Low Molecular Weight Alcohols Research Articles

Optimising the Effect of Stimulants on Citric Acid Production from Cocoyam Starch Using Aspergillus Niger

Additives such as low molecular weight alcohols, trace metals, phytate, lipids etc have been reported to stimulate citric acid production. Hence the objective of this study was to investigate the effect of stimulating the metabolic activity of Aspergillus niger for the purpose of improved citric acid production from cocoyam starch. A three-variable, three-level Box-Behnken design (BBD) was used to develop a statistical model to study the effects of Zinc (II) ion, Iron (III) ion and methanol on the production of citric acid. Response surface methodology (RSM) was used to optimise the effects of these stimulants. The results of analysis of variance (ANOVA) carried out on the model showed that the model was statistically significant (p< 0.0001) and did not show lack of fit (R 2 =0.997). The results also showed that citric acid production increased when the levels of zinc and methanol were increased. Intermediate levels of iron were required to produce citric acid at optimum levels. Results obtained from RSM showed that the optimum levels of zinc, iron and methanol were 4.5 g/L, 6.87 g/L and 3.0 %v/v respectively. Under these conditions, the maximum citric acid concentration was obtained as 108 g/L. Validation of the model indicated no significant difference between predicted and experimental values. http://dx.doi.org/10.4314/njt.v34i4.9

Preliminary Investigation on the Electrochemical Activity of Butanol Isomers as Potential Fuel for Direct Alcohol Fuel Cell

Low molecular weight alcohols have been proposed as promising alternative fuels to H2 in low temperature fuel cells due to their liquid nature, high energy density, availability in nature and easy handling1. Methanol and ethanol have been widely studied as fuel for direct alcohol fuel cell (DAFC); however methanol is toxic whereas ethanol is non-toxic and can be produced by fermentation of sugar. However, there is on-going public debate on the ethics of utilizing food stocks for fuel production instead of nutrition2. An alternate renewable source, which does not compete with the food, is required for a sustainable long-term energy production. Thus, 2nd generation bio-fuels are produced from non-food based feedstock such as lignocellulose biomass (LCB)2-3. Butanol is considered as a 2nd generation bio-fuel with better infrastructure compatibility than ethanol. These C4 alcohols have higher energy content, lower water adsorption, and better blending ability with gasoline than ethanol and is considered as a promising substitute for gasoline in automobiles2-3. In fuel cell, butanol provides 24 electrons on complete oxidation compared to 12e- and 6e- from ethanol and methanol respectively. In this regard, with the recent developments in the bio-butanol production, butanol has the potential to be used as fuel for DAFC. However increasing carbon will increase the number of possible intermediates and complicates the reaction pathway and thus reduces the efficiency. Within this study, different butanol isomers were examined as potential fuel for DAFC using a three electrode cell set up on Pt and PtSn electrodes prepared by electrodeposition on glassy carbon both in acid and alkaline media. The Sn coverage was calculated from the difference in the hydrogen desorption charge before and after the Sn deposition. A clear difference in behaviour was observed for different butanol isomers in the cyclic voltammetry (CV) indicating their different oxidation activity. N-butanol and iso-butanol showed similar CV features whereas 2-butanol and ter-butanol showed completely different CV features. Ter-butanol was found to be inactive for electrochemical oxidation at room temperature on Pt. Comparing the CV of Pt in butanol and acid, it was clear that the presence of OHads is necessary to initiate the n-butanol and iso-butanol oxidation on Pt. To enhance this, an oxophilic metal (Sn) was added to Pt so as to initiate the water dissociation at a lower potential. The PtSn electrode showed an improved oxidation activity compared to Pt with a pre-peak at ~500 mV (Figure 1) lower than the onset potential found using Pt for n-butanol oxidation in acidic media. Since this pre-peak appears at a potential region where PtOx is not formed, the oxygenated species for the butanol oxidation was assumed to be provided by the Sn on the catalyst surface 4. The higher activity of PtSn was thought to be due to a bi-functional mechanism where the water dissociate on Sn surface to provide OHads at lower potential which helps in the removal of poisoning species CO from the Pt as CO2 (equation1-2). The activation energy calculated at the pre-peak, 0.25 V vs. Ag/AgCl (3M NaCl) for the PtSn was about ~11 kJ mol-1 which is significantly lower than that on pure Pt at the first anodic peak, 0.7 V vs. Ag/AgCl-3M NaCl (25 kJ mol-1). The lower activation energy on PtSn at lower potential could be attributed to their effectiveness in the dissociative adsorption and oxidation of butanol 5. These results suggests PtSn could be an active catalyst for n-butanol electro oxidation and shows promise for further studies on long chain organic molecules. Sn+H2O --> Sn-OHads +H++e- (1)Pt + COads + Sn-OHads --> CO2 + H+ +e- (2) Figure 1. The voltammogram of Pt and PtSn electrodes (a) Pt and PtSn in in 0.1M H2SO4 and (b) Pt and PtSn in 0.1M BtOH+0.1M H2SO4 . Scan rate 50 mVs-1. Sn coverage ~25%. Reference (1) (a) Catalysts for Alcohol-fuelled Direct Oxidation Fuel Cells; Liang, Z. X.; Zhao, T. S., Eds.; Royal Society of Chemistry, Cambridge, UK, 2012(b) Song, S.; Maragou, V.; Tsiakaras, P. Journal of Fuel Cell Science and Technology 2006, 4, 203. (2) Dürre, P. Biotechnology Journal 2007, 2, 1525. (3) Tao, L.; He, X.; Tan, E. C. D.; Zhang, M.; Aden, A. Biofuels, Bioproducts and Biorefining 2014, 8, 342. (4) (a) Gupta, S. S.; Singh, S.; Datta, J. Materials Chemistry and Physics 2009, 116, 223(b) Beyhan, S.; Coutanceau, C.; Léger, J.-M.; Napporn, T. W.; Kadırgan, F. International Journal of Hydrogen Energy 2013, 38, 6830. (5) Sen Gupta, S.; Singh, S.; Datta, J. Materials Chemistry and Physics 2010, 120, 682. Figure 1

