It is intended to provide a method capable of lowering a formic acid concentration in product acetic acid by a simple approach. The method for producing acetic acid according to the present invention comprises at least one step selected from a step that satisfies the following operating conditions (i) and a step that satisfies the following operating conditions (ii) in an acetic acid production process: (i) operating conditions involving a hydrogen partial pressure of less than 500 kPa (absolute pressure), a carbon dioxide partial pressure of less than 70 kPa (absolute pressure), and an operating temperature of more than 175 C.; and (ii) operating conditions involving a hydrogen partial pressure of not more than 5 kPa (absolute pressure), a carbon dioxide partial pressure of less than 20 kPa (absolute pressure), and an operating temperature of more than 100 C.

A method for producing acetic acid includes an absorption step that suppresses corrosion inside a distillation column when a solution after that has absorbed a target component is subjected to distillation. The method for producing acetic acid also includes an absorption step of supplying, to an absorption column, at least a portion of offgas generated in an acetic acid production process, bringing the offgas into contact with an absorbent containing one or more liquids selected from a hydrocarbon, an ester of a carboxylic acid having 3 or more carbon atoms, an ester of a carboxylic acid and an alcohol having 2 or more carbon atoms, and an ether, to allow the absorbent to absorb an iodine compound in the offgas, and separating into a gas component having a lower iodine compound concentration than the offgas and a solution containing the absorbent and the iodine compound.

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; and (b) feeding the liquid reaction mixture at a feed temperature to a flash vessel which is maintained at a reduced pressure.

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.

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.

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 a method capable of lowering a formic acid concentration in product acetic acid by a simple approach. The method for producing acetic acid according to the present invention comprises at least one step selected from a step that satisfies the following operating conditions (i) and a step that satisfies the following operating conditions (ii) in an acetic acid production process: (i) operating conditions involving a hydrogen partial pressure of less than 500 kPa (absolute pressure), a carbon dioxide partial pressure of less than 70 kPa (absolute pressure), and an operating temperature of more than 175 C.; and (ii) operating conditions involving a hydrogen partial pressure of not more than 5 kPa (absolute pressure), a carbon dioxide partial pressure of less than 20 kPa (absolute pressure), and an operating temperature of more than 100 C.

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 acetates, acetic anhydride, and propionic acid. A column bottom pressure of the distillation column is preferably less than 0.255 MPaG.

Process for producing acetic acid are disclosed in which a vapor sidedraw is withdrawn from the second column in the primary purification train. The vapor sidedraw comprises acetic acid and lithium-containing compounds at a concentration of no more than 100 wppb. A bottoms stream that is enriched in lithium-containing compounds, such as lithium acetate, or lithium acetate dihydrate, is also withdrawn from the second column. Advantageously, the vapor sidedraw, or a condensed portion thereof, is directly fed to a metal-exchanged ion exchange resin having acid cation exchange sites to produce purified acetic acid. This prevents displacement of the metals in the ion exchange resin.