WO2017085603A2

WO2017085603A2 - Methods for the conversion of co2 into syngas for use in the production of olefins

Info

Publication number: WO2017085603A2
Application number: PCT/IB2016/056781
Authority: WO
Inventors: Aghaddin Mamedov; Xiankuan Zhang; Clark Rea
Original assignee: Sabic Global Technologies B.V.
Priority date: 2015-11-16
Filing date: 2016-11-10
Publication date: 2017-05-26
Also published as: WO2017085603A3

Abstract

The presently disclosed subject matter provides methods for the production of low carbon dioxide containing syngas through carbon dioxide hydrogenation reaction. In a non- limiting embodiment, a method for making a syngas mixture involves contacting a gaseous feed mixture containing carbon dioxide and hydrogen of appropriate composition to a chromium containing catalyst at a high temperature. The resulting syngas mixture contains a low level of non-converted carbon dioxide and is suitable for olefin synthesis with Fischer-Tropsch processes without having to remove the non-converted carbon dioxide.

Description

METHODS FOR THE CONVERSION OF C0₂ INTO SYNGAS FOR USE IN THE

PRODUCTION OF OLEFINS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 62/256,064, filed November 16, 2015. The contents of the referenced application are incorporated into the present application by reference.

FIELD

[0002] The presently disclosed subject matter relates to the production of a syngas through C0₂ hydrogenation.

BACKGROUND

[0003] Syngas, also known as synthesis gas, is an important feedstock in the chemical industry. It is a gas mixture consisting primarily of hydrogen (H₂) and carbon monoxide (CO) and may further contain other gas components such as carbon dioxide (C0₂), water (H₂0), methane (CH₄) and/or nitrogen (N₂). Syngas has been used in the production of chemical products, such as methanol, oxo alcohol, olefins, dimethyl ether and methyl ethyl glycol, or can be used in the Fischer-Tropsch process to generate higher hydrocarbons, such as fuels.

[0004] Syngas can be produced from many sources, including natural gas, coal, biomass, or other hydrocarbon feedstock. Syngas is frequently produced by using methane as a main feed gas component, which can be converted to syngas through steam reforming reaction. One potential issue associated with syngas production by steam reforming of methane is the high hydrogen content in the resulting syngas mixture due to the reaction stoichiometry. Such hydrogen rich syngas mixture may be suitable for methanol synthesis but cannot be directly used for certain olefin synthesis with Fischer-Tropsch type processes. [0005] Increased awareness of the environmental impact of carbon dioxide emissions has led to efforts to convert carbon dioxide into useful chemical materials. Techniques for converting carbon dioxide into syngas have been applied in certain chemical factories and oil refineries where a relatively large amount of carbon dioxide is generated.

[0006] Certain methods for conversion of carbon dioxide into syngas are known in the art. U.S. Patent No. 8,288,446 discloses catalytic hydrogenation of C0₂ into syngas with a Cr based catalyst. However, the disclosed hydrogenation reactions are disclosed at a moderate temperature, e.g. at a temperature below 8O0C, preferably below 750C. The resulting syngas contains high concentration of C0₂, making removal of non-converted C0₂ necessary before subjecting the syngas to olefin synthesis.

[0007] U.S. Patent Application Pub. No. 2010/0190874 discloses catalytic hydrogenation of C0₂ with mixed oxides of Mn and other transition metals. U.S. Patent Application Pub. No. 2011/0301386 also discloses catalytic hydrogenation of C0₂ into syngas. U.S. Patent U.S. Patent No. 8,540,898 discloses catalytic hydrogenation of C0₂ into syngas with use of Ti and/or Zr catalysts. U.S. Patent No. 8,658,554 discloses catalytic hydrogenation of C0₂ into syngas and teaches a range (14 elements) of transition metals that can be incorporated into the catalyst, including Cr. U.S. Patent Application Pub. No. 2013/0345326 discloses catalytic hydrogenation of C0₂ into syngas. However, each disclose moderate hydrogenation reaction temperatures below 800C, and each fails to provide a low C0₂ syngas composition suitable for olefin synthesis.

[0008] There is a need for methods for producing low C0₂ containing syngas for olefin synthesis.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

[0009] The presently disclosed subject matter provides methods for producing low C0₂ containing syngas through C0₂ hydrogenation reaction. [0010] In certain embodiments, methods for making a syngas mixture can involve contacting a gaseous feed mixture containing carbon dioxide and hydrogen with a chromium containing catalyst at a temperature from about 800 °C to 850 °C. In certain embodiments, the catalyst contains from about 10% to about 20 % by weight of chromium, e.g., 15%. In certain embodiments, the catalyst is supported by alumina.

