Production of a new second generation biodiesel with a low cost lipase derived from Thermomyces lanuginosus: Optimization by response surface methodology

Biodiesel Is Dead: Long Life to Advanced Biofuels—A Comprehensive Critical Review

Many countries are immersed in several strategies to reduce the carbon dioxide (CO2) emissions of internal combustion engines. One option is the substitution of these engines by electric and/or hydrogen engines. However, apart from the strategic and logistical difficulties associated with this change, the application of electric or hydrogen engines in heavy transport, e.g., trucks, shipping, and aircrafts, also presents technological difficulties in the short-medium term. In addition, the replacement of the current car fleet will take decades. This is why the use of biofuels is presented as the only viable alternative to diminishing CO2 emissions in the very near future. Nowadays, it is assumed that vegetable oils will be the main raw material for replacing fossil fuels in diesel engines. In this context, it has also been assumed that the reduction in the viscosity of straight vegetable oils (SVO) must be performed through a transesterification reaction with methanol in order to obtain the mixture of fatty acid methyl esters (FAMEs) that constitute biodiesel. Nevertheless, the complexity in the industrial production of this biofuel, mainly due to the costs of eliminating the glycerol produced, has caused a significant delay in the energy transition. For this reason, several advanced biofuels that avoid the glycerol production and exhibit similar properties to fossil diesel have been developed. In this way, “green diesels” have emerged as products of different processes, such as the cracking or pyrolysis of vegetable oil, as well as catalytic (hydro)cracking. In addition, some biodiesel-like biofuels, such as Gliperol (DMC-Biod) or Ecodiesel, as well as straight vegetable oils, in blends with plant-based sources with low viscosity have been described as renewable biofuels capable of performing in combustion ignition engines. After evaluating the research carried out in the last decades, it can be concluded that green diesel and biodiesel-like biofuels could constitute the main alternative to addressing the energy transition, although green diesel will be the principal option in aviation fuel.

Co-immobilization of multi-enzyme on reversibly soluble polymers in cascade catalysis for the one-pot conversion of gluconic acid from corn straw

The difficulties in the process of cellulose cascade conversion based on immobilization technology lies in the recycling enzymes from rich solid-containing straw hydrolysate and the incompatibility of conventional immobilization with this process. In this study, three types of enzyme (cellulase, glucose oxidase and catalase) were successfully immobilized on a reversible soluble Eudragit L-100. Through the determination of the preparation conditions, enzymatic properties and catalytic conditions, the co-immobilized enzyme was applied to the catalytic reaction of one-pot conversion of corn straw to gluconic acid. The yield of gluconic acid achieved 0.28 mg/mg, conversion rate of cellulose in corn straw to gluconic acid reached 61.41%. The recovery of co-immobilized enzyme from solid substrate was achieved by using reversible and soluble characteristics of the carrier. After 6 times of recycling, the activity of co-immobilized enzyme was maintained at 52.38%, confirming the feasibility of multi-enzyme immobilization strategy using reversible soluble carrier in cascade reactions.

One Pot Use of Combilipases for Full Modification of Oils and Fats: Multifunctional and Heterogeneous Substrates

Lipases are among the most utilized enzymes in biocatalysis. In many instances, the main reason for their use is their high specificity or selectivity. However, when full modification of a multifunctional and heterogeneous substrate is pursued, enzyme selectivity and specificity become a problem. This is the case of hydrolysis of oils and fats to produce free fatty acids or their alcoholysis to produce biodiesel, which can be considered cascade reactions. In these cases, to the original heterogeneity of the substrate, the presence of intermediate products, such as diglycerides or monoglycerides, can be an additional drawback. Using these heterogeneous substrates, enzyme specificity can promote that some substrates (initial substrates or intermediate products) may not be recognized as such (in the worst case scenario they may be acting as inhibitors) by the enzyme, causing yields and reaction rates to drop. To solve this situation, a mixture of lipases with different specificity, selectivity and differently affected by the reaction conditions can offer much better results than the use of a single lipase exhibiting a very high initial activity or even the best global reaction course. This mixture of lipases from different sources has been called “combilipases” and is becoming increasingly popular. They include the use of liquid lipase formulations or immobilized lipases. In some instances, the lipases have been coimmobilized. Some discussion is offered regarding the problems that this coimmobilization may give rise to, and some strategies to solve some of these problems are proposed. The use of combilipases in the future may be extended to other processes and enzymes.

