The choice of the redox catalyst, and consequently the redox pair, influences the thermodynamics of the process. Preferably, the redox catalyst is a metal oxide, more preferably selected from the list consisting of iron oxide, copper oxide, nickel oxide, manganese oxide, cobalt oxide. The inventors have surprisingly found that copper oxide and iron oxide are particularly advantageous, since complete conversion of CO to CO2 is thermodynamically feasible with these redox catalysts. The inventors also found that iron oxide is even more preferred. By using iron oxide instead of copper oxide more steam is obtainable in the process that can be advantageously recycled. Therefore, preferably the redox catalyst is a metal oxide, more preferably selected from iron oxide, copper oxide, and combinations thereof, even more preferably the redox catalyst is iron oxide, most preferably the redox catalyst is Fe2C>3.Detailed DescriptionGeneral Definitions

[0011] In this document and in its claims, the verb "to comprise" and its conjugations is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually means "at least one". The word "about" or "approximately" when used in association with a numerical value (e.g. about 10) preferably means that the value may be the given value more or less 1% of the value.

[0012] The present invention has been described below with reference to a number of exemplary embodiments. Modifications and alternative implementations of some parts or elements are possible and are included in the scope of protection as defined in the appended claims. All citations of literature and patent documents are hereby incorporated by reference.

[0013] Bar stands for bar absolute and concerns the pressure that is zero-referenced against a perfect vacuum. 1 bar is 100,000 N / m2. 1 bar is 100,000 Pascal.

[0014] The term "chemical looping" as used herein refers to an process comprising two steps, wherein the first step involves reduction of a redox catalyst to obtained a reduced redox catalyst, preferably a metal oxide is reduced from Mex0Yto Mex0Y-6 , and the second step involves oxidation of the reduced redox catalyst to regenerate the redox catalyst, preferably Mex0Y.6 is oxidised to Mex0Y. Typically, the steps are repeated, so after the second step the first step is carried out and so on. The reduction is by feeding a CO2 feedstock comprising impurities; the oxidation is by feeding an oxidant. These feedstocks are sequentially provided, so first a first feedstock is provided and then a second feedstock is provided. Preferably these steps are iterated, so the first feedstock and the second feedstock are iteratively provided. Obviously when the first feedstock is provided the second feedstock is not provided and when the second feedstock is provided the first feedstock is not provided. Optionally intermediate steps between the oxidation and reduction step may be carried out such as purging.

[0015] The term "carbon capture" as used herein refers to a process wherein a concentrated carbon dioxide (CO2) stream is obtained from an industrial process. In case the CO2 is transported to long term storage the process is referred to as "carbon capture and storage" (CCS), while in case the CO2 is utilized as starting material in further applications the process is referred to as "carbon capture and utilization" (CCU).

[0016] The term "post-combustion CO2 feedstock" as used herein refers to CO2 streams obtained from industrial process from which the CO2 is obtained by combustion (complete oxidation) of fossil fuels, waste or biomass. Examples of such post-combustion CO2 sources are flue gasses of energy plants, waste gasses of steel or cement production and the like.

[0017] The term "pre-combustion CO2 feedstock" refers to CO2 feedstock obtained from processes that reform and / or partial oxidize fossil fuel, waste or biomass. These are pre-combustion processes. So "pre-combustion CO2 feedstock" is feedstock obtained from a process in which fossil fuels, waste, and / or biomass are heated in the absence of oxygen or with a substoichiometric amount of oxygen. Such process converts the fossil fuels, waste, and / or biomass into syngas, so syngas is the reactionproduct of such process. Syngas is a mixture of mainly CO, CO2 and H2. Preferably pre-combustion CO2 feedstock is derived from pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification of fossil fuels, waste, or biomass. Pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification of fossil fuels, waste, or biomass are pre-combustion processes. Typically, the pre-combustion CO2 feedstock is obtained by separating the CO2 from the reaction product of the precombustion process, wherein the separated CO2 is the pre- combustion CO2 feedstock.

[0018] The term "dry CO2 feedstock" as used herein refers to the CO2 feedstock without accounting for water. The term "dry CO2 feedstock" or "mol % based on total of the dry CO2 feedstock" does not imply that the feedstock inherently comprises water. Instead, the term "dry" in "mol % based on total of the dry CO2 feedstock" points to that the mol % of a species relates to the total moles present in the feedstock wherein the moles of water in the feedstock are not included in the total moles, so based on the total feedstock excluding water. In case no water is present in the feedstock, "mol % based on total of the dry CO2 feedstock" is the same as the "mol % based on total of the CO2 feedstock". As known in the art, the mol % of a species in a feedstock or any composition can be based on all species in the feedstock, so based on the total feedstock. However, in some cases it is more convenient to express a mol % based on total of the dry feedstock, for example in case the water is not involved in the process that is concerned and / or in case the amount of water in the feedstock varies.

[0019] The term "water gas shift (WGS) reaction" as used herein refers to the reaction of carbon monoxide and water vapour to form carbon dioxide and hydrogen: CO + H2O CO2 + H2.

[0020] The term "bed material" as used herein refers to any material comprised in the reactor at any given moment during the process and includes at least a redox catalyst and optionally any inert material.

[0021] The term "inert material" as used herein refers to a material which is not a catalyst in the process of the invention and does not undergo any chemical reaction in the process of the invention. The inert material is not the redox catalyst of the invention.Description of the figures

[0022] Figures 1A and IB show the thermodynamic evaluation of the chemical looping process of the invention wherein the redox catalyst is NiO. Figure 1A shows the % CO conversion (y-axis) as a function of temperature °C (x-axis) for the redox catalyst reduction step (during which CO is oxidized) at different NiO / CO ratios = 1, 2, 3 (the lines for the different ratios are overlapping). At temperatures > 400 °C, the % CO conversion decreases with temperature for all Ni / CO ratios tested. CO conversion was found to be the highest at process temperatures up to 350 °C for all NiO / CO ratios. Figure IB shows the equilibrium composition of the gas phase expressed as molar fraction % (y-axis) at different temperatures °C (x-axis) in the reduction step at NiO / CO=l (CO2 solid line with round symbol, H2O solid line with triangular symbol, H2 dashed line with square symbol, CO dashed line with asterisk symbol). The right y-axis represents the mol.% of CO and H2 (reagents of the chemical looping process) and the left y-axis represents the mol.% of CO2 and H2O (products of the chemical looping process). The highest CO and H2 conversion to CO2 and H2O is observed up to 350 °C.

[0023] Figure 2 shows the thermodynamic evaluation of the chemical looping process of the invention wherein the redox catalyst is CuO. Figure 2 depicts the % CO conversion (y-axis) as a function of temperature °C (x-axis) at different CuO / CO molar ratios (1, 2, 3). The % of CO conversion for the CuO system does not depend on temperature and is always 100%, regardless of the process temperature.

[0024] Figures 3 shows the thermodynamic evaluation of the chemical looping process of the invention wherein the redox catalyst is FejOa. Figure 3 shows the % CO conversion (y-axis) as a function of temperature °C (x-axis) at different FejOa / CO molar ratios (1, 2, 3, 4 - ratio = 1 solid line with square symbol, ratio = 2 solid line with triangular symbol, ratio = 3 dashed line with round symbol, ratio = 4 dotted line with asterisk symbol) . At temperatures > 400 °C the % of CO conversion decreases for FejOa / CO ratios of 1 and 2. For FejOa / CO ratios of 1 and 2 CO conversion was found to be the highest at process temperatures up to 350 °C. For FejOa / CO ratios of 3 and 4, a 100% conversion for the entire temperature range is observed. Figure 3 shows that the % of CO conversion is the highest at process temperatures up to 350 °C for all FejOa / CO ratios (1, 2, 3, and 4).