[0011] In certain embodiments, the gaseous feed mixture has a H₂:C0₂ ratio from about 1.8: 1 to about 2: 1 and the hydrogenation reaction converts more than 60% of carbon dioxide in the gaseous feed mixture into carbon monoxide. In certain embodiments, the resulting syngas mixture contains less than 14% by mole carbon dioxide after removing water and has a H₂:CO ratio suitable for olefin synthesis with Fischer-Tropsch processes. In certain embodiments, the H₂:CO ratio is from about 2: 1 to about 2.5: 1.

[0012] The presently disclosed subject matter further provides methods for producing olefins from a gaseous feed mixture containing carbon dioxide and hydrogen. In certain embodiments, the gaseous feed mixture contacts a chromium containing catalyst at a temperature from about 800 °C to 850 °C, producing a syngas mixture suitable for olefin synthesis with Fischer-Tropsch processes without removing non-converted carbon dioxide.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a flow diagram depicting an exemplary method in accordance with one non-limiting embodiment of the disclosed subject matter. DETAILED DESCRIPTION

[0014] The presently disclosed subject matter relates to the production of low C0₂ containing syngas through C0₂ hydrogenation reaction.

[0015] In certain embodiments, the presently disclosed subject matter provides methods for adjusting the ratio of hydrogen to carbon monoxide in the generated syngas by controlling the temperature of the RWGS reaction and the ratio of the reactants, hydrogen and carbon dioxide.

[0016] Syngas can be produced from many sources, including natural gas, coal, biomass, or other hydrocarbon feedstock. Syngas is frequently produced by methane steam reforming reaction as follows:

CH₄ + H₂0→CO + 3H₂ (1) The resulting syngas generally has a H₂:CO ratio limited by the reaction stoichiometry of the methane steam reforming reaction to 3 or higher. Such hydrogen rich syngas is suitable for methanol synthesis but unfit for olefin synthesis with Fischer-Tropsch type reactions, which typically requires H₂:CO ratio close to from about 2: 1 to about 2.2: 1.

[0017] Carbon dioxide can be selectively converted into carbon monoxide by a reverse water gas shift (RWGS) reaction in the presence of a catalyst and hydrogen under certain reaction conditions. The resulting syngas formed by the RWGS reaction includes carbon monoxide and hydrogen, and can further contain water and non-converted carbon dioxide. The RWGS reaction can be represented by the following equation:

C0₂ + H₂ ^ CO + H₂0 (2)

As a reversible reaction, the conversion of reactants is generally incomplete. Non-converted carbon dioxide in the syngas composition can be undesirable for olefin production because inert C0₂ dilutes the feed for Fischer-Tropsch reactors and thus can decrease production capacity, therefore increasing production cost. Alternatively, C0₂ may be separated from the syngas mixture before olefin production. However, separation of C0₂ can increases the total cost of olefin production.

[0018] The degree of conversion of reactants depends on many factors, including starting composition, catalyst used, and reaction temperature. For instance, increasing hydrogen content in the gaseous feed mixture of RWGS reactions can shift the equilibrium to increase conversion of carbon dioxide to carbon monoxide but at the expense of a lower hydrogen conversion rate, resulting in a syngas with a high H₂:CO ratio unfavorable for Fischer- Tropsch conversion of the syngas to olefins.

[0019] Temperature also can play an important role in reversible chemical reactions. RWGS reaction is a moderately endothermic reaction and its reverse reaction is exothermic. Generally, higher temperature will not only thermodynamically favor the RWGS reaction but also kinetically improve reaction rates. However, too high a temperature, e.g. higher than 850 °C, may cause the catalyst to deactivate or lose selectivity and may require special reactor materials, incurring extra production costs. Therefore, the reaction temperature should to be carefully tailored to achieve a low C0₂ containing syngas mixture that is suitable for olefin synthesis with Fischer- Tropsch processes.

[0020] For the purpose of illustration and not limitation, Figure 1 is a schematic representation of a method according to a non-limiting embodiment of the disclosed subject matter. The C0₂ used in the gaseous feed mixture 101 can originate from various sources. In certain embodiments, the C0₂ can come from a waste gas stream, e.g., from a plant on the same site, or after recovering C0₂ from a gas stream. Recycling C0₂ as starting material in the methods of the presently disclosed subject matter can contribute to reducing the amount of C0₂ emitted to the atmosphere, e.g., from a chemical production site. In certain embodiments, the C0₂ is pressurized to have a pressure from about 0.2 to about 1 MPa, from about 0.5 to about 7 MPa, from about 1 MPa to about 4 MPa or from about 2 MPa to about 3 MPa.

[0021] The hydrogen in the feed mixture 101 may also originate from various sources, including streams coming from other chemical processes, like ethane cracking, methanol synthesis, or conversion of methane to aromatics.

