1.There are two recycling methods for PET beverage bottles: chemical recycling and physical recycling. Chemical recovery is a method of depolymerization of PET waste bottles under certain reaction conditions to produce useful chemicals, such as low-grade gasoline.
Physical recovery method is a method of separating, crushing, washing and drying waste PET bottles for re-granulation. Physical recovery methods mainly include the following two methods: first, the waste PET bottles are cut into pieces, HDPE, aluminum, paper and adhesive are separated from the PET, and the PET fragments are washed, dried and granulated. The second is to use mechanical method to separate the non-pet bottle cap, bottom, label and other magazines on the waste PET bottles, after washing, crushing and granulating.
In the former process, stones, wood, other plastics, and colored PET bottles are removed manually. Recycled PET must not contain PVC impurities, because its presence is a key factor affecting the color of PET.
When the mixing amount of PVC is low, it can be separated on the conveyor belt by manual means. That is to say, PVC and PET bottles will produce different physical phenomena in the stressed part under the action of torsion. When the PVC bottle shows opaque traces while the PET bottle doesn't, separation can be carried out. Some companies also use different melting points of PVC and PET to pass the broken PET and PVC fragments through a conveyor belt with a heater to control the temperature. After the PVC is melted, it sticks to the conveyor belt, which can be separated from the PET. The separation of iron USES a ferromagnetic separator.
Some PET bottles are broken only once, and some are broken by coarse crushing and then subdivided into fragments with the size of 1.0-1.5cm. The outlet of the crusher is equipped with a sieve with an aperture of 1.0-1.5cm to control the size of debris.
Cleaning and impurity separation are the key technologies to obtain high quality PET regeneration. Bottles usually use the plastic PE or index sign, paper label adhesives are available, and also can stick in the bottle blowing process, after the PET bottle broken, part of the label was broken into pieces, some still clung on PET pieces, to break the subsequent PET usually adopt blower and cyclone separator separation device, can remove about 98% of loose pieces of label, also can use extraction separation device separation tower, broken pieces of PET vertical separation from the top to join, debris and updraft form upstream, using PET and label debris density difference, the label is pumped to PET out from the bottom of the separator, In order to ensure the efficiency of label separation, more than two sets of separation devices can be used in production.
The purpose of washing is to remove the adhesive, ash, and residue from the original bottle. Washing the 80-100 oc hot water to soften or dissolved adhesive labels and EVA adhesive or other types of base adhesive, so as to prevent loss of bonding agent and adhesion of PET pieces, to add additive in water, such as alkali, emulsifying agent, or other special chemicals, cleaning fluid generally by the factory according to the sources of waste bottle and the formula composition and content is determined by the adhesive properties, cleaning fluid can filter the impurities reheating cycle after use, wash in the special cleaning tank with agitator, in order to guarantee the effect of cleaning, washing secondary washing process can be applied.
2.The separation of the base is made use of the HDPE density of the base and the different characteristics of PET density to separate it. Separation is carried out in the carrion wash tank, HDPE fragments overflow from the top of the tank, and sinking PET fragments escape from the bottom of the tank. Some use hydrocyclone instead of flotation tank separation, the separation effect is better. The moisture content of PET fragments is usually reduced to 2% by centrifugal dehydrator and then dried by belt or tube dryer to 0.5%.
Aluminum impurities cannot be contained in PET, and even small amounts of aluminum impurities will affect the transparency of recycled PET. Therefore, aluminum content in recycled PET should be lower than 50×10-6. The simplest way to separate aluminum is to manually remove the aluminum cover and ring before crushing or to reduce the aluminum content to 100×10-6 by electrostatic separation. If the PET fragment is further purified through the metal detection separation system, the aluminum content can be lower than 5×10-6.
There is little difference between recycled PET extruding granulation and original PET extruding granulation except some difference in feed. Single screw or double screw extruder can be used for extruder granulation, but the design must consider that the feeding pressure of the traditional extruder is too large, use the screw with larger feeding size, if using double screw extruder is better.
The latter process: the recycling method is to separate the non-pet components from the PET bottles, and then break them up for recycling. It is the first to manually separate rocks, wood and other plastics, and colored beverage bottles. PVC bottles can be separated by manual selection or PVC separation equipment. The separation of metal iron can be carried out by magnetic separator. After passing through the conveyor, the beverage bottle enters the cleaning machine. The bottle enters the processing production line vertically. The bottle cap and pull ring are removed by the ring removing machine and the cap removing machine.
Then, 100ml of boiled water is injected into each waste PET bottle to dissolve the remaining drinks in the bottle. Meanwhile, the bottle is clamped and hung up. Remove the bottom of the bottle after washing and release the water. Crushing is just like the equipment in the first process. PET bottle fragments are dried by a continuous dryer until the moisture content is less than 0.05%. Extrusion granulation is the same as the bottom of a recovery method.
The above two recycling technologies are adopted by factories. The process has its own characteristics. The first method is easy to form large-scale production, but the separation technology is more complex, separation equipment is more, the investment is larger. The second method has a higher product purity, less equipment and less investment, but it is only applicable to complete beverage bottles without damage. Crushed or damaged beverage bottles need to be separated and recycled by other methods. As a matter of fact, waste plastic bottles should be crushed and bandaged before being transported in consideration of economic rationality. Secondly, the recovery of the bottle base is basically carried out according to the first method, so the second method has great limitations.
In China, recycled PET is used to manufacture colored pesticide bottles instead of glass bottles to reduce product breakage. Overseas use of recycled PET manufacturing PET packaging. Recycled PET is used as the intermediate material of three-layer packaging bottles in Australia. Recycled PET is widely used to produce 3-17dtex staple fiber, which is used as non-woven fabric. The us also USES recycled PET to produce 6.6-9.9dtex hollow fibers for use as wadding material.
Recycled PET can also be used for apparel fibers. For example, Dyersburg fabric factory in the United States USES 100% waste PET bottles for recycled PET slices to produce flannelage cloth, and WellmanFiber in the United States develops outdoor fabrics. The blended rate of recycled PET fiber and other fibers can reach 89%. Patagonia USES recycled PET fiber to blend with other fibers to produce sportswear with a blend rate of 80%.
Depolymerizing the PET at the boiling point of EG and at a pressure of 0.1mpa, depolymerizing the PET to produce hydroxy ethyl terephthalate (BHET). After filtration, filter residue and additives are removed to make BHET react with methanol. At the boiling point temperature of methanol and the pressure of 0.1mpa, DMT and EG are generated through transesterification.
After distillation, DMT and EG are separated, and then the DMT is refined through recrystallization. EG is purified by distillation and methanol can be recycled. The recovered DMT and EG are 99.99% pure, and the production cost is comparable to that of the common DMT and EG methods. DMT can be converted into pure TPA (terephthalic acid) to make bottle grade PET resin.