[0025] Figure 4 demonstrates the influence of two different redox catalysts on the exit temperature of the oxidation step (y-axis) for a fixed bed reactor in the first cooling strategy (feed excess gas): Cu- based system (top), Fe-based system (bottom). On the x-axis the ratio of O2 to metal oxide is represented, on the y-axis the temperature of the bed material and gas exiting in °Celcius. Figure 4 gives an indication on the amount of air feed required to reach a certain outlet temperature. For a chosen outlet temperature of 400°C, an O2 to redox catalyst ratio equal to 4.32 was found for the Cu- based system and 3.52 for the Fe-based system. Since the maximum outlet temperature observed for the Fe-based system is much lower than the one observed for the Cu-based system, a lower O2 to redox catalyst ratioi is required for the Fe-based system. In addition, the energy efficiency improves when feeding (and preheating) less air.

[0026] Figure 5 shows the ratio of oxygen to redox catalyst (y-axis), wherein the redox catalyst is a metal oxide as a function of the inert content (x-axis, the inert content is plotted as a percentage of the total of inert content and redox catalyst) for an exit temperature of the oxidation step of 400°C in the second cooling strategy (adding inert material): Cu-based system (top), Fe-based system (bottom). For the Cu-based system (top) the ratio of oxygen to redox catalyst increases with the increase in inert content in the bed from 4.3 (when no inert material is present) to 7.3 at an inert content of 90%. In contrast, for the Fe-based system (bottom), the presence of an inert material in the bed does not influence the ratio of oxygen to redox catalyst which remains rather constant at about 3.5.

[0027] Figure 6 shows the outlet temperature of the reduction step (left y-axis, temperature in0Celsius) and the heat duty obtained of the oxidation step (in MJ, right y-axis) wherein for the oxidation step the outlet temperature is set to 400°C and considering stoichiometric amount of C / MexOv-s as a function of inert content (x-axis) in the bed in the third cooling strategy (removing heat from the reactor): Cu-based system (top) and Fe-based system (bottom). "Hex3" (solid line) corresponds to the heat duty removed from the reactor considering heat is removed directly from the reactor in a heat exchanger reactor design. "Tout_red" (solid line with filled triangle markers) corresponds to the outlet temperature of the reduction step. Both the outlet temperature and the heat removed are when the respective reduction and oxidation are completed.

[0028] Figure 7 shows the CO level as a function of time for the reduction step of different chemical looping cycles with iron oxide as redox catalyst for a dry feed. On the y-axis the CO concentration is plotted, the CO concentration that is plotted corresponds to the MS signal for CO (having a mass number of 28 g / mol). On the x-axis time is plotted in minutes. 4 cycles are in figure 7 , cycle 2 (black dashes), cycle 5 (grey dashes, the dash-length is shorter than for cycle 2), cycle 10 (black intermitted dots and dashes) and cycle 15 (black dotted line).

[0029] Figure 8a shows the CO level as a function of time for the reduction step of different chemical looping cycles with iron oxide as redox catalyst that is mixed with inert solid (aluminium oxide) for a dry feed. On the y-axis the CO concentration is plotted, the CO concentration that is plotted corresponds to the MS signal for CO (having a mass number of 28 g / mol). On the x-axis time is plotted in minutes. 5 cycles are in figure 8a, cycle 1 (grey dashes, the dash-length is shorter than for cycle 3 and 15), cycle 3 (black dashes), cycle 5 (black intermitted dots and dashes), cycle 10 (black dashes, shorter dashes than cycle 3) and cycle 15 (grey dashes).

[0030] Figure 8b shows the CO level as a function of time for the reduction step of different chemical looping cycles with iron oxide as redox catalyst that is mixed with inert solid (aluminium oxide) for a wet feed. On the y-axis the CO concentration is plotted, the CO concentration that is plotted corresponds to the MS signal for CO (having a mass number of 28 g / mol). On the x-axis time is plotted in minutes. 5 cycles are in figure 8b, cycle 1 (grey dashes), cycle 3 (black dashes, shorter dashes than cycle 15), cycle 6 (dark grey dashes, shorter dashes than cycle 1), cycle 11 (grey dashes, shorter dashes than cycle 1) and cycle 15 (black dashes).

[0031] Figure 9 shows the CO level as a function of time for the reduction step of different chemical looping cycles with iron oxide as redox catalyst that is impregnated on an inert solid (aluminium oxide) for a wet feed. On the y-axis the CO concentration is plotted, the CO concentration that is plotted corresponds to the MS signal for CO (having a mass number of 28 g / mol). On the x-axis time is plotted in minutes. 5 cycles are in figure 9, cycle 111 (grey dashes, shorter dashes than cycle 113), cycle 112 (black dashes, shorter dashes than cycle 114), cycle 113 (dark grey dashes), cycle 114 (black dashes) and cycle 115 (dark grey intermitted dots and dashes).Process

[0032] The process of the invention can be used to purify a CO2 feedstock obtained from any carbon capture process known in the art. Purify refers to that the concentration of impurities in the CO2 feedstock is reduced, or in other words that the concentration of CO2 in the CO2 feedstock is increased. The process of the invention purifies the CO2 feedstock by oxidizing the impurities. Subsequently, the resulting oxidized impurities can be easily removed, or the oxidized impurity is CO2. The process according to the invention is referred to as a chemical looping process. Chemical looping processes are well known in the art, for example it is known for the production of CO2 and H2 from hydrocarbons (W02010099555A1). The chemical looping process consists at least of two main steps: a reduction step and an oxidation step. During the feeding of the CO2 feedstock a redox catalyst is reduced in a reduction step, during the feeding of the oxidant the redox catalyst is oxidized in an oxidation step. Depending on process setup, reactor design, and bed type additional steps may be present. Preferred additional step involve heating and / or cooling the bed, one or more purge steps, or combinationthereof. A preferred cooling step may be present after the oxidation step and / or reduction step, a preferred purge step may be present after the oxidation step and / or reduction step. Accordingly, the process of the invention comprises a reduction step, an oxidation step, and preferably additional steps before and / or after the reduction and / or oxidation steps.

[0033] Preferably the chemical looping reactor during the process of the invention is at a temperature in the range of 100 - 1200 °C , more preferably 200 - 1000 °C, even more preferably 300 - 900 °C, most preferably 400 - 800 °C. Preferably the process of the invention is carried out at a temperature in the range of 100 - 1200 °C , more preferably 200 - 1000 °C, even more preferably 300 - 900 °C, most preferably 400 - 800 °C. In a preferred embodiment, the chemical looping reactor during the process of the invention is at a temperature of above 300 °C, more preferably above 400 °C or the process of the invention is carried out at a temperature of above 300 °C, more preferably above 400 °C. Preferably the temperature difference between the oxidation step and the reduction step is in the range of 0 - 200°C, more preferably in the range of 0 - 100°C, even more preferably in the range of 0 - 50°C, most preferably in the range of 0 - 20°C. A smaller temperature difference between the oxidation step and the reduction step is beneficial as it reduces complexity as no or less additional heating or cooling steps are needed, in addition energy losses are prevented.

[0034] In a preferred embodiment the process of the invention is carried out at a pressure of 1 - 50 bar, more preferably 2 - 30 bar, most preferably 5 - 20 bar.

[0035] The general reactions that take place in the two chemical looping steps of the invention are reported in Zhu et al. (Chemical looping beyond combustion - a perspective - Energy & Environmental Science (RSC Publishing) D0l:10.1039 / C9EE03793D). In Table 1 an example is provided wherein the redox catalyst is a metal oxide and CO, Hz and CH4are exemplary impurities and O?, H?O and CO? are exemplary oxidants. The process steps are further illustrated in the paragraphs below.Table 1. Reactions taking place in the chemical looping process.

