PEP Review 92-3-3
Methyl Chloride Manufacture
Published: April 1994
Methyl chloride is manufactured by chlorination of methane or by hydrochlorination of methanol. Chlorination of methane produces by-products containing 2, 3, or 4 chlorine atoms, and the demand for these compounds is declining. Methanol hydrochlorination is a preferred route, and we evaluate two variations of the process in this Review.
A major use for methyl chloride is for the manufacture of dimethyldichlorosilane, a key intermediate in the production of silicones. Major silicones producers make their own methyl chloride, often using HCl recovered from the hydrolysis of dimethyldichlorosilane during silicones production.
We evaluated an uncatalyzed liquid-phase process in which an excess of an hydrous HCI vapor is bubbled through methanol. Methyl chloride product is vaporized from the reactor, scrubbed, and stripped of HCl. The HCl is recycled, and some of the HCl is removed with the water that forms during the reaction. This type of process is preferred in the United States.
We also evaluated a process in which methanol vapor and an excess of anhydrous HCl vapor pass together over a catalyst bed. The methyl chloride product is distilled twice to remove excess HCl and unreacted methanol. This type of process is used more in Europe and Asia than in the United States.
Of these two processes, the commercial liquid-phase process has the lower capital investment and a product value. The vapor-phase process is less attractive because it requires a higher capital investment and has a higher product value.
We also examined a noncommercial process in which excess methanol reacts with cheap by-product aqueous HCl in the liquid phase. A series of continuous stirred-tank reactors is used. No catalyst is used. However, the product contains up to 4% of dimethyl ether, and the cost of removing the DME eliminates the advantage of using a cheap HCI stream as raw material.