Regeneration And Modification Of APAP Decolorized Activated Carbon

Powdered activated carbon(PAC)is prerequisite in the process of refining acetaminophen(APAP)crude product,and will subsequently produce a large amount of spent activated carbon(SPAC).SPAC generated in the pharmaceutical industry is a hazardous solid wastes,the factory usually recycled it to reduce pollution and costs.Thermal regeneration is a commonly used regeneration method in the factory,however,there have many problems need to be solved such as high regeneration temperature,low recovery rate and high impurity content of T-RAC decolorized products.Therefore,to address these issues,we firstly improved the industrial thermal regeneration process to increase the recovery rate and lower the regeneration temperature;then the T-RAC is modified to improve its refining performance;finally,we systematically investigated the side reactions in the decolorization section,which will provide some suggestions for improving the decolorization process.This paper will have a contribution for the improving the quality of APAP and reducing production costs.Firstly,to improve the SPAC recovery rate,and achieve energy saving and emission reduction,combined chemical regeneration with thermal regeneration.The effects of parameters such as the type and amount of chemical regenerant,chemical regeneration temperature and time,thermal regeneration temperature and time on the regeneration rate(RE)were studied to obtain the optimal regeneration conditions and processing route.The optimal regeneration conditions of SPAC were as follows: reacted in 0.9 mol/L Na OH-ethanol at 78 ℃ for 3 h,then re-reacted in 10 vt% acetic acid at 100 ℃ for 1 h,finally took the heat treatment at 400 ℃ for 1 h,the RE was 100.5%.The regeneration mechanism was analyzed by the HPLC and TGA,it was found that the phenolate was formed and quickly desorbed in the alkaline regeneration stage,the residue reacted with acetic acid to form phenol and was desorbed by acid and heat regeneration.After the PAC was decolorized and regenerated for five times,the RE only decreased by 3.8%,and the quality of the APAP obtained from the purification process all met the European Pharmacopoeia standards.The microwave-assisted chemical-thermal regeneration method can reduce the alkaline regeneration time,however,the cycle times decreased.The chemical-thermal regeneration method has a better regeneration effect and lower cost compared with industrial thermal regeneration which required 1200 ℃ high temperature.The improvement of T-RAC refines performance by chemical thermal modification method.The effects of parameters such as modifier type,modifier concentration,modification temperature and time on the refinement performance were investigated to obtain the optimal modification conditions.T-RAC was firstly immersed in 100 g/L ammonium sulfate for 24 h,after filtered and dried,it was heat-treated at 600 ℃ for 3 h,which performed the best modification,and the decoloring power of the modified carbon(MAC)was increased by 24.5%.The ammonium sulfate decomposed into ammonium pyrosulfate with strongly oxidizing due to high temperature during the modification process,which can increase the mesoporous pore volume and oxygen-containing groups of MAC,and then improve the decolorization power.After modification,the adsorption capacity of impurities for MAC increased,while the adsorption capacity of APAP decreased.Thence,the thermal modification of ammonium sulfate is conducive to improving product yield and quality,and reducing production costs.Finally,the effect of APAP oxidative coupling catalyzed by decolorized PAC on APAP decolorization and SPAC regeneration was studied.The impurities in APAP products were isolated and identified as the APAP polymers.During the decolorization process,PAC can catalyze the decomposition and oxidative coupling reactions of APAP,and will increase the impurity content of the APAP product.Through the investigation of the effect of PAC chemical properties and reaction conditions on the catalytic reaction,it was found that the oxygen can promote the oxidative coupling reaction of APAP,the reaction mechanism was Michael’s addition,and modification by ammonium sulfate can reduce the catalytic performance of PAC.At the same time,the PAC can also catalyze the adsorpted APAP occurr oxidative coupling reaction during the storation of the SPAC,which can increase the irreversible adsorption,and the reaction mechanism was free radical reaction.Therefore,the PAC catalyzed APAP occurr oxidative coupling reaction was the main reason for the decline in of product quality and the RE for SPAC,the ammonium sulfate modification of the T-RAC or recycle the SPAC by chemical-thermal regeneration are good methods to improve the industrial production level of APAP.