Description:

The present invention relates to a method for CO2 hydrogenation of any CO2 and CO containing gas mixture by means of water removal.

Processes for CO2 hydrogenation of feedstock gases are known in the art, e.g. the synthesis of dimethyl ether and methanol.

German Offenlegungsschrift DE10 2009 053357 relates to a method for producing dimethyl ether from crude methanol in gas phase as a raw material through catalytic dehydration, the method comprises the following process steps: providing crude methanol by a methanol synthesis method, evaporating the crude methanol, and adjusting reaction temperature and reaction pressure, charging the evaporated crude methanol at a defined space velocity into a reactor packed with dehydration catalyst, discharging gaseous products including dimethyl ether, unreacted methanol and water mixture, cooling, partial condensation and separation of the gaseous product mixture, wherein gaseous dimethyl ether is obtained as product together with liquid water and methanol, wherein methanol is recycled.

US 2018/016218 relates to a system for synthesis of dimethyl ether from carbon dioxide and hydrogen, the system comprising: a catalytic membrane reactor including a plurality of channels and having an outer surface with a water permeable membrane coating, the reactor further containing a bi-functional catalyst material including a methanol synthesis catalyst component to catalyse reaction of carbon dioxide and hydrogen to form methanol and water and a dehydration catalyst component to catalyse dehydration of methanol to form dimethyl ether, wherein upon formation formed water permeates through the water permeable membrane coating and exits the reactor.

US 2004/064002 relates to a method for preparing dimethyl ether from methanol using a membrane reactor, which comprises a step of injecting methanol into a reactor equipped with membrane and filled with a catalyst; and a step of obtaining dimethyl ether simultaneously as water vapor generated by dehydration of methanol is separated by the membrane, wherein the dehydration and separation of water vapor by the membrane are both carried out at 0.150-300[deg.] C. and at 0.1-3.0 MPa, wherein the membrane reactor uses a membrane selected from a group consisting of a ceramic membrane, a metal membrane and a composite membrane of these thereof.

A scientific article written by Dieterich Vincent at al, titled " Power-to-liquid via synthesis of methanol, DME or Fischer-Tropsch-fuels: a review ", Energy Environ. Sci. , 2020,13, 3207, provides an overview of state of the art synthesis technologies as well as current developments and pilot plants for the most prominent Power-to-liquid (PtL) routes for methanol, DME and Fischer-Tropsch-fuels.

WO 2021/257379 relates to a membrane reformer to produce hydrogen, comprising: multiple membrane reactors, wherein each membrane reactor comprises a feed conduit to receive hydrocarbon and steam into a region external to a tubular membrane in the feed conduit, catalyst disposed in the region in the feed conduit to convert the hydrocarbon into hydrogen and carbon dioxide, the catalyst comprising steam-reforming catalyst, the tubular membrane in the feed conduit to diffuse the hydrogen from the region through the tubular membrane to a bore of the tubular membrane, wherein the region is a retentate side of the tubular membrane to discharge retentate comprising carbon dioxide, and wherein the bore is a permeate side of the tubular membrane to discharge permeate comprising hydrogen, and an insertion tube disposed in the bore to facilitate flow of sweep gas through the bore in a direction counter current to flow of hydrocarbon and steam in the region external to the tubular membrane.

An object of the present invention is to provide a plant design with the synergetic operation of a membrane reactor and a preferably but not necessarily pressurized high-temperature co-electrolysis stack, for example a new design for dimethyl ether (DME) production plant.

Another object of the present invention is to combine process units in a synergistic manner.

Another object of the present invention is to provide a dimethyl ether production plant wherein unconverted reactants are recycled into the process.

The present invention thus relates to a method for CO2 hydrogenation of a syngas containing feedstock by means of water removal, which comprises: a step of feeding carbon dioxide and syngas to a reactor equipped with membrane and filled with catalyst; a step of obtaining permeate and retentate from the reactor; a step of feeding the retentate to a recovery section for obtaining a hydrogenation reaction product; a step of feeding the permeate to a high temperature solid oxide electrolyser for obtaining syngas; a step of feeding the syngas to a separation module to separate the syngas feed into a H2/CO2 stream and a purge stream; and a step of recycling the recycled H2/CO2 stream thus obtained to the reactor equipped with membrane and filled with catalyst.

On basis of the above method one or more objects are achieved. The present method thus provides a process design which combines electrolyser and membrane reactor units in a synergistic manner.

