METHOD IN THE PRODUCTION OF METHYL FORMATE AND METHANOL IN A LIQUID PHASE

Abstract: A method in the production of methyl formate and methanol from a syngas comprising carbon monoxide and hydrogen in one reaction step, the reaction being carried out catalytically in a liquid phase mainly consisting of methanol, simultaneously with continuous removal of methyl formate and methanol from the reaction as a gas.

Description: METHOD IN THE PRODUCTION OP METHYL FORMATE AND METHANOL IN A LIQUID PHASE. The present invention relates to a process for the production of methyl formate and methanol from carbon monoxide and hydrogen - so-called syngas. The production of methyl formate and methanol is carried out in one step and is catalyzed by a system of catalysts comprising an alkali or earthalkali metal alcoholate and a heterogeneous Cu, Cr catalyst. The reaction occurs in a liquid phase. Methanol and methyl formate are formed by a chemical reaction of carbon monoxide and hydrogen according to the following total reactions: I. CO + 2 H 2 CH OH carbon monoxide hydrogen methanol II. 2 CO + 2 H 2 HCOOCH-. carbon monoxide hydrogen methyl formate It is previously known to provide methyl formate from methanol and carbon monoxide in the presence of an alkali or earth alkali metal alcoholate (cf. DE-AS 1 147 214, Norw. Specification 135 749) , nad it is, furthermore, known that methanol can be produced by hydrogenolysis of methyl formate. DE-PS 902 375, thus, indicates a method, wherein methyl formate and hydrogen are reacted in a catalytic gas phase reaction to form methanol. It is, furthermore, known to manufacture methyl formate and methanol in a catalytic gas phase reaction at elevated tem¬ peratures, although this has not been utilized for industrial production at a large scale. Also, it has been suggested to carry out the reactions I and II in one and the same step (cf. DE-PS 809 803) , where the formation of methanol is indicated. This method has not been O PI utilized industrially so far, since the catalyst systems stated have low productivity and are rapidly deactivated. In¬ dustrial production of methanol to day is carried out by a catalytic gas phase reaction of carbon monoxide and hydrogen by the aid of a heterogeneous metal catalyst. The reaction takes place at a pressure of approx. 100 atm. and a tempera¬ ture of approx. 250°C. The gas phase reaction has the dis¬ advantage that relatively large amounts of gas must be re- compressed and resirculated to the reactor, the conversion in each passage through the reactor is relatively low. This disadvantage is strongly enhanced by the fact that the cost of energy is rapidly increasing. The object of the invention is characterized by the features stated in claim 1. In connection with the present invention it was surprisingly found that the product methyl formate together with methanol are advantageously removed from the reaction zone as a gas simultaneously with their formation by the chemical reaction in the liquid phase. This fact indicates that methanol is not formed via methyl formate as an intermediate product as conventionally assumed, but rather by a reaction which is independent of the methyl formate concentration, even though the mechanism of such reaction is not known. The principle of driving-off produced methanol/methyl formate from the reactor brings several advantages, technically speaking, which are so important that they will make the process technically/economically competitive. The chemical reactions taking place at the formation of methyl formate and methanol involves the liberation of con¬ siderable quantities of heat. Since the process i.a. requires defined temperatures in the reactor, heat must be removed from the zone of reaction. The reaction occurring in a liquid phase, this can be done in a simple and efficient manner as compared to a gas phase reactor. As the product, furthermore, OMPI is driven off from the liquid phase and removed from the reactor together with non-reacted carbon monoxide and hydrogen, the reaction heat will gradually be compensated by loss of heat due to the evaporation of reaction products. As regards heat economy, this is very advantageous, since the quantities of energy that would otherwise be necessary in the reactor for cooling/ can thus be reduced. The evapo¬ ration of the product also in an advantageous manner renders it possible to achieve an indirect heat control of the process by varying the amount of driven off product, since the temperature of the reactor can be adjusted in this manner. By removing the product as a gas process technical advantages associated with the catalyst, its activity and lifetime and and its handling in the process are also achieved. The catalyst, which is present as suspended material and dissolv¬ ed salt (alcoholate) in the reaction medium, will not be removed, but on the contrary remain in the reactor when the product is driven off. This means the elimination of