A process for preparing a product

Abstract

The present invention provides a process for producing an alcohol product stream from a gas fermentation process. A feed gas stream comprising hydrogen and a carbon oxide is subjected to fermentation to convert at least a portion of the feed gas stream to an alcohol. A major portion of the alcohol from the reactor is removed in a first gaseous product stream. A gas / liquid mixture is separated to obtain a second gas product stream and an alcohol-enriched liquid stream. The second gas product stream is recycled to the reactor.

Description

A PROCESS FOR PREPARING A PRODUCTFIELD OF THE INVENTION

[0001] The present invention relates to a process for producing a product, in particular an alcohol. More in particular, the present invention relates to a process for producing a product using gas fermentation in a reactor containing a fermentation broth.BACKGROUND OF THE INVENTION

[0002] Processes for producing a product using a gas fermentation are known in the art.

[0003] As one example, WO2018 / 175481 Al discloses the use of a vacuum distillation vessel to recover products from a fermentation broth. A problem of the use of a vacuum distillation vessel to recover products directly from a fermentation broth is that the viability of the microorganisms present in the fermentation broth may be negatively impacted. Also, as acknowledged in paragraph

[0027] of WO2018 / 175481A1, the use of a vacuum distillation vessel may cause the production of foam which results in a decrease in performance.

[0004] As a further example, US2023 / 0105160A1 discloses an integrated process using gas fermentation to convert CO2 into a product, where low conversion reverse water gas shift is employed to convert CO2 into CO before passing to a gas fermentation bioreactor. As mentioned in paragraph

[0029] , “.. . target products are recovered from the fermentation broth by continuously removing a portion of the broth from the bioreactor, separating microbial cells from the broth (conveniently by filtration), and recovering one or more target products from the broth”, .. . and “Desired products are removed from gas fermentation process 155 in gas fermentation product stream 158.”.

[0005] In this respect it is noted that paragraph

[0030] of US2023 / 0105160A1 mentions that a ‘bioreactor off gas stream’ is produced which contains ‘unreacted Ci gases and inert gases.’

[0006] A problem of the know n process according to US2023 / 0105160A1 is that the removal of the actual desired product from the liquid fermentation broth by, for example, filtration may be cumbersome as the microorganisms present in the fermentation broth may block or clog the filters. Other known issues of the removal of the desired product from the liquid fermentation broth are foaming of the broth, operation costs and extra maintenance.

[0007] It is an object of the present invention to solve, minimize or at least reduce one or more of the above problems.

[0008] There is a need to provide an alternative process for producing a product using a gas fermentation process, wherein the product is obtained from the fermenter without the need for filtration or distillation of the fermentation broth.SUMMARY OF THE INVENTION

[0009] According to one aspect of the present invention, there is provided a process for producing a product, in particular an alcohol, the process at least comprising the steps of: (a) providing a carbon-containing gas stream; (b) subjecting the carbon-containing gas stream to fermentation in a reactor containing a fermentation broth thereby obtaining at least a first gaseous product stream; (c) removing the first gaseous product stream obtained in step (b) from the reactor; (d) cooling the first gaseous product stream removed in step (c) thereby obtaining a gas / liquid product mixture; (e) separating the gas / liquid mixture obtained in step (d) in a gas / liquid separator thereby obtaining a second gas product stream and an alcohol-enriched liquid stream; (f) recycling the second gas product stream obtained in step (e) to the reactor.

[0010] According to another aspect of the present invention, there is provided an apparatus suitable for performing the process for producing a product according to the present invention, the apparatus at least comprising: a reactor containing a fermentation broth for performing a fermentation reaction, the reactor having at least an inlet for a carbon-containing stream and an outlet for a first gaseous product stream; an optional compressor for compressing the first gaseous product stream; a heat exchanger for cooling the first gaseous product stream to obtain a gas / liquid product mixture; a gas / liquid separator for separating the gas / liquid mixture to obtain a second gas product stream and an alcohol-enriched liquid stream; a recycle line for recycling the second gas product stream to the reactor.BRIEF DESCRPTION OF THE DRAWINGS

[0011] The process of the present invention will be better understood by referring to the following detailed description of preferred embodiments and the drawings referenced therein, in which:

[0012] Fig. 1 schematically illustrates one embodiment of the process of the present invention; and

[0013] Fig. 2 schematically illustrates another embodiment of the process of the present invention.

