Feasibility of thermal separation in recycling of the distillable ionic liquid [DBNH][OAc] in cellulose fiber production

The objective of this work was to explore the feasibility of 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]) recovery from water solution by thermal separation. The evaporation behavior of pure [DBNH][OAc] was first studied using low pressure distillation in the pressure range of 0.5–2 kPa. The dew points of the distillation products from [DBNH][OAc] were measured in the pressure range of 0.5–15 kPa and modeled using an Antoine equation. Measurements for vapor liquid equilibrium (VLE) of water + [DBNH][OAc] system were carried out using a static total pressure method. The temperature range for the VLE measurement was 303–353 K. The results showed negative deviation from the Raoult's law. The NRTL activity coefficient model was used to correlate the VLE data. The experiments of [DBNH][OAc] product recovery from a solution containing 80 wt.% water were performed using a pilot-scale agitated thin-film evaporator. The performance of the evaporation system was analyzed as a function of the feed flow rate, the evaporator jacket temperature and the operating pressure. The analyses results indicated that the [DBNH][OAc] product with small water content (5–11.7 wt.%) was achieved by low pressure evaporation in a single stage.