Biodiesel production

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Biodiesel production is the process of producing the biofuel, biodiesel, through the chemical reactions of transesterification and esterification. [1] This process renders a product (chemistry) and by-products.

Contents

The fats and oils react with short-chain alcohols (typically methanol or ethanol). The alcohols used should be of low molecular weight. Ethanol is the most used because of its low cost, however, greater conversions into biodiesel can be reached using methanol. Although the transesterification reaction can be catalyzed by either acids or bases, the base-catalyzed reaction is more common. This path has lower reaction times and catalyst cost than those acid catalysis. However, alkaline catalysis has the disadvantage of high sensitivity to both water and free fatty acids present in the oils. [2]

Biorefinery process steps

The major steps required to synthesize biodiesel are as follows:

Feedstock pretreatment

Common feedstock used in biodiesel production include:

Lignocellulose generates byproducts that act as enzyme inhibitors, such as acetic acid, furfural, formic acid, vanillin, and these chemical inhibitors affect cell growth. [4]

Recycled oil is processed to remove impurities from cooking, storage, and handling, such as dirt, charred food, and water. Virgin oils are refined, but not to a food-grade level. Degumming to remove phospholipids and other plant matter is common, though refinement processes vary.[ better source needed ] [5] Water is removed because its presence during base-catalyzed transesterification results in the saponification (hydrolysis) of the triglycerides, producing soap instead of biodiesel.[ citation needed ]

A sample of the cleaned feedstock is then tested via titration against a standardized base solution, to determine the concentration of free fatty acids present in the vegetable oil sample.[ citation needed ] The acids are then either removed (typically through neutralization), or are esterified to produce biodiesel[ citation needed ] (or glycerides[ citation needed ]).

Reactions

Base-catalyzed transesterification reacts lipids (fats and oils) with alcohol (typically methanol or ethanol) to produce biodiesel and an impure coproduct, glycerol. [6] If the feedstock oil is used or has a high acid content, acid-catalyzed esterification can be used to react fatty acids with alcohol to produce biodiesel. Other methods, such as fixed-bed reactors, [7] supercritical reactors, and ultrasonic reactors, forgo or decrease the use of chemical reaction that reduces the quality of substance in chemistry.

Product purification

Products of the reaction include not only biodiesel, but also the byproducts soap, glycerol, excess alcohol, and trace amounts of water. All of these byproducts must be removed to meet the standards, but the order of removal is process-dependent.

The density of glycerol is greater than that of biodiesel, and this property difference is exploited to separate the bulk of the glycerol coproduct. Residual methanol is typically recovered by distillation and reused. Soaps can be removed or converted into acids. Residual water is also removed from the fuel.

Reactions

Base-catalysed transesterification mechanism

The transesterification reaction is base catalyzed. Any strong base capable of deprotonating the alcohol will work (e.g. NaOH, KOH, sodium methoxide, etc.), but the sodium and potassium hydroxides are often chosen for their cost. The presence of water causes undesirable base hydrolysis, so the reaction must be kept dry.

In the transesterification mechanism, the carbonyl carbon of the starting ester (RCOOR1) undergoes nucleophilic attack by the incoming alkoxide (R2O−) to give a tetrahedral intermediate, which either reverts to the starting material, or proceeds to the transesterified product (RCOOR2). The various species exist in equilibrium, and the product distribution depends on the relative energies of the reactant and product.

General transesterification mechanism.png

Production methods

Supercritical process

An alternative, catalyst-free method for transesterification uses supercritical methanol at high temperatures and pressures in a continuous process. In the supercritical state, the oil and methanol are in a single phase, and reaction occurs spontaneously and rapidly. [8] The process can tolerate water in the feedstock, free fatty acids are converted to methyl esters instead of soap, so a wide variety of feedstocks can be used. Also the catalyst removal step is eliminated. [9] High temperatures and pressures are required, but energy costs of production are similar or less than catalytic production routes. [10]

