Regenerating spent acid produced by HZSM-5 zeolite preparation by bipolar membrane electrodialysis

•Regenerating spent acid produced by HZSM-5 zeolite preparation is proved feasible by BMED.•The pure sodium hydroxide in the base chamber can be recycled.•The recycled acid solution can replace the pure acid solution completely.

A large amount of acid wastewaters containing sodium chloride (NaCl) is usually generated during the production of HZSM-5 zeolite (H-form Zeolite Socony Mobile Five). It can cause contamination of the environment if discharged directly. In this study, a method was reported to regenerate hydrochloric acid (HCl) and sodium hydroxide (NaOH) from the acid wastewater by bipolar membrane electrodialysis (BMED). The effects of operation parameters, such as initial base concentration and current density, on the spent acid solution regeneration were investigated. The results indicated that the initial concentration of sodium hydroxide had little or no effect on the acid wastewater regeneration. But it was also demonstrated that current density have a great influence on the acid wastewater regeneration, and a higher current density applied to the BMED stack usually resulted in lower current efficiency and higher energy consumption. After the operation of BMED process, the comparison between the recycled acid solution and the pure acid solution illustrates the recycled acid solution by BMED process can replace the pure acid solution completely. Therefore, this experiment can not only achieve the elimination of environmental pollution, but also the recycling of resources.