KR20010071265A - Method of Preparing Alkyl Carboxylic Acids by Carboxylation of Lower Alkanes Methane - Google Patents

Abstract

The present invention relates to a process for producing alkyl carboxylic acids such as acetic acid directly by carboxylation of alkanes such as methane, comprising reacting carbon dioxide with alkanes in the presence of a heterogeneous catalyst to form lower alkyl carboxylic acids. It is about.

Description

Method for preparing alkyl carboxylic acid by carboxylation of lower alkanes such as methane {Method of Preparing Alkyl Carboxylic Acids by Carboxylation of Lower Alkanes Methane}

Organic acids are widely used as intermediates and solvents in chemical processes. One of the most widely used of these acids is acetic acid, which is an expensive bulk chemical currently produced in quantities of 6 x 10 ⁶ tonnes annually around the world. Acetic acid is widely used as starting material in the production of vinyl acetate, acetic anhydride, and cellulose acetate, and as industrial and pharmaceutical solvents.

Although prior art exists that indirectly converts methane and other alkanes into acids, there is no prior art that directly synthesizes acetic acid on solid catalysts from methane or other low molecular weight alkanes. U.S. Patent No. 5,659,077 discloses that a feed mixture consisting of (a) methane gas and (b) gaseous oxygen, air, or mixtures thereof is partially oxidized at elevated temperature and pressure without producing syngas in the reaction zone without producing synthesis gas. A process for producing acetic acid is disclosed by forming a reaction mixture containing methane and water vapor. At least some water vapor is removed from the reaction mixture and the remaining partial oxidation reaction mixture is fed through a carbonylation reaction zone at elevated temperature and pressure with additional methanol from an external source to give acetic acid and / or methyl acetate and methanol The reaction product containing is formed. Methanol produced by partial oxidation and additional methanol provide additional methanol in an amount sufficient to nearly convert both the carbon monoxide produced by partial oxidation. Excess methane and carbon dioxide are recycled from the carbonylation reaction zone to the partial oxidation zone and methanol in the carbonylation reaction product is recycled to the carbonylation reaction zone to recover acetic acid and / or methyl acetate as product. This process actually produces acetic acid by partially oxidizing methane with methanol and then carboxylating with acetic acid. Unlike the present invention, oxygen is required and methanol is produced as a separable intermediate product. The methanol is then carbonylated in a manner analogous to conventional commercial techniques to form acetic acid.

U.S. Patent 5,510,525 describes a process for the direct oxidation of lower alkanes to carbonylated acids with one more carbon atom. This method uses a homogeneous metal salt catalyst system which requires both CO and oxygen as reactants and is promoted by halide ions and / or metals (with oxygen as oxidants) in an aqueous medium. This method converts methane to acetic acid. However, this also uses oxygen as in US Pat. No. 5,659,077 and requires carbonylation as a separate step. Neither US 5,659,077 nor US 5,590,525 considers the use of CO ₂ , and it is absolutely necessary to react oxygen with methane. In addition, US Pat. No. 5,510,525 requires an aqueous homogeneous catalyst system, unlike the solid phase heterogeneous catalyst of the present invention.

US Pat. No. 5,393,922 discloses hydrocarbons, in particular C ₁ -C ₆ alkanes and monocyclic aromatics, by hydrogen peroxide (or dihydrogen or dioxygen) using a liquid metal or metal salt catalyst at mild temperature conditions (70-200 ° C.). A method for obtaining an acid by direct catalytic oxidation is described. This method is similar to US Pat. No. 5,510,525, but uses an aqueous metal salt catalyst system, where CO and dioxygen must be present. Acetic acid is formed only from ethane and methane reacts to form formic acid. Thus, U. S. Patent 5,393, 922 does not consider the formation of carbon-carbon bonds that form acetic acid or more acids from methane, for example, and therefore certain carbon number alkanes, such as methane, react with CO ₂ to give more carbon number. It differs from the present invention which forms large aliphatic acids.

