Phillip Pendleton

Properties of activated carbon controlling 2-Methylisoborneol adsorption

2-Methylisoborneol (MIB) is one of the most common taste and odour molecules found in water supplies. The use of activated carbons is known to be effective in removing MIB from water. In this work, it was found that the selection of an appropriate carbon for removing MIB from water depends on the carbon surface hydrophilicity, which can be determined via water adsorption analysis or elemental analysis. Provided the carbons used are microporous, the less hydrophilic carbons adsorb more MIB.

The influence of surface chemistry on activated carbon adsorption of 2-methylisoborneol from aqueous solution

Abstract An activated carbon with a relatively high oxygen content was heated at various temperatures in an argon atmosphere to produce a series of carbons with decreasing oxygen content. A second activated carbon with a relatively low oxygen content was treated with an ozone–oxygen mixture to produce a series of carbons with increasing oxygen content. In both cases, the pore size distribution and pore volume were unaffected by the treatment conditions. Adsorption isotherm and enthalpy of water displacement measurements were made for adsorption of 2-methylisoborneol (MIB) by these carbons in water. Both measurements show the importance of the oxygen content on the adsorption of MIB from aqueous solution. Increasing surface oxygen content at a constant pore volume leads to a decrease in both the amount adsorbed and the enthalpy of adsorption. To test the role of the solvent in this adsorption process, a relatively non-polar solvent, dichloromethane (DCM), was used to make adsorption measurements. Adsorption isotherms show that the amount of MIB adsorbed from DCM solution is independent of the oxygen content. These results indicate that the solvent plays an important role in the control of the adsorption from solution of a sparingly soluble solute.

Oxidation of aldehydes using silica-supported Co(II)-substituted heteropolyacid

A supported Co(II)-substituted heteropolyacid salt, Cs6H2P2W17O61Co·OH2, on silica was prepared and characterized by BET surface area measurements, thermal analysis (TGA/DTA) and infrared spectroscopy. The infrared spectroscopy and thermal analysis revealed that the supported heteropolyacid salt preserves Wells-Dawson structure and is stable upto 500 ◦ C. The BET result shows that by supporting the above heteropolyacid salt on silica, surface area increases. The supported heteropolyacid was used as a heterogeneous catalyst for the oxidation of aldehydes to corresponding carboxylic acids with molecular oxygen. Silica-supported heteropolyacid is an effective catalyst for the oxidation of aldehydes to carboxylic acids.

Kinetics of dodecanoic acid adsorption from caustic solution by activated carbon

This study examines the influences of adsorbent porosity and surface chemistry and of carbon dosage on dodecanoic acid adsorption kinetics from aqueous and 2 M NaOH solutions as batch adsorption processes. Both adsorbents are steam-activated carbons prepared from either coconut or coal precursors. Prior to use the adsorbents were washed in deionized water or 2 M NaOH. Mass transfer coefficients and effective overall diffusion coefficients indicate a minor contribution from adsorbent porosity. In contrast, high surface oxygen content impedes transport to and into the adsorbent structure. Carbon dosage shows a proportional increase in transport coefficients with increasing mass; these coefficients are constant when normalized per unit mass. Neither water nor NaOH treatment of the adsorbents has a significant influence on dodecanoic acid adsorption kinetics. Molecular and Knudsen diffusion coefficients are defined to demonstrate that the overall effective diffusion coefficient values and the diffusion process are controlled by surface diffusion.

Determination of geosmin and 2-methylisoborneol in water using solid-phase microextraction and gas chromatography-chemical ionisation/electron impact ionisation-ion-trap mass spectrometry

A method for the determination of geosmin and 2-methylisoborneol (MIB) in water by solid-phase microextraction (SPME) is presented. Various SPME fibre chemistries have been compared for their efficiency in extracting MIB from water. Extraction conditions including the extraction time and temperature have been optimised. A 30 ml water sample is extracted for 20 min at 60 degrees C using a divinylbenzene fibre, and the extract analysed by gas chromatography with ion-trap mass spectrometry detection. d5-Geosmin and d3-MIB are added as internal standards to compensate for any variability in the SPME process which is not carried out to equilibrium. Chemical ionisation, using acetonitrile as the reagent gas, was found to give superior sensitivity to electron impact ionisation (EI) for the detection of MIB. EI was used as the ionisation mode for detection of geosmin. The method shows good linearity over the concentration range 5-40 ng l-1 and gives detection limits of 1 ng l-1 for both geosmin and MIB. Recovery (93-110%) and precision (3-12%) over this concentration range, for both raw and treated drinking waters, are comparable to currently employed methods such as closed-loop stripping analysis (CLSA). The method offers the advantage of being simple to use, with much shorter analysis times in comparison to CLSA.

