Alkylation and Hydrodearomatization over Zeolite cCatalysts
The alkylation of aromatic compounds is widely used in the large-scale synthesis of petrochemicals, and a great variety of fine chemicals and intermediates. Acid catalysts used for alkylation of aromatic hydrocarbons are Brønsted acids containing acidic protons. ZSM-5 catalysts were chosen hereby in the alkylation reactions of toluene with methanol, and benzene with ethanol.
The experiments have been done at the different reaction temperatures and using the different catalysts in the reactor to study the change of activity and selectivity of desired product. Organic products were collected and analysed by gas chromatograph (GC).
In the alkylation of toluene with methanol, the experiments have been done between 300~500 ºC. The objective with the experiment is to determine the effect of SiO2/Al2O3 ratio. At a reaction temperature of 500 ºC the para-selectivity is the best one while using EZ112 zeolite. At the different temperatures, EZ112 and EZ062 catalysts display the much better para-selectivities, in which the SiO2/Al2O3 ratios are 137 and 331 respectively, than those of the other three catalysts. At the same time the alkylation conversion of toluene decreased with the para-selectivity increasing. At the different reaction conditions methanol was almost converted completely.
For synthesis of ethylbenzene, a raw material for styrene manufacture, in the one step alkylation of benzene with ethanol over shape selective high silica zeolite catalysts could have great commercial importance. Several simple conclusions are achieved from the experimental results at the different temperatures over different Si/Al ratios unmodified or boron-, magnesium- modified ZSM-5 catalysts with using 95 % aqueous ethanol or pure ethanol.
Ethylbenzene is the primary product and small amount of diethylbenzene isomers exists in the mixture of products. The highest activity for ethylbenzene formation is at a SiO2/Al2O3 ratio of 80~100. The better selectivity for ethylbenzene goes through a maximum area between 400~450 ºC.
It is possible to use 95 % ethanol and water mixture as alkylating agent instead of pure ethanol solution over the unmodified catalysts. With the existence of water, it showed the clear reduction of the conversion of benzene at lower Si/Al ratio of boron modified catalysts B-EZ332, B-EZ472 and the magnesium modified catalysts Mg-EZ062, Mg-EZ112, Mg-EZ212. But the effect of water is different with using two types of modified catalysts. Both of boron and magnesium modified catalysts could be chosen for further studies because of their higher selectivity for ethylbenzene. But the existence of the abundant ethanol helps the alkylation of benzene to produce ethylbenzene and then further alkylation to diethylbenzene. Thus, the reduction of ethanol in the reaction is necessary. With the boron modified catalysts, the diluted ethanol and pure ethanol give the same selectivity of ethylbenzene and diethylbenzene.
Hydrodearomatization (HDA) of dearomatized diesel fuel with 4.8 % aromatic content was done over a commercial Pt on a Y-zeolite. The temperature and pressure used were 300 to 400 ˚C and 5.0 to 7.5 MPa, respectively. The minimum aromatic content in the product fuel was 0.3 % at 325 ˚C. The hydrocracking reaction was severed at the temperatures 350 ˚C and above, shifting the product to gasoline. The dependence of pressure was higher at the high temperature than at the lower temperature used. These results indicate that the lower temperature can be selected to control the aromatics hydrogenation at lower PH2.
activity and selectivity
alkylation of aromatics