As an example of current commercial techniques used to prepare aliphatic acids from alkanes, acetic acid is widely prepared from methane in a series of independent steps, typically in which each catalyst and reactant are used:

In step (1), methane is typically converted to a synthesis gas, ie a mixture of CO and hydrogen, using a nickel based catalyst. This syngas can also be formed by gasifying coal or other carbonaceous materials using conventional techniques that are well known. Syngas is then used to produce a variety of chemicals, including methanol, usually using a Cu-based catalyst as shown in step (2). Finally, methanol is reacted with CO in the carbonylation step using a homogeneous Rh-based catalyst. This three-step process currently accounts for about 98% of the acetic acid market. Typically, syngas generation alone costs more than 60% of the total production cost of acetic acid. It is clearly desirable to eliminate this step in order to reduce the synthesis cost of aliphatic acids such as acetic acid.

In step (3), this conventional method relies on the reaction of methanol and CO to form acetic acid using an expensive Rh catalyst dissolved in the liquid phase or often using an iodine based promoter. The economic cost of this method depends on the successful recovery and recycling of the catalyst. As an example of the importance of developing solid phase heterogeneous catalysts, the cost of the separation unit may be at least 110% of the cost of the reaction unit. In addition, Rh-based catalysts are expensive, and I-based promoters (usually CH ₃ I) are toxic and corrosive and require expensive metallurgy and therefore are expensive.

In theory, acetic acid may be prepared using a two-step reaction sequence in which the synthesis gas is first converted to methanol and then carbonylated to acetic acid in the gas phase using a heterogeneous catalyst. Although gaseous methanol carbonylation has been the subject of laboratory-scale intensive research over the past few years, no catalyst has been reported to be of industrial interest. Catalysts for gas phase reactions include silica, alumina and RhCl ₃ supported on SiO ₂ -Al ₂ O ₃ . Ni has also been reported as an active catalyst for this reaction (Fujimoto et al., 1987). Nickel supported on activated carbon (AC) has also been studied for this reaction and tin has been studied as a promoter [Liu and Chiu, 1994a, 1994b]. Although the catalyst was active, severe inactivation through the formation of Ni carbides was observed with the reduction of Ni to an inactive form, and the reduction of Ni by the AC support.

Thus, until now, no industrially practical heterogeneous catalyst for gas phase carbonylation of methanol has been developed. Even if such heterogeneous catalysts have been developed, the overall process of converting methane to acetic acid is still indirect and must go through steps (1) and (2) above. Thus, there is a clear need for a process based on solid phase heterogeneous catalysts for producing aliphatic acids such as acetic acid through direct reaction of lower alkanes (such as methane) with CO ₂ . It also provides an environmentally sound route to producing acetic acid based on inexpensive feedstock.

Another conceptual route to synthesizing acetic acid involves the reaction with methane, CO and small amounts of oxygen. Oxidative conversion to this type of carboxylic acid has been reported using homogeneous catalysts for various lower alkanes such as methane and ethane [Nishiguchi et al., 1992; Kurioka et al., 1995; Lin et al., 1997; Sen and Lin, 1996]. For example, at 80 ° C. in the presence of Pd (OAc) ₂ , Cu (OAc) ₂ (0.05 mmol each) and K ₂ S ₂ O ₈ (9 mmol) in trifluoroacetic acid (TFA) (5 ml) Reaction of ₄ (20 atm) with CO (15 atm) yields acetic acid in high yield. The results are summarized in Table 1 below. However, the reaction time was 20 to 40 hours. In addition, homogeneous catalysts such as Cu (OAc) ₂ , Pd (OAc) ₂ and K ₂ S ₂ O ₈ are required and are used in the reaction medium (such as trifluoroacetic acid (TFA)). If the product (acetic acid) is dissolved in the reaction mixture, the use of a homogeneous reaction medium requires the use of cost and energy intensive separation methods, which adds cost and complexity to the overall process design.