Biodiesel at the Crossroads: A Critical Review

The delay in the energy transition, focused in the replacement of fossil diesel with biodiesel, is mainly caused by the need of reducing the costs associated to the transesterification reaction of vegetable oils with methanol. This reaction, on an industrial scale, presents several problems associated with the glycerol generated during the process. The costs to eliminate this glycerol have to be added to the implicit cost of using seed oil as raw material. Recently, several alternative methods to convert vegetable oils into high quality diesel fuels, which avoid the glycerol generation, are being under development, such as Gliperol, DMC-Biod, or Ecodiesel. Besides, there are renewable diesel fuels known as “green diesel”, obtained by several catalytic processes (cracking or pyrolysis, hydrodeoxygenation and hydrotreating) of vegetable oils and which exhibit a lot of similarities with fossil fuels. Likewise, it has also been addressed as a novel strategy, the use of straight vegetable oils in blends with various plant-based sources such as alcohols, vegetable oils, and several organic compounds that are renewable and biodegradable. These plant-based sources are capable of achieving the effective reduction of the viscosity of the blends, allowing their use in combustion ignition engines. The aim of this review is to evaluate the real possibilities that conventional biodiesel has in order to success as the main biofuel for the energy transition, as well as the use of alternative biofuels that can take part in the energy transition in a successful way.

Rhizomucor miehei Lipase Supported on Inorganic Solids, as Biocatalyst for the Synthesis of Biofuels: Improving the Experimental Conditions by Response Surface Methodology

Two inorganic solids have been evaluated as supports of Lipozyme RM IM, a Rhizomucor miehei lipase immobilized on a macroporous anion exchange resin, in order to improve its application as a biocatalyst in the synthesis of biofuels. The experimental conditions have been optimized to get the selective transesterification of sunflower oil, by using a multi-factorial design based on the response surface methodology (RSM). In this way, the effects of several reaction parameters on the selective ethanolysis of triglycerides to produce Ecodiesel, a biodiesel-like biofuel constitute by one mole of monoglyceride (MG) and two moles of fatty acid ethyl ester (FAEE), have been evaluated. Thus, it was obtained that a 6:1 oil/ethanol molar ratio, 0.215 g of biocatalyst supported in silica-gel (0.015 g Lipase/0.2 g silica-gel), 50 µL of 10 N NaOH, together with previous optimized reaction parameters, 35 °C reaction temperature and 120 min of reaction time, gave the best results (conversions around 70%; selectivity around 65%; kinematic viscosities about 9.3 mm2/s) in the reaction studied. Besides, Lipozyme RM IM, supported on silica-gel, biocatalyst exhibited a very good stability, remaining its activity even after 15 cycles.

Evaluation of Lipases from Wild Microbial Strains as Biocatalysts in Biodiesel Production

In this study, the evaluation of the catalytic behavior of several wild bacterial strains in the 1,3-selective ethanolysis of triglycerides with ethanol to produce a new type of biodiesel (Ecodiesel) that integrates glycerol as monoacylglycerols was carried out. The Ecodiesel production not only avoids the elimination of glycerol, which is largely generated as a by-product in the biodiesel industry, but also results in an increase in the biofuel yield. The wild microbial strain samples were obtained from several lipophilic organisms. In addition to evaluate the enzymatic extracts, the minimum grade of purification of the strains, necessary to obtain similar results to those attained with commercial lipases was studied. This purification treatment included a dialysis followed by a lyophilization process. Such extracts were directly used as biocatalysts in the transesterification reaction of sunflower oil with ethanol, attaining much better results (yield close to 100%) than those obtained with strains which were not submitted to the purification process (yields lower than 10%). Furthermore, the results here obtained are similar to those obtained with commercial lipases but were achieved under mild conditions and lower reaction time (2 h). In addition, the stability of the enzymatic extracts was corroborated by subsequent reactions, showing no loss of activity. Thus, this study brings to light that enzymatic extracts obtained by a very simple purification process can be economically competitive with the conventional biodiesel production methods.

Application of Enzymatic Extracts from a CALB Standard Strain as Biocatalyst within the Context of Conventional Biodiesel Production Optimization

The application of biocatalysts in the transesterification process of triglycerides (TG) allows integrating the glycerol in the form of monoglyceride (MG), sharply increasing the yield and the environmental sustainability of the conventional biodiesel production process. This is known as Ecodiesel. To overcome the inconvenient of the high cost of the currently employed highly purified commercial enzymes, the use of scarcely purified extracts obtained from standard strains of the same species of commercial lipases currently applied in this process is being investigated. Thus, Candida antarctica type B (CALB) was chosen to determine the optimal conditions of culture of this yeast. The standard strain was obtained from the Spanish Type Microbial Cultures Collection (CECT) and has been used to carry out several studies to elucidate its optimum growth conditions. Through a process of lyophilization with prior dialysis of the liquid cultures, the enzymatic extracts were obtained. The different obtained cultures have been applied as biocatalysts in the 1,3-selective transesterification reaction of sunflower oil with ethanol to obtain Ecodiesel (FAEE + MG). Selectivity and reaction yields were obtained by gas chromatography. Acceptable yields are obtained during the reaction time as well as in successive reactions, demonstrating the feasibility of using these CALB enzymatic extracts as biocatalysts.

