Abstract: A problem of the invention is to provide a process of producing high purity terephthalic acid by selectively recovering p-toluic acid in wastewater which has hitherto been discarded and using it as a raw material of terephthalic acid.

Abstract: A separation system has a distillation column, an overhead vapor supply pipe connected to the top of the distillation column, first and second branch pipes branching from the overhead vapor supply pipe and a superheater connected to the first branch pipe. A separator downstream of the superheater has a separation membrane for separating overhead vapor from the top of the distillation column into permeable vapor and nonpermeable vapor by allowing only a selected portion of the overhead vapor to permeate the separation membrane. A reflux unit has a condenser connected to the second branch pipe for cooling a portion of the overhead vapor into a liquid and a gas-liquid separator for separating gas from the liquid produced by cooling and returning the separated liquid into the top of the distillation column.

Abstract: In a process for producing an aromatic carboxylic acid, it is a dehydrating process which can achieve compactification of a step for removing water from a mixture of acetic acid and water produced in the production process, and which can reduce the consumed energy. In a production process of an aromatic carboxylic acid having an oxidation reaction step for producing a slurry of an aromatic carboxylic acid by carrying out liquid-phase oxidation reaction of an alkyl aromatic compound with an oxygen-containing gas in a solvent containing acetic acid in the presence of an oxidation catalyst, at least a portion of a mixture containing acetic acid and water produced in the production steps is separated into a permeable gas mainly comprising water and nonpermeable substances mainly comprising acetic acid, using a separation membrane having water selectivity.

Abstract: A screen bowl type centrifugal separator which can not only eliminate the problem of the productivity being lowered resulting from the occurrence of clogging with the crystals in the screen part, but also minimize the amount of leakage of the object to be treated in the screen part. Inside of the hub (41) of the screw conveyor (40), a cleaning liquid receiving part (43) which receives the cleaning liquid for the cleaning nozzle (45) is provided, and further, in the cleaning liquid receiving part (43), a residual layer crystal cleaning liquid receiving part (46) which receives the cleaning liquid for cleaning the residual layer object to be treated in the screen part (30) is provided, being partitioned independently of the inside of the cleaning liquid receiving part (43).

Abstract: In order to provide a method for producing a high-purity aromatic dicarboxylic acid such as terephthalic acid with high energy efficiency using a simplified process, in the method for producing terephthalic acid according to the present invention, solid-liquid separation and cleaning steps are carried out using a single device, and in a step for removing any liquid adhered to terephthalic cakes by evaporation, internal energy stored in the terephthalic acid cakes and/or the liquid adhered thereto is used at least part of the energy for evaporating the liquid adhered to the cakes.

Abstract: A process for producing aromatic dicarboxylic acids which comprises subjecting an aromatic compound having an alkyl substituent or a partially oxidized alkyl substituent to liquid-phase oxidation with a molecular oxygen-containing gas in a reaction solvent in the presence of a catalyst, then conducting solid-liquid separation of the formed slurry containing crystals of the produced aromatic dicarboxylic acid, and recovering the crystals, wherein when carrying out solid-liquid separation of the slurry by continuously supplying it to a screen-type centrifugal separator having a screw conveyor disposed therein, a screen with an opening size that allows partial escape of crystals in the supplied slurry through the screen openings is used as the screen of the screen-type centrifugal separator. According to this method, clogging of the centrifugal separator is prevented and solid-liquid separation can be carried out efficiently.

Abstract: An object of the invention is to provide a process of producing a compound for forming a slurry under pressure and/or heating, which is quite economical on an industrial scale such that a drying machine is not necessary and that it is possible to reduce energy to be used for drying.

Abstract: Carbon black is introduced into a granulating machine 3 through an inlet 1 and water is introduced into the same through an inlet 2 to prepare granulated carbon black, which is fed to a cylindrical rotary type dryer 5 through a line 4 and is dried. A product of carbon black is discharged through a line 6. Temperature in the dryer 5 is measured by a plurality of thermometers 10. A combustion control device performs the arithmetical processing of temperature data to obtain the initial point at which the state of the carbon black is changed from the constant rate of drying to the falling rate of drying. The control device controls each flow rate of fuel supplied from each line 7 or 8 to burners 9 for the front and rear half portions of the dryer by using the critical point and the temperature of the carbon black at the outlet of the dryer, whereby a temperature profile for the carbon black in the dryer 5 can be made stable for a long time.