WO2012078276A1

WO2012078276A1 - CONVERSION OF SYNGAS TO MIXED ALCOHOLS ON SUPPORTED CoMoSx CATALYSTS

Info

Publication number: WO2012078276A1
Application number: PCT/US2011/059503
Authority: WO
Inventors: Gerolamo Budroni; Rainer Bruening; Daniela Ferrari; Davy Nieskens; Neelesh Rane
Original assignee: Dow Global Technologies Llc
Priority date: 2010-12-06
Filing date: 2011-11-07
Publication date: 2012-06-14

Abstract

Convert synthesis gas to an alcohol using a catalyst that is a combination of molybdenum, cobalt, an alkali metal and, optionally, chromium on a hydrotalcite support. The hydrotalcite is an anionic clay that contains aluminum magnesium carbonate hydroxide hydrate.

Description

CONVERSION OF SYNGAS TO MIXED ALCOHOLS ON SUPPORTED CoMoS_x

CATALYSTS

This application is a non-provisional application claiming priority from the U.S. Provisional Patent Application No. 61/419,935, filed on December 06, 2010, entitled "CONVERSION OF SYNGAS TO MIXED ALCOHOLS ON SUPPORTED CoMoS_x

CATALYSTS" the teachings of which are incorporated by reference herein, as if reproduced in full hereinbelow.

This invention relates generally to catalysts used in converting synthesis gas (also known as "syngas", a mixture of carbon monoxide (CO) and hydrogen (H₂)) to a mixture of alcohols that comprises at least ethanol and n-propanol, more particularly to supported cobalt-molybdenum sulfide (CoMoS_x) catalysts used in such conversion, and still more particularly to such supported catalysts wherein the support is hydrotalcite.

Skilled artisans recognize that unsupported CoMoS_x catalysts have utility in converting syngas to such a mixture of alcohols. Skilled artisans also recognize that hydrocarbons such as methane and ethane constitute undesirable byproducts of syngas conversion and seek to minimize production of such undesirable byproducts.

Lower alcohols, such as methanol, ethanol and propanol, constitute important commodity chemicals. The lower alcohols can be converted to olefins, with methanol conversion via a process known as methanol to olefins or MTO being one example, and conversion of ethanol and propanol to, respectively, ethylene and propylene via dehydration being another example. The olefins, in turn, are important raw materials in, for example, a variety of polymerization processes such as those used to make polyethylene (e.g. low density polyethylene, high density polyethylene and linear low density polyethylene), polypropylene, and copolymers that contain both ethylene and propylene (e.g. ethylene- propylene rubber (EPR) and ethylene-propylene-conjugated diene (EPDM) interpolymers).

United States Patent Application Publication (USPAP) 2007/0004588 (Wang et al.) discloses a catalyst composition, its preparation and its use in converting syngas to alcohols. The catalyst comprises an anionic clay, especially hydrotalcite clay, and at least one catalytically active metal component selected from Groups 3 to 15 of the Periodic Table of the Elements (e.g. rhodium (Rh), manganese (Mn), cobalt (Co), and copper (Cu)). In paragraph [0007], Wang et al. place catalysts used for mixed alcohol synthesis into three groups, referring to publications such as P. Forzatti et al., Catalysis Reviews - Science Engineering, Volume 33, Number 1-2, pages 109-168 (1991). One group includes mixed metal oxides made via co-precipitation and promoted with alkali metals such as sodium (Na), potassium (K), rubidium (Rb) or cesium (Cs). A second group is cobalt-molybdenum sulfide promoted with K (C0-M0S₂/K). Noble metals supported on an oxide support such as alumina or silica constitute a third group. Wang et al. teaches that hydrotalcite is a naturally occurring mineral that has a variable composition depending upon location of its source but is a hydrated magnesium, aluminum and carbonate-containing composition typically represented as Mg₆Al₂(OH)i6C0₃-4H₂0. Wang et al. also refers to a number of synthetic hydrotalcites and their preparation. Want et al. suggests that catalyst compositions may be prepared by any of a number of methods, but provides a general method wherein one first dissolves a compound of each desired catalytically active metal in a solvent (e.g. water, a mineral acid, or an organic solvent such as acetone or methanol) to form a solution, combining the solutions with the hydrotalcite clay, either by impregnation or slurry mixing, and then drying the resultant mixture. Suitable metal compounds include acetates, halides, oxides, oxyhalides, hydroxides, sulfides, sulfonates, borides, borates, carbonates, nitrates, carboxylates, tartrates, oxalates , oxynitrates or other soluble inorganic or organometallic precursors and mixtures thereof. Subsequent to drying, one typically forms the dried material into a suitable shape, then calcines or heat treats the shaped material.

