GB1010302A - Improvements in or relating to a process for the purification of poly-olefins - Google Patents

Abstract

<PICT:1010302/C3/1> Polyolefines containing metallic catalyst residues are purified by first treating the polymer suspension with small quantities of alcohol and thereafter treating the suspension with water in counterflow in at least two stages, the suspension being fed to the lower portion of each stage and rising therein and the water fed to the lower portion of each stage is circulated from the same stage while the water fed to the upper portion of each stage is circulated from the next succeeding stage and/or is fresh water, the proportion of water drawn off from the lower portion of the first stage corresponding to the total quantity of fresh water added to the last stage. Preferably fresh water is only added in the upper portion of the last washing stage. In the apparatus shown in the drawing, polypropylene is produced in reactor 1 in benzene and the contents of the reactor are then passed to decomposer 2 where 2 to 5% of n-propanol is added to 80 DEG C. to convert the catalyst into a soluble form. The contents of the decomposer are then passed to column 3 which forms the first washing stage. Used washing water is pumped into the lower portion A1 of the column and it becomes intimately mixed with the polypropylene suspended in the benzene. The benzene containing phase rises upwards and is washed again in the portion A2 with washing water drawn off at the bottom of column 4, the next washing stage. In the uppermost portion B of column 3, the benzene layer separates from the washing water and is pumped into the bottom of column 4 where it is treated with washing water as in column 3 and then the benzene layer is passed into column 5, the upper portion of which is fed with fresh washing water. The polypropylene can be separated from the benzene by centrifuging or by distillation; in the latter case the benzene distillation may be performed in column 5 by adding steam instead of water, and the polymer obtained has an ash content of less than 0.01%. The alcohol may be recovered by evaporation of the used washing water. The washing water used may contain acids, alkalis, ammonia, compounds which form soluble complex compounds with the catalyst residues, e.g. oxalates, or surfaceactive substances, e.g. soaps. This purification process can be employed in all polymerization processes employing organometallic compounds and metal salts, e.g. polymerization of olefines using Ziegler catalysts, stereospecific polymerization of styrene and other vinyl compounds according to NaHa and in the poly merization of butadiene and isoprene with metal alkyls.