The present inventors found that by the present method coke-forming species are removed via steam reforming in the high temperature solid oxide electrolyser before recycling into the reactor equipped with membrane and filled with catalyst, thereby mitigating catalyst deactivation.

In addition, the specific method of the present invention maintains a high H2 content at the inlet of the high temperature solid oxide electrolyser, thereby mitigating oxidation and global stack degradation.

Furthermore, according to the present method high-pressure steam used to drive turbo-compressors is directly valorised as steam source for the high temperature solid oxide electrolyser. It is important to note that if another technology is used for compression, this steam must be sourced by other means for the electrolyser. Any steam removed from the CO2 hydrogenation reaction in the membrane reactor is valorised by the electrolyser as well.

An example of a hydrogenation reaction product according to the present invention is dimethyl ether (DME) but other chemicals produced from syngas and CO2 feedstock may apply. In the present application the production of DME is an example of such chemical but should not be interpreted as a limitation of the scope of protection.

The present inventors found that coke formation on - and therefore deactivation of - the membrane reactor bifunctional catalyst (specifically the proton-donating catalyst like HZSM-5) due to recycled e-fuel is mitigated (steam reformation occurs in the electrolyser). In addition, a high H2/CO ratio at the inlet of the high-temperature electrolyser mitigates oxidation of the Ni catalyst, wherein a higher concentration is beneficial to the lifetime of the electrolyser with only minimal impact on performances.

The present invention combines and synergizes the processes for H2 production from a high temperature solid oxide electrolyser and dimethyl ether (or DME) and methanol (or MeOH) or methane (CH4) fuel production from a catalytic reactor with membrane-based water removal, with steam and CO2 feedstocks along with heat provided by local industrial actors. Recycle streams for the high temperature electrolyser and membrane reactor are combined, and the sweep gas used to promote the catalytic synthesis is fed directly into the electrolysis stack. The present process can be generalized to produce any e-fuel or chemical that is synthesized from a syngas and CO2 feedstock.

According to an example the present method further comprises a step of recycling unconverted carbon dioxide and syngas obtained in the recovery section to the high temperature solid oxide electrolyser.

According to an example the present method further comprises a step of circulating a sweep gas containing CO, CO2 and H2 with the feed in the reactor equipped with membrane and filled with catalyst.

According to an example the composition of the sweep gas is identical to the composition of the feed for the reactor equipped with membrane and filled with catalyst.

According to an example the sweep gas circulates in inner tubes of the membrane at a pressure that is lower than the pressure of the feed of the reactor equipped with membrane and filled with catalyst, preferably at a pressure that is at least 3 bar lower.

According to an example the sweep gas is circulated in the inner tubes of the membrane with a flow rate that is larger than the feed of the reactor equipped with membrane and filled with catalyst, preferably at least 1-2 times larger.

According to an example the reactor comprises water-selective membranes, such as supported or self-supported carbon molecular sieve membranes.

According to an example the recovery section comprises one or more of condensation units, gas separation units and distillation units.

The present invention also relates to a membrane reactor for CO2 hydrogenation of a syngas containing feedstock by means of water removal, wherein the membrane reactor is equipped with membrane and filled with catalyst, the membrane reactor comprising a feed, an outlet of retentate and an outlet of permeate, further comprising a recirculation loop wherein where a sweep gas is circulated with the feed to promote the water and heat removal simultaneously from the catalytic bed.

According to an example the membrane reactor comprises inner tubes for circulating sweep gas.

According to an example the membrane reactor further comprises supported or self-supported carbon molecular sieve membranes.

The present invention also relates to a system for CO2 hydrogenation of a syngas containing feedstock by means of water removal reactor as discussed above, comprising a membrane reactor and a high temperature solid oxide electrolyser, the membrane reactor comprising a feed, an outlet of retentate and an outlet of permeate, wherein the permeate is fed to the high temperature solid oxide electrolyser and an outlet of the high temperature solid oxide electrolyser is processed such that the effluent stream is used as a feed of the membrane reactor.

According to an example the system further comprises a recovery section for obtaining a hydrogenation reaction product

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the block flow diagram of the production plant according to the present invention.

FIG. 2 shows in detail the process design of the production plant according to the present invention.

FIG. 3 shows a high temperature solid oxide electrolyser for producing syngas - hydrogen (H2) and carbon monoxide (CO) - via high-temperature co-electrolysis.