F. Cavani et al., in "Hydrotalcite-type anionic clays: preparation, properties and applications", Catalysis Today, volume 11 (1991), pages 173-301, provides a detailed study of hydrotalcite-type clays. Such clays have a number of uses, one of which, per Figure 1 and the paragraph immediately following Figure 1 on page 175, is as a catalyst support in a broad field of heterogeneous catalysis. See also subparagraph 3) of paragraph 6.1 (page 213) relative to catalytic applications of hydrotalcites, specifically "hydrogenation reactions (production of CH₄, CH₃OH, higher alcohols, paraffins and olefins from syngas; hydrogenation of nitrobenzene)".

B. Sels et al., in "Hydrotalcite-like anionic clays in catalytic organic reactions", Catalysis Reviews, volume 43(4) (2001), pages 443-488, reviews hydrotalcite- like anionic clays and a number of uses for such clays including use in a broad spectrum of organic reactions. Section II of the review, which begins on page 47, notes that the clays, especially those that include CuZnAl and Cu(M(II)Cr mixed oxides, have utility in synthesizing higher alcohols from syngas.

United States Patent (US) 4,377,643 (Pesa et al.) relates to a process for upgrading syngas to alkanes and alcohols by contacting syngas with a catalyst comprising mixed oxides of ruthenium (Ru), Cu, at least one alkali metal, and at least one of Rh, iridium (Ir), palladium (Pd), and platinum (Pt). The catalyst can include a carrier or support selected from alumina, silica, alumina-silica, Alundum, clay and silicon carbide.

US 4,442,228 (Leupold et al.) teaches a process for manufacturing ethanol by catalytically reacting syngas using a supported Rh catalyst that consists of Rh and at least one co-catalytic metal selected from zirconium (Zr), hafnium (Hi), lanthanum (La), Pt, chromium (Cr) and mercury (Hg). Rh and the co-catalytic metal are impregnated onto a catalyst carrier or support of silicic acid or silicates of elements of Groups Π to VII of the Periodic Table of the Elements. Illustrative supports includes silicates of magnesium (Mg), calcium (Ca), aluminum (Al), and Mn, as well as less preferred supports such as aluminum dioxide, thorium dioxide, zeolites and spinels.

D. Li et al., in "Ni/ADM: a high activity and selectivity to C₂₊ OH catalyst for catalytic conversion of synthesis gas to C1-C5 mixed alcohols", Topics in Catalysis, Volume 32, Numbers 3-4 (2005), pages 233-239, teaches that nickel (Ni), a well-known methanation catalyst, shows an excellent promotional effect to enhance both the activity and selectivity to C₂₊ OH over the ADM (alkali doped molybdenum sulfide) catalyst for mixed alcohols synthesis. Li et al. refers to prior work on the use of transition metals, especially cobalt (Co), iron (Fe), Ni, rhodium (Rh) and palladium (Pd), that suggests possible activity and C₂₊ OH selectivity enhancements stemming from their addition. See also D. Li et al., "The performances of higher alcohol synthesis over nickel modified K₂C0₃/MoS₂ catalyst", Fuel Processing Technology 88 (2007) pages 125 - 127.

J. Iranmahboob et al., in "K₂C0₃/Co-MoS₂/clay catalyst for synthesis of alcohol: influence of potassium and cobalt", Applied Catalysis A: General 231 (2002), pages 99-108, presents a study of catalyst productivity and selectivity as a function of cobalt composition, K CO₃ loading and temperature. X-ray photoelectron spectroscopy (XPS) analyses of the clay show that oxygen, silicon, aluminum and carbon are major elements of uncalcined pyrophyllite clay. J. Nunan et al., in "Higher Alcohol and Oxygenate Synthesis over Cs/Cu/ZnO/M₂0₃ (M = Al, Cr) Catalysts", Journal of Catalysis 116 (1989), pages 222-229, teaches that surface doping of Cu/ZnO/M₂0₃ (M = Al, Cr) catalysts made from hydrotalcite precursors with cesium (Cs) significantly enhances alcohol synthesis rates under higher alcohol synthesis conditions. With aluminum (Al) doping, product selectivity shifts toward methanol while Cr doping shifts product toward ethanol. Nunan et al. teaches that hydrotalcite is a naturally occurring mineral or synthetically prepared compound having a typical composition represented as Mg₆Al₂(OH)i6CC>₃-4H₂0. Nunan et al. uses precursors that contain Cu or Zn in place of Mg or Cr or gallium (Ga) in place of Al.

