PROCESS AND CATALYST SYSTEM FOR THE PRODUCTION OF HIGH QUALITY SYNGAS FROM LIGHT HYDROCARBONS AND CARBON DIOXIDE

Abstract

The present invention describes a process and catalysts for the conversion of a light hydrocarbon and carbon dioxide input stream into high quality syngas with the subsequent conversion of the syngas into fuels or chemicals. In one aspect, the present invention provides an efficient, solid solution catalyst for the production of a carbon containing gas from carbon dioxide and light hydrocarbons. The catalyst comprises a single transition metal, and the transition metal is nickel.

Claims

1. A solid solution catalyst for the production of high quality syngas from carbon dioxide and light hydrocarbons, wherein the catalyst comprises a single transition metal, and wherein the transition metal is nickel.

2-31. (canceled)

32. A nickel-based, solid solution catalyst for producing syngas, wherein the catalyst is in contact with CO.sub.2, and wherein the catalyst is capable of producing syngas with a pre-selected ratio of H.sub.2/CO, and wherein the H.sub.2/CO ratio is capable of being varied based on the production process used to produce the syngas, wherein the nickel-based, solid solution catalyst comprises only one transition metal, and wherein the transition metal is nickel.

33. The nickel-based, solid solution catalyst according to claim 32, wherein the catalyst is stable up to 1,100 C.

34. The nickel-based, solid solution catalyst according to claim 32, wherein the catalyst does not include a precious metal.

35. The nickel-based solid solution catalyst according to claim 32, wherein the catalyst contains 5-20 wt. % nickel.

36. The nickel-based, solid solution catalyst according to claim 32, wherein the catalyst is capable of producing syngas with a H.sub.2/CO ratio ranging from 1.5 to 2.5.

37. The nickel-based, solid solution catalyst according to claim 32, wherein the catalyst is capable of producing syngas with a H.sub.2/CO ratio ranging from 0.7 to 1.0.

38. A nickel-based catalyst for producing syngas, wherein the catalyst is in contact with CO.sub.2, and wherein the catalyst is capable of producing syngas with a pre-selected ratio of H.sub.2/CO, and wherein the H.sub.2/CO ratio is capable of being varied based on the production process used to produce the syngas, wherein the nickel-based catalyst comprises only one transition metal, and wherein the transition metal is nickel.

39. The nickel-based catalyst according to claim 38, wherein the catalyst is stable up to 1,100 C.

40. The nickel-based catalyst according to claim 38, wherein the catalyst does not include a precious metal.

41. The nickel-based catalyst according to claim 38, wherein the catalyst contains 5-20 wt. % nickel.

42. The nickel-based catalyst according to claim 38, wherein the catalyst is capable of producing syngas with a H.sub.2/CO ratio ranging from 1.5 to 2.5.

43. The nickel-based catalyst according to claim 38, wherein the catalyst is capable of producing syngas with a H.sub.2/CO ratio ranging from 0.7 to 1.0.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0020] FIG. 1 shows a graph related to the ability of a catalyst to dry reform mixtures of CO.sub.2 and CH.sub.4.

[0021] FIG. 2 shows a graph related to the performance of a catalyst with a CO.sub.2/CH.sub.4 (1.1/1.0) feed.

[0022] FIG. 3 shows a graph related to a dry reforming test run at an intermediate ratio of CO.sub.2/CH.sub.4 (1.5/1.0).

[0023] FIG. 4 shows a graph related to a catalyst that was found to be stable with lower water content in the feed (at <2.0/1.0H.sub.2O/CH.sub.4) as demonstrated in a test with CO.sub.2/CH.sub.4/H.sub.2O (0.6/1.0/1.4) at 900 C.

[0024] FIG. 5 shows a graph related to a catalyst tested at 900 C. and 10,400 hr.sup.1 (7,800 cc/g-hr) at 850 C. using a gas composition of CO.sub.2/CH.sub.4/H.sub.2O (0.4/1.0/0.93).

[0025] FIG. 6 shows a graph related to a catalyst that was stable when operating with a gas composition of CO.sub.2/CH.sub.4/H.sub.2O (0.6/1.0/1.4) from 800-900 C.

