International Journal of Chemical & Petrochemical Technology (IJCPT) ISSN 2277-4807 Vol. 3, Issue 2, Jun 2013, 55-70 © TJPRC Pvt. Ltd.
THE ADVANCES IN PROCESSES AND CATALYSTS FOR THE PRODUCTION OF METHYL FORMATE BY METHANOL CARBONYLATION – A REVIEW
BIJAY N PATTANAIK R&D Centre, GNFC Ltd, Narmadanagar, Bharuch, Gujarat, India ABSTRACT
Synthesis of methyl formate from six varieties of routes from different feed stocks is discussed. The commercial processes presently available for carbonylation of methanol to methyl formate using homogeneous catalyst (potassium methoxide /sodium methoxide) are summarized. This review also covers the advances in process technologies and research development to improve the efficiency of both homogeneous and heterogeneous catalysts for carbonylation of methanol to methyl formate.
KEYWORDS: Methyl Formate, Methanol Carbonylation, Homogeneous Catalyst, Heterogeneous Catalyst, Anion Exchange Resins
INTRODUCTION
Methyl formate is one of the important chemical products of chemistry with varieties of applications. It is a versatile chemical precursor to a wide range of other chemicals such as formic acid, acetic acid, acetaldehyde, methyl acetate, ethylene glycol and formamide. The methyl formate is mainly used for production of formic acid by hydrolysis. The six routes for synthesis of methyl formate from different feed stocks are reported by Lee et.al[1].Presently industrial processes for production of methyl formate is dominated by methanol carbonylation using potassium methoxide /sodium methoxide catalyst[2]. Recent reported research studies to improve the current process technologies, alternative catalysts, both homogeneous and heterogeneous for carbonylation of methanol to methyl formate have been discussed.
DIFFERENT ROUTES FOR METHYL FORMATE PRODUCTION
Synthesis of methyl formate from six different routes is summarized in Figure 1. The details about different routes for the production of methyl formate are discussed below.
Figure 1: Synthesis Routes for Methyl Formate 56 Bijay N Pattanaik
Carbonylation of Methanol Dehydrogenation of Methanol Oxidative Dehydrogenation of Methanol Dimerization of Formaldehyde Direct Synthesis from Synthesis Gas Hydrocondensation of Carbon Dioxide with Methanol Carbonylation of Methanol The synthesis of methyl formate by carbonylation of methanol is well known chemistry. The methanol ─ carbonylation occurs through two step mechanism the methoxide ion reacts with CO to form CH3OCO which then reacts with methanol producing methyl formate and restoring the active catalyst. This is achieved by using an alkali metal methoxide catalyst dissolved in methanol at 60-120◦C and with 20-70 bar of CO. [3, 4] ─ ─ CH3O + CO (CH3OCO) (1) ─ ─ (CH3OCO) + CH3OH HCOOCH3 + CH3O (2)
The overall reaction is given below
CH3OH +CO HCOOCH3 (3)
The nucleophilic attack of methoxide ion on carbon monoxide was proposed by Christansen [5] in 1942 and the kinetic studied by Tonner et.al.[6]. Some research work in methyl formate synthesis from methanol and CO aims at developing more robust catalyst systems that could avoid the problems experienced in alkali methoxide catalyst. This includes homogeneous ruthenium [7, 8], platinum [9] and tungsten [10] complexes and non metallic catalysts (guanidines) [11]. Unlike processes requiring the activation of carbon-oxygen bonds, these transition metal complex catalysts do not need halide promoters to form methyl formate by activation of the oxygen-hydrogen bond of methanol. These catalytic systems, however, are either in the stage of fundamental research or not as efficient as the current homogeneous sodium methoxide catalyst system.
Details on the carbonylation of methanol using alkali metal methoxide are discussed later on.
Dehydrogenation of Methanol
Dehydrogenation of methanol over copper catalysts to yield methyl formate has been known since 1920s [12].