B. Sels et al., in "Hydrotalcite-like Anionic Clays in Catalytic Organic

Reactions", Catalysis Reviews, 43(4) (2001), pages 443-488, provides teachings relative to hydrotalcite-like anionic clays (HTs, or layered double hydroxides (LTHs)) and their use as precursors to mixed oxides and in a broad spectrum of organic reactions with advantages such as improved activity, selectivity, metal dispersion, less waste production, and improved recuperation of immobilized catalysts. The HTs can be used in as-synthesized form or after different pretreatments. Specific metals can be incorporated either as a cation in the octahedral layer or as an anion via exchange. The teachings include use of catalysts such as ZnCr-type mixed oxide catalysts, CuZnAl and Cu(M(II)Cr mixed oxide catalysts, any of which can be modified with an alkali promoter, in converting synthesis gas to alcohols higher than methanol (e.g. ethanol or propanol). An example of such a catalyst is a CuAlZnLa HT precursor impregnated with an amount of Cs. Co and Cu-containing HT precursors may be used for Fischer- Tropsch synthesis of hydrocarbons from syngas.

In some aspects, this invention is a synthesis gas conversion catalyst comprising a combination of molybdenum, cobalt, an alkali metal and, optionally, chromium on a hydrotalcite support, the hydrotalcite being an anionic clay that contains aluminum magnesium carbonate hydroxide hydrate.

In some aspects, the above catalyst contains chromium in an amount within a range of from 0.1 percent by weight to 8 percent by weight, based upon combined weight of molybdenum, cobalt, alkali metal, chromium and the hydrotalcite support.

The aforementioned catalysts have utility in converting synthesis gas to a mixture of alcohols such as ethanol and propanol. The catalyst comprises a combination of molybdenum, cobalt and, optionally, chromium on a hydrotalcite support. The hydrotalcite is an anionic clay that contains aluminum magnesium carbonate hydroxide hydrate.

Hydrotalcite is available in both natural and synthetic form. Natural hydrotalcite is a hydrated magnesium, aluminum and carbonate-containing composition having a composition that is represented as:

Mg₆Al2(OH)₁₆(C03>4H₂0 (Formula 1)

Various synthetic "hydrotalcites" may include those of identical composition with natural hydrotalcite, but may further include "hydrotalcites" that are defined herein as "hydrotalcite- like compounds." These "hydrotalcite-like compounds" have compositions wherein the carbonate anion (CO₃ ² ) is replaced with another anion such as phosphate (PO4³ ), molybdate (M0O4² ), sulfate (SO4² ), nitrate (NO₃ ), chlorate (CIO₃ ), and combinations thereof. Such "hydrotalcite-like compounds" may also differ from natural hydrotalcite in comprising differing types and proportions of the divalent and trivalent metal ions, i.e., the Mg and Al. For example, either or both of these may be replaced, in whole or in part, by nickel (Ni) and/or cobalt (Co), respectively. In view of these variances, an alternated expression for suitable hydrotalcite and hydrotalcite-like compounds, including natural hydrotalcite, is:

M²⁺ ₁._xM³⁺ _x(OH)₂(C03)x/2- mH₂0, (Formula 2) wherein M²⁺ is a divalent metal selected from magnesium and nickel; M³⁺ is a trivalent metal selected from aluminum and cobalt; x is the number of moles of the trivalent metal; and m is the number of moles of waters of hydration.

The molybdenum and cobalt are present in a molar ratio within a range of 0.5:1 to 4:1, preferably from 1:1 to 3:1, and more preferably from 1.5:1 to 2.5:1.

The catalyst has a molybdenum content within a range of from 1 percent by weight (wt ) to 30 wt , preferably from 5 wt to 25 wt and more preferably from 10 wt to 20 wt , a cobalt content within a range of from 0.1 wt to 8 wt , preferably from 2 wt to 6 wt and more preferably from 4 wt to 5.5 wt , a chromium content within a range of from 0 wt to 8 wt , preferably from 2 wt to 6 wt and more preferably from 3.5 wt to 5 wt , an alkali metal within a range of from 0.1 wt to 20 wt , preferably from 2 wt to 10 wt and more preferably from 5 wt to 7 wt , and hydrotalcite support content within a range of from 10 wt to 90 wt , preferably from 20 wt to 80 wt and more preferably from 50 wt to 75 wt , each wt being based upon combined weight of molybdenum, cobalt, chromium, alkali metal and hydrotalcite support.

The alkali metal may be any element in Group 1 (new notation) of the Periodic Table of the Elements which includes sodium, lithium, potassium, rubidium, cesium and francium, but is preferably potassium.