[0036] When in this document a redox catalyst or metal oxide is mentioned the oxidized form of the redox catalyst or metal oxide is referred to. In case the redox catalyst or metal oxide is reduced the redox catalyst or metal oxide is named the reduced redox catalyst or reduced metal oxide.

[0037] In addition, dependent on the impurities present other reactions may occur. For example, when sulphur S is present in the CO? feedstock, S may be oxidized to SO?. If hydrocarbons of general formula CxHyare present, they get oxidised to CO?.Reduction step

[0038] In the first chemical looping step which is the reduction step the redox catalyst is reduced by impurities in the CO? feedstock and the impurities in the CO? feedstock are oxidized, yielding thereduced redox catalyst and a treated CO2 feedstock. In a preferred embodiment, the impurities in the CO2 feedstock are one or more of CO, H2, CH4and CxHywherein x<4, more preferably one or more of CO, H2, and CH4, most preferably one or more of CO and H2. Preferably, in process of the invention the impurities are completely converted to CO2 and H2O. H2O can be separated by any means known in the art, preferably by condensing the H2O and removing the condensed H2O.

[0039] Preferably the chemical looping reactor during the reduction step is at a temperature in the range of 100 - 1000 °C, more preferably 150 - 800 °C, most preferably 250 - 700 °C, or in other words preferably the reduction or the reduction step is at a temperature in the range of 100 - 1000 °C, more preferably 150 - 800 °C, most preferably 250 - 700 °C.

[0040] In a preferred embodiment the reduction or the reduction step is at a pressure of 1 - 50 bar, more preferably 2 - 30 bar, most preferably 5 - 20 bar.Oxidation step

[0041] In the second chemical looping step which is the oxidation step the reduced redox catalyst is regenerated by oxidation with an oxidant, yielding the redox catalyst and a spent oxidant. Depending on the oxidant and the redox catalyst, the oxidation step can be exothermic or endothermic. Preferably, the oxidation step is exothermic. Preferably the oxidant is selected from oxygen, air, steam, CO2, or combinations thereof, more preferably the oxidant is air. When steam is used as an oxidant, hydrogen is obtained in the spent oxidant as a by-product. This hydrogen can be easily retrieved from the steam and is a valuable product. When CO2 is used as oxidant, the spent oxidant contains mainly CO. The spent CO may serve as a valuable feedstock for further utilization. When the oxidant is air, the spent oxidant mainly contains nitrogen and unreacted oxygen. The oxidant may be selected based on the redox catalyst chosen for the chemical looping. When the redox catalyst in the reduction step is a metal oxide selected from nickel oxide, copper oxide, or iron oxide, the preferred oxidant is air or oxygen, more preferably air. Preferably the quantity of oxidant in the oxidation step is sufficient to obtain complete oxidation of the reduced redox catalyst.

[0042] Preferably the chemical looping reactor during the oxidation step is at a temperature in the range of 100 - 1200 °C , more preferably 200 - 1000 °C, even more preferably 300 - 900 °C, most preferably 400 - 800 °C, or preferably the oxidation or the oxidation step is at a temperature in the range of 100 - 1200 °C , more preferably 200 - 1000 °C, even more preferably 300 - 900 °C, most preferably 400 - 800 °C. In a preferred embodiment, the chemical looping reactor during the oxidation step is at a temperature of above 300 °C, more preferably above 400 °C or the oxidation or the oxidation step is at a temperature of above 300 °C, more preferably above 400 °C.

[0043] In a preferred embodiment the oxidation or the oxidation step is at a pressure of 1 - 50 bar, more preferably 2 - 30 bar, most preferably 5 - 20 bar.Optional cooling step

[0044] Preferably, the process comprises a cooling step after the reduction step and / or after the oxidation step, more preferably both. The cooling step after the reduction step lowers the temperature of the bed to the temperature required for the oxidation step. The cooling step after the oxidation step lowers the temperature of the bed after the second chemical looping step down to thetemperature of the first chemical looping step. This is particularly useful when the reduction reaction and / or oxidation reaction are exothermic and / or when the temperature of the reduction step and oxidation step is different. The cooling step is particularly useful if the chemical loop reactor is a fixed bed reactor. Cooling may be done by any means known in the art. Preferably the cooling step is performed by: i. providing a cooling gas to the chemical looping reactor, wherein the gas is preferably selected from nitrogen gas, air, any inert gas, or combinations thereof, more preferably the gas is air; and / or ii. by removing heat directly from the reactor, preferably by heat exchange.

[0045] An alternative or additional way of cooling is having an inert material in the chemical looping reactor, wherein the inert material is preferably selected from SiOj, AI2O3, or combinations thereof, more preferably the inert material is AI2O3. The inert material acts as heat sink that takes up the heat in the oxidation step and dissipates this heat in the reduction step, by providing this heat to an endothermic reduction reaction and / or transferring the heat to the CO2 feedstock, therewith heating the CO2 feedstock. In a preferred embodiment the chemical looping reactor comprises an inert material, wherein the inert material is preferably selected from SiC>2, AI2O3, or combinations thereof, more preferably the inert material is AI2O3. Preferably the inert material is a particulate material. Preferably the chemical looping reactor comprises a mixture of an inert material and a redox catalyst.

[0046] The hot outlet streams from the cooling step are preferably used to heat up water, thus creating steam while they cool down. Thus, preferably the cooling step generates steam, which can be advantageously re-used, for example in the process to obtain the CO2 feedstock. For example, if the CO2 feedstock is obtained from WGS treated syngas, the steam generated in the cooling step may be recycled as feedstock steam in the WGS reaction. Hence, preferably the steam generated in the cooling step is used in the process to obtain the CO2 feedstock. More preferably the CO2 feedstock is obtained from WGS-treated syngas and the steam generated in the cooling step is recycled as feedstock in the WGS treatment. The amount of steam generated can be related to the amount of inlet carbon in a steam to inlet carbon ratio (S / C(co+co2j). The amount of inlet carbon C(co+co2j is the sum of CO and CO2 present in the inlet stream expressed in mol / s. In a preferred embodiment the cooling step generate an amount of steam that provides for a steam to inlet carbon ratio of at least 0.5, more preferably at least 0.7, most preferably at least 0.9 expressed as S / C(co+co2j ratio.Optional purge step

[0047] Preferably the process comprises a purge step after the reduction step and / or a purge step after the oxidation step, more preferably both. In a purge step a purge gas is provided to the chemical looping reactor. Preferably the purge gas is steam, CO2, or a combination thereof. Preferably the pressure of the purge gas equals the pressure of the CO2 feedstock. The amount of purge gas needed depends on the amount of bed material. Bed material refers to the material in the reactor at any given moment during the process and includes the redox catalyst and any inert material. Preferably the amount of purge gas is 1 - 15 •IO-6kmol per kg of bed material, more preferably 2 - 8 -IO'6kmol per kg of bed material, most preferably 3 - 5 -IO"6kmol per kg of bed material. Advantageously it wasfound that both for copper oxide and iron oxide based bed material a relative small amount of purge gas (around 3.5 - 4.5 -10'6kmol per kg of bed material) is required for purging the bed.Redox catalyst

[0048] The choice of redox catalyst influences the thermodynamics of the chemical looping process. The redox catalyst is sequentially reduced and oxidized in the chemical looping process. This process involves the redox pair redox catalyst / reduced redox catalyst, preferably the redox pair is metal oxide / reduced metal oxide or MexOv / MexOv-s. Preferably the redox catalyst is selected such that the oxidation step and / or the reduction step is exothermic. More preferably, the redox catalyst is selected such that both the oxidation step and the reduction step are exothermic. Preferably the redox catalyst is selected such that full conversion of CO, Hz, and / or CH4to CO? and / or H?O is achieved. When a specific redox catalyst or metal oxide is mentioned, the oxidized form of the redox catalyst or metal oxide is mentioned.

