Liquid Phase Contact

The catalyst makes contact with melted MWP. Good contact between plastic particles and the catalyst is one of the key points for process development. Melted plastics can be degraded in a fluidized-bed reactor or a fixed-bed reactor. Since the usage of fixed beds leads to problems of blockage, scale-up to industrial size is not feasible. However the fluidized bed has a number of special advantages for catalytic degradation of plastics, because it is characterized by a good contact between catalyst and plastics as well as an excellent heat and mass transfer [4], In addition to selection of a snitable reactor, the catalyst used is very important in the process. 

Catalytic degradation involving liquid phase contact of common plastics, such as PE and PP has already been tested extensively [5-10], The most commonly nsed catalysts 

On the other hand, activated carbon may be considered as a catalyst in the cracking of waste plastics. This is because it is a neutral catalyst with a high surface area and, therefore, it might be more resistant to impurities and coke formation. It has been reported that Pt-, Fe- and Mo-supported activated carbon catalysts were effective for the pyrolysis ofPEandPP [11,14,15]. Use of metal-supported activated carbon catalysts has enhanced the formation of aromatics via dehydrocychzation of straight- or branched-chain radicalic intermediates. 

Although a large variety of catalysts have been used, even if performing well, many can be uiu-ealistic for MWP. Thus, although the option based on cracking of plastic wastes by direct contact with catalyst seems the simplest way, the catalyst cost can affect the economics of the process considerably 

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The effective friction loss, or gas-phase contacting power, is easily determined by direct measurements. However, the liquid-phase contacting power, supplied from the stream of scrubbing liquid, and the mechanical contacting power, supplied by a mechanically driven rotor, are not direc tly measurable the theoretical power inputs can be estimated, but the portions of these quantities effectively converted to contac ting power can only be inferred from comparison with gas-phase contacting power. Such data as are available indicate that the contributions or contacting power from different sources are directly additive in their relation to scrubber performance. 

The power input from a liquid stream injected with a hydraulic spray nozzle may usually be taken as approximately equal to the product of the nozzle feed pressure pf and the volumetric hquid rate. The liquid-phase contacting power Pe may then be calculated from the following formulas ... 

Materials in the whole system must be appropriate, that means reactor and piping for ozone gas as well as for ozonated water must be chosen carefully. For example, the material of the reactor and sampling system, especially the seals, has also to be chosen to avoid not only corrosion from ozone, but adsorption of the compound(s) being studied. It is advisable to let the liquid phase contact only glass and stainless steel. In stirred reactors for example, the stirrer seals (unless the stirrer is a magnetic bar) and all connectors for piping are best placed at the top of the reactor, so that the liquid does not come in contact with them. 

Catalyst/sorbent with liquid phase contact... 

Shiraga and Uddin [6] carried out thermal and catalytic degradation of mixed plastic containing PVC. The solid acid catalyst employed in this study is silica-alumina with a chlorine sorbent such as goethite hydrated Iron Oxide FeO (OH). The dechlorination ability effects of contact mode, liquid phase contact, (LP) or vapor phase contact (VP) were studied. Dechlorination results show that the vapor phase contact was more effective for chlorine removal. 

Liquid-phase contacting power. This is given by the equation Pl = pKGl/Gg). where pf is the nozzle feed pressure in kPa, and Ql and Qo are the liquid and gas flow rates, respectively, in m /s. 

Rewetting of hot surface. In this case, the liquid phase contacts a hot surface and rewets it, with the accompanying formation of vapor. Examples here are the quenching of hot metal objects in metal forming processes and the rewetting of hot fuel elements in a nuclear reactor following a loss-of-coolant accident. 

Catalytic cracking is the cracking of heavy hydrocarbons using catalyst. The polyolefins such as PP and PE are recycled through this method. In the laboratory scale setup, these reactions are carried out in a flow reactor. There are two modes of catalytic treatment, liquid phase contact and vapor phase contact. In first case, the catalyst is in contact with molten polymers and here the catalyst reacts mainly with oligomers. In vapor phase contact, the catalyst is in contact with thermally degraded polymer [27]. 

Herskovitz et al. [30], Sedriks et al. [72], Satterfield et al. [70] have proposed diagnostic procedures to determine whether or not liquid phase contacting and catalyst wetting may affect the apparent reaction rate. The first procedure, suitable for low conversions of the gas phase reactant, compares the apparent reaction rate for... 

Considering the difficulty of observing the shape of the moving interface in the very vicinity of the contact line, the flow conditions on both sides of the interface, which demonstrate the effect of the contact line motion in visible dimensions, were investigated. The flow of two liquid phases contacting each other along one fluid interface in a capillary tube was carried out at a constant velocity. Velocity fields of both liquids were determined simultaneously at the moving interface in order to obtain some information about the effect of the motion of a meniscus on tube flow, its extension and the flow behaviour of the fluid interface itself. 

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