via line 49 to heat exchanger 130 where it is cooled and returned to the bottom of main stripper 124 via line 48 overhead is removed from stripper 131 via line 131t and heated in reflux heat exchanger 138 with a portion being returned to stripper 131 via line 131r and the remainder being passed via line 62 to a compressor 152 and thence to mixer 139 from stripper 131 bottoms are withdrawn via line 51 to divider 132 where they are subjected to limestone treatment from the divider 132 a portion of the bottoms are passed via line 52 to distillation column 137 from column 137 bottoms which consist essentially of organic solvent and low molecular weight polymer are withdrawn via line 54 and overhead which is a mixture of hydrogen c 4 h 2 and organic solvent is withdrawn via line 53 a stream of mostly solvent is removed from column 137 via line 55 and passed to a filtration mechanism 133 in which it is mixed with a portion of bottoms from stripper 131 which is introduced via line 56 from divider 132 from the filtration mechanism a predominantly organic solvent stream is withdrawn through line 57 heated in heat exchanger 136 and.