Raymond C. Everson

Structural and chemical modifications of typical South African biomasses during torrefaction

Torrefaction experiments were carried out for three typical South African biomass samples (softwood chips, hardwood chips and sweet sorghum bagasse) to a weight loss of 30 wt.%. During torrefaction, moisture, non-structural carbohydrates and hemicelluloses were reduced, resulting in a structurally modified torrefaction product. There was a reduction in the average crystalline diameter (La) (XRD), an increase in the aromatic fraction and a reduction in aliphatics (substituted and unsubstituted) (CPMAS (13)C NMR). The decrease in the aliphatic components of the lignocellulosic material under the torrefaction conditions also resulted in a slight ordering of the carbon lattice. The degradation of hemicelluloses and non-structural carbohydrates increased the inclusive surface area of sweet sorghum bagasse, while it did not change significantly for the woody biomasses.

The adsorption of copper in a packed-bed of chitosan beads: Modeling, multiple adsorption and regeneration

In this study, exoskeletons of Cape rock lobsters were used as raw material in the preparation of chitin that was successively deacetylated to chitosan flakes. The chitosan flakes were modified into chitosan beads and the beads were cross-linked with glutaraldehyde in order to study copper adsorption and regeneration in a packed-bed column. Five consecutive adsorption and desorption cycles were carried out and a chitosan mass loss of 25% was observed, after the last cycle. Despite the loss of chitosan material, an improved efficiency in the second and third cycles was observed with the adsorbent utilizing 97 and 74% of its adsorbent capacity in the second and third cycles, respectively. The fourth and fifth cycles, however, showed a decreased efficiency, and breakage of the beads was observed after the fifth cycle. In the desorption experiments, 91-99% of the adsorbed copper was regenerated in the first three cycles. It was also observed that the copper can be regenerated at a concentration of about a thousand fold the initial concentration. The first cycle of adsorption could be accurately described with a shrinking core particle model combined with a plug flow column model. The input parameters for this model were determined by batch characterization methods, with as only fitting parameter, the effective diffusion coefficient of copper in the bead.

Selective Adsorption of Platinum from Mixed Solutions Containing Base Metals Using Chemically Modified Activated Carbons

Abstract: Bituminous coal was activated by using steam at 750°C in a furnace. The activated carbon (AC) particles were chemically treated with thiophosphoric and amine type extractants, then characterized and tested for precious metal selectivity in chloride media. The adsorption of anions [PtCl3−4, PdCl2−4] or cations [PtCl+, PdCKH2O)3+, Ni(H2O)+, Cu2+) on the carbon surface was elucidated by means of complexation and physical adsorption models. Owing to electrostatic repulsion in acidic media (> 1 M HC1), the thio- and amine-treated bituminous ACs did not react with copper and nickel cations. The adsorption rate constant for platinum showed a dependence on solution pH and extractant dosage on the surface of the carbon and was of the order 10− 2 min_1. A three-parameter Toth isotherm best described the adsorption data for single component solutions. Furthermore, platinum adsorption was described by pseudo first order kinetics neglecting the intraparticle diffusivity.

Chemical and structural characterization of char development during lignocellulosic biomass pyrolysis

The chemical and structural changes of three lignocellulosic biomass samples during pyrolysis were investigated using both conventional and advanced characterization techniques. The use of ATR-FTIR as a characterization tool is extended by the proposal of a method to determine aromaticity, the calculation of both CH2/CH3 ratio and the degree of aromatic ring condensation ((R/C)u). With increasing temperature, the H/C and O/C ratios, XA and CH2/CH3 ratio decreased, while (R/C)u and aromaticity increased. The micropore network developed with increasing temperature, until the coalescence of pores at 1100°C, which can be linked to increasing carbon densification, extent of aromatization and/or graphitization of the biomass chars. WAXRD-CFA measurements indicated the gradual formation of nearly parallel basic structural units with increasing carbonization temperature. The char development can be considered to occur in two steps: elimination of aliphatic compounds at low temperatures, and hydrogen abstraction and aromatic ring condensation at high temperatures.

The carbon dioxide gasification characteristics of biomass char samples and their effect on coal gasification reactivity during co-gasification

The carbon dioxide gasification characteristics of three biomass char samples and bituminous coal char were investigated in a thermogravimetric analyser in the temperature range of 850-950 °C. Char SB exhibited higher reactivities (Ri, Rs, Rf) than chars SW and HW. Coal char gasification reactivities were observed to be lower than those of the three biomass chars. Correlations between the char reactivities and char characteristics were highlighted. The addition of 10% biomass had no significant impact on the coal char gasification reactivity. However, 20 and 30% biomass additions resulted in increased coal char gasification rate. During co-gasification, chars HW and SW caused increased coal char gasification reactivity at lower conversions, while char SB resulted in increased gasification rates throughout the entire conversion range. Experimental data from biomass char gasification and biomass-coal char co-gasification were well described by the MRPM, while coal char gasification was better described by the RPM.

A Predictive Model for Permeation Flux in a Membrane Reactor: Aspects of Esterification

Abstract: A polymeric membrane (PERVAP® 2201) was used to study permselectivity and flux of water from esterification mixtures at different temperatures (30°C-90°C) and compositions. The pervaporation flux of water from binary mixtures such as butyl acetate/H2O, butanol/H2O, and acetic acid/H2O was accurately predicted by using a solution-diffusion model with concentration-dependent diffusion coefficients. Furthermore, on the basis of a lower activation energy of diffusion and higher (lux for water, we concluded that butyl acetate production can be enhanced significantly by inserting a reactor membrane (PERVAP® 2201)in the esterification process.