Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/10—Preparation of carboxylic acids or their salts, halides or anhydrides by reaction with carbon monoxide
  • C07C51/14—Preparation of carboxylic acids or their salts, halides or anhydrides by reaction with carbon monoxide on a carbon-to-carbon unsaturated bond in organic compounds
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C51/00—Preparation of carboxylic acids or their salts, halides or anhydrides
  • C07C51/15—Preparation of carboxylic acids or their salts, halides or anhydrides by reaction of organic compounds with carbon dioxide, e.g. Kolbe-Schmitt synthesis

Definitions

• the present invention relates to a method of preparing acetic and higher carbon number aliphatic acids directly by carboxylation of lower molecular weight alkanes such as methane using a solid, heterogeneous catalyst without the intermediate formation of synthesis gas, e.g., CH 4 + CO 2 - CH 3 COOH.
• Organic acids are widely used as intermediates and as solvents in chemical processing.
• One of the most widely used of these acids is acetic acid, which is a high- value, high- volume chemical currently produced at the rate of 6 x 10 6 tons/yr. worldwide.
• Acetic acid is widely used as a raw material in the production of vinyl acetate, acetic anhydride, and cellulose acetate, and as an industrial and pharmaceutical solvent.
• U.S. 5,510,525 describes a process for direct oxidative carbonylation of lower alkanes to acids having one greater carbon atom.
• the process requires both CO and oxygen as reactants and uses a homogeneous metal salt catalyst system promoted by halide ions and/or a metal (with oxygen as the oxidant) in an aqueous medium.
• oxygen is used and carbonylation is required as a separate step.
• U.S. 5,659,077, nor U.S.5, 590,525 contemplate the use of CO 2 and both absolutely require oxygen to react with methane. Additionally, U.S.
• U.S. 5,393,922 describes a process for direct catalytic oxidation of hydrocarbons, particularly C, - C 6 alkanes and single ring aromatics to acids by hydrogen peroxide (or dihydrogen and dioxygen) under mild temperature conditions (70 - 200 °C) using liquid phase metal or metal salt catalysts. This process is similar to that of U.S. 5,510,525, where an aqueous metal salt catalyst system is used, and the presence of CO and dioxygen is required. Acetic acid is formed only from ethane, and methane reacts to form formic acid.
• U.S. 5,393,922 thus contemplates no formation of a carbon-carbon bond, e.g., no formation of acetic or higher acids from methane and is therefore unlike the present invention in which a given carbon number alkane, such as methane, reacts with CO 2 to form a higher carbon number aliphatic acid.
• acetic acid is widely produced from methane in a series of independent steps in which a separate catalyst and reactor is typically used in each step:
• step (1) methane is typically converted to synthesis gas, a mixture of CO and hydrogen using a nickel-based catalyst.
• This synthesis gas can also be produced by gasification of coal or other carbonaceous material using widely known conventional technology.
• Synthesis gas is used to produce a number of chemicals, including methanol as shown in step (2), typically using a Cu-based catalyst.
• methanol is reacted with CO in a carbonylation step using a homogeneous Rh-based catalyst.
• This three- step process currently fulfills about 98% of the acetic acid market. Syngas generation alone typically accounts for at least 60% of the overall production cost of acetic acid. Obviating this step is clearly desirable to reduce the cost of synthesizing aliphatic acids such as acetic acid.
• step (3) this conventional process relies on the reaction of methanol and CO to form acetic acid using an expensive Rh catalyst dissolved in the liquid phase, often using iodine-based promoters.
• Rh catalysts are expensive, and I-based promoters (mostly CH 3 I) are toxic and corrosive, requiring expensive metallurgy, thus resulting in higher costs.
• acetic acid might be made using a two-step reaction sequence where syngas is first converted into methanol, and methanol is then carbonylated into acetic acid in the vapor phase using heterogeneous catalysts.
• vapor phase methanol carbonylation has been a subject of intense lab-scale research for the past several years, no catalyst has been reported to be of industrial interest.
• the catalysts for vapor phase reactions have included RhCl 3 supported by silica, alumina, and SiO 2 -Al 2 O 3 . Ni is also reported to be an active catalyst for this reaction (Fujimoto et al., 1987).
• nickel supported on activated carbon has been investigated for this reaction and tin has been studied as a promoter (Liu and Chiu, 1994a, 1994b). Although the catalyst was active, significant deactivation was observed via reduction of Ni to an inactive form and reduction of Ni by the AC support to form Ni carbide.
