US Patent No. 10,428,005

METHOD FOR PRODUCING ACETIC ACID


Patent No. 10,428,005
Issue Date October 01, 2019
Title Method For Producing Acetic Acid
Inventorship Masahiko Shimizu, Himeji (JP)
Assignee DAICEL CORPORATION, Osaka-Shi, Osaka (JP)

Claim of US Patent No. 10,428,005

1. A method for producing acetic acid, comprising:carbonylating methanol with carbon monoxide in the presence of a catalyst system containing a metal catalyst and methyl iodide, as well as acetic acid, methyl acetate, and water in a reaction vessel to produce acetic acid;
evaporating a reaction mixture obtained by the carbonylation to separate into a vapor stream and a residual liquid stream in an evaporator;
removing a lower boiling point component to separate the vapor stream by a first distillation column into a first overhead stream rich in at least one lower boiling point component selected from methyl iodide and acetaldehyde, and a first acetic acid stream rich in acetic acid, and condensing and separating the first overhead stream to obtain an aqueous phase and an organic phase;
dehydrating the first acetic acid stream by a second distillation column to separate into a second overhead stream rich in water and a second acetic acid stream more enriched with acetic acid than the first acetic acid stream;
recycling at least a portion of the aqueous phase and/or organic phase in the first overhead stream to a reaction vessel; and
separating and removing crotonaldehyde by treating at least another portion of the aqueous phase and/or organic phase by a distillation column;
wherein a potassium permanganate test value of the second acetic acid stream is more than 50 minutes; and
wherein with respect to a reflux ratio of the first distillation column, when only the aqueous phase is refluxed to the first distillation column, a reflux ratio of the aqueous phase is not less than 2, when only the organic phase is refluxed, a reflux ratio of the organic phase is not less than 1, and when both the aqueous phase and the organic phase are refluxed, a total reflux ratio of the aqueous phase and the organic phase is not less than 1.5; and when removing the crotonaldehyde, the distillation column is operated such that all of the following conditions (i) to (iii) are satisfied:
(i) the reflux ratio of the distillation column is not less than 0.01;
(ii) a ratio of a crotonaldehyde concentration in ppm by mass in a distillate liquid of the distillation column to a crotonaldehyde concentration in ppm by mass in a charging mixture, former/latter, is less than 1; and
(iii) a ratio of a crotonaldehyde concentration in ppm by mass in a bottom fraction of the distillation column to the crotonaldehyde concentration in ppm by mass in the charging mixture, former/latter, is more than 1.