process of petrochemical include the review of bio-fuel production

1. 3.0 Literature reviews
3.1 Sewage Sludge
The demand for worldwide fuel and biodiesel increase rapidly. However, the expansion
of biodiesel is currently limited due to 70-80% of overall biodiesel production cost is associated
with raw materials costs (Siddiquee & Rohani, 2011). Several waste alternative raw materials had
searched to use as cheaper feedstock to produce biodiesel, such as waste animal fats, waste cooking
oil and lipids in sewage sludge (Olkiewicz, et al., 2012).
Sewage sludge is an organic waste or byproduct generated during waste water treatment.
Waste water treatment plant (WWTP) will produces two main types of sludge which is primary
and secondary sludge (Olkiewicz, et al., 2012). Primary sludge is a combination of floating grease
and solids. It is collected after screening and grit removal and found at the bottom of the primary
clarifier (Siddiquee & Rohani, 2011) (Olkiewicz, et al., 2012). Secondary sludge is also known as
activated sludge which is collected in the secondary settler. Activated sludge contains microbial
cells and suspended solids produced during the aerobic biological treatment (Olkiewicz, et al.,
2012).
Sewage sludge is available in large quantities and ready in the market as municipal
wastewater treatment plants will produce it in a huge amount at free of cost. According to M.
Olkiewic, et al., (2012), there is estimated that the generation of sludge in EU in 2020 has an
overall increase of 30% when comparing to 2005. However, the usage of sewage sludge as
fertilizer is restricted in many countries due to its bad odor, containing of heavy metals, toxic
substances and pharmaceutical chemicals (Siddiquee & S. Rohani, 2011). Besides that, it creates
a disposal problem in landfill where the sludge involves with health problem and inherent chemical
energy loss. A viable alternative choice in managing disposal problem of sludge is to utilize the
sludge as one of the source of lipid feedstock that use in produce biodiesel (Siddiquee& S. Rohani,
2011).

2. 1
Based on research by M. Olkiewic, et al., (2012), the sludge could comprise a significant
amount of 30wt% in lipid fraction could be converted to into FAMEs. The lipid fraction which is
type of composite organic matrix is also characterized as oils, greases, fats and long chain fatty
acid. Lipids from the sewage sludge are usually extracted with organic solvent to prevent
interference in the synthesis process (Siddiquee & Rohani, 2011).
Primary sludge and secondary sludge could affect biodiesel yield and lipid extraction. This
is due to different types of composition will influence the fatty acids composition. In 2012, M.
Olkiewicz, et al.’s study of evaluation of different sludge stated that primary sludge achieved the
greatest lipids yield which is 25.3% and also highest biodiesel yields which is 13.9%. Secondary
sludge had 9.3% of lipids yield and 2.9% of biodiesel yields. This is due to primary sludge consists
of organic matter which is a combination of floating grease and solids whereas secondary sludge
has less grease and oil composition as it is composed mainly of microbial cells and suspended
solids ( Olkiewicz, et al., 2012).
In 2011, M.N. Siddiquee and S.Rohani had studied that there were great challenges in lipid
extraction for biodiesel production from municipal sewage sludge in commercial realization. The
five main challenges are the pre-treatment of raw sludge for efficient lipid extraction, the lipid
extraction from the sludge, the biodiesel production methods from solid sludge, the quality of
biodiesel and process economics and safety.
According to the research, M.N. Siddiquee and S.Rohani (2011) found that the pre-
treatment of raw sludge which includes collecting, dewatering and drying of sludge is costly.
Besides, it is energy and time consuming to get dry sludge from freeze drying system. In order to
get lipid extraction from sludge, it will require large volume of organic solvent and also expensive.
All these factors had poses the challenges faced in extracting biodiesel from sewage sludge.
Therefore, during wastewater treatment, it is highly desirable to reduce the amount of
sludge generated during wastewater treatment process due to expensive cost. In order to accelerate

