Catalytic reforming waste

A number of refinery processes require the use of a fixed-bed catalyst These processes include catalytic reforming, hydrodesulfurization, hydrotreating, hydro-cracking, and others. These catalysts become inactive in six months to three years and are eventually replaced in the reactors with fresh catalyst during a unit shutdown. Many of these catalysts contain valuable metals which can be recovered economically. Some of these metals, such as platinum and palladium, represent the active catalytic component other metals such as nickel and vanadium are contaminants in the feed which are deposited on the catalyst during use. After valuable metals are recovered (a service usually performed by the outside companies), the residuals are expected to be disposed of as solid waste. 

Figure 3.17 Flowsheet of a waste plastic liquefaction plant based on thermal cracking and subsequent catalytic reforming [102]. (Reproduced by permission of the International Solid Waste Association (ISWA))...

The Likun Process (China) uses a two-stage cracking process under normal pressures where the waste plastics are first pyrolyzed at 350-400°C in the pyrolysis reactor and then the hot pyrolytic gases flow to a catalyst tower where they undergo catalytic reforming over zeolite at 300-380°C. By having the catalyst in the second stage this overcomes the problems of rapid catalyst deactivation from coke deposits on the surface of the catalyst. 

The Likun process [40] is another two-step cracking process operated under normal pressure. The process is shown in Figure 28.6. Waste PE, PP and PS are used as raw materials for oil recovery. In the first phase, the plastics are pyrolyzed at 350-400°C. In the second phase, the cracked gases undergo catalytic reforming over zeolite at 300-380°C. The... 

In some cases, such profiles are desirable. For example, with fast reactions and external diffusion resistance, the reaction occurs only on the outside of the pellet. Platinum deposited deep inside the particle is wasted. Shell deposition is not satisfactory, however, in reactions that are not diffusion controlled, such as catalytic reforming. It can be avoided by adding hydrochloric acid to the solution. The HCI competes with chloro-platinic acid for adsorption sites, driving platinum deeper into the particle. 

One of the key factors controlling the overall product spectrum is the "basicity" of the catalyst. This depends not only on the amount and type of alkali promoter present but also on its dispersion and how it has interacted with other promoters and impurities present (ref. 2). In the case of the fluidized-bed Synthol process the CH selectivity has been progressively lowered over the years from 15 to the current 1%. As the market for fuel gas is limited in South Africa, the excess CH must be catalytically reformed back to CO and (ref. 2). Not only is the production of CH wasteful in that it consumes more and CO than is needed for the formation of olefins but the reforming process itself is inefficient. Cutting back on the CH selectivity has therefore greatly benefited the overall economics of the Synthol FT process. 

The waste generated in oil refineries contains many different chemical compositions, depending on the complexity of the refinery, the existing processes and the type of oil used. The effluents are produced mainly by physical separation processes, such as atmospheric distillation and vacuum distillation, deparaffinization, deasphalting and also by processes involving chemical conversions by isomerization, alkylation, etherification, catalytic reform, etc. 

Ethanol is a nontoxic substance with relatively high H2 content, and its advantage is that it can be produced from renewable sources, for example, from various biomasses and wastes. In addition, purification of the produced reforming gas has been of interest to researchers. Hydrogen purification has been studied, for instance, with membranes [19] which can also have catalytic performances. 

The catalytic aqueous phase reforming might prove useful for the generation of hydrogen-rich gas from carbohydrates extracted from renewable biomass and biomass waste streams. The biomass-derived hydrocarbons are suitable to hydrogen generation from biomass, as well as for the reforming. 

This paper reported analysis concerning DME steam reforming and related processes with the use of (waste) heat, as well as catalytic properties for reforming. The Xx molecular orbital theory has been successfully applied to... 

Figure 15.6 Process flow for commercial pyrolysis plant (Thermofuel ) for converting waste plastics into diesel fuel. The plastic is heated to 375-425°C and the pyrolysis vapours are catalytically cracked and then selectively condensed. Note that the pyrolysis vessel is purged with nitrogen gas and that the hot pyrolytic vapours pass from the pyrolysis vessel to the catalytic reaction tower where they are cracked and reformed to give a high-purity diesel stream. (Reproduced by permission of Ozmotech Pty Ltd)...

Ozmotech have developed a Thermofuel process whereby waste plastic is converted into diesel by thermal degradation in the absence of oxygen. In this process the plastic waste is first melted and then cracked in a stainless steel chamber at a temperature of 350-425°C under inert gas (nitrogen). The catalytic reaction tower is designed in such a way that hot pyrolytic gases take a spiral or zigzag path to maximize contact area and time with the metal catalyst. The metal catalyst cracks hydrocarbon chains longer than C25 and reforms chains shorter than Ce. This leads to the formation of saturated alkanes. 

Since its foundation the Department of Chemical Engineering and Industrial Chemistry of the V.U.B. acquired considerable experi-eice in the field of high temperature processes, -with studies on steam-reforming of natural gas, pyrolysis of hydrocarbons and catalytic combustion of hydrocarbons. The Department conducted fundamental studies as well as contract work for industry, e.g. in the domain of fluidized bed techniques, incinerator grate mechanisms and small waste-fed boilers. An assessment on current thermal disposal techniques was prepared on behalf of E.E.C.[ 5 57958] ... 

Figure 3.9 shows the proposed flowscheme. The natural gas, sourced from the pipeline, is desulfurized, preheated and led into a reactor where it is reformed to synthesis gas. The temperature controlled reactor continuously combines reaction and heat exchange, to maximize the utilization of the energy contained in the waste stream (discussed later). The synthesis gas is compressed and led into the methanol reactor. The methanol reactor is preferably of the temperature controlled type, again to maximize the heat transfer and maximize the intensity of the catalytic operation. The partially converted stream is subsequently flashed to remove methanol and water. Rather than recycling and recompressing the stream, it is expanded in a gas turbine, producing power. 

While many studies have been carried out aimed at the feedstock recycling of rubber wastes by pyrolysis and hydrogenation processes (see Chapters 5 and 7), little information is found on the catalytic cracking and reforming of rubber alone. Larsen35 has disclosed that waste rubber, such as used tyres, can be degraded in the presence of molten salt catalysts with properties as Lewis acids, such as zinc chloride, tin chloride and antimony iodide. The decomposition proceeds at temperatures between 380 and 500 °C to yield gases, oil and a residue, in proportions similar to those obtained by simple thermal decomposition. 

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