[0026] FIG. 7 shows a graph related to a catalyst tested with a gas composition of CO.sub.2/CH.sub.4/H.sub.2O (0.6/1.0/1.4) at 800 C.

[0027] FIG. 8 shows a graph related to a tri-reforming test conducted at CH.sub.4 (1.0)/CO.sub.2 (1.0)/H.sub.2O (1.0)/O.sub.2 (0.1) at 900 C. at 13,333 hr.sup.1 (10,000 cc/g-hr).

[0028] FIG. 9 shows a graph related to testing conducted at a feed gas composition CH.sub.4 (1.0)/CO.sub.2 (1.0)/H.sub.2O(1.0)/O.sub.2(0.05) at 900 C. and 16,000 hr.sup.1 (12,000 cc/g-hr).

[0029] FIG. 10 shows a graph related to a test conducted with a feed gas composition of CH.sub.4 (1.0)/CO.sub.2 (1.0)/H.sub.2O (1.0)/O.sub.2(0.2) at 900 C. and 17,333 hr.sup.1 (13,000 cc/g-hr).

[0030] FIG. 11 shows a graph related to a tri-reforming test.

[0031] FIG. 12 shows a graph related to a test where the CO.sub.2 ratio was increased to 0.6, the steam ratio was increased to 1.7, and O.sub.2 increased to 0.2. Gas hourly space velocity was 18,666 hr.sup.1 (14,000 cc/g hr).

[0032] FIG. 13 shows a graph related to a test where the carbon dioxide ratio was increased to 0.8, the steam to methane ratio was varied between 1.7 and 1.35, while keeping O.sub.2 at 0.1 (GHSV=16,333 hr.sup.1 or 12,250 cc/g hr).

[0033] FIG. 14 shows a graph related to a test where the carbon dioxide ratio was increased to 0.8, the steam to methane ratio was varied between 1.7 and 1.35, while keeping O.sub.2 at 0.1 (GHSV=18,000 hr.sup.1 or 13,500 cc/g hr).

SUMMARY OF THE INVENTION

[0034] The present invention relates to a process whereby a mixture of light hydrocarbons and carbon dioxide is catalytically converted into a high-quality syngas which can then be used to produce diesel fuel grade liquid hydrocarbon and/or other valuable higher hydrocarbon steams, whereby the carbon dioxide steam is generated by separation from a flue gas stream or by other means or exists as part of the natural gas stream. The light hydrocarbons and carbon dioxide are supplied to a first reactor that utilizes a first catalyst whereby the light hydrocarbons and carbon dioxide are converted into high quality syngas. The syngas output of the first reactor is connected as an input to a second reactor that utilizes a second catalyst to form a diesel fuel grade liquid hydrocarbon and other hydrocarbon byproducts.

[0035] The first catalyst used in the process is a high-performance solid solution Ni-based catalyst that is highly versatile, and which efficiently produces high-quality syngas under dry reforming (CH.sub.4 and CO.sub.2), combination dry/steam reforming (CH.sub.4, CO.sub.2 & H.sub.2O), or tri-reforming (CH.sub.4, CO.sub.2, H.sub.2O & O.sub.2) conditions. The robust, solid solution Ni-based catalysts have high thermal stability up to 1,100 C., do not form carbon (coking), and have good resistance to contaminants that may be present in captured CO.sub.2 streams, natural gas, biogas or other gas feedstock sources.

[0036] The first catalyst is also capable of reforming complex and higher molecular weight hydrocarbons without coking or other deactivation that occurs on traditional steam methane reforming (SMR) and other reforming catalyst systems. This catalyst exhibits high activity at low Ni concentrations (5-20 wt. %), compared to other catalysts that require at least 30 wt. % Ni. Furthermore, the use of expensive precious metals to enhance catalyst performance is not necessary. High conversion efficiencies of light hydrocarbons in the feed stream of 90-100% are achieved when the catalyst is operated under the recommended space velocities and temperature conditions outlined in this invention.

