For the first step, the transesterification was carried out with the molar ratio of methanol to WCO of 2.5:1, and the amount of catalyst 0.7 wt.%.. A yield of FAME of around 99% was attain
Trang 1A two-step continuous ultrasound assisted production of biodiesel fuel
from waste cooking oils: A practical and economical approach to produce
high quality biodiesel fuel
Le Tu Thanha,b,*, Kenji Okitsuc, Yasuhiro Sadanagaa, Norimichi Takenakaa, Yasuaki Maedaa,
a Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
b
Faculty of Environmental Sciences, University of Science, Vietnam National University, Ho Chi Minh City, 227 Nguyen Van Cu St., Dist 5, Ho Chi Minh City, Vietnam
c
Department of Materials Science, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531, Japan
a r t i c l e i n f o
Article history:
Received 28 December 2009
Received in revised form 9 February 2010
Accepted 11 February 2010
Available online 9 March 2010
Keywords:
Biodiesel production
Transesterification
Waste cooking oils
Ultrasonic reactor
a b s t r a c t
A transesterification reaction of waste cooking oils (WCO) with methanol in the presence of a potassium hydroxide catalyst was performed in a continuous ultrasonic reactor of low-frequency 20 kHz with input capacity of 1 kW, in a two-step process For the first step, the transesterification was carried out with the molar ratio of methanol to WCO of 2.5:1, and the amount of catalyst 0.7 wt.% The yield of fatty acid methyl esters (FAME) was about 81% A yield of FAME of around 99% was attained in the second step with the molar ratio of methanol to initial WCO of 1.5:1, and the amount of catalyst 0.3 wt.% The FAME yield was extremely high even at the short residence time of the reactants in the ultrasonic reactor (less than
1 min for the two steps) at ambient temperature, and the total amount of time required to produce bio-diesel was 15 h The quality of the final biobio-diesel product meets the standards JIS K2390 and EN 14214 for biodiesel fuel
Ó 2010 Elsevier Ltd All rights reserved
1 Introduction
Biodiesel, a liquid fuel consisting of mono-alkyl esters of
long-chain fatty acids derived from vegetable oils or animal fats, can
be used as a substitute for diesel fuel (Hu et al., 2004; Veljkovíc
et al., 2006) Some of the advantages of using biodiesel fuel are
its renewability, easy biodegradability, non-toxicity and safer
han-dling due to its higher flash point compared to those of fossil fuels
(Wang et al., 2006) In addition, biodiesel fuel is also primarily free
of sulfur and aromatics, producing more tolerable exhaust gas
emissions than conventional fossil diesel (Demirbas, 2009)
Biodiesel produced from virgin vegetable oils costs much more
than petro-diesel; this is a major drawback to the
commercializa-tion of biodiesel in the market Therefore, it is necessary to find the
ways to minimize the production cost of biodiesel In this context,
methods that can reduce the costs of raw materials as well as the
energy consumption are of special concern The use of waste
cook-ing oils (WCO) is one of the more attractive options to reduce the
raw material cost (Encinar et al., 2005; Kulkarni and Dalai, 2006)
Biodiesel is synthesized by the transesterification of triglycer-ides (TG), the main components of vegetable oils and animal fats, with mono-alcohol in the presence of a catalyst, into fatty acid al-kyl esters The TG is converted stepwise to diglycerides (DG), monoglyceride (MG) intermediates and finally to glycerin (GL) (Darnoko and Cheryan, 2000)
The transesterification can be carried out in batch or continuous reactors (Meher et al., 2006a; West et al., 2008; Zhang et al., 2003) The batch transesterification process requires large reactors and longer reaction and separation times because the reaction and the separation stages are usually carried out in the same tank In con-trast, the reactor for the continuous process can be smaller than that
of the batch process for the same production capacity Several types
of continuous reactors have been studied and applied for biodiesel production (Lertsathapornsuk et al., 2008; Zhang et al., 2010) On the laboratory scale, continuous reactor systems assisted by micro-wave have been demonstrated Other continuous-flow processes using a rotating packed bed, supercritical methanol or gas–liquid reactor have been found to be more effective for the transesterifica-tion (Chen et al., 2010; He et al., 2007; Behzadi and Farid, 2009)
It is believed that the transesterification of TG with methanol is
an equilibrium reaction system Therefore, the equilibrium can be shifted to the right, i.e., the formation of FAME, by performing a multi-step transesterification processes To minimize the influence
0960-8524/$ - see front matter Ó 2010 Elsevier Ltd All rights reserved.