[0049] Nickel oxide (redox pair NiO / Ni) was found to be a suitable redox catalyst for the chemical looping process of the invention. However, CO oxidation to CO? with nickel oxide is limited by equilibrium (Example 1). Copper oxide and iron oxide (redox pairs CuO / CujO and FejOa / FeaO^ were found to be more advantageous redox catalysts, because full conversion of CO to CO? is thermodynamically feasible. Iron oxide is particularly preferred because it ensures a that a higher amount of steam is generated during the cooling process compared to when copper oxide is used (Example 2). The higher amount of steam can be advantageously recycled in the upstream process to obtain the CO? feedstock, for example in the WGS reaction. Also for other processes steam is a valuable and useful product.

[0050] Thus, preferably the redox catalyst is a metal oxide, preferably selected from the list consisting of iron oxide, copper oxide, nickel oxide, manganese oxide, cobalt oxide and any combination thereof, more preferably the metal oxide is selected from the list consisting of nickel oxide, iron oxide, copper oxide, and any combination thereof, even more preferably the metal oxide is selected from the list consisting of copper oxide and iron oxide, and combinations thereof, most preferably the metal oxide is iron oxide. Preferably the redox catalyst is selected from CuO, FejOa, and combinations thereof, most preferably the redox catalyst is FejOa.

[0051] The chemical looping reactor comprises a redox catalyst and optionally an inert solid. In a preferred embodiment, the chemical looping reactor comprises an inert solid, more preferably a particulate inert solid. Preferably the inert solid is selected from TiO?, ZrO?, silica (SiOz), alumina (AI2O3), or combinations thereof, more preferably the inert solid is selected from silica (SiC ), alumina (AI2O3), or combinations thereof more preferably the inert solid is AI2O3. Preferably the bed material in the chemical looping reactor during the reduction step comprises 0 - 90 wt.% inert material based on total weight of the bed material, more preferably 10 - 90 wt.% inert material based on total weight of the bed material, even more preferably 50 - 90 wt.% inert material based on total weight of the bed material, even more preferably 10 - 50 wt.% inert material based on total weight of the bed material. Inert solid is inert material, so the bed material in the chemical looping reactor during the reduction step comprises 0 - 90 wt.% inert solid based on total weight of the bed material, more preferably 10 - 90 wt.% inert solid based on total weight of the bed material, even more preferably 50 - 90 wt.%inert solid based on total weight of the bed material, even more preferably 10 - 50 wt.% inert solid based on total weight of the bed material. In an alternative preferred embodiment, the chemical looping reactor does not comprise any inert solid Inert material is useful for preventing sintering and agglomeration and for improving chemical looping reactions. For example, when copper oxide is used as redox catalyst, inert material may be needed to prevent sintering and agglomeration at high temperatures.

[0052] The combination of redox catalyst with inert material may be in different forms. In a preferred embodiment the particulate inert solid is mixed with the redox catalyst, the particulate inert solid is mixed with the redox catalyst wherein at least part of the inert solid particles and part of the redox catalyst are bound, or the redox catalyst is impregnated on the particulate inert solid. More preferably, the particulate inert solid is mixed with the redox catalyst or the redox catalyst is impregnated on the particulate inert solid. As is known to the skilled person the redox catalyst is in particulate form in case being mixed with the particulate inert solid. Also when the redox catalyst is present without inert solid typically the redox catalyst is in particulate form.

[0053] In a preferred embodiment the redox catalyst is impregnated on a particulate inert solid. Such particulate inert solid is also named a carrier. Preferably the carrier is selected from silica (SiOj), alumina (AI2O3), TiC , ZrC and combinations thereof, more preferably the carrier is selected from SiC , alumina AI2O3, and combinations thereof, even more preferably the carrier is AI2O3. Preferably the carrier is porous. Typically, TiC , ZrC>2, silica and alumina are porous by nature. In the field of catalysis, impregnation is known. Impregnation refers to a material preparation method that involves depositing a catalyst precursor onto a support leading to the catalyst remaining on the surface and / or inside the pores of the support material after drying and activation. Typically, the activation is by heating (also named calcination).Feedstock

[0054] The process of the invention can be used to purify CO2 streams obtained from any process known in the art. The CO2 feedstock typically is obtained from carbon capture technology. Preferably the CO2 feedstock is a pre-combustion CO2 feedstock, a post-combustion CO2 feedstock or combinations thereof. Examples of pre-combustion CO2 feedstocks are CO2 feedstocks derived from pyrolysis of fossil fuels, waste, or biomass, optionally coupled with physical CO2 separation technologies like Selexol and Rectisol. Examples of post-combustion CO2 feedstocks are CO2 feedstocks derived from the combustion of fossil fuels, waste, or biomass to generate energy, or cement / coke / lime production. Preferably the CO2 feedstock is a pre-combustion CO2 feedstock. More preferably, the CO2 feedstock is obtained from pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification of biomass, waste and / or fossil fuel wherein preferably the CO2 feedstock is separated from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product.

[0055] In a preferred embodiment the CO2 feedstock is obtained from syngas, even more preferably from water-gas shift (WGS)-treated syngas, most preferably from WGS-treated syngas obtained by a sorption enhanced WGS (SEWGS) process. Syngas is a precombustion CO2 feedstock. The SEWGS process already provides high purity CO2. Nevertheless, small amounts of H2 and CO may remain, if theSEGWS process is not run at its optimal conditions, for example due to overall process efficiency considerations. Therefore, the chemical looping process of the invention may improve SEGWS process efficiency.

[0056] Typically, the CO2 content of the CO2 feedstock is high. The CO2 feedstock comprises more than 80 mol% CO2 based on total of the dry CO2 feedstock, preferably more than 90 mol%, even more preferably more than 95 mol%, most preferably more than 99 mol%. Preferably the CO2 feedstock comprises in the range of 10 - 80 mol% CO2 based on total of the CO2 feedstock, more preferably in the range of 20 - 70 mol% CO2 based on total of the CO2 feedstock, most preferably in the range of 30- 60 mol% CO2 based on total of the CO2 feedstock.

[0057] The CO2 feedstock comprises impurities. Preferably, the total amount of impurities in the CO2 feedstock is less than 20 mol% based on total of the dry CO2 feedstock, more preferably less than 10 mol% based on total of the dry CO2 feedstock, most preferably less than 5 mol% based on total of the dry CO2 feedstock. Preferably, the total amount of impurities in the CO2 feedstock is in the range of 0.00001 to 20 mol% based on total of the dry CO2 feedstock, more preferably in the range of 0.001 to 5 mol% based on total of the dry CO2 feedstock, even more preferably in the range of 0.01 to 5 mol% based on total of the dry CO2 feedstock, most preferably in the range of 0.1 to 5 mol% based on total of the dry CO2 feedstock. Preferably the CO2 feedstock comprises an amount of CH4less than 1 mol%, more preferably less than 0.5 mol%, most preferably less than 0.3 mol% based on total of the dry CO2 feedstock. Preferably the CO2 feedstock comprises an amount of CH4in the range of 0.00001 to 1 mol%, more preferably 0.001 to 0.5 mol%, most preferably 0.01 to 0.3 mol% based on total of the dry CO2 feedstock. Preferably the CO2 feedstock comprises an amount of H2 less than 10 mol%, more preferably less than 8 mol%, most preferably less than 6 mol% based on total of the dry CO2 feedstock. Preferably the CO2 feedstock comprises an amount of H2 in the range of 0.00001 to 10 mol%, more preferably 0.001 to 8 mol%, most preferably 0.1 to 6 mol% based on total of the dry CO2 feedstock. Preferably the CO2 feedstock comprises an amount of CO less than 2 mol%, more preferably less than 1 mol%, most preferably less than 0.5 mol% based on total of the dry CO2 feedstock. Preferably the CO2 feedstock comprises an amount of CO in the range of 0.00001 to 2 mol%, more preferably 0.001 to 1 mol%, most preferably 0.1 to 0.5 mol% based on total of the dry CO2 feedstock. The CO2 feedstock comprises an amount of CO2 of at least 90 mol%, preferably at least 95 mol%, most preferably at least 99 mol% based on total of the dry CO2 feedstock.