Fuel Production from the Electroreduction of CO2

Introduction Electrochemical reduction is a highly effective method for converting CO2 to CO, organic acids, low molecular weight hydrocarbons and alcohols. Product distribution from the reduction of CO2 is highly dependent on the composition and preparation of the catalysts and reduction potential, as such, multiple reduction pathways are observed depending on the catalysts material and the preparation methods. Copper and its alloys have been found to produce higher molecular weight hydrocarbons, such as ethylene, methanol and ethanol. Here we demonstrate a high surface area Cu alloy catalysts that has a preferential selectivity towards the formation of C2 and C3 species. This paper will also discuss our attempts to understand the mechanistic pathway using in-situ vibrational spectroscopy under reaction conditions. Experimental A copper/aluminum alloy was used as the starting material for producing a high surface area copper catalyst. The aluminum was removed through an etching procedure in strong base. The resulting nanoporous copper was crushed and mixed with Nafion, a binding agent, then casted over a copper foil substrate. Carbon dioxide electroreduction was performed by placing the catalyst in a specially designed flow cell. A bubbler in the cell was used to deliver CO2 to saturate the electrolyte, 0.1 M KHCO3, at a rate of 10 mL/min. The catalyst acts as the working electrode in this electrochemical cell. The product distribution from the electroreduction process was collected at a series of potentials. Gaseous products were identified and quantified using gas chromatography coupled with both mass spectrometry and a thermal conductivity detector. Liquid products were analyzed using nuclear magnetic resonance. The surface morphology and composition of the catalyst was characterized using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). The SEM images show a rough surface that retains a porous structure before and after experiments. XPS studies incorporated depth profiling, and show that ruthenium from the surface of the material migrates to the bulk after electrolysis.

