Degradation system adipic acid

Table I. Summary of Bench-Scale System Adipic Acid Degradation Results...

The addition of adipic acid to limestone-based FGD wet scrubbers results in improved limestone utilization and enhanced S02 sorption kinetics. The use of adipic acid was first proposed by Rochelle (1) and has been tested by the EPA in pilot systems at the Industrial Environmental Research Laboratory, Research Triangle Park, North Carolina and at the TVA Shawnee Test Facility at Paducah, Kentucky. Adipic acid in the concentration range of 1,000-2,000 mg/1 has been found effective as a scrubber additive. During scrubber operation, however, adipic acid is lost from the system in the liquid and solid phase purge streams and by chemical degradation (2,3). 

The topics presented in this paper include a description of the bench-scale system, the experimental approach, and the results of degradation testing. Also included are the results of batch precipitation experiments designed to study coprecipitation of adipic acid in scrubber waste solids. 

The desire to simulate the operation of full-scale FGD systems which would allow results from the bench-scale system to be used to anticipate adipic acid degradation in larger systems, and... 

With this information, the adipic acid degradation rate and other aspects of operation with adipic acid can be related to specific process variables. And, results obtained with the bench-scale system can then be used to anticipate adipic acid degradation rates in full-scale systems. 

The chemical adipic acid degradation rate constant, K(j, was assumed to be 0.5 M-1. This is typical of the degradation expected at pH 5.1 for systems in which manganese is present at concentrations of about 20 ppm. 

Heserole, F.B. Lewis, D.L. Nichols, A.W. and Rochelle, G. "Adipic Acid Degradation Mechanism in Aqueous FGD System," Final Report, EPA-600/7-79-224, Environmental Protection Agency, Research Triangle Park, NC, September, 1979. 

Quantity and Concentration. Depending on the operating parameters, the degree of degradation, and the tightness of the liquor loop, the quantity of adipic acid required is quite small in relation to the alkali feed. At Shawnee, where a filter is normally used as the final sludge dewatering device, the adipic acid consumption rate is usually less than 10 lb/ton of limestone fed to the system, and sometimes as low as 2 lb/ton of limestone. These values correspond to only 0.6 to 3.0 tons of adipic acid per day for a 500 MW plant. 

Because of the obvious identity in average chemical group composition of both polymers, it should be possible to reconcile both kinetic laws [188]. However, nylon-6,6 data have been obtained at high water concentrations and relatively low temperatures, and data on nylon-6 are in the opposite situation. Degradation reactions of nylon-6,6 through adipic acid chain ends (see Section 3.3.3.3) complicate the interpretation of kinetic data at higher temperatures. Schaffer, McAuley et al. [189] have recently obtained experimental data on the nylon-6,12 system, which does not present these problems, and these kinetics are now much better understood. 

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