Ultra- and high-shear in-line and batch reactors

Ultra- and High Shear in-line or batch reactors allow production of biodiesel continuously, semi- continuously, and in batch-mode. This drastically reduces production time and increases production volume.[ citation needed ]

The reaction takes place in the high-energetic shear zone of the Ultra- and High Shear mixer by reducing the droplet size of the immiscible liquids such as oil or fats and methanol. Therefore, the smaller the droplet size the larger the surface area the faster the catalyst can react.[ citation needed ]

Ultrasonic reactor method

In the ultrasonic reactor method, the ultrasonic waves cause the reaction mixture to produce and collapse bubbles constantly; this cavitation simultaneously provides the mixing and heating required to carry out the transesterification process.[ citation needed ] Use of an ultrasonic reactor for biodiesel production can drastically reduce reaction time and temperatures, and energy input.[ citation needed ] Using such reactors, the process of transesterification can run inline rather than using the time-consuming batch processing.[ citation needed ] Industrial scale ultrasonic devices allow for processing of several thousand barrels per day.[ clarification needed ][ citation needed ]

Lipase-catalyzed method

Large amounts of research have focused recently on the use of enzymes as a catalyst for the transesterification. Researchers have found that very good yields could be obtained from crude and used oils using lipases. The use of lipases makes the reaction less sensitive to high free fatty-acid content, which is a problem with the standard biodiesel process. One problem with the lipase reaction is that methanol cannot be used because it inactivates the lipase catalyst after one batch. However, if methyl acetate is used instead of methanol, the lipase is not in-activated and can be used for several batches, making the lipase system much more cost-effective. [11]

Volatile fatty acids from anaerobic digestion of waste streams

Lipids have been drawing considerable attention as a substrate for biodiesel production owing to its sustainability, non-toxicity and energy efficient properties. However, due to cost reasons, attention must be focused on the non-edible sources of lipids, in particular oleaginous microorganisms. Such microbes have the ability to assimilate the carbon sources from a medium and convert the carbon into lipid storage materials. The lipids accumulated by these oleaginous cells can then be transesterified to form biodiesel. [12]

See also

Related Research Articles

<span class="mw-page-title-main">Triglyceride</span> Any ester of glycerol having all three hydroxyl groups esterified with fatty acids

A triglyceride is an ester derived from glycerol and three fatty acids. Triglycerides are the main constituents of body fat in humans and other vertebrates, as well as vegetable fat. They are also present in the blood to enable the bidirectional transference of adipose fat and blood glucose from the liver, and are a major component of human skin oils.

<span class="mw-page-title-main">Biodiesel</span> Fuel made from vegetable oils or animal fats

Biodiesel is a renewable biofuel, a form of diesel fuel, derived from biological sources like vegetable oils, animal fats, or recycled greases, and consisting of long-chain fatty acid esters. It is typically made from fats.

Transesterification is the process of exchanging the organic functional group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. Strong acids catalyze the reaction by donating a proton to the carbonyl group, thus making it a more potent electrophile. Bases catalyze the reaction by removing a proton from the alcohol, thus making it more nucleophilic. The reaction can also be accomplished with the help of other enzymes, particularly lipases.

<span class="mw-page-title-main">Vegetable oil</span> Oil extracted from seeds or from other parts of fruits

Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are mixtures of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of seed oils, or fats from seeds. Olive oil, palm oil, and rice bran oil are examples of fats from other parts of fruits. In common usage, vegetable oil may refer exclusively to vegetable fats which are liquid at room temperature. Vegetable oils are usually edible.

Rancidification is the process of complete or incomplete autoxidation or hydrolysis of fats and oils when exposed to air, light, moisture, or bacterial action, producing short-chain aldehydes, ketones and free fatty acids.

