Separation equipment, waste minimization

Revamp of a toluene hydrodealkylation process. This prob-lan considers some waste-minimization concepts. Our operating toluene hydrodealkylation unit, shown in Figure 5.13, involves the hydrogenation of toluene to benzene and methane. An equi-lihium side reaction produces a small quantity of biphenyl. To be more competitive, and eliminate waste, the process needs to be studied for a possible revamp. The customer for our small production of biphenyl has informed us that it will not renew its contract with us, and we have no other prospective buyer for biphenyl. Also, a membrane separator company believes that if we install their equipment, we can reduce our makeup hydrogen requirement. Make preliminary process design calculations with a simulator to compare the two alternatives below, and advise me of the technical feasibility of the second alternative and whether we should consider such a revamp further. For your studies, you will have to perform mainly material balance calculations. You will not make detailed distillation calculations, and liquid pumps need not be modeled. For the second alternative, calculate the required area in square feet of the membrane unit and determine if it is reasonable. 

A more straightforward way to minimize wastes from separation devices is to focus on the heat exchange equipment associated with the units. Methods such as those described earlier for heat exchangers can also be effective for reboilers and condensers. 

Some simple operational improvements can also help minimize mixed waste. Surpluses can be minimized by limiting the acquisition of chemicals and radioactive materials to immediate needs. Contaminated equipment can sometimes be reused within restricted areas or decontaminated. Establishing procedures for noncontaminated materials can enable generators to keep normal trash separate from contaminated waste. 

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