Recuperation of H2SO4 in the hybrid sulphur process using pervaporation

Abstract

In this experimental study the sorption and pervaporation characteristics of commercial Nafion–117 and Nafion–212 membranes with mixtures of water (H2O) and sulfuric acid (H2SO4) were investigated. During experimentation the feed concentration and temperature were varied and quantities such as the flux, selectivity and degree of swelling of the membrane were measured. The main objective of the study was to investigate the separation capabilities of the pervaporation process in order to determine if it can effectively replace the existing sulfuric acid recuperation section in the HyS (Hybrid Sulfur) process. The experimentation was conducted over the entire water sulfuric acid concentration range with the temperatures being varied from 25°C to 55°C. Both the Nafion membranes were found to be highly selective towards water, with the permeate selectivity ranging from 25 to approximately 930 and flux values increased from approximately 7 mol/(hour.m2) at 25°C to approximately 65 mol/(hour.m 2) at 55°C, showing an approximate increase in flux of 900% as the feed temperature of the mixture to the process is increased.. The water can thus be successfully removed from sulfuric acid mixtures by using pervaporation, as it is preferentially absorbed and permeated through both membranes. The permeation of the components through the membrane was modeled, using the solution diffusion model. The predicted values showed good agreement with the experimental measurements obtained. The Suzuki and Onozato model, with an exponential dependence of the diffusivity on concentration, gave the best fit for the experimental data with a standard deviation of 97, compared to that of the Greenlaw and Long models, being 161 and 319, respectively. The separation capabilties of the pervaporation process were compared with the capabilities of the flash separation section proposed in the reference design completed by Savanah Rivers National Laboratory (SRNL) and found to be as effective. It is recommended that the operational and capital costs for implementing these two processes in industry be studied and investigated in detail in order to make an informed decission between these two processes.