3. 2
the degradation of the organic compounds in the excess sludge, several types of method had been
investigated such as thermal hydrolysis, mechanical disintegration, acidification and alkaline
addition (Feng, et al., 2009). Among these treatment methods, ultrasonication and ozonation are
the most non-hazardous method to the environment.
Cavitation which is favoured at low frequencies and chemical reactions due to the
formation of OH*, HO2*, H* radicals at high frequencies are the two key mechanisms that linked
to ultrasonic treatment (Carrere, et al., 2010). It also indicated that low frequencies which are from
the range of 20-40 kHz are the most efficient in sludge treatment (Carrere, et al., 2010). Besides,
ultrasounds have been applied mainly as pretreatment for anaerobic digestion in industry (Carrere,
et al., 2010).
3.2 Ultrasonification
In previous study by X. Feng, et al. (2009), it stated that ultrasonication can change the
physical- chemical characteristics of sludge significantly. This is because in the process of
ultrasonication, it could destroy the floc structure, facilitates the transfer of matter into the aqueous
phase, and breaks up cell walls (Feng, et al., 2009). In the first stage of ultrasonication, the floc
structure is interrupted and sludge settleability is improved. In the second stage, disintegration and
solubilisation are occurred. Ultrasound caused the acoustic cavitation, agitation and local heating
simultaneously (Feng, et al., 2009). Therefore, the physical and chemical characteristic of sludge
could change in different stage of ultrasonication process.
3.3 Palm oil sludge
Oil palm industries are one of the most successful stories in the world agricultural sector.
Palm oil mill effluent (POME) had risen as an emergence in the biofuel processing industries.
According to the study, oil palm processing could produce waste products consisting of oil palm
trunks, oil palm fronds, empty fruit bunches, palm pressed fibres and palm kernel shells ( Fatameh
Rupani, et al., 2010). Besides, it could also produce less fibrous material such as palm kernel cake
and liquid discharge palm oil mill effluent (Fatameh Rupani, et al., 2010).
Palm oil mill effluent would discharge palm oil mill sludge (POMS) as it consists of
suspended solid and dissolves solid after POME treatment. Based on the study by P. Fatameh

4. 3
Rupani, et al., (2010), palm oil mill sludge has high amount of moisture content and nutrients.
However, this sludge has a bad odor and is treated as a way to surface and ground pollution due to
containing of nitrogen, phosphorus and potassium contents. Hence, In POME treatment is playing
important role to find a suitable technology in mitigating wastes produced in palm oil mill sludge
(POMS) management (Fatameh Rupani, et al., 2010).
3.4 Transesterification Reaction
Transesterification refer to the reaction of an ester group with an alcohol which has a structure
different to that of the original alcohol moiety of the ester, such that a new ester group is formed in which
the original alcohol moiety is exchanged with that of the reacting alcohol (Sivasamy et al., 2009). In the
transesterification process of triglycerides of fatty acids with methanol, the three ester group of a
triglyceride molecule in which three fatty acid moieties are attached to a single alcohol moiety react with
three molecules of methanol to yield three molecules of esters each containing single fatty acid and
methanol moieties and one molecule of glycerol (Scheme 1) .
Scheme 1. Transesterification reaction of a triglyceride with methanol.
Methanol is commonly used in industrial biodiesel production as a result of its relatively low cost
and easy availability (Sivasamy et al., 2009). As non-catalytic transesterification is too slow and
energetically unfavorable, acid and base catalysts are used. For the reaction mechanisms of the
transesterification of triglycerides with acid and base catalysts, it shows in Scheme 2 and Scheme 3,
respectively.
The conventional reaction for the transesterification of triglycerides with methanol is using
methanol homogeneous catalysts such as sodium methoxide (Sivasamy et al., 2009). After the ester is
separated, other purification steps may be required, such as washing, distillation, and extraction.

5. 4
Sodium hydroxide (NaOH) or potassium hydroxide (KOH) is used as a catalyst with methanol or
ethanol in the alkali process. Initially, during the process, alcoxy is formed by reaction of the catalyst with
alcohol and the alcoxy is then reacted with any vegetable oil to form biodiesel and glycerol (Ranganathan
et al., 2007). Glycerol which is denser and settling at the bottom and biodiesel can be decanted. This
process is the most efficient and least corrosive of all the processes and the reaction rate is reasonably
high even at a low temperature of 60 o
C (Ranganathan et al., 2007). There may be risk of free acid or
water contamination and soap formation is likely to take place which makes the separation process
difficult (Ranganathan et al., 2007).
Another conventional way of producing biodiesel is using an acid catalyst instead of a base. Any
mineral acid can be used to catalyze the process such as sulfuric acid and sulfonic acid. Although yield is
high, the acids, being corrosive, may cause damage to the equipment and the reaction rate was also
observed to be low.
The transesterification process can be carried out even without catalyst but with considerable
increase in temperature. Yield is very low at temperatures below 350 o
C and therefore higher
temperatures were required. However at temperatures greater than 400 o
C thermal degradation of esters
occurred (Ranganathan et al., 2007). Recently it has been found that alcohols in their supercritical state
produce better yield and researchers have experimented this process with methanol in its supercritical
state. The process efficiency can be increased by using calcium oxide as a catalyst (Ranganathan et al.,
2007).

