Title of Invention

A PROCESS FOR PREPARATION OF FORMIC ACID BY CATALYSED HYDRATION OF CARBON MONOXIDE.

Abstract

A process for the preparation of formic acid by catalysed hydration of carbon monoxide by dissolving metal complex catalyst ethylenediaminetetraacetato ruthenate (Ru -EDTA) in water in a molar ratio of catalyst: water from 1 :1000 to 1 : 70000 ; maintaining the pH between 2 to 8 of the dissolved catalyst in solution using disodium hydrogen phosphate and potassium dihydrogen phosphate buffer; bubbling the reaction mixture at 1 atmospheric pressure of carbon monoxide at the rate of 0.5 to 5 ml/min followed by continuous stirring; or directly pressurizing the reaction mixture in the reactor by carbon monoxide gas at constant pressure in the range 2 to 20 atmosphere at a temperature ranging 5 to 50 °C, separating the formic acid by conventional distillation method.

Full Text

The present invention relates to a process for preparation of formic acid by catalysed hydration of carbon monoxide and more particularly this invention relates to metal complex catalysed homogeneous hydration of carbon monoxide to formic acid. Formic acid is maximally used as a silage additive, to feed the catties to enhance their milk yields. Formic acid is also used as an antisalmonella additives in animal feeds for decontamination of feed raw material and prevention of flock infection in the poultry industry. Formic acid is diversely used in, leather industry for tanning, textile industry for dyeing, latex rubber industries as coagulating agent, pharmaceutical industries lor drugs, and cosmetic industry for perfume components and flavours. Reference may be made to R. J. Camm et al. in US Patent No 3,859,346, 07 Jan. 1975, which reports the industrial production of sodium formate and calcium formate and their acidolysis to produce formic acid by acidifying the formate salts by sulfuric acid. This is a two stage process in which carbon monoxide reacts with sodium/calcium hydroxide to produce respective formate salts in the first stage. In a second stage, stoichiometric amount of formate salt and sulfuric acid are passed through an automatic balance pump at 35 °Celsius and formic acid is produced along with sodium/calcium sulphate. The major drawback of this process is that sulfuric acid, is corrosive, and handling is difficult. The byproduct, unwanted sulphate salts, is difficult to separate from formic acid. E. Germann et al. in German patent No. 1,215,130 03 July 1962, described that production of formic acid by formamide route has largely been supplanted by process based on the direct hydration of methyl formate, which is two stages process for hydration of carbon monoxide to formic acid. In first stage methyl formate is formed by the carbonylation of methanol and in second stage methyl formate is hydrolysed to formic acid. The process runs in liquid rase at 80 °Celsius and 45 atmospheric pressure, wherein sodium methoxide with 2.5 % w/w was used as a base catalysl. The drawbacks of this process are higher temperature and pressure and occurring of hydration reaction in two stages. Hydrolysis of methyl formate equilibrium, being relatively unfavourable, make the process to get associated with excess water, which requires an energy efficient method to remove this water. Also the water content present in methanol even in 10 to 20 ppm level, causes deactivation of the catalyst. Furthermore methyl formate is highly volatile (bpt = 32 °Celsius) and formic acid is a sufficiently strong acid to catalyse the reestrification, hence it makes very difficult to remove unreacted methyl formate. J. D. Leonard in US patent No. 912,189, 05 June 1978, had described the methyl formate hydrolysis process for production of formic acid by carbon monoxide hydration, by using two hydrolysis reactors in series to remove the excess amount of unreacted water and ester formed from the reaction mixture from the first and second reactors respectively. A flash distillation is done to rapidally remove the unconverted methyl formate in a column of low residence time. Higher conversion to formic acid was obtained from hydrolysis of methyl formate and discharging the product in to the lower pressure zone from which methyl formate was vaporised and recycled. The drawback of this process is flash distillation of methyl formate which requires additional unit operations and heat equipments. 