Pervaporative recovery of isopropanol from industrial effluents

In this work the recovery of isopropanol from an industrial waste mixture coming from a pharmaceutical process was studied. The waste stream contains water (76.7%), isopropanol (17%), hydrochloric acid (3.4%) and sodium chloride (2.9%), with trace amounts of other impurities. A pretreatment process combining neutralization and distillation was successful to eliminate salts and the acidic character of the waste. The resulting water/isopropanol mixture was convenient for the pervaporative recovery of isopropanol. Using the commercial membrane CMC-CF-23 from Celfa the water content in the isopropanol/water mixture was reduced from the initial 35 wt.% to a final value of 0.3 wt.%, providing a dry solvent adequate for recycling to the production process. Increasing the operation temperature in the range 50–80 °C resulted in higher water fluxes and higher selectivity towards water permeance. For a fixed water concentration value in the feed of 10 wt.%, the water flux increased from 0.36 kg m−2 h−1 (50 °C) to 1.15 kg m−2 h−1 (80 °C) while the water content of the permeate increased from 86.1 wt.% (50 °C) to 93.4 wt.% (80 °C). The mathematical characterization of the membrane performance in terms of flux and selectivity as a function of the activity of the components in the feed mixture and the operation temperature was achieved. A semiempirical model based on Fick's law with concentration dependent diffusivity parameters was applied. The mass transfer parameters needed for the design of a pervaporation process for the dehydration of isopropanol/water mixtures were obtained.