[0037] The second catalyst contains from about 2 to about 50 parts-by-weight cobalt and from about 0.1 to about 20 parts-by-weight of at least one metal selected from a group consisting of cerium, ruthenium, lanthanum, platinum, or rhenium per 100 parts-by-weight of a support selected from a group consisting of silica, alumina, and combinations thereof.

[0038] The carbon dioxide supplied as an input to the process is either contained within the natural gas stream or is obtained by separating the carbon dioxide from a flue gas stream exiting the first reactor, whereby an alkylamine is used to remove the carbon dioxide from the flue gas steam. Alkylamines used in the process include monoethanolamine, diethanolamine, methydiethanolamine, disopropylamine, aminoethoxyethnol, or combinations thereof.

DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention describes a process and catalysts for the conversion of a light hydrocarbon and carbon dioxide input stream into a diesel fuel grade liquid hydrocarbon usable as a compression ignition fuel which may contain a majority of C8-C24 paraffins.

[0040] The invention utilizes a first reactor system whereby light hydrocarbons which may include but are not limited to natural gas, naphtha, natural gas liquids, bio-gas containing methane, or other similar gases are blended with carbon dioxide and optionally steam, oxygen, or oxygen containing gases such as air.

[0041] The first reactor system utilizes a first catalyst that is a robust, Ni based solid-solution catalyst that reforms the feed gases into a carbon containing output gas.

[0042] In comparison to other catalysts developed for this application, this first solid-solution catalyst utilizes only one transition metal, Ni, whereas all other reforming catalysts employ two or more transition metals. See, U.S. Pat. Nos. 6,423,665, 7,432,222, WO 2000/016899, and US Pat. Pub. No. 0314993. Several other prior art formulations require the use of expensive precious metals (e.g. Pt, Pd, Rh, Ru and Ir). See, U.S. Pat. Nos. 6,409,940 and 5,431,855.

[0043] Other formulations require that the active catalyst material needs to be coated on catalyst substrates (e.g. Al.sub.2O.sub.3). Moreover, this is the only solid-state catalyst formulation that is versatile and is able to produce high-quality carbon containing product gas under dry reforming (CH.sub.4 and CO.sub.2), combination dry/steam reforming (CH.sub.4, CO.sub.2 & H.sub.2O), or tri-reforming (CH.sub.4, CO.sub.2, H.sub.2O & O.sub.2) conditions.

[0044] The carbon containing product gas is then fed into a second reactor system that utilizes a second catalyst that contains from about 2 to about 50 parts-by-weight cobalt and from about 0.1 to about 20 parts-by-weight of at least one metal selected from a group consisting of cerium, ruthenium, lanthanum, platinum, or rhenium per 100 parts-by-weight of a support selected from a group consisting of silica, alumina, and combinations thereof.

[0045] The integrated process above requires a carbon dioxide input. In one embodiment, the carbon dioxide is supplied from the separation of the carbon dioxide in the flue gas stream exiting the first reactor, and the separation is done using an alkylamine.

[0046] Alkylamines used in the process can include monoethanolamine, diethanolamine, methydiethanolamine, disopropylamine, am inoethoxyethnol, or combinations thereof. In another embodiment, the carbon dioxide is already contained in the natural gas feedstock.

[0047] In another embodiment, the carbon dioxide exists as part of the natural gas or natural gas liquids stream.

[0048] The manufacturing process for the first catalyst is important as well in that it produces a catalyst that forms a unique solid solution phase, bi-metallic crystalline phase that leads to no segregation of the metal phases. This unique chemical structure leads to enhanced resistance to coking, when compared to conventional metal supported reforming catalysts. This also leads to enhanced resistance to syngas poisons such as sulfur and ammonia. In addition, this catalyst has enhanced catalytic activity at lower surface area compared to monometallic segregated catalyst phase for example Ni on alumina. This catalyst requires no alkali promotion needed to curb the carbon deposition typically seen with feed gases as described herein. The catalyst is operable in a variety of dry, steam, combined dry/steam and tri-reforming feeds. Mixes of higher hydrocarbon feedstocks are also achievable with this catalyst.