Candida antarctica Lipase B Immobilized onto Chitin Conjugated with POSS® Compounds: Useful Tool for Rapeseed Oil Conversion

A new method is proposed for the production of a novel chitin-polyhedral oligomeric silsesquioxanes (POSS) enzyme support. Analysis by such techniques as X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy confirmed the effective functionalization of the chitin surface. The resulting hybrid carriers were used in the process of immobilization of the lipase type b from Candida antarctica (CALB). Fourier transform infrared spectroscopy (FTIR) confirmed the effective immobilization of the enzyme. The tests of the catalytic activity showed that the resulting support-biocatalyst systems remain hydrolytically active (retention of the hydrolytic activity up to 87% for the chitin + Methacryl POSS® cage mixture (MPOSS) + CALB after 24 h of the immobilization), as well as represents good thermal and operational stability, and retain over 80% of its activity in a wide range of temperatures (30-60 °C) and pH (6-9). Chitin-POSS-lipase systems were used in the transesterification processes of rapeseed oil at various reaction conditions. Produced systems allowed the total conversion of the oil to fatty acid methyl esters (FAME) and glycerol after 24 h of the process at pH 10 and a temperature 40 °C, while the Methacryl POSS® cage mixture (MPOSS) was used as a chitin-modifying agent.

Biocatalytic behaviour of immobilized Rhizopus oryzae lipase in the 1,3-selective ethanolysis of sunflower oil to obtain a biofuel similar to biodiesel

A new biofuel similar to biodiesel was obtained in the 1,3-selective transesterification reaction of sunflower oil with ethanol using as biocatalyst a Rhizopus oryzae lipase (ROL) immobilized on Sepiolite, an inorganic support. The studied lipase was a low cost powdered enzyme preparation, Biolipase-R, from Biocon-Spain, a multipurpose additive used in food industry. In this respect, it is developed a study to optimize the immobilization procedure of these lipases on Sepiolite. Covalent immobilization was achieved by the development of an inorganic-organic hybrid linker formed by a functionalized hydrocarbon chain with a pendant benzaldehyde, bonded to the AlPO4 support surface. Thus, the covalent immobilization of lipases on amorphous AlPO4/sepiolite (20/80 wt %) support was evaluated by using two different linkers (p-hydroxybenzaldehyde and benzylamine-terephthalic aldehyde, respectively). Besides, the catalytic behavior of lipases after physical adsorption on the demineralized sepiolite  was also evaluated. Obtained results indicated that covalent immobilization with the p-hydroxybenzaldehyde linker gave the best biocatalytic behavior. Thus, this covalently immobilized lipase showed a remarkable stability as well as an excellent capacity of reutilization (more than five successive reuses) without a significant loss of its initial catalytic activity. This could allow a more efficient fabrication of biodiesel minimizing the glycerol waste production.

New biofuel integrating glycerol into its composition through the use of covalent immobilized pig pancreatic lipase

By using 1,3-specific Pig Pancreatic lipase (EC 3.1.1.3 or PPL), covalently immobilized on AlPO(4)/Sepiolite support as biocatalyst, a new second-generation biodiesel was obtained in the transesterification reaction of sunflower oil with ethanol and other alcohols of low molecular weight. The resulting biofuel is composed of fatty acid ethyl esters and monoglycerides (FAEE/MG) blended in a molar relation 2/1. This novel product, which integrates glycerol as monoacylglycerols (MG) into the biofuel composition, has similar physicochemical properties compared to those of conventional biodiesel and also avoids the removal step of this by-product. The biocatalyst was found to be strongly fixed to the inorganic support (75%). Nevertheless, the efficiency of the immobilized enzyme was reduced to half (49.1%) compared to that of the free PPL. The immobilized enzyme showed a remarkable stability as well as a great reusability (more than 40 successive reuses) without a significant loss of its initial catalytic activity. Immobilized and free enzymes exhibited different reaction mechanisms, according to the different results in the Arrhenius parameters (Ln A and Ea). However, the use of supported PPL was found to be very suitable for the repetitive production of biofuel due to its facile recyclability from the reaction mixture.

Lipases as biocatalyst for biodiesel production

The global shortages of fossil fuels, significant increase in the price of crude oil, and increased environmental concerns have stimulated the rapid growth in biodiesel production. Biodiesel is generally produced through transesterification reaction catalyzed either chemically or enzymatically. Enzymatic transesterification draws high attention because that process shows certain advantages over the chemical catalysis of transesterification and it is "greener." This paper reviews the current status of biodiesel production with lipase-biocatalysis approach, including sources of lipases, kinetics, and reaction mechanism of biodiesel production using lipases, and lipase immobilization techniques. Factors affecting biodiesel production and economic feasibility of biodiesel production using lipases are also covered.