Biodiesel Production

biodiesel production, fermentation
Image by Chokniti Khongchum from Pixabay

As fuel costs rise, novel alternatives are continually being sought to replace traditional crude oil and petrodiesel. Biodiesel is  the promising alternative because it is also a renewable fuel.

History

Rudolf Diesel who invented the diesel engine showed for the Paris Exhibition in 1900 that a fuel could be prepared from peanut oil. At the time the French government was interested to know if peanut oil which was produced in their African colonies might be a viable commercial energy source.

So began biofuels!

Biofuels: A Short Overview

Biofuels are produced from various organic products and wastes. The three most common forms are bioethanol, biodiesel and biomethane. Bioethanol is made from sugar, algae, sugar beet and wheat. Biodiesel is prepared from plant and animal lipid sources such as vegetable oil, animal fat and algal lipids. Biomethane is manufactured from waste organic materials, agricultural and domestic waste and sewage. Biodiesel is the main focus of our attention here.

What is Biodiesel?

As a compound it is described as non-petroleum based diesel consisting of short chain alkyl methyl and ethyl esters. It is used alone or blended with conventional petro-diesel in unmodified diesel engines. 

Biodiesel Production

Biodiesel is produced by two approaches which either involve triglycerides or fatty acids.  In the first approach, triglyceride is reacted with methanol or ethanol  using acid or alkaline hydrolysis to produce a fatty acid methyl ester (FAME)  and glycerol.   

A triglyceride as the name suggests is a glycerol molecule  to which is bound three fatty acid esters. In this approach, glycerol is the main byproduct of reaction where it forms 10% w/w of the final reaction with 90% w/w being biodiesel.

The second approach is to take a source of fatty acids and react with methanol or ethanol usually under acid hydrolysis to produce the same type of FAME. This process is just called esterification. 

Biodiesel is defined in regulations by a European Standard for biodiesel fuel (EN 14214).

The Process

The basic process is:

  1. To collect oil and fat as a feedstock for the process
  2. Pretreatment of the oil by heating to 120F
  3. Early Esterification reactions
  4. Transesterification reaction
  5. Atmospheric (non-pressure) distillation
  6. Washing and drying
  7. Biodiesel refinement

Feedstocks

Biodiesel is synthesized from animal fats which are waste from the meat processing industry and from vegetable oils. These feedstocks of glycerides are industrially found in oleaginous products such as cooking oil, soybean oil, rapeseed oil, waste greases, pork and beef lard, biomass from algae – in fact almost any vegetable oil or animal fat. Most feedstock sources are oleaginous crops (Girio et al., 2017).

Lard is often treated with the catalyst of potassium hydroxide (Berrios et al., 2009).

Why is neat vegetable oil not used?

The major reason for not using a neat vegetable oil as fuel is its high viscosity, usually in the range of 28–40 mm2/s, which leads to operational problems in diesel engine including formation of deposits and injector coking due to poorer atomization upon injection into the combustion chamber. Transesterification of the oil reduces the viscosity of the oil to a range (usually 4–5 mm2/s) closer to that of petrodiesel.

Catalytic Reactions

Different catalysts are used for biodiesel production primarily in transesterification. Acid catalysts are the most commonly employed (Su & Guo, 2014).

Those most typically used in transesterification reactions are alkalis (sodium hydroxide, sodium methoxide, potassium hydroxide, potassium methoxide, sodium amide, sodium hydride, potassium amide and potassium hydride), acids (sulphuric acid, phosphoric acid, hydrochloric acid or organic sulfonic acid), heterogeneous catalysts like enzymes (lipases) and complex catalysts like silicates, zirconias, nanocatalysts, etc. (Ma & Hanna, 1999).

In a number of cases catalysts such as p-toluenesulphonic acid (tosyl acid) or methylsulphonic acid are preferred. 

Economics Of Glycerol Production

If the feedstock is oil and fat, every gallon of biodiesel produced generates 105 pounds of glycerol. The price of crude glycerol is very low because of the biodiesel industry and new processes using this material are needed.