[0049] The first catalyst manufacturing may involve some or all of the following steps that will achieve a commercial solid solution catalyst: A) mixing of Ni.sub.2O powders at the 5-15 wt. % level with one or more alkali metal oxides (e.g. MgO, CaO); B) fusing of these oxide mixtures at temperatures in the range of 900-1,100 C. for 4-12 hours; C) calcining the catalyst the first time; D) grinding of the fused mixtures to produce the proper catalyst size, typically in the 500-3,000 urn range; E) calcining the catalyst the second time.

EXAMPLES

[0050] A variety of tests were conducted on the first catalyst including dry reforming (CO.sub.2 and CH.sub.4), combination dry/steam reforming (CO.sub.2, CH.sub.4 & H.sub.2O), and tri-reforming (CO.sub.2, CH.sub.4, H.sub.2O & O.sub.2). CH.sub.4 and CO.sub.2 conversions averaged up to 95-100% at the optimum temperatures and gas space velocities. No formation of carbon deposits (coking) on the catalyst was observed in any of these tests. The following sections provide examples that support the superior performance of these catalysts over currently available technologies.

[0051] Dry ReformingIn Dry (or CO.sub.2) Reforming, methane and carbon dioxide are reacted and produce a syngas with low H.sub.2/CO ratio of 0.7-1.0:

##STR00001##

[0052] Steam ReformingSteam Methane Reforming (SMR) is an endothermic process where methane is reacted with steam at high temperatures to produce a syngas with a high H.sub.2/CO ratio:

##STR00002##

[0053] Partial OxidationReactions for the exothermic oxidation of methane are shown below:

CH.sub.4+2O.sub.2.fwdarw.CO.sub.2+2H.sub.2OH.sub.1173K=802.5 kJ mol.sup.13

CH.sub.4+1.5O.sub.2.fwdarw.CO+2H.sub.2OH.sub.1173K=520.6 kJ mol.sup.13

CH.sub.4+O.sub.2.fwdarw.CO+2H.sub.2H.sub.1123K=23.1 kJ mol.sup.15

[0054] Water-Gas-Shift EquilibriumThe Water-Gas Shift (WGS) equilibrium reaction, equation 6, also occurs during reforming and will adjust the final syngas product ratio depending on how the equilibrium is influenced. If, for instance, dry reforming is conducted in an excess of CO.sub.2, then the reverse WGS will be favored which will increase the CO content and produce water. Likewise, excess steam in the SMR reaction will tend to drive the forward water gas shift resulting in higher H.sub.2 and some CO.sub.2 products.

CO+H.sub.2O.Math.CO.sub.2+H.sub.2H.sub.298 K=34.3 kJ mol.sup.16

[0055] Reactions for Coke Formation and DestructionThe desired reforming reactions above are often accompanied by side or intermediate reactions that involve elemental carbon (or coke). The equations below show some of the ways that carbon can be formed and reformed from the reactants and products. One possible pathway to the desired products of CO and H.sub.2 is methane decomposition on the catalyst (Eq. 7) and or carbon monoxide disproportionation (Eq. 8) followed by carbon reforming (Eq. 9-11). However, it is the buildup of elemental carbon in reactors that is one of the main factors of catalyst lifetime and much research is focused on limiting its formation. Catalysts were analyzed for carbon formation during test runs.

##STR00003##

[0056] As discussed above, this catalyst performed well under mixed reforming conditions and was selected based on several reasons. First, the catalyst shows high thermal stability and negligible carbon formation under a variety of target reforming conditions including dry reforming, which is typically a challenge for other reforming catalysts. Another benefit of the catalyst is that the base material has high thermal stability and shock resistance, both of which are important for commercial plants. Also, the catalyst provides acceptable commercial costs as well as good conversion efficiencies and stability over time. In addition, another benefit is that this catalyst performs well in the reformation of the small percentage of higher hydrocarbons that are in the feed stream from both natural gas and other feed streams. Experimental results on the catalyst for tri-reforming, dry-reforming, and combination reforming are summarized below.

