Deepak Kunzru

Hydrocracking: a review

Abstract In this article the technology, kinetics, chemistry and reactor modelling of hydrocracking have been reviewed. While it is intended to provide a general overview of the recent advances in this process, greater emphasis has been given to technology and reactor modelling because of their industrial importance. Over ninety references have been cited.

Fabrication of microchannels on stainless steel by wet chemical etching

Microchannels in stainless steel were fabricated by using solutions of various concentrations of FeCl3, HCl and HNO3 in water as etchants. This study shows that for obtaining smooth uniform channels on stainless steel substrates, an etchant consisting of FeCl3, HCl and HNO3 is necessary. An increase in the concentration of HCl in the etchant increases the etch rate as well as the etch factor but adversely affects the roughness. Addition of HNO3 is necessary to obtain smooth uniform channels. The depth and etch factor are significantly affected by the composition of etchant, operating temperature and initial width of opening. In the range of operating conditions studied, an etchant containing 10 wt% FeCl3, 10 wt% HCl and 5 wt% HNO3 at 40 °C and an initial width of 190 µm gave the best results. With this etchant, the channels were smooth and uniform without any cavities on the edges of the channels. Initial width also plays a vital role in obtaining the final desired depth and etch factor.

Pyrolysis of n-heptane: kinetics and modeling

Abstract The kinetics and product distribution during the pyrolysis of n -heptane have been investigated in the temperature range 953–1023 K at atmospheric pressure, with steam as the inert diluent. The overall n -heptane decomposition can be represented by a first-order reaction with a frequency factor of 6.02 × 10 13 s −1 and an activation energy of 250.7 kJ mol −1 . The experimental product yields could be satisfactorily modeled by use of a molecular reaction scheme, consisting of a first-order primary reaction and 24 secondary reactions among the primary products.

Modeling of a hydrocracking reactor

Abstract A three parameter model has been developed for a two-stage vacuum gas oil hydrocracker unit. The feed and the products were lumped into 23 pseudocomponents, each characterized by its boiling range and specific gravity. The model assumes that each pseudocomponent can only form lighter products by a pseudohomogeneous first order reaction. The model parameters were determined using information from literature and plant data. Given the feed characterization and the inlet conditions, the concentration and temperature profiles throughout the reactors, the amount of recycle and hydrogen consumption can be calculated. The model was validated against plant data and the agreement was generally good. The effect of variation in the model parameters and operating conditions has also been discussed.

Pyrolysis of methylcyclohexane: Kinetics and modelling

Abstract Steam pyrolysis of methylcyclohexane has been investigated in a tubular reactor at atmospheric pressure in the temperature range 953-1073 K. Using non-linear regression, the overall decomposition was found to be approximately first-order with a pre-exponential factor and activation energy of 1.7110 11 s −1 and 209.0 kJ mol −1 , respectively. The experimental product yields and conversion could be satisfactorily simulated using a molecular model consisting of an overall primary reaction and twenty-four secondary reactions.

Effect of adsorbent particle size distribution on breakthrough curves for molecular sieve columns

Abstract A model has been proposed to predict breakthrough curves for packed bed adsorption columns. Adsorbent particle size distribution has been taken into account. Compared to uniform crystals, the breakthrough for non-uniform crystals occurred after a longer time interval and the delay increased as the size distribution became broader. The dynamic capacity was found to be higher for non-uniform crystals.

Potassium-containing calcium aluminate catalysts for pyrolysis of n-heptane

Abstract The effectiveness of potassium promoted calcium aluminate to catalyze the steam pyrolysis of n-heptane has been investigated at 1023 K and atmospheric pressure. Various amounts of potassium were incorporated on calcium aluminate (12CaO7Al2O3) by three different methods. Compared to thermal pyrolysis, addition of the calcium aluminate catalyst (either promoted or unpromoted) significantly increased the conversion as well as the yields of CH4, C2H4 and C3H6. The presence of potassium significantly reduced the coke deposited on the catalysts due to the enhanced rate of the coke gasification reaction. A significant amount of potassium was lost from the catalysts during preparation as well as during reaction. The gasification activity was higher for the catalysts in which the K2CO3 was incorporated by incipient wetness method but the potassium loss during reaction was also higher in comparison to catalysts in which the potassium was incorporated by co-sintering.

Catalytic pyrolysis of methylcyclohexane : kinetics and modeling

Abstract Steam pyrolysis of methylcyclohexane has been studied over potassium carbonate impregnated calcium aluminate catalyst in a fixed bed reactor at atmospheric pressure in the temperature range of 973–1073 K. Compared to noncatalytic pyrolysis, the conversion was significantly higher but the hydrocarbon product selectivities were not affected in the presence of the catalyst. Incorporation of K2CO3 in the catalyst significantly reduced the coke deposited on the catalyst. The overall catalytic pyrolysis reaction could be represented by a first-order reaction with a preexponential factor of 1.1 × 103 m3/(kg s) and an activation energy of 106.9 kJ/mol. The experimental product yields could be satisfactorily modeled by use of a molecular reaction scheme, consisting of a first-order primary reaction and twenty four secondary reactions among the primary products.

Vapor grown carbon fibers from pyrolysis of hydrocarbons: Modeling of filament growth and poisoning

A kinetic scheme has been proposed as a feasible model to explain the lengthening step in vapor grown carbon fibers from the pyrolysis of hydrocarbons. The two-parameter model assumes that the filaments lengthen by the reaction of a pyrolysis product with the growing filaments, and that the growth process ceases when the catalyst particle attached to the growing filament is poisoned by some reactive species in the gas phase. The model results show that the rate of filament growth is initially high and decreases monotonically. The final average filament length is found to depend only on the ratio of the rate of growth to the rate of poisoning. The model results can satisfactorily correlate the limited experimental data available in the open literature.

Theoretical prediction of sorption curves for molecular sieves

Abstract A model is proposed to take into account the non-linearity of equilibrium isotherm, concentration dependence of diffusivity and zeolite crystal size distribution while calculating the sorption curve for a single component adsorption on molecular sieves. The effect of size distribution is modelled by assuming the adsorption to take place on a progressively swelling crystal. Such a model allows the consideration of size distribution to be detached from other aspects while solving the diffusion equation. This reduces the computational efforts considerably.