2CH3OH HCOOCH3 + 2H2 (4)
In addition to copper, silver, and tungsten carbide have been reported to be efficient catalyst for the dehydrogenation reaction. The catalytic dehydrogenation of methanol to methyl formate over copper supported catalysts has been studied [13].It is reported that the copper/silica and copper/zirconium oxide catalyst are very active and selective towards methyl formate formation.
Oxidative Dehydrogenation of Methanol
Methyl formate has also been synthesized by oxidative dehydrogenation of methanol to achieve a thermodynamically more favorable process.
2CH3OH + O2 HCOOCH3+ 2H2O (5)
A liquid phase process at elevated pressure has been proposed due to the higher exothermic nature of the reaction soluble chromium compounds [14] or ruthenium complexes [15] are used as catalysts. The Advances in Processes and Catalysts for the Production of 57 Methyl Formate by Methanol Carbonylation – A Review The selective oxidation of methanol to formaldehyde, methyl formate and dimethoxymethane with the use of ruthenium oxide cluster supported on SnO2, ZrO2, TiO3 and SiO2 catalyst has been reported [16].The structure and properties of zirconia-supported ruthenium oxide catalyst for selective oxidation of methanol to methyl formate to design more effective catalysts has been studied in another paper[17]. A silver catalyst has been used for production of methyl formate for long catalyst life in an upgraded temperature [18].
The catalytic synthesis of methyl formate via a novel route from methyl nitrite in vapor phase has been reported
◦ by Zhuo et.al [19].The catalysts used for studies were H-Y zeolites, Na-Y zeolite, 4A molecular sieve, -Al2O3 and silica
(KSG). The zeolites H-Y and Na-Y exhibit higher selectivity and yield of methyl formate. Two steps oxidation of methanol using heterogeneous catalyst have been suggested. The advantages of the process are the reaction conditions are fairly mild, the yield and selectivity of methyl formate was quite high and catalyst contained no precious metals i.e. Rh or Pd.
Dimerization of Formaldehyde
Methyl formate has been synthesized by dimerization of formaldehyde. This is a Tischenko type intermolecular oxidation-reduction reaction.
2HCHO HCOOCH3 (6)
Methyl formate has also been synthesized by a Cannizaro reaction followed by esterification of formic acid with methanol.
2HCHO+ H2OCH3OH+HCOOH (7)
CH3OH+HCOOHHCOOCH3+ H2O (8)
Both homogeneous and heterogeneous catalytic systems have been reported for the above reactions. The reaction can be carried out more efficiently in the vapor phase over Cu-Zn. The reaction also can be carried out with SnO2-WO3 catalyst [20].
Direct Synthesis from Synthesis Gas
The direct synthesis of methyl formate from synthesis gas can be achieved in a high-pressure liquid-phase reaction in the presence of homogeneous transition metal catalysts.
2CO + 2 H2 HCOOCH3 (9)
Methyl formate and methanol are selectively produced with complexes of cobalt [21-23], ruthenium [23-26], or iridium [23] as a catalyst.
Hydrocondensation of Carbon Dioxide with Methanol
The hydrocondensation of carbon dioxide with alcohol has been described relatively recently. Methyl formate has been synthesized from methanol, CO2 and H2 in benzene in the presence of a catalyst composed of ruthenium, iridium, osmium or platinum complexes and BF3[27].
CO2+ H2+CH3OHHCOOCH3 + H2O (10)
A low-valent complex of palladium, ruthenium, rhodium or iridium and a tertiary amine [28, 29], anionic ruthenium carbonyl clusters [30], and anionic group 6B metal carbonyl [31] are among recently reported catalysts. These catalysts show much greater activity for methyl formate formation from CO and CH3OH. 58 Bijay N Pattanaik
A recent study for synthesis of methyl formate from methanol using a novel thermal coupled reactor (TCR) has been reported by Goosheneshin et.al. [32].The thermal coupled reactor containg methyl formate production in endothermic side and methanol synthesis in exothermic side has been investigated. The interesting feature of this TCR is the productive methanol in the exothermic side could be recycled and used as feed of the endothermic side for methyl formate synthesis.