(Invited) Electrosynthesis of Fuels Directly from CO2

Introduction Carbon dioxide (CO2) is a readily available industrial byproduct that can be used to produce useful chemical compounds. Electrochemical reduction is a highly effective method for converting CO2 to CO, organic acids, low molecular weight hydrocarbons and alcohols. Product distribution from the reduction of CO2 is highly dependent on the composition and preparation of the catalysts and reduction potential, as such, multiple reduction pathways are observed depending on the catalysts material and the preparation methods. Copper-based catalysts have been found to produce higher molecular weight hydrocarbons, such as ethylene, methanol and ethanol. Here we demonstrate a high surface area Cu catalysts that has a preferential selectivity towards the formation of C2 and C3 species. This paper will also discuss our attempts to understand the mechanistic pathway using in-situ vibrational spectroscopy under reaction conditions. Experimental A copper/aluminum alloy was used as the starting material for producing a high surface area copper catalyst. The aluminum was removed through an etching procedure in strong base. The resulting nanoporous copper was crushed and mixed with Nafion, a binding agent, then casted over a copper foil substrate. Carbon dioxide electroreduction was performed by placing the catalyst in a specially designed flow cell. A bubbler in the cell was used to deliver CO2 to saturate the electrolyte, 0.1 M KHCO3, at a rate of 10 mL/min. The catalyst acts as the working electrode in this electrochemical cell. The product distribution from the electroreduction process was collected at a series of potentials. Gaseous products were identified and quantified using gas chromatography coupled with both mass spectrometry and a thermal conductivity detector. Liquid products were analyzed using nuclear magnetic resonance. The surface morphology and composition of the catalyst was characterized using scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). The SEM images show a rough surface that retains a porous structure before and after experiments. XPS studies incorporated depth profiling, and show that ruthenium from the surface of the material migrates to the bulk after electrolysis.

VOLATILES IN TAMAIOASA ROMANEASCA VIA SUPERCRITICAL FLUID EXTRACTION (SFE) ANALYSIS

Wine analysis is a complex process, requiring multiple techniques and very in-depth multidisciplinary knowledge. Moreover, when talking about sensorial potent wines, like Muscat or Tamâioasa Româneasca (from aromatic Romanian grape variety), the identification and characterization of its volatile compounds is achieved through different methods, most calling for powerful solvents to separate the aroma substances. Supercritical fluid extraction is a powerful technique with great promise in organic analytical chemistry. To date, little has been published on the use of SFE in the analysis of wine aromas. The main objective of this study is the analysis of volatiles in samples of Tamâioasa româneasca wines through a custom-made SFE method. The wine variants have been obtained by applying the general technological processes for aromatic wines, using specific oenological products. An in-house SFE analysis method was developed and applied, the obtained extracts were then analyzed by gas chromatography coupled to mass spectrometry (GC-MS) to identify the captured compounds. Regarding the total number of findings in respect to volatiles, the highest concentrations occur with low molecular weight alcohols, esters and acetic acid. Besides, there were also identified other volatile compounds, such as terpenoides and phenols. These specific compounds originate from the grape variety and give the “varietal” character to the wines.

Solubility of Organics in Triethylene Glycol: Phase Equilibrium Modelling Using the Dortmund and LYNGBY Modified UNIFAC Models

 Abstract—This work is an attempt to predict the solubility of 60 volatile organic compounds (VOCs) in triethylene glycol aimed at thermodynamically testing the suitability of this solvent as an absorbent for the selected organics. The VOC main groups studied were alkanes, alkenes, alkynes, aldehydes, carboxylic acids and alcohols. The Modified UNIFAC Dortmund and Lyngby models were to study the required phase equilibrium as a function of temperature and composition. Triethylene glycol was found to be suitable for the absorption of low molecular weight aldehydes, alcohols and carboxylic acids. Generally, the infinite dilution activity coefficients computed in this study were low (below 100) indicating that the polymeric solvent studied in this work gave favourable phase equilibrium compared to water, the common industrial solvent. The solubility of VOCs was also found to decrease with increase in solute molecular weight. Compared with literature findings, the Dortmund performed better than the Lyngby procedure. However both models failed to accurately predict phase equilibrium behaviour. The authors therefore agree with literature findings that a specialised group interaction needs to be created for this solvent in the UNIFAC models in order to satisfactorily predict activity coefficients for the studied binary interactions.

