510

33 Valorization of Waste Cooking Oil into Biodiesel, Biolubricants, and Other Products

Vegetable oils primarily consist of triacylglycerols (TAGs, 92–98%), polar lipids

(phospholipids and galactolipids), monoacylglycerols, diacylglycerols, and trivial

quantity of free fatty acids and polyisoprenoids [5]. During the frying of vegetable

oil (160–200 ^∘C), numerous physical and chemical reactions occur and toxic com-

pounds are formed through oxidation reactions, hydrolysis, and polymerization

of TAGs [6]. Physical parameters like viscosity, color, and surface tension of the

oil will also change after the process of deep frying. Also the food that is fried

releases water into the oil. Once the frying process takes place in an open air

environment, the structure of vegetable oil will be changed by oxidation reaction

and produces hydrogen peroxide which will be further oxidized into toxic products

like 4-hydroxy-2-alkenals [7].

While producing biodiesel and biofuel from vegetable oil, various things should

be considered like cultivating immense amount of oilseed crops. The compounds

present in WCOs are found to be mutagenic, carcinogenic, neurotoxic, and hepotoxic

[8]. However, the WCOs can be wisely used, so that it will be not only econom-

ical but also good from the ecological point of view. Reprocessing and reutilizing

will be important for saving the environment. Biodiesel has the potential to supple-

ment or even to replace the fossil oils. But, the cost of production for biodiesel is

always higher than that of petroleum diesel, since the biodiesel production is from

edible vegetable oils which are expensive [9]. The feedstock of biodiesel is impacted

by not only current land usage but also previous land usage pattern. The require-

ments of both the quantity and quality of biofertilizers for the production of these

oil-bearing crops depend variably on different geographical locations. These various

factors eventually sum up to stand as a barrier in the way of using vegetable oils for

biodiesel or lubricant production. Hence, utilizing WCOs will be advantageous.

33.2

Treatment

After treatment and reprocessing, WCO can be conveniently used for various

industrial purposes like production of biofuels and biolubricants, as additives

for asphalts, and can also be utilized as animal feed [10–12]. The currently used

protocol for the production of biodiesel is alkali-catalyzed transesterification of

triglycerides, and the obtained biodiesel will have low molecular weight alcohol

and this process is operated in batch mode. This process is preferable due to its

efficiency and lower corrosive nature than the acid catalyzed transesterification.

Acid catalyzed transesterification is a faster reaction and occurs in the presence of

lower amount of catalyst. But, alkaline catalysts are most preferred, for example

NaOH, KOH, NaOCH3, etc. The alkali-catalyzed process also has a few hindrances

like glycerol separation, sensitivity to the impurities of lipid feedstock, large reaction

time, and complex biodiesel purification steps [13].

33.2.1

Chemical Treatment

The UVO is subjected to water treatment while the waste water is cleared. The

utilized degummed oil is pushed through a pressure pipeline and subjected to a