BTX production

A completely new approach for BTX production has emerged in recent years. It converts to paraffins into aromatics using a modified ZSM-5 zeoHte catalyst which contains gallium (19). An example of this approach, the Cyclar process, has been in commercial operation by British Petroleum at Grangemouth, Scotiand since August 1990 (20). It uses C —feed and employs UOP s CCR technology to compensate for rapid catalyst coking. 

The mechanistic steps are as follows paraffins dehydrogenate to olefins the olefins oligomerize and cyclize and the cycHcs aromatize. Because the first step is rate controlling, very Httie olefin is actually present. The BTX product is relatively free of nonaromatics and therefore is very desirable as a chemical feed. As in reforming, some C —C2 fuel gas is produced along with a valuable hydrogen stream. Prom a C —feed the BTX product is roughly 35 45 20, respectively. 

Downstream Processing. In addition to extraction, various downstream operations are often carried out on the BTX product to produce products in proportions to fit the market demand. A typical aromatics processing scheme is shown in Eigure 8 in which ben2ene, xylene, and o-xylene are the products. 

That coal-derived liquids consist largely of aromatic and cyclic structures suggests that, with appropriate hydroprocessing, high yields of benzene, toluene, and xylenes (BTX s) should be obtained. If the by-products of that BTX production could be directed toward linear... 

IFP BTX, production Naphtha Aromizing maximizes BTX production with high yields of high-quality aromatics 9 1998... 

The statisties for a naphtha cracker integrated with polymer and BTX production are illustrated in Table 9.2. The complex is based on the CLOSED case and only ethylene, propylene and pyrolysis gasoline pass to downstream processing. For brevity it is assumed the polymers are produced at 100% yield and require no other feedstock. The pyrolysis gasoline is passed to an aromatics extraction plant and produces 298 kt/y benzene, 149 kt/y toluene and 52 kt/y xylene. The rest of the pyrolysis gasoline (246 kt/y) produees a raffinate, whieh is sold as a gasoline. 

Paraffin conversion to valuable BTX products over HZSM-5 catalyst is due to... 

Case 04 (Figure 4) adds hydrodealkylation of both toluene and the alkylnaphthalene concentrate fraction. To produce the necessary hydrogen as well as to increase BTX production catalytic reforming of all naphtha in the crude is added. Case 04 represents a relatively complete development of the all-chemical configuration of the petrochemical refinery. 

The rich net gas (offgas) is further compressed in downstream separation to recover the valuable aromatic-rich liquid. The final product streams after downstream separation include dry gas, LPG, and premium gasoline or benzene, toluene and xylene (BTX) products. The regeneration is a typical coke-burning step. 

Bourdelais et al. (2002) identified BTXs PbTx-2, PbTx-3, and PbTx-9 in seawater samples from the Delaware coast, USA associated with fish kills and a bloom of Chattonella cf. verruculosa. The identity of the toxins was confirmed by chromatographic, immnnochemical, nuclear magnetic resonance spectroscopy and mass spectrographic analyses, and the toxin content of cells was inferred from cell counts and toxin concentrations, to be on the order of 6 pg /cell. This is comparable to the levels found in Florida K. brevis (Table 21.1). However, despite this strong circumstantial association, it has not yet been possible to demonstrate BTX production by cultures of Ch. cf. verruculosa isolated from Delaware coast waters (Bourdelais, pers. comm.)... 

Figure 6.8 BTX product purities for benzene and xylene feed composition changes with fixed reflux and stage temperature.

Since we wish to use this model to model BTX production as well, we need to predict the composition of the all the relevant isomers of A8 (ethylbenzene, orthoxylene, para-xylene, meta-xylene). In our model, we assume that these isomers take on fixed equilibrium ratios as a function of temperature. Figure 5.10 shows the equilibrium distribution of these isomers at various temperatures [40,41]. The distributions correspond to expected temperatures in the reforming process. 

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