Bachan S. Rawat

Liquid—liquid equilibrium studies on hydrocarbon (C10C20)—sulfolane systems

Abstract Equilibrium tie line data have been determined at 60 and 100°C with sulfolane and five model hydrocarbon mixtures consisting of butylbenzene—dodecane, hexylbenzene—dodecane, hexylbenzene—cetane, octylbenzene—dodecane and octylbenzene—cetane. The data so obtained have been predicted by UNIFAC and correlated by NRTL and UNIQUAC model equations. The alkylbenzenes used in the study were prepared in the laboratory.

Isobaric vapour—liquid equilibria of the systems: Benzene—triethylene glycol, toluene—triethylene glycol and benzene—N-methylpyrrolidone

Abstract Isobaric vapour—liquid equilibria have been determined at 101.325 kPa for three binary mixtures: benzene—triethylene glycol, toluene—triethylene glycol and benzene— N -methylpyrrolidone. The data have been correlated with reasonable accuracy using the NRTL, Wilson and UNIQUAC equations using a non-linear regression approach based on the maximum-likelihood principle.

Studies on the permeation of aromatic hydrocarbons through liquid surfactant membranes

Abstract The effect of operating parameters on the batch scale permeation of hydrocarbons from benzene—heptane mixtures and a straight run naphtha through liquid membrane is reported. The thirteen operating parameters studied include: mixing intensity, surfactant concentration, treat ratios, contact times, temperature and additives. The variations observed in the two key properties of selectivity and aromatic recoveries as well as in product compositions with change in operating parameter is discussed. Surfactant concentration contact time during permeation, type and concentration of additive used appear to exert a marked effect on the enrichment obtained. The careful optimization of operating parameters give selectivities as high as 50 and aromatic recoveries of 75% in one stage at 30°C. Comparison of data with batch liquid—liquid extraction data from extraction of similar feed mixtures with the most widely used solvent, sulpholane, under typical industrial conditions, has shown that selectivities and aromatic recoveries in liquid membrane permeation (LMP) are much higher. Batch scale LMP experiments with straight run naphtha as feed show that under optimum conditions of membrane stability and operating parameters the dearomatization of naphtha from an initial aromatic level of 22 vol.% to 10.5 vol.% is possible in one stage at 30°C with a raffinate yield of 63%. The results obtained on benzene—heptane model mixture compare fairly well with those obtained on naphtha feed.

Studies on permeation of hydrocarbons through liquid membranes in a continuous contactor

Abstract This paper reports experimental studies, in a continuous cocurrent packed column, on the removal of aromatics from hydrocarbon streams by making use of selective transfer through aqueous surfactant membranes. Two types of feed mixtures were used: (i) benzene—heptane and (ii) straight run naphtha from Bombay High crude oil. The receiving phase in both cases was kerosene. The height of a mass transfer unit (HTU) was determined and found to largely lie in the range 2-2.5 m, irrespective of feed composition and solvent/feed ratio. The experimental study confirms the feasibility of a liquid membrane process for dearomatization and provides HTU data for further feasibility and scale-up studies.

Mass transfer studies in liquid membrane hydrocarbon separations

Abstract The effects of operating parameters on mass transfer coefficients of benzene permeating through liquid surfactant membranes have been studied. The study indicates that major resistance to mass transfer lies in the aqueous membrane phase. Mixing intensities used in forming the emulsion and dispersing it in the external phase have relatively less influence. Using a simple membrane film model approach, these mass transfer coefficients can be predicted within reasonable limits. The membrane film thickness to be used in these predictions varies with the holdup of micro phase in the emulsion, and can be estimated from the recently proposed equation of Kataoka .