1. 1. Moiseev et al. in Belgium patent No. 0893,357, 29 Nov. 1982 had revealed the methyl formate hydrolysis process by hydrolysing methyl formate at 80-107 °Celsius in vertical column containing acid cation exchange resin as the catalyst. In vertical column, water (180 grn/hr) was added from the top (80 °Celsius) and methyl formate (192.2 gm/hr) from bottom (103 °Celsius) of the column containing strong acid cation exchanger. The mixture (4.6 gm/hr) of 91 % methanol and 9% methyl formate was separated from top of the column, as the mixture (274.6 gm/hr) of formic acid 53 %, water 44.8 % and methanol 2.2 % was separated from bottom of the column. The drawback of this process is the use of strong acid in regenerating cation exchanger resin. Also a mixture of methanol, formic acid and water are separated, which requires an additional unit to distil the formic acid from it's mixture. A. Ricci et al. in European patent No. 0248,259, 17 April 1991, had revealed the preparation of formic acid from carbon monoxide and water in the two steps, in presence of primary or secondary hydroxyalkylamine. In first step carbon monoxide carbonylates hydroxyalkylamine to hydroxyalkyl formamide and in the second step in presence of acid catalysts, (viz sulfuric acid, hydrochloric acid, alumina, zeolite, and acid ion exchange resins) formamide gets hydrolysed and formic acid and amines are produced as the final products. Formic acid is separated through distillation with water vapour under pressure. Subsequently water containing formic acid is dried through azeotropic distillation with di-isopropyl ether or formic acid ester. The maximum hydrolysis degree obtained was 45% in the temperature rang 70 to 150 °Celsius. The drawbacks of this process are high temperature and very slow rate of hydrolysis having conversion time from 4 to 20 hour. R. Brockhaus et al. in German patent No. 390,3664, 09 Aug. 1990, described the synthesis of formic acid from carbon monoxide and water in presence of tertiary hydroxyalkylamine, at >I5 atmospheric pressure and 100 to 150 °Celsius from synthesis gas. The amount of water used was less ( note of formic acid. The drawback of this process are high temperature required for the reaction. Use of syn gas in which hydrogen gas is required along with carbon monoxide. Cooling of the reaction mixture which requires coolants or low temperature equipments. F. Lippert et al. in European patent No. 0583695, 05 Aug. 1993, revealed the process of preparation of formic acid by carbon monoxide and water in presence of tertiary amine at elevated temperature of 100 to 250 °Celsius and pressure 100 to 350 atmosphere, of the reaction. Amine and formic acid, in the form of ammonium formate, were the reaction products. Product formic acid was obtained by the thermal treatment of ammonium formate. Yield of formic acid obtained was 68 %. Drawbacks of this process are that the process requires high temperature around 250 °Celsius and pressure around 350 atmosphere. Also formic acid is formed in the form of formate, which again requires energy for thermal treatment to separate formic acid from ammonium formate. The main object of the present invention is to provide a process for preparation of formic; acid by catalysed hydration of carbon monoxide which obviates the drawbacks as detailed above. Another object of the present invention is to catalytically activate carbon monoxide and water for direct hydration of carbon monoxide to formic acid. Still another object is the preparation of formic acid at moderate conditions of temperature and pressure. Yet another object is to obtain selective hydration of carbon monoxide to formic acid. Still another object is to reduce the number of reaction steps in preparation of formic acid. Yet another object is to use ethylenediaminetetraacetato ruthenate (Ru-EDTA) catalyst to increase the rate of hydration of carbon monoxide to formic acid. Still another object is to use water