* Corresponding author Address: Department of Applied Chemistry, Graduate
School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai,
Osaka 599-8531, Japan Tel./fax: +81 72 254 9326.
E-mail address: lethanh@chem.osakafu-u.ac.jp (L.T Thanh).
Contents lists available atScienceDirect
Bioresource Technology
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / b i o r t e c h
Trang 2of glycerin on the back reaction, the glycerin in the reaction
mix-ture should be taken out after each step
Over the past two decades, applications of sonochemistry have
been widely developed in many areas of chemical technologies
Ultrasound energy is well known as a useful tool to make fine
emulsions from immiscible liquids Owing to this aspect, the
transesterification reaction of vegetable oil and alcohol can reach
equilibrium in a short reaction time with a high yield of alkyl esters
even at low temperatures (Stavarache et al., 2003, 2006; Hanh
et al., 2008; Georgogianni et al., 2008a, 2009) In the previous work,
a pilot plant using ultrasound irradiation method for biodiesel
pro-duction from canola oil and methanol was developed by our group
(Thanh et al., 2010), in which the transesterification was carried
out by a circulation process at room temperature The high yield
of FAME can be obtained even in a short reaction time under the
molar ratio of methanol to oil 5:1, and potassium hydroxide
(KOH) catalyst, at 0.7 wt.%
In this work, the transesterification of WCO with methanol in
the presence of KOH catalyst was carried out in the continuous
ultrasonic reactor by a two-step process The effects of the
resi-dence time of reactants in the reactor, molar ratio of methanol to
WCO and separation time of glycerin from the reaction mixture
in each step were investigated The objective of this work is to
pro-duce biodiesel of high quality meeting the specifications of the
standard for B100 (pure 100% biodiesel) fuel with minimal costs
of materials and energy
2 Methods 2.1 Materials The WCO used were those after domestic use, collected by mu-nicipal activities, and then filtered and settled in a drum to remove particles remaining in the oils The physical and chemical proper-ties of WCO are shown inTable 1 KOH (grade 95.5%) and methanol (grade 99%) were purchased from Wako Pure Chemical Industries, Osaka, Japan, and used without further purification Chemical stan-dards such as methyl oleate, methyl linoleate, methyl linolenate, methyl palmitate, methyl stearate, monoolein, diolein, and triolein, were obtained from Sigma–Aldrich, Tokyo, Japan
2.2 Apparatus The major units of the pilot plant include the liquid pumps, flow meters and ultrasonic reactors with a working volume of 0.8 L, and separation and purification tanks An ultrasound source was a horn type transducer generating low-frequency ultrasounds of 20 kHz with an input capacity of 1 kW The experimental setup for the transesterification and purification of crude biodiesel using the pi-lot plant is schematically depicted inFig 1 This system was de-scribed in more detail in the previous paper (Thanh et al., 2010)
2.3 Procedures KOH was pre-mixed with a known amount of methanol adapted
to each experiment and kept at ambient temperature (20–25 °C)
In the first step of the transesterification, 120 L of WCO was fed with methanol, in the desired molar ratios 2.5:1, 3:1, 3.5:1 or 4:1, to the reactor The feeding of WCO and methanol was carried out by piston and peristaltic pumps, respectively, and both were connected to flow meters to control the mixing ratio of the reac-tants accurately The flow rate of the reaction mixture was set in the range of 0.5–2.5 L min1 After passing through the reactor, the reaction mixture was transferred to the separation tank, where the transesterification and phase separation of glycerin from the reaction mixture proceeded simultaneously It took 4 h to com-plete the phase separation The lower layer, containing glycerin, catalyst and excess methanol, was drained from the separation tank On the other hand, the upper layer, mainly FAME, TG and small amounts of DG and MG, was used for the second-step transesterification
Table 1
Chemical and physical properties of WCO used in this study (five samples were
analyzed, n = 5).
