In this process, the polymerization solvent is n-hexane, and the catalyst is high active Z-N catalyst. Ethylene and hydrogen are mixed and then enter the first reactor, which is mixed with the catalyst to produce the polymerization reaction. The polymer in the reactor is suspended in hexane in the form of slurry. The polymerization temperature is about 80 ℃, and the polymerization pressure is less than 10 bar. This process can produce products with a density range of 0.942-0.965 G / cm3, the melt index range is 0.2-80, the comonomer is propylene and butene-1, the traditional HDPE and bimodal HDPE are produced, the high-density pipe has excellent performance, and it is suitable for making pressure pipe, reaching PE100 +. The characteristics of slurry reactor continuous polymerization process are: low operating pressure and temperature; double reactor can produce single peak and double peak products by using different forms of parallel connection and series connection; the process has high operating flexibility, fast product brand conversion and low requirements for raw material purity; the comonomer adopts propylene, 1-butene; hexane is used as solvent, and the recovery unit is simple.
The process is characterized by polymerization in an inert hydrocarbon diluent. The process flow is as follows: after the polyethylene (ethylene 99.9%, ethane 0.1%) is sent to the dryer, it enters the reactor together with the circulating diluent composed of n-hexane, and the catalyst adopts the brand with titanium, manganese and triethylaluminum as auxiliary catalyst on the support. Adding a small amount of hydrogen to control the molecular weight, the polyethylene particles are formed in the polymerization. The reaction temperature is 90 ℃, and the pressure is 1.8MPa. The reaction can be carried out in two polymerizers in two steps. The concentration of slurry solid is 34% (mass fraction), and the monomer conversion rate can reach 97%. The polymer flows out from the second reactor and is flashed to a pressure of 0.14MPa. The unreacted ethylene, ethane in the effluent and 2% cyclohexane diluent are compressed twice and cooled to 2.5MPa. The ethane is recovered and recycled in the degassing tower. The slurry left after flash evaporation is centrifuged to recover most diluents, and the solid filter cake is sent to the dryer to reduce the volatile component content to about 5% (mass fraction). The dryer is operated by closed cycle with nitrogen protection. The dried polymer powder is sent to the fluidized bed for drying to remove all hydrocarbon diluents. After drying, the polymer particles are sent to the mixing section for adding various additives and then granulating. (2) The typical representatives of loop reactor process are Phillips process of Phillips company and innovene s process of Ineos company. In Phillips process, isobutane is used as diluent and chromium catalyst is used.
The catalyst should be activated before use. The activated catalyst powder forms catalyst slurry with high-purity isobutane under the protection of nitrogen, and then enters the loop reactor. After the raw ethylene monomer is refined, it is premixed with hydrogen and co monomer Hexene-1, and then injected into the loop reactor, ethylene Polyethylene is formed under the action of catalyst. The axial flow pump keeps the high-speed flow of materials in the reactor and mixes them very evenly, and the reaction heat is uniformly withdrawn from the jacket cooling water. The MI range is 0.15-100 and the density is 0.936-0.972 g / cm3. The characteristics of the loop reactor process are: less equipment, short process, low investment cost; no wax and oligomer, no wall sticking; good shape of powder, easy to transport; reaction heat depends on the reactor jacket cooling water, easy to remove heat, easy to adjust; high requirements for raw materials, need purification; comonomer adopts hexene; isobutane is used as solvent, easy to remove residual solvent. The process flow is as follows: after the fresh polymerized grade ethylene is dried, the molecular weight regulator hydrogen, antifreeze and circulating diluent isobutane are mixed, and then sent to the multi loop continuous process reactor, and the catalyst is supplemented with isobutane and charged into the reactor.
The reaction temperature is 106.7 ℃ and the pressure is 3.9Mpa. The polymer and diluent residual slurry pass through the loop reactor with the help of axial flow pump at the speed of 6m / s. The water in the reactor jacket controls the reaction temperature, and the polymer solid is discharged from the vertical settling port in the loop reactor. Thus the slurry concentration can reach 55%, and the conversion rate is 98% - 99%. After the polymer is discharged, desflash will discharge isobutane and residual monomer into the diluent recovery device. Other solid polymers are mixed with additives and granulated. 2. The typical representative of gas-phase polymerization (gas-phase fluidized bed method) process is the innovation technology of Dow Chemical Company and the innovation technology of innos company. The low-pressure gas-phase fluidized bed reactor is used. The Z / N catalyst and chromium catalyst are used. The purified raw materials are injected into the reactor to produce polymerization reaction under the effect of catalyst storage. The reaction range is 85-110. [=. Under the pressure of 2.41 MPa, the ethylene single-way conversion rate is about 1% ~ 2%.
The removal of reaction heat is mainly through the cooling of circulation logistics. The MI range of production products is 0.01 ~ 150, and the density range is 0.915 ~ 0.970 g / cm3. The characteristics of gas-phase fluidized bed polymerization process are: low operating pressure and low temperature; full density polyethylene can be produced; catalyst system includes titanium system and chromium system; metallocene catalyst; high purity requirements for raw materials, all raw materials should be refined; no solvent is required, low energy consumption, low maintenance and operation costs. The production process is: dry monomer and hydrogen are added to the reactor system together, and raw materials are added