A critical look at the microalgae biodiesel

The quantitative production of microalgae oil is often overestimated. The cost of the salts invested in the production of 1 kg algal diesel approximates the actual price of 1 kg mineral diesel. Total sum of electrical energy expenses for production of biodiesel from microalgae is several‐fold higher than the energy income from combustion of the same quantity. The biological value of cultivated microalgae as food is much higher than as fuel. An opinion is shared that money ought to be invested in microalgal biomass production as a food additive, forage, and pharmaceuticals. The aim is to prevent making too hasty steps and investments in microalgal biodiesel.     

Model-based optimisation of biodiesel production from microalgae

This work presents a superstructure-based optimisation model to optimise the microalgae to biodiesel production flowsheet for the minimum net annualised life cycle cost (ALCC) of biodiesel. The model includes the important processing steps of converting microalgae into biodiesel, viz. microalgae growth, harvesting, lipid extraction, and transesterification of lipid. Different options to perform these steps are considered. The mass and volumetric balance for each process and equipment, and the equipment capacity limitations constitute the important model constraints. The decision variables include growth duration, medium, as well as the techniques and specifications to be followed in each of the downstream steps. The mixed integer linear programming model was applied to a case study of producing 30,000 kg/d biodiesel from Chlorella. The minimum ALCC was US $ 13.286/l for the flowsheet and equipment details recommended by the model. Sensitivity analysis showed that lipid extraction was the most crucial step in the flowsheet.     

Optimal processing pathway for the production of biodiesel from microalgal biomass: A superstructure based approach

In this study, we propose a mixed integer nonlinear programming (MINLP) model for superstructure based optimization of biodiesel production from microalgal biomass. The proposed superstructure includes a number of major processing steps for the production of biodiesel from microalgal biomass, such as the harvesting of microalgal biomass, pretreatments including drying and cell disruption of harvested biomass, lipid extraction, transesterification, and post-transesterfication purification. The proposed model is used to find the optimal processing pathway among the large number of potential pathways that exist for the production of biodiesel from microalgae. The proposed methodology is tested by implementing on a specific case with different choices of objective functions. The MINLP model is implemented and solved in GAMS using a database built in Excel. The results from the optimization are analyzed and their significances are discussed.     

Lipid enhancement in microalgae by temporal phase separation: Use of indigenous sources of nutrients

Microalgae have been recommended as superior candidate for fuel production because of their advantages of higher photosynthetic efficiency,biomass & lipid productivity,and faster growth rate as compared to other energy crops.To meet up all these criteria,we have developed a continuous outdoor micro-algal raceway pond reactor (RPR) and a lab scale indoor tubular photo bioreactor (PBR) for biofuel production.An attempt to utilise indigenous sources of nutrients to improve the economics also revealed that micro-algal culturing can also be used as a mode of nutrient removal and water treatment.The photosynthetic rate and lipid production were enhanced by arresting daytime cell division and promoting night-time cell division.A 50％ lipid improvement was observed for the particular algal consortia.Microscopic studies revealed that temporal phase separation could be achieved by adjusting nutrient distribution pattern.To monitor temporal phase separation,it is required to know DNA multiplication model.Quantification of gDNA in RPR confirmed that cell division happens during the night which positively affects the photosynthetic efficiency and lipid productivity of microalgae.     

Technologies for production of biodiesel focusing on green catalytic techniques: A review

Biodiesel production is undergoing rapid technological reforms in industries and academia. This has become more obvious and relevant since the recent increase in the petroleum prices and the growing awareness relating to the environmental consequences of the fuel overdependency. In this paper, various technological methods to produce biodiesel being used in industries and academia are reviewed. Catalytic transesterification, the most common method in the production of biofuel, is emphasized in the review. The two most common types of catalysts; homogeneous liquids and heterogeneous solids, are discussed at length in the paper. Two types of processes; batch and continuous processes, are also presented. Although batch production of biodiesel is favored over continuous process in many laboratory and larger scale efforts, the latter is expected to gain wider acceptance in the near future, considering its added advantages associated with higher production capacity and lower operating costs to ensure long term supply of biodiesel.     