Iodine value g I 2 /100 g oil 112.5 ± 0.5
0.15 ± 0.03 Oleic acid (C18:1) a
Linoleic acid (C18:2) a wt.% 31.42 ± 0.48
Linolenic acid (C18:3) a wt.% 10.21 ± 0.18
Palmitic acid (C16:0) a
Stearic acid (C18:0) a
Mean molecular weight of WCO g mol 1
876.60 ± 15.76 a
Carbon atoms number: double bond number.
b SD: one standard deviation of five samples.
O: Oil tank; M1, M2: Methanol and catalyst tanks; P: Liquid pumps; V: Valves; F: Flow meters US1, US2: Ultrasonic reactors; S1, S2: Separation tanks; G1, G2: Glycerin tanks
P’: Purification tank; B: Biodiesel product tank; W1, W2: fresh and waste water tanks
P
V
US2
P’
S2
B G2
P
P M1
O
P
P
V
V
V
V
V
US1
S1
G1
M2
V W1
W2
V
F
F
F
F
Trang 3The second-step transesterification was performed in the same
manner as the first step, except that the molar ratios of methanol
to initial WCO that is 1:1, 1.5:1 or 2:1 for the second step After
the transesterification and the phase separation were completed,
the crude FAME was transferred to the purification tank Here,
the KOH catalyst, excess methanol and glycerin remaining in the
crude FAME were removed by washing three times with tap water
of the ratio of 20% by weight to crude FAME for each washing After
washing, the water content in the FAME was effectively eliminated
by heating the FAME to 70 °C under reduced pressure around
500 torr while flushing with a small amount of dried air for 3 h
All experiments were performed at ambient temperature of 20–
25 °C After passing through the reactor, the temperatures of the
reaction mixtures were in the range of 30–32 °C and 27–29 °C for
the first and second steps, respectively, due to the heating effect
of the ultrasound
2.4 Analysis
A 200 mL sample of the reaction mixture was withdrawn from
the pipe connecting the ultrasonic reactor and the separation tank,
and the sample was stored in a 250 mL beaker The time zero of the
reaction was defined when the reactants, including WCO,
metha-nol and KOH were introduced to the ultrasonic reactor Five
milli-liters of samples were taken from the beaker in prescribed time
intervals and were immediately neutralized by the addition of
1 mL of 5% phosphoric acid aqueous solution to stop the reaction
The samples were left to settle for 3 h for phase separation before
analysis of the samples The concentrations of the reactants such as
TG, DG, MG and FAME, were quantified by a high performance
li-quid chromatograph connected to a refractive index detector The
analytical method employed in this study is described in more
de-tail in the previous paper (Thanh et al., 2010)
The FAME yields of each transesterification step were calculated
from the weight of FAME in the FAME phase and the theoretical
material balance of the transesterification reaction, as shown in
Eq.(1):
FAME yield ð%Þ ¼wFAME=MFAME
where wFAMEand wWCOare the weight of FAME in the FAME phase
and the weight of WCO used, respectively, MFAMEand MWCOare the
average molecular weights of the FAME and the WCO, respectively,
and the factor 3 indicates that one mole of triglyceride yields three
moles of FAME
The amount of the glycerin phase obtained from phase
separa-tion was determined by the gravity method and was calculated by
Eq.(2):
GL ðwt:%Þ ¼wGL
where wGLand wmwere the weights of the glycerin phase and the
reaction mixture, respectively The weight of the reaction mixture
was the sum of the weights of the raw materials, including the
WCO, methanol and catalyst used for the transesterification
In this study, each experiment used 120 L of WCO; thus, a
lim-ited number of experiments were performed in triplicate, and the
results are shown as average values with one standard deviation
3 Results and discussion
3.1 Choice of type and amount of catalyst
The choice of a catalyst for the transesterification depends on
the quality of raw materials If the oils have high free fatty acid