Diffusion of alcohols and aromatics in a mesoporous MCM-41 material

The aim of the present paper was to measure the apparent diffusivities, Knudsen diffusivities, pore diffusivities and activation energies of diffusion at 26–32°C and to determine the modes of transport of some alcohols (methanol, ethanol, propanol, n-butanol) and aromatics (benzene, ethylbenzene, propylbenzene, toluene, o-xylene, m-xylene, p-xylene) into the mesoporous structure of MCM-41 synthesized. As the molecular weight of the alcohols and aromatics increased, apparent diffusivities decreased and the activation energy for diffusion increased. Lower molecular weight alcohols and aromatics had higher diffusivities compared to those with higher molecular weight alcohols at the same temperatures. The diffusion of isomeric molecules within the mesoporous channels were affected by the position of branching. The deterministic behavior depended on the molecular weight, length of side chain and ortho, meta and para isomerism of the molecule. Increasing the temperature raised the kinetic energy of the molecules, which resulted in an increase in the diffusivities of the alcohols and aromatics in MCM-41. Diffusion rate constants of alcohols and aromatics increased with increasing temperature within the range of 26–32°C, and the rate decreased as the molecular weight of the diffusing chemical increased. The diffusion of alcohols and aromatics in MCM-41 obeyed the anomalous transport mechanism. Diffusion exponents, n, being in the range of 0.99–1.07, indicated an anomalous diffusion (non-Fickian/super-Case II) mechanism for alcohol diffusion. However, for the case of aromatics, diffusion exponents, from 0.7 to 1.00, indicated that the diffusion mechanisms were either non-Fickian or non-Fickian/super-Case II depending on the substitution to the benzene ring. Activation energies of alcohols and aromatics were also in good agreement with the values of diffusivities of alcohols and aromatics such that larger activation energies resulted in smaller diffusivities. Alcohols and aromatics with greater solubility parameters were found to have greater diffusivities.

Atomistic modeling of peptide adsorption on rutile (100) in the presence of water and of contamination by low molecular weight alcohols.

Previous models for the interface between titanium implants and biosystems take into account the oxide passivation layer and the hydroxylation, but omit the hydrocarbon contamination on air-exposed samples. The authors develop a consistent model for the contamination of the rutile (100) surface by small alcohols, which are known to be present in ambient atmosphere, and use this approach in molecular dynamics calculations. Contact angle evaluation reveals that hydrophobic surfaces can be generated. During molecular dynamics simulations with three peptides (RPRGFGMSRERQ, WFCLLGCDAGCW, and RKLPDA), polar side chains penetrate the hydrocarbons and become immobilized on the titanium dioxide. In the carbon layer, the peptide recognizes a hydrophobic environment, which was not present on the clean surface, and the authors attribute changes in the secondary structure in one case to this interaction. The authors further include the popular Matsui-Akaogi approach [M. Matsui and M. Akaogi, Mol. Simul. 6, 239 (1991)] into the frame of the AMBER force field and quote van der Waals parameters for fitting the original Buckingham part. With the new potential, the authors evaluated lattice parameters, thermal fluctuation, and bulk modulus. Translational diffusion coefficients and dipole autocorrelation functions of water on the surface are discussed in relation to surface properties, and it is shown that the water layers are more rigid than on earlier titanium dioxide models, and that contacts between peptide and surface are less direct.

