Production Methods
1,6-Hexanediol is produced industrially by the catalytic hydrogenation of adipic acid or of its esters. Mixtures of dicarboxylic acids and hydroxycarboxylic acids with C6 components formed in other processes (e.g., in cyclohexane oxidation) are also used. Esterifification of "distillation heavies" with lower alcohols is often carried out before hydrogenation. The acids are hydrogenated continuously at 170-240 ℃ and at 15.0-30.0 MPa on a suitable catalyst either in a trickle-flflow (downflflow) or a bubble-flflow (upflflow) fifixed-bed reactor. The reactor temperature is controlled by circulating part of the reactor discharge. The hydrogen required for the hydrogenation is fed together with the recycle gas through the recycle gas compressor to the reactor. Side products of the synthesis are alcohols, ethers, diols, and esters. Pure 1,6-hexanediol is obtained by fractional distillation of the crude reactor discharge. For the hydrogenation of dicarboxylic acids, catalysts containing cobalt, copper, or manganese are suitable. For the hydrogenation of esters, catalysts such as copper chromite or copper with added zinc and barium are used as "full catalysts" or on inert carriers. Ruthenium, platinum, or palladium on inert supports can also be used. Gas-phase hydrogenation of esters of adipic or 6-hydroxyhexanoic acid can be carried out at 1-7 MPa. Both acids and esters also may be hydrogenated using suspended catalysts. Oligomeric esters of the product diol and adipic acid can also be hydrogenated.