CARBONYLATION OF METHANOL TO METHYL FORMATE USING ALKALI METAL METHOXIDE CATALYST (POTASSIUM METHOXIDE / SODIUM METHOXIDE)
Among these above routes to methyl formate, the carbonylation of methanol is more advantageous in terms of energy-efficiency and atom-efficiency, which currently, performed homogeneously using alkali metal methoxide catalysts dissolved in methanol with high CO conversions and methyl formate selectivities. However, the use of strong bases in this effective industrial process leads to inevitable problems such as corrosion and waste byproducts and in particular, deactivation by CO2 and H2O impurities.
The carbonylation of methanol to methyl formate was described by BASF [33] in 1925. The sodium methoxide or potassium methoxide has also been proposed as a catalyst. It is more soluble in methyl formate and gives a higher reaction rate. High pressures were initially preferred for the carbonylation reaction but afterwards the carbonylation is carried out at lower pressure in the new plants. Under these conditions, reaction temperature and catalyst concentration must be increased to achieve acceptable conversion. The carbonylation reactions is carried out at 45 bar pressure, 80°C temperature and 2.5% sodium methoxide or potassium methoxide as catalyst. About 95 % carbon monoxide, but only about 30 % methanol, is converted under these circumstances. Nearly quantitative conversion of methanol to methyl formate can, nevertheless, be achieved by recycling the unreacted methanol. The carbonylation of methanol is an equilibrium reaction. The reaction rate can be raised by increasing the temperature, the carbon monoxide partial pressure, the catalyst concentration, and the interface between gas and liquid:
In a side reaction, sodium methoxide reacts with methyl formate to form sodium formate and dimethyl ether and becomes inactivated. The methanol, CO gas and the catalyst used must be anhydrous; otherwise, sodium formate is precipitated to an increasing extent: Sodium formate is considerably less soluble in methyl formate than in methanol.
Commercial Processes for Production of Methyl Formate by Carbonylation of Methanol
The four commercial processes for the production of methyl formate by carbonylation of methanol using sodium methoxide or potassium methoxide catalyst have been reported [2]. All these industrial processes are producing both methyl formate and formic acid. The details about the four commercial processes are summarized.
Kemira – Leonard Process
BASF Process
USSR Process
Scientific Design – Bethlehem Steel Process
Kemira – Leonard Process
The Leonard Process Co. [34] was built at Kemira in Finland and put into operation in 1982. The process has been developed further by Kemira, and licenses for it have been issued in Korea, India and Indonesia.
In the Kemira – Leonard process, carbonylation of methanol is carried out at about 40 bars and a temperature of The Advances in Processes and Catalysts for the Production of 59 Methyl Formate by Methanol Carbonylation – A Review approximately 80°C, with additive-containing alkoxides used as catalyst
Compressed carbon monoxide and methanol are converted into methyl formate in reactor. Catalyst is fed into the reactor in a methanol solution. The amount of methanol introduced in this way makes up for methanol losses in the process. The discharge from reactor is flashed and fed into the methyl formate column from which methyl formate is drawn off as the distillate. Methanol and the dissolved catalyst are returned to the reactor and inactivated catalyst (primarily sodium formate) is crystallized and discharged.