as reactant as well as solvent. Yet another object of the present invention is to use toxic gas carbon monoxide to convert into value added product, formic acid. Still another object of the present invention is to prepare formic acid by environment friendly and by-product free route. Yet another object of the present invention is to prepare formic acid by a catalytic route which is energically, ecologically and economically valuable. Accordingly the present invention provides an improved process for the preparation of formic acid by catalysed hydration of carbon monoxide which comprises characterized in that (i) dissolving metal complex catalyst ethylenediaminetetraacetato ruthenate (Ru -EDTA) in water in a molar ratio of catalyst: water from 1 :1000 to 1 : 70000 ; (ii) maintaining the pH between 2 to 8 of the dissolved catalyst in solution using disodium hydrogen phosphate and potassium dihydrogen phosphate buffer; (iii) bubbling the reaction mixture at 1 atmospheric pressure of carbon monoxide at the rate of 0.5 to 5 ml/min followed by continuous stirring; or directly pressurizing the reaction mixture in the reactor by carbon monoxide gas at constant pressure in the range 2 to 20 atmosphere at a temperature ranging 5 to 50 °C, separating the formic acid by conventional distillation method. In an embodiment of the invention the metal complex catalyst may be a ethylenediaminetetraacetato ruthenate (Ru-EDTA) of characteristic yellow colour with 20 % ruthenium by weight In another embodiment of the invention the water may be a substrate as well as solvent in the molar ratio of catalyst: water selected from the range of 1:1000 to 1:70000. In yet another embodiment of the invention carbon monoxide gas may be bubbled at 1 atmosphere, pressure at the rate selected from the range of 1 to 4rnl/min. In still another embodiment of the invention carbon monoxide gas may be pressurised in the reactorjn the reaction mixture at constant pressure selected from the range of 5 -15 atmosphere. In yet another embodiment of the invention the pH of the reaction mixture may be selected in the range from of 5 to 8 by using phosphate buffer of sodium and potassium In yet another embodiment of the invention the temperature of the reaction mixture may be selected in the range from 15 to 50 °Celsius. According to the present invention, number of physical and chemical conditions are varied to obtain formic acid by improved process by using ethylenediaminetetraacetato ruthenate (Ru-EDTA) catalyst One such important aspect of the present invention involves the concentration of the catalyst, and water which is used as solvent as well as substrate in the reaction system. For those skilled in the art of catalytic reactions, it is understood that catalytic reaction involving minimum amount of catalyst are always favourable towards the process of catalyst separation and also to economy. In practising this invention carbon monoxide was hydrated to formic acid using catalyst in the concentration range 1 to 50 millimoles per litre. The hydration of carbon monoxide to formic acid was done by conducting the experiments at different concentration of the catalyst in which molar ratio of catalyst : water was maintained from 1 : 1000 to 1 : 70000. An increase on the rate of formation of formic acid was obtained on increasing the concentration of the catalyst, hi absence of the catalyst experiments conducted under identical conditions did not give formic acid, indicating that the reaction is completely catalytic and the catalyst is required for the hydration reaction to proceed The pH of the reaction mixture were maintained in the range of 2 to 8 particularly and preferably in the range of 4 to 7 by using disodium hydrogen phosphate and potassium dihydrogen phosphate buffer. The rate of formation of formic acid was found to be independent on pH indicating that variation of pH does not help in improving the rate of formic acid formation. It is found in this investigation that the role of pH is to maintain the required species of the catalyst. In practising this invention physical parameters viz temperatures and pressures of the reaction mixture were varied in