Recovery of oxygenated ignitable liquids by zeolites, Part I: Novel extraction methodology in fire debris analysis

The recovery of low molecular weight oxygenates in fire debris samples is severely compromised by the use of heated passive headspace concentration with an activated charcoal strip, as outlined in ASTM E-1412. The term “oxygenate” is defined herein as a small, polar, organic molecule, such as acetone, methanol, ethanol, or isopropanol, which can be employed as an ignitable liquid and referred to in the ASTM classification scheme as the “oxygenated solvents” class. Although a well accepted technique, the higher affinity of activated carbon strips for heavy molecular weight products over low molecular weight products and hydrocarbons over oxygenated products, it does not allow for efficient recovery of oxygenates such as low molecular weight alcohols and acetone. The objective of this study was to develop and evaluate a novel method for the enhanced recovery of oxygenates from fire debris samples. By optimizing conditions of the heated passive headspace technique, the utilization of zeolites allowed for the successful collection and concentration of oxygenates. The results demonstrated that zeolites increased the recovery of oxygenates by at least 1.5-fold compared to the activated carbon strip and may complement the currently used extraction technique.

Extraction of Pectin from lemon peel: Technology development

Pectin is widely used as a gelling agent, thickener, emulsifier and stabilizer in different food processing operations. Chemically it represents a polysaccharide, which is present in different amount in cell walls of all land plants. But citrus fruit is very rich in this component and can be used as source for its production commercially. In this study, lemon peel was selected as a representative of the citrus fruit family to extract pectin because of the abundance of the fruit in Bangladesh. Grounded lemon peel was digested in a solution of 0.01N HCl at a temperature of 80-90°C for 1.5 hours. The solid mass is filtered out and the filtrate is treated with different low molecular weight alcohol such as methanol, ethanol and isopropanol to precipitate the pectin out. The precipitate is dried at 40°C under vacuum. The structure of the product is yet to confirm by Fourier transform infrared spectroscopy (FTIR) analysis. The product is characterized by the parameters as methoxyl content, anhydrouronic acid content, degree of esterification, equivalent weight and intrinsic viscosity. The characteristic parameters are found to be in the same range as those shown by the product proposed in the market as ‘Pectin’. The yield of pectin extracted by the present method is as low as 1.08~1.38%, which is too low to make the method feasible for commercial purposes. Researchers are underway to improve the yield as well quality of the product. DOI: http://dx.doi.org/10.3329/jce.v27i2.17797 Journal of Chemical Engineering, IEB Vol. ChE. 27, No. 2, December 2012: 25-30

Effect of the Addition of Low Molecular Weight Alcohols on Heavy Oil Recovery during Alkaline Flooding

This study presents an experimental study, including interfacial tension (IFT) measurements, sandpack flood tests, and microscopic studies, for investigating the effect of the addition of low molecular weight alcohols on heavy oil recovery during alkaline flooding. According to the IFT results, the addition of low molecular weight alcohols can be detrimental to IFT reduction for the alkaline/heavy oil system, due to the partitioning of the alcohol molecules at the oil–water interface reducing the interfacial space available for surfactant molecules. However, sandpack floods conducted with the addition of the low molecular weight alcohols show a marked improvement in oil recovery over the alkaline-only flooding. The incremental oil recovery increases with the alcohol chain length from methanol to n-pentanol, but for the less water-soluble isoamyl alcohol and n-hexanol, the incremental oil recovery starts to decrease. The microscopic studies indicate that the alcohol additives can accelerate the reaction ra...

Characterization of volatile compounds of pu-erh tea using solid-phase microextraction and simultaneous distillation–extraction coupled with gas chromatography–mass spectrometry

Two extraction methods, namely, solid-phase microextraction (SPME) and simultaneous distillation–extraction (SDE) both followed by gas chromatography–mass spectrometry were applied for the determination of a wide range of volatile compounds in pu-erh tea. The conditions of solid-phase microextraction including fiber selections and sampling condition optimization have been previously investigated. By the two methods, 79 volatile compounds belonging to different categories were identified. Among them, 61 volatile compounds were extracted by SDE and 67 by SPME. Qualitative and quantitative differences of pu-erh tea volatile profiles were observed by applying the two aforementioned extraction methods. SDE technique achieved higher percentages of high molecular weight alcohols, acids, and esters of low volatility, whereas SPME technique was found useful for analyzing low molecular weight alcohols, methoxy-phenolic compounds, aldehydes, ketones, and hydrocarbons of high volatility that were closely related to the characteristics of pu-erh tea aroma and its sensory perception. Therefore, SPME technique was a reliable extraction method for controlling pu-erh tea quality flavor.