BASF Process
BASF process began operating in Ludwigshafen (Federal Republic of Germany) in 1981. In this plant, a technology for the hydrolysis and dehydration was used for the first time. The production of methyl formate by carbonylation of methanol has been carried out on a large scale for many years at BASF [33, 35]. The carbonylation stage is largely identical to that of the Kemira – Leonard process. Carbon monoxide and methanol react in the methyl formate reactor in the presence of sodium methoxide. Methyl formate and methanol are fed to distillation column. Methyl formate product is drawn off from the top of the distillation. Methanol and dissolved catalyst are drawn off from the bottom of column and returned to reactor and catalyst decomposition products are discharged by crystallization
USSR Process
The USSR process [36] developed in the former Soviet Union is being built in Saratov (Ukraine) and is expected to be operational in 1989.Carbon monoxide reacts with methanol in column reactor, in the presence of the catalyst and a stabilizer, at about 30bar, to yield methyl formate. Separation of methyl formate (distillate) and methanol plus catalyst takes place in the methyl formate column at 2 bars. The exhaust gas produced is partially recycled in this process.
Scientific Design – Bethlehem Steel Process
The process developed jointly by Scientific Design and Bethlehem Steel [37] has not yet been implemented industrially on a large scale. The carbonylation stage is essentially similar to the processes described previously. This process recommends a single back mixed reactor when the concentration of carbon monoxide is higher than 90mol% and a two stage countercurrent back mixed reactor system when the carbon monoxide concentration is in between 50 to 90 mol%. The total pressure must be increased considerably when the carbon monoxide concentration is low.
The Acid Amine technologies (AAT), USA offers the process for both methyl formate and formic acid. This process combines the best feature of Leonard process and the Scientific Design – Bethlehem Steel Process for which it has acquired the rights [38].
THE CARBONYLATION OF METHANOL TO METHYL FORMATE USING BOTH HOMOGENEOUS AND HETEROGENEOUS CATALYSTS
The present review attempts to provide an updated research studies on the advances in process technologies and catalysts both homogeneous and heterogeneous for carbonylation of methanol to methyl formate.
Use of Homogeneous Catalyst for Carbonylation of Methanol to Methyl Formate
In recent years some patents claim improved processes for preparation of methyl formate from methanol and CO by using homogeneous alkali metal methoxide catalyst (potassium methoxide and sodium methoxide).The details of these processes have been summarized below. The research studies for use of promoter along with the homogeneous catalyst to improve the rate reaction have also been discussed. 60 Bijay N Pattanaik
Couteau et al.[39] discloses a process for production of methyl formate by reacting carbon monoxide with methanol at operating temperature and pressure of 70-110◦C and 20-110 bar respectively. The concentration of alkali metal or alkaline earth metal methoxide catalyst (sodium methoxide) is used in the range of 0.2 to 4.0% by weight of methanol. .The molar ratio of carbon monoxide to methanol is maintained in the range of 0.30 to 0.85. The product methyl formate is recovered from the output liquid mixture of the reactor. The recycled liquid reaction mixture is used for sucking and dispersing the current gas in the reaction mixture by venture means inside the reactor and maintained the temperature of 70-110◦C in the reaction zone. Thus excellent heat exchange is achieved in this process. The other advantages of the process are high productivity, absence of solid deposits on the internal surfaces of the apparatus, lower operating pressures and temperatures, use of small dimension of equipment due to utilization 80 to 90% of the volume of the reactor and suppression of recycling of carbon monoxide.
US Patent by Chang et al. [40] discloses a process operates at 70 -130◦C and 4.83 - 68.95 bar of CO partial pressures by using homogeneous sodium methoxide catalyst for carbonylation of methanol to methyl formate. The catalyst concentration is maintained in the range of 1.0 to 8.0 mol% of methanol. The product methyl formate is removed by distillation. The unreacted CO containing gas is further reacting with a fresh methanol containing about 1.0-8.0 mol% of catalyst in the second reaction zone at 60 to 80◦C to convert substantial amount of unreacted CO to methyl formate. This process operates with two reactors, higher catalyst concentration, higher temperature and low conversion of methanol to methyl formate .The advantages of this process is with free of catalyst precipitation and no salt removal process is required.
