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.