Reference product: formic acid [kg]
Location: RoW - Rest-of-World
This dataset represents the production of 1 kg of formic acid by hydrolysis of methyl formate, which is obtained by carbonylation of methanol. Formic acid is a colorless liquid with a pungent odor, which is completely miscible with water and many polar solvents but only partially miscible with hydrocarbons. It is used primarily in dyeing, in the textile and leather industries; in rubber production; and as an intermediate in the chemical and pharmaceutical industries. The use of formic acid as an aid in the ensilage of green forage has increased sharply. Raw materials and energy consumptions are modelled with literature data. The emissions are estimated. Infrastructure is included with a default value.
Sutter, J. (2007) Life Cycle Inventories of Petrochemical Solvents. ecoinvent report No. 22. Swiss Centre for Life Cycle Inventories, Dübendorf, 2007.
[This dataset has been generated using the system model "Allocation, cut-off by classification". A system model describes how activity datasets are linked to form product systems. The allocation cut-off system model subdivides multi-product activities by allocation, based on a physical properties, economic, mass or other properties. By-products of waste treatment processes are cut-off, as are all by-products classified as recyclable. Markets in this model include all activities in proportion to their current production volume.
Version 3 of the ecoinvent database offers three system models to choose from. For more information, please visit: https://www.ecoinvent.org/database/system-models-in-ecoinvent-3/system-models-in-ecoinvent-3.html)]
The worldwide installed capacity for producing formic acid was about 330 000 t/a in 1988.
Synthesis of formic acid by hydrolysis of methyl formate is based on a two-stage process: in the first stage, methanol is carbonylated with carbon monoxide; in the second stage, methyl formate is hydrolyzed to formic acid and methanol. The methanol is returned to the first stage.
Although the carbonylation of methanol is relatively problem-free and has been carried out industrially for a long time, only recently has the hydrolysis of methyl formate been developed into an economically feasible process. The main problems are associated with work-up of the hydrolysis mixture. Because of the unfavorable position of the equilibrium, reesterification of methanol and formic acid to methyl formate occurs rapidly during the separation of unreacted methyl formate. Problems also arise in the selection of sufficiently corrosion-resistant materials
Carbonylation of Methanol
In the two processes mentioned, the first stage involves carbonylation of methanol in the liquid phase with carbon monoxide, in the presence of a basic catalyst:
[To see the image, please follow the link https://db3.ecoinvent.org/images/a0ec6e15-92c8-4d44-82bb-84e90e58b171]
As a rule, the catalyst is sodium methoxide. Potassium methoxide has also been proposed as a catalyst; it is more soluble in methyl formate and gives a higher reaction rate. Although fairly high pressures were initially preferred, carbonylation is carried out in new plants at lower pressure. Under these conditions, reaction temperature and catalyst concentration must be increased to achieve acceptable conversion. According to published data, ca. 4.5 MPa, 80 °C, and 2.5 wt % sodium methoxide are employed. 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.
To synthesize methyl formate, gas mixtures with a low proportion of carbon monoxide must first be concentrated. In a side reaction, sodium methoxide reacts with methyl formate to form sodium formate and dimethyl ether, and becomes inactivated. The substances 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. The risk of encrustation and blockage due to precipitation of sodium formate can be reduced by adding poly(ethylene glycol). The carbon monoxide used must contain only a small amount of carbon dioxide; otherwise, the catalytically inactive carbonate is precipitated.
Basic catalysts may reverse the reaction, and methyl formate decomposes into methanol and carbon monoxide. Therefore, undecomposed sodium methoxide in the methyl formate must be neutralized.
Hydrolysis of Methyl Formate
In the second stage, the methyl formate obtained is hydrolyzed:
[To see the image, please follow the link https://db3.ecoinvent.org/images/2ddc19c0-905f-42c3-b14c-e68332befec9]
The equilibrium constant for methyl formate hydrolysis depends on the water: ester ratio. With a molar ratio of 1, the constant is 0.14, but with a water: methyl formate molar ratio of 15, it is 0.24. Because of the unfavorable position of this equilibrium, a large excess of either water or methyl formate must be used to obtain an economically worthwhile methyl formate conversion. If methyl formate and water are used in a molar ratio of 1 : 1, the conversion is only 30 %, but if the molar ratio of water to methyl formate is increased to 5 – 6, the conversion of methyl formate rises to 60 %. However, a dilute aqueous solution of formic acid is obtained this way, and excess water must be removed from the formic acid with the expenditure of as little energy as possible.
Another way to overcome the unfavorable position of the equilibrium is to hydrolyze methyl formate in the presence of a tertiary amine, e.g., 1-(n-pentyl)imidazole. The base forms a salt-like compound with formic acid; therefore, the concentration of free formic acid decreases and the hydrolysis equilibrium is shifted in the direction of products. In a subsequent step formic acid can be distilled from the base without decomposition.
A two-stage hydrolysis has been suggested, in which a water-soluble formamide is used in the second stage; this forms a salt-like compound with formic acid. It also shifts the equilibrium in the direction of formic acid.
To keep undesirable reesterification as low as possible, the time of direct contact between methanol and formic acid must be as short as possible, and separation must be carried out at the lowest possible temperature. Introduction of methyl formate into the lower part of the column in which lower boiling methyl formate and methanol are separated from water and formic acid, has also been suggested. This largely prevents reesterification because of the excess methyl formate present in the critical region of the column.
Dehydration of the Hydrolysis Mixture
Formic acid is marketed in concentrations exceeding 85 wt %; therefore, dehydration of the hydrolysis mixture is an important step in the production of formic acid from methyl formate. For dehydration, the azeotropic point must be overcome. The concentration of formic acid in the azeotropic mixture increases if distillation is carried out under pressure, but the higher boiling point at high pressure also increases the decomposition rate of formic acid. At the same time, the selection of sufficiently corrosion-resistant materials presents considerable problems. A number of entrainers have been proposed for azeotropic distillation.
Gräfje, H., Körnig, W., Weitz, H.-M., Reiß, W.: Butanediols, Butenediol, and Butynediol, Chapter 1. In: Ullmann's Encyclopedia of Industrial Chemistry, Sev-enth Edition, 2004 Electronic Release (ed. Fiedler E., Grossmann G., Kersebohm D., Weiss G. and Witte C.). 7 th Electronic Release Edition. WileyInterScience, New York, Online-Version under: http://www.mrw.interscience.wiley.com/ueic/articles/a04_455/frame.html