Fatty acid methyl esters (FAME) are a type of fatty acid ester that are derived by transesterification of fats with methanol. The molecules in biodiesel are primarily FAME, usually obtained from vegetable oils by transesterification. They are used to produce detergents and biodiesel. FAME are typically produced by an alkali-catalyzed reaction between fats and methanol in the presence of base such as sodium hydroxide, sodium methoxide or potassium hydroxide. One reason for using FAME in biodiesel production, rather than free fatty acids, is to mitigate the potential corrosion they can cause to metals of engines, production facilities, and related infrastructure. While free fatty acids are only mildly acidic, over time they can lead to cumulative corrosion. In contrast, their esters, such as FAME, are less corrosive and therefore preferred for biodiesel production. As an improved quality, FAMEs also usually have about 12-15 units higher cetane number than their unesterified counterparts.

In chemistry, acid value is a number used to quantify the acidity of a given chemical substance. It is the quantity of base, expressed as milligrams of KOH required to neutralize the acidic constituents in 1 gram of a sample. The acid value measures the acidity of water-insoluble substances like oils, fats, waxes and resins, which do not have a pH value.

<span class="mw-page-title-main">Monoglyceride</span> Class of glycerides

Monoglycerides are a class of glycerides which are composed of a molecule of glycerol linked to a fatty acid via an ester bond. As glycerol contains both primary and secondary alcohol groups two different types of monoglycerides may be formed; 1-monoacylglycerols where the fatty acid is attached to a primary alcohol, or a 2-monoacylglycerols where the fatty acid is attached to the secondary alcohol.

<span class="mw-page-title-main">Sodium methoxide</span> Ionic organic compound (CH3ONa)

Sodium methoxide is the simplest sodium alkoxide. With the formula CH3ONa, it is a white solid, which is formed by the deprotonation of methanol. It is a widely used reagent in industry and the laboratory. It is also a dangerously caustic base.

<span class="mw-page-title-main">Fatty acid ester</span>

Fatty acid esters (FAEs) are a type of ester that result from the combination of a fatty acid with an alcohol. When the alcohol component is glycerol, the fatty acid esters produced can be monoglycerides, diglycerides, or triglycerides. Dietary fats are chemically triglycerides.

Oleochemistry is the study of vegetable oils and animal oils and fats, and oleochemicals derived from these fats and oils. The resulting product can be called oleochemicals (from Latin: oleum "olive oil"). The major product of this industry is soap, approximately 8.9×106 tons of which were produced in 1990. Other major oleochemicals include fatty acids, fatty acid methyl esters, fatty alcohols and fatty amines. Glycerol is a side product of all of these processes. Intermediate chemical substances produced from these basic oleochemical substances include alcohol ethoxylates, alcohol sulfates, alcohol ether sulfates, quaternary ammonium salts, monoacylglycerols (MAG), diacylglycerols (DAG), structured triacylglycerols (TAG), sugar esters, and other oleochemical products.

Hydrotreated vegetable oil (HVO) is a biofuel made by the hydrocracking or hydrogenation of vegetable oil. Hydrocracking breaks big molecules into smaller ones using hydrogen while hydrogenation adds hydrogen to molecules. These methods can be used to create substitutes for gasoline, diesel, propane, kerosene and other chemical feedstock. Diesel fuel produced from these sources is known as green diesel or renewable diesel.

<span class="mw-page-title-main">Chicken fat</span> Animal fat from domestic chicken

Chicken fat is fat obtained from chicken rendering and processing. Of the many animal-sourced substances, chicken fat is noted for being high in linoleic acid, an omega-6 fatty acid. Linoleic acid levels are between 17.9% and 22.8%. It is a common flavoring, additive or main component of chicken soup. It is often used in pet foods, and has been used in the production of biodiesel. One method of converting chicken fat into biodiesel is through a process called supercritical methanol treatment.

Winterizationof oil is a process that uses a solvent and cold temperatures to separate lipids and other desired oil compounds from waxes. Winterization is a type of fractionation, the general process of separating the triglycerides found in fats and oils, using the difference in their melting points, solubility, and volatility.

<span class="mw-page-title-main">Glycerolysis</span>

In organic chemistry glycerolysis refers to any process in which chemical bonds are broken via a reaction with glycerol. The term refers almost exclusively to the transesterification reaction of glycerol with triglycerides (fats/oils) to form mixtures of monoglycerides and diglycerides. These find a variety of uses; as food emulsifiers, 'low fat' cooking oils and surfactants.