(FFA) content and water, the acid-catalyst transesterification pro-cess is preferable However, this propro-cess requires higher tempera-tures and longer reaction times, in addition to causing undesired corrosion of the equipment Therefore, to reduce the reaction time, the process with an acid-catalyst is adapted as a pretreatment step only when necessary to convert FFA to esters, and is followed by an alkaline-catalyst addition for the transesterification step to trans-form triglycerides to esters (Leung and Guo, 2006) In contrast, when the FFA content in the oils is less than 1 wt.%, many research-ers have recommended that only an alkaline-catalyst assisted pro-cess should be applied because this propro-cess requires fewer and simpler equipment than that mentioned above (Meher et al., 2006b; Freedman et al., 1984) Among alkaline-catalysts, sodium and potassium hydroxide have most often been used in industrial biodiesel production, both in the concentration range from 0.4 to
2 wt.% of the oil (Meher et al., 2006b).Encinar et al (2005)studied the effects of alkaline-catalyst types, such as sodium hydroxide, potassium hydroxide, sodium alkoxide and potassium alkoxide,
on the methanolysis of WCO They concluded that the best yield
of methyl esters was obtained at KOH concentration of 1 wt.% In our previous work, the transesterification of canola oil, containing 0.4 wt.% of FFA, with methanol, was assisted by ultrasound irradi-ation in the circulirradi-ation process The optimal FAME yield was ob-served at a KOH concentration of 0.7 wt.% (Thanh et al., 2010) In another previous study, the transesterification of WCO containing 1.7 wt.% of FFA was conducted with the same system mentioned above The best yield of FAME was attained when the amount of KOH catalyst was 1.0 wt.% (Thanh et al., 2008)
Generally, as noted above, KOH is an effective catalyst for the transesterification, and as such, it was chosen for this study As shown inTable 1, the acid value of the WCO was 1.07, correspond-ing to FFA 0.54 wt.% Based on the previous work, the total KOH concentration of 1.0 wt.%, i.e 0.7 and 0.3 wt.% for the first and the second steps, respectively, was conservatively used for all of the transesterification experiments on the WCO
3.2 Effect of flow rate
In the continuous reactor, the flow rate is one of the most important parameters affecting the reaction yield Lower flow rates lead to longer residence times of the reaction mixture in the reac-tor One could expect a low flow rate to enhance the emulsification efficiency of the reactants, resulting in increased FAME yield In the present study, with the reactor volume of 0.8 L, the flow rates were
70 75 80 85 90 95 100
Flow rate/ L min-1
First-step Second-step
Fig 2 Effect of flow rate on the FAME yields for methanolysis of WCO in the continuous ultrasonic reactor The molar ratio of methanol to WCO and the amount
of KOH catalyst were (2.5:1 and 0.7 wt.%), and (1:1 and 0.3 wt.%) for the first and
Trang 4varied from 0.5 to 2.5 L min1, corresponding to residence times of
the reactants in the reactor from 1.60 to 0.32 min In the first step,
the molar ratio of methanol to WCO and the catalyst amount were
2.5:1 and 0.7 wt.%, respectively When the first step was completed
and phase separation accomplished, the FAME phase was used for
the second step In the second step, the molar ratio of methanol to
initial WCO and the catalyst amount were 1:1 and 0.3 wt.%,
respec-tively, added to the FAME phase As shown inFig 2, the FAME yield
value increased, from 72.3% to 81.0% and from 95.3% to 97.5% for
the first and second steps, respectively, as the flow rate decreased
from 2.5 to 0.5 L min1 The maximum FAME yields were 81.0%
and 97.5%, which were obtained at the flow rates less than 1.5
and 2.0 L min1for the first and second steps, respectively Even
with a short residence time of 0.93 min and a small molar ratio
of methanol to WCO of 3.5:1, for the sum of the two steps, the
FAME yield was 97.5% As demonstrated in the literature (
Stavar-ache et al., 2007; Georgogianni et al., 2008b; Ramachandran
et al., 2006), ultrasonic irradiation is a tremendously useful tool
for forming fine emulsions of immiscible liquids
3.3 Effect of the molar ratio of methanol to WCO
The molar ratio of methanol to oil is also other the important
factor affecting the yield of FAME Although the molar ratio of
methanol to oil necessary to complete the transesterification is
3:1, an excess amount of methanol is helpful to shift the reaction
toward the FAME formation Thus in practice, the molar ratio of
methanol to oil used is usually more than 6:1
Because methanol and oil are immiscible liquids, the
transeste-rification reaction occurs on the interface between the oil and the
