Measurement of free glycerol in biofuels

A method has been developed to determine the free glycerol content in esters derived from vegetable oils. After extraction of glycerol, its measurement in small quantities in biofuels (methyl or ethyl esters) is possible by high-pressure liquid chromatography combined with pulsed amperometric detection, HPLC-PAD. The method has proved to be simple, rapid and accurate. The limit of detection is 1 microg/g.     

Role of Epoxides in the Oxidation of Allyl Alcohol,Allyl Formate,and Allyl Acetate in Acetic Acid

The formation of epoxy derivatives as intermediate products in the oxidation of allyl alcohol, allylformate, allyl acetate in acetic acid was proved. Intermediate epoxy compounds undergo further trans-formations: They react with acetic acid to give glycerol esters or are converted into polyethers of glyceroland its esters. The rate constants for transformations of 2,3-epoxypropanol, 2,3-epoxypropyl formate, and 2,3-epoxypropyl acetate along these pathways were measured. Higher selectivity of glycerol ester formation from allyl formate was substantiated.     

Determination of esters in glycerol phase after transesterification of vegetable oil

In biodiesel production, glycerol is formed as a side product and it is contained in the glycerol phase. This phase contains (besides glycerol): water, soaps, alcohol, traces of catalyst and glycerides and the remaining esters. In this paper, a new method for the determination of esters in the glycerol phase is introduced. The determination enables the minimization of the losses of biodiesel within the production process. It is based on the gradient RP-LC method (water and acetonitrile) with refractometric detection. The analysis is easy and the samples do not need any treatment (only dilution by water) and has a low detection limit. The results of this method were compared with the results of two other published methods: isocratic HPLC and GC. The disadvantage of these two methods is that they need extensive treatment of the sample, which takes many hours, and they are able to determine only the sum of esters. The new method is reliable, much faster and able to differentiate esters of almost each higher fatty acid (e.g. linoleic, linolenic, strearic alkyl ester) in the glycerol phase.     

Measurement of free glycerol in biofuels

A method has been developed to determine the free glycerol content in esters derived from vegetable oils. After extraction of glycerol, its measurement in small quantities in biofuels (methyl or ethyl esters) is possible by high-pressure liquid chromatography combined with pulsed amperometric detection, HPLC-PAD. The method has proved to be simple, rapid and accurate. The limit of detection is 1 g/g.     

From symmetric glycerol derivatives to dissymmetric chlorohydrins

The anticipated worldwide increase in biodiesel production will result in an accumulation of glycerol for which there are insufficient conventional uses. The surplus of this by-product has increased rapidly during the last decade, prompting a search for new glycerol applications. We describe here the synthesis of dissymmetric chlorohydrin esters from symmetric 1,3-dichloro-2-propyl esters obtained from glycerol. We studied the influence of two solvents: 1,4-dioxane and 1-butanol and two bases: sodium carbonate and 1-butylimidazole, on the synthesis of dissymmetric chlorohydrin esters. In addition, we studied the influence of other bases (potassium and lithium carbonates) in the reaction using 1,4-dioxane as the solvent. The highest yield was obtained using 1,4-dioxane and sodium carbonate.     

A tandem Finkelstein-rearrangement-elimination reaction: a straightforward synthetic route to allyl esters

Allyl esters can be obtained by a Finkelstein-rearrangement-elimination reaction of 2-chloro-1-(chloromethyl)ethyl esters induced by NaI. Sodium iodide can be used below equivalence using a reductive agent as sodium thiosulfate. High yields are obtained with most of the diverse esters studied. The method described avoids the use of allyl alcohol as a reagent. 2-Chloro-1-(chloromethyl)ethyl esters are prepared from glycerol, the main by-product of biodiesel industry. The effectiveness of iodine as reagent to hydrolyze allyl esters is also confirmed.     

Pure short-chain glycerol fatty acid esters and glycerylic cyclocarbonic fatty acid esters as surface active and antimicrobial coagels protecting surfaces by promoting superhydrophilicity

Pure glycerol fatty acid esters and glycerylic cyclocarbonic fatty acid esters have an amphiphilic structure, giving these biomolecules a broad range of physico-chemical and biological properties. Physico-chemical properties depend on chain lengths, odd or even carbon numbers on the chain, and glyceryl or cyclocarbonic polar heads. The spectrum of melting-point values for these molecules is large. Surface-activity is very important and through determination of the critical aggregation concentration (CAC), some fatty-acid esters are considered as solvo-surfactant biomolecules. Coupling these self-aggregation and crystallization properties, superhydrophilic surfaces were obtained. An efficient durable water repellent coating of various metallic and polymeric surfaces was allowed. Moreover, these fatty acid esters promoting superhydrophilicity showed biological activity against Gram positive, Gram negative, and yeast-like micro-organisms. Such surfaces coated by self-assembled fatty acid esters in a stable coagel state present a novel solution to surface-contamination risks from pathogen proliferation.     