[0058] In another preferred embodiment the total amount of impurities in the CO2 feedstock is in the range of 0.01 - 10 mol% based on total of the dry CO2 feedstock, more preferably in the range of 0.05- 7 mol% based on total of the dry CO2 feedstock, most preferably in the range of 0.1 - 5 mol% based on total of the dry CO2 feedstock. Preferably the CO2 feedstock comprises an amount of CH4in the range of 0.01 - 1 mol%, more preferably 0.05 - 0.5 mol%, most preferably 0.1 - 0.3 mol% based on total of the dry CO2 feedstock. Preferably the CO2 feedstock comprises an amount of H2 in the range of 0.1 - 10 mol%, more preferably 1 - 8 mol%, most preferably 2 - 6 mol% based on total of the dry CO2 feedstock. Preferably the CO2 feedstock comprises an amount of CO in the range of 0.01 - 2 mol%, more preferably 0.05 - 1 mol%, most preferably 0.1 - 0.5 mol% based on total of the dry CO2 feedstock.

[0059] In a preferred embodiment, the CO2 feedstock comprises an amount of H2O of 1 - 80 mol%, more preferably 20 - 70 mol%, most preferably 40 - 60 mol% H2O based on total of the CO2 feedstock.Preferably the CO2 feedstock comprises an amount of CH4in the range of 0.00001 - 0.7 mol%, more preferably 0.001 - 0.2 mol%, most preferably 0.01 - 0.15 mol% based on total of the CO2 feedstock. Preferably the CO2 feedstock comprises an amount of H2 in the range of 0.00001 - 10 mol%, more preferably 0.001 - 6 mol%, most preferably 0.1 - 4 mol% based on total of the CO2 feedstock. Preferably the CO2 feedstock comprises an amount of CO in the range of 0.00001 - 1 mol%, more preferably 0.001 - 0.5 mol%, most preferably 0.05 - 0.3 mol% based on total of the CO2 feedstock. Preferably the CO2 feedstock comprises an amount of CO2 in the range of 10 - 99 mol%, more preferably 20 - 90 mol% most preferably 30 - 60 mol% based on total of the CO2 feedstock. In an alternative preferred embodiment, the CO2 feedstock does not comprise any H2O. In this embodiment, preferably the CO2 feedstock contains H2O in an amount of less than 5 mol%, more preferably less than 2 mol%, most preferably less than 1 mol% based on total of the CO2 feedstock.

[0060] Preferably the CO2 feedstock is obtained from syngas or from WGS treated syngas by separating the CO2 feedstock from the syngas or from the WGS treated syngas, preferably wherein the syngas comprises based on total of the dry syngas in the range of 10 - 70 mol % H2, 5 - 20 mol % CO2 and 20 - 70 mol % CO or wherein the WGS treated syngas comprises based on total of the WGS treated syngas in the range of 20 - 90 mol % H2, 20 - 75 mol % CO2 and 0 - 10 mol % CO.

[0061] Typically, a pre-combustion feedstock does not comprise O2, whilst typically a post-combustion feedstock comprises O2. The presence of oxygen is disadvantageous in the process for the oxidation of impurities in a CO2 feedstock as the O2 may carry over to the treated CO2 feedstock. O2 in the treated CO2 feedstock is not desirable as it may affect the further processing of the treated CO2 feedstock in a negative way or violate CO2 purity specifications. In the process for the oxidation of impurities in a CO2 feedstock, O2 is likely to react with the impurities instead of the redox catalyst but will not result in 100% conversion. In a preferred embodiment the CO2 feedstock comprises less than 0.1 mol% O2 based on total of the dry feedstock, even more preferably less than 0.01 mol% O2, most preferably the CO2 feedstock does not comprise O2.Process setup

[0062] The process of the invention can be carried out in any reactor known in the art. Suitable reactors include but are not limited to fixed bed reactor, fluidised bed reactor, moving bed reactor. Preferably the chemical looping reactor is a fixed bed reactor or a fluidized bed reactor.

[0063] In one embodiment, the process of the invention comprises the following sequential steps: a. a reduction step wherein the CO2 feedstock is provided to a chemical looping reactor, the redox catalyst is reduced, and impurities in the CO2 feedstock are oxidized to yield a treated CO2 feedstock; and b. optionally a first cooling step, wherein the temperature of the chemical looping reactor is lowered; and c. optionally a first purge step wherein a first purge gas is provided to the chemical looping reactor and the treated CO2 feedstock is purged from the reactor; and d. an oxidation step wherein an oxidant is provided to the chemical looping reactor, the reduced redox catalyst is oxidized, and the oxidant is reduced to yield a spent oxidant; ande. optionally a second cooling step wherein the temperature of the chemical looping reactor is lowered; and f. optionally a second purge step wherein a second purge gas is provided to the chemical looping reactor and the spent oxidant is purged from the reactor, wherein steps (b) and (c) may be performed in any order, wherein steps (e) and (f) may be performed in any order. Considering chemical looping is a cyclic process, preferably the sequence of steps is repeated after the last step.

[0064] In a preferred embodiment, the process of the invention involves an upstream process to obtain the CO2 feedstock prior to the chemical looping. Therefore, preferably the process of the invention involves the following sequential steps:I. A process to obtain a CO2 feedstock; andII. The process for the oxidation of impurities in a CO2 feedstock as described above to oxidize the impurities in the CO2 feedstock obtained in step (I) to obtain a treated CO2 feedstock, wherein the CO2 feedstock comprises more than 80 mol% CO2 based on total of the dry CO2 feedstock, wherein the CO2 feedstock and an oxidant are sequentially provided to a chemical looping reactor comprising a redox catalyst, and wherein the impurities in the CO2 feedstock are oxidized when the CO2 feedstock is provided to the chemical looping reactor, wherein preferably the impurities in the CO2 feedstock are one or more of CO, CH4, and H2, more preferably one or more of CO and H2, and are oxidized to CO2 and H2O; andIII. Optional separation of H2O from the treated CO2 feedstock by condensation.

[0065] Preferably the upstream process to obtain the CO2 feedstock is selected from pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification of biomass, waste, and / or fossil fuel, wherein the CO2 feedstock is separated from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product, wherein preferably the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product is subjected to a water-gas-shift (WGS) step before the CO2 feedstock is separated from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product, wherein more preferably the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product is subjected to a sorption-enhanced water-gas-shift (SEWGS) step by which the CO2 feedstock is separated from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product. An example of a suitable SEWGS process is disclosed in WO 2022 / 053692.