methanol As a result, only methanol on the surface of droplets is
effective for the transesterification reaction if there is droplet
for-mation in the reaction mixture, whether the reaction takes place
using the conventional stirring method or the ultrasound assisted
method such as the present study Additionally, glycerin is also
formed as a by-product Because glycerin and methanol are polar
compounds, they can dissolve each other at any ratio Therefore,
the presence of glycerin absorbs significant amounts of methanol,
requiring large amounts of methanol for the transesterification
However, the use of large amounts of excess methanol has adverse
effects on the phase separation of glycerin and FAME, and increases
the energy and time consumption for the recovery of excess
meth-anol Moreover, as mentioned above, using the ultrasonic reactor
reactants form a fine emulsion, which increases the interface area
between methanol and oil Therefore, in this case, the rate of the
transesterification can be enhanced, and it can reduce the amount
of excess methanol required Overall, to enhance the effectiveness
of methanol, the transesterification was carried out by a two-step
process A proper amount of methanol was used, and the glycerin
and excess methanol were removed after each step
3.3.1 The first transesterification step
The first step of transesterification was conducted with molar
ratios of methanol to WCO in the range from 2.5:1, 3.0:1, 3.5:1
or 4:1 in the presence of KOH 0.7 wt.% of WCO The flow rate of
the reactants was fixed at 1.5 L min1, corresponding to a residence
time of 0.53 min After passing through the reactor, the reaction
mixture became a fine emulsion, and thus the reaction proceeded
efficiently After 10 min of reaction time, the yield of FAME reached
about 80% for all cases, and thus the reaction mixture had become
homogeneous To determine the amount of time required to reach
equilibrium and the yield of FAME during the experiments, the
reaction mixture was analyzed for FAME content at every sampling
interval As shown inFig 3a at the initial 5 min of the reaction
time, the conversion rate of FAME was found to be faster at the
lower molar ratios of methanol to WCO This can be explained by
the fact that the concentration of catalyst was lower in the cases with larger amounts of methanol because the same amount of cat-alyst was used based on the amount of WCO As reported by
Vicen-te et al (2004), the transesterification is initiated by attacks of methoxide ions (CH3O) on the carbonyl carbon atoms of TG, DG and MG molecules Because the KOH catalyst is a strong base, its dissociation constant is very large Therefore, higher concentra-tions of methoxide ions on the surface of the methanol droplets were obtained when lower molar ratios were used As a result, the lower molar ratios of methanol to WCO increased the reaction rate during initial stage of the reaction This result agrees with the previous work, where the same reactor was used in the circulation process (Thanh et al., 2010) However, after 5 min of the reaction, higher conversion of FAME was achieved when higher molar ratios were employed The equilibrium state of the reaction was reached
at 25, 30, and 40 min with the molar ratios of 2.5:1, 3:1, and 4:1, respectively
As shown inFig 3a, when the molar ratio of methanol to WCO increased from 2.5:1 to 4:1, the yield of FAME increased from 81.0%
to 90.1% Although the addition of methanol was increased signif-icantly by 60%, the yield of FAME increased only by 10% This result can be explained as follows: methanol and glycerin are structurally similar molecules, containing hydroxyl groups, which can easily stimulate the intermolecular H-bonding between glycerin and methanol, and thus dissolve each other well Therefore, even
0 10 20 30 40 50 60 70 80 90
Time/ min
Fig 3a Effect of molar ratio of methanol to WCO on the FAME yield in the presence
of KOH catalyst 0.7 wt.% for the first step of the transesterification.
0 10 20 30 40 50 60 70 80 90
Molar ratio of methanol to WCO
Fig 3b Composition of products in the FAME phase of the first step of the transesterification of WCO with various molar ratios in the presence of KOH catalyst 0.7 wt.% after the reaction and phase separation were completed.