Simultaneous gas chromatographic determination of methanol and free glycerol in biodiesel

Summary The methanol and free glycerol content of vegetable oil methyl esters used as diesel fuel (biodiesel) is very important in describing the quality of this fuel and is therefore limited by specifications. A previously described GLC method for the determination of free glycerol in biodiesel has been further developed and also allows the simultaneous determination of methanol. Sample preparation includes dissolving in dimethylformamide, silylation with bis-trimethylsilyltrifluoracetamide (BSTFA) and separation on a methylsilicone fluid, coated-capillary column using either FID or MS-detection. Ethanol and 1,4-butanediol were used as internal standards. Both detection systems show sufficient sensitivity for concentrations relevant to biodiesel samples. The recovery was tested using a RME-sample containing known amounts of methanol and glycerol.     

Resolving the enigma of prebiotic C?O?P bond formation: Prebiotic hydrothermal synthesis of important biological phosphate esters

Important biological phosphate esters such as sn‐glycerol‐3‐phosphate, glycerol‐2‐phosphate, and phosphoethanolamine were synthesized under hydrothermal conditions. Phosphorus was incorporated into the biomolecules, leading to the formation of C O P type compounds hydrothermally. Only perlite‐catalyzed reaction at 180°C could result in the formation of sn‐glycerol‐3‐phosphate, whereas glycerol‐2‐phosphate could be easily synthesized at 100°C with or without minerals and phosphoethanolamine was obtained within a temperature range of 100 to 120°C. © 2010 Wiley Periodicals, Inc. Heteroatom Chem 21:161–167, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20591     

Reaction of 2-methyl-5-(2′-carbochloroethyl) furan with polyhydric aliphatic alcohols

Summary The reaction of 2-methyl-5-(2-carbochloroethyl)furan with ethylene glycol, diethylene glycol, 1,3-butanediol or glycerol gave the previously unknown furan esters and chloro esters.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1096–1097, June, 1965     

Evaluation of a glycerol derived biofuel by thermal analysis

This work describes thermal analysis evaluation of a glycerol derived compound (fatty acid esters of (2,2-dimethyl-1,3-dioxolan-4-yl) methanol) developed to work as a biofuel. Mixtures of these ketal–glyceryl esters with fatty acid methyl esters typical of soybean biodiesel were prepared and evaluated in relation to biodiesel critical thermal properties such as temperature of crystallization, thermal stability and volatilization measured by differential scanning calorimetry and thermogravimetric analysis. The volatility of the products containing fatty acid methyl esters and (2,2-dimethyl-1,3-dioxolan-4-yl) methyl esters could be predicted by thermogravimetric analyses conducted in nitrogen that avoided time consuming distillation and greatly reduced material expenditure.     

Phase equilibria modeling of biodiesel related mixtures using the GCA-EoS model

In this work, a group-contribution equation of state that takes into account association effects (GCA-EoS) is extended to model the phase behavior of fatty esters (biodiesel) in binary mixtures with glycerol, alcohols and water and ternary mixtures with glycerol and methanol. A new associating group (glycerol hydroxyl group: OH^Gly) was defined to take into consideration the association effects in the glycerol molecule. Self-association of methanol, water and glycerol and cross-association between methanol–glycerol, alcohol–ester, water–ester and glycerol–ester groups were considered. New pure-group, binary interaction and association parameters have been determined. The correlations and predictions of the model are found in acceptable agreement with selected experimental data reported in the literature.     

Baker’s yeast catalyzed asymmetric reduction in glycerol

Free and immobilized baker’s yeast were successfully employed in the asymmetric hydrogenations of prochiral β-keto esters and ketones in glycerol. The activities with immobilized cells were always higher then with free cells while the enantioselectivity was very high (99%) with both catalysts. Using glycerol, a non-toxic, biodegradable and recyclable liquid, as an environmentally friendly solvent allowed easy separation of the product by simple extraction with diethyl ether.     

Retention indices of glycerol esters

The retention indices of 27 mono-, di-, and trisubstituted esters of glycerol and C₁–C₆ carboxylic acids were determined on an OV-101 nonpolar phase in the temperature range 110–250°C. The dependence of the retention indices on temperature and the number of carbon atoms in the acid residue was linear for all compounds. The data obtained can be used for identifying glycerol esters in various mixtures and for predicting their thermodynamic properties.     

用裂解色谱法鉴定羧酸酯的结构

研究了用裂解气相色谱法鉴定羧酸酯结构的方法。对一些一元酸酯和二元酸酯进行了普通裂解和与碱石灰混合后的裂解,依据裂解产物可确定酯的母体酸和母体醇。直接从薄层板上取分离后的组分,不用去除吸附剂就能进行鉴定,可用于常见羧酸酯的剖析工作。     

A review of chromatographic characterization techniques for biodiesel and biodiesel blends

This review surveys chromatographic technology that has been applied to the characterization of biodiesel and its blends. Typically, biodiesel consists of fatty acid methyl esters produced by transesterification of plant or animal derived triacylglycerols. Primary attention is given to the determination of trace impurities in biodiesel, such as methanol, glycerol, mono-, di-, and triacylglycerols, and sterol glucosides. The determination of the fatty acid methyl esters, trace impurities in biodiesel, and the determination of the biodiesel content of commercial blends of biodiesel in conventional diesel are also addressed.     

