Fatty acid esterification by reactive distillation: Part 2—kinetics-based design for sulphated zirconia catalysts

In a previous study on the basis of reaction equilibrium, it was demonstrated that the synthesis of fatty acids esters of heavy alcohols by catalytic reactive distillation (RD) is basically feasible. Presently, the analysis is expanded to the kinetics-based design applied to the synthesis of 2-ethylhexyl dodecanoate. Experimental data for a super-acidic sulphated zirconia catalyst are employed. It is shown that this catalyst is highly selective even for the high alcohol/acid ratios as prevail in a RD column. To avoid catalyst deactivation, liquid-liquid segregation into an organic and an aqueous phase must be prevented, and operating temperatures beyond must be chosen. A kinetic model based on liquid activities is proposed, with parameters determined from both kinetic and equilibrium measurements. A typical column design has 13 reactive stages with a catalyst loading of , temperature profile of 400-, and a space velocity of for 99.9% purity product ester. A modified Damköhler number is proposed.     

A generalized analysis on material invariant characteristics for microwave heating of slabs

A generalized dimensionless formulation has been developed to predict the spatial distribution of microwave power and temperature. The ‘dimensionless analysis’ is mainly based on three numbers: wave number, ; free space wave number, ; and penetration number, , where is the ratio of sample thickness to wavelength of microwaves within a material, is based on wavelength within free space and is the ratio of sample thickness to penetration depth. The material dielectric properties and sample thicknesses form the basis of these dimensionless numbers. The volumetric heat source due to microwaves can be expressed as a combination of dimensionless numbers and electric field distributions. The spatial distributions of microwave power for uniform plane waves can be obtained from the combination of transmitted and reflected waves within a material. Microwave heating characteristics are obtained by solving energy balance equations where the dimensionless temperature is scaled with respect to incident microwave intensity. The generalized trends of microwave power absorption are illustrated via average power plots as a function of , and . The average power contours exhibit oscillatory behavior with corresponding to smaller for smaller values of . The spatial distributions of dimensionless electric fields and power are obtained for various and . The spatial resonance or maxima on microwave power is represented by zero phase difference between transmitted and reflected waves. It is observed that the number of spatial resonances increases with for smaller regimes whereas the spatial power follows the exponential decay law for higher regimes irrespective of and . These trends are observed for samples incident with microwaves at one face and both the faces. The heating characteristics are shown for various materials and generalized heating patterns are shown as functions of , and . The generalized heating characteristics involve either spatial temperature distributions or uniform temperature profiles based on both thermal parameters and dimensionless numbers ().     

Carbon dioxide absorption with aqueous potassium carbonate promoted by piperazine

Many commercial processes for the removal of carbon dioxide from high-pressure gases use aqueous potassium carbonate systems promoted by secondary amines. This paper presents thermodynamic and kinetic data for aqueous potassium carbonate promoted by piperazine. Research has been performed at typical absorber conditions for the removal of CO₂ from flue gas.Piperazine, used as an additive in 20- potassium carbonate, was investigated in a wetted-wall column using a concentration of at 40-80°C. The addition of piperazine to a potassium carbonate system decreases the CO₂ equilibrium partial pressure by approximately 85% at intermediate CO₂ loading. The distribution of piperazine species in the solution was determined by proton NMR. Using the speciation data and relevant equilibrium constants, a model was developed to predict system speciation and equilibrium.The addition of piperazine to potassium carbonate increases the rate of CO₂ absorption by an order of magnitude at 60°C. The rate of CO₂ absorption in the promoted solution compares favorably to that of MEA. The addition of piperazine to potassium carbonate increases the heat of absorption from 3.7 to . The capacity ranges from 0.4 to for PZ/K₂CO₃ solutions, comparing favorably with other amines.     

A kinetic study on anaerobic reduction of sulphate, part II: incorporation of temperature effects in the kinetic model

The effects of temperature on the kinetics of anaerobic sulphate reduction were studied in continuous bioreactors using acetate as an electron donor. Across the range of temperatures applied from 20 to , the increasing of volumetric loading rate up to 0.08 to resulted in a linear increase in reduction rate of sulphate. The increasing reaction rate showed a lower dependence on volumetric loading rate in the range 0.1-. Further increase in volumetric loading rate above was accompanied by wash out of bacterial cells and a sharp decrease in reaction rate. Despite a similar pattern for dependency of reaction rate on volumetric loading at all temperatures tested, the magnitude of reaction rate was influenced by temperature, with a maximum rate of observed at . The effect of temperature on maximum specific growth rate (μ_max) and bacterial yield was insignificant. The values of maximum specific growth rate and yield were and 0.56-0.60 kg bacteria (), respectively. The decay coefficient (k_d) and apparent saturation constant () were both temperature dependent. The increase of temperature resulted in decreased values of , and higher values for k_d. Using the experimental data effect of temperature was incorporated in a kinetic model previously developed for anaerobic reduction of sulphate.     