Trang 5though excess methanol is added to the reaction mixture, larger
proportions of the excess methanol could be removed from the
reaction zone by dissolution into the glycerin phase once the
glyc-erin phase has formed during the transesterification reaction In
other words, a very limited portion of the methanol added could
act as the reactant for the transesterification This phenomenon
may be the reason why the mechanical stirring method applied
for the transesterification needs a higher molar ratio i.e., at least
6:1, a higher temperature, and a longer reaction time to enhance
the effect of methanol
Fig 3bshows the composition of products of the first step of
transesterification after the phase separation was completed The
concentrations of TG, DG, and MG changed insignificantly when
the molar ratio increased from 2.5:1 to 4:1 The concentrations of
MG and DG were in the range from 4 to 6 wt.%, obtained at the
mo-lar ratio from 4:1 to 2.5:1, and the concentration ratios of DG and
MG changed slightly in all the molar ratios used The concentration
of TG remaining in the FAME phase was 7.6, 6.9, 4.5, and 4.1 wt.%,
acquired at the molar ratios of 2.5:1, 3:1, 3.5:1, and 4:1,
respec-tively This result agrees with the conversion of FAME described
above Consequently, the molar ratio of 2.5:1 between methanol
and WCO has been judged as the best compromise point between
the acceptable FAME conversion for the first step and the least
methanol usage Therefore, the crude FAME consisting of FAME
81 wt.%, TG 7.6 wt.%, and the rest of TG and DG was used for the
second transesterification step
3.3.2 The second transesterification step
The molar ratio of methanol to initial WCO was in the range
from 1:1; 1.5:1 or 2:1, and the amount of KOH catalyst was
0.3 wt.% of initial WCO The flow rate of reactants was fixed at
2 L min1, corresponding to the residence time of 0.4 min in the
reactor After 3 min of reaction time, the reaction mixture attained
homogeneity by emulsification As shown inFig 4a, when the
mo-lar ratio was increased from 1:1 to 2:1, the yield of FAME was
in-creased from 97.2% to 99.3% It should be noted that the conversion
of FAME became extremely high, and the equilibrium was almost
reached after around 20 min of reaction in all cases Because the
average concentration of TG in the crude FAME was 7.6 wt.%, the
molar ratios of methanol to initial WCO of 1:1, 1.5:1 and 2:1,
cor-responded to the ratios of methanol to TG in the crude FAME phase
of 12.7:1, 19.1:1 and 25.5:1, respectively These ratios are much
higher than the theoretical molar ratio of methanol to TG, i.e.,
3:1 Furthermore, the starting material containing 81 wt.% of FAME
has low viscosity Therefore, methanol can easily diffuse in the
FAME phase to facilitate the reaction between the methanol and the TG as well as the DG and MG remaining in the FAME phase These effects may be the main cause of the outstandingly high yield of FAME
Fig 4b shows the composition of the products in the FAME phase of the second step of the transesterification To demonstrate the changes in the concentrations of the products more clearly, the concentrations of TG, DG, and MG shown inFig 4b are plotted along a scale multiplied by 10 The concentrations of TG, DG, and
MG were 1.1, 1.0, and 0.7 wt.%, respectively, at the molar ratio of methanol to initial WCO 1:1 At the molar ratios from 1.5:1 to 2:1, TG was not detected in the FAME phase, indicating that TG was converted completely to the products, and the concentrations
of DG and MG were also less than 0.2 and 0.8 wt.%, respectively Compared to the biodiesel standard, JIS K 2390 and EN 14214, the concentrations of TG, DG, and MG should be less than 0.2, 0.2, and 0.8 wt.%, respectively Therefore, the optimal molar ratio for the second step of the transesterification was 1.5:1
3.4 Glycerin separation
Separation of glycerin is an important factor to determine the final product quality and FAME recovery, as well as the time neces-sary for the full process of the biodiesel production Therefore, the separation of glycerin was investigated intensely In this discus-sion, the time for the separation of the glycerin phase was defined
