Page 117 - Materials Chemistry, Second Edition

Life Cycle Assessment of Biodiesel from Palm Oil 103

POME which are also a major liquid wastes from the palm oil mill are mostly
mismanaged and disposed off wrongly. The direct rampant release of these
effluents can cause water pollution which can affect downstream biodiversity and
human beings. It has been reported that the average biochemical oxygen demand
(BOD) of palm oil processing effluents is 25,000 ppm (Clay 2004). In Malaysia,
for instance, effluents can legally be discarded into water bodies when their BOD
levels are less than 100 ppm. However, the effluents also produce biogas mainly
methane (Yusoff and Hansen 2007; Schmidt 2007) which can be tapped and used
to generate electricity.
The biomass (mostly palm oil mills fruit fiber and kernel shells) powered
combined heat and power (CHP) plants of the palm oil mills mostly operate
without flue gas cleaning devices, hence causing the emissions of heavy metals
and particulate matter which accounts for about 93 and 79 % of the human toxicity
potential and heavy metals emissions to the air, respectively (Yusoff and Hansen
2007). Therefore, exhaust gas cleaning may help to reduce some of these envi-
ronmental impacts drastically.

2.3 CPO Refinery

The refining of CPO helps to remove much FFA, odoriferous materials, phos-
phatides, waxes dirt, metal traces, etc., from the CPO. This process is achieved
either through chemical or physical means. However, the physical process of CPO
refining is the most commonly applied technology because of its simplicity, low
capital cost, and high efficiency. Steam or physical refining involves degumming,
bleaching, deodorizing, and fractionation into liquid olein and solid stearin frac-
tions. CPO is acid treated in the degumming process to precipitate and separated
out the gums or phosphatides. The oil is then bleached with activated clay or
carbon under vacuum pressure to remove coloring pigment and metal ions.
Deodorizing is carried out at high temperatures from 240 to 260 °C and pressure of
2–6 mmHg by injecting open steam which distills off the odoriferous matter
present in the oil (Bockish 1998; Kheok and Lim 1982). The deodorized oil is then
fractionated into palm olein and stearin by allowing the oil to crystalize under
controlled temperature where the slurry passes through a filter press to obtain the
stearin and olein fractions. The simple flow diagram of CPO treatment into refined
palm oil (RPO) is shown in Fig. 4.

2.4 Transesterification of Palm Oil into Biodiesel

Biodiesel production from vegetable oil can be achieved through various means
including pyrolysis, micro-emulsion, thermal cracking, transesterification.
Transesterification of vegetable oil into biodiesel has been the most commonly