Evaluation of small-scale batch biodiesel production options for developing economies

Abstract

Biodiesel is a renewable fuel that can be produced from animal fats, vegetable oils or recycled used cooking oil. From the 1970’s, biodiesel received increased focus as an alternative to crude oil and its component products. Among various processes used for biodiesel production, transesterification of glyceride and alcohol in the presence of a catalyst to produce ester (biodiesel) and glycerin remains the most common. In Africa, biodiesel is currently produced industrially in a number of ways via different methods. In South Africa, there are a number of biodiesel production plants that are continuous processes with feed samples from different sources. Reviewing the batch systems for developing economies, various observations were made. Some produced biodiesel using batch systems at room or day temperatures, another used different temperatures, some also used flat based buckets for their mixing and so on. This becomes difficult for local producers who desired to produce biodiesel on a very small scale for their farms or business. Hence, the study was aimed at evaluation batch biodiesel systems and to come up with a simplified approach for a producer in a developing economy or a local user. The objectives of this study were as follows; To evaluate biodiesel production options, and hence develop a simplified process that can be used to produce biodiesel in developing economies. The criteria for evaluation will include: ease of operation, non-specialist equipment, range of feedstock, product quality and product yield. To evaluate various factors that affect these criteria and make recommendations that will enable a local producer to remain within an optimum range Compare the produced biodiesel properties against general biodiesel and petroleum diesel ASTM standard range Recommend simplified equipment design for a local producer Perform economic evaluation to establish cost required both for equipment and raw materials for a local producer. After literature review on the existing processes, base catalyzed transesterification was selected. This is because of the simplicity as well as ease of operation. Experimental trials commenced using feeds from pure vegetable oil (PVO) and waste vegetable oil (WVO) to familiarize biodiesel production, as well as study the behavior of each having the research criteria in focus. Various variables that affect ease of operation, product quality, and yield were also investigated. These include temperature, type of catalyst (KOH or NaOH), type of alcohol (Methanol or Ethanol), concentration of catalyst, and purity of alcohol, and nature of feed (PVO or WVO). The effect of temperature was compared against product quality, yield, and ease of operation. Other variables were also compared against the same criteria. Treatment of WVO because of impurity and moisture contamination associated with such samples was also studied. The product was then tested using some ASTM procedures to compare biodiesel quality to acceptable standards. Efficient reaction time is paramount for a quality biodiesel. It was observed that biodiesel required between 25 and 30 minutes for a complete reaction. Lower temperatures clearly affected the quality of biodiesel produced. Best operating range was found to be between 55 oC – 75 oC is usually recommended for a transesterification reaction to obtain optimum yield and quality. The use of KOH compared to NaOH yields similar results even though NaOH is usually selected because of the reduced cost. The use of methanol compared to ethanol also yields similar results, even though methanol is usually preferred due to cost. Purity of available alcohol is vital as its reduction from 99.5 % to 75 % during experimental trials, yielded poor quality biodiesel. This is mainly due to moisture content that usually gives room for bacteria growth and corrosion of fuel lines in engines. As long as a titration test is carried out on the feed, the use of WVO is a good option. Varying catalyst concentrations from 0.5 % to 1.75 % were considered and the best regimes identified. This test will enable a producer from a growing economy to use the appropriate reagent, which will ensure the transesterification reaction is complete. After comparing appleseed and cone based design, the latter was selected as it will eliminate any difficulty that a local producer might encounter in making the biodiesel batch. In terms of costs, it was discovered that the major costs to a local producer will be the biodiesel mixer and fittings which will be fixed costs. Other variable costs are considered to be affordable, as the cost of waste vegetable oil is very low as well as other industrial reagent grade that will be required. In summary, batch biodiesel production for a local user or developing economy is a very feasible exercise. One needs to ensure that the recommendations regarding pre-treatment of feed oil, basic reaction criteria and other generic parameters are considered during production.