Oxygen-based recycle processes

The shift from air-based, once-through processes to oxygen-based recycle processes, and the corresponding change from reactant-lean to oxidant-lean processes. This not only considerably reduces the emissions and makes purge streams more concentrated and hence more easily combusted but also may lead to improved selectivity and productivity. Examples are the oxychlorination of ethylene to 1,2-dichloroethane and the epoxidation of ethylene. 

Figure 3 shows a simple schematic diagram of an oxygen-based process. Ethylene, oxygen, and the recycle gas stream are combined before entering the tubular reactors. The basic equipment for the reaction system is identical to that described for the air-based process, with one exception the purge reactor system is absent and a carbon dioxide removal unit is incorporated. The CO2 removal scheme illustrated is based on a patent by Shell Oil Co. (127), and minimises the loss of valuable ethylene in the process. 

Description The flowsheet for an oxygen-based unit is one of several possible process schemes. Compressed oxygen, ethylene and recycle gas are mixed and fed to a multitubular catalytic reactor (1). The temperature of oxidation is controlled by boiling water in the shell side of the reactor. 

An enzyme electrode based on coimmobilized cytochrome b2 and laccase (Scheller et al., 1987b) allows an explanation of the principle of substrate recycling in enzyme electrodes in greater detail (Fig. 100). The advantage of this system is that the cosubstrate, oxygen, as well as the analytes, hydroquinone and benzoquinone, are electrochemically active. This permits one to study different parts of the recycling process. Recycling of the analyte in the presence of the substrate of cytochrome b2, lactate, results in an increase in the sensitivity by a factor of 500 as compared with lactate-free operation. Under conditions that are optimal for laccase the analyte is almost completely in the oxidized state, i.e. it... 

The oxygen-based process benefits from a by-product credit for carbon dioxide. High purity carbon dioxide is recovered from the recycle gas and sold for use in carbonated beverage and dry ice manufacture. This revenue partially offsets the higher cost for oxygen although the air-based process has a significant by-product credit for steam. 

Chemical recycling is a process by which the polymer starting chemicals are retrieved from the plastic with high temperatures and in the absence of oxygen. The chemical recycling process can produce primary chemicals to produce new polymers. Chemical recychng process can be used for petroleum-based and biobased plastics. 

Q.6.8 Pyrolysis is a chemical recycling process that recovers the chemicals from carbon-based materials by heating materials to very high temperatures, for example, 700°C or higher, in the absence of oxygen. T or F ... 

Au and Pt catalysts in the presence of high amounts of NaOH was recendy investigated with the use of isotopically labeled dioxygen and water. The source of inserted oxygen was shown to be water rather than oxygen. Unfortunately, in all the studied gold-based samples, process efficiency and catalyst stabffity were rather low. However, the modification of Au-based catalysts with Pt or Pd metal produced stable and recyclable cat-... 

This type of recycling process to generate valuable by-products is not exclusive to waste rubber and can be applied to any hydrocarbon-based polymers. These processes have some similarities to the pyrolysis routes in that they result in the formation of low-molecular-weight molecules. The main difference is often that the pyrolysis process takes place in the absence of oxygen, whereas it can be present in these processes. 

With the unique reactor and smart particle designs, the oxygen carrying capacity and recyclability of the iron-based chemical looping particles have been radically improved, and OSU s SGR process has shown a great potential for commercialization. Its pilot-scale demonstration is currently under way. In addition, the sulfur present in coal is expected to react with Fe and form FeS. Flence, the SGR process has the capability of removing... 

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