In another US patent by Lippert et al.[41] describes a process for continuous preparation of methyl formate by reacting carbon monoxide and methanol under elevated pressure between 210 - 215 bar and temperature of 50 - 150◦C. The reaction is carried out with 0.2% wt of alkali metal methoxide as catalyst. Both sodium methoxide and potassium methoxide used as catalyst in the examples of the patent. This process claims low salt formation as it operates with high temperature and pressure of CO with low concentration of catalyst.
Recent invention by Auer et al.[42] discloses for preparation of methyl formate by reacting excess of methanol with carbon monoxide under super atmospheric pressure and at elevated temperature in presence of alkali metal methoxide or alkaline earth metal methoxide ( sodium methoxide /potassium methoxide)as catalyst. The reaction is carried out in a pressure rated reactor at 80 - 120C, carbon monoxide pressure of 90 -180 bar in presence of catalyst in the range of 0.05 - 0 .5% by wt. based on the weight of the liquid feed .This process is preferably operated in countercurrent. The molar ratio of carbon monoxide to methanol is set from 3:1 to 0.5:1. The reactor output mixture is passed to distilling apparatus where methyl formate is stripped from the reaction mixture. About 20 to 80% of the remaining liquid phase from distillation apparatus is circulated back to the reactor and a part of this send to desalting apparatus. The desalting apparatus is operated as an integrated heat system with distillation apparatus. The remaining methanol from the desalting apparatus is also fed to distillation apparatus. The process is very economical, trouble free production of methyl formate of any desired quality and with very good production capacity
An US patent by Adami et al.[43] claims an improved process for the preparation of methyl formate by reacting methanol with carbon monoxide at a pressure of 5 -100 bar and 50 -150◦C in presence of potassium methoxide as catalyst in a reactor. The entrained methyl formate is removed from the gas stream by condensation, and all or some of the remaining gas stream is return to the reactor as circulating gas stream. The mean gas superficial velocity of 1 to 20cm/s is set at least one region of the reactor in which the gas flows essentially in one direction. This is a simple process for the preparation of methyl formate with very little salt-like deposition. This process requires low equipment complexity because it is operated with low pressure compared to the other known processes. The advantages of the process are low energy The Advances in Processes and Catalysts for the Production of 61 Methyl Formate by Methanol Carbonylation – A Review consumption, low consumption of catalyst and facilitate space-time yield of methyl formate .This advantages are achieved in particular by the high gas superficial velocity and the removal of gaseous methyl formate from the reactor.
The Mueller et al.[44] discloses for the use of complexing agent along with the sodium methoxide catalyst for preparation of methyl formate. A nonionic complexing agent is used to bind the alkali metal cations or alkaline earth metal cations of the catalyst to reduce the formation metal formate. The nonionic complexing agent is selected from the group consisting of acyclic compounds containing a polyethylene glycol structural unit. The use stoichiometric amount of complexing agent of the metal cation of the catalyst can reduce precipitation of metal formate.Some of the plants is using the complexing agent to reduce the salt formation and reduce catalyst consumption.
The studies of kinetics and deactivation of catalyst for methyl formate synthesis by carbonylation of methanol have been reported [45] In the liquid phase reaction, alkali catalyst drove the methanol carbonylation rapidly to equilibrium and showed almost 10% selectivity to methyl formate. The kinetic study showed that the reaction was first order in methanol and CO concentrations. The rate dependant on alkali metal of the catalyst is reported in the order of K>Na>Li
.The sensitivity of the alkaline metal catalyst to the small amount of H2O or CO2 is also investigated and reported.
The carbonylation of methanol using sodium methoxide catalyst has been studied in the temperature range of 60- 110C and pressure range of 20-40 bars in a mechanical agitated reactor [46]. The kinetic parameters and kinetic expression including forward and reverse reaction has been determined for the carbonylation of methanol. The negative effects of CO2 and H2O on the carbonylation reaction were studied and reported. The poisoning effect of CO2 is irreversible at the conditions used has been reported.