Acetic acid synthesis from CH ₄ and CO ^a Perform K ₂ S ₂ O ₈ / mmol Time (h) AcOH yield (%) ^b One - 20 240 2 - 40 410 3 - 20 ^c - 4 9 ^d 20 120 ^a CH ₄ (20 atm), CO (15 atm), O ₂ (15 atm), Pd (OAc) ₂ = Cu (OAc) ₂ = 0.05 mmol, TFA (5 ml), 80 ° C. ^b Yields based on Pd metal content. ^{c No} catalyst used. ^{d No} oxygen.

Although these results indicate the possibility of this route, these catalysts are not practical in industry as the reaction time takes 20-40 hours. This is also different from the present invention using a solid heterogeneous catalyst.

Direct conversion of methane to acetic acid using oxygen as the oxidant without adding CO has also been studied by other researchers [Lin et al., 1997; Lin and Sen, 1994; Sen and Lin, 1996]. Optionally producing acetic acid by oxidative carbonylation of methane was carried out at 95 ° C. in a glass tube stainless steel (SS) reactor. Reactor comprising 800 psi (54 atm) CH ₄ , 150 psi (10 atm) CO, and 50 psi (3.6 atm) oxygen with RhCl ₃ , HCl, and HI, and 5 ml of D ₂ O as solvent Was added. As measured by nuclear magnetic resonance (NMR) spectroscopy, after 420 hours no methanol was produced in the reaction product and only acetic acid was recovered with trace amounts of formic acid. The results clearly suggest that CO and O ₂ can be used to carboxylate CH ₄ , but likewise a homogeneous catalyst is required. Activation of methane using heterogeneous catalysts has not been explained experimentally.

In this regard, since a reversible reaction (ie, decomposition of acetate to methyl groups) is observed on Rh (110) [Bowker and Li, 1991], it is one possibility to form acetate by reacting adsorbed methyl groups with CO _2. [Bowker, 1992]. Formation of acetate from degradable adsorption of CH ₃ I and CO ₂ on Ni (110) catalysts has also been demonstrated using high resolution electron energy loss spectroscopy (HREELS) [Wambach and Freund, 1994], but the formation of acetate is clearly identified. It didn't work. The fact that heterogeneous catalysts can activate methane and form acetic acid has not been demonstrated before the present invention.

The present invention provides a process for producing acetic acid, and aliphatic acids having more carbon atoms, directly via carboxylation of low molecular weight alkanes such as methane, without forming intermediates of the synthesis gas using solid heterogeneous catalysts. CH ₄ + CO ₂ → CH ₃ COOH.

1 shows an integrated CO ₂ recovery and recycling scheme.

Figure 2 shows a schematic economic cost of integrated gasification combination cycle (IGCC) -acetic acid (AA) co-production.

3 shows FTIR spectra on a 5% Pd / C catalyst after exposure to acetic acid at various temperatures.

4 shows FTIR spectra on 5% Pd / C demonstrating the formation of acetate at various temperatures.

Summary of the Invention

Accordingly, the present invention uses a heterogeneous (solid) catalyst to produce lower alkanoic acids by carboxylating these alkanes using CO ₂ and C ₁ -C ₁₂ alkanes to directly produce acids with one more carbon atoms. Provide a method.

The present invention provides a process for synthesizing an acid, such as acetic acid, by carboxylation of an alkane, such as methane. As mentioned above, the conventional route to industrially synthesizing acetic acid converts methane or other carbon sources into syngas (a mixture of hydrogen and carbon monoxide) first and then hydrogenates to obtain methanol, using CO Is an indirect route to carbonylating methanol and producing acetic acid using a homogeneous catalyst. Some of the advantages of the synthesis of acetic acid via the direct route provided in the present invention are as follows.

First, energy- and cost-intensive methane modification steps are unnecessary. This step may account for more than 60% of the total production cost of acetic acid.

Second, the rhodium-based homogeneous catalysts currently used in methanol carbonylation (MC) are replaced by heterogeneous catalysts that separate the product more simply and produce it at lower cost. Thus, the intermediate methanol also does not need to be formed and no carbonylation is required.

Third, the MC stage using toxic, corrosive and very dangerous iodine-based promoters such as methyl iodide is replaced.

