BOEGILD HANSEN JOHN (DK)
FRIIS PEDERSEN CLAUS (DK)
| US20080023338A1 | 2008-01-31 |
NI ET AL: "Modeling of a solid oxide electrolysis cell for carbon dioxide electrolysis", CHEMICAL ENGINEERING JOURNAL, ELSEVIER SEQUOIA, LAUSANNE, CH, vol. 164, no. 1, 15 October 2010 (2010-10-15), pages 246 - 254, XP027381904, ISSN: 1385-8947, [retrieved on 20100822]
| Claims 1. Process for the production of a chemical compound from a carbon dioxide comprising starting material, comprising the steps of a) providing a feed stream comprising carbon dioxide; b) electrolysing in an electrolysis stage at least a part of the amount of the carbon dioxide in the feed stream to a first gas stream containing carbon monoxide and a second gas stream containing oxygen, wherein the molar ratio between carbon monoxide and oxygen is about 1:0.5; c) introducing carbon dioxide into the first and/or the se¬ cond gas stream either by maintaining a degree of conversion of carbon dioxide in the electrolysis stage of less than 100% and/or sweeping either the first or the second gas stream or both gas streams with a sweep gas containing carbon dioxide and/or at some stage between the electroly¬ sis stage and a subsequent reaction stage with a gas con¬ taining carbon dioxide to obtain a first process stream containing carbon monoxide and a second process stream containing oxygen, wherein the first and/or second process stream further contains carbon dioxide and the molar ratio of carbon monoxide in the first process stream to oxygen in the second process stream is about 1:0.5; and d) introducing the first and second process stream into the reaction stage and reacting the first and second process stream combined or in succession with a substrate to the chemical compound by means of an oxidative carbonylation reaction with the carbon monoxide and oxygen contained in the process feed stream. 2. The process of claim 1, wherein the substrate is re- acted with the first carbon monoxide containing process stream prior to be reacted with the second oxygen containing process stream. 3. The process of claim 1, wherein the substrate is re- acted with the second oxygen containing process stream prior to be reacted with the first carbon monoxide containing process stream. 4. The process of anyone of claims 1, 2 or 3, wherein the electrolysis stage is carried out in a solid oxide elec¬ trolysis cell. 5. The process of anyone of claims 1 to 4, wherein the substrate comprises methanol. 6. The process of anyone of claims 1 to 4, wherein the substrate comprises ethylene. 7. The process of anyone of claims 1 to 4, wherein the substrate comprises propene . 8. The process of anyone of claims 1 to 7, wherein the chemical compound is used as a solvent for capturing carbon dioxide . 9. The process of anyone of claims 1 to 8, wherein the oxidative carbonylation reaction is carried out in a single reactor in the gas phase. 10. The process of anyone of claims 1 to 8, wherein the oxidative carbonylation reaction is carried out in a single reactor in the liquid phase. 11. The process of anyone of claims 1 to 8, wherein the oxidative carbonylation reaction is carried out in two suc¬ cessive reactors in the gas phase or in the liquid phase. 12. The process of anyone of claims 10 to 11, wherein a solvent for the liquid phase reaction is expanded with CO2 so as to contain up to 40% by weight CO2. 13. The process of anyone of claims 1 to 8, wherein super¬ critical carbon dioxide is used as solvent for the oxida¬ tive carbonylation reaction. 14. The process of anyone of claims 1 to 9, wherein unre- acted substrate is recycled to the oxidative carbonylation reaction . 15. The process of anyone of claims 1 to 10, including the further step of separating the chemical product from the carbon dioxide and recycling the separated carbon dioxide to the electrolysis stage. 16. The process of anyone of claims 1 to 15 wherein the carbon monoxide containing gas stream and the oxygen con- taining gas stream obtained in step b) are not combined pri¬ or to introduction into step d) . 17. The process of anyone of claims 1 to 15 wherein the carbon monoxide containing gas stream from step b) is mixed with the oxygen containing stream form step b) pior to introduction into step d) . 18. The process according to anyone of the preceeding claims, wherein current needed for the electrolysis of car¬ bon dioxide is provided fully or in part by conversion of solar or wind energy. |
The present invention relates to production of chemical compounds, e.g. fuels, chemicals and polymers from carbon dioxide (C0 2 ) · The invention combines two known technolo ¬ gies, i.e. carbon dioxide electrolysis and an oxidative carbonylation reaction into an integrated process where the two technologies show mutual synergies. The invention is a process, which is environmentally benign and results in the production of valuable and much needed chemical compounds as well as in a gross consumption of carbon dioxide.
