PET bottles processing

The test results for PET bottle processing arc shown in Table 3.2. The optical sensing mechanism for glass was reported to be compatible for PET bottles without recalibration. Smaller one liter PET bottles Jammed at the chute entry, as previously indicated. Ninety-five percent of the processed clear PET bottle stream contained clear bottles while 100% of the color stream contained colored PET bottles when considering bottle runs where alignment was not a problem. An estimate of the mass flow rate can be made using 0.113 lbs/1 liter bottle and 0.163 lbs/2 liter bottle. 

Table 3.5 Cost Analysis Summary of Rutgers PET Bottle Processing Plant (Phillips and - Alex, 1990]...

The principal solvolysis reactions for PET are methanolysis with dimethyl terephthalate and ethylene glycol as products, glycolysis with a mixture of polyols and BHET as products, and hydrolysis to form terephthalic acid and ethylene glycol. The preferred route is methanolysis because the DMT is easily purified by distillation for subsequent repolymerization. However, because PET bottles are copolyesters, the products of the methanolysis of postconsumer PET are often a mixture of glycols, alcohols, and phthalate derivatives. The separation and purification of the various products make methanolysis a cosdy process. In addition to the major product DMT, methanol, ethylene glycol, diethylene glycol, and 1,4-cyclohexane dimethanol have to be recovered to make the process economical.1... 

Contamination problems act as a barrier to the recycling of PET bottle waste. The presence of impurities that generate acid compounds at the high temperatures reached during the extrusion process prior to blow molding is a major problem in the reprocessing of PET because chain cleavage reactions are acid catalyzed. EVA... 

Polybutylene terephdialate (PBT) has been produced from PET scrap by transesterification widi 1,4-butanediol.1 In die process, classified and cleaned polymer Bake from postconsumer PET bottles is reacted witit 1,4-butanediol in an extruder. PBT is used as an engineering plastic. Ethylene glycol and tetrahydrol uran produced as by-products are recovered by distillation. 

Ammonolysis of PET involves the reaction of PET with ammonia at temperatures of 70-180°C, usually under pressure in EG. The ammonolysis of PET postconsumer bottles has been canied out at temperatures in the range of 120-180°C and a pressure of ca. 2 MPa for 1-7 h. The TPA diamide formed may be converted to terephthalonitrile. Terephthalonitrile may be hydrogenated to form p-xylylenediamine and l,4-bis(aminomethyl)cyclohexane.12 A low-pressure PET ammonolysis process in EG has been developed. The process is catalyzed by 0.5 wt% zinc acetate at a temperature of 70°C and a PET-NH3 ratio of 1 6 (w/w). The yield of TPA diamide was 87%. 

In a continuous process, ground PET bottles (830 parts) in an aqueous slurry were pumped into an autoclave equipped with a stirrer and maintained at 450-550 psig pressure and 191-232°C. Ammonium hydroxide (300 parts) solution consisting of water (7857 parts), ethylene glycol (493 parts), and ammonium sulfate (918 parts) was introduced into the reactor. The retention time in the reactor varied from 5 to 45 min. The aqueous diammonium terephthalate and edtylene glycol solution was withdrawn from the reactor and filtered while hot to remove solid impurities such as pigments, pieces of metal caps, labels, and cap liners. Hie filtrate was acidified widi sulfuric acid solution to liberate the TPA product. Hie recovered TPA usually had a purity of 99% or higher. 

In a joint project between the Waste and Resources Action Programme (WRAP) and Coca Cola Enterprises in the UK it proved possible by redesigning bottle production to reduce the weight of 500 ml PET bottles by 8%. These lighter bottles meet all of the required performance standards, and when production reaches the full scale of 700 million p.a. will save 1400 tonnes of PET. This may seem to be a small improvement, but lightweighting of drinks bottles has been a continuous process for many years, and yet progress is still possible. 

Terephthalic acid manufacture, platinum-group metal catalysts in, 29 622 Terephthalic acid PET bottle resin process, 20 48-50... 

The lower investment and running costs of the continuous SSP process, which does not require the high temperatures and vacuums associated with the melt phase. The cost splits for a 600 t/d continuous PET bottle grade plant are shown in Figures 4.2 and 4.3. The investment costs are some five times lower and the process costs approximately half for the SSP process when compared to the melt phase. 

Degradation and side reactions are limited in the solid state due to the lower processing temperatures used. PET, for use in bottle applications, is a notable example. Small concentrations of acetaldehyde (AA), a by-product of degradation and side reactions in PET, can affect the taste of carbonated soft drinks and mineral water. The SSP process is the best means of achieving PET bottles with acceptable levels of AA. 

Indeed, the increasing industrial significance of the SSP process can be directly related to the success of the PET bottle. PET was introduced for use in drinking bottle applications in the mid 1970s and the SSP process was required to reduce the AA level below that achievable in the melt phase while increasing... 

As an example for process succession D, the Buhler bottle-to-bottle process fulfils all of the requirements listed above. Acetaldehyde levels are even below those of virgin PET (Figure 4.23). 

Figure 4.23 Schematic of the Buhler PET bottle-to-bottle recycling process...

The dual treatment in the Buhler botde-to-bottle process is an important aspect in food safety considerations. The bulk of the contaminants are removed in the extruder. However, the SSP process provides a back-up to remove any residual contaminants, which are now homogeneously distributed in the PET pellets. The cleaning becomes a well-defined and predictable diffusion controlled process, which is defined by pellet diameter, treatment temperature and time. The same parameters also regulate the SSP process. For products with similar reactivity, a known increase in molecular weight during the solid-state process will also provide a known cleaning efficiency. 

This section will look at seven processes to convert post-consumer PET bottles to raw materials suitable for use to make new food and beverage bottles. The processes are as follows ... 

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