[0014] For the purpose of this description, same reference numbers refer to same or similar components.DETAILED DESCRIPTION

[0015] The present invention provides a process for producing an alcohol product stream from gas fermentation of a feed gas stream. In particular, the process of the present invention provides a process for more efficiently recovering an alcohol product stream from a gas fermentation. It has surprisingly been found according to the present invention that a target product, specifically an alcohol product, can be obtained in a gas fermentation process without the need for filtration or distillation of the fermentation broth. According to the present invention, a maj or portion of the target alcohol product is obtained from the reactor in a gas stream produced in the fermentation process, rather than from a liquid stream also containing the fermentation broth. Hence, no complicated liquid / liquid separation of the fermentation broth and target alcohol product is required.

[0016] A further advantage of the process according to the present invention, is that lower product losses in the gas stream (which is usually seen as an ‘off-gas stream’) produced in the fermentation process are achieved. Also, less processing steps and less energy for downstream processing of a liquid stream are required. Furthermore, excess water produced in the conversion of feed gas to alcohol product may be removed with the gas stream and then distilled and recycled as needed thereby controlling the water balance in the reactor to reduce the overall water footprint of process.

[0017] Referring to Fig. 1 illustrating one embodiment of the present invention 1, a carbon-containing gas stream, namely a feed gas stream 10 comprising a carbon oxide and hydrogen, is provided. Carbon oxides include carbon monoxide (CO) and carbon dioxide (CO2). The feed gas stream 10 may be provided as a pressurized stream and / or compressed in an optional compressor (not shown) to bring the feed gas stream 10 to a desired pressure. The feed gas stream 10 may be provided at a pressure, for example, in a range of from 0 - 100 kPaG. An advantage of an elevated pressure is to enhance transfer of carbon oxides and hydrogen to the fermentation broth.

[0018] The feed gas stream 10 comprises carbon oxide and hydrogen. The feed gas stream 10 may have various origins, such as electrolysis, fermentation, water gas shift reaction, natural gas or biogas reforming, etc. Preferably, the feed gas stream 10 containshydrogen and at least one of CO and CO2. The feed gas stream 10 may be provided as a mixture of carbon oxide and hydrogen. Alternatively, the feed gas stream 10 may be provided as a separate stream for each component and / or as a supplement of one component. The feed gas stream 10 may further comprise a mixture or separate stream of an inert gas. such as nitrogen. Though not depicted in the drawings for simplicity, it will be understood that the same or different feed gas stream 10 may be introduced through two or more injectors to the reactor 2.

[0019] When CO is present, the feed gas stream 10 preferably comprises 5-40 mol.% CO, more preferably 10-35 mol.% CO.

[0020] When CO2 is present, the feed gas stream 10 preferably comprises 5-45 mol.% CO2, more preferably 10-30 mol.% CO2.

[0021] The feed gas stream 10 also comprises 10-90 mol.% H2, preferably 10-60 mol.% H2. more preferably 10-40 mol.% H2.

[0022] Preferably, the feed gas stream 10 has a hydrogen to carbon oxide molar ratio in a range of from 2: 1 to 9: 1 , preferably less than or equal to 6: 1.

[0023] Preferably, the feed gas stream 10 is a syngas-containing stream, i.e. containing at least hydrogen and CO. Preferably, the syngas-containing stream comprises at least 50 mol.% H2 and CO, preferably at least 70 mol.% H2 and CO, more preferably at least 80 mol.% H2 and CO.

[0024] The feed gas stream 10 is subjected to fermentation in a reactor 2 to convert at least a portion of the feed gas stream 10 to an alcohol. The fermentation broth is provided in a liquid phase. Additional water is formed in the conversion of hydrogen and carbon oxide to alcohol.

[0025] The person skilled in the art will readily understand that various embodiments of the fermentation and reactor 2 can be used for carrying out the process of the present invention 1.