In a high-temperature electrolysis cell by the application of a current, carbon dioxide is split into carbon monoxide (CO) and oxygen (0 2 ) according to the half cell equations
1) C0 2 (g) + 2e " = CO(g) + O 2" (electrolyte) 2) O 2" (electrolyte) = ½0 2 (g) + 2e ~
With the overall reaction being 3) C0 2 (g) = CO(g) + ½0 2 (g)
Two separate gas streams are thus produced; namely carbon monoxide and oxygen in the molar ratio 2:1.
In the following, oxidative carbonylation reactions may be referred to as oxidative carbonylations for simplicity. Ox ¬ idative carbonylations are - usually catalytic - processes which combine carbonylation and oxidation. Normally, an "oxidative carbonylation" reaction is a term describing the simultaneous reaction of carbon monoxide and oxygen together with at least one more substrate to yield a reaction product . The term "oxidative carbonylation" shall in context with the present invention be understood in a broader sense.
Thus, two-step reactions where at least one substrate other than CO and O2 is first reacted with oxygen and the inter- mediate product thereof is subsequently reacted with carbon monoxide or vice versa will be considered as oxidative car ¬ bonylation processes and are considered to be part of the present invention. If the oxidative carbonylation reaction is carried out as two consecutive reactions, the individual reactions may optionally be carried out in two different reactors, optionally with different catalysts and optional ¬ ly at different reaction conditions; optionally the two consecutive reactions may be carried out by introducing carbon monoxide and oxygen at different positions in the same reactor. The simultaneous reaction of carbon monoxide and oxygen together with at least one more substrate to yield a reaction product is in the following referred to as "combined oxidative carbonylation" and the above two-step processes are referred to as "successive oxidative car- bonylation". These reactions may overall also be referred to as "oxidative carbonylation" and are comprised by the present invention.
In its broadest embodiment the invention relates to a pro- cess for the production of a chemical compound from a car ¬ bon dioxide comprising starting material, comprising the steps of a) providing a feed stream comprising carbon dioxide; b) electrolysing in an electrolysis stage at least a part of the amount of the carbon dioxide in the feed stream to a first gas stream containing carbon monoxide and a second gas stream containing oxygen, wherein the molar ratio between carbon monoxide and oxygen is about 1:0.5; c) introducing carbon dioxide into the first and/or the se- cond gas stream either by maintaining a degree of conversion of carbon dioxide in the electrolysis stage of less than 100% and/or sweeping either the first or the second gas stream or both gas streams with a sweep gas containing carbon dioxide and/or at some stage between the electroly- sis stage and a subsequent reaction stage with a gas con ¬ taining carbon dioxide to obtain a first process stream containing carbon monoxide and a second process stream containing oxygen, wherein the first and/or second process stream further contains carbon dioxide and the molar ratio of carbon monoxide in the first process stream to oxygen in the second process stream is about 1:0.5; and d) introducing the first and second process stream into the reaction stage and reacting the first and second process stream combined or in succession with a substrate to the chemical compound by means of an oxidative carbonylation reaction with the carbon monoxide and oxygen contained in the process feed stream.
It must be noted that at any degree of conversion of CO 2 in the electrolysis cell and no matter how the two gas streams are mixed and/or diluted the electrolysis cell will gener ¬ ate carbon monoxide and oxygen in a molar ratio of about 1:0.5 As already mentioned the oxidative carbonylation may also be performed in succession. Thus in an embodiment of the invention, the substrate is reacted with the first process stream prior to be reacted with the second process stream. In further an embodiment of the invention the substrate is reacted with the second process stream prior to be reacted with the first process stream.
It is preferred that every gas stream at any position in the process has a composition which is outside the explo ¬ sion regime for the given gas composition at the given temperature and pressure. This is obtained by dilution of one or both of the reactant streams with a C0 2 -rich gas before mixing the 0 2 -containing gas stream with a reducing gas stream.
In another embodiment of the invention the oxygen containing gas is diluted with a gas rich in carbon dioxide before being cooled to the inlet temperature of the oxidative car- bonylation reactor.
