Polyethylene and Polypropylene Production
SEPCOR provides Adsorbents and Catalysts for Olefin Processing. We have solutions for cryogenic ethylene and propylene feed prepurification and dehydration with 3A molecular sieves that are specially formulated to withstand the rigors of olefinic service. In order to process olefins and protect downstream catalysts, feedstocks to the primary and secondary cracked gas purification systems must be stripped of trace impurities. SEPCOR Adsorbents and Catalysts are specially formulated for your specific application in Ethylene, Propylene, Polyethylene and Polypropylene processing.
Ethylene/Polyethylene Processing and Purification
Ethylene/Polyethylene feedstocks often come from refinery offgas or salt cavern storage and must be purified to chemical grade prior to usage. Typically these feedstocks must be purified of CO, O2, H2O, NH3, RSH, Oxygenates, CO2, H2S, COS and mercury. This is accomplished typically by first taking the feedstock through a catalyst feed converter where acetylene is removed. Next a copper oxide type catalyst removes CO and O2. Water is then removed with a 3A type molecular sieve followed by specially promoted adsorbents to remove NH3, RSH, oxygenates, CO2, H2S, COS, and then a special carbon to remove mercury to prevent the downstream aluminum heat exchanger from corroding (Fig. 1)
Propylene and Polypropylene from the same FCC source or Dome Storage are purified to produce chemical grade propylene which is further processed to make polypropylene (Fig 2). Here the propane/propylene mixture is taken through a propane/propylene splitter to fractionate off the propane. The propylene is then dehydrated with 3A molecular sieves to remove water. Specially promoted adsorbents then remove oxygenates, NH3, RSH, CO2, COS, and H2S. A special catalyst removes arsine and finally mercury is removed with a specially promoted carbon.
In addition to purification of the ethylene and propylene feedstocks, special adsorbents are required for the production of High Density Polyethylene(HDPE), and Linear Low Density Polyethylene(LLDPE). In HDPE production, polymerization occurs in a vessel filled with a either a cyclohexane, hexane or isobutane solvent. These solvents are meant to control the heat generated from the reaction during polymerization. Trace contaminants need to be removed from the feed streams to the reactor, the comonomer streams and the diluent streams. In many cases adsorbents are employed to protect the very expensive and high activity Ziegler-Natta catalysts.
LDPE or Low Density Polyethylene requires ethylene and oxygen/peroxide and heat to produce the polymer. The reactor is operated adiabatically whereas the feed rates and catalyst rates are controlled. Product is drawn off as LDPE. Adsorbents are used to for feed pretreatment.
Linear Low Density Polyethylene(LLDPE) is produced from a Ziegler-Natta type catalyst and alpha olefin comonomers. Typically, LLDPE is produced in processes like the gas phase EXPOL or UNIPOL type processes where butene-1 employed. Solution type processes like the DOW/DUPONT process use octene-1, Hexene-1 comonomers. The Phillips process uses hexene-1. Hydrogen is added to regulate the reaction and molecular weight of the reactants. Adsorbents are used for feed pretreatment, N2, H2, recycle solvent streams and the working solutions.
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