Toluene, production

Extractive distillation, using similar solvents to those used in extraction, may be employed to recover aromatics from reformates which have been prefractionated to a narrow boiling range. Extractive distillation is also used to recover a mixed ben2ene—toluene stream from which high quaUty benzene can be produced by postfractionation in this case, the toluene product is less pure, but is stiU acceptable as a feedstock for dealkylation or gasoline blending. Extractive distillation processes for aromatics recovery include those Hsted in Table 4. 

For aromatics production, similar considerations apply. Maximum yields of xylenes and other heavy aromatics can be obtained in cyclic units, but, again, at somewhat higher investments. The process selection, thus, again requires the balancing of process credits versus debits for the specific application. For light aromatics (benzene-toluene) production, however, the situation tends to favor a... 

The 1994 U.S. toluene production (of all grades) was approximately 6.8 billion pounds. Hydrodealkylating toluene to benzene was the largest end use in United States and West Europe, followed by solvent applications. 

A comparison of the feed and product compositions achievable by this approach is shown in Figure 16.8, which shows the depletion of multi-ring aromatics from the feed in favor of a variety of single ring aromatics with short alkyl chains. A more challenging approach that leads to a higher-value product involves optimization of the catalyst and process conditions to maximize xylene and toluene production for aromatic complex feeds [60]. 

One toluene production process commences with mixed hydrocarbon stocks and can be used for making both toluene and benzene, separately or simultaneously. The process is a combination of extraction and distillation. An aqueous dimethyl sulfoxide (DMSO) solution is passed countercur-rently against the mixed hydrocarbon feed. A mixture of aromatic and paraffinic hydrocarbons serves as reflux. 

The reformate produced in the OCR Platforming unit is sent to a debutanizer column, which strips off the light ends. The debutanizer bottoms are sent to a reformate splitter (3). The C7 fraction from the overhead of the reformate splitter is sent to a Sulfolane unit (4). The C8+ fraction from the bottom of the reformate splitter is sent to a xylene fractionation section. The Sulfolane unit extracts the aromatics and then individual high-purity benzene and toluene products are recovered in a BT fractionation section (5 6). 

The conversion of ortho- to meta- and para-xylene was carried out on a series of decationated catalysts which were subjected to thermal treatment at various temperatures. 10-/xl pulses of o-xylene were used, the catalyst amount was 300-350 mg, and the flow rate of the helium carrier gas was 50-100 ml/min. The products were analyzed on 7.8-benzoquinoline on Chromosorb W gas-chromatographic column. The m-xylene predominated over the para isomer. A small toluene production seemed to parallel that of isomerization. The conversion of xylene X... 

If the toluene product must be cooled to 20°C, how much of the feed heat can be supplied by heat exchange with the bottoms ... 

It was found that toluene production rate exibited a maximum near the inlet of the catalyst bed and the maximun rate moved down the bed as the catalyst deactivated. 

Eollowing are two examples (16.1 and 16.2) of a distillation column that demonstrate the effect of applying different pairing strategies. In both examples the control loops for the column pressure and the liquid levels in the condenser accumulator and the column bottom are determined independently based on practical considerations. Thus, the column pressure is controlled by various techniques that may involve the condenser coolant rate, and the liquid levels are controlled by the product flow rates. What remains to be decided is how to pair the distillate and bottoms compositions with the reflux rate and the reboiler heat duty. The same distillation column is used in both examples, having a total condenser and a reboiler, one feed and two products. The column is designed to separate a benzene-toluene mixture into benzene and toluene products with specified purities. 

A 100 kmol/h stream containing 50% mole benzene and 40% mole toluene is sent to a 12-stage distillation column on the sixth stage from the top. The column pressure is 100 kPa, with a total condenser and a reboiler. The distillate is the benzene product with a specification of 6.0% mole toluene, and the bottom is the toluene product with a specification of 6.0% mole benzene. These specifications will be met by manipulating the reflux rate and the reboiler heat duty. It is required to determine the best pairing between the manipulated and controlled variables. 

The same distillation column of Example 16.1 is operated such that the benzene product contains 2.0% mole toluene and the toluene product contains 2.0% mole benzene. The manipulated variables are the reflux rate and the reboiler heat duty. At design conditions the reflux rate is 208.0 kmol/h and the reboiler duty is 6.7915 X 10 kJ/h. Evaluate the control-loop options. 

The weakness of retardation by added aromatics now becomes understandable Added benzene or xylene does reduce the surface area accessible to MCH. However, this also reduces the rate of toluene production and, thereby, the toluene coverage, so that the denial of surface to MCH is partially offset. 

Aging these benzyllithium solutions to remove the ring-isomer content is not practical in most cases, and use of large amounts of TMEDA to promote conversion can also cause problems later in synthetic use. Since heating the toluene product solution did not cause serious decomposition at 60 °C, this could provide a solution to the problem for most... 

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