Intensification of biodiesel production using dual-frequency counter-current pulsed ultrasound

Accepted Manuscript Intensification of biodiesel production using dual-frequency counter-current pulsed ultrasound Xiulian Yin, Xuejuan Zhang, Miaomiao Wan, Xiuli Duan, Qinghong You, Jinfeng Zhang, Songlin Li PII: DOI: Reference:

S1350-4177(16)30475-8 http://dx.doi.org/10.1016/j.ultsonch.2016.12.036 ULTSON 3491

To appear in:

Ultrasonics Sonochemistry

Received Date: Revised Date: Accepted Date:

18 August 2016 20 December 2016 28 December 2016

Please cite this article as: X. Yin, X. Zhang, M. Wan, X. Duan, Q. You, J. Zhang, S. Li, Intensification of biodiesel production using dual-frequency counter-current pulsed ultrasound, Ultrasonics Sonochemistry (2016), doi: http:// dx.doi.org/10.1016/j.ultsonch.2016.12.036

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Intensification

of

biodiesel

production

using

dual-frequency

counter-current pulsed ultrasound Xiulian Yina,b,c,Xuejuan Zhanga, Miaomiao Wana, Xiuli Duana, Qinghong Youc,d,e,*,Jinfeng Zhanga,Songlin Lia a Huaiyin Institute of Technology, School of Life Science and Food Engineering, Huaian, Jiangsu 223003, China b Jiangsu Key Lab of Biomass-based Green Fuels and Chemicals, Nanjin Forestry University, Nanjing, Jiangu 210037, China c Jiangsu Provincial Engineering Laboratory for Biomass Conversion and Process Integration, Huaiyin Institute of Technology; Huaian 223003, China d Key Laboratory of medicinal exploitation and utilization of regional resources, Huaiyin Institute of Technology, Huaian, Jiangsu 223003,China e Jiangsu Provincial Key Laboratory of Palygorskite Science and Applied Technology, Huaiyin Institute of Technology, Huaian 223003, China *Address all correspondence to Qinghong You, Huaiyin Institute of Technology, School of Chemical Engineering, Jiangsu,China; Tel: +86 517 83591044; E-mail address: [email protected]

Abstract Biodiesel production from soybean oil deodorizer distillate intensified by dual-frequency counter-current pulsed ultrasound and the kinetics were studied. Results indicated that the biodiesel conversions enhanced by single-frequency were lower than those enhanced by dual-frequency. For dual-frequency, the biodiesel conversion of SMM was higher than those of SQM. The biodiesel conversion of the combination of 20/28 kHz is the highest. The effects of 20/28 kHz SMM on biodiesel production were studied and optimal conditions were: methanol to triglyceride molar ratio 8:1, catalyst content 1.8%, the water content in feedstock should be less than 0.4%, the acid value of feedstock should be less than 2 mgKOH•g-1, the biodiesel conversion could reach 96.3%. The kinetics of SMM and SSPU were studied and results showed that the transesterification reaction was pseudo-second order and the energy activation 1

obtained by SMM and SSPU were 18.122 kJ•mol-1 and 26.034 kJ•mol-1, respectively. These results showed that transesterification reaction intensified by SMM is easier to take place than SSPU. Keywords:

Biodiesel;

soybean

oil

deodorizer

distillate;

dual-frequency

counter-current pulsed ultrasound; kinetic

1. Introduction Biodiesel is a mixture of fatty acid methyl esters (FAME) produced by transesterification of triglycerides with methanol or other short chain alcohols in the presence of appropriate catalyst[1-3].Biodiesel has better properties than that of petroleum diesel such as biodegradable, renewable, non-toxic, and free of aromatics and sulfur [4]. Biodiesel has a lot of advantages compared to petrodiesel, the main barrier to its commercial use is that its price is high [5,6]. Biodiesel price depends mainly on the cost of feedstocks, which makes 70-95% of the total biodiesel cost [7-8]. Edible oils are the main resources for biodiesel production [9]. The use of cheap non-edible oils can be a way to improve the economy of biodiesel production and its commercial production at the industry scale. Soybean oil deodorizer distillate (SODD) is a byproduct in the refining of soybean oil. It contains triglycerides (45-55%), free fatty acids (FFAs) (from 3 wt.% to 50 wt.%), sterols (7-8%), tocopherols (3-12%), hydrocarbons and other unsaponifiables in trace amounts [10]. The high contents of triglycerides and FFAs make it a potential cheap feedstock for biodiesel production [11]. 2