<span class="mw-page-title-main">Lipase</span> Class of enzymes which cleave fats via hydrolysis

In biochemistry, lipase refers to a class of enzymes that catalyzes the hydrolysis of fats. Some lipases display broad substrate scope including esters of cholesterol, phospholipids, and of lipid-soluble vitamins and sphingomyelinases; however, these are usually treated separately from "conventional" lipases. Unlike esterases, which function in water, lipases "are activated only when adsorbed to an oil–water interface". Lipases perform essential roles in digestion, transport and processing of dietary lipids in most, if not all, organisms.

In the food industry and biochemistry, interesterification (IE) is a process that rearranges the fatty acids of a fat product, typically a mixture of triglycerides. The process implies breaking and reforming the ester bonds C–O–C that connect the fatty acid chains to the glycerol hubs of the fat molecules. The reactions involve catalysts, either inorganic chemicals or enzymes.

Potassium methoxide is the alkoxide of methanol with the counterion potassium and is used as a strong base and as a catalyst for transesterification, in particular for the production of biodiesel.

Single cell oil, also known as Microbial oil consists of the intracellular storage lipids, triacyglycerols. It is similar to vegetable oil, another biologically produced oil. They are produced by oleaginous microorganisms, which is the term for those bacteria, molds, algae and yeast, which can accumulate 20% to 80% lipids of their biomass. The accumulation of lipids take place by the end of logarithmic phase and continues during station phase until carbon source begins to reduce with nutrition limitation.

<span class="mw-page-title-main">Cooking oil</span> Oil consumed by humans, of vegetable or animal origin

Cooking oil is a plant or animal liquid fat used in frying, baking, and other types of cooking. Oil allows higher cooking temperatures than water, making cooking faster and more flavorful, while likewise distributing heat, reducing burning and uneven cooking. It sometimes imparts its own flavor. Cooking oil is also used in food preparation and flavoring not involving heat, such as salad dressings and bread dips.

