The recovery of acetic acid from wastes of tanning extract manufacture

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Virginia Polytechnic Institute


The tannin extract industry disposes of large volumes of condensate liquors evolved during concentration of weak leach liquors obtained by extraction of wood chips. The liquors are highly corrosive due to acetic acid contained therein along with lesser quantities of other organic substances common to woody materials. Recovery of the acetic acid would be desirable from two standpoints: (1) the value of the acetic acid, and (2) reuse of the acid-free condensate in the manufacturing process.

The purpose of this investigation was to recover acetic acid from the wastes of tannin extract manufacture. An ion exchange process was given primary consideration to accomplish the recovery by adsorption of the acetic acid from the waste liquor with subsequent elution of the acid from the ion exchange material by use of stronger acid.

Tests were conducted using De-Acidite, a synthetic aliphatic amine anion exchange resin produced by the Permutit Company, New York, N.Y.. For all tests 200 ml. of resin were used at temperatures within 20-30°C. A total acid-binding capacity of 19,700 grains CaCO₃/ft.³ was found when De-Acidite was exposed to 0.5 percent acetic acid in batch operation.

Optimum rate of flow determinations in column operation within the range of 1 to 5 gal./ft.²/min. were conducted. Variations of flow rates between these limits failed to produce substantial differences in breakthrough capacities.

To prepare the De-Acidite bed in the ion exchange column between runs regeneration was effected with 1 percent sodium hydroxide. Rinse was by downflow operation until data was obtained which indicated its unsuitability; thereafter backwash rinse was used and found more satisfactory.

The waste liquor used in the investigation was obtained from the 2nd and 3rd effects of a triple effect evaporator employed in the Mead Corporation Plant at Lynchburg, Virginia. Successive exposures of De-Acidite to the waste liquor resulted in sharp reduction of breakthrough capacity, discoloration of the De-Acidite, and deterioration of the resin with the formation of fines.

It was found that the extremely small quantities of tannin present in the waste liquor were the cause of the rapid depreciation of the De-Acidite.