| 摘要 |
In a process for the manufacture of dimethyl terephthalate and/or isophthalate by esterification of the appropriate acid(s) with excess methanol, the reaction-product is passed to a distillation column where it is fractionated under such conditions of temperature and pressure that methanol is withdrawn from the head of the column, and liquid ester and liquid water are withdrawn, separately or together, from the lower section of the column. The temperature in the lower part of the column should be higher than 140 DEG C., and the pressure should exceed 3.6 atm. If the ester and water are drawn off together, they are separated in a phase-separator maintained at a temperature higher than the melting-point of the ester and at a pressure higher than the vapour-pressure of water, corresponding to the temperature. The methanol obtained at the head of the column may contain less than 1% by weight of water, and is returned to the esterification reactor. In an example, a solution of terephthalic acid in an excess of methanol is passed at 250 DEG C. and a pressure of 85 atm. gauge through a tubular reactor divided by partitions into 10 compartments connected in series. The mixture leaves the tenth compartment after a residence time of two hours, and is introduced into a distillation column in which the pressure is 4 atm. absolute. Liquid ester is withdrawn from the bottom of the column at a temperature of 155 DEG C. Water is removed some distance above the bottom, and methanol is withdrawn from the top of the column. Dimethyl terephthalate is distilled off in vacuo from the liquid ester, until approximately equimolar quantities of dimethyl terephthalate and monomethyl terephthalate remain behind as residue. This residue is returned to the tubular reactor. The dimethyl terephthalate, obtained as distillate, may be purified by crystallization from methanol; and the mother-liquor may be passed to the reactor.ALSO:In a process for the manufacture of dimethyl terephthalate and/or isophthalate by esterification of the appropriate acid(s) with excess methanol, the reaction product is passed to a distillation column where it is fractionated under such conditions of temperature and pressure that methanol is withdrawn from the head of the column and liquid ester and liquid water are withdrawn, separately or together, from the lower section of the column. The temperature in the lower part of the column should be higher than 140 DEG C. and the pressure should exceed 3.6 atm. If the ester and water are drawn off together, they are separated in a decanter maintained at a temperature higher than the melting point of the ester and at a pressure higher than the vapour-pressure of water, corresponding to the temperature. The methanol obtained at the head of the column may contain less than 1% by weight of water, and is returned to the esterification reactor. |