[0066] Preferably the process of the invention comprises the following sequential steps:I. A process to obtain a CO2 feedstock, wherein the process is selected from pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification of biomass, waste and / or fossil fuel wherein the CO2 feedstock is separated from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product, wherein preferably the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product is subjected to a water-gas-shift (WGS) step before the CO2 feedstock is separated from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product,wherein more preferably the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product is subjected to a sorption-enhanced water-gas- shift (SEWGS) step by which the CO2 feedstock is separated from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product; andII. A chemical looping process to oxidize the impurities in the CO2 feedstock obtained in step (I) to obtain a treated CO2 feedstock, wherein preferably the impurities in the CO2 feedstock comprise one or more of CO, CH4, and H2, more preferably one or more of CO and H2, and are oxidized to CO2 and H2O, wherein the chemical looping process comprises the following sequential steps: a. a reduction step wherein the CO2 feedstock is provided to a chemical looping reactor comprising a redox catalyst, the redox catalyst is reduced, and impurities in the CO2 feedstock are oxidized to yield a treated CO2 feedstock, and b. optionally a first cooling step, wherein the temperature of the chemical looping reactor is lowered; and c. optionally a first purge step wherein a first purge gas is provided to the chemical looping reactor and the treated CO2 feedstock is purged from the reactor, and d. an oxidation step wherein an oxidant is provided to the chemical looping reactor, the reduced redox catalyst is oxidized, and the oxidant is reduced to yield a spent oxidant, and e. optionally a second cooling step wherein the temperature of the chemical looping reactor is lowered, and f. optionally a second purge step wherein a second purge gas is provided to the chemical looping reactor and the spent oxidant is purged from the reactor wherein steps (b) and (c) may be performed in any order, wherein steps (e) and (f) may be performed in any order; andIII. Optionally separation of H2O from the treated CO2 feedstock by condensation.

[0067] In a most preferred embodiment, the process of the invention comprises the following sequential steps:I. A sorption-enhanced water-gas shift (SEWGS) process for the formation of a CO2 feedstock and an H2 stream, comprising: a. a reaction step, wherein a feed gas comprising COX, wherein x = 1 - 2, and H2O is fed into a SEWGS reactor containing a catalyst and sorbent material capable of adsorbing CO2, thereby forming the H2 stream and a sorbent material loaded with CO2, and b. optionally a rinse step, wherein steam is fed to the SEWGS reactor, thereby establishing a pressure in the range of 5 - 50 bar, and c. optionally a pre-blowdown step, wherein the pressure in the SEWGS reactor is reduced to establish a blowdown pressure in the range of 0.5 - 1.5 times the partial pressure of CO and CO2 in the feed gas of step (a), andd. a blowdown step, wherein the pressure in the SEWGS reactor is reduced to the regeneration pressure in the range of 1 - 5 bar, thereby releasing at least part of the CO2 from the loaded sorbent material, thereby forming the CO2 feedstock; and e. a purge step, wherein steam is fed to the SEWGS reactor, thereby releasing further CO2 feedstock from the SEWGS reactor, wherein the off gas released from the reactor during step (c) is collected separately from the CO2 released from the reactor during step (d); andII. the chemical looping process of the current invention to oxidize the impurities in the CO2 feedstock obtained in step (I) to obtain a treated CO2 feedstock, wherein preferably the impurities in the CO2 feedstock are one or more of CO, CH4, and H2, more preferably one or more of CO and H2, and are oxidized to CO2 and / or H2O, wherein the chemical looping process comprises the following sequential steps: a. a reduction step wherein the CO2 feedstock is provided to a chemical looping reactor comprising a redox catalyst, the redox catalyst is reduced, and impurities in the CO2 feedstock are oxidized to yield a treated CO2 feedstock, and b. optionally a first cooling step, wherein the temperature of the chemical looping reactor is lowered; and c. optionally a first purge step wherein a first purge gas is provided to the chemical looping reactor and the treated CO2 feedstock is purged from the reactor, d. an oxidation step wherein an oxidant is provided to the chemical looping reactor, the reduced redox catalyst is oxidized, and the oxidant is reduced to yield a spent oxidant, e. optionally a second cooling step wherein the temperature of the chemical looping reactor is lowered, and f. optionally a second purge step wherein a second purge gas is provided to the chemical looping reactor and the spent oxidant is purged from the reactor wherein steps (b) and (c) may be performed in any order, wherein steps (e) and (f) may be performed in any order; andIII. Optionally separation of H2O from the treated CO2 feedstock by condensation.ExamplesExample 1: thermodynamic evaluation of the process with Ni-, Cu- and Fe- oxides systems

[0068] In this example, the thermodynamics of the process of the invention were evaluated for three different redox catalyst: Nickel, Copper, and Iron oxides.Method

[0069] Thermodynamic evaluation of metal oxides based on Ni, Fe and Cu for CO oxidation to CO2 was carried out using HSC Chemistry v5.11 software. The assumed CO2 feedstock for the chemical looping reduction step is reported in Table 2.Table 2. Assumed CO2 feedstock for the reduction step.Results

[0070] Starting from the most oxidized form of Ni-based oxygen carrier (i.e., NiO), CO oxidation to CO2 was investigated thermodynamically at three different NiO / CO molar ratios (i.e., 1-3). As represented in Figure 1A, the conversion of CO decreases with temperature from 100% at 250°C to 97% at 700°C, irrespective of the NiO / CO ratio.

[0071] Looking at the outlet gas phase composition illustrated in Figure IB it can be noted that CO2 and H2O are slightly decreasing with temperature while H2 and CO are slightly increasing. This indicates that some side reaction(s) may take place in the evaluated temperature range. If we consider only the species participating in the reaction: NiO + CO(gj = Ni + CO2(g), as reported in Table 3, without taking into account any H2 and H2O, the observed CO conversion seems to be lower than in the case where H2 and H2O are also included as components (not shown). The conversion of CO has the same values and trend as the case where H2 and H2O are included as components (Figure 1A) but the starting CO2 concentration is different, indicating that the reduction of NiO with CO is equilibrium-limited.Table 3 Simplified inlet composition in the reduction step in case of Ni-based materialStarting from the most oxidized form of Cu-based oxygen carrier (i.e., CuO), CO oxidation to CO2 was investigated thermodynamically at three different CuO / CO molar ratios (i.e., 1-3). Full oxidation of COto CO2 is thermodynamically feasible in the evaluated temperature range for all cases as seen from Figure 2.

[0072] Starting from the most oxidized form of Fe-based oxygen carrier (i.e., FezOa), CO oxidation to CO2 was investigated thermodynamically at different Fe2Oa / CO molar ratios. Full oxidation of CO to CO2 is thermodynamically feasible in the evaluated temperature range for Fe2O3 / CO>3 (e.g., 3 Fe20a + CO = 2 Fe2O4+ CO2) as it can be seen in Figure 3. At Fe2O3 / CO < 3 (e.g., FeaOa + CO = 2 FeO + CO2), hydrogen starts to form as well, slightly lowering the conversion of CO but still remaining well above 99.5%. In case of nickel the operating temperature should be kept below 450°C to maintain similar CO conversions which would be challenging given the exothermic nature of the process.