[0026] The fermentation reactor 2 can be, for example, without limitation, a CSTR (continuous stirred tank reactor), an ICR (immobilized cell reactor), a TBR (trickle bed reactor), etc. Suitable fermentation reactors have, for example, been mentioned in the article E.M. de Medeiros et al., “Production of ethanol fuel via syngas fermentation: Optimization of economic performance and energy efficiency”, Chemical Engineering Science: X, Volume 5, 2020, 100056. The fermentation reactor 2 is preferably configured to increase residence time of the gas stream in the reactor 2, for example, by using reactorinternals, for example, without limitation, trays or packing. Advantageously, the reactor 2 is provided with a plurality of trays, as described in US Provisional Application No. 63 / 666,313, filed 01 Jul 2024.

[0027] The fermentation may be run batchwise or in a semi-continuous or continuous mode. Preferably, the fermentation is run in a continuous mode.

[0028] Preferably, the feed gas 10 (and recycle gas 50, as discussed below), is injected in the reactor to increase residence time for improving contact with the microorganisms. The actual feed gas rate will be dependent on the ty pe of reactor used. Preferably, the feed gas 10 and recycle gas 50 are introduced at or near the bottom of the reactor 2 in an upflow configuration. The feed gas 10 and recycle gas 50 are injected through the same (as shown in Fig. 2) or separate injection nozzles (as shown in Fig. 1) in counter-current operation with fermentation broth introduced at or near the top of the reactor 2.

[0029] In the embodiment of Fig. 1, the recycle gas stream 50 is passed through a heat exchanger 8 to warm or cool the gas, depending on the desired temperature. In the embodiment of Fig. 2, the combined feed gas 10 and recycle gas 50 stream is warmed or cooled in a heat exchanger 8 and fed as stream 15 into the reactor 2.

[0030] The reactor 2 comprises a fermentation broth containing one or more microorganisms. Other components in the fermentation broth can for example be nutrients (such as Mg2+, Ca2+, NFLf, NOT, CH4N2O, POr2-, SO42’, Cl'), water, trace metals (such as Fe2+, Zn2. Mn2+, Co2. Cu2+, MoO2'. Ni2+), pH-controlling agents (such as NaOH, KOH, NH4OH, H2SO4, H3PO4, CO2, citric acid, acetic acid, formic acid), etc. One or more fermentation broth components may be added continuously or periodically to the reactor 2, for example, by combining with recycle stream 70.

[0031] Suitable fermentation conditions and microorganisms have for example been mentioned in US2023 / 0105160A1.

[0032] The microorganisms are preferably anaerobic. Examples of suitable microorganisms include, without limitation, microorganisms from the classes Clostridium, Escherichia coli, Moorella, methylococcus , Acetobacterium, Methanosarcina, Ruminococcus , Carboxydothermus , Syntrophobacter , Eubacterium, Butylbacterium, Oxobacter, etc. Preferably, a microorganism from the class Clostridium is used.

[0033] Preferably, the fermentation is performed at a temperature of from 5 to 70°C, preferably from 20 to 48°C. This, as most of the microorganisms will typically not surviveat temperatures above 48°C, unless they are thermophilic (such as Clostridium clariflavum).

[0034] The gas pressure to be used in the reactor 2 is not particularly limited. Also, the gas pressure may vary over the reactor 2. Preferably, the reactor 2 has a maximum gas pressure of 7.5 bara (0.75 MPa (abs)) at the gas inlet (21. 25) of the reactor 2. Also, it is preferred that the gas pressure at the gas outlet 22 of the reactor 2 is in a range of 0.5-6.0 bara (0.05 - 0.6 MPa (abs)), preferably 0.9-1.5 bara (0.09 - 0.15 MPa (abs)).

[0035] In accordance with the present invention, the feed gas 10 and recycle gas 50 are injected at a higher rate than conventional gas fermentation injection rates with an objective to carry the produced alcohol to the gas outlet 22 of the reactor 2. In one embodiment, the feed gas 10 may also include nitrogen to increase the gas volume while not affecting the pH of the fermentation broth. The actual injection rate is dependent on the size and type of reactor 2.