The other way to reduce the biodiesel price is to develop new reaction intensification method which could maximize the interfacial surface area between the two immiscible reactants to improve the performance of the reaction [12].The most commonly used technology for the production of biodiesel is the transesterification of triglycerides (oil) with alcohol giving fatty acid alkyl esters (biodiesel) as the main product. Often the transesterification reaction is severely limited by mass transfer giving much lower rates of reaction and hence there is always scope for intensification. In a range of techniques available for intensification, ultrasonic irradiation based approach could be considered as an effective one to assist and intensify the transesterification reaction [13]. Use of ultrasonic reactors can favor the reaction chemistry and propagation by way of enhanced mass transfer and interphase mixing between the phases and also can lower the requirement of the severity of the operating conditions in terms of temperature and pressure [14,15]. The collapse of cavitation bubbles could interrupt the phase boundary and could cause emulsification. Ultrasound can provide mechanical energy for mixing and the activation energy for originating the transesterification process. The intensification is mainly due to the formation of fine emulsion and the mechanical effects leading to better mixing [16]. Although many studies have focused on the ultrasonic assisted biodiesel production from a variety of feedstock, very few studies focused on two-frequency counter-current pulsed ultrasound [17,18]. The major shortcoming of single-frequency reactors is non-uniform volumetric energy dissipation in the reaction medium that limits the yield of the chemical transformation. To overcome this deficiency, 3

application of dual or multifrequency ultrasound field has been extensively investigated in recent years. Employment of two or more ultrasound frequencies produces a strong interference pattern in the reactor that overcomes the directional effects[19]. Manickam et al[13] studied intensification of synthesis of biodiesel from palm oil using multiple frequency ultrasonic flow cell, results showed that using multiple frequency ultrasonic

irradiation is beneficial in intensifying the

transesterification reaction. Tatake et al [20] studied the modelling of a dual frequency ultrasonic reactor to understand the effect of introducing a second wave on the cavity dynamics as compared to a single sound wave. Results indicated that the introduction of the second sound wave resulting in higher chemical yields. Zhang et al[21] studied the acoustical scattering cross section of gas bubbles under dual-frequency acoustic excitation, results showed that compared with single-frequency approach, the dual-frequency approach displays more resonances termed as ‘‘combination resonances’’ and could promote the acoustical scattering cross section significantly within a much broader range of bubble sizes due to the generation of more resonances. Moholkar’s [21] study showed that two major shortcomings of the sonic reactor, viz., directional sensitivity of the cavitation events and erosion of the sonicator surface can be overcome by application of a dual frequency acoustic field. In this paper, biodiesel production from soybean oil deodorizer distillate intensified by dual-frequency counter-current pulsed ultrasound and the kinetics were studied. Effect