[0073] At Fe2O3 / CO molar ratios of 1 / 3 (e.g. Fe20s + 3 CO = 2 Fe + 3 CO2) the CO conversion decreases significantly with increasing temperature. Analysing gas phase composition at the outlet of the reduction step, it can be observed that both CO and H2O are increasing while CO2 and H2 are decreasing. This could indicate that the reverse water-gas-shift reaction (CO2 + H2 = CO + H2O) occurs.Conclusion

[0074] Copper and iron oxides are able to fully oxidize CO to CO2 in the temperature range 250-700°C, while in the case of the nickel oxide CO conversion is limited by equilibrium, decreasing with increasing temperature from 100% at 250°C to 97% at 700°C. The process of the invention is feasible with all redox catalyst tested. However, CuO and Fe20s are more advantageous than NiO, since full oxidation of CO to CO2 is thermodynamically feasible.Example 2: evaluation of possible cooling strategies

[0075] In this example, a fixed bed configuration with the operating temperature of the first chemical looping step (i.e., reduction) of 400°C is considered. Given the high outlet temperatures at the outlet of the second chemical looping step (i.e., oxidation), different cooling strategies were proposed to return the bed to the temperature of the first chemical looping step (400°C), such as: i. Feed excess air, ii. Have an inert solid material in the bed to limit the temperature increase then feed excess air to further cool down the bed, or ill. Remove heat from the oxidation reactor - heat exchanger reactor design.This presents also a great opportunity for employing heat recovery at the outlet of the oxidation step. The steam generated can be integrated into the upstream capture process lowering the energy demand. Therefore, the higher amount of steam generate is advantageous.Method

[0076] A material balance was calculated in Microsoft Excel and used as input in HSC Chemistry v5.11- "Heat and Material Balance" section. Outlet temperature of the chemical looping steps was calculated in this section assuming adiabatic process (Heat balance=0). Heat recovery in the form of steam was evaluated in the case the bed material contains only redox catalyst or it is mixed with an inert material (i.e. AI2O3). Steam is generated by a heat exchanger wherein the outlet host streams are used to heat up water. To make sure there is enough oxygen carrier to completely oxidize CO but on the other handto limit the material consumption, a MexOY / CO molar ratio equal to 3 was selected for the Cu-based system, and MexOY / CO = 4 for the Fe-based. Different rations of MexOYand AI2O3 are evaluated. Generation of medium pressure (MP) steam with the specifications reported in Table 1 was evaluated.

[0077] The theoretical maximum of steam that can be generated by recovering heat from the chemical looping process was evaluated using Equation (1), considering an efficiency of 80% for the waste heat recovery boiler (WHRB) and an inlet water temperature of 20°C. usable heat (HEXi) * efficiencv%WHRBcavacitv[kg] = - — - - - - - = - - - - - — pyheat required per kg of steam h4— hxResults

[0078] Figure 4 illustrates the influence of the O2 / MexOY-i ratio on the outlet temperature of the oxidation step for the previously fixed Mex0Y / C0 ratios. This gives an assessment of the first cooling strategy: i. feed excess air. The amount of steam generated in this case is reported in Table 4. This includes also the steam generated by recovering heat from the outlet of the reduction step.Table 4. Theoretical amount of steam generated in the first cooling strategy.

[0079] As a next step, the second cooling strategy was evaluated: ii. Adding an inert solid material in the bed to limit the temperature increase then feed excess air to further cool down the bed. Figure 5 illustrates the O2 / MexOY-6 required to cool the bed to 400°C (i.e., temperature of the first looping step) as a function of the inert content in the bed. The amount of steam generated in this case is reported in Table 5. This includes also the steam generated by recovering heat from the outlet of the reduction step.Table 5. Average theoretical amount of steam generated in the second cooling strategy.

[0080] The last cooling strategy consists of removing heat directly from the reactor. Figure 6 shows the temperature profile of the reduction step as a function of the inert content as well as the heat duty removed from the oxidation reactor by setting the outlet temperature of the oxidation step to 400°C and considering stoichiometric amount of C / MexOv-s. The amount of steam generated in this case is reported in Table 6. This includes also the steam generated by recovering the heat from the outlet of the two chemical looping steps.Table 6. Average theoretical amount of steam generated in the third cooling strategy.Discussion and conclusion

[0081] In the first cooling strategy, i.e. feed excess air, the C / MexOv-s ratio required to get the temperature of oxidation step down to the inlet temperature of the reduction step (i.e. 400°C) is equal to 4.32 for the Cu-based system and 3.52 for the Fe-based system. A lower C / MexOv-s is required for the Fe-based system since the maximum outlet temperature is much lower than the one observed for the Cu-based system. The energy efficiency improves when feeding less air, thus Fe-based system is more energy efficient that the Cu-based system. The amount of steam generated in this case, translated into steam to inlet carbon ratio (S / co+cozj), amounts to an average value of S / C=0.89 for the Cu-based system and 0.95 for the Fe-based system.

[0082] In the second cooling strategy, i.e. adding an inert solid material in the bed to limit the temperature increase then feed excess air to further cool down the bed, for the Cu-based system the Oj / MexOv-s seems to increase with the increase in inert content in the bed from 4.3 to 7.3 at an inert content of 90%. On the other hand, for the Fe-based system, the presence of an inert material in the bed does not influence the C / MexOv-s ratio which remains rather constant at 3.5. The amount of steam generated in this case translates into a S / C=0.91 for the Cu-based system and 0.97 for the Fe- based system.

[0083] A main drawback of Cu-based systems is the low melting point of Cu (i.e., 1079°C), which requires the process to be operated at lower temperatures (e.g., 800-850°C) to avoid agglomeration of the particles. This means that for the Cu-based system an inert content of at least 30% is needs to provide structural stability and avoid sintering at stoichiometric C / MexOv-i (see Figure 5).

[0084] In case of the last cooling strategy, i.e. removing heat directly from the reactor, the amount of steam generated in this case corresponds to an average S / C=0.81 for both the Cu-based system and the Fe-bases system. In this case the amount of steam generated is the same even if there is a higher energy recovery potential in the Fe-based system as seen from Figure 6. The final value is balanced out by the extra steam generated at the outlet of the reduction step in the Cu-based system which has ahigher outlet temperature. One drawback of this cooling strategy is that it will lead to a more complex reactor design.

[0085] The results on the cooling strategies are obtained at the chosen process temperatures. The same trend of results is expected when the process is run at a different temperature. Taken together these results show that the Fe-based system has some significant advantages over the Cu-based system in terms of energy recovery potential. With the Fe-based system more steam is generated in all of the cooling strategy, which leads to availability of steam to be recycled in the upstream carbon capture process. Fe-based systems have the additional advantages of being more environmentally friendly and less expensive than Cu-based systems.Example 3 - TestsA 'Microflow 5' test-rig (React. Chem. Eng., 2021, 6, 244-257, figure 1 and method section) was used as a chemical looping reactor. In this test-rig the temperature and feedstock could be accurately varied, and the outlet gas composition could be accurately measured. The test-rig was equipped with a quartz reactor having a 9.2 mm internal diameter connected to a Mass Spectrometer (MS) for reactor outlet gas analysis. The quartz reactor was filled with different redox catalysts and chemical looping experiments were performed at atmospheric pressure wherein alternatingly a CO2 feedstock and air were provided to the reactor. A wet CO2 feedstock (comprising 5 mol% CO, 45 mol% CO2, 15 mol% H2O, Ar to balance) and a dry CO2 feedstock (comprising 5 mol% CO, 45 mol% CO2, Ar to balance) were tested. The experiment was carried out in a cyclic mode in isothermal conditions at 400°C.Iron oxide as redox catalyst

[0086] Iron oxide (Fe20a, Thermo Scientific, 99.999%, -100 mesh) was used in the experiment. The powder was pelletized using a manual press, followed by crushing and sieving to obtain the desired particle size of 0.212-0.425 mm.