[0036] In accordance with the present invention, a major portion of the produced alcohol, preferably C2-C4 alcohols, more preferably C2-C3 alcohols, is carried to the gas outlet 22 of the reactor 2. Preferably, at least 50% of the produced alcohol is carried to the gas outlet 22, more preferably 80%, most preferably 100% of the produced alcohol is carried to the gas outlet 22. This is in contrast to conventional gas fermentation processes, where the major portion of produced alcohol is collected from the fermentation reactor in the liquid phase. The gaseous product stream 20 contains the produced alcohol, unconverted carbon oxide(s), unconverted hydrogen, and water vapour. The gaseous product stream 20 may also contain C2+ aldehydes, alkenes, and / or ketones. The gaseous product stream 20 will also contain nitrogen if added to supplement the feed gas stream 10.

[0037] Preferably, the gaseous product stream 20 removed from the reactor 2 comprises at least 0.50 mol.% C2+ (i.e. components having 2 or more carbon atoms such as ethanol, ethanal, acetone, acetaldehyde, 1 -propanol, 2-propanol, propanal, etc.). More preferably, the gaseous product stream 20 comprises at least 0.9 mol.% C2+. There is no upper limit for the C2+ product as high a yield of product as possible is desirable.Preferably, the gaseous product stream 20 comprises up to 8 mol.% C2+, more preferably up to 10 mol.% C2+.

[0038] In this respect it is noted that paragraph

[0030] of US2023 / 0105160A1 mentions that a bioreactor off gas stream is produced which contains unreacted Cl gases and inert gases. This bioreactor off-gas stream is, after compression passed back to the gasfermentation process. No mention is made in US2023 / 0105160A1 that this bioreactor offgas stream is cooled or contains any C2+. Also, no mention is made in US2023 / 0105160A1 of a separation device to separate liquids from the bioreactor off-gas stream.

[0039] Further it is preferred that the gaseous product stream 20 removed from the reactor 2 has a partial C2+ pressure in a range of from 9 mbar (900 Pa) to 0.2 bar (20 kPa). Also, the gaseous product stream 20 will be saturated with water, which is produced in the conversion of the feed gas 10 to alcohol product.

[0040] The gaseous product stream 20 is removed via an outlet 22 at or near the top of the reactor 2.

[0041] The removed gaseous product stream 20 has a temperature in a range of from 5 to 70°C, preferably greater than or equal to 20°C, more preferably greater than or equal to 30°C, even more preferably greater than or equal to 35°C, and preferably less than or equal to 48°C. more preferably less than or equal to 45°C. The gaseous product stream has a pressure in a range of from 0.5 to 10.0 bara (50 kPa to 1 MPa (abs)), preferably 1.5-7.0 bara (150 to 700 kPa).

[0042] The gaseous product stream 20 is then cooled in heat exchanger 3 to obtain a gas / liquid product mixture 40. Although the temperature of the gas / liquid product mixture 40 is not particularly limited, it may have a temperature of in a range of from 0 to 40°C, preferably from 5 to 25°C. In one embodiment, as illustrated in Fig. 2, the gaseous product stream 20 is compressed in compressor 9 before being cooled, for example, to a pressure in the range of from 1.5 to 11.0 bara (150 kPa to 1. 1 MPa (abs)). In another embodiment, as illustrated in Fig. 2. the recycle gas stream 50 is compressed in compressor 7 before being mixed with feed gas stream 10. Alternatively, depending on the desired inlet pressure, the feed gas stream 10 pressure, and the recycle gas stream 50 pressure, the compressor 7 may not be used or the compressor 7 may be provided after the feed gas stream 10 and the recycle gas stream 50 are combined.

[0043] When cooling the gaseous product stream 20, water produced by the conversion of the feed gas 10 to alcohol is also actively separated from the gaseous product stream 20. Based on the amount of water that is recycled from a distillation section downstream of the fermentation, the water balance can be controlled in the reactor 2 to reduce the overall water footprint of process.

[0044] The gas / liquid product mixture 40 is separated in a gas / liquid separator 4 to obtain a second gas product stream 50 and an alcohol-enriched liquid stream 60. The second gas product stream 50 is depleted in C2+ components.

