Pyrolysis recycled polymers

A pilot plant for the high temperature pyrolysis of polymers to recycle plastic waste to valuable products based on rotating cone reactor (RCR) technology. The RCR used in this pilot plant, the continuous RCR was an improved version of the bench-scale RCR previously used for the pyrolysis of biomass, PE and PP. 9 refs. 

W. Kaminsky, Chemical Recycling of Mixed Plastics by Pyrolysis, Adv. Polym. Technol. 14 (1995) 337-344. 

U. Arena and M. L. Mastellone, Production of multi-wall carbon nanotubes by means of fluidized bed pyrolysis of virgin or recycled polymers, in Proceedings of ENS-European Nano Systems 2005, B. Courtois (ed.), ISBN 2-916187-02-2, pp. 7-12 (2005). 

The Hamburg Fluidized-bed Pyrolysis Process to Recycle Polymer Wastes and Tires... 

Recently the pyrolysis of polymer mixtures has become a focus of interest due to the increasing role of plastics recycling. Many researchers have investigated the thermal decomposition of various polymers in the presence of PVC. Kniimann and Bockhom [25] have studied the decomposition of common polymers and concluded that a separation of plastic mixtures by temperature-controlled pyrolysis in recycling processes is possible. Czegfny et al. [31] observed that the dehydrochlorination of PVC is promoted by the presence of polyamides and polyacrylonitrile however, other vinyl polymers or polyolefins have no effect on the dehydrochlorination. PVC generally affects the decomposition of other polymers due to the catalytic effect of HCI released. Even a few per cent PVC has an effect on the decomposition of polyethylene (PE) [32], HCI appears to promote the initial chain scission of PE. Day et al. [33] reported that PVC can influence the extent of degradation and the pyrolysis product distribution of plastics used in the... 

W. Kaminsky, Pyrolysis of Polymers, ACS Symposium Series, 513, 60-72 (1992). W. Kaminsky, Recycling of polymers by pyrolysis, Journai of Physique IV, 3, 1543-1552 (1993). 

Microwave heating is an appropriate tool for recycling polymer waste. For example, it can be applied to separate metal from polymer/metal laminates by pyrolysis, to depolymerize polyamide and poly(ethylene terephthalate) by solvolysis, or to devulcanize rubber (see Table 1.6). Detailed information on this topic is available in Ref. [19]. 

Pyrolysis of polymer wastes to produce useful gases and liquids is still another route of recycling. ... 

Manufacture. For the commercial production of DPXN (di-/)-xylylene) (3), two principal synthetic routes have been used the direct pyrolysis of -xylene (4, X = Y = H) and the 1,6-Hofmaim elimination of ammonium (HNR3 ) from a quaternary ammonium hydroxide (4, X = H, Y = NR3 ). Most of the routes to DPX share a common strategy PX is generated at a controlled rate in a dilute medium, so that its conversion to dimer is favored over the conversion to polymer. The polymer by-product is of no value because it can neither be recycled nor processed into a commercially useful form. Its formation is minimised by careful attention to process engineering. The chemistry of the direct pyrolysis route is shown in equation 1 ... 

For chemical recycling of plastics refuse, a cascade of cycled-spheres reactors was developed which combined separation and decomposition of polymer mixtures by stepwise pyrolysis at moderate temps. In low-temp, pyrolysis, mixtures of PVC, PS and PE or PS, polyamide-... 

Advances in Polymer Technology 14, No.4, Winter 1995, p.337-44 CHEMICAL RECYCLING OF MIXED PLASTICS BY PYROLYSIS... 

Pyrolysis of scrap tires was studied by several mbber, oil, and carbon black industries [14]. Pyrolysis, also known as thermal cracking is a process in which polymer molecules are heated in partial or total absence of air, until they fragment into several smaller, dissimilar, random-sized molecules of alcohols, hydrocarbons, and others. The pyrolysis temperature used is in the range of 500°C-700°C. Moreover, maintenance of partial vacuum during pyrolysis in reactors lowered the economy of the process. Several patents were issued for the pyrolysis of worn out tires to yield cmde oil, monomers, and carbon black in economic ways [15-18]. The major drawback of chemical recycling is that the value of the output is normally low and the mixed oils, gases, and carbon black obtained by pyrolysis cannot compete with similar products from natural oil. Pyrolyzing plant produces toxic wastewater as a by-product of the operation [19]. 

Among the most frequently used nitrogen containing polymers in electrical, electronic, and automotive applications are PA and ABS. Pyrolysis proved to be a suitable method for recycling plastic waste. 

The cracked gases are cooled and fractionated to remove fuel oil and water (2-5) then compressed (6), processed for acid-gas removal (8) and dried (9). The C3 and lighter material is separated as an overhead product in the depropanizer (10) and acetylene is hydrogenated in the acetylene converter (11). The acetylene converter effluent is processed in the demethanizer system (12-14) to separate the fuel gas and hydrogen products. The demethanizer bottoms is sent to the deethanizer (15) from which the overhead flows to the C2-splitter (16), which produces the polymer-grade ethylene product and the ethane stream, which is recycled to the furnaces as a feedstock. The deethanizer bottoms flows to the C3-splitter (18) where the polymer-grade propylene is recovered as the overhead product. The C3-splitter bottoms product, propane, is typically recycled to the furnaces as a feedstock. The depropanizer bottoms product, C4S and heavier, flow to the debutanizer (19) for recovery of the mixed-C4 product and aromatic-rich pyrolysis gasoline. 

High-temperatnre pyrolysis and cracking of waste thermoplastic polymers, such as polyethylene, polypropylene and polystyrene is an environmentally acceptable method of recycling. These type of processes embrace both thermal pyrolysis and cracking, catalytic cracking and hydrocracking in the presence of hydrogen. Mainly polyethylene, polypropylene and polystyrene are used as the feedstock for pyrolysis since they have no heteroatom content and the liquid products are theoretically free of sulfur. 

Dr John Scheirs is a polymer research specialist with an emphasis on plastic recycling and pyrolysis of waste plastics into fuels. He serves as a consultant for Ozmotech Australia and has worked on the development of their Thermofuel process which can convert unwashed mixed plastics into low-sulfur diesel transportation fuel. He has studied the pyrolysis of HDPE, PP, PET and engineering plastics. 

Professor Walter Kaminsky was bom 1941 in Hamburg and studied chemistry at the University of Hamburg. His thesis was in the field of metallocene chemistry and his habilitation in the field of recycling of polymers by pyrolysis. Since 1979, he has occupied the role of Full Professor of Technical and Macromolecular Chemistry at the University of Hamburg. 

---