ChemInform Abstract: Lewis Acid‐Water/Alcohol Complexes as Hydrogen Atom Donors in Radical Reactions

AbstractReview: 39 refs.

Effect of suspension medium on the electrophoretic deposition of hydroxyapatite nanoparticles and properties of obtained coatings

The suspensions of hydroxyapatite (HA) nanoparticles were prepared in different alcohols. The zeta potential of HA nanoparticles was the highest in butanolic suspension (65.65mV) due to the higher adsorption of RCH2OH2+ species via hydrogen bonding with surface P3OH group of HA. Electrophoretic deposition was performed at 20 and 60V/cm for different times. Deposition rate was faster in low molecular weight alcohols due to the higher electrophoretic mobility of HA nanoparticles in them. The coating deposited from butanolic suspension had the highest adhesion strength and corrosion resistance in SBF solution at 37.5°C. The surface of this coating was covered by apatite after immersion in SBF solution for 1 week.

Molecular Dynamics Investigation of the Effects of Concentration on Hydrogen Bonding in Aqueous Solutions of Methanol, Ethylene Glycol and Glycerol

Hydrogen bonding interaction between alcohols and water molecules is an important characteristic in the aqueous solutions of alcohols. In this paper, a series of molecular dynamics simulations have been performed to investigate the aqueous solutions of low molecular weight alcohols (methanol, ethylene glycol and glycerol) at the concentrations covering a broad range from 1 to 90 mol %. The work focuses on studying the effect of the alcohols molecules on the hydrogen bonding of water molecules in binary mixtures. By analyzing the hydrogen bonding ability of the hydroxyl (-OH) groups for the three alcohols, it is found that the hydroxyl group of methanol prefers to form more hydrogen bonds than that of ethylene glycol and glycerol due to the intra-and intermolecular effects. It is also shown that concentration has significant effect on the ability of alcohol molecule to hydrogen bond water molecules. Understanding the hydrogen bonding characteristics of the aqueous solutions is helpful to reveal the cryoprotective mechanisms of methanol, ethylene glycol and glycerol in aqueous solutions.

Iridium Application in Low‐Temperature Acidic Fuel Cells: Pt‐Free Ir‐Based Catalysts or Second/Third Promoting Metal in Pt‐Based Catalysts?

AbstractPt and Ir have similar properties, that is, same period and block (6d) of the periodic table, same fcc crystal structure, similar mass and atomic size. The cost of iridium, however, is ca. 60 % lower than that of platinum, so it could be a good substitute for Pt as a catalyst in fuel cells, also if it has to be taken into account that a large use of iridium in fuel cells could noticeably increase its price. Moreover, iridium is stable towards dissolution in acid medium. For these reasons, Pt‐free Ir‐based catalysts and Ir‐containing Pt‐based catalysts have been tested both as anode and cathode materials in low‐temperature acid fuel cells. In this work an overview of the application of Ir and Ir‐containing catalysts as anode materials for hydrogen, methanol and ethanol oxidation, and as cathode materials for oxygen reduction in low‐temperature polymer electrolyte fuel cells fuelled with hydrogen or low molecular weight alcohols, is presented. The more suitable application of iridium in fuel cell electrodes, either as non‐Pt Ir‐based catalysts, maintaining an acceptable catalytic activity, or as co‐catalysts in Pt‐based materials, to increase fuel cell performance simultaneously to a slight decrease of the cost, is discussed.