[0045] Preferably, the separation in the gas / liquid separator 4 is performed at a pressure greater than or equal to 150 mbara (15 kPa (abs)). preferably greater than or equal to 0.9 mbara (90 Pa (abs)). The pressure is preferably less than or equal to 10 bara (1 MPa (abs)).

[0046] In accordance with the present invention, the second gas product stream 50 is recycled to the reactor 2. The recycled gas 50 may be injected separately into the reactor 2 (as shown in Fig. 1) or combined with the feed gas stream 10 prior to injection (as shown in Fig. 2). In the embodiment of Fig. 1, the second gas product stream 50 is compressed in compressor 5, cooled in second heat exchanger 8 and fed into the reactor 2 as stream 90 at inlet 25.

[0047] The alcohol-enriched liquid stream 60 may be further processed (such as by distillation, rectification, dehydration, extraction, membranes and adsorption processes) to remove undesired components, increase the concentration of the desired target components, and / or further convert into the desired end product. The composition of the alcohol-enriched liquid stream 60 is dependent on the composition of the fee gas stream 10, the microorganisms, and conditions as used in the reactor 2.

[0048] According to an especially preferred embodiment of the process according to the present invention, the process further comprises the step of removing a liquid stream 30 from the reactor 2 and recycling the liquid stream 30 to the reactor 2.

[0049] The liquid stream 30 removed from the reactor 2 comprises at least a part of the fermentation broth as used in the reactor 2. By recycling the liquid stream 70, gradients in the reactor 2 are reduced, gas transfer is increased, and undesirable by-products may be removed (not shown). Preferably, the whole fermentation broth is recycled, i.e., with microorganisms. Those skilled in the art will understand the equipment and operating conditions for recycling the microorganisms to avoid shear forces. The liquid stream 30 may, after removal from the reactor 2, be processed before being recycled, for example with pump 6, back to the reactor 2 to inlet 24 as recycle liquid stream 70. Non-limiting examples of further processing steps are supplementing with fresh microorganisms, nutrients, pH-controlling agents, etc. Also, if desired, the temperature of the liquid stream 30 may be cooled or heated, as desired, before being recycled back to the reactor 2 asrecycle liquid stream 70. Also, the energy balance of the process and apparatus of the present invention 1 may be optimized by applying heat integration of various streams.EXAMPLES

[0050] The following non-limiting examples of embodiments of the process of the present invention as claimed herein are provided for illustrative purposes only.Example 1

[0051] The flow scheme of Fig. 1 was used for illustrating the producing of an isopropanol-enriched product according to the present invention in a non-limiting manner. The compositions and conditions of the gas and liquid streams in the various flow lines are provided in Table 1 below, where V means vapour, whilst L means liquid.

[0052] The values in Table 1 were calculated using a model generated with commercially available Aspen Plus software VI 1, whilst using standard thermodynamic packages with settings such that conversion, gas / liquid separation, etc. are simulated. In the model, the reactor was represented by a counter-current two-phase gas / liquid column.

[0053] For a microorganism favouring the production of isopropanol, the following stoichiometric conversion from CO2, CO and hydrogen to isopropanol was assumed to take place to supplement the Aspen model:CO2 + 2CO + 7H2-> C3H8O + 3H2O.

[0054] For this stoichiometry, the pathway for CO and CO2 fixation has been based on the article by Wu et al., “Acetyl-CoA synthesis through a bicyclic carbon-fixing pathway in gas-fermenting bacteria” Nature Synthesis, 1(8), (2022) 615-625.Table 1Example 2

[0055] The flow scheme of Fig. 1 was used for illustrating the producing of an ethanol - enriched product according to the present invention in a non-limiting manner. The compositions and conditions of the gas and liquid streams in the various flow lines are provided in Table 2 below.

[0056] The values in Table 2 were calculated using a model generated with commercially available Aspen Plus software VI 1, whilst using standard thermodynamic packages with settings such that conversion, gas / liquid separation, etc. are simulated. In the model, the reactor was represented by a counter-current two-phase gas / liquid column.

[0057] For a microorganism favouring production of ethanol, the following stoichiometric conversion from CO2, CO and hydrogen to ethanol was assumed to take place to supplement the Aspen model:CO2 + CO + 5H2-> C2H6O + 2H2O.

