Cracking polymers

A number of cracking/depolymerisation processes are currently operating commercially. These include the Texaco gasification process and the BP Chemicals polymer cracking process. Both have been operating since the mid 1990s. 

The BP Chemicals polymer cracking process is based at Grangemouth in Scotland and uses mixed plastics as the raw material. The reactor uses a fluidised bed which operates at 500 °C in the absence of air, and under these conditions the plastics crack thermally to yield hydrocarbons. These vaporize and are carried away from the bed with the fluidising gas. Solid impurities such as metals from PVC stabilisers accumulate in the bed or are carried away in the hot gas to be captured by a cyclone further along in the plant. PVC decomposes to HCl and this is neutralized on a solid lime absorbent to yield CaCl2 which is disposed of in landfill. The purified gas is cooled to condense most of the hydrocarbon which can be employed as commercially useful distillate feedstock. The light hydrocarbons which are less easy to condense are compressed, reheated and recycled as fluidising gas. 

Polymer cracking process (consortium project, pilot)... 

Polymer cracking MPW 2% 200 (100-175) Pilot 1. Liquid/gas 2. CaCl (landfill) 3. In various residues Uncertain 5% chlorine possible for short periods... 

The Texaco, Polymer Cracking, VEBA and BASF processes all produce mainly liquid organics or gases that replace primary oil- or gas-based resources. However, it has to be acknowledged that both BASF and VEBA have been closed down or will be closed down shortly, and that the other two processes have not yet been realised on a large scale. 

Landfill MSWI Cement kiln Blast furnaces Texaco, VEBA, SVZ, Polymer cracking... 

Macromolecular Symposia Vol.135, Dec.1998, p.113-20 POLYMER CRACKING - NEW HYDROCARBONS FROM OLD PLASTICS... 

Acidic chloroaluminate ionic liquids are excellent media for polymer cracking reactions. With the huge quantities of polymers that need to be disposed of each year the ability to break them down into useful compounds for new synthesis or to use as liquid fuels is extremely important. While certain polymers such as poly(methyl methacrylate) are easily cracked into their constituent monomers that can be reused, the majority of polymers are extremely difficult to crack into useful organic compounds. However, merely dissolving polyethylene in acidic chloroaluminate ionic liquids containing a proton source results in the formation of a mixture of alkenes and cyclic alkenes [48], The key compounds produced are shown in Figure 10.10. 

The earliest works of trying to model different length scales of damage in composites were probably those of Halpin [235, 236] and Hahn and Tsai [237]. In these models, they tried to deal with polymer cracking, fiber breakage, and interface debonding between the fiber and polymer matrix, and delamination between ply layers. Each of these different failure modes was represented by a length scale failure criterion formulated within a continuum. As such, this was an early form of a hierarchical multiscale method. Later, Halpin and Kardos [238] described the relations of the Halpin-Tsai equations with that of self-consistent methods and the micromechanics of Hill [29],... 

During the last years ROMP has been developed to generate self-healing polymers. In these polymers droplets of dicyclopentadiene and of Grubbs-catalyst are incorporated. When the polymer cracks the droplets burst open, the catalyst comes into contact with the monomer and the plastic ideally heals itself [111]. This methodology is still far from application but it does indicate the power of ROMP. 

Liquid hydrocarbons are considered to be the most valuable products of a potential recycling process as they can be used as blends for motor engine fuels. In such a process short-chain hydrocarbons in the gas phase are also produced and they are crucial to provide the heat needed for an endothermic reaction such as polymer cracking, bnt their value is considered low due to their transportation cost. 

Polymer Cracking Process (Consortium Project, Pilot)... 

BP Chemicals has led promotion of a liuidized-bed cracking process that could be used to convert plastic waste into petrochemicals. The Polymer Cracking Process was first tested on a laboratory scale and then on a continuous pilot scale (having a nominal 400 t/yr capacity) at BPs Grangemouth site in the UK. 

J. Bez and T. Nilrrenbach, Feedstock Recycling of Plastic Waste in the Polymer Cracking Process of the BP-consortiim, Fraunhofer-Institut Final Report for APME, 2001. 

In its simplest definition pyrolysis is the degradation of polymers at high temperatures under nonoxidative conditions to yield valuable products (e.g. fuels and oils). Pyrolysis is also referred to as polymer cracking and its main advantages are that it can deal with plastic waste which is otherwise difficult to recycle and it creates reusable products with unlimited market acceptance. 

Ffg. 4.16. SKM fractographs of RCG bands in different polymers. Crack propagation direction is indicated by urroH-s... 

Laminate, aluminium foil, polymer, crack, fracture toughness INTRODUCTION... 

Acrylic polymer crack injection low viscosity in uncured state high degree of penetration cracks with width less than 0.3 mm wet cracks... 

At temperatures above 225°C, polymer cracking defined by Step 1 becomes extremely rapid and takes control of the overall ion extraction process. This... 

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