Effect of surfactant type on selectivity for the separation of 1-methylnaphthalene from dodecane using liquid membranes

The selective removal of aromatics from kerosine for the purposes of smoke-point improvement and to meet the specifications for aviation turbine fuel is an industrially important operation. The present study is part of a programme for developing an energy-efficient aqueous surfactant membrane process with high selectivities for aromatics removal. In the experimental studies, carried out in a batch mixer-settler unit, the kerosine feed was modelled using a synthetic mixture of 1-methylnaphthalene and dodecane. The objective of the experimental study was to study the influence of the surfactant type on the selectivity for removal of l-methylnaphthalene. Eight different types of surfactants were used in the studies, with HLB (hydrophile-lipophile balance) numbers ranging from 12.8 to 17.8. The selectivity β, defined as the ratio of the mass transfer coefficients for transfer of aromatics to that of the non-aromatics, was determined after correcting for nonselective transport due to emulsion breakage. The selectivity thus obtained correlated very well with W, the work of transfer, which reflects the ease of adsorption of the surfactant to form a monolayer relative to the ease of micellization. For high W (i.e., lower ease of micellization) the selectivities are higher, as might be expected because micelle formation leads to non-selective transport through the membrane barrier. The study sheds light on the appropriate choice of surfactant to obtain increased selectivities.

Permeation of hydrocarbons through liquid surfactant membranes and formation of liquid crystalline structures

Abstract The separation of benzene from its mixture with heptane can be achieved by emulsifying the feed mixture to form an oil-in-water emulsion and then dispersing this emulsion in kerosene. At high agitation intensity a gel-like structure develops which prevents phase separation and thereby interferes with the overall mass transfer process. These gel-like structures have very high viscosities, and show rheopectic behaviour; polarising microscopic examination of these gel-like structures revealed the existence of liquid crystalline structures on the surface of the emulsion globules dispersed in kerosene. A possible mode of development of such liquid crystalline structures is presented, 1-Pentanol added to kerosene prevents gel formation and assists phase separation. Its action is explained on the basis of Winsors theory of solubilization. Typical results for selectivity and benzene yield are presented.

Estimation of trace amounts of benzene in solvent-extracted vegetable oils and oil seed cakes

A new method is presented for the qualitative and quantitative estimation of trace amounts (up to 0.15 ppm) of benzene in crude as well as refined vegetable oils obtained by extraction with food grade hexane (FGH), and in the oil seed cakes left after extraction. The method involves the selection of two solvents; cyclohexanol, for thinning of viscous vegetable oil, and heptane, for azeotroping out trace benzene as a concentrate from the resulting mixture. Benzene is then estimated in the resulting azeotrope either by UV spectroscopy or by GC-MS subject to availability and cost effectiveness of the latter. Repeatability and reproducibility of the method is within 1-3% error. This method is suitable for estimating benzene in vegetable oils and oil seed cakes.

Drop size prediction in liquid membrane systems

Abstract The design of separation equipment using liquid membranes requires predictive methods for the estimation of drop diameters of the dispersed liquid membrane “macrodrop”. Existing models for drop breakage in liquid-liquid systems underpredict drop diameters of liquid membrane macrodrops even after incorporating the effects of dispersed phase viscosity and hold-up. By considering that the microdroplets within a liquid membrane macrodrop cause a damping of induced drop oscillations arising from external turbulence, the recently proposed model of Calabrese et al. (1986) has been modified and the resulting model equations have been shown to predict drop diameters of both oil as well as water liquid membrane macrodrops reasonably well.

Liquid-liquid phase equilibria for dearomatisation of ATF fraction

Abstract The present work describes a method to develop a simulation model for dearomatisation of the straight-run fraction that boils in the range 140–240°C (also called Aviation Turbine Fuel fraction) of Bombay high crude (India—offshore). Sulpholane was used as a solvent to extract aromatics from this fraction. A mass spectrometric analysis of the ATF fraction identified six hydrocarbon types; each of these was represented by one or more components. The group contribution model, UNIFAC, has been investigated for the prediction of the multicomponent liquid—liquid equilibria. The compositions of the extract and raffinate phases, thus predicted, compare closely with single stage experimental data. Multistage countercurrent extraction calculations have also been carried out using the above model and checked satisfactorily against experimental data that were available on a 27 mm-diameter packed laboratory extraction column. It has been shown that the representation of ATF fraction by model hydrocarbons, together with the equilibria predictions by UNIFAC, form a sufficiently accurate data base for the simulation model.