The reaction of water with CH3ONa is equilibrium controlled and produced NaOH.The studies for the carbonylation of methanol with carbon monoxide to methyl formate have been carried out using sodium suphide as catalyst [47]. It has been reported that the anhydrous sodium suphide is an effective catalyst for carbonylation of methanol to methyl formate and the presence of SO2 gas in CO deactivates the carbonylation reaction in this paper.
The production of methyl formate from methanol and carbon monoxide in the presence of potassium methoxide in a laboratory-scale semi-batch reactor has been reported [48]. Mechanisms for the formation of the main product, methyl formate and traces of side products, dimethyl ether and trimethoxymethane are proposed. Methyl formate formation involved the reaction between the methoxide ion of the catalyst and carbon monoxide to form an intermediate.
Then, proton is transferred from methanol to the intermediate to form the main product, methyl formate with the resultant regeneration of the dimethyl ether (DME) and trimethoxymethane (TMM) as the side-products in very small amount. Dimethyl ether, one of the side products detected may be formed by the nucleophilic displacement of formate ion by the methoxide. The formation of the other side product is trimethoxymethane. The detailed mechanism as proposed is given below in Figure 2. The main reaction is favored by low temperature and high pressure, while the side reaction was enhanced by high temperature and high stirring rate.
The decomposition of the catalyst occurs along with the formation of the side products. It is suggested that the catalyst decomposition is not only due to the presence of water, an impurities in methanol but also for the formation of the ether. The decomposition rate of the catalyst is estimated, along with the demonstration that the stirring speed has a pronounced effect on mass transfer of carbon monoxide and thus the reaction rate. A new kinetic model, which consists of methyl formate synthesis reaction and the catalyst consumption rate together with gas–liquid mass transfer limitations, has been developed and the model (concentration- based or activity-based) is able to predict the experimental observations 62 Bijay N Pattanaik successfully. All the experiments in this paper have been carried out with a fixed concentration of potassium methoxide catalyst. However lot of information has been shared in this paper.
Main reaction
O O
MeOH H C──O ─ + C H C─O──C ─ 3 ◦ ◦ 3 Methanolate A
O O
─ ─ H3C─O── C + H──O──CH3 H3C──O──CH + O──CH3
A methyl formate
Side reaction 1
O O
─ ─ H3C ─O + H3C──O ───CH H3C── O──CH3 + O──CH dimethyl ether
Side reaction 2&3 O- O
─ H3C ─O + H3C─O── CH H3C─O──CH
Methyl formate O─CH3
Dimethoxymethanolate ( as intermediate)
The Advances in Processes and Catalysts for the Production of 63 Methyl Formate by Methanol Carbonylation – A Review
Side reaction 2
─ O O─CH3 O
─ H3C─O─CH + H3C────O── CH H3C─O──CH + O──CH
O ─CH3 O─CH3 dimethoxymethanolate trimethoxymethane
Side reaction 3
O─ O──CH
─ H3C─O─CH + C H ─── O ── CH3 H3C─O──CH + O──CH3 ° °
O ─CH3 O─CH3 dimethoxymethanolate dimethoxymethyl formate
Figure 2: Mechanism for Methyl Formate and Traces of by Products
The promotion effect of strong polar aprotogetic compounds in the carbonylation of methanol to methyl formate using sodium methoxide was investigated and reported by Shi-Zhong et.al [49].The N, N-dimethyl formamide (DMF), dimethyl sulfoxide (DMSO) and N-methyl pyrrolidone (NMP) are more efficient promoter. The strong promotion effect of DMF and DMSO in methanol carbonylation to methyl formate catalyzed by sodium methoxide results is evident from the decrease of activation energy of the carbonylation reaction. It is also concluded that DMF and DMSO are not only the high effective promoters but also constructive promoter when used with ethylene glycol. The experiments are carried out with continuous bench scale unit to confirm the data obtained from a batch autoclave.