Fourth, the direct route of the present invention reduces the emission of CO ₂ , a greenhouse gas, and also uses methane, a greenhouse gas in the case of acetic acid.

Fifth, the solid phase heterogeneous catalyst of the present invention makes it possible to be modified to much higher throughput industrial processes, to simplify product separation, and to be relatively inexpensive.

Sixth, the main environmental advantage of the present invention is that compared to current technology, the risk of mass production and secondary pollution is reduced. More than 55% of the world's acetic acid production uses methanol carbonylation (MC) technology, which uses expensive Rh catalysts, uses toxic I-based promoters and involves cost-intensive separation methods. The potential environmental risks of these compounds provide a second obvious environmental motivation to develop better acetic acid production methods.

According to the invention, solid phase heterogeneous catalysts are used to directly synthesize alkyl carboxylic acids such as acetic acid from alkanes such as CO ₂ and methane.

One important reaction is shown below.

For this reaction Is +55.7 kJ / mol CO ₂ , which corresponds to the equilibrium conversion of CO ₂ and CH ₄ , and the equilibrium yield of extremely small amounts of acetic acid. Despite this equilibrium limitation, the reaction can be carried out in non-equilibrium conditions to maximize the yield of acetic acid.

Another method of synthesizing acetic acid from methane uses oxygen and carbon monoxide as an oxidant instead of or in addition to CO ₂ . To form acetic acid from the reaction of methane, carbon monoxide and oxygen Is actually a negative value of -212.2 kJ / mol, ie this reaction is thermodynamically preferred. Of course, reactor design and catalyst selection can be used to maximize the yield of acetic acid. For these two different routes to produce acetic acid The calculation of is summarized as follows.

1.Acetic acid synthesis from CH ₄ and CO ₂

2. Acetic Acid Synthesis from CH ₄ , CO and O ₂

The large negative free energy of the reaction of 2 is a thermodynamically preferred reaction with a very high equilibrium conversion. Some non-limiting examples below illustrate how the present invention can be useful for the production of acetic acid.

Example 1 CO in a Power Plant ₂ remove

Primarily, one of these methods that can be used to recover CO ₂ in a conventional thermal power plant is shown in FIG. 1. 1998 total CO ₂ emissions in the US was approximately 4,400 Mt, including about 1,700 metric tons (Mt) CO ₂ emissions from power plants. Large-scale removal of CO ₂ from plant power plants is carried out industrially; There are currently _two large coal-based power plants with large CO ₂ recovered. One is the ABB Rumus Crest's Shady Point, Oklahoma process where CO ₂ is recovered in large quantities. CO ₂ production costs of the power plant is measured in the range of CO ₂ 1 $ 20 to $ 30 per ton. This provides a useful application of the invention to the removal of CO ₂ from this type of combustion source.

Example 2 CO ₂ Conceptual Economics of Elimination

Some preliminary cost estimates shown in FIG. 2 in a CO ₂ removal scheme indicate that the process is economically viable and that the provided CO ₂ / CH ₄ reaction can form acetic acid quantitatively in good yield with extremely high selectivity. The conceptual economic cost of CO ₂ reuse from an integrated gasification combined cycle (IGCC) power plant for acetic acid production is shown in FIG. 2. Economic costs assume a carbon tax on CO ₂ emissions emitted CO ₂ 1 $ 50 per ton. Although preliminary, this cost represents the possibility of a commercially viable process.

Example 3 CO from Natural Gas Airflow ₂ remove

CO ₂ is also generated as a by-product in natural gas processing operations using natural gas containing up to 20 to 30% CO ₂ . Such gases directly reduce the costs for the reactions observed in the present invention, simplify the process design, and provide a direct process as a feedstock that provides a direct process of converting the type of gas required for operations far from natural gas sources into liquids. Can be used.

As indicated above, the present invention employs heterogeneous catalysts, in particular Group 8-11 transition metal catalysts, to directly carboxylate alkanes such as methane to form one more carbon acid such as acetic acid. Such heterogeneous transition metal catalysts may be prepared according to known production methods including impregnation, incipient wetness and co-precipitation.

