Selected conversion processes

Figure 7.10 Bioresource utilization efficiency of selected conversion processes applied in Hamburg, Germany.

The processing of polymeric materials such as plastics is characterized by a wide variety of distinct methods or techniques. Each technique has a different set of melt rheology requirements that are dictated by the processing mechanism and the equipment design. A qualitative assessment of the effect of major melt rheology properties on selected conversion processes is shown in Tab. 14-2. 

Tab. 14-2 Qualitative assessment of major melt rheological properties versus selected conversion processes.

Although many problems still remain to be overcome to make the process practical (not the least of which is the question of the corrosive nature of aqueous HBr and the minimization of formation of any higher brominated methanes), the selective conversion of methane to methyl alcohol without going through syn-gas has promise. Furthermore, the process could be operated in relatively low-capital-demand-ing plants (in contrast to syn-gas production) and in practically any location, making transportation of natural gas from less accessible locations in the form of convenient liquid methyl alcohol possible. 

Ca.ta.lysts, Catalyst performance is the most important factor in the economics of an oxidation process. It is measured by activity (conversion of reactant), selectivity (conversion of reactant to desked product), rate of production (production of desked product per unit of reactor volume per unit of time), and catalyst life (effective time on-stream before significant loss of activity or selectivity). 

There are many different routes to organic chemicals from biomass because of its high polysaccharide content and reactivity. The practical value of the conversion processes selected for commercial use with biomass will depend strongly on the availabiUty and price of the same chemicals produced from petroleum and natural gas. 

Cyclohexane. The LPO of cyclohexane [110-82-7] suppUes much of the raw materials needed for nylon-6 and nylon-6,6 production. Cyclohexanol (A) and cyclohexanone (K) maybe produced selectively by using alow conversion process with multiple stages (228—232). The reasons for low conversion and multiple stages (an approach to plug-flow operation) are apparent from Eigure 2. Several catalysts have been reported. The selectivity to A as well as the overall process efficiency can be improved by using boric acid (2,232,233). K/A mixtures are usually oxidized by nitric acid in a second step to adipic acid (233) (see Cyclohexanol and cyclohexanone). 

Powerforming is basically a conversion process in which catalytically promoted chemical reactions convert low octane feed components into high octane products. The key to a good reforming process is a highly selective dual-function catalyst. The dual nature of this catalyst relates to the two separate catalyst functions atomically dispersed platinum to provide... 

Conversion processes are either thermal, where only heat is used to effect the required change, or catalytic, where a catalyst lowers the reaction activation energy. The catalyst also directs the reaction toward a desired product or products (selective catalyst). 

Figure 1 shows tire relationship betweai CHO conversion, CL selectivity and process time (time on str m) over TS-ls with different Si/11 ratio and SSZ-41, The result over ZSM-5 (Si/Al ratio=90) is also represented in Figure 1. The CHO conversion decreases with process time, whereas the CL selectivity is almost constant during the process time. The deactivation of SSZ-31 is largest among toe zeolites. The CL selectivity over SSZ-31 is lowest among the zeolites. The catalyst dractivation of TS-1(45) is larpr than fliat of TS-1(200). These results suggest that the acidity and micro pesre size of the zeolite siraultaiKously affected the catalyst deactivation.

In this paper, the selective conversion of methane to C2 hydrocarbons over ternary Ca0-Mn0/Ce02 catalysts in the CO2 OCM process are presented. The synergistic effect between catalyst reducibility and distribution of basic sites are highlighted. The most promising catalyst was then tested towards its stability. 

Titanium containing hexagonal mesoporous materials were synthesized by the modified hydrothermal synthesis method. The synthesized Ti-MCM-41 has hi y ordered hexa rud structure. Ti-MCM-41 was transformed into TS-l/MCM-41 by using the dry gel conversion process. For the synthesis of Ti-MCM-41 with TS-1(TS-1/MCM-41) structure TPAOH was used as the template. The synthesized TS-l/MCM-41 has hexagonal mesopores when the DGC process was carried out for less than 3 6 h. The catalytic activity of synthesized TS-l/MCM-41 catalysts was measured by the epoxidation of 1-hexene and cyclohexene. For the comparison of the catalytic activity, TS-1 and Ti-MCM-41 samples were also applied to the epoxidation reaction under the same reaction conditions. Both the conversion of olefins and selectivity to epoxide over TS-l/MCM-41 are found hi er flian those of other catalysts. 