[0058] For this stoichiometry, the pathway for CO and CO2 fixation has been based on the article by M. Mohammadi et al. “Sustainable ethanol fermentation from synthesis gas by Clostridium ljungdahlii in a continuous stirred tank bioreactor” Journal of Chemical Technology & Biotechnology, 2012, 87(6). 837-843.Table 2Example 3

[0059] The flow scheme of Fig. 2 was used for illustrating the producing of an isopropanol-enriched product according to the present invention in a non-limiting manner. The compositions and conditions of the gas and liquid streams in the various flow lines are provided in Table 3 below.

[0060] Again, the values in Table 3 were calculated using a model generated with commercially available Aspen Plus software VI 1, whilst using standard thermodynamic packages with settings such that conversion, gas / liquid separation, etc. are simulated. In the model, the reactor was represented by a counter-current two-phase gas / liquid column.

[0061] For a microorganism favoring the production of isopropanol, the same stoichiometric conversion from CO2, CO and hydrogen to isopropanol as in Example 1 was assumed to take place to supplement the Aspen model.Table 3Discussion

[0062] As can be seen from Figs. 1 and 2 and Tables 1-3, the process according to the present invention allows for an effective way of producing an alcohol-enriched liquid stream.

[0063] An important advantage of the process according to the present invention is that a target alcohol product can be obtained in a gas fermentation process in a surprisingly simple manner, without the need of filtration means or distillation of the fermentation broth. According to the present invention, a major portion of the target alcohol product is obtained from the reactor in a gas stream produced in the fermentation process, rather thanfrom a liquid stream also containing the fermentation broth. Hence, no complicated separation of the fermentation broth and target alcohol product is required.

[0064] The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention.

Claims

C L A I M S1. A process for producing a product, in particular an alcohol, the process at least comprising the steps of:(a) providing a carbon-containing gas stream;(b) subjecting the carbon-containing gas stream to fermentation in a reactor containing a fermentation broth thereby obtaining at least a first gaseous product stream;(c) removing the first gaseous product stream obtained in step (b) from the reactor;(d) cooling the first gaseous product stream removed in step (c) thereby obtaining a gas / liquid product mixture;(e) separating the gas / liquid mixture obtained in step (d) in a gas / liquid separator thereby obtaining a second gas product stream and an alcohol-enriched liquid stream;(f) recycling the second gas product stream obtained in step (e) to the reactor.

2. The process according to claim 1, wherein the carbon-containing gas stream provided in step (a) is a syngas-containing stream.

3. The process according to claim 1 or 2, wherein the fermentation in step (b) is performed at a temperature of from 5 to 70°C, preferably from 20 to 48°C.

4. The process according to any one of the preceding claims, wherein the first gaseous product stream obtained in step (b) comprises at least 0.50 mol.% C2+.

5. The process according to any one of the preceding claims, wherein the first gaseous product stream obtained in step (b) has a partial C2+ pressure of from 9 mbar to 0.2 bar (900 Pa to 20 kPa).

6. The process according to any one of the preceding claims, wherein the first gaseous product stream removed in step (c) is, before being cooled in step (d). compressed.

7. The process according to any one of the preceding claims, wherein the separation in step (e) in the gas / liquid separator is performed at a pressure of above 150 mbara (15 kPa (abs)), preferably above 0.9 mbara (90 Pa (abs)).

8. The process according to any one of the preceding claims, wherein the process further comprises the step of:(g) removing a liquid stream from the reactor, and recycling the liquid stream to the reactor.

9. An apparatus suitable for performing the process for producing a product according to any one of the preceding claims 1-8, the apparatus at least comprising:- a reactor containing a fermentation broth for performing a fermentation reaction, the reactor having at least an inlet for a carbon-containing stream and an outlet for a first gaseous product stream;- an optional compressor for compressing the first gaseous product stream;- a heat exchanger for cooling the first gaseous product stream to obtain a gas / hquid product mixture;- a gas / liquid separator for separating the gas / liquid mixture to obtain a second gas product stream and an alcohol-enriched liquid stream;- a recycle line for recycling the second gas product stream to the reactor.

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