[0022] The gaseous feed mixture 101 including carbon dioxide and hydrogen may further contain other gases that do not negatively affect the reaction. For example, if methane is found not to be reactive in the process and a hydrogen stream containing methane may be used to make the feed mixture. It is important to control H₂:C0₂ ratio to produce a syngas mixture with suitable composition for olefin synthesis. If the hydrogen content is too low, hydrogenation of carbon dioxide will be insufficient, resulting in high concentration of non- converted carbon dioxide. Too high a level of hydrogen content will lead to a syngas containing too much hydrogen unsuitable for olefin synthesis. In certain embodiments, the gaseous feed mixture 101 has a H₂:C0₂ ratio from about 1.5: 1 to about 2.5: 1, from about 1.8: 1 to about 2: 1, or about 2: 1.

[0023] As used herein, the term "about" or "approximately" means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, "about" can mean a range of up to 20%, up to 10%, up to 5% and/or up to 1% of a given value.

[0024] In certain embodiments, the catalyst hydrogenation catalyst used in 102 includes chromium as an active constituent. The catalyst compositions can further include an inert carrier or support material. Suitable supports can be any support materials, which exhibit good stability at the reaction conditions of the disclosed methods, and are known by one of ordinary skill in the art. In certain embodiments, the support material can include aluminium oxide (alumina), magnesia, silica, titania, zirconia and mixtures or combinations thereof. In certain embodiments, the catalyst compositions of the present disclosure further include one or more promoters. Promoter is a substance added to a solid catalyst to improve catalytic performance but by itself the promoter has little or no catalytic effect. Non-limiting examples of suitable promoters include lanthanides, alkaline earth metals and combinations thereof. U.S. Patent Nos. 8,551,434 and 8,288,446, incorporated herein by reference in their entireties, disclose catalysts that can be used in the methods of the present disclosure. The catalyst may further contain other inert components, like a binder material, or usual impurities, as known to the skilled person. The catalysts used in the present disclosure can be prepared by any catalyst synthesis process well known in the art. Examples include, but are not limited to, spray drying, precipitation, impregnation, incipient wetness, ion exchange, fluid bed coating, physical or chemical vapor deposition.

[0025] The Cr content of the catalyst may vary. A certain minimum content is needed to reach a desired level of catalyst activity, but a high content can increase the chance of particle (active site) agglomeration, and reduce efficiency of the catalyst. In certain embodiments, the Cr content is from about 5% to about 30% by weight (elemental Cr based on total weight of the catalyst), from about 10% to about 20% by weight, or about 15% by weight.

[0026] The present disclosure also provides methods for generating the disclosed catalyst. The catalysts of the present disclosure can be prepared by any catalyst synthesis process well known in the art. Examples include, but are not limited to, spray drying, precipitation, impregnation, incipient wetness, ion exchange, fluid bed coating, physical or chemical vapor deposition.

[0027] At 102, the gaseous feed mixture is put in contact with a hydrogenation catalyst, which can be performed over a wide pressure range. A high pressure, e.g. above the atmospheric pressure, tends to increase reaction rate but higher pressure also increases facility cost and even becomes not practical. Furthermore, a high pressure may increase unwanted methane formation. In certain embodiments, the contacting 102 is performed at a atmospheric pressure, at a pressure above about atmospheric, but below 5 MPa, below 4 MPa, or below 2 MPa.

[0028] RWGS reactions can be sensitive to temperature. High temperature is needed to achieve a high C0₂ conversion rate while too high a temperature will increase the chance of particle (active site) agglomeration, and reduce efficiency of the catalyst. At moderate temperatures, such as those disclosed in U.S. Patent No 8,288,446, the C0₂ conversion rate tends to be insufficient, leaving behind significant amount of non-converted C0₂. In certain embodiments, the contacting 102 is carried out at a temperature from about 800°C to about 85aC, from about 80aC to about 82aC, or at about 82aC.

[0029] In certain embodiments, the contacting 102 can be performed in a reactor unit of any reactor type used for a reverse water gas shift (RWGS) reaction. For example, but not by way of limitation, such reactors include fixed bed reactors, such as tubular fixed bed reactors and multi-tubular fixed bed reactors, fluidized bed reactors, such as entrained fluidized bed reactors and fixed fluidized bed reactors, and slurry bed reactors such as three-phase slurry bubble columns and ebullated bed reactors. The dimensions and structure of the reactor unit of the presently disclosed subject matter can vary depending on the capacity of the reactor. The capacity of the reactor unit can be determined by the reaction rate, the stoichiometric quantities of the reactants and/or the feed flow rate. The feed flow rate in the contacting 102 may vary widely based on the reactor design. The space velocity is from about 10 hour^"1 to about 400 hour^"1, from about 100 hour^"1 to about 400 hour^"1, or from about 300 hour^"1 to about 400 hour^"1.

