Provided is an acetic acid production method that enables, in a scrubbing system, efficient separation and obtaining of methyl iodide and an absorbing solvent; restrainment of corrosion of the interior of a distillation column; efficient separation between and recovery of hydrogen iodide and methyl iodide; or sufficient recovery of hydrogen iodide. The acetic acid production method according to the present invention includes a first absorption step and a second absorption step. In the first absorption step, an offgas is brought into contact with a first absorbent to allow the first absorbent to absorb an iodine compound from the offgas, to give a first gas, where the first absorbent includes at least one of C2 or higher alcohols, esters of C3 or higher carboxylic acids, esters between carboxylic acids and C2 or higher alcohols, ethers, ketones, water, and basic aqueous solutions. In the second absorption step, the first gas is brought into contact with a second absorbent to allow the second absorbent to absorb an iodine compound from the first gas, where the second absorbent includes at least one of C2 or higher alcohols, esters of C3 or higher carboxylic acids, ethers, esters between carboxylic acids and C2 or higher alcohols, ketones, water, basic aqueous solutions, and acetic acid and differs in composition from the first absorbent.

Polystyrene-containing polymers are converted to benzoic acid by catalytic oxidation of dissolved polystyrene under elevated temperature and pressure. The produced benzoic acid is recovered by evaporation.

Provided is a method for industrially efficiently producing acetic acid that yields a good potassium permanganate test result, without enormous cost. A light ends column (first distillation column) is operated with a reflux ratio at a specific level or more, a distillation column (crotonaldehyde-removing column) is provided for treating an organic phase of an overhead condensate from the light ends column, and the crotonaldehyde-removing column is operated under such conditions as to meet at least one of conditions (i) to (iii) as follows: (i) a reflux ratio at the distillation column is 0.01 or more; (ii) at the distillation column, the ratio of a crotonaldehyde concentration in a distillate to a crotonaldehyde concentration in a charge liquid is less than 1; and (iii) at the distillation column, the ratio of a crotonaldehyde concentration in bottoms to a crotonaldehyde concentration in the charge liquid is greater than 1. The crotonaldehyde concentration in an acetic acid stream (first acetic acid stream) resulting from light ends removal in the light ends column is controlled at a specific level or less, and/or the reflux ratio at a dehydration column (second distillation column) is controlled at a specific level or more, and at least one of the ratios C.sub.CR/C.sub.ECR and C.sub.CR/C.sub.BA in at least one of the first acetic acid stream and an acetic acid-rich stream resulting from further purification of the first acetic acid stream is lowered, to give an acetic acid product that yields a better potassium permanganate test result.

A carbonylation process for producing acetic acid including: (a) carbonylating methanol or its reactive derivatives in the presence of a Group VIII metal catalyst and methyl iodide promoter to produce a liquid reaction mixture including acetic acid, water, methyl acetate and methyl iodide; (b) feeding the liquid reaction mixture at a feed temperature to a flash vessel which is maintained at a reduced pressure; (c) flashing the reaction mixture to produce a crude product vapor stream.

Provided is a method for producing acetic acid that is capable of greatly improving the life of a silver-substituted ion exchange resin (IER) for removing organic iodine compounds in acetic acid. With the method for producing acetic acid according to the present invention, in a carbonylation process of a methanol method, a nickel base alloy or zirconium is used as a material of a distillation column in a dehydration step, and as metal ion concentrations in a charging mixture of the distillation column in the dehydration step, an iron ion concentration is less than 10,000 ppb by mass, a chromium ion concentration is less than 5,000 ppb by mass, a nickel ion concentration is less than 3,000 ppb by mass, and a molybdenum ion concentration is less than 2,000 ppb by mass.

It is intended to provide an acetic acid production method capable of industrially advantageously separating and removing a by-product acetaldehyde in the separation step of separating a process stream into aqueous and organic phases. In the present invention, the separation step satisfies, for example, the following conditions (vi) to (viii), and at least a portion of the aqueous phase is treated in the acetaldehyde separation and removal step: (vi) acetaldehyde concentrations in the aqueous and/or organic phases are not more than 28.1 mass % and not more than 24.8 mass %, respectively; (vii) a separation temperature is not more than 70 C.; and (viii) methyl acetate concentrations in the aqueous and/or organic phases are not more than 12.0 mass % and not more than 47.6 mass %, respectively, and/or the sum of the methyl acetate concentrations in the aqueous and organic phases is not more than 59.6 mass %.

It is intended to provide a method capable of suppressing distillation apparatus corrosion as a method for producing acetic acid, comprising the step of distilling a crude acetic acid solution containing acetic acid and an impurity having a higher boiling point than that of acetic acid to purify the acetic acid. The method for producing acetic acid of the present invention comprises the step described above, wherein the distillation of the crude acetic acid solution is performed under a condition involving a distillation column bottom temperature of not more than 165 C. An acetic acid concentration in the crude acetic acid solution to be subjected to the distillation is preferably not less than 90 mass %. Examples of the impurity having a higher boiling point than that of acetic acid include acetate salts, acetic anhydride, and propionic acid. A column bottom pressure of the distillation column is preferably less than 0.255 MPaG.

It is intended to provide a method capable of industrially and efficiently producing acetic acid having a good potassium permanganate test value without a large cost. The method includes a step of distilling an aqueous phase and/or an organic phase of a column top condensate of a lower boiling point component removal column by a crotonaldehyde removal column; and the reflux ratio of the lower boiling point component removal column is not less than 2 (when the aqueous phase is refluxed), and the crotonaldehyde removal column is operated such that at least one of the following conditions (i) to (iii) is satisfied: (i) the reflux ratio of the distillation column is not less than 0.01; (ii) the ratio of the crotonaldehyde concentration (ppm by mass) in a distillate liquid of the distillation column to the crotonaldehyde concentration (ppm by mass) in a charging mixture (former/latter) is less than 1; and (iii) the ratio of the crotonaldehyde concentration (ppm by mass) in a bottom fraction of the distillation column to the crotonaldehyde concentration (ppm by mass) in a charging mixture (former/latter) is more than 1.

A process for purifying methyl methacrylate. The method comprises: (a) feeding a product mixture comprising methyl methacrylate, methanol, water and oligomers of methyl methacrylate to a divided section of a distillation column comprising a dividing wall; (b) removing an overhead stream and a bottoms stream from the distillation column, and removing a middle side draw stream from the distillation column; wherein the crude product enters the dividing wall distillation column in a divided section on an opposing side of the dividing wall from the middle side draw stream; and (c) removing an upper side draw stream from a point above the dividing wall and below the top of the distillation column, separating a portion of water from the upper side draw stream to produce a dewatered upper side draw stream and returning the dewatered upper side draw stream to the distillation column.

A carbonylation process for producing acetic acid including: (a) carbonylating methanol or its reactive derivatives in the presence of a Group VIII metal catalyst and methyl iodide promoter to produce a liquid reaction mixture including acetic acid, water, methyl acetate and methyl iodide; (b) feeding the liquid reaction mixture at a feed temperature to a flash vessel which is maintained at a reduced pressure; (c) heating the flash vessel while concurrently flashing the reaction mixture to produce a crude product vapor stream, wherein the reaction mixture is selected and the flow rate of the reaction mixture fed to the flash vessel as well as the amount of heat supplied to the flash vessel is controlled such that the temperature of the crude product vapor stream is maintained at a temperature less than 90 F. cooler than the feed temperature of the liquid reaction mixture to the flasher and the concentration of acetic acid in the crude product vapor stream is greater than 70% by weight of the crude product vapor stream.