Process waste reactors

The third source of process waste after the reactor and separation and recycle systems is process operations. 

The catalytic vapor-phase oxidation of propylene is generally carried out in a fixed-bed multitube reactor at near atmospheric pressures and elevated temperatures (ca 350°C) molten salt is used for temperature control. Air is commonly used as the oxygen source and steam is added to suppress the formation of flammable gas mixtures. Operation can be single pass or a recycle stream may be employed. Recent interest has focused on improving process efficiency and minimizing process wastes by defining process improvements that use recycle of process gas streams and/or use of new reaction diluents (20-24). 

Solution Polymerization. In this process an inert solvent is added to the reaction mass. The solvent adds its heat capacity and reduces the viscosity, faciUtating convective heat transfer. The solvent can also be refluxed to remove heat. On the other hand, the solvent wastes reactor space and reduces both rate and molecular weight as compared to bulk polymerisation. Additional technology is needed to separate the polymer product and to recover and store the solvent. Both batch and continuous processes are used. 

Both continuous and batch methods may be used in methanolysis. The batch mediod requires an autoclave, crystallizer, and centrifuge and a system for the melting and distillation of the DMT obtained. In the two-stage Hoechst continuous process, waste PET is melted and fed to a reactor. Preheated methanol is added to the autoclave, which is equipped with a mixer. The conversion reaches 70-90% in the first reactor, after which the reaction stream is introduced into a second autoclave at a lower temperature near the bottom, where it rises slowly and die higher density impurities settle at the bottom. The reaction stream leaves the second autoclave and its pressure is reduced to 0.3 MPa. On further reduction of the pressure and cooling, DMT precipitates and is subsequently purified.12... 

Processing wastes containing chlorine, sulfur, or phosphorus generates acids that must be neutralized in the reactor to prevent corrosion. 

One of the most important applications of nuclear and radiochemistry is in the area of nuclear power. Chemistry and chemical processes are intimately involved in reactor operation, the preparation and processing of reactor fuel, and the storage and ultimate disposal of radioactive waste. In this chapter, we shall examine some of the most important chemistry associated with nuclear power. 

Figure 13.18 Continuous recycle fermentor membrane reactor. An ultrafiltration module removes the liquid products of fermentation as a clean product. This system is being developed for production of ethanol, acetone and butanol by fermentation of food processing waste streams...

Fig. 5. A flow-through reactor designed for silver recovery from photographic process waste streams CE, counter electrode RE, reference electrode. (Adapted from [24]).

Your supervisor at Kleen Petrochemical wishes to use a hydrodesulfurization reaction to produce ethylbenzene from a process waste stream. You have been assigned the task of designing a reactor for the hydrodesulfurization reaction. Focus reactor design. 

Waste materials cover a diversity of products such as wood waste, used tires, waste from agricultural products such as rice husks, and municipal solid waste. Some of these waste materials are very heterogeneous while others are more uniform. Different types of waste are commonly processed using incinerators or reactors that process waste material by heat. The processed materials are commonly classified in char, liquid, and gasses. The municipal solid waste (refuse derived fuel), which is probably the most heterogeneous, is initially processed by the removal of metals, is shredded, dried, and pelletized, and only after that is it processed in heated reactors. 

Hansen, C. L., Hwang, S. H. (1990). Use of upflow anaerobic sludge blanket (UASB) reactor to treat whey permeate. In Proceedings of the Sixth International Symposium on Agriculture and Food Processing Wastes. Am. Soc. Ag. Eng., Chicago, Vol. Ill, p. 124. 

When a decision is made to pilot a process, the Pilot Plant Director schedules the review sequence and notifies the R D Chemist who provides a process summary to individual members of the Hazard Review Team. The Safety Officer will then examine the process for the presence of possible toxic or irritating compounds while the Environmental Coordinator decides the ultimate fate of any process waste streams. The Hazard Evaluation Chemist identifies any thermal or reactive hazards associated with the process. If a hazard is identified, the Process Engineer determines the suitability of a particular reactor grouping to handle the specific conditions involved. 

---