INTRODUCTION
Malaysia is currently the world’s largest exporter of palm oil with 16.66
million tonnes of palm oil products been exported in 2010. Among all the palm
oil products, Crude Palm Oil (CPO) and refined palm oil are the most commonly
traded commodities. Extraction of CPO from fresh fruit bunches requires steam
for sterilisation and water for dilution which finally contribute to substantial
amount of water discharged in the form of Palm Oil Mill Effluent (POME). Palm
Sludge Oil (PSO) is the floating residual oil that separated during the initial
stage of POME discharge to the pond. The small amount of oil that fails to be
extracted and leach out from various stages of the milling process will end
up in the open ponds as poor quality sludge oil. The PSO will then become the
substrate for microbes that present in the natural environment. The fatty acids
content in the PSO varies depending on its exposure time in the open ponds (Chow
and Ho, 2002). The PSO is currently being categorised under sludge oil as
it exhibits high Free Fatty Acids (FFA) and very low Deterioration of Bleachability
Index (DOBI) values. Due to the inferior quality of PSO, this residual oil cannot
be used directly as food source but normally being used for low-grade laundry
soap formulation to substitute palm fatty acids distillate. The typical FFA
content in PSO can be ranging from 40 to 80% (by weight). PSO is dark brown
in colour, bad odour and solid at 25°C.
If refined, the PSO can be applied directly as boiler fuel, raw material for
biodiesel production, replace 100% of palm fatty acid distillate in the soap
making industry. Hayyan et al. (2011) and Hayyan
et al. (2010) investigated the production of biodiesel from PSO using
conventional method including esterification process in order to reduce high
FFA content in PSO via acid catalyst followed by transesterification process
to produce biodiesel. Chow and Ho (2002) studied on
the chemical compositions of oil droplets in the PSO and reported that the composition
of the major lipids of PSO is similar to that of commercial palm oil. Huang
et al. (2010) studied the production of biosurfactant from the PSO.
The relatively high concentration of such biosurfactant in the oil droplets
may have commercial potential as a value-added resource from the palm oil mill.
This study aimed to recover very short chain fatty acid (VSCFA) from PSO. The process includes producing VSCFA from PSO via degumming, discolourisation and vacuum distillation. Strong bleaching agents such as hydrogen peroxide and sodium hypochlorite are added to discolourise the PSO. The VSCFA was reacted with selected alcohols in the presence of sulphuric acid. The treated PSO was also esterified and transesterified for the production of biodiesel. The fuel properties of PSO biodiesel were analysed and discussed.
MATERIALS AND METHODS
Materials: The PSO was collected from a Tennamaram palm oil mill, Selangor,
Malaysia. The PSO was made up of 65% FFA with remaining elements consist of
triglycerides and traces of impurities. Analytical grade methanol (98%), ethanol
and sodium hydroxide were purchased from Merck KGaA, Darmstadt, Germany. Phosphoric
acid was purchased from Merck KGaA, Darmstadt, Germany; hydrogen peroxide (30%)
and sodium hypochlorite (10% with chlorine) and para-toluene sulfonic acid (ρTSA)
were purchased from R and M Chemicals, Essex, United Kingdom.
Recovery of very short chain fatty acids from palm sludge oil: About 300 g of PSO was weighed accurately in a three-neck round flask. The PSO was heated under nitrogen blanketing to 90°C. Degumming step was carried out by adding 0.5 wt.% phosphoric acid (20% in aqueous) into PSO at 90°C and stirred for 10 min. Accurately 1.0 wt.% of strong bleaching agents e.g. hydrogen peroxide and sodium hypochlorite was added after 10 min of reaction, subsequently raising the reaction temperature to 105°C and hold for 15 min. The mixture was then filtrated under vacuum. The filtered oil was transferred into another two-neck round flask. Anti-bumping granules were added to the mixture and subjected to vacuum distillation step at temperature of 240°C under vacuum for 20 min. The VSFCA was collected as distillate and analysed using GC-FID. The treated PSO was further processed into biodiesel.
Synthesis of VSCFA esters: Approximately 100 g of VSCFA and 50 mL of
ethanol were mixed in the presence of 3 mL of concentrated sulphuric acid in
a two-neck round bottom flask. The two-neck round bottom flask was immersed
into hot oil bath at 120°C for 20 min. Water was added to the mixture after
reaction to wash out excess ethanol and sulphuric acid. The esters layer was
subjected to steam distillation by bubbling steam into the mixture under vacuum.
The perfume ester was collected in the steam condensate and dried using drying
agent e.g. sodium sulphate anhydrous. A total of 60 g of perfume esters with
fruity smell was collected and analysed.
Production of palm sludge oil biodiesel : About 500 g of treated PSO with FFA content of 65% was weighed accurately into two-neck flask. Catalyst was prepared by dissolving 5 g of ρTSA in 120 g of methanol based on molar ratio of methanol and treated PSO of 1:1. The ρTSA solution was added into PSO and reacted at 65°C for 60 min under atmospheric condition with magnetic stirring. The reaction mixture was poured into a separating funnel and allowed to settle into two layers. The bottom layer was decanted and sample was taken from top layer to determine its FFA content. The top layer was subjected to second step esterification by adding 0.35 wt.% of ρTSA (based on feed) into 53 g of methanol (based on molar ratio of 1:1 of methanol and FFA of feed). The bottom layer was drained after the reaction followed by water neutralisation and removal of water from the top layer thereafter. The esterified PSO was further transesterified using 0.5 wt.% of NaOH in methanolic solution (based on molar ratio of methanol and esterified PSO of 4:1) at 65°C for 60 min. Bottom layer was decanted and the reaction mixture was purified by water washing and drying. The final PSO biodiesel produced was then analysed for its critical parameters based on EN 14214:2003 specifications.