The homogeneous production of methyl formate from methanol, syngas, CO and H2 co-catalyzed by Mo (CO) 6 in the presence of an alkali methoxide (KOCH3) is reported [50]. The slight increase in the amount of methyl formate produced by the mixture of Mo (CO) 6 and KOCH3 over the potassium methoxide alone, probably due to the electrophilic nature of Mo co-ordinated carbon monoxide compared to free CO. The mechanism proposed for the production for methyl ─ formate proceeds via a methoxy carbonyl intermediate ([Mo (CO) 5(COOCH3)] ), which is then protonated to eliminate methyl formate. The stoichiometric effect of Mo (CO) 6 to KOCH3 in the production of methyl formate is also reported. 64 Bijay N Pattanaik
Activity of alkali methoxide catalyst (sodium methoxide and potassium methoxide) in carbonylation of methanol was studied [51]. The IR, GC, and GC-MS instruments were used to identify products and changes of the catalyst. Under the conditions used in this work, the results show that activity of the alkali methoxide decreases after certain time of steady state operation. The main reason for the deactivation of alkali methoxide catalyst is that the catalysts react directly with methyl formate produce to form alkali formate (sodium formate and potassium formate) and dimethyl ether. Sodium formate is much less active for the carbonylation of methanol than sodium methoxide. The deactivation rate of catalyst decreases with decreasing temperature has been reported in this paper.
The kinetics of synthesis of methyl formate from carbon monoxide and methanol, using sodium methoxide as the catalyst and pyridine as the promoter was studied [52]. The apparent activation energies had decreased 6.44kJ/mol and rate constant had increased more than 1.5 times when pyridine was used as the promoter in the catalyst system. The pyridine has a good promoter function on the carbonylation reaction is reported.
Use of Heterogeneous Catalyst for Carbonylation of Methanol to Methyl Formate
In order to overcome the limitations of the homogeneous alkali metal alkoxide catalyst system particularly salt formation and reduction of catalytic activity for the carbonylation methanol to methyl formate the heterogeneous catalyst has been the subject of considerable investigation.
Recent time attempts have been made to use the anion exchange resin, methoxide modified anion exchange resins and zeolites as catalyst for carbonylation of methanol to methyl formate. Some of the research work on heterogeneous catalyst for methanol carbonylation to methyl formate has been reported in this paper.
The process for making methyl formate by contacting an intimate mixture of gaseous CO and methanol with a strongly basic anion exchange resin was disclosed by Smathers et.al [53]. The process is carried out by passing the methanol and the CO countercurrently through the catalyst bed at temperature range of 0-200◦C and CO partial pressure of 7 -345 bar. About 10 to 50% of the product mixture recycled after cooling along with fresh methanol. The polymer matrix of the anion exchange resin is poly styrene divinyl benzene and ionic active group is derived from dimethyl ethanol amine. Higher conversion of methanol to methyl formate is favored by longer contact times of CO and methanol with the resin bed is reported in this patent. It is claimed that the residence time as large as 20-30 minutes is to be used to attain extremely high conversions methanol to methyl formate.