as zero when the reaction mixture of the first step of the transeste-rification was completely transferred to the separation tank The glycerin phase was drained from the bottom of the separation tank every 0.5 h As shown inFig 5, at the initial stage of separation within 1 h, the higher the molar ratios of methanol to WCO, the faster the glycerin separation took place This fact can be eluci-dated as follows: at higher molar ratios, higher FAME yield could
be attained In this case, the amount of excess methanol remaining
in the reaction mixture was large As a result, the viscosity of the reaction mixture was reduced Furthermore, as mentioned in the effect of molar ratio, when a larger amount of methanol was used, the gathering probability of methanol in the glycerin phase was large Therefore, methanol and glycerin easily encounter each other to form a large droplet, resulting in the faster separation of glycerin and methanol from the reaction mixture This phenome-non agrees with the conversion of FAME, which only rose by 10% when the molar ratio increased from 2.5:1 to 4:1 On the other hand, in the case of settling for more than 1 h, the time would be long enough for methanol and glycerin dissolving each other; the smaller the amount of methanol, the faster the glycerin separation took place Because glycerin has a much higher density
80
85
90
95
100
Time/ min
Fig 4a Effect of molar ratio of methanol to initial WCO on the FAME yield in the
0 20 40 60 80 100
Molar ratio of methanol to initial WCO
Fig 4b Composition of products in the FAME phase of the second step of the transesterification of WCO with various molar ratios in the presence of KOH catalyst
Trang 6(d20= 1.26 g cm3) than methanol (d20= 0.79 g cm3), the density
of the glycerin phase decreases as the amount of methanol in the
glycerin phase increases Therefore, a slower acceleration of phase
separation between the FAME layer (typical density is ca
0.885 g cm3for WCO in this study) and the glycerin layer takes
place owing to the larger difference in the densities of the two
layers
Due to the presence of excess methanol in the glycerin phase,
the weight of glycerin phase separated increased from 8.3 to
12.5 wt.% when the molar ratio increased from 2.5:1 to 4:1
Practi-cally, phase separation could be completed within 4 h after settling
the reaction mixture in the separation tank
The behavior of the glycerin separation in the second step was
the same as in the first step However, the time required for entire
separation in the second step was 3 h
Table 2shows the product compositions and the distribution of
methanol in both phases at different molar ratios of five runs
When the total molar ratios of methanol to WCO used for the
two steps were all higher than 4:1, the concentrations of the
impu-rity components TG, DG and MG in the FAME phase of the second
step met the biodiesel standards, JIS K 2390 or EN 14214 In these
cases, of course, the lowest total molar ratio of 4:1 would be
favor-able for biodiesel production, and this ratio was applied in runs #2
and #3 The molar ratios for the first and second steps of runs #2
0
2
4
6
8
10
12
Time/ h
2.5:1 3:1 3.5:1 4:1
Fig 5 The amount of glycerin phase separation in the first step of the
transeste-rification with the molar ratios of 2.5:1, 3:1, 3.5:1, and 4:1 and the KOH catalyst
0.7 wt.%.
WCO
100 ± 2.0
Methanol 9.13 ± 0.10
KOH 0.70 ± 0.01
First-step transesterificationm
Glycerin separation
1
FAME 1 98.76 ± 1.8
Glycerin phase 9.75 ± 0.30
Methanol 0.26 ± 0.10
Second-step transesterificationm
Methanol 5.48 ± 0.10
KOH 0.30 ± 0.01
Glycerin separation
2
FAME 2 96.23 ± 2.0
Glycerin phase 5.81 ± 0.25
Methanol 1.71 ± 0.10
Purification
FAME product 93.83 ± 2.1
Methanol 1.50 ± 0.22
Methanol 0.16 ± 0.10
Tap water
60 ± 2
Wastewater
63 ± 2
Fig 6 Material balance for the full process under the optimal conditions (The materials are shown in proportions by weight, over three runs, n = 3).
Table 2
Methanol content in the FAME and glycerin phases from each step after phase separation.
Run Step Molar ratio
CH 3 OH:WCO
Product composition (wt.%) of FAME phase FAME phase Glycerin phase
(kg)
CH 3 OH (wt.%)
CH 3 OH (kg)
Weight (kg)
CH 3 OH (wt.%)
CH 3 OH (kg)
2 First 2.5:1 81.61 a ± 1.52 b 5.93 ± 1.00 4.85 ± 0.70 7.61 ± 0.90 105.3 ± 1.8 0.17 ± 0.10 0.18 ± 0.10 9.85 ± 0.27 2.91 ± 0.55 0.29 ± 0.05 Second 1.5:1 98.65 ± 1.30 0.63 ± 0.15 0.20 ± 0.10 ND 104.9 ± 1.3 1.61 ± 0.32 1.65 ± 0.34 6.40 ± 0.24 29.35 ± 1.73 1.88 ± 0.11
Notes:
ND: not detectable.
