Kartic C. Khilar

Influence of mineral matter on biomass pyrolysis characteristics

Studies on wood and twelve other types of biomass showed that in general, deashing increased the volatile yield, initial decomposition temperature and rate of pyrolysis. However, coir pith, groundnut shell and rice husk showed an increase in char yield on deashing, which is attributed to their high lignin, potassium and zinc contents. These results were supported by studies on salt-impregnated, acid-soaked and synthetic biomass. A correlation was developed to predict the influence of ash on volatile yield. On deashing, liquid yield increased and gas yield decreased for all the biomass studied. The active surface area increased on deashing. The heating value of the liquid increased, whereas the increase in char heating value was only marginal.

Pyrolysis characteristics of biomass and biomass components

Biomass pyrolysis studies were conducted using both a thermogravimetric analyser and a packed-bed pyrolyser. Each kind of biomass has a characteristic pyrolysis behaviour which is explained based on its individual component characteristics. Studies on isolated biomass components as well as synthetic biomass show that the interactions among the components are not of as much significance as the composition of the biomass. Direct summative correlations based on biomass component pyrolysis adequately explain both the pyrolysis characteristics and product distribution of biomass. It is inferred that there is no detectable interaction among the components during pyrolysis in either the thermogravimetric analyser or the packed-bed pyrolyser. However, ash present in biomass seems to have a strong influence on both the pyrolysis characteristics and the product distribution.

The existence of a critical salt concentration for particle release

Abstract A critical salt concentration (CSC) was found to exist in the water sensitivity of Berea sandstone. If the salinity of the permeating fluid falls below the CSC, the sandstone permeability is significantly reduced as a result of clay particles being released from the pore walls and blocking the pore throats. However, when changes in salinity occur above this threshold value, clay particles are not released from the pore walls in the sandstone and therefore no reduction in core permeability occurs. The CSC was determined by core flood experiments in conjunction with particle analysis of core effluent samples. The CSC exists only in the case of monovalent cations and is virtually nonexistent for cations having a valence greater than one. Even among monovalent cations the CSC varies considerably and it decreases with increasing ion exchange affinity of the clay for the counterion. For polyvalent counterions, the release of clay particles is effectively prevented due to the strong ion-exchange affinity of clay for the counterion. The critical salt concentration was also found to depend on the temperature, but not on the flowrate, of the electrolyte solution. The temperature dependence has been explained by using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of stability of colloidal dispersions.

Water sensitivity of sandstones

Experimental and theoretical studies have been carried out to elucidate the mechanism of water sensitivity of Berea Sandstone and quantify a number of important parameters. Based on the results of a number of novel experiments, a physical model has been developed. In this model, clay particles are released only when the salt concentration falls below a critical salt concentration. These colloidal clay particles remain dispersed in fresh water and are carried with the flowing fluid until they are captured at a local pore constriction, thereby decreasing permeability. A mathematical model based on this mechanism has been developed. This model contains two parameters stemming from the rate equations of the release and capture of clay particles. Correlations of these parameters with flowrate and temperature are presented. 9 refs.

Adsorption of Cu2+ and Ni2+ on iron oxide and kaolin and its importance on Ni2+ transport in porous media

Adsorption of divalent heavy metal ions on iron oxide and kaolin is important to determine the transport and ultimate fate of ions in underground water and soil. In this study, kinetics and equilibrium adsorption of Cu 2� and Ni 2� metal ions from their aqueous solutions on iron oxide, kaolin and sand have been investigated. Batch adsorption studies show that Cu 2� and Ni 2� adsorb more strongly on the colloidal fines, iron oxide and kaolin than on the sand material. It is shown that the adsorption of Cu 2� and Ni 2� is a function of system pH, and solid adsorbent concentration. The equilibrium data follow the most widely used nonlinear Freundlich isotherm equilibrium model which has the general form of X� /KF C n . It is found that ‘n ’ is strongly dependent on the nature of the adsorbent and virtually independent of conditions such as pH. The other parameter, ‘KF’ strongly depends on the pH of the solution. Finally, predictions of contaminant transport of Ni 2� due to the presence of colloidal fines, kaolin based on batch

Release rates from semi-crystalline polymer microcapsules formed by interfacial polycondensation

Microencapsulation of active agents, for their controlled release, can be brought about by the method of interfacial polycondensation [1]. In this paper, the permeabilities of the polyurea microcapsules for encapsulated cyclohexane have been determined. It is shown that the product of the permeability and membrane thickness can be changed over at least an order of magnitude by changing the degree of crystallinity of the polymer forming the membranes.

Colloidally induced fines migration in porous media

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Colloidally-induced fines release in porous media

Khilar, K.C., Vaidya, R.N. and Fogler, H.S., 1990. Colloidally-induced fines release in porous media. J. Pet. Sci. Eng., 4: 213-221. A critical value of the total ionic strength (CTIS) has been found to exist for mixed salt solutions flowing in porous media. If the ionic strength drops below this value, significant amounts of fines are released in-situ due to colloidal forces, causing drastic formation damage. For a NaCI/CaC12 system, the CTIS is strongly dependent on the relative amount of CaC12 present in the solution. The concept of a critical salt concentration (CSC) and the analysis based on DLVO theory has been extended to mixed salt systems to estimate the CTIS. The difference between critical flocculation concentration (CFC), and the present definition of CTIS has been pointed out. Predictions of this analysis are consistent with experimental observations.

Enhancement of stability of aqueous foams by addition of water-soluble polymers: measurements and analysis

Abstract It is experimentally shown that the stability of aqueous foams can be significantly enhanced by the addition of a small amount of water-soluble polymers. Such enhancement is attributed to the retardation both in the rate of drainage and in the rate of interbubble gas diffusion. Addition of water-soluble polymer increases the bulk viscosity and thereby decreases the rate of drainage. It also decreases the gas permeability of liquid lamella and as a result the rate of interbubble diffusion is retarded. A simple analysis incorporating both lamella drainage and interbubble diffusion has been developed. The qualitative predictions of this analysis are found to be consistent with our experimental observations.

Stability of aqueous foams with polymer additives: II. Effects of temperature

Abstract The stability of aqueous foams with polymer additives has been studied at temperatures ranging from 30 to 80°C. It is found that the enhancement of stability due to the addition of water-soluble polymer additives as reported by D. S. H. S. Sarma, J. Pandit, and K. C. Khilar (J. Colloid Interface Sci. 124, 339 (1988)) is substantially retained, although it is reduced at higher temperatures. In the case where cosurfactant is the only additive, the enhancement of stability is entirely lost at about 70°C. It is also found that the decrease in drainage half-life and the increase in initial drainage rate are gradual with the increase in temperature, without any indication of sudden transition. The modified lamella drainage analysis is extended and used to qualitatively describe this effect. The experimental data and the analytical results are used to discern the importance of interfacial mobility in the variation of stability with temperature.