[0030] Through careful choice of the gaseous feed mixture 101 composition and reaction conditions of contacting 102, a conversion rate of C0₂ higher than about 60%, or even 65% can be achieved, producing a syngas composition 103 useful for olefin synthesis by Fischer- Tropsch processes. In certain embodiments, the H₂:CO ratio of the syngas mixture is from about 2: 1 to about 2.5: 1, or from about 2: 1 to 2.2: 1. In certain embodiments, the syngas mixture can contain less than about 15% by mole, or even less than about 14% by mole carbon dioxide after removing the water 104. The water removal 104 can be accomplished with a condenser adapted to separate water from syngas in the product stream by cooling and condensing the water or with equivalent structures. In certain embodiments, the dried syngas mixture may be directly used as feed for olefin synthesis by Fischer-Tropsch processes 105. In certain embodiments, the non-converted carbon dioxide may be removed from the syngas mixture, further improving the Fischer-Tropsch process efficiency. Carbon dioxide removal may be accomplished by amine adsorption or by any means known by one of ordinary skill in the art.

[0031] In certain embodiments, olefin synthesis 105 can be performed in a reactor unit of any reactor type used for a Fischer-Tropsch process. For example, but not by way of limitation, such reactors include multi-tubular fixed bed reactors, entrained flow reactors, slurry bed reactors, and fluid-bed and circulating catalyst reactors.

[0032] The following examples are merely illustrative of the presently disclosed subject matter and should not be considered as a limitation in any way.

Example 1: This example describes hydrogenation of C0₂ by H₂ at 800C in the presence of a Cr/Al₂0₃ based catalyst.

[0033] A gaseous feed mixture made by mixing H₂ at a flow rate of 28.8 cc/min and C0₂ at flow rate of 14.4 cc/min was fed into a small scale quartz fixed bed reactor in the presence of about 8 ml of commercial Cr/Al₂0₃ dehydrogenation catalyst, CATOFIN^®, containing about 15% by weight Cr. The operating conditions were as follows: 800C with a space velocity between about 300 ~ 400 hour^"1 and at about atmospheric pressure. After removing water from the resulting syngas mixture with a cold trap, in-line gas chromatography was used to measure the gas composition. The measurement data are summarized in Table 1.

Example 2: This example describes hydrogenation of C0₂ by H₂ at 820C in the presence of a Cr/Al₂0₃ based catalyst, using the same process conditions as in Example 1 except that hydrogenation of C0₂ by H₂ was carried out at 820C. The resulting gas composition after separation of water is also summarized in Table 1.

TABLE 1

[0034] In addition to the various embodiments depicted and claimed, the disclosed subject matter is also directed to other embodiments having other combinations of the features disclosed and claimed herein. As such, the particular features presented herein can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. The foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.

[0035] It will be apparent to those skilled in the art that various modifications and variations can be made in the systems and methods of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents.

Claims

1. A method of making a syngas mixture, the method comprising:

(a) introducing a gaseous feed mixture comprising carbon dioxide and hydrogen into a reactor;

(b) contacting the gaseous feed mixture with a catalyst comprising chromium at a temperature from about 800 °C to 850 °C.

2. The method of claim 1, wherein the catalyst contains from about 10% to about 20 % by weight of chromium.

3. The method of claim 2, wherein the catalyst further comprises alumina as support.

4. The method of claim 2, wherein the catalyst does not contain substantial amounts of manganese or other transition metal.

5. The method of claim 1, wherein the method converts more than 60% of carbon dioxide in the gaseous feed mixture into carbon monoxide, and wherein the gaseous feed mixture has a H₂:C0₂ ratio from about 1.8: 1 to about 2: 1.

6. The method of claim 5, wherein the H₂:C0₂ ratio is about 2: 1.

7. The method of claim 1, wherein the syngas mixture contains less than 14% by mole carbon dioxide after removing water and has a H₂:CO ratio suitable for olefin synthesis with Fischer-Tropsch processes.

8. The method of claim 7, wherein the H₂:CO ratio is from about 2: 1 to about 2.5: 1.

9. The method of any one the claims 1-8, wherein the syngas mixture is used for olefin synthesis without removing residual C0₂.

10. A method for making olefin, the method comprising:

(a) introducing a gaseous feed mixture comprising carbon dioxide and hydrogen into a reactor; (b) contacting the gaseous feed mixture with a catalyst comprising chromium at a temperature from about 800 °C to about 850 °C to produce a syngas mixture; and

(c) producing olefin with the syngas mixture without removing nonconverted carbon dioxide.

11. The method for claim 10, wherein the gaseous feed mixture has a H₂:C0₂ ratio from about 1.8: 1 to about 2: 1.