Activity of solid catalysts for biodiesel production: A review

Heterogeneous catalysts are promising for the transesterification reaction of vegetable oils to produce biodiesel. Unlike homogeneous, heterogeneous catalysts are environmentally benign and could be operated in continuous processes. Moreover they can be reused and regenerated. However a high molar ratio of alcohol to oil, large amount of catalyst and high temperature and pressure are required when utilizing heterogeneous catalyst to produce biodiesel. In this paper, the catalytic activity of several solid base and acid catalysts, particularly metal oxides and supported metal oxides, was reviewed. Solid acid catalysts were able to do transesterification and esterification reactions simultaneously and convert oils with high amount of FFA (Free Fatty Acids). However, the reaction rate in the presence of solid base catalysts was faster. The catalyst efficiency depended on several factors such as specific surface area, pore size, pore volume and active site concentration.     

A review of laboratory-scale research on lipid conversion to biodiesel with supercritical methanol (2001-2009)

Biodiesel production from lipids (vegetable oils and animal fats) with non-catalytic supercritical methanol (SCM) has several advantages over that of homogeneous catalytic process, including a high production efficiency, environmentally friendliness and a wide range of possible feedstocks. This article reviews the effect of the operating parameters on the lipid conversion to biodiesel with SCM, such as the temperature, pressure, methanol to oil molar ratio, and reaction time, for both batch and continuous systems, including the effect of the mixing intensity and dispersion in tubular reactors. The operating temperature is the key parameter to control either extent of reaction or other parameters. Studies on evaluating the chemical kinetics, phase behavior, binary vapor-liquid equilibrium (VLE) of lipid conversion in SCM are summarized. The pseudo-first order model is suitable to simplify the system at high methanol to oil molar ratios, but it is inadequate at a low methanol concentration which instead requires the second order model. Transition temperatures of reaction mixture depend on the critical point of reaction mixture which is assigned by methanol to oil molar ratio and amount of co-solvents in the system. For binary VLE studies, no single thermodynamic model for the overall process is available, probably because of the differences in the polarity between the initial and the final state of the reaction system. Since traditional operating parameters of the lipid conversion in SCM involve elevated temperatures and pressures, techniques for allowing milder operating conditions that employ the addition of co-solvents or catalysts are discussed. The ongoing and more extensive research on co-solvents, heterogeneous catalysts, phase behavior and multicomponent VLE of lipid conversion to biodiesel with SCM should provide a better understanding and achieve the goal of green biodiesel production technology in the near future.     

A review of ionic liquids as catalysts for transesterification reactions of biodiesel and glycerol carbonate production

Biodiesel production has been rapidly increasing due to the strong governmental policies and incentives provided leading to an oversupply of its by-product, glycerol. Therefore, finding ways of utilizing glycerol is essential to increase the net energy and sustainability of biodiesel. Ionic liquids have been used successfully as catalyst for both the production of biodiesel and the conversion of glycerol to glycerol carbonate. These catalysts are relatively environmentally friendly as they have the potential to enable sustainable processes. Herein, the prospect of using ionic liquids to catalyze transesterification triglycerides for the production of biodiesel and the conversion of glycerol to glycerol carbonate will be discussed. Elucidation of the reaction mechanism is expected to provide an in-depth understanding of the process with respect to the effects of cation and anion based on the reactions of interest.     

Advancements in development and characterization of biodiesel: A review

An ever increasing demand of fuels has been a challenge for today’s scientific workers. The fossil fuel resources are dwindling day by day. Biodiesel seems to be a solution for future. Biodiesel is an environmentally viable fuel. Out of the four ways viz. direct use and blending, micro-emulsions, thermal cracking and transesterification, most commonly used method is transesterification of vegetable oils, fats, waste oils, etc. Latest aspects of development of biodiesel have been discussed in this work. Yield of biodiesel is affected by molar ratio, moisture and water content, reaction temperature, stirring, specific gravity, etc. Biodegradability, kinetics involved in the process of biodiesel production, and its stability have been critically reviewed. Emissions and performance of biodiesel has also been reported.     

