**3.2 Pyrolysis or thermal cracking**

Generally, pyrolysis may be defined as the thermochemical decomposition of feedstock at medium (300–800°C) to high temperatures (800–1300°C) in an inert atmosphere. Pyrolysis means a chemical change that is caused by the application of thermal energy in the absence of oxygen or air or by the application of heat in the presence of catalyst that results in the bonds cleavage and formation of various small molecules [15]. Being a type of destructive distillation, it is performed in an inert atmosphere in the temperature range of 300–1300°C. Based on the operating conditions, pyrolysis may be classified into three subclasses such as conventional pyrolysis that occur in the temperature range of 550 K–900 K, (400–500°C) fast pyrolysis occurring in 850 K–1250 K (400–650°C) and the flash pyrolysis occurs in the 1050 K–1300 K (700–1000°C) range of temperature. Pyrolysis is the process used for the synthesis of fuel from triglycerides, vegetable oil, animal fats or natural fatty acids. Fast pyrolysis is used for the bio-oil production. Vegetable oils can be cracked to improve cetane number and reduce the viscosity. The products obtained as a result of cracking include carboxylic acids, alkanes, alkadienes, alkenes and aromatics in various proportions. Rape seed oil, cotton seed oil, soybean oil and other oils with the use of appropriate catalyst were successfully cracked to get biofuel.

### **3.3 Micro-emulsions**

Micro-emulsions are isotropic, translucent or clear, thermodynamically stable dispersion of water, oil, surfactants, co-surfactants (amphiphilic molecule) for stabilization. In micro-emulsions, the droplet diameters range from 100 to 1000 Å (10 nm–100 nm). A micro-emulsion can be made of vegetable oils with an ester and dispersant (co-solvent) or vegetable oil with alcohol and surfactant with or without diesel fuels [16].

## *Feasibility of Biodiesel Production in Pakistan DOI: http://dx.doi.org/10.5772/intechopen.101967*

Alcohols such as ethanol or methanol are frequently used as a viscosity lowering additives. Whereas higher alcohols are used as surfactants. The alkyl nitrates are also used as cetane improvers. It has been reported that micro-emulsion can results in the reduction of viscosity, increase in cetane number and good spray characters in the biodiesel. However, continuous use of micro-emulsified diesel causes problems in engine such as formation of carbon deposits, injector needle sticking and incomplete combustion.
