-In the present study, transalkylation of 1,4-diispropylbenzene (DIPB) with benzene in the presence of modified beta zeolite was performed to produce cumene in a fixed bed reactor. Beta zeolite was exchanged with cerium in order to modify its catalytic activity. Activity of the modified catalyst was evaluated in the range of temperature 493K-593K, space time 4.2 kg h/kmol-9.03 kg h/k mol and benzene/1,4-DIPB molar ratio 1-15 to maximize the reactant conversion and selectivity of cumene. The activity and selectivity of the modified catalyst was found to increase with increase in cerium loading. Maximum selectivity of cumene (83.82%) was achieved at 573 K, benzene/1,4-DIPB 5:1 at one atmosphere pressure. A suitable kinetic model for this reaction was proposed from the product distribution pattern following the Langmuir-Hinshelwood approach. Applying non-linear regression, the model parameters were estimated. The activation energy for the transalkylation reaction was found to be 116.53 kJ/mol.
The activation energy for the transformation of silica gel to cristobalite, a partial reaction of first order, was determined from a single DTA curve by the methods available in the literature. The values obtained were not in agreement with those obtained by the isothermal method. This suggested that the methods were not applicable to reactions which are partial. A modified equation was derived which could be utilized for the determination of the activation energy of first-order reactions from a single DTA curve, if the fraction transformed during the reaction was known.A number of equations [1][2][3][4] have been proposed for the study of the kinetics of chemical reactions by DTA. The evaluation of kinetic parameters by DTA or TG has sometimes been found to lead to very poor agreement in results. This has given rise to a flurry of controversy concerning the validity of the non-isothermal methods of kinetic analysis [5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The assumptions which are involved in such equations are subject to many theoretical and experimental objections. It has been revealed that the present concepts of both isothermal and non-isothermal kinetics have many deficiencies.Verduch [19] studied the kinetics of transformation of silica gel to cristobalite by the isothermal method. In the present communication attempts have been made to study the kinetics of this transformation by DTA. The limitations of some of the DTA methods, as detected during the investigation, are discussed in the light of the present controversy.
ExperimentalA Netzsch thermoanalyser 404 was used for DTA investigations. The apparatus consisted of a vertical furnace and calibrated [20] Pt-PtRh 10% thermocouples.Silica gel samples used in the investigation were: 1. Column chromatographic grade silica gel, BDH, UK. 2. Silica gel prepared in the laboratory. After drying at 140 ~ , the gel contained 4.2 per cent water, 0.72 per cent alumina and 0.13 per cent other impurities.Calcined alumina (BDH) was used as both diluent and reference material. The sample holders were platinum sleeves (dia 8 ram, height 25 mm) mounted on top
In the present investigation transalkylation of cumene with toluene was carried over a series of zeolite containing rare earth metals such as lanthanum (La), cerium (Ce), and praseodymium (Pr). The modified zeolites were further characterized by EDS, XRD, BET and TPD. The surface area and acidities of the modified zeolite catalysts were reported. The transalkylation reactions were carried out varying different parameters such as metal loading (2–10 wt%), temperature (448–573 K), reactant ratio (1–15), and space-time (3.2–9.29 kg h/kmol). Praseodymium-modified X zeolite (PrX) showed the highest cumene conversion (60 wt%) and cymene selectivity (65.7 wt%) compared to the other zeolites. The maximum cumene conversion and cymene selectivity were obtained at 523 K, the toluene-to-cumene ratio of 9:1, and space-time of 9.29 kg h/kmol. Mass transfer resistances were studied in the said reaction conditions.
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