invention without restricting its scope a membrane filtered fluoropolymer dss alfa laval pore size 0 15 u03bcm libob solution is used for all experiments the libob being produced as described in de c 19839030 production of solvate free libob crystallisate evaporative crystallisation crystallisate separation at approx 100 u00b0 c 5064 g of a 17 solution of libob in propylene carbonate pc having a water content of 230 ppm were evaporated at approx 8 to 10 mbar and approx 120 u00b0 c after distilling off approx 0 8 kg of pc the vacuum was broken for a short time and 1 g of libob crystallisate according to the invention was added during the course of the further vacuum distillation process the libob solution became turbid 2 34 kg of pc were distilled off in total the vacuum was broken and the suspension formed was cooled to 110 u00b0 c whilst stirring then the suspension was discharged onto a heatable sintered glass filter and filtered the filtration time was around 3 minutes the crystallisate was washed three times with 100 ml of preheated toluene each time and vacuum dried at a temperature of 80 to 90 u00b0 c the residual pc content is below 0 2 wt the dust content is below 1 production of a libob 0 2 pc solvate evaporative crystallisation crystallisate separation at room temperature 639 g of a 16 1 solution of libob in propylene carbonate pc were introduced into a dry 1 liter.