The liquid phase methanol carbonylation to methyl formate has been investigated both with homogeneous sodium methoxide, the industrial catalyst for the process and with heterogeneous strongly basic resins by Girolamo et.al [54]. The strongly basic resins, such as Amberlyst A26 or Amberlyst IRA 400 (Rohm & Haas Co.) are more active catalyst than sodium methoxide in the methanol carbonylation to methyl formate. The activation procedure and the dependence of the reaction rate on CO pressure have also been investigated. The catalytic performance of several basic resins differing in polymer matrix (polystyrene or polyacrylates) has been tested and compared with the sodium methoxide homogeneous catalyst [55].The use of strongly basic resins, as Amberlyst A26( Rohm & Haas Co), appears as valuable tool for significantly improving the current industrial process for methyl formate production. The heterogeneous systems allow reaching the equilibrium concentrations in a shorter reaction time and at lower reaction temperatures (50-70◦C) compared to sodium methoxide. The strong basic resin catalyst maintains its activity after several cycles also at temperature as high as 67◦C. The preliminary results indicate that Amberlyst A26 seems to be a very attractive catalyst for methanol carbonylation but in order to make possible an industrial application at least longer life time tests have to be accomplished. The Advances in Processes and Catalysts for the Production of 65 Methyl Formate by Methanol Carbonylation – A Review However more experiments are required to use the modified anion exchange resin catalyst in plant scale operation for the carbonylation of methanol to methyl formate.
The catalytic activity and thermal stability of the anion exchange resin has been investigated [56]. The rate of methanol carbonylation on the resin catalyst was almost equivalent to that on homogeneous sodium methoxide catalyst based on methoxide amount. It is reported that the thermal stability of catalyst mainly depends on that of functional group of the resin.
─- ◦ The carbonylation of methanol using CH3O exchange resin as a heterogeneous catalyst at 80 C is examined systematically in order to drive the kinetic rate expression for the reaction [57]. The activation energies for the carbonylation and decarbonylation reactions are found to be 68kJ/mol and 105kJ/mol, respectively. There has been no ─ degradation of the catalytic activity of CH3O exchange resin upon repeated separation. Experiments were carried out in slurry phase reactor.
The formation of methyl formate from methanol and CO through two parallel reaction routes on Cu/ZnO catalyst was studied [58] .It is reported that the high Cu content catalyst has been more active than that of high ZnO catalyst.
The liquid -phase synthesis of methyl formate was investigated for green carbonylation of methanol with CO on a soluble copper nanocluster catalyst with high activities and 100% methyl formate selectivities under mild reaction conditions of temperature 80 to 170◦C and at 3 to 30 bar pressure of CO [59]. The heterogeneous liquid phase carbonylation of methanol to synthesize methyl formate on a soluble copper nanocluster catalyst is reported. This catalyst in methanol behaves like homogeneous catalyst but with ease operation, separation and scale up as a result of its heterogeneous nature. It is reported that Cu nanoclusters can potentially replace the caustic catalysts of alkali metal alkoxide (e.g. CH3ONa) required for the current carbonylation processes in industry. More experiments are required to arrive at the conclusion for the use of Cu nanocluster as replacement of metal alkoxide catalyst for carbonylation of methanol to methyl formate.
The use of zeolite-supported alkali methoxide liquid-film catalyst, such as KOCH3-PEG/NaZSM-5 (or NaY) the heterogeneous catalytic carbonylation of methanol to methyl formate is investigated in a fixed bed continuous flow reactor [60]. The reaction was carried out at temperature 80C and 10 bar pressure with the molar ratio of CO to methanol 6.48. The ─ experimental results indicated that the CHO3 is the crucial catalytically active species. The role of the additive polyethylene glycol (PEG) on the zeolite behavior in the carbonylation reaction has been discussed.
CONCLUSIONS
Methanol carbonylation has emerged as the dominant route to produce methyl formate by using homogeneous catalyst (potassium methoxide/ sodium methoxide).Significant innovation has occurred even in this production route resulting in greatly improved yield, selectivity in greatly milder operating conditions and lower cost of production to improve the current process technology and catalyst. The use of promoters and complexing agent along with the alkaline metal methoxide catalyst to increase the reactivity of the carbonylation reaction and reduce formation metal fomate respectively has been reported. The commercialization of heterogeneous catalyst for carbonylation of methanol to methyl formate has yet to be developed. Some of recent research studies to develop heterogeneous catalyst i.e. anion exchange resin, modified anion resins / zeolites for carbonylation of methanol to methyl formate have been reviewed.
66 Bijay N Pattanaik
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