Hydrothermal processing of microalgae using alkali and organic acids

Aquatic organisms such as microalgae have been identified as a potential source of third generation biofuels due to their fast growth rate, ability to sequester CO₂ and their potential for producing lipids. Conversion by hydrothermal liquefaction is ideally suited to high moisture content feedstocks such as microalgae and involves the processing of biomass in hot compressed water with or without the presence of a catalyst. This study aims to investigate the conditions for producing high quality, low molecular weight bio-crude from microalgae and cyanobacteria containing low lipid contents including Chlorella vulgaris and Spirulina. Liquefaction experiments have been performed in a high pressure batch reactor at 300 °C and 350 °C. The influence of process variables such as temperature and catalyst type has been studied. Catalysts employed include the alkali, potassium hydroxide and sodium carbonate and the organic acids, acetic acid and formic acid. Liquefaction yields have been determined and the bio-crude has been analysed for CHNOS content and calorific value. The bio-crude has been analysed by GC/MS to examine composition and thermal gravimetric analysis (TGA) to estimate its boiling point range. The aqueous fraction has been analysed for typical cations and anions by ion exchange chromatography and for total organic carbon (TOC). The yields of bio-crude are higher using an organic acid catalyst, have a lower boiling point and improved flow properties. The bio-crude contains a carbon content of typically 70-75% and an oxygen content of 10-16%. The nitrogen content in the bio-crude typically ranges from 4% to 6%. The higher heating values (HHV) range from 33.4 to 39.9 MJ kg⁻¹. Analysis by GC/MS indicates that the bio-crude contains aromatic hydrocarbons, nitrogen heterocycles and long chain fatty acids and alcohols. A nitrogen balance indicates that a large proportion of the fuel nitrogen (up to 50%) is transferred to the aqueous phase in the form of ammonium. The remainder is distributed between the bio-crude and the gaseous phase the latter containing HCN, NH₃ and N₂O depending upon catalyst conditions. The addition of organic acids results in a reduction of nitrogen in the aqueous phase and a corresponding increase of NH₃ and HCN in the gas phase. The addition of organic acids has a beneficial effect on the yield and boiling point distribution of the bio-crude produced.     

Compatibility of automotive materials in biodiesel: A review

Use of biodiesel in automobile can significantly reduce our dependence of fossil fuel and help reduce environmental pollution. However, there are concerns over the compatibility of currently used automotive materials in biodiesel. A few automobile manufacturers extended their warranty only to lower blends of biodiesel (e.g. B5). Higher blends (e.g. B50 or B100) are still not covered by warranty. In automobile fuel system, metallic materials like ferrous alloy and non-ferrous alloys, and elastomers come in contact with fuel. Biodiesel, having different chemical characteristics from diesel, can interact with materials in a different way. It can cause corrosive and tribological attack on metallic components and degrade elastomer parts. This paper attempts to present an overview of the work done so far on the compatibility of biodiesel with automotive materials.     

Implications of biodiesel production and utilisation on global climate – A literature review

Over the last few years, the favourable political environment has led to an increasing use of biofuels in the worldwide transportation sector. This development is mainly driven by concerns about the security of energy supplies and the intention to mitigate anthropogenic greenhouse gases (GHG). However, recently, the sustainability of a broad biofuel production and use has, in particular, been strongly questioned. Against this background, in this study a literature review on available and recently published life cycle assessment (LCA) studies for biodiesel has been carried out and the potential GHG emission savings from biodiesel production and use compared to fossil diesel have been analysed. The results of the reviewed studies underline the significant influence of the effects of land use change and the importance of avoiding the conversion of natural land into agricultural areas. If no land use change takes place, the results show moderate to good GHG savings for biodiesel (depending on the type of converted raw materials as well as on the chosen biomass conversion technology). In particular, the biodiesel feedstock production and the source of energy for the production process strongly influence the overall result of the GHG balance of biodiesel.     