Calculations of phase equilibria for mixtures of triglycerides,fatty acids,and their esters in lower alcohols

The objects of study were mixtures containing triglycerides and lower alcohols and also the products of the transesterification of triglycerides, glycerol and fatty acid esters. The Redlich-Kwong-Soave equation of state was used as a thermodynamic model for the phase state of the selected mixtures over wide temperature, pressure, and composition ranges. Group methods were applied to determine the critical parameters of pure substances and their acentric factors. The parameters obtained were used to calculate the phase diagrams and critical parameters of mixtures containing triglycerides and lower alcohols and the products of the transesterification of triglycerides, glycerol and fatty acid esters, at various alcohol/oil ratios. The conditions of triglyceride transesterification in various lower alcohols providing the supercritical state of reaction mixtures were selected.     

Critical review on analytical methods for biodiesel characterization

Biodiesel is an alternative fuel composed of mono-alkyl esters and obtained mainly from the base-catalyzed transesterification reaction of oils or fats. Its use (pure or blended) does not demand any modification in the diesel engine and in the existing fuel distribution and storage infrastructure. Moreover, biodiesel has a high energetic yield, fixes the solar energy and contains insignificant amounts of sulphur. Therefore, biodiesel is currently the best substitute for fossil diesel fuel.Besides mono-alkyl esters, glycerol (main co-product), alcohol, catalyst, free fatty acids, tri-, di- and monoglycerides compose the final mixture of biodiesel production process. These and other kinds of contaminants can lead to severe operational and environmental problems. Therefore, the quality control of biodiesel is greatly significant to the success of its commercialization and market acceptance. Some important issues on the biodiesel quality control involve the monitoring of transesterification reaction, the quantification of mono-alkyl esters and free- and bonded glycerol as well as determination of residual catalysts and alcohol. Moreover, the determination of blend levels is another key aspect of biodiesel analyses. Chromatography and spectroscopy are the analytical methods most used for the biodiesel characterization, but procedures based on physical properties are also available.Previously, a review on analytical methods used to evaluate biodiesel quality was written by Knothe. Due to the importance of this field, we made an update of Knothes’ review. Therefore, in this paper, we will describe new developments in biodiesel analyses and some references showed in Knothes’ paper. Specially, we will describe analytical methods used for quantification of glycerol, mono-, di-, triglycerides, methanol, water, Na, K, P, and steroids in biodiesel or along the transesterification reaction. Also, the determination of biodiesel content in blends and some physicochemical parameters are discussed. At the end, we will assess the available techniques and point out some improvements on analytical methods for biodiesel characterization.     

Selenium Enrichment on <Emphasis Type="Italic">Cordyceps militaris</Emphasis> Link and Analysis on Its Main Active Components

To investigate the effects of selenium on the main active components of Cordyceps militaris fruit bodies, selenium-enriched cultivation of C. militaris and the main active components of the fruit bodies were studied. Superoxide dismutase (SOD) activity and contents of cordycepin, cordycepic acid, and organic selenium of fruit bodies were sodium selenite concentration dependent; contents of adenosine and cordycep polysaccharides were significantly enhanced by adding sodium selenite in the substrates, but not proportional to sodium selenite concentrations. In the cultivation of wheat substrate added with 18.0 ppm sodium selenite, SOD activity and contents of cordycepin, cordycepic acid, adenosine, cordycep polysaccharides, and total amino acids were enhanced by 121/145%, 124/74%, 325/520%, 130/284%, 121/145%, and 157/554%, respectively, compared to NS (non-selenium-cultivated) fruit bodies and wild Cordyceps sinensis; organic selenium contents of fruit bodies reached 6.49 mg/100 g. So selenium-enriched cultivation may be a potential way to produce more valuable medicinal food as a substitute for wild C. sinensis.     

From glycerol to chlorohydrin esters using a solvent-free system. Microwave irradiation versus conventional heating

Esterification-chlorination of glycerol provides chlorohydrin esters in high yields. A ratio of reagents close to equivalence can be used, so that atom economy of the reaction is optimized. The reaction can be carried out using either classical or microwave heating, and no solvent is required. 2-Chloro-1-(chloromethyl)ethyl esters can be obtained in high regioisomeric relationship when either low or moderate temperature is used. In contrast, microwave irradiation allows the use of higher reaction temperatures that render mixtures of both regioisomers in variable relationships. Kinetic control of the process is proposed for classical heating, and experimental results are analyzed with the aid of ab initio calculated values. Non-thermal phenomena can be used to explain the high efficiency of microwave irradiation at low temperature.