An example of this is the commercial process for preparing puru-xylene, the precursor to terephthalic acid, which is polymerised to give polyjethy-lene terephthalate) (PET). In this case, the mixture of xylenes obtained from crude oil is reacted in a zeolite (known as HZSM5). The relative rates of diffusion in and out of the pores are sufficiently different (by a factor of about ten thousand) to allow the extremely efficient and selective conversion of all the isomers to the desired paia isomer, which is the narrowest and can thus move through the structure most rapidly (Figure 4.3). 

GP 2] [R 3a] The selectivity-conversion behavior was determined for the commercial Shell Series 800 catalyst, in a fixed bed and electrophoretically deposited in micro channels (20 vol.-% ethylene, 80 vol.-% oxygen 0.3 MPa 230 °C) [101] 54% selectivity at 17% conversion was found at the maximum, when processing without promoters. 

Yield/selectivity/conversion - benchmarking to industrial bubble-column processing... 

Process Evaluation and Improvement. As homogeneous asymmetric hydrogenation processes are scaled up, one major concern is cost because the catalyst is usually expensive. Hence, several criteria for a commercially viable process (2), including selectively, conversion, catalyst loading (S/C, the molar ratio of substrate to catalyst), reaction time, and TOF (turnover frequency, the ratio of catalyst loading to reaction time), should be considered to evaluate the process and provide a guide for improvement. 

In view of the size of operation being contemplated, it is unlikely that homogeneous catalysts will play a primary role in the production of synthetic oil. However, from the standpoint of the chemical industry, the complex mixture of products obtained from the classical Fischer-Tropsch process is generally unattractive owing to the economic constraints imposed by costly separation/purification processes. What is needed is a catalyst system for the selective conversion of CO/H2 mixtures to added-... 

USC [Ultra Selective Conversion] A front-end process for improving the operation of catalytic crackers for making ethylene. Developed and offered by Stone Webster Engineering Corporation. 

As a result of steric constraints imposed by the channel structure of ZSM-5, new or improved aromatics conversion processes have emerged. They show greater product selectivities and reaction paths that are shifted significantly from those obtained with constraint-free catalysts. In xylene isomerization, a high selectivity for isomerization versus disproportionation is shown to be related to zeolite structure rather than composition. The disproportionation of toluene to benzene and xylene can be directed to produce para-xylene in high selectivity by proper catalyst modification. The para-xylene selectivity can be quantitatively described in terms of three key catalyst properties, i.e., activity, crystal size, and diffusivity, supporting the diffusion model of para-selectivity. 

Intermediate pore zeolites typified by ZSM-5 (1) show unique shape-selectivities. This has led to the development and commercial use of several novel processes in the petroleum and petrochemical industry (2-4). This paper describes the selectivity characteristics of two different aromatics conversion processes Xylene Isomerization and Selective Toluene Disproportionation (STDP). In these two reactions, two different principles (5,j6) are responsible for their high selectivity a restricted transition state in the first, and mass transfer limitation in the second. 

This chapter surveys different process options to convert terpenes, plant oils, carbohydrates and lignocellulosic materials into valuable chemicals and polymers. Three different strategies of conversion processes integrated in a biorefinery scheme are proposed from biomass to bioproducts via degraded molecules , from platform molecules to bioproducts , and from biomass to bioproducts via new synthesis routes . Selected examples representative of the three options are given. Attention is focused on conversions based on one-pot reactions involving one or several catalytic steps that could be used to replace conventional synthetic routes developed for hydrocarbons. 

The chapters of this book have been selected to provide an introduction to the catalytic issues of biomass conversion processes. The introductory chapters make clear the political decisions, especially in the EU, that drive biomass conversion technology, its prospects compared with other options for renewable energy, and the main technological options for conversion of biomass into secondary energy carriers. 

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