Utilization of lignocellulosic natural fiber (jute) components during a microbial polymer production

Lignocellulosic fiber (jute), a low cost natural complex carbon source, was introduced in a fermentation medium to observe the effects of its constituents on the production of a commercially potent bacterial extracellular polysaccharide (EPS) synthesized by Bacillus megaterium RB-05. It has been found that among all the fiber components the bacterium has utilized cellulose most for the EPS production. Maximum polymer yield of 0.297 g g^− 1 substrate was found after 72 h fermentation. Consumption of fiber components was typically driven by in situ bacterial enzyme activity as EPS production was found significantly (p < 0.05) accelerated from 36 h onwards with considerable cellulase activity. Utilization of fiber components during different fermentation hours were characterized using scanning electron microscopy, FT-IR spectroscopy, X-ray diffraction, tensile property, and contact angle measurement.     

Biocatalytic production of biodiesel from cottonseed oil: Standardization of process parameters and comparison of fuel characteristics

The enzymatic production of biodiesel by transesterification of cottonseed oil was studied using low cost crude pancreatic lipase as catalyst in a batch system. The effects of the critical process parameters including water percentage, methanol:oil ratio, enzyme concentration, buffer pH and reaction temperature were determined. Maximum conversion of 75–80% was achieved after 4 h at 37 °C, pH 7.0 and with 1:15 M ratio of oil to methanol, 0.5% (wt of oil) enzyme and water concentration of 5% (wt of oil). Various organic solvents were tested among which a partially polar solvent (t-butanol) was found to be suitable for the reaction. The major fuel characteristics like specific gravity, kinematic viscosity, flash point and calorific value of the 20:80 blends (B20) of the fatty acid methyl esters with petroleum diesel conformed very closely to those of American Society for Testing Materials (ASTM) standards.     

Reliability Indices for a Power Network Considering Static, Transient, and Dynamic Performance

We propose to include stability margin violations which characterize the static, dynamic, and transient performance in the face of contingencies (e.g., loss of lines, loss of generation, load variations, and short circuits) in the definition of reliability indices, besides the usual continuity of supply at load points. Using the method of Lyapunov, the stability margins are defined to be a norm of the steady-state power angle differences, an estimate of the dynamic stability domain, and an estimate of the transient stability domain. The reliability indices are derived from a decision theoretic model; the decision surface incorporates the criterion of stability margin violations. The utility of the proposed index is shown by analyzing an example of a realistic system.     

Boundary value problems in transport with mixed and oblique derivative boundary conditions,steady state and transient solutions

The transport of heat or mass from a stationary medium into a flowing fluid leads generally to boundary value problems in which the boundary condition (on the temperature or concentration) specifies the oblique derivative or the mixed second derivative with respect to the normal and tangential directions on the solid surface[1,2]. Such boundary value problems are generally nonselfadjoint. It is shown in this paper that the differential operators have, however, the important property of possessing an assured spectral representation, which, when determined, may be readily employed to solve steady state and transient problems of the foregoing type. The method of separation of variables is shown to be applicable for the determination of the above spectral representation of the operators in certain cases. These include (i) cylinder, cooled by a fluid flowing circumferentially around it, (ii) the infinite slab or infinite cylinder cooled by a fluid flowing along the axial direction. Solutions are obtained for steady and unsteady state problems. The boundary value problems of this paper are of considerable importance to nuclear reactor cooling and many separation processes.     

A coalescence redispersion model for drop-size distributions in an agitated vessel

A population balance model has been developed accounting for coalescence and redispersion of drops in an agitated liquid—liquid dispersion. It is assumed that drop coalescence is followed by immediate redispersion into two drops whose sizes are distributed according to a uniform distribution in the ratio of the daughter drop-volume to the parent drop-volume. If it is assumed that the coalescence frequency is independent of drop-size, the resulting non-linear integral equation admits an exponential solution for the equilibrium drop-volume distribution in a batch vessel. On comparing experimental data obtained from several sources with the prediction of this model, it is found that for flat-blade turbine agitated systems, the agreement is very good; in fact, the sign test ranks the model as better fitting than empirical expressions for drop-sizes proposed by other workers. For circulation stirring systems, e.g. those having Waldhof agitator, the model predictions are substantially improved by assuming that the coalescence frequency is proportional to the diameters of the interacting drops.     

KINETICS OF AQUEOUS ETHYLENEDIAMINE-ETHANOL-ANTHRAQUINONE DELIGNIFICATION PROCESS

A new organosolv pulping method has been investigated. Delignification can be carried out by digesting the lignocellulosic material in an aqueous solution of ethylenediamine (EDA) and ethanol (EtOH) in combination with catalytic amounts of anthraquinone (AQ). This aqueous EDA-EtOH-AQ pulping is found to be highly selective in delignification and is flexible to softwoods. Bulk delignification was found to take place according to a pair of first-order mechanisms, like aqueous ethanol pulping. In the initial phase of delignification more than 50% lignin is removed, while the rest is extracted in the second slower step. The rate constants for each step are of the same order of magnitude and higher than those obtained in ethanol pulping. This indicated that overall delignification is faster when compared to aqueous ethanol pulping. The Arrhenius activation energy for the initial step was found to be 6.4 kcal/mole. The high selectivity in the detignification during the EDA-EtOH—AQ process is observed at all levels of delignification and shows at least an 18—20% increase in yield when compared with ethanol pulping.     

Digital controller design for enhancing steady-state stability of interconnected power systems

This paper presents a microprocessor based digital controller design for static phase-shifters used with other stability enhancement tools to damp inter-area electromechanical modes of oscillations and stabilize AC interties. The digital controller's robustness under different contingency conditions such as system parameter changes, disturbances, control loop and sensor failures are assessed.     

Population balance modeling. Promise for the future

Population balance modeling has received an unprecedented amount of attention during the past few years from both academic and industrial quarters because of its applicability to a wide variety of particulate processes. In this article, a fresh look is taken of the basic issues of the application of population balances towards strengthening the approach as well as widening the scope of their applications with regard to formulation, computational methods for solution, inverse problems, control of particle populations and stochastic modeling.     

Population balance modelling of bubbling fluidized beds. II. Axially dispersed dense phase

The population balance model of Sweet, Gustafson and Ramkrishna for a steady state gas-solid fluidized bed reactor is extended in this work to include axial mixing in the dense phase. A trivariate population balance equation for the bubble phase, and an axial dispersion equation for the dense phase are solved simultaneously by combining a Monte Carlo simulation technique with the method of successive approximations. Conversion for a first-order reaction is analysed in terms of five dimensionless groups including: a coalescence parameter controlling the extent of coalescence, a Peclet number measuring the amount of mixing in the dense phase, a Damkohler number which relates the dispersive mixing time in the dense phase to the reaction time, a dimensionless group representing the ratio of the dispersive mixing time to the time scale of mass transfer, and a dimensionless reaction rate constant. The computations show that coalescence can significantly affect reactor conversion. It appears that the effect of mixing is less significant particularly at higher reaction rates. Comparison of these results with those obtained earlier in which the dense phase was assumed to be perfectly mixed shows that higher conversions could be obtained in the latter case for sufficiently fast reactions while the opposite is true for slow reactions. This paper is dedicated to Dr L K Doraiswamy on his sixtieth birthday.