• reaction times are 20 to 40 h.
• homogeneous catalysts such as Cu(OAc) 2 , Pd(OAc) 2 , and K 2 S 2 O 8 are required and are used in a reaction medium (such as trifluoroacetic acid, TFA).
• TFA trifluoroacetic acid
• Figure 1 illustrates an integrated CO 2 recovery and reuse scheme.
• Figure 2 illustrates conceptual economics of an integrated gasification combined cycle (IGCC) - acetic acid (AA) co-production scheme.
• IGCC integrated gasification combined cycle
• AA acetic acid
• Figure 3 illustrates FTIR spectra over a 5% Pd/C catalyst after exposure to acetic acid under variable temperatures.
• Figure 4 illustrates an FTIR spectra evidencing formation of acetate with 5% Pd/C under variable temperatures.
• the present invention provides a process for the preparation of lower alkane acids by carboxylation of C,-C 12 alkanes by utilizing CO 2 and these alkanes to directly produce acids of one higher carbon number using heterogeneous (solid) catalysts.
• the present invention provides a process for synthesis of acids such as acetic acid via carboxylation of alkanes such as methane.
• the conventional route practiced industrially for synthesis of acetic acid is an indirect route in which methane or other carbon source(s) are first reformed into syngas, a mixture of hydrogen and carbon monoxide (CO),
• CO is then hydrogenated to methanol, and methanol is carbonylated with CO to produce acetic acid using homogeneous catalysts.
• Some of the benefits of the direct route to acetic acid provided by the present invention are as follows. First, the energy- and cost-intensive methane reforming step is not necessary. This step can contribute at least 60 percent to the overall production costs of acetic acid.
• the MC step using toxic, corrosive, and potentially hazardous iodine-based promoters like methyl iodide, is replaced.
• the direct route of this invention reduces emissions of the greenhouse gases, CO , and, in the case of acetic acid, also utilizes the greenhouse gas methane.
• the solid, heterogeneous catalysts of the present invention are much more amenable to high throughput industrial processes, and product separation is simple and relatively inexpensive.
• a principle environmental advantage of the present invention is the reduced risk and secondary pollution produced as compared to the current technology. At least 55 percent of the worldwide acetic acid production uses the methanol carbonylation (MC) technology, which uses expensive Rh catalysts, employs toxic I-based promoters, and involves cost-intensive separations. The occupational and potential environmental hazards of the compounds provide a second clear environmental incentive to develop benign manufacturing processes for acetic acid.
• MC methanol carbonylation
• solid heterogeneous catalysts are used for the direct synthesis of alkyl carboxylic acids such as acetic acid from CO 2 and alkanes, such as methane.
• the ⁇ G° 298 for this reaction is +55.7 kJ/mol CO 2 . corresponding to an equilibrium conversion of CO 2 and CH 4 and equilibrium yield of acetic acid that are extremely low. Despite the is equilibrium limitation, the reaction can be carried out at non-equilibrium conditions to maximize the yield of acetic acid.
• ⁇ G° 298K (G° f )CH 3 COOH - (G°,)CH 4 - (G° f )CO 2 - +55.7 kJ/mol.
• Example 1 CO 2 Removal from Power Plants.
• One way in which this process can, in principle, be used is to recover CO 2 from conventional coal-fired power plants, is shown in Figure 1.
• the total CO 2 emissions in the United States in 1998 were approximately 4,400 metric tones (Mt), with about 1,700 Mt CO 2 coming from the power plants.
• Mt metric tones
• the removal of CO 2 on a large scale from industrial power plants is practiced industrially; there are currently two large coal-based power plants where CO 2 is recovered in large quantities.
• One is ABB Lummus Crest's Shady Point, Oklahoma, operation where CO 2 is recovered in large quantities.
• the cost of CO2 production from such plants is estimated to be in the range of $20 to $30/ton CO 2 . This provides a useful application of the present invention to removal of CO 2 from this type of combustion source.
• Example 2 Conceptual Economics of CO 2 Removal. Some preliminary cost estimates shown in Figure 2 for CO 2 removal scheme indicate that the process is economically viable, provided CO 2 /CH 4 reaction can quantitatively form acetic acid, in good yields with extremely high selectivities.
• the conceptual economics of CO 2 reuse from an integrated gasification combined cycle (IGCC) power plant for acetic acid production is shown in Figure 2. The economics assumes a carbon tax of CO 2 emissions of $50/ton of CO 2 emitted. Although preliminary, these costs show the possibility of a commercially practical process.
