BTX reaction

For the purposes of the investigation, the BTX reaction is independent of both temperature and pressure. It is assumed that the toluene concentration inside the reactor is simple to measure, so that concentrations are easily recorded, and that it is also possible to initiate and terminate the reaction easily. 

Suppose that a new set of experiments are carried out, in an attempt to understand the hydrogen minimization problem, and that Table 1.3 provides a summary of those experiments. These data originate from the same BTX reaction used in the previous sections. 

In Section 1.2, we described how Sam, Alex, and Donald approached the BTX problem from an experimental perspective. How might our approach change if we are given mathematical expressions for the rates of reaction In the following sections, we wish to describe some common ideas and approaches in theoretically designing a network of reactors (the reactor network synthesis problem), and also describe a central challenge faced in reactor network synthesis, even when mathematical and optimization techniques are available. For example, suppose that kinetics is also available for the BTX reaction and assumed to follow the data in Table 1.4 ... 

Perhaps, as a first attempt, the BTX reaction could be compared using a number of different, common, reactor models, such a continuous-flow stirred tank reactor (CSTR). One could solve the CSTR equation and then compare the... 

We write this book out of a need to understand a very basic question—when do we know we have achieved the best AR theory is an approach that seeks to help answer this question for chemical reactor networks (reactor structures). In this chapter, we described how problems of this nature arise when attempting to optimally produce toluene in the BTX reaction. In general, three approaches to the solution of this problem emerged, which are summarized pictorially in Figure 1.11. 

Let us isolate the components in the BTX reaction that are of interest to us. Since we are interested in maximizing toluene production, and since benzene is a required feed component, selectivity could be calculated based on the... 

We have therefore gained some insight into how the BTX reaction should be carried out. And although this result is simple, it highlights an important approach in AR theory In AR theory, we will seek to interpret all concentration data graphically. Visualizing data in this manner allows us to adopt a different perspective of reactors but to understand why, we must first introduce a number of fundamental concepts. 

In Chapter 2, batch data for the BTX reaction were plotted in a manner that allowed us to infer useful geometric properties related to concentration and mixing. We now understand that mixing allows for two physically separate yet achievable points to be connected by a straight line in concentration space. If more than two unique concentrations are available, it is possible to produce a filled convex region in space. In doing so, concentrations that were previously unachievable can be made achievable via mixing of the appropriate points. 

We can find the reaction time required to achieve point by plotting c versus reaction time and locating the specific time where the value of c is equal to that given by a. The line segment FGa is therefore representative of the solution trajectory obtained by running the BTX reaction from the feed until the concentration at point a is achieved. 

Two experiments are now needed to achieve the appropriate starting concentration for the BTX reaction. For each new iteration, an improvement over the current best is obtained, although, additional effort is required in realizing the correct starting concentration (in the form of obtaining the appropriate intermediate mixtures x,). 

In Chapter 3, we used partial emptying and refilling to improve the concentration of toluene in the BTX reaction. This arrangement of retaining a fraction of product and mixing with feed in the batch is equivalent to running a PFR with recycle. 

Increasing the octane number of a low-octane naphtha fraction is achieved by changing the molecular structure of the low octane number components. Many reactions are responsible for this change, such as the dehydrogenation of naphthenes and the dehydrocyclization of paraffins to aromatics. Catalytic reforming is considered the key process for obtaining benzene, toluene, and xylenes (BTX). These aromatics are important intermediates for the production of many chemicals. 

Isomerization and transalkylation reactions to redistribute methyl groups on aromatic molecules are important processes in the production of benzene, toluene and xylenes (BTX). In particular, the production of para-xylene is preferred. The interconversion of C8 aromatics is covered in much greater depth in Section 14.3. 

The DRE of BTX decreased with increasing pH value at pH greater than 4. For pH less than 4, the DREs of benzene, toluene, and xylene are about 87,88, and 83%, respectively. At fixed pH and Fe2+, the DRE of BTX increased almost linearly with increasing H202 concentration until 60 mg/L with an increase in concentration of H202, the DRE of BTX remained at 80 to 90%, revealing a zero-order reaction. 

As Haber and Weiss (1934) suggested, at lower H202 concentrations and fixed Fe2+ the oxidation reaction approaches second order however, when the ratio of H202 Fe2+ increases, the reaction kinetic approaches zero order and the reaction process depends on the competition between hydroxyl radicals and superoxide radicals. If an excess of hydrogen peroxide is present, then the reactions as shown in Equation (6.123) and Equation (6.124) for 2,4-dinitrotoluene are dominant. The amount of H202 was used up quickly in this study, indicating the importance of Equation (6.123). At concentrations of Fe2+ greater than 600 mg/L, the DRE of BTX reached a maximum value at approximately 82% for benzene and toluene and 73% for xylene. 

Cracking temperature and vapor residence time were the most important parameters controlling the cracking reactions. Within the range of conditions tested, other variables such as type and area of cracking surface, the vapor concentration of the feedstock and presence of steam made little difference to the yields of BTX and ethylene. Steam is used as a diluent and... 

The thermal and catalytic conversion of different hydrocarbon fractions, often with hydrotreating and other reaction steps, is characterized by a broad variety of feeds and products (Table 1, entry 4). New processes starting from natural gas are currently under development these are mainly based on the conversion of methane into synthesis gas, further into methanol, and finally into higher hydrocarbons. These processes are mainly employed in the petrochemical industry and will not be described in detail here. Several new processes are under development and the formation of BTX aromatics from C3/C4 hydrocarbons employing modified zeolite catalysts is a promising example [10],... 

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