Generally, transition metal catalysts include one or more transition metals on the periodic table, with particular attention being given to Group 8-11 transitions such as Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au Metal. Such transition metal catalysts may be supported on inert or acidic / basic supports such as carbon, silica, alumina or even diatomaceous earth. Generally, at least one transition metal is used in an amount of 0.5 to 20% with respect to the support. For example, 5% Pd / AC can be noted.

In general, the reaction temperature may be from about 100 ° C to about 500 ° C. While ambient pressure may be used, pressures of CO ₂ and CH ₄ at about 0.5 to about 200 atmospheres may also be used at high equilibrium conversions at high pressures. However, preference is given to using pressures of CO ₂ and CH ₄ at about 10 to 150 atmospheres.

In addition, any relative amounts of lower alkanes and CO ₂ may be used, but are generally used in approximately equimolar amounts, respectively. "Equal molar" means a molar ratio range of CH ₄ / CO ₂ of 0.1 to 10. In general, the amount of catalyst used is typically the amount used as a catalyst and is the same as that used with known catalysts in other reactions. Generally, about ^10-6 moles to about 0.5 moles are used per mole of each reactant. Preferably, the amount used is at most 0.1 mole per mole of reactant.

We conducted various experiments demonstrating the formation of an acetate group of acetic acid from a mixture of CO ₂ and CH ₄ . The following examples are for illustrative purposes only and are not intended to be limiting.

Example 5

Acetic acid was adsorbed onto 5% Pd / AC catalyst, exhibiting an infrared absorption band corresponding to acetic acid on 5% Pd / C as follows. The adsorption of acetic acid was carried out on a 5% Pd / C catalyst at 25 ° C. in a chamber of high temperature environment (HTEC). The catalyst was mixed with KBr powder (transparent to IR radiation) and loaded into a sample cup in HTEC. Helium was bubbled through an acetic acid impeller (maintained at 25 ° C. using circulating refrigerant) and adsorbed onto the catalyst for 60 minutes at 40 standard temperature and pressure (STP) mL / min. Spectra were collected under flow-through and sealed conditions and scaled against the background (FIG. 3). The temperature programmed desorption (TPD) of the chemisorbed species was then performed up to 320 ° C. at a rate of 50 ° / min, and the spectra were collected at each temperature after the spectra reached a stable stage (after approximately 30 minutes).

CO ₂ / CH _{4 was} then adsorbed on the same catalyst in advance, TPD-dispersed reflectance infrared Fourier transform spectroscopy (DRIFTS) was performed, and the appearance / disappearance of the spectral band was changed to the same catalyst (5% Pd / C) -KBr mixture. Acetic acid spectral data on the phases were compared.

In this case, adsorption was carried out for 60 minutes followed by desorption up to 420 ° C. at a rate of 50 ° / min (FIG. 4). The purpose of this experiment was to determine if a 5% (5% Pd / C) 95% KBr mixture promoted the CO ₂ / CH ₄ reaction with acetic acid. The spectra at 25 ° C. under through (spectrum a) and sealed (spectrum b) conditions were identical. At 25 ° C. characteristic bands were observed at 3,729, 3,010, 2,362 and 1,301 cm ⁻¹ . The bands at 3,010 and 1,301 cm ⁻¹ can be pointed to gaseous methane [Zhang et al., 1996], the strong band at 2,362 cm ⁻¹ due to CO ₂ . The small shoulder band at 2,371 cm ⁻¹ seen in the adsorption spectra (spectrum a, b) of FIG. 4 is due to the naturally occurring ¹³ CO ₂ (Burkett et al., 1990). The spectrum at 120 ° C. (spectrum c) is similar to the adsorption spectrum, suggesting no reaction between the adsorbates. However, at high temperatures of 220 to 420 ° C. (spectrum d to f), small but distinct peaks in the 1790 to 1740 cm ⁻¹ region corresponding to the characteristic carbonyl carboxylate bonds are observed, which is due to the synthesis of carbonyl species Indicates first proof. Furthermore, small bands of 1,513 and 1,565 cm ⁻¹ can be pointed to the acetate (CH ₃ COO) species (Viswanathan et al., 1990). This was, at best, a study of the clear evidence of synthesis of acetic acid from CO ₂ and CH ₄ on heterogeneous catalysts.