In succeeding paragraphs, Arabic numerals designate examples (Ex) of the invention and capital letters designate comparative examples (CEx).

Ex 1

Calcine hydrotalcite (PURAL® 63 MG HT) at 450 °C for two hours using a heating rate of 5 °C per minute (°C/min). Press, crush and sieve the calcined hydrotalcite to a particle size between 40 mesh (373 micrometer (μιη)) and 80 mesh (177 μιη). Prepare a mixed solution of 1.4 milliliters (ml) of an aqueous (0.08 molar) solution of ammonium heptamolybdate and 1.95 ml of an aqueous (0.2 molar) solution of cobalt(II)nitrate hexahydrate. Place 500 milligrams (mg) of the sieved/sized, calcined hydrotalcite in a 250 ml round bottom flask. Add the mixed solution to the hydrotalcite, place the flask on a rotary evaporator device with a 60 °C water bath and operate the rotary evaporator at 140 revolutions per minute (rpm) speed under medium vacuum (9 millibars (mbar) (900 pascals (Pa)) until a visual examination of rotary evaporator contents shows no apparent remaining liquid. Calcine rotary evaporator contents in air at 450 °C for four hours. Using an agate mortar and pestle, mix and grind the calcined material with potassium carbonate (10 percent by weight (wt ) based upon combined weight of calcined material and potassium carbonate) to yield a catalyst having a nominal composition of 15 wt molybdenum, 4.6 wt cobalt and 6 wt potassium on a hydrotalcite support, each wt being based upon combined weight of molybdenum, cobalt, potassium and hydrotalcite. The molybdenum and cobalt are present in a molar ratio of 2: 1.

Load 100 microliters (μΐ) of the catalyst into a stainless steel reactor that has an internal diameter of 3 millimeter (mm). Dry the catalyst in situ by heating reactor contents to a temperature of 150 °C (5 °C/minute (min) heating rate) and passing a flow of nitrogen of 5 ml/min while pressurizing to 35 bars (3.5 megapascals (MPa)). Pre-sulfurize the catalyst in situ in a hydrogen (¾) atmosphere at a pressure 35 bars (3.5 MPa) by passing a solution of 10 wt of dimethyl disulfide (DMDS) in pentane through the catalyst at a liquid hourly space velocity (LHSV) of 2 hr^"1 while increasing temperature from 150 °C to 400 °C at a rate of 1 °C/min. Maintain the catalyst under these condition at 400 °C for six hours, then cool the catalyst to a temperature of 310 °C at a rate of 5°C/min under flowing nitrogen (N₂) (5 ml/min). Before starting catalyst evaluation with a syngas feedstream, stabilize the catalyst under a flow of syngas (H₂:CO ratio of 1:1) with 50 parts by volume per million parts by volume (ppm) of syngas of hydrogen sulfide (H₂S) for 60 hours. After stabilizing the catalyst, evaluate the catalyst under the conditions shown in Table 1 below at a reaction pressure of 90 bars (9 MPa).

Analyze effluent gas from the reactor via gas chromatography (GC) to determine product composition and amount of CO converted. Raise catalyst temperature to 330 °C at a rate of 5 °C/min, holding catalyst temperature at 330 °C to collect 3 measurements of catalyst performance at each condition using GC analysis. Table 1 below summarizes operating conditions and the relative catalyst performance.

Ex 2

Replicate Ex 1, but add 2.56 ml of an aqueous (0.15 molar) solution of chromium (III) nitrate nonahydrate to the mixed solution. The catalyst has a nominal composition identical to that of Ex 1 except that it also includes 4 wt chromium.

CEx A

Prepare a mixed solution of ammonium heptamolybdate tetrahydrate (103.4 mg in 930.5 μΐ of water), and use 281.6 microliters (μΐ) of the mixed solution to impregnate 500 milligrams (mg) of the sieved/sized (40 mesh (373 μιη)-80 mesh (177 μιη) magnesia (Siid Chemie) by incipient wetness. Dry the impregnated magnesia in air at 80 °C for 3 hours. Impregnate the dried, impregnated magnesia a second and a third time with 281.6 μΐ of the same ammonium heptamolybdate solution and dry again at 80 °C for 3 hours after each impregnation. Prepare a solution containing 73.3 mg of ammonium heptamolybdate tetrahydrate and 162.5 mg of cobalt nitrate hexahydrate dissolved in 1.04 ml of water. Use this solution to impregnate three times the dried, ammonium heptamolybdate solution- impregnated magnesia support with 276 μΐ and dry at 80 °C for 3 hours between each impregnation. Prepare a solution with 364.5 mg of potassium nitrate dissolved in 364.5 μΐ of water. Impregnate the previously impregnated and dried magnesia twice with 221 μΐ of the potassium solution and dry in air at 80 °C for 3 hours after each impregnation. Calcine under nitrogen flow (200 ml/min) according to the following temperature program: 120 °C for 2 hours (ramp rate 5 °C/min); 210 °C for 2 hours (ramp rate 5 °C/min); 350 °C for 3 hours (ramp rate 5 °C/min). The nominal composition of the catalyst is 15.5 wt molybdenum, 2.3 wt cobalt, 2 wt chromium, and 19.7 wt potassium (K Mo molar ratio of 3) on a magnesia support, each wt being based upon combined weight of molybdenum, cobalt, chromium, potassium and magnesia. The molybdenum, chromium and cobalt are present in a molar ratio of molybdenum to a combination of chromium and cobalt of 2:1.