FIG. 4 shows a membrane reactor for the DME production with the sweep gas recirculation loop.

FIG.5 shows in detail another process design of the production plant according to the present invention.

According to Figure 1 , the main components of the process are the high temperature solid oxide electrolyzer stack for co-electrolysis of the feedstock gas to syngas and the membrane reactor which enhances the CO2 hydrogenation of feedstock gases to MeOH and DME by means of water removal. In order to achieve the desired DME yield and selectivity, water must be selectively removed from the reaction zone. Therefore, a sweep gas is circulated in the membrane tubes in order to enhance water removal and, at the same time, inhibit the permeation of the reactants. The sweep gas, while circulating in the membrane tubes, collects water from the reaction environment. The stream coming out of the membranes (permeate), which contains pressurized steam, is recirculated to the electrolyzer (first recycle ratio, ai).The main stream coming out of the membrane reactor (retentate) is first condensed to separate the crude DME from the unconverted gases (mainly H2 and CO), which are recycled to the electrolyzer (second recycle ratio, 02). In order to process the crude DME, a first distillation stage is required to separate DME and CO2 (top product) from MeOH and water. The 2 ^nd distillation stage purifies DME (bottom product) from CO2 (top product). The CO2 stream is recycled back to the electrolyzer (third recycle ratio, □3). A 3 ^rd distillation tower separates MeOH from water to recover MeOH as a byproduct.

Figure 2 shows in detail the process design of the production plant according to the present invention. The process can be divided into three zones: Zone 1 for pressurized high temperature co-electrolysis, Zone 2 for the production of the crude product (i.e. DME) with a carbon-based membrane catalytic reactor, and Zone 3 for the purification of the crude product.

Zone 1 produces syngas - hydrogen (H2) and carbon monoxide (CO) - via high- temperature co-electrolysis, two key reactants for the synthesis of e-fuels and e- molecules (any hydrogen-based molecules synthetized thanks to hydrogen produced by electrolysis) in Zone 2. High pressure steam (preferably >100 bars) from local industrial sources is used in turboexpander TE100 to compress reactants in Zone 2. The remaining steam is then injected via S104 into S105. The water must be treated upstream to ensure that the vapor quality conforms to the electrolyser stack specifications, which can vary depending on provider. This is symbolized by F100 in Figure 2.

All recycle streams from Zones 2 and 3 (S203, S301 , S310) are combined into S105. Finally, captured CO2 via stream S311 is also injected into S105. The final composition for S105 is expected to contain H2, CO, CO2, H2O and trace amounts of e-fuel (i.e. MeOH, DME). The operating pressure for S105 can vary between 0 - 35 barg, though the economics of the plant design are most favorable at elevated pressures. A high-temperature solid oxide electrolyzer stack unit ES100 shown in Figure 3 is proposed for the plant design, with operating temperatures between 650 - 850 °C. Current models on the market include elcoStack® and SteelCell™. At elevated pressures above 7 barg, efficiency of the stack is expected to increase by 3-5%. Furthermore, co-electrolysis at mild conditions (current densities below 1 A/cm ² ) will eliminate degradation assuming adequate removal of impurities (though impurities present in the electrode production process may adversely impact degradation). Steam reformation of trace e-fuels will also eliminate their presence at the inlet of the membrane reactor in Zone 2, avoiding coking and catalyst deactivation. Finally, the gas matrix at the inlet of the cathode is expected to be high in reductive gases (H2/CO). Current systems typically introduce 10-25% H2 at the inlet to ensure a sufficiently reductive environment to avoid oxidation of the Ni cathode, so a higher concentration is expected to mitigate degradation phenomena with minimal increase to the OCV (i.e. decrease in performance) below a certain threshold. Finally, an oxygen-rich product stream S108 can be valorized depending on the needs of local industrial actors.

The outlet stream S109 will be comprised primarily of syngas (H2/CO), along with H2O and CO2. The H2O will be removed by condensation in FD100, whereby the waste heat will be re-used for heating elements shaded in red. CO2 will be injected via S112 into S111 , and the resulting mixture will be compressed to 35barg.

Zone 2 produces the crude e-fuel via a catalytic reactor. It must be noted that practically all synthetic fuels that use H2, CO2 and/or CO as the main reactants can be implemented in the present process design, such as Fischer-Tropsch and Sabatier processes. Furthermore, multiple reactor types - such as adiabatic fixed-bed reactors, boiling-water reactors, gas-cooled reactors, membrane reactors, etc. - can be implemented into the design with minimal modification as long as a recycle loop is implemented.

