Kinetic and transport analysis of immobilized oxidoreductases that oxidize glycerol and its oxidation products

Glycerol has drawn increasing attention as a possible fuel, because it has many desirable qualities and is abundant due to the fact that it is a byproduct of biodiesel production. Previous research has shown that non-natural enzyme cascades can be used to create a bioanode that can stepwise oxidize glycerol to carbon dioxide. Two of these enzymes are pyrroloquinoline quinone (PQQ) dependant alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (AldDH) derived from Gluconobacter. The third enzyme, which is responsible for carbon bond cleavage, is oxalate oxidase (OxOx) derived from barley. Previous research has shown that all three enzymes have demonstrated the ability to undergo direct electron transfer to a carbon electrode which allows for a simple and efficient bioanode that completely oxidizes glycerol. In this study, each enzyme was individually immobilized within modified Nafion^® on a glassy carbon rotating disc electrode (GC-RDE) and voltammetric analysis was performed employing different rotation rates in a solution containing each enzyme's respective substrate. This substrate was glycerol for alcohol dehydrogenase, glyceraldehyde for aldehyde dehydrogenase, and mesoxalic acid for oxalate oxidase. From the voltammograms, Levich plots were produced and the solution diffusion coefficient (D_soln), the membrane diffusion coefficient (D_film), k_CAT, K_M, and V_MAX were determined.     

Oxygenated compounds derived from glycerol for biodiesel formulation: Influence on EN 14214 quality parameters

The methyl esters of fatty acids (biodiesel) obtained via transesterification of vegetable oils or animal fats are an alternative to current fossil fuels. A large amount of glycerol as a by-product is generated in this process and new applications for this surplus need to be found. Thus, the transformation of glycerol into branched oxygen-containing compounds could be an interesting solution to provide an outlet for increasing glycerol stocks. In this work, several oxygenated compounds, obtained by transformation of glycerol via etherification, esterification and acetalisation, have been assessed as components for biodiesel formulation. Different quality parameters have been evaluated following the procedures listed in the EN 14214 European Standard for biodiesel specifications. These parameters have been correlated with the amount and chemical nature of oxygenated derivate present in the biodiesel. The best performance as component for biodiesel formulation has been achieved by the mixture of ethers produced via etherification of glycerol with isobutylene. The addition of these compounds has not only improved the low-temperature properties of biodiesel (i.e. pour point and cold filter plugging point) and viscosity, but also did not impair other important biodiesel quality parameters analyzed. Although most of the studied oxygenated derivates do not significantly improve any biodiesel property, they do not exert a significant negative effect either. Furthermore, all of them allow an enhancement of overall yield in the biodiesel production. Nevertheless, further improvement could be addressed with a better purification to reduce the presence of non-desired impurities such as di-isobutylenes and unreacted acetic acid, which have a negative influence especially in acid number and oxidation stability.     

Autothermal steam reforming of glycerol for hydrogen production over packed-bed and Pd/Ag alloy membrane reactors

In this study, glycerol, with its high H/C ratio feature, was steam reformed with oxygen to produce hydrogen in packed-bed and Pd/Ag membrane reactors. The addition of oxygen, which causes the partial oxidation, was to achieve thermal neutral for the energy saving purposes.     

Efficient Synthesis of α-Monoglycerides via Solventless Condensation of Fatty Acids with Glycerol Carbonate

Highly pure α-monoglycerides (5a–e) were successfully prepared in high yields by the condensation of fatty acids such as lauric, myristic, palmitic, stearic and oleic (2a–e) with glycerol carbonate (4-hydroxymethyl-1,3-dioxolan-2-one) (1) in the presence of triethylamine as catalyst. Reaction conditions and spectroscopic identification of products will be presented in this article.     

Concentration of glycerol from dilute glycerol wastewater using sweeping gas membrane distillation

In this work, experimental results for the concentration of dilute glycerol wastewater using membrane distillation (MD) with a microporous hydrophobic flat-sheet PTFE membrane are reported. Experiments were performed using the sweeping gas mode of the MD (SGMD) process. The effects of various operating variables, such as feed temperature, glycerol concentration in aqueous phase, feed flow rate and sweeping gas flow rate were studied. A Taguchi analysis has been performed on the experimental results which determined the effects and contribution of each of the factors on the distillate flux and the interactions between the operating variables. Results showed that the most influential factor was feed temperature. The second significant contribution was observed for the sweeping gas flow rate. Feed concentration had a negative effect on the distillate flux. At optimum conditions (i.e. 65 °C, 400 mL/min, 1 mass%, and 0.453 Nm³/h), the Taguchi model predicted the value of the response (the distillate flux) as 20.93 L/m² h, which had good agreement with the experimental results.     