Techno-economic study of different alternatives for biodiesel production

Biodiesel has become an attractive diesel fuel substitute due to its environmental benefits since it can be made from renewable resource. However, the high costs surrounding biodiesel production remains the main problem in making it competitive in the fuel market either as a blend or as a neat fuel. More than 80% of the production cost is associated with the feedstock itself and consequently, efforts are focused on developing technologies capable of using lower-cost feedstocks, such as recycled cooking oils and wastes from animal or vegetable oil processing operations.     

Experimental analysis of lipid extraction and biodiesel production from wastewater sludge

The most promising renewable alternative fuel, biodiesel, is produced from various lipid sources. Primary and secondary sludge of municipal wastewater treatment facilities are potential sources of lipids. In this study, factorial experimental analyses were used to study the influence of different variables on the lipid extraction and biodiesel production from dried municipal primary and secondary sludge (Adelaide Pollution Control Plant, London, ON, Canada). The empirical models were developed for each factorial analysis. The temperature turned out to be the most significant variable for lipid extraction by using methanol and hexane as solvents. Extraction using methanol resulted in a maximum of 14.46 (wt/wt) % and 10.04 (wt/wt) % lipid (on the basis of dry sludge), from the primary and secondary sludge sources respectively. A maximum of 11.16 (wt/wt) % and 3.04 wt/wt% lipid (on the basis of dry sludge) were extracted from the primary and secondary sludge sources, respectively, using hexane as a solvent. The FAME (fatty acid methyl ester) yield of the H₂SO₄ catalyzed esterification–transesterification of the hexane and methanol extracted lipids were 41.25 (wt/wt) % and 38.94(wt/wt) % (on the basis of lipid) for the primary sludge, and 26.89 (wt/wt) % and 30.28 (wt/wt) % (on the basis of lipid) for the secondary sludge. The use of natural zeolite as a dehydrating agent was increased the biodiesel yield by approximately 18 (wt/wt) % (on the basis of lipid). The effect of temperature and time was also investigated for biodiesel production from the lipid of wastewater sludge. The yield and quality of the FAME were determined by gas chromatography.     

Biomass to fuels: A water-free process for biodiesel production with phosphazene catalysts

Non-ionic triamino(imino)phosphoranes (phosphazenes) give excellent results as base catalysts for the water-free alcoholysis of vegetable fatty esters. Two phosphazene catalysts, with different intrinsic basicities, P₁-t-Bu and P₄-t-Bu, together with reaction parameters, such as temperature, alcohol/oil molar ratio, or catalyst concentration, have been studied. It was found that activity can be directly correlated to the basicity of the catalyst. Very high biodiesel yields (93–95% mol) were achieved under mild reaction conditions with methanol and ethanol. The catalyst can be recovered and recycled.     

Enzymatic biodiesel production: Technical and economical considerations

It is well documented in the literature that enzymatic processing of oils and fats for biodiesel is technically feasible. However, with very few exceptions, enzyme technology is not currently used in commercial‐scale biodiesel production. This is mainly due to non‐optimized process design and a lack of available cost‐effective enzymes. The technology to re‐use enzymes has typically proven insufficient for the processes to be competitive. However, literature data documenting the productivity of enzymatic biodiesel together with the development of new immobilization technology indicates that enzyme catalysts can become cost effective compared to chemical processing. This work reviews the enzymatic processing of oils and fats into biodiesel with focus on process design and economy.     

Latest developments on application of heterogenous basic catalysts for an efficient and eco friendly synthesis of biodiesel: A review

Heterogeneous catalysts are now being tried extensively for biodiesel synthesis. These catalysts are poised to play an important role and are perspective catalysts in future for biodiesel production at industrial level. The review deals with a comprehensive list of these heterogeneous catalysts which has been reported recently. The mechanisms of these catalysts in the transesterification reaction have been discussed. The conditions for the reaction and optimized parameters along with preparation of the catalyst, and their leaching aspects are discussed. The heterogeneous basic catalyst discussed in the review includes oxides of magnesium and calcium; hydrotalcite/layered double hydroxide; alumina; and zeolites. Yield and conversion of biodiesel obtained from the triglycerides with various heterogeneous catalysts have been studied.