order to see their effects on the rate of formation of formic acid. Carbon monoxide pressure was varied from 1 to 20 atmosphere pressure in which at 1 atmosphere pressure the reaction was bubbled by carbon monoxide gas, where as in the range of 2-20 atmosphere pressure the reaction mixture was pressurised by carbon monoxide gas in the reactor. It is found in this investigation that carbon monoxide gas dissolved in the water in the reaction mixture react with water to form formic acid in the homogeneous conditions. The experiments conducted by varying the pressure, indicate that the rate of formic acid formation increased on increasing the pressure of carbon monoxide. The effect of temperature on the rate of formation of formic acid was studied by varying the temperature in the range of 5 to 50 °Celsius in which the rate of formic acid formation was found to be increased on increasing the temperature. In typical catalytic experiments, in a pressure reactor of 300 ml capacity with provisions of automatic temperature control, thorough gas - liquid mixing agitation and sampling, 1 x 10" to 50 x 10-3 moles per litre catalyst were dissolved in 50 ml of double distilled water, containing disodium hydrogen phosphate and potassium dihydrogen phosphate buffer in the pH range 2 to 8. After thorough mixing of catalyst and buffer solution in water for 5 to 20 minutes, the reactor was continuously pressurised by carbon monoxide gas in the pressure range 2 to 20 atmosphere, in the temperature range 5 to 50 °Celsius. The reactions were continued and liquid samples were withdrawn at desired times to analyse formic acid titrimetrically. The amount of formic acid produced in the reaction mixture was estimated by known method by using 0.1 N sodium hydroxide as titrant and phenolphthalein indicator by autotitroprocessor having provisions to monitor pH, volume of titrant and temperature. Separation of formic acid from reaction mixture was done by distillation. The properties of the product formic acid are : molecular weight, 46.03 ; density, 1.22 gm/ml at 20 °C ; melting point, 8.4 °Celsius ; boiling point, 100.7 °Celsius ; viscosity, 1.784 megapascal s at 20 °Celsius; surface tension, 37.67 dyn/cm. at 20 °Celsius. In present invention hydration of carbon monoxide has been conducted in homogeneous catalytic conditions in the pressure range, 1 to 20 atmosphere at temperature range 5 - 50 °Celsius in which formic acid is obtained as selective hydration product with 100 % selectivity with maximum formation of 75 millimoles/litre of formic acid. A ruthenium based metal complex ethylenediaminetetraacetato ruthenate (Ru-EDTA) found to be an efficient novel homogeneous catalyst was used to hydrate carbon monoxide to formic acid. Novelty resides in the catalyst's function for the process of hydration of carbon monoxide in which catalyst ethylenediaminetetraacetato ruthenate (Ru-EiDTA) effectively catalyses and increases the rate of hydration of carbon monoxide to formic acid. This hydration process involve a series of inventive steps (i) the catalytic hydration of carbon monoxide to formic acid process does not require high temperature and works in the ambient/moderate temperature 5 to 50 °Celsius, (ii) the catalytic hydration of carbon monoxide to formic acid process does not require high pressure and works in the ambient/moderate pressure 1 to 20 atmosphere, (iii) the catalytic hydration process utilises water as a reactant as well as solvent, without using any additional solvent/reactant, (iv) the process occurs in single step for direct hydration of carbon monoxide to formic acid, which obivates the need of multistep reaction, (v) the hydration of carbon monoxide produces formic acid at lower temperature and pressure making the process energy and cost effective. The following examples are given by way of illustration and therefore should not to be construed to limit the scope of the present invention. EXAMPLE- 1 A hot solution of Na2(H2edta) (0.5g) in 0.001 M perchloric acid (10 ml) was added to a warm solution of [RuCl5 H2O]K2 (0.5g) in 0.001 M perchloric acid (10 ml) and mixture was refluxed for 30 min. Concentration of the yellow solution on