Robert D. Sproull

Surface hydrophobic influences on β-lactoglobulin adsorption kinetics

Abstract The adsorption isotherms and kinetic behavior exhibited by β-lactoglobulin at silanized silicon surfaces of varying hydrophobicity were examined using ellipsometry. Adsorption isotherms indicated that the adsorbed mass of β-lactoglobulin increased with increasing surface hydrophobicity, within a defined range of hydrophobicity. Adsorption kinetics recorded for β-lactoglobulin on each surface were compared to the kinetic behavior predicted by a simple model for protein adsorption. The model described the data well in all cases, enabling interpretation of the kinetic behavior in terms of contact surface hydrophobicity influences on rate constants affecting protein attachment and unfolding at the interface. In particular, both experimental and simulation results seem to be in support of a hypothesis that rate constants defining protein arrival and conversion to an irreversibly adsorbed state increase with increasing surface hydrophobicity, while the rate constant defining desorption of protein from a reversibly adsorbed state decreases with increasing surface hydrophobicity. Contact surface hydrophobicity was quantified using contact angle analysis to determine the nondispersive component of the work required to remove water from unit area of surface. Quantitative consideration of possible mass transfer influences on the observed adsorption rates supports the notion that the experiments were not conducted in a transport-limited regime.

The effect of pH and NaCl concentration on adsorption of β-lactoglobulin at hydrophilic and hydrophobic silicon surfaces

Abstract The effect of pH and NaCl concentration on the equilibrium adsorptive behavior of β-lactoglobulin at hydrophilic and hydrophobic silicon surfaces was studied using ellipsometry. Experimental conditions studied included pH 3.00, 0.1 M Na + ; pH 6.60, 0.1 M Na + ; pH 8.90, 0.1 M Na + ; and pH 8.90, 0.5 M Na + . Plots of adsorbed mass as a function of protein concentration exhibited attainment of plateau values beyond a protein concentration of 0.25 mg/ml. At a given pH and ionic strength, as expected, plateau values associated with hydrophobic surfaces were observed to be greater than those associated with hydrophilic surfaces. A Langmuir-type adsorption isotherm was chosen as an appropriate model to represent the data and was used to compare results obtained under different experimental conditions. Effects of pH and NaCl concentration on protein adsorption at hydrophilic surfaces indicate that electrostatics play a major role, while pH and NaCl concentration effects on adsorption at hydrophobic surfaces reflect a greater importance of nonelectrostatic interactions.

Design and performance considerations for the development of hydrogen selenide effluent processing systems

One of the gases which may be used in processes for fabrication of electro‐optical materials including some solar cells is hydrogen selenide. This gas is included in the Environmental Protection Agency (EPA) list of toxic chemicals and requires care in use and treatment. No data were identified in the literature relating to scrubbing or other processes which have been used to control process effluents. This paper presents and discusses criteria for the development of an effective scrubbing system to handle hydrogen selenide based on current emission standards. Problems considered include the development of reactor and piping enclosure scrubbers as well as scrubbers for the effluent gas stream. Extrapolation of available data was used to predict performance of scrubbers based on typical designs. Data for the operation of a dual scrubbing system are presented which show that emissions of hydrogen selenide can be reduced well below threshold limit value (TLV) for a range of gas throughput rates. Future areas...

Iron oxidation by Thiobacillus ferrooxidans

ConclusionsResults of the parametric study of factors affecting ferrous iron oxidation show that the maximum conversion rate, which corresponds to the relative effectiveness of a given strain ofT. ferrooxidans on iron oxidation, is a function of initialpH, initial ferrous iron concentration, and cell number of inoculum size. However, the lag time, which corresponds to the time required to obtain the maximum conversion rate, is affected by initial ferrous iron concentration and initial cell number, but not by initialpH.Measuring ferrous iron concentration during its oxidation in 9K medium is a quick and simple method for predicting the relative potential of various strains ofT. ferrooxidans in microbial leaching operations. However, according to Norris(16), developing better strains ofT. ferrooxidans may not improve leaching rates if mineral dissolution is slower than iron oxidation in solution. Therefore, as better iron-oxidizing strains of the bacterium are identified, other improvements in microbial leaching operations need to be developed.Based on the data presented in this paper, a low initial ferrous iron concentration and a large inoculum volume (initial cell number) are recommended for comparative studies of various strains ofT. ferrooxidans. A low initialpH (1.8–2.0) is also recommended to prevent ferrous iron precipitation. In addition, before determining its maximum rate of oxidation of ferrous iron, each strain ofT. ferrooxidans grown for a comparative study should be washed thoroughly to obtain cell suspensions containing a minimum amount of ferric iron.

The characterization of charcoal and high-density carbon pellets produced from Douglas-fir bark

High-density carbon pellets (HDCP) produced from Douglas-fir bark could provide an alternate source of carbon for industry. The production of HDCP in vertical retorts is discussed. Scanning electron microscopy (SEM), atomic absorption spectroscopy (AAS), carbon elemental analysis, and other analytical methods were used to characterize HDCP. HDCP produced from Douglas-fir bark in this work have 90% fixed carbon, an average density of 1.3 g/mL, and 1.18% average ash content with negligible metal impurities. These pellets should be particularly suited for use in the production of adsorbents, high-grade carbons, reductants, carbon black, carbon electrodes, and activated carbons.

The Utilization of Douglas-Fir Bark for the Production of Oxalic Acid and High Density Carbon Pellets

The production of oxalic acid by the catalytic oxidation of Douglas-fir (Psedotsuga menfiesii (Mirb) Franco) bark and subsequent pyrolysis of the residue to produce high density carbon pellets is discussed. Kinetic rate data are presented for oxalic acid production from Douglasfir bark. A maximum yield of 38 wt% oxalic acid has been obtained in 8 h at 80°C with 62.5 vol% HNO3 and 0.5 mg V2O5/g of bark. Additional oxalic acid can be produced by the conversion of pyrolytic oils and tars (obtained during carbonization of the residue) to increase the total yield to 45 wt%. An economic analysis based on the current cost of oxalic acid indicates the viability of the proposed process.