• IGCC integrated gasification combined cycle
• Example 3 CO 2 Removal from Natural Gas Streams.
• CO 2 is also generated as a byproduct in natural gas processing operations, with raw natural gas containing up to 20 to 30 percent CO 2 .
• Such a gas can be used directly as a feedstock for the reaction envisaged in the present invention, reducing its cost, simplifying the process design, and providing a direct gas-to-liquids process of the type needed for remote gas field operations.
• the present invention utilizes heterogeneous catalysts, particularly Group 8-11 transition metal catalysts, in a direct carboxylation of alkanes such as methane to form acids of one higher carbon number such as acetic acid.
• heterogeneous transition metal catalysts may be prepared according to known preparatory procedures, including impregnation, incipient wetness and co-precipitation.
• the transition metal catalyst contains one or more transition metals from the Periodic Table, however, of particular note are Group 8-1 1 transition metals, such as Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au. These transition metal catalysts may be supported on an inert or acidic/basic support, such as carbon, silica, alumina or even diatomaceous earth. Generally, one or more transition metals are used in an amount of 0.5 to
• the reaction temperature may be from about 100°C to about 500°C. While ambient pressures may be used, pressures of CO 2 and CH 4 of from about 0.5 to about 200 atmospheres can also be used with higher equilibrium conversions at higher pressures. However, it is preferable to use a pressure of CO 2 and CH 4 of from about 10 to 150 atmospheres.
• any relative amounts of lower alkane and CO 2 may be used, in general, approximately equimolar amounts of each are used.
• equimolar is meant a molar ratio range of from 0.1 to 10 of CH 4 /CO 2 .
• the amount of catalyst used is that typically used as a catalyst, and as is used for these known catalysts in other reactions. Generally, from about 10 "6 moles to about 0.5 moles per mole of each reactant is used. Preferably, the amount used is 0.1 mole or less of catalyst per mole of reactant.
• the present inventors carried out various experiments demonstrating the formation of the acetate group of acetic acid from a mixture of CO 2 and CH 4 .
• the following examples are provided solely for purposes of illustration and are not intended to be limitative.
• Acetic acid was absorbed on a 5 % Pd/AC catalyst to identify the infra-red adsorption bands corresponding to acetic acid on 5 % Pd/C as follows.
• the adsorption of acetic acid was carried out at 25 °C over a 5 percent Pd/C catalyst, in a high temperature environmental chamber (HTEC).
• the catalyst was mixed with KBr powder (transparent to IR radiation), and loaded onto the sample cup in a HTEC.
• Helium was bubbled through an acetic acid impinger (maintained at 25 °C using a circulating coolant) and adsorbed on the catalyst at 40 standard temperature and pressure (STP) mL/min for 60 min.
• STP standard temperature and pressure
• the spectra were collected under flow-through conditions and under sealed conditions and ratioed to the background (Figure 3). Subsequent temperature programmed desorption (TPD) of chemisorbed species was carried out at 50 min to 320°C, and spectra were collected at each temperature, after the spectra reached stable levels (after ca. 30 min). Then, CO 2 /CH 4 were preadsorbed on the same catalyst and TPD-diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was carried out and the appearance/disappearance of spectral bands was matched with pure acetic acid spectral data on an identical catalyst (5% Pd/C)-KBr admixture.
• TPD temperature programmed desorption
• DRIFTS TPD-diffuse reflectance infrared Fourier transform spectroscopy
• the bands at 3,010 and 1,301 cm “1 can be assigned to gas-phase methane (Zhang et al., 1996) and a pronounced band at 2,362 cm “1 is due to CO 2 .
• a small shoulder band at 2,371 cm “1 visible in the adsorption spectra (spectra a, b) in Figure 4 is due to naturally occurring 13 CO 2 . (Burkett et al., 1990).
• the spectrum at 120° C (spectrum c) is similar to adsorption spectra, suggesting that no reaction has occurred among the adsorbates.
• higher carboxylic acids may be prepared from higher alkanes in accordance with the following scheme:
• n has a value of from 1 to about
• n have a value of from 1 to 8.
• This reaction may be used with CO 2 and any of methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane, undecane and/or dodecane.
• methane ethane
• propane butane
• pentane hexane
• heptane octane
• nonane decane
• undecane and/or dodecane dodecane
• one may use any of the n-. sec-, tert- or iso- isomers of these alkanes.

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• 1999
  • 1999-05-14 WO PCT/US1999/010709 patent/WO1999059952A1/en not_active Application Discontinuation
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