Example #1

[0057] In this example, the ability of the catalyst to dry reform mixtures of CO.sub.2 and CH.sub.4 are described. Dry reforming tests were initiated at 1.75/1.0 CO.sub.2/CH.sub.4 and 900 C. (Run A). The results are shown in FIG. 1. The ratio of CO.sub.2/CH.sub.4 changed slightly as the space velocity was altered due to insufficient calibration of the flow meters. This problem was discovered during data analysis and was corrected in later runs. At 900 C., full methane conversion was achieved, and the sample operated without loss of activity or pressure increase. At 650 C., the methane conversion was low. The catalyst achieved 95% methane conversion at 800 C. and demonstrated stable performance without pressure increase.

[0058] In the next set of tests, the performance of the catalyst under more challenging conditions was examined (see FIG. 2). The performance of the catalyst with a CO.sub.2/CH.sub.4(1.1/1.0) feed was carried out. At 900 C., the complete conversion of methane and carbon dioxide was observed over the first several hours, and complete conversion continued overnight at 800 C. for 18 hours. There was no loss in performance at the higher temperatures, although the pressure drop through the reactor increased from 2 psi to about 4 psi overnight.

[0059] The catalyst was tested at 650 C. the following day, but immediate loss in performance and reactor blockage quickly ensued. Analysis of the sample, as discussed in the following section, confirmed that the catalyst coked (produced carbon that plugged the reactor). This is typical for reforming catalysts at lower temperatures under dry reforming conditions and the catalyst performed well, without carbon deposition, at CO.sub.2/CH.sub.4 ratios greater than 1.5/1.0 and temperatures greater than 800 C.

[0060] Finally, a dry reforming test was run (Test C) at an intermediate ratio of CO.sub.2/CH.sub.4 (1.5/1.0) as shown in FIG. 3. At 900 C., the catalyst was stable for 2 days of operation before the run was terminated to analyze the catalyst for carbon. The pressure didn't increase during the test, and the activity did not change.

[0061] Dry reforming, under all of the conditions described above, produces a syngas with a H.sub.2/CO<1.0 that is not entirely suitable for subsequent conversion to diesel fuel. However, if a source of external renewable hydrogen was available or if hydrogen already exists in the flue gas stream from a stationary emissions source (for example in IGCC power plants), then dry reforming is an attractive option for use in this catalytic system which provides high CO.sub.2 conversion efficiencies and a methane to carbon dioxide input ratio that provides very attractive commercial economics (since the feed gas can contain up to 70% CO.sub.2).

Example #2

[0062] The ability of the catalyst to carry out a combination of dry and steam reforming of CO.sub.2, CH.sub.4 & H.sub.2O is summarized in this example. Combination dry reforming/steam methane reforming tests includes CO.sub.2, CH.sub.4 and H.sub.2O reactants in various molar ratios. In addition to the dry reforming reactions, Steam Methane Reforming (SMR) also occurs and is an endothermic process where methane reacts with steam at high temperatures to produce syngas.

[0063] By combining dry and steam reforming, a syngas with an ideal H.sub.2/CO can be produced. Mixed steam and dry methane reforming tests were conducted to demonstrate activity and determine product composition with methane, CO.sub.2, and steam in the feed. In the first test, the reforming mixture was run with the following gas composition: CO.sub.2/CH.sub.4/H.sub.2O (0.9/1.0/2.2) at 900 C.

[0064] The catalyst was found to be stable with lower water content in the feed (at <2.0/1.0H.sub.2O/CH.sub.4) as demonstrated in a test with CO.sub.2/CH.sub.4/H.sub.2O (0.6/1.0/1.4) at 900 C. (Test D). Stable catalyst performance was achieved as shown in FIG. 4.

[0065] In the next set of test conditions using a gas composition of CO.sub.2/CH.sub.4/H.sub.2O (0.4/1.0/0.93), the catalyst was tested at 900 C. and 10,400 hr.sup.1 (7,800 cc/g-hr) at 850 C. (see FIG. 5).

[0066] As shown in FIG. 6 (test F), the catalyst was stable when operating with a gas composition of CO.sub.2/CH.sub.4/H.sub.2O (0.6/1.0/1.4) from 800-900 C.