Zone 3 purifies the crude e-fuel product. This section’s design can vary considerably depending on the impurities present during the process. Furthermore, this patent does not seek to innovate on these well-established processes in the industrial sector. The only remarks worth making are that CO2 from this section is reinjected into the main process via S311 , and there exists considerable potential for the use of waste heat in the boilers of the distillation columns. Figure 4 shows a membrane reactor for the DME production with the sweep gas recirculation loop. In the membrane reactor a sweep gas containing CO, CO2 and H2 is concurrently circulated with the feed, to promote the water and heat removal simultaneously from the catalytic bed. The removal of water from the reaction environment is promoted by its dilution in the sweep gas stream, which circulates in the inner tubes of the membrane at a pressure ~ 5 bar lower than the pressure of the reaction mixture. Such a configuration has two advantages, i.e. the permeation of the reactants is hindered due to the very low driving force across the membranes (i.e., difference in partial pressure), and the membranes do not need to withstand large mechanical stress, contrary to when vacuum conditions are applied in the inner tubes to promote the permeation.

Figure 5 shows in detail another process design of the production plant according to the present invention and is quite similar to the process design shown in Figure 2. Figure 5 is a more general process flow diagram for the production of product 1 and product 2. As can be seen, carbon dioxide and syngas is fed to a reactor equipped with membrane and filled with catalyst. Permeate and retentate are obtained from the reactor, and the retentate is fed to a recovery section for obtaining a hydrogenation reaction product. The permeate is fed to a high temperature solid oxide electrolyser, i.e. as fuel-in for the cathode side. The product obtained from the high temperature solid oxide electrolyser is identified as fuel-out and sent to the reactor equipped with membrane and filled with catalyst. According to Figure 5 contaminants present in the fuel-out stream are selectively removed via a separation module SM100, which is designed to selectively remove H2 and/or CO2 via S200 at the desired ratio necessary for the reactant feed in Zone 2 before entering the reactor equipped with membrane and filled with catalyst. Thus, Figure 5 clearly shows the position of a separation module between the high temperature solid oxide electrolyser outlet and membrane reactor inlet. This releases a CO-rich stream (also containing H2, CO2, and CH4) sent via S104 as a purge or preferably to other downstream offtakers. SM100 can be based on membrane separation technology. Finally, the process is simplified and all gas is compressed by a single turbocompressor TC100.

In an example the sweep gas is circulated in the membrane tubes with a very large flow rate (up to 10-20 times larger than the feed), to promote a turbulent flow, corresponding to high heat transfer coefficients. Therefore, the sweep gas, which is fed at a lower temperature, removes the heat produced by the exothermic reactions, minimizing the temperature gradients in the catalytic bed.

The sweep gas stream contributes only to the water and heat removal; thus, the stream can be recycled directly to the electrolyzer to undergo co-electrolysis.

The membrane reactor can be equipped with any water-selective membrane, with known examples including and Zeolite membranes and carbon molecular sieve membranes. Supported or self-supported carbon molecular sieve membranes, such as AI-CMSMs, are integrated in the catalytic bed. These membranes fulfill all the requirements of this process: stability in hot humid environment and high affinity to water, when the membrane synthesis conditions are correctly tuned. Indeed, carbon membranes derives from the pyrolysis of a polymeric precursor and according to the carbonization temperature, different groups of atoms are removed from the precursor. The residual functional groups are responsible for the membrane hydrophilicity.

AI-CMSMs are characterized by ultra-micropores (i.e. , pores smaller than 0.6 nm), where the capillary condensation phenomena can easily occur. Therefore, when water condenses - partially or totally - in the pores, it will reduce or block the gases permeation. This aspect is usually considered as a drawback of the carbon membranes, when they are used for humid gas separation. On the contrary, this is what makes them even more attractive for the DME membrane reactor, since the reactant permeation has to be avoided.

The reactor shell is packed with a Cu-ZnO-Al2O3/HZSM-5 bifunctional catalyst, with a weight ratio between the Cu-catalyst and the zeolite of 5. This catalyst is industrially used for the syngas-to-DME process. However, we experimentally proved its activity for the CO2 direct conversion to DME as well.

The membrane reactor can be optimized by tuning the space velocity (GHSV) and the membrane area (i.e. membrane area/feed flow and catalyst volume).