steam bath gave a yellow precipitate which was washed with cold water and ethanol; yield 0.25 g. The metal complex ethylenediaminetetraacetato ruthenate (Ru-EDTA) was characterised by elemental (CHN) analysis and i spectrophotometer and electrochemical methods. The calculated C,H, and N percentage being 24 %, 3.42 % and 5.59 % respectively, was found to be C=23.5 % H=3.27 % and N=5.27 % respectively in the metal complex. Spectrophotometric analysis showed two characteristic peaks at 280 nanometer (molar extinction coefficient = 2800) and 350 nanometer (molar exinction coefficient =770) of the metal complex. Electrochemically determination of half wave potential, for Ru111/Ru11 couple of the metal complex against Ag/AgCl electrode, is -0.30 volts. EXAMPLE - 2 To 50 ml of water containing phosphate buffer of disodium hydrogen and potassium dihydrogen of pH 7.4, catalyst was dissolved in the molar ratio of catalyst : water, 1: 55000. After complete dissolution of the catalyst carbon monoxide gas at 1 atmosphere was continuously bubbled at the rate of 1 ml/min at 30 °Celsius. Concentration of formic acid formed in the reaction mixture was determined and 4 x 10-3 mole/litre formic acid was obtained with initial rate 2.88 x 10° mole/litre/min in 140 min. Formic acid from the reaction mixture was seperated by distillation. EXAMPLE - 3 To 50 ml of water containing phosphate buffer of disodium hydrogen and potassium dihydrogen of pH 7.4, catalyst was dissolved in the molar ratio of catalyst : water, 1: 55000. After complete dissolution of the catalyst carbon monoxide gas at 1 atmosphere was continuously bubbled at the rate of 3 ml/min at 30 °Celsius. Concentration of formic acid formed in the reaction mixture was determined and 7.0 x 10-3 mole/litre formic acid was obtained with initial rate 4.5 x 10-5 mole/litre/min in 180 min. EXAMPLE - 4 In 50 ml of water, containing phosphate buffer (pH 7.4) of disodium hydrogen and potassium dihydrogen, catalyst was dissolved in the molar ratio of catalyst : water, 1 : 11000 and carbon monoxide gas at 1 atmosphere was continuously bubbled at the rate of 1 ml/min at 30 °Celsius. Titrimetrically estimated formic acid obtained was 12 x 10° mole/litre with initial rate 11.0 x 10° mole/litre/min in 115 min. EXAMPLE - 5 A 50 ml solution of water, having disodium hydrogen and potassium dihydrogen phosphate buffer at pH 7.4 and dissolved catalyst in the molar ratio of catalyst : water, 1:11000 was pressurised by carbon monoxide at constant pressure of 5 atmosphere, in a pressure reactor of 300 ml capacity at 30 °Celsius. Titrimetrically estimated formic acid obtained was 25 x 10-3 mole/litre with initial rate 50 x 10-5 mole/litre/min in 50 min. EXAMPLE - 6 A 50 ml homogeneous solution of water, containing disodium hydrogen and potassium dihydrogen, phosphate buffer at pH 5.00 and dissolved catalyst in the molar ratio of catalyst : water, 1 : 11000 was pressurised by carbon monoxide at constant pressure of 10 atmosphere, in a pressure reactor of 300 ml capacity at 30 °Celsius. Titrimetrically estimated formic acid obtained was 28 x 10-3 mole/litre with initial rate 99.98 x 10-5 mole/litre/min in 35 min. EXAMPLE - 7 A 50 ml solution of water, having disodium hydrogen and potassium dihydrogen phosphate buffer at pH 7.4 and dissolved catalyst in the molar ratio of catalyst : water, 1 : 11000 was pressurised by carbon monoxide at constant pressure of 15 atmosphere, in a pressure reactor of 300 ml capacity at 30 °Celsius. Titrimetrically estimated formic acid obtained was 32 x 10-3 mole/litre with initial rate 140 x 10-5 mole/litre/min in 25 min. EXAMPLE - 8 A 50 ml homogeneous solution of water, containing disodium hydrogen and potassium dihydrogen, phosphate buffer at pH 7.4 and dissolved catalyst in the molar ratio of catalyst: water, 1 : 1100 was pressurised by carbon monoxide at constant pressure of 10 atmosphere, in a pressure reactor of 300 ml capacity at 40 °Celsius. Titrimetrically estimated formic acid obtained was 75 x 10° mole/litre with initial rate 145 x 10° mole/litre/min in 55 min. EXAMPLE - 9 A 50 ml homogeneous solution of water, containing disodium hydrogen and potassium dihydrogen, phosphate