of

different

ultrasound

modes

including

single-frequency,

dual-frequency of sequential mode (SQM) and simultaneous mode (SMM) on 4

biodiesel were studied with the reactants in a counter-current state. The main factors that affect biodiesel conversion were studied. The kinetics of SMM and single-frequency static pulsed ultrasound were also studied and compared. 2. Materials and methods 2.1 Materials and chemicals The SODD was supplied by Zhenjiang branch of China Grain Reserves Corporation. The chemical and physical properties and the pretreatment method of the SODD were described in our previous published manuscript [11]. Methanol, H2SO4, anhydrous sodium sulfate and phosphoric acid were of analytical grade and were purchased from Sinopharm Chemical Reagent Co.,Ltd. 2.2 Dual-frequency power ultrasound intensified transesterification In this study, the ultrasound was equipped with probes of three different frequencies (15, 20, 28 kHz) and the probes transmit the ultrasound into the liquid. They were about 100 mm in length and 22 mm in diameter. Two probes could be put to the reactor at the same time. When the experiments began, certain reactants were put into the reactor (the volume of the reactor was 4L), and then the probes were dipped into the reaction mixture. This equipment could be operated in two frequency modes, single frequency and dual-frequency. For dual-frequency mode, the two probes can work in sequential mode (SQM) and in simultaneous mode (SMM).Sequential mode means that when one probe is pulse-on, the other probe is pulse-off. The pulse-on-time and pulse-off-time of the two probes are the same. Simultaneous mode means the two probes work at the same time and the 5

pulse-on-time and pulse-off-time of the two probes are the same, too. The state of the reactants could be set at static or counter-current. “Counter-current” means that the direction of the ultrasound wave is from high to low while the reactants flow direction is from low to high. This state was kept by two peristaltic pumps, one pump pumped the reactants from the above to a container and the other pump pumped the reactants from the container to the reactor through the bottom of the reactor. The schematic of the ultrasound reactor was shown in Fig.1 2.3 Transesterification of pre-esterified SODD The pre-esterified SODD was put into the ultrasound reactor to produce biodiesel. The reaction was catalyzed by NaOH. NaOH was pre-dissolved in a known amount of methanol adapted to each experiment. The sodium hydroxide and methanol were added to the reactor in a given ratio, and reacted under certain conditions according to each experiment. During the procedure, the ultrasonic probe was immersed directly into the reaction vessel at the interfacial region of the two immiscible phases. Samples were collected at different pre-designated time and the reaction was stopped by adding phosphoric acid immediately. The samples were then transferred into a separating funnel and were washed by deionized water to remove the excess methanol, catalyst, and the glycerin. The water remained in the biodiesel phase was eliminated by adding anhydrous sodium sulfate (25 wt% of the weight of the ester product). The samples were diluted in 10 mL n-hexane and filtered by microporous membrane before analysis. The biodiesel was analyzed by gas chromatography. The biodiesel conversion (methyl ester conversion) was calculated as follows: 6

（Wtotalfame -W prefame ) × M glyeride biodiesel conversion(%) = × 100% 3 × Wglyceride × M Fame

(1)

Where Wtotalfame is the total weight of fatty acid methyl esters (FAME) that was measured after the alkali catalyzed transesterification and Wprefame is the weight of FAME that was got after the pre-esterification, M Fame and M glyeride are the average molecular weights of the FAME and the glyceride, respectively, and the factor 3 indicates that one mole of triglyceride yields three moles of FAME [19]. 2.4. Statistics All data are presented as mean ± standard error. Statistical analysis was performed using one-way analysis of variance (one way ANOVA). The difference between the groups was considered significant when the probability (p-value) was less than the significance level of 0.05. 3 Results and discussion 3.1 Effect of different ultrasound modes on biodiesel conversion Effect of different modes including single-frequency, dual-frequency of sequential mode (SQM) and simultaneous mode (SMM) on biodiesel were studied with the reactants in a counter-current state. The conditions for SMM were: The pulse-on-time and pulse-off-time for the two probes were 4s and 2s, total working time was 30 min, the rate of two peristaltic pumps 150mL/min, triglyceride to methanol molar ratio 1:8, NaOH 1%(by weight of the pretreated SODD),initial temperature 25oC. The power of each probe was set 200 W and the power density was 400 W/L. The conditions for SQM were: The pulse-on-time and pulse-off-time for the two 7

