Extraction of Biodiesel from waste vegetable oil

The production of biodiesel from waste vegetable oil offers a triple-facet solution: economic, environmental and waste management. The term “waste vegetable oil” (WVO) refers to vegetable oil which has been used in food production and which is no longer viable for its intended use. India’s biodiesel processing capacity is estimated at 600,000 tons per year. Waste used Cooking Oil (WCO) is a residue from a variety of sources, e.g., restaurants, food industrial or domestics, which not only harms human’s health but also causes environmental problems. However, WCO can be used as a raw material for biodiesel production. By this manner, the production of biodiesel from WCO to partially substitute petroleum diesel is an alternative way for environment protection and energy security. The American Society for Testing and Materials (ASTM) defines biodiesel fuel as mono alkyl esters of long chain fatty acids derived from a renewable lipid feedstock, such as vegetable oil or animal fat. Bio-diesel types can be classified according to their source and manufacturing process as well:

1. Esterificated oils

2. Non-esterificated oils

3. Waste vegetable oils

The new process technologies developed during the years have made it possible to produce biodiesel from recycled frying oils comparable in quality to that of virgin vegetable oil biodiesel with an added attractive advantage of being lower in price. Thus, biodiesel produced from recycled frying oils has the same possibilities to be utilized.

While transesterification is well- established and becoming increasingly important making it the most common way to produce biodiesel. Transesterification, refers to a catalysed chemical reaction involving vegetable oil and an alcohol to yield fatty acid alkyl esters (i.e. Biodiesel) and glycerol (Fig.1).

General vegetable oils or animal fats, comprise the main constituent of Triglycerides (TGs) with lower density compared to water and may be solid or liquid at normal room temperature. Triacylglycerol the main component of vegetable oil consists of three long chain of fatty acids. In case of base catalysed transesterification; When triacylglycerol reacts with an alcohol (methanol, ethanol or both), the three fatty acids chains are released from the glycerol skeleton and combine with the alcohol to yield fatty acid alkyl esters known as fatty acid methyl ester (FAME). Glycerol is produced as a by-product.R1, R2, and R3 in fig.1 represent long carbon chains that are too lengthy to include in the diagram.

Biodiesel acts as an alternative to fossil fuels, because of few reasons such as it reduces the need for importation of fuels, helps in reducing the Green House Gases (GHG) emissions, prevents air pollution, benefits the domestic economy. With slight variations, performance and fuel economy of biodiesel is the same as petro-diesel. Also it can be used in any diesel engine without modification, One gallon (4.54 litre) of biodiesel provides with the same benefits wheather used neat (100%) or used in blends, such as B20 (20% biodiesel with 80% diesel fuel).

Comparison of biodiesel with conventional fossil-fuel-petroleum diesel

1. Biodiesel is a much cleaner fuel

than conventional fossil-fuel petroleum diesel.

2. Biodiesel burns up to 75% cleaner than petroleum diesel fuel.

3. Biodiesel reduces unburned hydrocarbons (93% less), carbon monoxide (50% less) and particulate matter (30% less) in exhaust fumes, as well as cancer-causing PAH (80% less) and nitrited PAH compounds (90% less). (US Environmental Protection Agency

4. Sulphur dioxide emissions are eliminated (biodiesel contains no sulphur)

5. Biodiesel is plant-based and using it adds no extra CO2 greenhouse gas to the atmosphere

6. The ozone-forming (smog) potential of biodiesel emissions is nearly 50% less than petro-diesel emissions

7. Nitrogen oxide (NOx) emissions may increase or decrease with biodiesel but can be reduced to well below petro-diesel fuel levels

8. Biodiesel exhaust is not offensive and does not cause eye irritation (it smells like French fries)

9. Biodiesel is environmentally friendly: it is renewable, and “more biodegradable than sugar and

less toxic than table salt” (US National Biodiesel Board, based on US Environmental Protection Agency studies)

10.Biodiesel is a much better lubricant than petro-diesel and extends engine life .Even a small amount of biodiesel means cleaner emissions and better engine lubrication: 1% biodiesel added to petro-diesel will increase lubricate property by 65%.

11.Biodiesel can be mixed with petro-diesel in any proportion, with no need for a mixing additive.

12.Biodiesel has a higher certain number than petroleum diesel because of its oxygen content. The higher the certain number, the more efficient the fuel; the engine starts more easily, runs better and burns cleaner.

Materials and Methodology

Approximately 80% by volume of the feed stock of biodiesel is vegetable oil or animal fats and about 20% is methanol. Proper reaction of the raw oil requires 20% methanol. The ratio of catalyst varies depending on materials used.

Materials

a) Sodium hydroxide (NaOH)

b) Glycerol

c) Waste oil (peanut oil)

d) Vibrater or stirrer

Before waste oil is used for the extraction of biodiesel, it should be first filtered through muslin cloth to avoid the floating residue. Further, for maximum extraction of bio diesel from waste oil correct amount of sodium hydroxide is required. So for that a titration must be performed on the oil being transesterified.

