Hydrodealkylation Processes

Toluene Hydrodeall lation. Benzene is produced from the hydrodemethylation of toluene under catalytic or thermal conditions. The main catalytic hydrodealkylation processes are Hydeal (UOP) and DETOL (Houdry) (49). Two widely used thermal processes are HD A (Arco and Hydrocarbon Research Institute) and THD (Gulf). These processes contribute 25—30% of the world s total benzene supply. 

Bextol A catalytic hydrodealkylation process using an oxide catalyst. 

Pyrolysis gasoline gasoline produced by thermal cracking as a byproduct of ethylene manufacture. It is used as a source of benzene by the hydrodealkylation process. 

Other than benzene, 30% of which is made from toluene by the hydrodealkylation process, there are no other top 50 chemicals derived from... 

Figure 2.11 Input/output structure by toluene hydrodealkylation process.

IFP Benzene Toluene No catalyst is needed with hydrodealkylation process onstream time exceeds 95% 6 1998... 

This study was undertaken with the objective of closely following the relationships of silica/alumina ratio with catalytic properties of ZSM-5 zeolite in toluene transformation under hydrodealkylation process conditions. It was hoped that the data would reveal the reaction pathway of the dealkylation and subsequently shed light on the mechanism of H-ZSM-5 catalyzed transformation of toluene. 

Control system. For subsequent selection and sizing of pumps and compressors, we need to map out the number and location of the control valves. Since the number of control valves is related to the number of control degrees of freedom, identify the control degrees of freedom. For example, a typical hydrodealkyllation process with a reactor, furnace, vapor-liquid separator, recycle compressor, two heat exchangers, and three distillation columns has 23 control degrees of freedom (Luyben et al., 1997). This requires 23 control valves whose location affects the rest of the design and the safety and hazards (see Section 16.7). 

Change the operating conditions. Alter the reaction conditions to eliminate the hazards or production of toxic waste. Waste by-products from the reactor can be eliminated if the reaction to produce the by-products is reversible (as for biphenyl production in the hydrodealkyllation process). 

Since the introduction of hydrodealkylation processes some 11 years ago (2), the pace has quickened in the development of processes specifically designed to manufacture chemicals from liquid petroleum feedstocks. This volume is designed to unify and stimulate further development of new concepts, ultimately leading to establishment of the... 

Most hydrodealkylation processes can be adapted to produce xylenes or naphthalene... 

Be able to use the process simulators systematically during process creation, following sequences similar to those illustrated later in this chapter for a toluene hydrodealkylation process. The reader will learn to simulate portions of the process (the reactor section, the distillation section, etc.) before attempting to simulate the entire process with its recycle loops. Many examples and exercises enable the reader to master these techniques. 

Figure 4.19 Reaction section for the toluene hydrodealkylation process with the temperature-, pressure-, and phase-change operations.

Figure 4.20 Flowsheet showing a task integration for the toluene hydrodealkylation process.

Figure 4.22 Toluene hydrodealkylation process-distillation section.

Toluene hydrodealkylation process—separation section. As discussed in Section 4.3, the following stream at 100°F and 484 psia is to be separated by two distillation columns into the indicated products. 

Return to the design of the toluene hydrodealkylation process, as it is presented in Section 4.3. In the reactor section, after heuristics are utilized to set (1) the large excess of H2 in the hydrodealkylation reactor, (2) the temperature level of the quenched gases that enter the feed-product heat exchanger, and (3) the temperature in the flash vessel, the simulator is used to complete the material and energy balances and to examine the effects of these heuristics on the performance of the reactor section. In the distillation section, after heuristics are used to set (1) the quahty of the feed, (2) the use of partial or total condensers, (3) the use of cool-... 

Often small quantities of chemicals are produced in side reactions, such as the reaction of benzene to form biphenyl in the toluene hydrodealkylation process. When the reaction proceeds irreversibly, small quantities of byproducts must be separated away, as in Figure 4.20, or purged otherwise they will build up in the process until the process must be shut down. 

This example follows the simulation of the complete toluene hydrodealkylation process at the end of Section 4.3 and is presented without a solution because it is the basis for Exercise 5.4. To recycle the biphenyl to extinction, the flowsheet in Figure 4.20 is modified to eliminate the last distillation column, and unreacted toluene from the second column is recycled with biphenyl. This is accomplished by the reversible reaction... 

Heuristic 32 Quench a very hot process stream to at least l,15(fF brfore sending it to a heat exchanger for additional cooling and/or condensation. The quench fluid is best obtained from a downstream separator as in Figure 4.21 for the toluene hydrodealkylation process. Alternatively, if the process stream contains water vapor, liquid water may be an effective quench fluid. 

In Figure 4.20 for the toluene hydrodealkylation process, the pressure of the recycle gas leaving the flash drum at 100°F and 484 psia is increased with a compressor to 569 psia, so that, after pressure drops of 5 psia through the heat exchanger and 70 psia through the furnace, it enters the reactor at a required pressure of 494 psia. 

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. 

Vapor-liquid case. The reactor effluent for a toluene hydrodealkylation process, of the type discussed in Section 4.3, is a gas at 1,150°F and 520 psia. When brought to 100°F at say 500 psia by a series of heat exchangers, the result is a vapor phase in equilibrium with a single liquid phase. A two-phase flash calculation using the SRK equation of state gives the following results ... 

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