Factors Affecting Skin Tannin Extractability in Ripening Grapes

The acetone-extractable (70% v/v) skin tannin content of Vitis vinifera L. cv. Cabernet Sauvignon grapes was found to increase during late-stage ripening. Conversely, skin tannin content determined following ethanol extraction (10, 20, and 50% v/v) did not consistently reflect this trend. The results indicated that a fraction of tannin became less extractable in aqueous ethanol during ripening. Skin cell walls were observed to become more porous during ripening, which may facilitate the sequestering of tannin as an adsorbed fraction within cell walls. For ethanol extracts, tannin molecular mass increased with advancing ripeness, even when extractable tannin content was constant, but this effect was negligible in acetone extracts. Reconstitution experiments with isolated skin tannin and cell wall material indicated that the selectivity of tannin adsorption by cell walls changed as tannin concentration increased. Tannin concentration, tannin molecular mass, and cell wall porosity are discussed as factors that may influence skin tannin extractability.

Development of an automated gas adsorption apparatus for the characterization of the surface area, pore size distribution, and density of powdered materials

An automated apparatus for the characterization of the surface area, pore size distribution, and density of powdered materials is described. A newly developed liquid nitrogen level control system maintains the nitrogen level around the tube containing the sample within ±0.2 mm of the initial predefined level. The dosing volume and pneumatically operated control valves are maintained at 25.00±0.05 °C. Equilibrium pressure is measured with the accuracy of ±0.05% of reading. The apparatus may be operated either in a manual or an automatic mode. The control software developed, using the VISIDAQ Version 3.11 software package, operates involving equilibrium and barometric pressure measurements, opening and closing pneumatically operated valves, and transferring experimental data to MS EXCEL spreadsheets. The subroutines developed within the spreadsheet program plot the adsorption and desorption isotherms, calculate the sample specific surface area and density, and provide αs- and t-plots and mesopore and microp...

Analysis of uncertainties in manometric gas-adsorption measurements II. Uncertainty in αs-analyses and pore volumes

We describe procedures to propagate the uncertainty in adsorption data and alpha(S)-values to generate uncertainty in apparent primary, secondary, and total micropore volumes for porous activated carbons exhibiting Type I and IV character. The alpha(S)-data are interpolated from selected non-porous reference material (NPRM) adsorption isotherm data with some adsorbents exhibiting surface chemistry quite different from and some similar to that of the porous adsorbents (PA). We show that a statistically constant apparent total micropore volume can be determined independent of the NPRM surface chemistry. In contrast, NPRM surface chemistry appears to influence our ability to identify unequivocally the filling and condensation ranges of micropore filling, leading to statistically different apparent primary and secondary micropore volumes.

Dehydration products of 2-methylisoborneol

Abstract 2-Methylenebornane and 2-methyl-2-bornene have previously been identified as dehydration or degradation products of 2-methylisoborneol (MIB), a compound responsible for taste and odour problems in various water environments. Previously, the identification of these products has been based on mass spectral analysis only. The dehydration of MIB under a variety of conditions was reinvestigated and the products fully characterised by 1 H and 13 C n.m.r. and GC-MS. Comparison of EI mass spectra of the dehydration products of MIB with those published previously indicate that earlier assignments of MIB dehydration products are incorrect.

Analysis of ionic strength effects on the adsorption of simple amino acids.

HYPOTHESIS Amino acid adsorption by metals and/or oxide surfaces is important in many biomedical and industrial processes, however limited information exists discussing ionic strength influences on the mechanism of adsorption. A comparison of pure water solution and added 1:1 electrolyte should highlight the effects of electrolyte on amount adsorbed. ATR spectroscopy of the adsorbed phase should demonstrate the effects on the mechanism of adsorption. EXPERIMENTS Low solution concentration adsorption isotherms for glycine, lysine and glutamic acid on Aerosil 200 silica were generated in pure water and 10 and 100 mmol/L sodium chloride solutions. A systematic study of the adsorption isotherms as well as adsorbent and adsorptive solution properties was performed. ATR-IR spectroscopy was used to analyse the adsorbed phase in solution. FINDINGS Glycine adsorbs primarily through electrostatic interactions; lysine also adsorbs through electrostatic interactions in a parallel conformation with the surface. Glutamic acid adsorbs via hydrogen bonding and forms intermolecular clusters around an adsorbed nucleus. ATR-IR spectrum deconvolution shows a peak shift for glycine and lysine associated with the δ(ad)NH3(+) vibration, indicating interaction through the amino moieties. Amount adsorbed was decreased significantly by the addition of 10 mmol/L sodium chloride and completely inhibited by the addition of 100 mmol/L sodium chloride.