Waste plastic recycling technology

Second, the waste plastic cleaning and drying

Waste plastics are often contaminated with oil, waste, sand, etc. to varying degrees. These impurities can seriously affect the quality of recycled plastic products. Therefore, waste plastics must be cleaned. The methods of cleaning are manual cleaning and mechanical cleaning.

(1) Manual cleaning and drying Manual cleaning depends on the product type and the degree of contamination to determine the specific cleaning method. General agricultural film and packaging film cleaning process is as follows: warm alkali cleaning (degreasing) - brushing - cold water rinse - dried. The process of cleaning the membranes and containers for packaging toxic chemicals is as follows: Lime washing (neutralization and detoxification) - Scrubbing - Rinse water rinsing - Drying

(2) There are two kinds of intermittent cleaning and dry cleaning for mechanical cleaning and drying. In intermittent mode, waste plastics are first soaked in a hot alkaline aqueous solution for a certain period of time, and then the films are rubbed against each other by mechanical agitation. The method of hitting and removing the contaminated dirt to remove the washed film. Continuous is an intermittent improvement. The chopped waste plastic is continuously fed and the cleaned film is continuously discharged.

Third, renewable granulation

The washed and dried wastes are generally pelletized prior to molding. After the waste plastics are used, they all produce different degrees of aging, and the auxiliaries contained also have different degrees of losses. Therefore, it is often necessary to add certain auxiliaries before granulation, especially for soft polyethylene plastics. It is often necessary to add plasticizers and stabilizers. Since recycled plastics are often made up of a mixture of many different colors of waste, it is generally necessary to add dark coloring agents during the reprocessing time. It should be noted here that the use of lower-priced species should be considered when adding additives. The prices of products are generally low.

IV. Pyrolysis Recovery of Waste Plastics

There are many methods for recovering oil and gas by thermal cracking, such as melting tank method, screw type thermal decomposition method, reaction tube evaporator method, fluidized bed reactor method, catalytic cracking method, etc. Different methods can be used for thermal cracking of different types of plastics. Recycling is as follows.

1. Melting tank method

The melting tank method uses a molten salt as the heating medium to heat and decompose waste plastics. After the decomposed hot steam passes through an electric dust collector, it is condensed into a decomposition product in the condenser. This method can be used in polyethylene, and the random polymerization Propylene, polypropylene, polystyrene.

2. Screw thermal decomposition

The screw-type thermal decomposition method can be used for the recovery of polyethylene, polypropylene, polystyrene, and polymethyl methacrylate. A key part of this type of device is a screw-type thermal decomposition reactor. External electric heating is generally used and the temperature can reach 500 to 550 degrees. The material is preheated with a microwave heater before entering the screw pyrolysis reactor. The reaction products were recovered by light oil and heavy oil.

3. Reaction tube evaporator method

The reaction tube evaporator method is used for the recycling of waste plastics which are uniform raw materials and easily become liquid monomers. Applicable waste plastics include atactic polypropylene (APP), polystyrene and the like.

4. Fluidized bed reactor

Fluidized bed reactor method has been used in a variety of devices for the recovery of waste plastic oil, this method can be applied to: polypropylene, cross-linked polyethylene, polypropylene, polyvinyl chloride and other plastics.

5. Catalytic cracking

The catalytic cracking method is a method for low-temperature oiling of waste plastics using a suitable catalyst, and is generally used for the oilification of a single type of plastic. Suitable plastics include polyethylene, polypropylene, and polyvinyl chloride. Due to the use of low-temperature oiling, the oil yield of this method is relatively high. In addition, the use of the catalyst makes the resulting oil more homogeneous and the added price of the product is higher.

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