Characterization of anion diffusion in polymer hydrogels used for wastewater remediation

Ion exchange systems for the removal of nutrient pollutants, even at extremely low concentrations, from wastewater effluents are a major environmental need. This work reports on the features of batch sorption processes for the ultimate removal and recovery of reactive phosphorus, nitrogen, and sulfur anions from aquaculture production wastewater effluents. The sorbent used was a crosslinked polyamine (PAA·HCl) polymeric hydrogel. The PAA·HCl hydrogels were prepared by chemically crosslinking aqueous solutions of linear PAA·HCl chains with epichlorohydrin (EPI). The nutrient anion binding capacity of the gels was studied as a function of various processing parameters. Lab scale batch and experiments showed maximum anion removal, from aquaculture wastewater, with regard to by 99%, by 70%, and by 95%. diffusivities of 16, 10, and 8×10⁻⁶ cm²/s were measured at pH levels of 5.5, 7.0, and 8.5.     

Anomalous IR optical properties of aggregates of Pd nanoparticles induced through electrochemical cyclic voltammetry

IR optical properties of Pd nanoparticles with different size and aggregation state were studied in the current paper. The dispersed Pd nanoparticles () stabilized with poly(N-vinylpyrrolidone) (PVP) were synthesized by the seeding growth method, in which the seeds were formed step by step through reducing H₂PdCl₄ with ethanol. The dispersed Pd nanoparticles of much large size () were grown from the by keeping the colloid of undisturbed for 150 days at room temperature around 20 °C. The aggregates of () were prepared through an agglomeration process induced during a potential cyclic scanning between −0.25 V and 1.25 V for 20 min at a scan rate of 50 mV s⁻¹. Scanning electron microscope (SEM) patterns confirmed such aggregation of . Fourier transform infrared (FTIR) spectroscopy together with CO adsorption as probe reaction was employed in studies of IR optical properties of the prepared Pd nanoparticles. The results demonstrated that CO adsorbed on films substrated on CaF₂ IR window or glassy carbon (GC) electrode yielded two strong IR absorption bands around 1970 cm⁻¹ and 1910 cm⁻¹, which were assigned to IR absorption of CO bonded on asymmetric and symmetric bridge sites, respectively. Similar IR bands were observed in spectra of CO adsorbed on films, except the IR bands were much weak, whereas CO adsorbed on film produced an IR absorption band near 1906 cm⁻¹, and an anomalous IR absorption band whose direction has been completely inverted around 1956 cm⁻¹. The direction inversion of the IR band of CO bonded to asymmetric bridge sites on was ascribed to the interaction between Pd nanoparticles inside the aggregates. Based on FTIR spectroscopic and cyclic voltammetric results, the aggregation mechanism of Pd nanoparticles from to has been suggested that the agglomeration of Pd nanoparticles was driven by the alteration of electric field across electrode-electrolyte interface, when the PVP stabilizer was stripped via oxidation during cyclic voltammetry.     

Electrochemical performances of gel polymer electrolytes using tetra(ethylene glycol) diacrylate

A gel polymer electrolyte (GPE) was prepared using tetra(ethylene glycol) diacrylate monomer, benzoyl peroxide, and (). The LiCoO₂/GPE/graphite cells were prepared and their electrochemical properties were evaluated at various current densities and temperatures.The viscosity of the precursor containing the tetra(ethylene glycol) diacrylate monomer was around . The ionic conductivity of the gel polymer electrolyte at 20°C was around . The gel polymer electrolyte had good electrochemical stability up to vs. Li/Li⁺. The capacity of the LiCoO₂/GPE/graphite cell at rate was 63% of the discharge capacity at rate. The capacity of the cell at −10°C was 81% of the discharge capacity at 20°C. Discharge capacity of the cell with gel polymer electrolyte was stable with charge-discharge cycling.     

A new method to determine the microbial kinetic parameters in biological air filters

This paper presents a new method to determine kinetic parameters of the biodegradation of various pollutants in a biofilter. Toluene, a readily biodegradable volatile organic compound, and methane, a hydrocarbon and a greenhouse gas, have been chosen as the target pollutants. The new protocol utilized biomass immobilized on bed pellets; these directly sampled from a continuous steady-state biofilter. The comparison of this method with the conventional experimental protocol utilizing micro-organisms suspended in a liquid medium was made using the pollutant toluene. Indeed, with both methods, the kinetic parameters have been evaluated by following the microbial growth in batch, thermostated reactors, using determined amounts of pollutant substrate. This experiment has confirmed the pertinence of the new procedure. The interesting features of the new method are that: (1) it is easy to operate (no preliminary treatment of the bed samples) and (2) it provides reproducible parameters that represent the real biofilter case more adequately than liquid cultures. In addition, modeling of the experimental specific growth rates in the case of toluene has shown that the values obtained with the use of solid extracts can be correlated by a Haldane's formulation, where , , and . The maximum specific growth rate was reached for an initial concentration of toluene near . The determination of the experimental specific growth rates of micro-organisms in the methane biofilter has also been performed. This study allowed highlighting two methane concentrations’ ranges: from 1000 to 14 500 ppmv and from 14 500 to 27 000 ppmv. For the first range, the Monod model proves to be suitable with the kinetic parameters: and . For the second range, neither the Monod nor the Haldane's formulation could directly be used. However, a mathematical adjustment of the Monod model allows to find kinetic parameters and . The biomass yields for the tested methane concentrations have also been determined and showed two different tendencies, depending on the same two ranges. For the first range of methane concentrations, the biomass yield was quite constant with an average value around while for the second range, it could be approached by a polynomial second-order regression. The maximum value of the biomass yield obtained on the second range was at a methane initial concentration of 20 000 ppmv.