References

  1. ↑ Leung, Dennis Y.C.; Wu, Xuan; Leung, M.K.H. (April 2010). "A review on biodiesel production using catalyzed transesterification". Applied Energy. 87 (4): 1083–1095. Bibcode:2010ApEn...87.1083L. doi:10.1016/j.apenergy.2009.10.006.
  2. ↑ Anastopoulos, George; Zannikou, Ypatia; Stournas, Stamoulis; Kalligeros, Stamatis (2009). "Transesterification of Vegetable Oils with Ethanol and Characterization of the Key Fuel Properties of Ethyl Esters". Energies. 2 (5 June 2009): 362–376. doi: 10.3390/en20200362 .
  3. 1 2 3 4 5 6 7 8 Boonyarit, Jeerapan; Polburee, Pirapan; Khaenda, Bongkot; Zhao, Zongbao; Limtong, Savitree (23 March 2020). "Lipid Production from Sugarcane Top Hydrolysate and Crude Glycerol with Rhodosporidiobolus fluvialis Using a Two-Stage Batch-Cultivation Strategy with Separate Optimization of Each Stage". MDPI. 8 (3): 453. doi: 10.3390/microorganisms8030453 . PMC   7143989 . PMID   32210119. Biodiesel can be divided into three generations based on the feedstock which generates the fuel. First-generation biodiesel is produced from edible plant oils, such as palm oil, soybean oil, and coconut oil, and second-generation biodiesel is produced from nonedible plant oils, such as jatropha, animal fats and waste oils [...] The most recent generation of biodiesel is derived from microbial lipids. Using recovered animal fats and frying oils of the second generation as feedstock for biodiesel can efficiently reduce the price of the fuel; however, the amount of these fats and oils is limited on an industrial scale and cannot meet the increasing needs of biodiesel production
  4. ↑ Boonyarit, Jeerapan; Polburee, Pirapan; Khaenda, Bongkot; Zhao, Zongbao; Limtong, Savitree (23 March 2020). "Lipid Production from Sugarcane Top Hydrolysate and Crude Glycerol with Rhodosporidiobolus fluvialis Using a Two-Stage Batch-Cultivation Strategy with Separate Optimization of Each Stage". MDPI. 8 (3): 453. doi: 10.3390/microorganisms8030453 . PMC   7143989 . PMID   32210119. [P]retreatment and hydrolysis of lignocellulosic biomasses usually produce inhibitory compounds, such as acetic acid, furfural, and 5-hydroxymethylfurfural, formic acid, and vanillin, which could have negative effects on growth, metabolism, and product formation of microorganisms
  5. ↑ Bryan, Tom (July 1, 2005). "Pure and Simple". Biodiesel Magazine (online). Retrieved December 18, 2019. Volga, S.D.-based South Dakota Soybean Processors is now offering SoyPure, a trademarked pretreated virgin soybean oil tailored for biodiesel production. Meanwhile, a large customer is about to come on line in neighboring Minnesota.
  6. ↑ Boonyarit, Jeerapan; Polburee, Pirapan; Khaenda, Bongkot; Zhao, Zongbao; Limtong, Savitree (23 March 2020). "Lipid Production from Sugarcane Top Hydrolysate and Crude Glycerol with Rhodosporidiobolus fluvialis Using a Two-Stage Batch-Cultivation Strategy with Separate Optimization of Each Stage". MDPI. 8 (3): 453. doi: 10.3390/microorganisms8030453 . PMC   7143989 . PMID   32210119. Crude glycerol (CG), a byproduct from biodiesel production plants which has been shown to have some inhibitory compounds to microorganism growth, is currently being explored as a possible large-scale carbon source in lipid production by many researchers. [...] The shaking speed supplies the oxygen required for yeast growth in the culture broth, and, as a result, different speeds resulted in different levels of oxygen dissolution. [...] shaking speed was found to be the factor with the highest influence on cell mass and lipid concentration
  7. ↑ C Pirola, F Manenti, F Galli, CL Bianchi, DC Boffito, M Corbetta (2014). "Heterogeneously catalyzed free fatty acid esterification in (monophasic liquid)/solid packed bed reactors (PBR)". Chemical Engineering Transaction 37: 553-558. AIDIC
  8. ↑ Bunkyakiat, Kunchana; et al. (2006). "Continuous Production of Biodiesel via Transesterification from Vegetable Oils in Supercritical Methanol". Energy and Fuels. 20 (2). American Chemical Society: 812–817. doi:10.1021/ef050329b.
  9. ↑ Vera, C.R.; S.A. D'Ippolito; C.L. Pieck; J.M.Parera (2005-08-14). "Production of biodiesel by a two-step supercritical reaction process with adsorption refining" (PDF). 2nd Mercosur Congress on Chemical Engineering, 4th Mercosur Congress on Process Systems Engineering. Rio de Janeiro. Archived from the original (PDF) on 2009-02-05. Retrieved 2007-12-20.
  10. ↑ Kusdiana, Dadan; Saka, Shiro. "Biodiesel fuel for diesel fuel substitute prepared by a catalyst free supercritical methanol" (PDF). Archived from the original (PDF) on 2013-10-19. Retrieved 2007-12-20.
  11. ↑ Du, Wei; et al. (2004). "Comparative study on lipase-catalyzed transformation of soybean oil for biodiesel production with different acyl acceptors". Journal of Molecular Catalysis B: Enzymatic. 30 (3–4): 125–129. doi:10.1016/j.molcatb.2004.04.004.
  12. ↑ Singh, Gunjan; Jeyaseelan, Christine; Bandyopadhyay, K. K.; Paul, Debarati (October 2018). "Comparative analysis of biodiesel produced by acidic transesterification of lipid extracted from oleaginous yeast Rhodosporidium toruloides". 3 Biotech. 8 (10): 434. doi:10.1007/s13205-018-1467-9. ISSN   2190-572X. PMC   6170317 . PMID   30306003.

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