buffer at pH 6.00 and dissolved catalyst in the molar ratio of catalyst : water, 1:11000 was pressurised by carbon monoxide at constant pressure of 10 atmosphere, in a pressure reactor of 300 ml capacity at 30 °Celsius. Titrimetrically estimated formic acid obtained was 28.1 x 10-3 mole/litre with initial rate 100 x 10-5 mole/litre/min in 40 min. EXAMPLE- 10 A 50 ml solution of water, having disodium hydrogen and potassium dihydrogen phosphate buffer at pH 7.4 and dissolved catalyst in the molar ratio of catalyst: water, 1:11000 was pressurised by carbon monoxide at constant pressure of 5 atmosphere, in a pressure reactor of 300 ml capacity at 40 °CeIsius. Titrimetrically estimated formic acid obtained was 30 x 10-3 mole/litre with initial rate 63.0 x 10° mole/litre/min in 42 min. The main advantages of present invention are : 1. Unlike the catalytic processes described in the literature which either require higher temperatures and pressure for production of formic acid, present process operates at ambient/moderate conditions of temperature and pressure. 2. Unlike reported process, where for production of formic acid along with carbon monoxide, other one, two and three more reactants like (i) methanol (one) in methyl formate process (ii) sodium hydroxide and sulphuric acid (two) in sodium/calcium formate process and (iii) methanol, ammonia and sulphuric acid (three) in formate process, are required, present process requires only carbon monoxide and water. 3. Unlike reported sodium/calcium formate and formamide process, present process avoids the use of corrosive sulfunc acid and production of sulphate salts. 4. Unlike conventional two or three stage process in present invention direct hydration of carbon monoxide to formic acid occurs in single stage . 5. The present process utilises water which acts as a reactant as well as solvents. 6. The present process is environment friendly, which utilises carbon monoxide and does not release any toxic product. 7. The present process can be easily adopted without major change in the existing industrial formic acid process and that to, by minimising the unit operation and heating equipments. WE CLAIM: 1. A process for the preparation of formic acid by catalysed hydration of carbon monoxide which comprises characterized in that (i) dissolving metal complex catalyst ethylenediaminetetraacetato ruthenate (Ru -EDTA) in water in a molar ratio of catalyst: water from 1: 1000 to 1 : 70000 ; (ii) maintaining the pH between 2 to 8 of the dissolved catalyst in solution using disodium hydrogen phosphate and potassium dihydrogen phosphate buffer ; (iii) bubbling the reaction mixture as herein described at 1 atmospheric pressure of carbon monoxide at the rate of 0.5 to 5 ml/min followed by continuous stirring ; or directly pressurizing the reaction mixture in the reactor by carbon monoxide gas at constant pressure in the range 2 to 20 atmosphere at a temperature ranging 5 to 50 °C, separating the formic acid by conventional distillation method. 2. A process as claimed in claim I wherein the water is used as substrate as well as solvent in the molar ratio of catalyst: water selected preferably from the range of 1:1000 to 1: 55000. 3. A process as claimed in claim I to 2 wherein carbon monoxide gas is bubbled at 1 atmospheric pressure, at the rate selected preferably from the range of 1 to 4 mMnh. 4. A process as claimed in daims 1 to 3 wherein carbon monoxide gas used was pressurized in the reactor in the reaction mixture preferably at constant pressure selected from the range of 5 to 15 atmosphere. 5. A process as claimed in claims I to 4 wherein the pH of the reaction mixture was maintained in the range selected from the range of 4 to 7 by using phosphate buffer of sodium and potassium. 6. A process as claimed in claims 1 to 5 wherein the, temperature of the reaction mixture is maintained in the range preferably selected from the range of 15 to 40°C. 7. A process for preparation of formic acid by catalysed hydration of carbon monoxide substantially as herein described with reference to examples accompanying this specification.

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