Titration

To determine the correct amount of NaOH required, a titration must be performed on the oil being transesterified. This is the most critical step in the process. If the FFA content exceeds 1% and if an alkaline catalyst must be used, then a greater amount of catalyst should be added to neutralize the FFA. However, the correct amount of catalyst should be used because both excess as well as insufficient amount of catalyst may cause soap formation. To determine the correct amount of catalyst required, a titration must be performed on the oil. For titration, 0.1% of NaOH in distilled water is titrated against the titration sample, which is essentially a solution of 10ml of Isopropyl alcohol and 1ml of oil sample with 2-3 drops of indicator. The end point of the titration is marked when the titration sample turns pink (magenta) and stays pink for 10s. The number of millilitres of 0.1% NaOH solution needed is equal to the number of extra grams of pure sodium hydroxide catalyst needed to produce the proper reaction to make biodiesel from WVO.

Methodology

The volume of waste cooking oil used in this study was 60ml for each sample. For this study, effect of different methanol to oil molar ratios and different concentration of catalyst ratios on biodiesel yields was investigated. For preparation, care must be taken to monitor the amount of water and free fatty acids in the incoming bio lipid (oil or fat). Here, the waste oil used was used for frying continuously for five days until it cannot be used further. (Fig. 2)

If the free fatty acid level or water level is too high it may cause problems with soap formation (saponification) and the separation of the glycerine by-product at downstream. Catalyst such as sodium hydroxide (or potassium hydroxide) is dissolved in the alcohol (methanol) using a standard agitator or mixer or vibrator. The alcohol/catalyst mix is then charged into a closed reaction vessel and the bio lipid (peanut oil) is added. The waste vegetable oil should be slightly warm at 600C so that the rate of reaction is fast (Fig. 3). From this step the system should be totally closed from the atmosphere to prevent the loss of alcohol. Further, it is blended or shaken or vibrated properly for 15 minutes, after that it is kept for 24 hours for separation of glycerine and biodiesel (Fig. 4). Excess alcohol is normally used to ensure total conversion of the fat or oil to its esters.

The glycerine phase is much denser than biodiesel phase and the two can be gravity separated with glycerine simply drawn off the bottom of the settling vessel. In some cases, a centrifuge is used to separate the two materials faster. Once the glycerine and biodiesel phases have been separated, the excess alcohol in each phase is removed with a flash evaporation process or by distillation.

In other systems, the alcohol is removed and the mixture is neutralized before the glycerine and esters have been separated. In either case, the alcohol is recovered using distillation equipment and is re-used. Care must be taken to ensure no water accumulates in the recovered alcohol stream. Once separated from the glycerine, the biodiesel is sometimes purified by washing gently with warm water to remove residual catalyst or soaps, then it is dried, and sent to storage. As shown in fig. 4 the Glycerine is precipitated out from the mixture and settled down on the bottom as thick, cloudy liquid. The thin, translucent liquid that remained on top was methyl alkyl ester i.e. biodiesel. Biodiesel is then separated from the mixture.

Results and Discussions

Table 1 presents the percentage of biodiesel yield with different weights of NaOH. The oil to Methanol ratio i.e. 1:6 was fixed after different sets of practicals. This ratio was considered for defining the biodiesel yield.

Few comments on the table findings are presented below,

1. When the methanol to oil molar ratio was 1:6, the highest biodiesel yield from waste vegetable peanut oil is 63.33% and the lowest biodiesel yield is 32.68%.

2. Generally, the biodiesel yields decreased with decreasing methanol to oil molar ratios.(Fig. 5)

3. Initial two readings are zero due to the soapanification. It is due to the high content of free fatty acid level or water level. This is the result of Na+ ions from the sodium hydroxide (NaOH) reacting with water created, when the methanol bonds with the ester chains along with any other water that gets suspended in the WVO.

4. The glycerine, which is a by-product during extraction of bio diesel, is an excellent industrial-type degreaser/soap. Pure glycerine is a valuable product for medicines, tinctures, hand lotions, dried plant arrangements etc,.

The depletion of world petroleum reserves and the increased environmental concerns have stimulated the search for alternative sources for petroleum-based fuel, including diesel fuels.

1 Biodiesel made from used cooking oil (WVO – waste vegetable oil) should also qualify. Most WVO ends up in the sewers and landfills which is not good and doesn’t offset any fossil-fuel use. Converting it to biodiesel is a much better option.

2 Because of its closer properties with diesel, biodiesel fuel (fatty acid methyl ester) from vegetable oil is considered as the best candidate for diesel fuel substitute in diesel engines.

3 The use of waste cooking oil to produce biodiesel reduced the raw material cost.

4 The acid-catalysed process using waste cooking oil proved to be technically feasible with less complexity than the alkali-catalysed process using waste cooking oil, thereby making it a competitive alternative to commercial biodiesel production using the alkali-catalysed process.

 

Mayuri A.Mistry
M.Tech (Final Year Research Student)
Civil Engineering Department
S.V. National Institute of Technology, Surat<>

 

A. K. Khambete
Lecturer, Civil Engineering Department
S.V. National Institute of Technology, Surat