In yet another embodiment of the invention the oxygen containing gas is diluted sufficiently with a gas rich in car ¬ bon dioxide to ensure that the concentration by volume of O 2 is less than 20%; more preferably less than 10%. In all embodiments of the invention, the electrolysis of carbon dioxide is preferably performed in a solid oxide electrolysis cell. In all embodiments of the invention the electrolysis of carbon dioxide is preferably carried out at a pressure of between 0.1 bar and 50 bar.
Useful substrates for the oxidative carbonylation process according to the invention comprise methanol, ethylene and propene being oxidatively carbonylated to dimethyl car ¬ bonate, β-propiolactone and methacrylic acid compounds, re ¬ spectively as explained in more detail by the examples which follow. Other substrates can be used for oxidative carbonylation and the above examples are not intended to limit the invention but serve merely as illustrative exam ¬ ples of how the invention can be applied.
The oxidative carbonylation reaction can be performed in a catalytic reactor in which both the oxygen-containing gas stream and the carbon monoxide-containing gas stream are introduced into the reactor.
Alternatively the reaction can be performed in separate steps, an oxidation reaction in a first reactor by introducing the oxygen-containing gas stream to the reactor in the presence of a substrate and carrying out the oxidation reaction at one set of reaction conditions, followed by a carbonylation reaction by introducing the carbon monoxide- containing gas stream to a second reactor at a similar or different set of reaction conditions or the reaction can be performed in a first reactor by introducing the carbon mon- oxide-containing gas stream to the reactor in the presence of a substrate and carrying out the carbonylation reaction at one set of reaction conditions, followed by carrying out an oxidation reaction by introducing the oxygen-containing gas stream to a second reactor at a similar or different set of reaction conditions.
The product contained in the effluent stream from the reac ¬ tor or reactors is separated from unreacted substrates. This separation process can be e.g. distillation but may be any separation process which affords a sufficiently good separation for the process to be useful.
Preferably, unreacted substrate is recycled to the oxida- tive carbonylation reactions.
The oxidative carbonylation reactions may be carried out in the gas phase in an adiabatic or cooled reactor or in a fluidized bed reactor; they may be carried out in the liq- uid phase in a trickle bed reactor or in a batch reactor; or they may be carried out in any other reactor that may prove useful for the particular reaction.
The reactions of the present invention can be catalyzed ei- ther by heterogeneous catalysts or by homogeneous catalysts or by a combination of these. If the reactions are carried out in the liquid phase, a solvent or co-solvent may be used or the liquid may consist mostly of the reaction prod ¬ uct. It is assumed that the reactions of the present inven- tion are carried out at elevated pressure and at elevated temperature . The solvent for the liquid phase reaction may advantageous ¬ ly be expanded with CO 2 so as to contain up to 40% by weight CO2. Super-critical carbon dioxide can be used as solvent for the oxidative carbonylation reaction.
All of the embodiments of the invention can include the further step of separating the chemical product from the carbon dioxide and recycling the separated carbon dioxide to the electrolysis stage.
The advantages of the invention are as follows: a) Generation of CO as well as O 2 as separate gases of high purity . b) Omitting syngas production, CO/¾ separation as well as air separation. c) Avoiding the risks and costs connected with storage, handling and transportation of CO and 0 2 . d) Consumption of CO 2 thus having the potential of reducing the global concentration of greenhouse gases. e) The option of diluting the reacting gases with CO 2
(present in the process in advance) which is very often an advantage in oxidation reactions since it may lead to bet- ter temperature control, higher selectivity and some times even to higher reaction rates. This subject is treated e.g. in [Sang-Eon Park and Jin S. Yoo Studies in Surface Science and Catalysis 153 (2004) 303-314] . f) The option of using super-critical CO2 as solvent for the oxidative carbonylation reaction since CO2 is already at hand by necessity. g) The option of using C02~expanded liquid solvents for the reaction or optionally one of the reactions. The use of C02~expanded solvents is well known to increase solubility of other gases (e.g. CO and 0 2 ) in the liquid reaction me ¬ dium. CO2 is available in the process in advance. h) The option of using a reaction product as a solvent for capturing CO2 from a source of dilute CO2. Both DMC and other dialkyl carbonates as well as e.g. 1 , 3-propanediol are likely to be good solvents for CO2. This embodiment of the invention represents a further integration step. Examples
Example 1 A: Combined oxidative carbonylation of methanol to dimethyl carbonate (DMC) : 4) 2CH 3 OH + CO + ½0 2 = CH3OCOOCH3 + H 2 0
The reaction can be catalyzed by CuCl, alternatively
Cu(OCH 3 )Cl, by Cu-Zeolite Y, by Pd-based or Cu-Pd based catalysts, by Au-based catalysts and possibly other cata- lysts. It is preferred to use a catalyst which does not de ¬ mand chlorine (in any form) to be active since chlorine containing compounds may give rise to corrosion problems and undesired contamination of the product. Instead of us ¬ ing methanol as substrate it is possible to use other alco ¬ hols, glycols or polyols. Thus, using ethanol will produce diethyl carbonate; using ethylene glycol will produce eth- ylene carbonate etc. Similarly, ethers may be used as sub ¬ strate instead of alcohols, whereby carbonate esters would be produced without the co-production of water.