any necessary separation to remove catalyst from product in case the product had been removed from the reactor in the liquid phase. The catalyst can, thus, be handled via a separate process flow for any desired supply of fresh or regeneration of used catalyst. In connection with the present invention it was also sur¬ prisingly found that there is a connection between the life¬ time of the catalyst and the utilization of the principle of driving off the products from the reaction medium. The principle of driving off methyl formate from the reaction medium can, thus, suitably be utilized to minimize the con¬ centration of methyl formate in order to increase the life¬ time of the catalyst. The reaction according to the invention occurs in a liquid reaction phase in the presence of an alkali or earth alkali alcoholate, preferably an alcoholate formed from methanol, and a heterogeneous catalyst comprising a Cu-Cr oxide com¬ pound suspended in the liquid reaction mixture • The pressure OMP and the temperature of the reaction may be varied within wide limits. Preferably, pressures from 10 to 100 bar are used. The temperature is chosed to achieve a practical rate of the reaction. Preferably, the reaction is carried out at a temperature in the range of 50°C to 240°C. It is known to produce "copper chromite" catalysts by calci¬ nation of a chemical compound with an approximate composition Cu(OH) (NH 4 )Cr0 4 in the presence of air at a temperature of approximately 350°C and subsequent reduction of the product with hydrogen. Copper chromite catalysts of said kind may be utilized in the process, but according to the present inven¬ tion it proved especially suitable to utilize spesific Cu-Cr oxide catalysts, which are produced when the above mentioned calcination process in air instead is carried out in an inert atmosphere, e.g. argon, helium, nitrogen or similar inert gases, and is subsequently reduced with hydrogen accord¬ ing to known methods. It is not known in detail what chemi ¬ cal changes occur to the catalyst during thermal decomposi¬ tion in an inert atmosphere as compared to the known method of calcination. The thermal decomposition of Cu(OH) (NH.)Cr0 4 in an inert atmosphere can be carried out at a temperature in the range of 250-500°C, most suitably in the range of 270-320°C. In addition to the above mentioned Cu-Cr oxide component, the catalyst system can naturally also comprise other components or carriers conventionally utilized in connection with hete¬ rogeneous hydrogenation catalysts, as for instance ZnO, Al-O.,, Fe ^ O,, MnO, MgO, CaO. BaO, Si0 2 , activated carbon and the like. The reaction occurs in a technical reactor that is known for solid/liquid phase/gas systems. Preferably a kind of reactor is chosen that is characterized by good mixture of gas/liquid /solids. In the reaction methyl formate as well as methanol are formed, and the ratio between said components in the product can be varied within wide limits by changin t h e process conditions and the composition of the catalyst. Methanol naturally functions as a solvent for the reaction. Other organic solvents, as for instance higher alcohols, ether, saturated hydrocarbons and aromatics could also be utilized. A syngas free of water, sulphur and C0 2 , and where¬ in the molar ratio of carbon monoxide and hydrogen can be varied, is used in the present method. On account of the conversion rate as well as the selectivity regarding the conversion to the desired products it is criti¬ 10 cal that the reaction takes place in an approximately anhydrous reaction medium. Methyl formate and methanol are recovered as top and bottom products respectively in a separation column. Part of the 15 produced amount of methanol is suitably returned to the reactor. The produced methanol has an especially high degree of purity (approximately anhydrous) and is, thus, especially well suited for this object. A sketch of such an embodiment of the process is shown in Figure 11. 20 The present invention represents an advantageous and very flexible process alternative for coproduction og methyl formate and methanol. The product composition may vary from pure methyl formate to pure methanol, and it is possible 25 to control production according to the actual state of the market at any time. The prospects of the market of methanol a well as methyl formate are very promising, as will be known. The characteristics of methanol are studied with a view to future utilization of methanol as an energy carrier. he δ& expected and considerable increase in production because of this will involve the need of additional plants with larger throughput. Thus, there should be a demand as well as good chances of adapting novel and improved process technology for methanol production in an industrial scale. 