a
Average value of three runs.
b
Trang 7and #3 were (2.5:1, 3:1) and (1.5:1, 1:1), respectively It is worth
noting that for the first step, the methanol content in the FAME
and glycerin phases in run #2 was lower than that in run #3 On
the other hand, in the second step of run #2, significantly excess
methanol remained in both phases Therefore, to reduce the
pro-cessing time and to save energy consumption, the recovery of
ex-cess methanol from the FAME and glycerin phase should be
carried out for the second step of run #2 We can conclude that
the optimal molar ratios of methanol to WCO with the two-step
process are 2.5:1 and 1.5:1 for the first and the second steps of
transesterification, respectively
3.5 Material balance and biodiesel quality
Fig 6shows the material balance by weight based for the full
process under the optimal conditions (the molar ratios of methanol
to WCO were 2.5:1, and 1.5:1 for the first and second steps,
respec-tively; and KOH was 1.0 wt.% for both steps.) The average
produc-tion of FAME recovered in this process was 93.8 ± 2.1 wt.% (one standard deviation for three runs)
To confirm the quality of the final product obtained under the optimal conditions, biodiesel samples were analyzed by an author-ity certified to analyze the characteristics of commercial biodiesel fuels (Nippon Kaiji Kentei Kyokai, Osaka Laboratory) The physical properties and chemical compositions of the product are given in
Table 3 The testing results show that the FAME product in the present study fulfills the standards JIS K2390 and EN 14214
3.6 Energy and time consumption for full process The continuous ultrasonic reactor is very efficient for the transesterification of WCO Moreover, the reaction was carried out at ambient temperature, and this fact gives this method a large advantage in that the electricity consumption by the transesterifi-cation can be greatly reduced As shown inTable 4, the overall elec-tricity needed to produce 116 L of biodiesel from 120 L of WCO was 8.35 kWh; thus, the average energy paid for 1 L of biodiesel was
Table 3
Properties of biodiesel produced from WCO under the optimal conditions (2.5:1 and 1.5:1 of molar ratio of methanol to initial WCO for the first and second steps, respectively; KOH catalyst 1.0 wt.%).
Notes:
This table gives the certified quality of our biodiesel product as analyzed by an authorized analysis organization.
CFPP: cold filter plugging point.
JIS: Japanese Industrial Standard for biodiesel (B100) and testing method.
EN: European Standard for testing method.
Table 4
The average electricity and time consumption for the full process under optimal conditions (with five runs, n = 5).
transesterification
Glycerin separation 1
Second-step transesterification
Glycerin separation 2
Purification Total Washing Drying
0
1300
0
Time consumption (h) 1.5
4
1
3
Electricity consumption
(kWh)
1.95
0
1.30
0
0.30 4.80 8.35
Trang 80.072 kWh The time consumption for the full process was 15 h,
and most of the time, the separation and purification steps took
12 h Therefore, if these steps are simultaneously continuous with
the transesterification step, one dramatically reduced the time
consumption for the full process
4 Conclusion
The continuous ultrasonic reactor with a two-step process is a
beneficial technique for the production of biodiesel from WCO
The use of WCO reduces the product cost of the raw material
The optimal conditions for the transesterification are the total
mo-lar ratio 4:1, KOH 1.0 wt.%, and the residence time in the reactor of
0.93 min for the entire process Under these conditions, the
recov-ery of biodiesel from WCO is 93.8 wt.% The properties of the
prod-uct satisfy the Japanese Industrial Standard (JIS K2390) and
European Committee Standard (EN14214) This process
signifi-cantly reduces the use of methanol compared to conventional
methods (the mechanical stirring and supercritical methanol
methods)
Acknowledgements
This study was supported in part by the Grant-in-Aid for
Coop-erative R&D Project under Industry-University-Government
Part-nerships between Osaka Prefecture University and Sakai
Municipal Government, FY 2008–2009 The author, L.T Thanh,
would like to thank the Vietnam Government Support Scholarship
for the PhD course
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