Methanol synthesis byproduct formation

The most recent advances in methanol synthesis are the Invv- and intermediate-pressure processes of (he type shown in Fig. I. The synthesis step of this process- relies upon a copper-based catalyst, which sites good yields or melhanol at pressures of 50 and 100 atmospheres. These pressures are substantially below those of the 250-350 atmospheres required hy earlier processes. The high catalyst activity allows the synthesis reaction to lake place at a relatively low temperature of 250-270 C. As a result, ineihunution is avoided, and byproduct formation is lower, giving increased process efficiency. 

Highly Selective Synthesis Catalyst. Very low byproduct formation, and very high loop carbon efficiency is achieved by the use of ICI s 51-2 methanol catalyst, which is highly selective. 

The synthesis loop consists of a recycle compressor, feed/effluent exchanger, methanol reactor, final cooler and crude methanol separator. Uhde s methanol reactor is an isothermal tubular reactor with a copper catalyst contained in vertical tubes and boiling water on the shell side. The heat of methanol reaction is removed by partial evaporation of the boiler feedwater, thus generating 1-1.4 metric tons of MP steam per metric ton of methanol. Advantages of this reactor type are low byproduct formation due to almost isothermal reaction conditions, high level heat of reaction recovery, and easy temperature control by... 

In addition to a small quantity of dissolved gas, mainly carbon dioxide, the raw methanol depending upon the CO2 content of the synthesis gas contains between 3.5 and 12 wt. % water as well as a number of impurities varying with the selectivity of the catalyst used and the CO content of the reactw feed gas. Crude methanol produced from synthesis gas with low CH4 content recovered from coal generally contains up to 3 500ppm byproduct in the case of a process operating with a gas loop. Byproduct formation rises to ten times this value in once through processes. Table 3.7 shows a typical crude methanol composition as can be expected on a catalyst with good selectivity and a CO partial pressure of about 6 bar in the reactor feed gas. 

Crude methanol as removed from the synthesis section contains water and impurities, which must be removed before the product is ready for commercial use. Althou fuel-grade methanol can be produced with a single distillation tower, two, three, and sometimes even four tower distillation systems are used to produce federal grade AA methanol. The amount of distillation required is dependent upon the byproduct formation of the methanol synthesis catalyst, which includes esters, ethers, ketones, aldehydes, higher alcohols, and parafinic hydrocarbons. The amount of by-product is dependent upon the type and age of the synthesis catalyst and the operating conditions in the loop. The most problematic impurity is ethanol. 

Formic acid is produced in nature (biofuels), commercially, and as a byproduct of commercial synthesis. Renewable, carbon neutral, synthesis processes are also under investigation to form formic acid from CO2 [13]. Reagent grade formic acid requires further purification to remove ppm levels of common substituent impurities, i.e., methyl formate, methanol, and acetic acid [14]. 

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