[0067] Additional testing was carried out with the same gas composition of CO.sub.2/CH.sub.4/H.sub.2O (0.6/1.0/1.4) at 800 C. (see FIG. 7, Test G). Post-testing Temperature Programmed Oxidation (TPO) and optical analysis did not show any signs of carbon deposition.

[0068] In conclusion, it was found that a combination of steam methane and dry reforming (including the reactants CO.sub.2, CH.sub.4, and H.sub.2O) produce a syngas with a H.sub.2/CO ratio of 1.8-2.0 that is ideal for subsequent liquid fuel production. Typically a H.sub.2O/CO.sub.2 ratio of 2.0-1.0 would be targeted in order to produce syngas in this ratio.

Example #3

[0069] The capability of the catalyst to tri-reform CO.sub.2, CH.sub.4, H.sub.2O & O.sub.2 is presented in this example. Tri-reforming is typically defined as a combination of endothermic CO.sub.2 (or Dry) reforming (Eq. 3) and steam reforming (Eq. 4) with exothermic oxidation of methane (Equations 5, 6, 7 described above).

[0070] Tri-reforming utilizes a single catalyst and the reactions outlined above occur in a single catalytic reactor system. This combination of reactions produces syngas with a H.sub.2/CO ratio in the proper range for subsequent diesel fuel production. Note again that oxygen is not required for achieving the appropriate syngas ratio and for stable operation of the catalyst, however since oxygen is available at in some flue gas applications and operation with some oxygen in the feed stream can allow for the flue gas to be used directly without separation.

[0071] When tri-reforming is used, oxygen levels should be kept under 6% of the total feed gas. Higher oxygen levels start to negatively affect CO.sub.2 conversion. This fact has been recognized by several groups and this is one of the reasons that under auto-thermal reforming (ATR), CO.sub.2 conversion is poor even at elevated temperatures.

[0072] In the first test, reforming was conducted at CH.sub.4 (1.0)/CO.sub.2 (1.0)/H.sub.2O (1.0)/O.sub.2 (0.1) at 900 C. at 13,333 hr.sup.1 (10,000 cc/g-hr) and the data for tri-reforming test H is shown in FIG. 8.

[0073] FIG. 9 shows the results for Test 1 at a feed gas composition CH.sub.4 (1.0)/CO.sub.2 (1.0)/H.sub.2O (1.0)/O.sub.2(0.05) at 900 C. and 16,000 hr.sup.1 (12,000 cc/g-hr).

[0074] FIG. 10 shows results (test J) for a feed gas composition of CH.sub.4 (1.0)/CO.sub.2 (1.0)/H.sub.2O (1.0)/O.sub.2(0.2) at 900 C. and 17,333 hr.sup.1 (13,000 cc/g-hr) (Oxygen levels were 200% of Tri-reforming Test H).

[0075] In the next test (E), the CO.sub.2 ratio was increased to 0.6, the steam ratio was increased to 1.7, and O.sub.2 increased to 0.2. Gas hourly space velocity was 18,666 hr.sup.1 (14,000 cc/g hr) as shown in FIG. 12 (Test L).

[0076] Under the final two conditions, the carbon dioxide ratio was increased to 0.8, the steam to methane ratio was varied between 1.7 and 1.35, while keeping O.sub.2 at 0.1. The results of these tests are shown in FIG. 13 (GHSV=16,333 hr.sup.1 or 12,250 cc/g hr) and FIG. 14 (GHSV=18,000 hr.sup.1 or 13,500 cc/g hr). Both tests were stable during the 20 hours of testing at 900 C. for each condition. Decreasing the steam in the feed improves carbon dioxide conversion. Overall, the catalyst was very stable for all of the tri-reforming conditions examined. No carbon formation or deactivation of the catalyst was observed.

[0077] In conclusion, tri-reforming was found to provide high gas hourly space velocities (GHSV), stable catalyst performance, and the proper H.sub.2/CO ratio (2.0) for subsequent conversion to diesel fuel or chemicals.