RETRACTED: The effects of using biodiesel on CI (compression ignition) engine and optimization of its production by using response surface methodology

Bio-fuel production provides an alternative non-fossil fuel without the need to redesign current engine technology. This study presents an experimental investigation into the effects of using biodiesel blends on diesel engine performance and its emissions. The biodiesel fuels were produced from Sunflower oil using the transesterification process with low molecular weight alcohols and sodium hydroxide then tested on a steady state engine test rig using a Euro 4 four cylinder CI (compression ignition) engine. This study also shows how by blending biodiesel with diesel fuel at intervals of B5, B10, B15, and B20 can decrease harmful gas emissions significantly while maintaining similar performance output and efficiency. Production optimization was achieved by changing the variables which included methanol/oil molar ratio, NaOH catalyst concentration, reaction time, reaction temperature, and rate of mixing to maximize biodiesel yield. The technique used was the RSM (response surface methodology). In addition, a second-order model was developed to predict the biodiesel yield if the production criteria is known. The model was validated using additional experimental testing. It was determined that the catalyst concentration and molar ratio of methanol to sunflower oil were the most influential variables affecting percentage conversion to fuel and percentage initial absorbance.

The effect of frother blends on the flotation performance of selected PGM bearing ores

Concentrators processing PGM bearing ores make use of polysaccharide depressants to reduce the recovery of the undesired naturally floatable gangue minerals, mainly silicates, present in the ore. Recent work has shown that high depressant dosages can completely depress naturally floatable gangue and thus prevent it from reporting to the concentrate. These high depressant dosages can, however, have a negative effect on the recovery of valuable minerals present in the ore by reducing the stability of the froth. In order to counterbalance the effects of depressant addition, frothers are added. It is, however, preferable to maintain independent control over bubble size and froth stability which is difficult to achieve with only one frother. An alternative strategy is to use a blend of frothers, e.g. a weaker frother in combination with a stronger frother. Such a system allows an additional degree of freedom: changing the ratio of the two frothers provides more independent control of bubble size and froth stability. This study demonstrates through the use of batch flotation tests how blending low molecular weight alcohols with commercially available frothers impacts the solids and water recovery, as well as the valuable mineral recovery and concentrate grade in different PGM ores. Higher water and solids recoveries together with higher valuable mineral recoveries (>90% copper and >70% nickel) were obtained from tests using frother blends.

Lewis Acid–Water/Alcohol Complexes as Hydrogen Atom Donors in Radical Reactions

Water or low molecular weight alcohols are, due to their availability, low price and low toxicity ideal reagents for organic synthesis. Recently, it was reported that, despite the very strong BDE of the O-H bond, they can be used as hydrogen atom donors in place of expensive and/or toxic group 14 metal hydrides when boron and titanium(III) Lewis acids are present. This finding represents a considerable innovation and uncovers a new perspective on the paradigm of hydrogen atom transfers to radicals. We discuss here the influence of complex formation and other association processes on the efficacy of the hydrogen transfer step. A delicate balance between activation by complex formation and deactivation by further hydrogen bonding is operative.

The optimization of biodiesel production by using response surface methodology and its effect on compression ignition engine

Bio-fuel production provides an alternative non-fossil fuel without the need to redesign current engine technology. This study presents an experimental investigation into the effects of using biodiesel blends on diesel engine performance and its emissions. The biodiesel fuels were produced from sunflower oil using the transesterification process with low molecular weight alcohols and sodium hydroxide then tested on a steady state engine test rig using a Euro 4 four cylinder compression ignition (CI) engine. This study also shows how by blending biodiesel with diesel fuel at intervals of B5, B10, B15, and B20 can decrease harmful gas emissions significantly while maintaining similar performance output and efficiency. Production optimization was achieved by changing the variables which included methanol/oil molar ratio, NaOH catalyst concentration, reaction time, reaction temperature, and the rate of mixing to maximize biodiesel yield. The technique used was the response surface methodology (RSM). In addition, a second-order model was developed to predict the biodiesel yield if the production criteria is known. The model was validated using additional experimental testing. It was determined that the catalyst concentration and molar ratio of methanol to sunflower oil were the most influential variables affecting percentage conversion to fuel and percentage initial absorbance.