HDPE recycling
HDPE is the fastest growing segment of the plastic stockpile recycling market. This is mainly due to its ease of reprocessing, minimal degradation properties and its extensive use in packaging applications. The main recycling is the reprocessing of 25% of recycled materials, such as post-consumer recycled content (PCR), with virgin HDPE to make non-food contact bottles.
In this process, the polymerization reaction solvent is n-hexane, the catalyst is a highly active z-N catalyst, ethylene and hydrogen are mixed into the first reactor, mixed with the catalyst to carry out the polymerization reaction, and the polymer in the reactor is suspended in the form of slurry in the hexane The polymerization temperature is about 80°C and the polymerization pressure is less than 10 bar. This process can produce products with a density range of 0.942 to 0.965 g/cm3 and a melt index of 0.2 to 80. The comonomers are propylene and 1-butene. Traditional HDPE and bimodal HDPE, high-density pipe with excellent performance, suitable for making pressure pipe, reaching PE100+. The characteristics of the continuous polymerization process of the slurry tank reactor are: low operating pressure and operating temperature; the double tank reactor can produce unimodal and bimodal products by adopting different forms of parallel and series connection; high process operation flexibility, product brand conversion It is fast and does not require high purity of raw materials; propylene and 1-butene are used as comonomers; hexane is used as solvent, and the recovery unit is simple. The characteristic of this process is that the polymerization is carried out in an inert hydrocarbon diluent. The technological process is as follows: the polymerized ethylene (99.9% ethylene, 0.1% ethane) is sent to the dryer and then enters the tank reactor together with the circulating diluent composed of n-hexane. The catalyst adopts the carrier containing titanium, manganese, triethyl The base aluminum is the grade of the cocatalyst. A small amount of hydrogen is added to control the molecular weight, and the polymerization reaction forms polyethylene particles. The reaction temperature is 90 °C and the pressure is 1.8 MPa. The reaction can be carried out in two polymerization kettles in two steps, and the production concentration is 34% (mass fraction) The slurry solid, the monomer conversion rate can reach 97%. The polymer was flashed from the second reactor to a pressure of 0.14MPa, and the flashed unreacted ethylene, the ethane in the discharge and the 2% cyclohexane diluent were compressed and cooled to 2.5MPa twice, and the gas was removed. The stripper recovers the ethane for recycling. The slurry left after flash evaporation is centrifuged to recover most of the diluent, and the solid filter cake is sent to the dryer to reduce the content of volatile components to about 5% (mass fraction). The dryer is operated in a closed loop with nitrogen protection.