Glycerol and Acetate Additions to Maximize Lipid Content in High-Density Cultures of Phagotrophic Alga Ochromonas danica

Waste organics conversion to algal lipid is environmentally friendly and it promotes sustainability. Achieving high-lipid content in cells is crucial to the economic feasibility of algal lipid production and collection. Here, a phagotrophic microalga Ochromonas danica was grown on waste ketchup and then stimulated to accumulate high-lipid content using glycerol and acetate. Individually, glycerol and acetate could increase lipid synthesis. Sequential glycerol-then-acetate addition was more effective; for an O. danica culture with 0.25 g L⁻¹ cells, the intracellular lipid content was increased to 70–80% (w/w) in 6–12 hours. However, acetate added at >1 g L⁻¹ damaged cells. For high-density (25 g L⁻¹) fermentations, glycerol and acetate addition strategies were evaluated to overcome this inhibition. Results indicated that glycerol could be added in batches or continuously as long as the amount was sufficient to satisfy the glycerol consumption rate of 6 mg (g cells-hour)⁻¹ while acetic acid needed to be added continuously, optimal at a rate of 0.27–0.30 g hour⁻¹ or 12–14 mg (g cells-hour)⁻¹. Intracellular lipid content could reach 70–80% after 2-day supplementation of glycerol and acetic acid. The methods of glycerol/acetate additions developed here enhance algal lipid production and enable effective conversion of organic wastes to algal lipids as sustainable bioproducts.     

Structural Analysis of Partial and Total Esters of Glycerol Undecenoate and Diglycerol Undecenoate

The direct esterification reaction between glycerol and undecylenic acid or between diglycerol and undecylenic acid generates all the possible types of glycerol or diglycerol esters. Purification by silica gel chromatography resulted in the isolation of each of these types of ester in a pure form. The molecular structures of the compounds isolated were characterized and identified by mass spectrometry, ¹H NMR, ¹³C NMR and DEPT‐135. We then studied the composition of esters of undecylenic acid formed with glycerol or diglycerol as a function of their reaction conditions, which constitute a highly complex system. We purified undecylenic acid esters from each polyol family to allow the structural identification of each ester of glycerol and each ester of diglycerol with undecylenic acid. We found that the polarity of these non‐ionic amphiphilic esters directly affected their affinity for organic and inorganic solvents and that these esters behaved very differently from anionic amphiphilic molecules, such as undecylenic acid.     

Effect of the structure of polymer inclusion membranes on zn(II) transport from chloride aqueous solutions

This article presents application of polymer inclusion membranes (PIM) containing polymer matrices: cellulose triacetate (CTA) or poly(vinyl) chloride (PVC), o‐nitrophenyloctyl ether (NPOE) as a plasticizer and phosphonium ionic liquids, i.e., trihexyltetradecylphosphonium chloride (Cyphos IL 101), bis(2,4,4‐trimethylpentyl)phosphinate (Cyphos IL 104) and tributyltetradecylphosphonium chloride (Cyphos IL 167), as carriers for Zn(II) transport from chloride medium. Cyphos IL167 application as an ion carrier in PIMs is reported for the first time. The membrane composition is found to affect Zn(II) transport significantly. SEM and AFM images show the differences in the surface morphology of PVC and CTA based membranes. Better transport abilities of CTA membranes (Zn(II) recovery factors exceed 80%) compared with those of PVC, indicate that the structural differences between the two polymers play a crucial role for the membrane permeability. The best initial flux and permeability coefficient are obtained for the membranes with Cyphos IL 101 and Cyphos IL 104 as carriers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42319.     

Sustainable value-added C_3 chemicals from glycerol transformations:A mini review for heterogeneous catalytic processes

It is of importance to convert glycerol, the primary by-product from biodiesel manufacturing, to various valuable C_3 chemicals, such as acrolein via dehydration, lactic acid, 1,3-dihydroxyacetone via oxidation,and 1,3-propanediol, allyl alcohol via hydrogenolysis. As compared to petroleum-based resources, C_3 chemicals from glycerol provide a benign, sustainable and atomically economic feature. Extensive heterogeneous catalysts have been designed, prepared and tested for these transformations. In recent five years,great progress, including high yields to target products over appropriate catalysts, insight into reaction mechanism and network, has been achieved. The present review systematically covers recent research progress on sustainable C_3 chemical production from catalytic glycerol transformations. We hope that it will benefit future research on transformations of glycerol as well as other polyols.     

Enzymatic transesterification for production of biodiesel using yeast lipases: An overview

Biodiesel has provided an eco-friendly solution to fuel crisis, as it is renewable, biodegradable and a non-toxic fuel that can be easily produced through enzymatic transesterification of vegetable oils and animal fats. Enzymatic production of biodiesel has many advantages over the conventional methods as high yields can be obtained at low reaction temperatures with easy recovery of glycerol. Microbial lipases are powerful biocatalysts for industrial applications including biodiesel production at lower costs due to its potential in hydrolyzing waste industrial materials. Among them, lipases from yeasts, Candida antarctica, Candida rugosa, Cryptococcus sp., Trichosporon asahii and Yarrowia lipolytica are known to catalyze such reactions. Moreover, stepwise addition of methanol in a three step, two step and single step reactions have been developed using yeast lipases to minimize the inhibitory effects of methanol. The latest trend in biodiesel production is the use of whole-cell as biocatalysts, since the process requires no downstream processing of the enzyme. Synthesis of value added products from the byproduct glycerol further reduces the production cost of biodiesel. This review aims at compiling the information on various yeast lipase catalyzed transesterification reactions for greener production of biodiesel.