**1. Introduction**

Biodiesel is getting the attention of policy makers to overcome serious concerns about climate change and maintain the security of the energy supply. Biodiesel has several advantages, such as being non-toxic, sustainable, non-explosive, environmentally friendly and biodegradable, which lessens toxic emissions and productions when used in a diesel engine [1–8]. Many observers consider biodiesel to be the one of the feasible options for the substitution of fossil diesel in the transport sector [9–19]. Increasing biodiesel supplies helps to reduce fuel imports and to cut down the emission of greenhouse

gases (GHG). There is a downside of biodiesel as well. The fuel performance in in the engine depends upon the derived cetane number, total acid number, viscosity, and oxidative stability, etc. Biodiesels usually have higher viscosity than petroleum diesel. The engine will not operate well when the viscosity of the fuel is too high. The derived cetane number (CN) is "the measure of the ignition delay from the time the fuel injected and the start of combustion". The higher the CN, the shorter the ignition delay and, therefore, the better the quality of the fuel [5,8,20–22].

Most importantly, food crop production for biodiesel often requires massive acreage and may lead to land-use conflicts in food production. Despite these using non-edible oil seed crops such as *Pongamia glabra, Jatropha curcas* and *Azadirachta indica* prove best suitable for the biodiesel synthesis. Several other disadvantages include higher cost, poor low temperature, flow properties, variation in ignition quality of biodiesel produced from di fferent feedstocks and clogging in engine etc. Biodiesel is unusable in cold areas. This is one of the major drawbacks of biodiesel use. If it gets below −1 ◦C, it will be solidifying in the engine and fuel tank. Usually, the temperature of congelation is relatively high for biodiesel. However, biodiesel can still be used in winter, if it is mixed with some sort of winterized diesel to remain a liquid. Biodiesel cold-flow properties are characterized by three temperature measures: cloud point (CP), "the temperature at which the fuel shows a haze from the formation of crystals"; cold filter plugging point (CFPP), "the temperature at which the crystals formed will cause the plugging of the filters"; and pour point (PP), "the lowest temperature at which the liquid will flow" [23].

The crude oils usually contains moisture, gums (lecithins), solids (insoluble), waxes, free fatty acids (FFA), and compounds of Na, K, Mg, Ca and other metals, which must be removed to make high-quality biodiesel more e fficient and stable against rancidity upon storage. A series of steps are used to remove these impurities, including degumming (to remove gums), neutralizing (to remove FFA), bleaching (to remove color), deodorizing (to remove odor and taste), and dewaxing or winterization (to remove waxes). The alternative methodology to improve quality of biodiesel adopted in this study was fractionation of *Azadirachta indica* seed oil followed by its transesterification for production of biodiesel. The high demand for biodiesel in replacing fossil fuels has driven many researchers to come out with new ideas and inventions. Neem (*Azadirachta indica*) belongs to the Maliaceae family. *Azadirachta indica* seed oil is a non-edible feedstock to produce biodiesel. *Azadirachta indica* seed contains up to 40% lipid contents [24]. The main purpose of the present study was to remove the components from the source oil that deteriorate the quality of the produced biodiesel. Biodiesel quality can be directly related to type and percentage amount of various fatty acids present in the source oil. The presence of fatty acids with short chains or overlong chains could have negative e ffects on biodiesel fuel standard parameters. Hence, it is possible to control and improve the quality of the produced biodiesel by controlling and maintaining the fatty acid composition of the source oil. In the present study, *Azadirachta indica* seed oil is separated into several fractions using high vacuum fractional distillation (HVFD) to produce biodiesel with superior flow and burning proprieties. The present study is based on the hypotheses that biodiesel produced from a specific oil fraction show more consistent fatty acid composition, low cloud point and low pour point.

## **2. Materials and Methods**

#### *2.1. Sample Collection and Oil Extraction*

The *Azadirachta indica* seeds (10 kg) were collected from the University of Agriculture Faisalabad, Pakistan. A sample cleanup using deionized distilled water (DDW) was carried out to eliminate impurities and dirt. The cleaned samples were dried at 40 ◦C in an electric oven until a constant weight was attained. The *Azadirachta indica* seed oil extracted using a cold press.

#### *2.2. Vacuum Fractional Distillation of Azadirachta Indica Oil*

Vacuum fractionation distillation of *Azadirachta indica* oil was carried out to separate out di fferent isolates based on boiling points. Vacuum fractional distillation apparatus consisted of an electric

heater (operation range: room temperature to 375 ◦C), boiling flask (500 dm3), condenser with vacuum adapter, one-stage vacuum pump (10 Pa, power = 14 , oil capacity = 250 dm3, Model TW-1A), short-path distillation receiver, cow shaped (with four 50 dm<sup>3</sup> flasks). In a single run, 300 dm<sup>3</sup> of *Azadirachta indica* oil was separated into fractions under a constant vacuum of −760 mmHg at varied temperatures. A digital thermometer was used to record temperature of vapors of boiling fractions (Figure 1). Table 1 present fractions obtained after the distillation of 650 g of *Azadirachta indica* oil. The oil left after fractionation consist of impurities that severely affect biodiesel properties. This oil can be further processed to produce lubricating liquid, *Azadirachta indica*-based antiseptic soap or in monoacylglycerol production as done previously in the literature [25]. The *Azadirachta indica* oil was distilled using vacuum fractions to isolate fraction F1 (120–150 ◦C), fraction F2 (180–190 ◦C), fraction F3 (202–230 ◦C) and fraction F4 (235–240 ◦C).

**Figure 1.** High vacuum fractionation distillation (HVFD) setup of *Azadirachta indica* oil.

**Table 1.** *Azadirachta indica* seed oil fractions separated using vacuum fractionation at −760 mmHg.

