Mechanism And Methods For Recovery Of Acetic Acid From Mixed Waste Acids Of Electronic Industry

To recover acetic acid from the mixed waste acid, generated from an electronicmanufacture industry in the procedure of etching, in Hubei province, China, complexextraction and a successful combination of part neutralization pretreatment/simpledistillation were investigated, respectively. The waste solution containing acetic acid（HAc）, nitric acid （HNO₃）, phosphoric acid （H₃PO₄）, hydrochloric acid （HCl） andhydrofluoric acid （HF）, in which HAc and HNO₃were the major component,was usedas a feed solution for process optimization. Provide a new way for the realization ofefficient recovery of acetic acid from the mixed waste acid.The recovery of acetic acid from the mixed waste acid was investigated by themethod of complexation extraction. Acetic acid recovery rate of95.3%was obtainedwith a system of TBP and kerosene under the optimal conditions: temperature of25℃, extraction equilibrium time of10min, phase ratio between the organic phaseand the aqueous phase of1:1, TBP and kerosene volume ratio of2:1, extraction stagesof5. Nitric acid was extracted simultaneously with the extraction of acetic acid, itwould seriously affect the regeneration of extraction agent. However, scrubbing withalkali solution and hot water before the distillation process, the extractant wasregenerated, with about86.7%HAc recovery and the concentration of HAc recoveredwas303.6g/L.To explore the extraction mechanism of HAc and the effect of HNO₃on HAcextraction, extraction kinetics of HAc and HNO₃from simulated feed consisting ofHAc and HNO₃, were investigated by the constant interfacial cell method under theoptimal extraction conditions. The effects of stirring rate, contact area between twophases, the initial concentration of HAc and HNO₃in aqueous phase on kineticscharacteristics of HAc and HNO₃were investigated. It was found that the extractionrate of HNO₃increased with increasing stirring speed, while the influence of stirringrate on the extraction rate of HAc was relatively flat, perhaps because the process ofHAc and HNO₃extraction with TBP were both controlled by a diffusion mode at lowstirring speed, and at higher stirring speed, the controlling mode of HAc extractionwith TBP was changed into a chemical reaction control mode. The extraction rate ofHAc and HNO₃increased with the increasing of contact area between two phases andthe initial concentration of HAc in the aqueous phase. The extraction rate of HNO₃increased with increasing initial concentration of HNO₃in aqueous phase, while theextraction rate of HAc decreased with increasing initial concentration of HNO₃. This might be because the interaction between HNO₃and TBP was stronger such that HAc,HNO₃would have inhibitory effect on the HAc extraction with TBP before theextraction equilibrium was achieved. The extraction kinetic equation of HAc andHNO₃were established as:,.Further, it was found that the extraction rate of HAc and HNO₃from the rawfeed agreed with the extraction rate of HAc and HNO₃from simulated feed.In order to simplify the extraction process and reduce the regeneration loss, aswell as the requirement of treatment with raffinate and to reduce water consumption,an innovative treatment process was developed to recover acetic acid from the mixedwaste acids. It is a combination of partial neutralization pretreatment and simpledistillation. The operational parameters were optimized by evaluating the effect oftypes and dosages of neutralization alkali, the distillation temperature and time, andthe ratio of acetic acid （HAc） and nitric acid （HNO₃） on the recovery and purity ofHAc. In the partial neutralization pretreatment stage, sodium hydroxide （NaOH） at adosage of12.2g in150mL raw mixed waste acid was found optimal. In thedistillation stage, distillation at140℃for5hours was found optimal. Under theseoptimal conditions,>99%of HNO₃, H₃PO₄, HF, HCl were converted to theircorresponding salts, and>94%HAc recovery was achieved with a purity of99.4%inthe distillate. In the simulated feed experiment, initial concentration of HNO₃in thesimulated feed had a greater impact on HAc recovery. This hybrid method wassuitable for HAc recovery from a mixed acid solution system consisting of HAc andvarious different strong acids, in which HAc was the major component. Under thecondition of invariable initial concentration of HNO₃, there was a positive linearcorrelation between the initial HAc concentration and the HAc concentrationrecovered within the initial HAc concentration of feed ranged from71.6g/L to576.8g/L, and the linear equation was established as: Y=0.9902X+11.3532，R2=0.9934.The method of PNP and a simple distillation was more effective thancomplexation extraction for the efficient recovery of acetic acid from mixed wasteacid because it was simpler and had lower materials consumption with satisfactoryrecovery rate and purity of HAc.