Example 1 B: Successive oxidative carbonylation of methanol to dimethyl carbonate using methyl nitrite as intermediate:
5) 2CH 3 OH + 2NO + ½0 2 = 2CH 3 ONO + H 2 0
6) 2CH 3 ONO + CO = CH3OCOOCH3 + 2NO Reaction 5) may be carried out as an uncatalyzed gas phase reaction. Reaction 6) can also be carried out in the gas phase catalyzed e.g. by Pd-containing catalysts such as Pd supported on alumina. In one embodiment of the invention, methanol is synthesized from CO generated at the cathode by application of the wa ¬ ter gas shift reaction to convert part of the CO to ¾, followed by traditional methanol synthesis catalyzed e.g. by a Cu/Zn/Al catalyst. Excess O2 generated at the anode can be vented or used for other purposes. For the DMC syn ¬ thesis either Example 1A or Example IB or any oxidative carbonylation can be used. In this particular embodiment of the invention the product DMC will be made entirely from C0 2 .
In another embodiment of the invention the current needed for the CO2 electrolysis is supplied fully or in part in the form of renewable energies such as a photovoltaic de- vice. The electric current may optionally be stored inter ¬ mediately in a suitable battery device to assure an even production . Example 2: Oxidation of ethylene to ethylene oxide followed by carbonylation to β-propiolactone (Successive oxidative carbonylation) :
It is possible to choose other olefins than ethylene. Thus, using propylene to generate propylene oxide in reaction 7) and methyl-propiolactone in reaction 8) is one alternative embodiment of the invention. Other olefins that may be used are 1-butene, 2-butene, styrene, cyclopentene, cyclohexene etc .
Example 3: Carbonylation of propene in the presence of ¾0 or an alcohol (ROH, where R may be H or an alkyl group) to give isobutyric acid or an ester of isobutyric acid, fol ¬ lowed by oxidation to methacrylic acid or an alkyl methac- rylate (Successive oxidative carbonylation) :
Reaction 9) can be catalyzed by strong acids while reaction 10) can be catalyzed by e.g. a Bi-Fe oxide catalyst.
The above examples 1-3 serve to illustrate the scope of the invention but are not intended to limit the invention. Di ¬ methyl carbonate (DMC) is considered to be a highly versa ¬ tile compound. It may replace hazardous chemicals such as dimethyl sulphate in methylation reactions and phosgene in carbonylation reactions (e.g. for the production of isocya- nates) . It is furthermore an excellent and environmentally benign solvent for many chemicals and polymers and has even found use in electrolyte formulations for lithium based batteries. Furthermore, DMC has a high octane number and may be used as a liquid fuel either in a blend with gaso ¬ line or (potentially) as the sole component. Some say that it may also be used as a diesel fuel. However, the rela ¬ tively high production cost of DMC has until now limited its use. β-propiolactone may be used for making a wide range of useful chemicals. Thus, it may be reacted to acrylic acid and polyacrylates , it may be hydrogenated e.g. over a Ni-, Cu- or Pd-based catalyst to yield 1,3- propanediol, it can be hydrolyzed to 3-hydroxy propanoic acid and several more. Methacrylic acid and methacrylate esters are widely used for making polymers.