[0087] Figure 7 shows the results from the MS measurements during the reduction step for CO for a dry CO2 feedstock. 60 ml-min1was fed to the reactor. Several cycles were combined in these figures (cycle 2, 5, 10 and 15). Complete conversion of CO to CO2 was observed for the dry feed for the first 30 - 60 min after which the CO concentration started to increase indicating that the redox catalyst was fully reduced. The longest conversion time is observed for cycle 2 after which the CO conversion period starts to decrease as more cycles are run. This is an indication that the redox catalyst is not stable and looses activity in time. The experimental results show that CO can be effectively oxidized to CO2 using iron oxide at 400°C. However, the performance of the process while using pure iron oxide decreases with the number of cycles indicating stability issues.Iron oxide as redox catalyst mixed with aluminium oxide as inert material

[0088] In a second experiment iron oxide as the redox catalyst was mixed with aluminium oxide. Iron oxide (Fe20a, Thermo Scientific, 99.999%, -100 mesh) and alfa-alumina from Alfa Aesar (AI2O3, 99.99%) were used in the experiments. Iron oxide powder and aluminium oxide powder were mixed thoroughly (20 wt.% iron oxide, 80 wt.% aluminium oxide) before pelletizing using a manual press; subsequentlythe tablets were crushed and sieved to obtain the desired particle size. For all experiments, a particle size of 0.212-0.425 mm was used.

[0089] Figures 8a and 8b shows the results from the MS measurements during the reduction step for CO. 30 ml-min1was fed to the reactor. Several cycles were combined in these figures (cycle 1, 3, 5 / 6, 10 / 11 and 15). Complete conversion of CO to CO2 was observed for the dry feed (figure 8a) for the first 45 min after which the CO concentration started to increase indicating that the redox catalyst was fully reduced. For the wet feed (figure 8b), the CO conversion in the first 40 minutes was about 80%. For a total of 15 cycles measured, good stability was observed as seen from the overlay of the CO profiles in Figure 8 for both the dry and wet feed. So for both wet and dry feed the redox catalyst was stable. The experimental results demonstrate that CO can be effectively oxidized to CO2 over a mixture of iron oxide and an inert material, wherein for a wet feedstock a satisfactory conversion could be obtained whilst for a dry feedstock excellent conversion was obtained.Iron oxide as redox catalyst impregnated on aluminium oxide

[0090] Iron oxide was impregnated on aluminium oxide as follows. 27.71 g Fe(NO3)3-9H2O was dissolved in demi water until a total volume of about 30 ml. The obtained solution was added bit by bit to 15.07 g gamma-alumina in a mortar. In between the addition the mixture was mixed thoroughly. The final paste-like material was dried overnight at 120°C and crushed until a fine powder was obtained. The powder was then calcined in air for 4 hours at 700°C which resulted in a yield of 15.66 g material comprising about 20 wt.% iron oxide. A sieve fraction of 0.212-0.424 mm was then made and filled in the reactor. The aluminium oxide is an inert material.

[0091] In this experiment after 110 cycles analyzed with a MS, a Micro Gas Chromatograph (uGC) was also used for gas analysis for an additional five cycles. 60 ml-min1was fed to the reactor. The results are depicted in figure 9. Figure 9 demonstrate the results from the GC measurements during the reduction step for the CO concentration. Complete conversion of CO to CO2 was observed for the first 50 min after which the CO concentration started to increase. Excellent stability was observed for over 100 cycles as seen from the overlay of the CO profiles in Figure 9.Conclusion

[0092] The proof of principle tests of example 3 demonstrate that impurities can be effectively reduced in a CO2 feedstock by a process according to the current invention wherein iron oxide was used as an example redox catalyst and aluminium oxide as an example inert material. Differences in conversion and stability were observed for the different forms of the redox catalyst. This opens the possibility for tailoring the process. For example, relatively cheap iron ore in powder form may be used as redox catalyst even whilst the stability to act as a redox catalyst under the test circumstances was lower than for the other tests. As soon as the ore loses activity the catalyst may be renewed, and the spend ore may be further processed by a steel mill. In case a longer stability is preferred, for a dry feedstock a redox catalyst mixed with a carrier material provides a surprisingly good result whilst when a high conversion is required for a CO2 feedstock comprising water impregnation of the redox catalyst was found to deliver a surprisingly stable and effective process.

Claims

Claims1. Process for the oxidation of impurities in a CO2 feedstock comprising impurities, wherein the CO2 feedstock comprises more than 80 mol% CO2 based on total of the dry CO2 feedstock, wherein the CO2 feedstock and an oxidant are sequentially provided to a chemical looping reactor comprising a redox catalyst, and wherein the impurities in the CO2 feedstock are oxidized when the CO2 feedstock is provided to the chemical looping reactor.

2. Process according to claim 1, wherein the redox catalyst is a metal oxide, preferably selected from the list consisting of iron oxide, copper oxide, nickel oxide, manganese oxide, cobalt oxide, and any combination thereof.

3. Process according to claim 1 or 2, wherein the redox catalyst is selected from the list consisting of iron oxide, copper oxide, and combinations thereof.

4. Process according to any one of the preceding claims, wherein the redox catalyst is iron oxide.

5. Process according to any one of the preceding claims, wherein the CO2 feedstock is a precombustion CO2 feedstock.

6. Process according to any one of the preceding claims, wherein the CO2 feedstock is obtained from pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification of biomass, waste and / or fossil fuel wherein the CO2 feedstock is separated from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product.

7. Process according to any one of the preceding claims, wherein the impurities comprise one or more of CO, H2, and CH4, preferably the impurities comprise one or more of CO and H2.

8. Process according to any one of the preceding claims, wherein the total amount of impurities in the CO2 feedstock is less than 20 mol% based on total of the dry CO2 feedstock, more preferably less than 10 mol% based on total of the dry CO2 feedstock.

9. Process according to any one of the preceding claims, wherein the oxidant is selected from oxygen, air, steam, CO2, or combinations thereof, more preferably the oxidant is air.

10. Process according to any one of the preceding claims, wherein the chemical looping reactor is a fixed bed reactor or a fluidized bed reactor.

11. Process according to any one of the preceding claims, wherein the chemical looping reactor comprises an inert solid, preferably a particulate inert solid.

12. Process according to any one of the preceding claims, wherein the total amount of impurities in the CO2 feedstock is in the range of 0.00001 to 10 mol% based on total of the dry CO2 feedstock, preferably 0.001 - 5 mol%.

13. Process according to any one of the preceding claims, wherein the CO2 feedstock comprises an amount of H2O of 1 - 80 mol%, more preferably 20 - 70 mol%, most preferably 40 - 60 mol% H2O based on total of the CO2 feedstock.

14. Process according to any one of the preceding claims, comprising the following sequential steps: a. a reduction step wherein the CO2 feedstock is provided to a chemical looping reactor, the redox catalyst is reduced, and impurities in the CO2 feedstock are oxidized to yield a treated CO2 feedstock; b. optionally a first cooling step wherein the temperature of the chemical looping reactor is lowered; c. optionally a first purge step wherein a first purge gas is provided to the chemical looping reactor and the treated CO2 feedstock is purged from the reactor; d. an oxidation step wherein an oxidant is provided to the chemical looping reactor, the reduced redox catalyst is oxidized, and the oxidant is reduced to yield a spent oxidant; e. optionally a second cooling step wherein the temperature of the chemical looping reactor is lowered; and f. optionally a second purge step wherein a second purge gas is provided to the chemical looping reactor and the spent oxidant is purged from the reactor, wherein steps (b) and (c) are performed in any order, wherein steps (e) and (f) are performed in any order.

15. Process according to claim 14, comprising step (b) and / or step (e).

16. A process for obtaining a purified CO2 feedstock comprising:I. pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification of biomass, waste and / or fossil fuel,II. separating the CO2 feedstock from the pyrolysis, partial oxidation, steam reforming, dry reforming, autothermal reforming, or gasification product wherein the CO2 feedstock comprises more than 80 mol% CO2 based on total of the dry CO2 feedstock,III. subjecting the CO2 feedstock to the process for the oxidation of impurities in a CO2 feedstock according to any one of claims 1-13 to deliver the purified CO2 feedstock, andIV. optionally separation of H2O from the purified CO2 feedstock by condensation.

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