Processing of Biodiesel

The separation of biodiesel from glycerol is often problematic. One method is to use membranes for separation. Ceramic membranes for microfiltration and ultrafiltration have been tested in a tangential filtration module (Gomes et al., 2010).  Glycerol was retained with a  0.2 μm membrane. These membranes were prepared as tubular Al2O3/TiO2 ceramic construction.

References

Ardi, M. S., Aroua, M. K., & Hashim, N. A. (2015). Progress, prospect and challenges in glycerol purification process: A review. Renewable and Sustainable Energy Reviews42, pp. 1164-1173.

Berrios, M., Gutiérrez, M. C., Martín, M. A., & Martín, A. (2009). Application of the factorial design of experiments to biodiesel production from lard. Fuel Processing Technology90(12), pp. 1447-1451.

Biodiesel 2020: Global Market Survey, Feedstock Trends and Forecasts. Emerging Markets Online. 2008, Multi-Client Study [http://www.healthtech.com/biodiesel2020]2

Díaz, I., Donoso-Bravo, A., Fdz-Polanco, M. 2011a. Effect of microaerobic conditions on the degradation kinetics of cellulose. Bioresour. Technol., 102, pp. 10139- 10142 (Article).

Díaz, I., Fdz-Polanco, M. 2012. Robustness of the microaerobic removal of hydrogen sulfide from biogas. Water Sci. Technol., 65, pp. 1368-1374.

Díaz, I., Lopes, A.C., Pérez, S.I., Fdz-Polanco, M. 2011b. Determination of the optimal rate for the microaerobic treatment of several H2S concentrations in biogas from sludge digesters. Water Sci. Technol., 64, 233-238.

Díaz, I., Lopes, A.C., Pérez, S.I., Fdz-Polanco, M. 2010. Performance evaluation of oxygen, air and nitrate for the microaerobic removal of hydrogen sulphide in biogas from sludge digestion. Bioresour. Technol., 101, 7724-7730.

Díaz, I., Pérez, S.I., Ferrero, E.M., Fdz-Polanco, M. 2011c. Effect of oxygen dosing point and mixing on the microaerobic removal of hydrogen sulphide in sludge digesters. Bioresour. Technol., 102, 3768-3775.

Fdz.-Polanco, M., Díaz, I., Pérez, S.I., Lopes, A.C., Fdz.-Polanco, F. 2009. Hydrogen sulphide removal in the anaerobic digestion of sludge by micro-aerobic processes: Pilot plant experience. Water Sci. Technol., 60, 3045-3050

Gírio, F.; Marques, S.; Pinto, F.; Oliveira, A.C.; Costa, P.; Reis, A.; Moura, P. (2017) Biorefineries in the World. In: Biorefineries, Targeting Energy, High Value Products, An Waste Valorization; Rabaçal, M., Ferreira, A., Silva, C., Costa, M., Eds.; Springer: Berlin, Germany, 2017; pp. 227–281

Gomes, M. C. S., Pereira, N. C., & de Barros, S. T. D. (2010). Separation of biodiesel and glycerol using ceramic membranes. Journal of Membrane Science352(1-2), pp. 271-276 (Article).

Ma, F.; Hanna, M.A. (1999) Biodiesel production: A review. Bioresour. Technol. 70, pp. 1–15.

Melero, J. A., Bautista, L. F., Morales, G., Iglesias, J., & Briones, D. (2009). Biodiesel production with heterogeneous sulfonic acid-functionalized mesostructured catalysts. Energy & Fuels23(1), 539-547 (Article).

Su, F., & Guo, Y. (2014). Advancements in solid acid catalysts for biodiesel production. Green Chemistry16(6), 2934-2957 (Article).

Zalouk, S.; Barbati, S.; Sergent, M.; Ambrosio, M. (2009) Disposal of animal by-products by wet air oxidation: Performance optimization and kinetics. Chemosphere 74, pp. 193–199

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