Analytical method: The ester content, monoacylglycerols (MG), diacylglycerols
(DG), triacylglycerols (TG) was analyzed using GC-FID (Hewlett-Packard 5890
Series II, Palo Alto, CA) according to modified method by Harrison
et al. (2007). The Fatty Acid Composition (FAC) was determined using
PerkinElmer GC-FID (AutoSystem XL, Shelton, CT) according to modified method
by Harrison et al. (2007).
RESULTS AND DISCUSSION
Composition of very short chain fatty acids: VSCFA has been successfully
recovered from PSO as distillate in the deodorisation process of PSO. A total
of 150 g of VSCFA was collected from 500 g of crude PSO. The fatty acid compositions
of VSCFA were shown in Table 1. The distillate was found to
contain 95 wt.% of VSCFA ranging from carbon 2 to 6. Conventionally, VSCFA has
been widely used as raw material in the fragrant industry for the production
of perfume via esterification process. VSCFA such as acetic and propionic acids
are produced during fermentation of dietary fiber and have shown to inhibit
HMG-CoA reductase, an enzyme involved in the production of cholesterol by the
liver (Demigne et al., 1995). Caproic acid is
not only used in the formation of esters but also commonly used as artificial
compound in production of butter, milk, cream, strawberry and other flavours.
| Table 1: |
Fatty acid compositions of very short chain fatty acid (VSCFA)
recovered from palm sludge oil |
 |
| Table 2: |
Composition of very short chain fatty acid (VSCFA) esters
produced from palm sludge oil distillate via esterification process |
 |
| Table 3: |
Two-stage esterification process of treated PSO using pTSA
as catalyst |
 |
Therefore, the recovered VSCFA has vast potential to convert into downstream
value-added products.
Synthesis of perfume esters from very short chain fatty acids: The synthesis of VSCFA perfume ester via esterification process by addition of ethanol has been carried out using sulphuric acid as catalyst. Table 2 shows the type of esters formed in the reaction which gives typical fruity smell of the ester. The VSCFA esters produced were light yellowish in colour comprising of ethyl acetate, ethyl butanoate, ethyl caproate, ethyl caprylate, ethyl caprate and ethyl laurate. The type of fruity smell and flavour varies depending on the percentage of fatty acid in the VSCFA.
Production of biodiesel from treated palm sludge oil: To further value-add
to the entire process, the treated PSO was esterified and transesterified for
the production of biodiesel using pTSA and caustic soda as catalyst, respectively.
Esterification process was used in order to pretreat the SPO by converting the
high content of FFA to fatty acid methyl ester using acid catalyst. The initial
content of FFA in SPO applied in this study which would not favorable for biodiesel
production indicated that transesterification process will not occur if the
FFA content in oil feedstock is more than 3%. Table 3 depicts
the reduction of FFA in PSO by esterification process using pTSA. The results
showed that two steps esterification reactions were sufficient to reduce FFA
from 65 to 1.65%. Total reduction in the content of FFA was 97.4% after two
steps of esterification process. Table 4 shows the properties
of PSO biodiesel benchmark on the European Standard Specification EN 14214:2003
for biodiesel. The findings showed that the biodiesel produced under the optimum
conditions meets the minimum specifications of fatty acids alkyl esters as stipulated
in EN 14214:2003.
| Table 4: |
Fuel properties of PSO biodiesel |
 |
| Table 5: |
Composition of fatty acid methyl esters of palm sludge oil
biodiesel |
 |
The high ester content of PSO biodiesel of 97.71% was achieved basically attributed
by employing a proper pre-treatment process on PSO before esterification and
transesterification reactions. The fatty acid composition of PSO biodiesel was
determined and results were shown Table 5. It was found that
the PSO biodiesel contains higher amount of saturated fatty acid with methyl
palmitate and methyl stearate of 49.1 and 3.76 wt.%, respectively.
CONCLUSIONS
The study revealed alternative processes for value addition of PSO which is a by-product from palm oil mills. The VSCFA has been successfully produced from PSO and further synthesised into ethyl esters or better known as perfume esters. The results indicate that different combinations of alcohols and VSCFA could produce VSCFA esters with dedicated fragrant at highest yield of 60 wt.% based on the feed. The result also indicates that the treated SPO can be an alternative and economical feedstock for biodiesel production. It was found that the two-stage of esterification process was sufficient to reduce the FFA content from 65 to 1.65% with pTSA as catalyst. The highest yield of biodiesel obtained after transesterification process was 86% with ester content of 97.91%. This study provides a new dimension on the value-addition and utilisation of by-product from palm oil mills for the production of VSCFA cum biodiesel.
ACKNOWLEDGEMENT
The authors would like to thank the Director General of Malaysian Palm Oil Board for her permission to publish this paper.