6. 5
Scheme 2: General reaction mechanism of transesterification of triglycerides with acid catalyst.
Scheme 3: General reaction mechanism of transesterification of triglycerides with base catalyst.

7. 6
3.5 Homogenenous Catalyst
Tranesterification reaction can be catalyzed by both homogenous and heterogeneous catalyst.
Typically, homogenous catalyst is function in same phase as the reactant. The same phase which is
referring to liquid or gaseous phase. It is dissolved in the solvent with the substrate and it can be divided
into basic and alkaline type.
Homogenous base catalyst is catalyzed by alkaline metal hydroxide such as sodium or potassium
hydroxides, sodium methoxide are used (Vicente et al., 2003). Transesterificaiton of triglycerids in
alkaline based catalyst is fast and high conversion. They are easily to achieve from 40 o
C to 65 o
C. The
standard value for the reaction is 60 o
C (Vicente et al., 2003). However, the temperature range is
depending on the type of catalyst as different types of catalyst will give a different degree of conversion.
The biodiesel yield for sodium hydroxide and potassium hydroxide was lower than the yield of using
methoxide as catalyst (Vicente et al., 2003). Homogeneous catalyst is relatively low cost comparing with
heterogeneous and enzymatic catalysts. Furthermore, it is more efficient and less corrosive than acidic
compounds. The base-catalyzed transesterification was 4000 times faster than acidic catalyst (Vicente et
al., 2003).
Homogeneous acid catalyst is insensitive to Free fatty acid (FFA) content in the oil and low
sensitive towards moisture (Srivastava et al., 2000). The conventional methods are using sulphuric acid,
hydrochloric acid and sulfonic acid in the process (Vicente et al., 2003). Homogenous acid catalysts are
able to perform esterification and transesterification simultaneously. When FFA reacts with alcohol in the
presence of acidic catalysts, esterification is occurred and it will form ester as product. Consequently, it
increases the yield of biodiesel. However, homogeneous acidic catalysts having strong acidic properties
which will cause corrosion to the equipment. Besides, it will also face difficulty in catalyst separation and
slower reaction rate when compared with alkali catalyst. Furthermore, it need to operate under extreme
pressure and temperature. Therefore, homogenous acid catalysts are more suitable in esterification
reaction rather than transesterification due to its simple molecular structure of FFAs (Vicente et al., 2003).
Figure 1 shows the typical continuous homogeneous catalyzed process.

8. 7
Scheme 4: Typical continuous homogeneous catalyzed process.
3.6 Heterogeneous catalyst
The heterogeneous catalysts are used in the biodiesel production which is normally mixing by
oxide of zinc and aluminum. Heterogeneous acid and base catalysts are classified as Bronsted or Lewis
catalysts. This catalyst determines the transesterification reaction rate and concluded that having strong
basicity and presence of more active sites to improve the performance of catalysts in the
transesterification reaction.

9. 8
The heterogenous base catalysts for transesterification in biodiesel synthesis can be classified into
six categories according to Hattori’s classification which are single metal oxides, mixed metal oxides,
zeolites, supported alkali earth metals, clay minerals, and non-oxides. The heterogeneous base catalysts
exhibited alkaline properties in its surface are being identified as a good option in replacement of current
homogeneous base catalysts.
A new continuous process is shown in Figure 2, where the transesterfication reaction is promoted
by a completely heterogeneous catalyst. This catalyst consists of a mixed oxide of zinc and aluminium
which promotes the transesterification reaction without catalyst loss. The reaction is performed at a higher
temperature than homogeneous catalysis processes, with an excess of methanol. This excess is removed
by vaporization and recycled to the process with fresh methanol (Hillion et al., 2003).
Scheme 5: Typical continuous heterogeneous catalyzed process.