In another aspect of the present invention, higher carboxylic acids may be prepared from higher alkanes according to the following scheme.

C _n H _2n + CO ₂ → C _n H _{2n + 1} COOH

Particular examples of this reaction are reactions using ethane and propane, respectively, with CO ₂ .

C ₂ H ₆ + CO ₂ → CH ₃ CH ₂ COOH

C ₃ H ₈ + CO ₂ → CH ₃ CH ₂ CH ₂ COOH

To achieve this reaction, the same conditions and heterogeneous catalysts were used as described above. In general, in the above formula, n is a value from 1 to about 12, but preferably n is a value from 1 to 8. This reaction may use CO ₂ with any of methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, decane, undecane and / or dodecane. Of course, any of the n-, sec-, tert- or iso- isomers of these alkanes can be used.

As described herein, it is apparent that various changes and modifications can be made in the above-described embodiments without departing from the scope of the present invention.

Claims (30)

A process for producing acetic acid directly by carboxylation of methane, comprising reacting methane with carbon dioxide in the presence of a heterogeneous catalyst. The method according to claim 1, which is carried out in the presence of oxygen and carbon monoxide. The method of claim 1, wherein the process is carried out without oxygen. The method of claim 1, wherein the carbon dioxide is obtained by recovery at a power plant based on the combustion and gasification of coal or other carbonaceous material. The method of claim 1, wherein the carbon dioxide is obtained as a by-product during natural gas processing operations. The process of claim 1, wherein the heterogeneous catalyst is a transition metal catalyst. The method of claim 6, wherein the transition metal catalyst comprises a transition metal selected from the group consisting of Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au. 8. The method of claim 7, wherein the transition metal catalyst is a bimetallic or multi-metallic system. The method of claim 1, wherein the heterogeneous catalyst is on an inert, acidic or basic support. 10. The group of claim 9, wherein the catalyst support consists of activated carbon, alumina, silica, silica / alumina, hydrotalcite, group 2 metal oxides, and / or mixed metal oxides of group 13 and 14 atoms. The method selected from. 8. The process of claim 7, wherein the transition metal catalyst is a 5% Pd / C catalyst system containing up to 20% Pd. The method according to claim 1, which is carried out at a temperature above 100 ° C. The method of claim 1, a) contacting a gaseous mixture of methane and carbon dioxide with said heterogeneous catalyst, and b) reacting the methane and carbon dioxide at elevated temperature under pressure of the heterogeneous catalyst How to include. 13. The method of claim 12, wherein step b) is performed at a temperature of at least 100 ° C. The method of claim 1 wherein the process is carried out in a single reaction step. The method of claim 1, wherein the C-C bond is formed. The method of claim 1, wherein the carbonylation of methanol is avoided. The method of claim 1, wherein generation of syngas is avoided. The method of claim 1, wherein the iodine based promoter is avoided. The process of claim 1 which is included in the integrated gasification combination cycle—acetic acid co-production process. Formula C _n H _2n-1 COOH comprising reacting carbon dioxide with an alkane of formula C _n H _2n , wherein n is an integer from 1 to 12, in the presence of a heterogeneous catalyst, wherein n is as defined above To lower alkyl carboxylic acid. The method of claim 21 wherein n is an integer from 1 to 8. The method of claim 21 wherein the process is carried out directly by carboxylation of the alkanes. The method of claim 21, wherein said alkanes are ethane. The method of claim 21, wherein said alkanes are propane. The method of claim 21, wherein the process is performed at a temperature above about 100 ° C. 23. The method of claim 21, wherein the C-C bond is formed. The method of claim 21, wherein the process is carried out in a single reaction step. The method of claim 21, wherein the heterogeneous catalyst is a transition metal catalyst. The method of claim 21, wherein the heterogeneous catalyst comprises a transition metal selected from the group consisting of Group 8 to 11 metals: Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au. How to be.