35 Methyl formate seems to become an essential intermediate in C- j -based chemistry, since it is reasonably priced for utili¬ zation as a raw material for a series of essential petro- chemical products. The following examples will further illuminate the object of the present invention. Examples 1 - 9 The reaction of carbon monoxide and hydrogen was studied in two essentially different reactor systems. It is common to both systems that the reaction occurs in one step in the presence of a catalyst system consisting of an alkali or earth alkali metal alcoholate and a Cu-catalyst.For both systems a micro reactor with a volume of 120 ml was used. In one reactor system formed methyl formate and methanol are removed from the reactor by bubbling an excess of carbon monoxide and hydrogen through the reactor. In this case the products are removed as gases. The amount of gas is adjusted to keep a constant liquid level. In this case the catalyst remains in the reactor. The results are shown by graph I in the Figures 1-9. In the other reactor system formed methyl formate and metha¬ nol are removed from the reactor in the liquid phase, so that dissolved and isuspended catalyst is carried with the product flow from the reactor. Heterogeneous catalyst is recovered in a hydrocyclone and is pumped back to the reactor. Methanol and methyl formate are flashed by the product flow in a separation zone and recovered homogeneous catalyst is re¬ circulated to the reactor. The results are shown in graph II of Figures 1-9. The activity of the catalyst system as a function of time is shown for various compositions of pressure, temperature and catalyst. As a heterogeneous catalyst a commercially available catalyst from Girdler-Sϋdchemie Katalysator GmbH, Munich, labelled "G 89" with the nominal composition: 39% Cu, 32% Cr, and 2,5% Mn was used in all tests. The activity is given as kg produced methanol per kg catalyst (alcoholate) per tirne ^ , „, unit, and the results are shown in the attached diagrarmtes. The results clearly show that the catalyst activity declines slower when the reaction products are removed in the gas phase and not the liquid phase. 5 Example 10 Small portions of Cu (OH) NH Λ CrO (approx. 2 g) were termally decomposed in an inert atmosphere (He) . The sample was kept ■ iO at maximum decomposition temperature as stated in Figure 10 for one hour. Simultaneously 120 ml/ in of helium were passed through the decomposition zone. 0,75 g of the decomposed product in 12 g methanol were then prereduced with hydrogen in a micro autoclave having a volume of 30 ml and provided i5 with magnetic stirring and temperature control at 185 C and 100 bar hydrogen. After 16 hours the mixture was cooled to 20°C and the catalyst was separated from the methanol by centrifugation. The catalyst remained in the autoclave where¬ as the methanol was removed. The autoclave was then supplied 20 with 10 g dried methanol containing 1 mole % Na methylab as catalyst 1. The conversion of carbon monoxide and hydrogen was then carried out at 130 C and 75 bar for 2,5 hours. After the test the reaction mixture was cooled to 20°C and analysed by gas/liquid chromatogranhy (glc) . The formation $ of methanol and methyl formate (indicated as % of weight increase) as a function of maximum decomposition temperature is shown by graph I in Figure 10. The selectivity of the reaction of CO and H 2 to methanol/methyl formate was more than 95% in all these tests. -0 For comparison Cu(OH)NH.CrO was calcinated in air according to the known methods and tested as a catalyst for the reaction of carbon monoxide and hydrogen according to the same method as stated above. The results are shown by graph II in Figure 10. The results show that a catalyst that is more active in an substantial degree is provided by thermal decomposition of CU(OH)NH 4 in an inert atmosphere, as compared to the ad achieved by known processes of calcination. v OMPI

Claims: CLAIMS : 1. A method for the production of methyl formate and methanol from a syngas comprising carbon monoxide and hydro¬ gen in one reaction step, c h a r a c t e r i z e d i n that the reaction occurs catalytically in a liquid phase main¬ ly consisting of methanol, simultaneously with continuous removal of methyl formate and methanol from the reaction zone as a gas. 2. A method as stated in claim 1, c h a r a c t e r i z e d i n that methyl formate and methanol are separated by fractional distillation, where¬ after all or part of the methanol is recirculated to the reaction step. 3. A method as stated in claims 1-2, c h a r a c t e r i z e d i n that the catalytical reaction is carried out in the presence of a catalyst system comprising an alkali or earth alkali alcoholate and a specific Cu-catalyst provided by thermal decomposition of Cu(OH) (NH.)CrO, in an inert atmosphere. 4. A method as stated in claims 1-3, c h a r a c t e r i z e d i n that the reaction is carried out at a temperature below 240°C and a pressure be¬ low 100 bar. PI

Inventors: ONSAGER OLAV T, ONSAGER, OLAV, T.
Applicants: SINTEF
Application year: 1982
Main classification: C07C27
IPC codes: C07C29