10. 9
The catalyst section includes two fixed bed reactors that are fed by oil and methanol at a given
ratio. Excess methanol is removed after each of the two reactors by a partial flash. Esters and glycerol are
then separated in a settler. Glycerol phases are joined and the last traces of methanol are removed by
vaporization. Then, biodiesel is recovered after final recovery of methanol by vaporization under vacuum
and then purified to remove the last traces of glycerol.
In this heterogeneous process, the catalyst is very stable with no metal leaching. There is no formation of
either glycerate salts or metal soaps which affords the following advantages which are no neutralization
step is required, no introduction of water, and no salt formation; this accounts for an exceptional glycerol
purity (Hillion et al., 2003).
3.6 Surfactant (Detergent)
A surfactant is identified as a material that can greatly reduce the surface tension of water
when used in very low concentration (Sweeney-Judd, 2002). It will cause a physical change at the
surface of liquid (J.Karnok, et al., 2004). Surfactants lower the surface tension of water by
disrupting hydrogen bonds between water molecules, thus increasing water molecules’ ability to
contact and wet a surface. A surfactant may act as detergent (V.Pattusamy, et al., 2013).
However, detergents are also surfactants, but not every surfactant can act as a detergent.
Surfactants are usually organic compounds that are amphiphilic which contain both hydrophobic
groups and hydrophilic groups due to they have polar hydrophilic head and at least one long chain
hydrophobic tail (Sweeney-Judd, 2002). Detergents also can be known as soaps. Soaps can be
manufactured by saponification. Saponification is a process of hydrolysis of a fat or oil (Eke, et
al., 2004). Soaps are water-soluble sodium or potassium salts of fatty acids (P.Oghome, et al.,
2012). Soaps are useful cleaning agents due to the different affinities of a soap molecule’s two
ends. The long chain hydrophobic tail of soap molecule can dissolve in the grease, while the
hydrophilic head will stay in the surface of the grease droplet. Once the grease droplet is
surrounded by soap molecules, a micelle can form around it with a tiny grease droplet at the center
(P.Oghome, et al., 2012). A micelle is an aggregate of surfactant molecules dispersed in a liquid
colloid. It can adopt different shapes with sizes less than 10nm, in which the surrounding water is
oriented by the hydrophilic region of each monomer, leaving an internal region where the
hydrophobic tails interact with each other (Poce-Fatou, 2006).

11. 10
The main contribution of micelles to detergency is their ability to spontaneously solubilize
immiscible materials by means of a reversible interaction with their internal hydrophobic tails, in
a process called solubilization (Poce-Fatou, 2006). The properties of the soaps are determined by
the fatty acids composition in oil (P.Oghome, et al., 2012). Wetting agent is fit into class of
surfactants. It is a substance that by becoming adsorbed prevents a surface from being repellent to
a wetting liquid and is used especially in mixing with liquids or spreading liquids on surfaces.
Although soaps are a type of surfactant, they cannot be used as wetting agent. It is due to they are
lacking of their surfactant properties to an anionic portion of the molecule (J.Karnok, et al., 2004).
The resulting mixture of two insoluble phases will be called as emulsion. Emulsion is presents as
droplets, of microscopic or ultramicroscopic size, distributed throughout the other (Poce-Fatou,
2006). Soaps can be used in products such as shampoos, laundry detergent, stain, odor, and rust
remover (Sweeney-Judd, 2002).
3.7 General Types of Detergents
Synthetic detergents are based upon the surface active ingredient or surfactant. Surfactant
molecules are composed of groups of opposing solubility tendencies. The classification of
surfactants is based upon the ionic charge of the water soluble group. They are cationic, anionic,
neutral and enzymatic detergents. Cationic detergents are the water-soluble group that has a
positive charge. It works by adsorbs orienting the hydrophobic tail towards the bath producing a
“greasy” monolayer that provides the substrate with a soft feel and prevents the damage caused by
friction. However, the anionic detergents are the water-soluble group that has a negative charge.
Anionic detergents show a strong tendency to adsorb particularly onto the surface of particles and
substrates causing repulsive forces that offset attractive forces which leads to the favoring of the
removal of dirt and avoids particle aggregation. One of the common anionic detergents is sodium
lauryl sulfate which found in shampoo. Non-ionic detergents are water-soluble group that has no
charge. They are effective for the production of steric barriers for the prevention of redisposition.
One of the examples for neutral detergents is polyoxyethylene alcohols. Enzymatic detergents
contain a specific class of enzyme that helps in breakdown and cleaning. One of the common
enzymatic detergents is a protease which is called as subtilism (Poce-Fatou, 2006).