CEx B

Prepare a mixed solution of ammonium heptamolybdate tetrahydrate (122.2 mg in 1099.6 μΐ of water), and use 300 μΐ to impregnate 500 mg of the same magnesia as that used in CEx A by incipient wetness. Dry in air at 80 °C for 3 hours. Repeat the impregnation and drying two times. Prepare a solution containing 61.1 mg of ammonium heptamolybdate tetrahydrate, 74.8 mg of cobalt nitrate hexahydrate and 103.2 mg of chromium nitrate nonahydrate dissolved in 1.05 ml of water. Impregnate the magnesia with 300 μΐ of this solution and then dry in air at 80 °C for 3 hours. Repeat the impregnation and drying two times. Prepare a solution with 364.5 mg of potassium nitrate dissolved in 1.093 ml of water. Impregnate the magnesia two times using this solution, with drying after each impregnation in air at 80 °C for 3 hours. Calcine under nitrogen flow (200 ml/min) according to the following temperature program: 120 °C for 2 hours (ramp rate 5 °C/min); 210 °C for 2 hours (ramp rate 5 °C/min); 350 °C for 3 hours (ramp rate 5 °C/min). The nominal composition of the catalyst is 15.5 wt molybdenum, 2.3 wt cobalt, 2 wt chromium, and 15.6 wt potassium (K Mo molar ratio of 2.6) on a carbon support, each wt being based upon combined weight of molybdenum, cobalt, chromium, potassium and magnesia. The molybdenum, chromium and cobalt are present in a molar ratio of molybdenum to a combination of chromium and cobalt of 2:1. Table 1

A comparison of the data in Table 1 for Ex 1 and CEx A shows that hydrotalcite provides greater CO conversion and greater selectivity to ethanol than magnesia under the same conditions and with same catalytic composition. A comparison of Ex 1 and Ex 2 suggests that with a hydrotalcite support, addition of chromium results in decreased catalyst activity but increased nPrOH selectivity with comparable hydrocarbon (CH₄) selectivity at similar conversion. When Cr is present, (Ex 2 vs. ExB), the positive effect of hydrotalcite is even more pronounced, giving much lower hydrocarbon selectivity at similar conversion levels especially considering that MgO contains a higher K concentration. An increased K loading typically results in lower hydrocarbon selectivity. Additionally, the use of hydrotalcite as a support yields a higher alcohol production than MgO as a support.

Claims

WHAT IS CLAIMED IS:

1. A synthesis gas conversion catalyst comprising a combination of molybdenum, cobalt, an alkali metal and, optionally, chromium on a hydrotalcite support, the hydrotalcite being an anionic clay that contains aluminum magnesium carbonate hydroxide hydrate.

2. The catalyst of Claim 1 , wherein molybdenum and cobalt are present in a molar ratio within a range of 0.5:1 to 4:1 and the catalyst contains chromium in an amount within a range of from 0.1 percent by weight to 8 percent by weight, based upon combined weight of molybdenum, cobalt, alkali metal, chromium and the hydrotalcite support.

3. The catalyst of Claim 1 or Claim 2, wherein cobalt is present in an amount within a range of from 0.1 percent by weight to 8 percent by weight, molybdenum is present in an amount within a range of from 1 percent by weight to 30 percent by weight, chromium is present in an amount within a range of from 0.1 percent by weight to 8 percent by weight, an alkali metal is present in an amount within a range of from 0.1 percent by weight to 20 percent by weight, and hydrotalcite support is present in an amount within a range of from 10 percent by weight to 90 percent by weight, each percent by weight being based upon combined weight of molybdenum, cobalt, chromium, alkali metal and hydrotalcite support.

4. The catalyst of any of Claims 1 through 3, wherein the alkali metal is potassium.