Improvement Of The Quality Of Hexafluoropropene (HFP) By Adsorption

Hexafluoropropylene is the basic material of organic fluoro industry as well as the main co-monomer of many fluorin containing co-polymers. Besides, it is also the intermediate of many fluorin containing chemicals, with its importance second only to tetrafluoroethylene (TFE) in the chemical manufacture of organic fluoro, and its output second only to tetrafluoroethylene and vinylidene fluoride (VDF). In the technological process of tetrafluoroethylene and octafluorocyclobutane pyrolysis to produce hexafluoropropylene, some organic impurities with properties similar to hexafluoropropylene, e.g., C₄F₆, C₃HF₅, C₃H₂F₄, are inevitable. Although very limited in quantity, they will negatively affect the polymerization reactions and quality of polymers, as well as the molecular weight, heat-endurance, climate-endurance, corrosion-resistance, dielectric property, etc. Therefore, in order to obtain high quality hexafluoropropylene-tetrafluoroethylene polymer resin (F-46), the quality of hexafluoropropylene should be very high, normally above 99.99%, with the impurities of C₄F₆, C₃HF₅ and C₃H₂F₄, below 10 ppm, respectively.In this article, possibility of improving the quality of hexafluoropropylene by adsorption was studied based on the analysis of relevant hexafluoropropylene purification technologies, and adsorption theories and methodologies. First of all, experiments on screening adsorbents by fixed bed adsorption column were conducted, considering the difference of adsorption capacities for hexafluoropropene and the impurities contained, from active carbon, silica gel, active alumina, molecular sieve, etc. In this way, active alumina was selected out, which adsorbed well hydric fluorin alkanes and alkenes. Secondly, first-class rectified hexafluoropropene was determined as raw material (which only contained W3 and W5). At the beginning, adsorbent was soaked for 3 h in advance and then feed was added at a speed of 50～100 ml/min (equipment dimension Φ 32/59*3*600 mm), meanwhile, adsorption temperature was controlled between40～60℃, pressure was not higher than 0.3 MPag. High quality hexafluoropropylene of above 99.997% in purity was obtained continuously from the outlet of adsorption column. Finally, a pilot plant (size: Φ 400/500×5×4782 mm) was established to examine the process. High quality hexafluoropropylene (polymer grade) with purity above 99.997% was obtained at about 20-25 kg/h.