probes were 4s, total working time was 30 min, the rate of two peristaltic pumps 150mL/min, triglyceride to methanol molar ratio 1:8, NaOH 1%, initial temperature 25 oC. The power of each probe was set 400 W and the power density was 400 W/L. Fig 2 depicts the effect of different ultrasound modes on biodiesel conversion. It can be observed from the figure that the biodiesel conversions that intensified by single-frequency ultrasound mode were less than those that intensified by dual-frequency ultrasound mode. The biodiesel conversion increased with the frequency increasing. According to ultrasonic-cavitation theory, the collapse of implosive cavitation bubble produced by multi-frequency ultrasound can produce higher pressures and temperature than that of single-frequency and result higher sonochemical yield[22]. Multi-frequency ultrasound have been reported to have better efficiency than the single frequency, which is an effect attributed to strong interference pattern between the two ultrasound waves. This interference reduces the directional sensitivity of single-frequency ultrasound and helps achieve more uniform spatial energy dissipation in the processor, which results in increase in overall volumetric efficiency [23]. For dual-frequency, results showed that the biodiesel conversions of SMM were higher than those of SQM. When two different single-frequency ultrasonic propagate simultaneously in the solution, on the one hand the cavitation nucleus generated by one ultrasound beam could help self-cavitation, on the other hand, it can provide new cavitation nucleus for the other bunch of ultrasonic. This effect improved the mass transfer of solution and at the same time, enhanced the uniformity of the ultrasound 8

effect. Besides this, simultaneous dual-frequency irradiation enhanced mechanical disturbance of the medium, which could make more air into the liquid through the liquid surface and could increase the number of cavitation nucleus. Ultrasonic cavitation bubbles generated by two beams of ultrasound propagation in the solution simultaneously is greater than those generated by sequential dual-frequency ultrasound. From figure 2, we can also see that the biodiesel conversion of the combination of 20/28 kHz was the highest. The effects of 20/28 kHz simultaneous mode (SMM) on biodiesel production were studied in the following experiments. The conditions for the SMM were: 20/28kHz simultaneous mode (SMM), the pulse-on-time and pulse-off-time for the two probes were 4s and 2s, the rate of two peristaltic pumps 150mL/min, the power of each probe was set 200 W and the power density was 400 W/L. 3.2 Effect of methanol to triglyceride molar ratio on biodiesel conversion The effect of methanol to triglyceride molar ratio on biodiesel conversion was studied with the other conditions as follows: NaOH 1% (by weight of the pretreated SODD), initial temperature 25oC. As the transesterification reaction is reversible, higher methanol to triglyceride molar ratio favours the reaction forward for the production biodiesel. The theoretical methanol to oil molar ratio is three as taken from stoichiometric, lower ratios have not been selected in this work as it is expected that the conversions will be lower. The effect of methanol to triglyceride molar ratio on biodiesel conversion was studied and 9

the obtained results have been shown in Fig.3. As seen in the figure, the biodiesel conversion increases with the increasing of methanol to triglyceride molar ratio. An excess of methanol resulted in limiting the backward reaction and giving an increase in the equilibrium conversion to biodiesel. A further increase in the methanol from8:1 to 10:1, the biodiesel conversion did not increase significantly and when it was 12, the biodiesel conversion decreased a little compared with that of 8:1. Ultrasound activity is easier in methanol than in oil, so much more cavitation bubbles were obtained with the increase in methanol to triglyceride molar ratio [21]. With further increase in methanol content, the content of triglyceride and catalyst were diluted, which might slow down the forward reaction and initiate the reverse reaction. So 8:1 was the optimal methanol to triglyceride molar ratio. 3.3 Effect of catalyst content on biodiesel conversion The effect of catalyst content on biodiesel conversion was studied with the other conditions as follows: methanol to triglyceride molar ratio8:1, initial temperature 25 oC. Results of are shown in Fig 4.The results showed that the biodiesel conversion increased with catalyst content increasing when catalyst content was lower than 1.8%. But the biodiesel conversion decreased slightly with the catalyst content further increased. The reason for this may be that high catalyst content resulted in serious saponification. Serious saponification could lead to two results, one was that the transesterification could not proceed completely, and the other one was that it makes serious emulsification in the separating step difficult, which resulted in lower biodiesel recovery, therefore 1.8% was the optimal catalyst content. 10

3.4 Effect of water content in the feedstock on biodiesel conversion After pre-esterification of the SODD, the samples were washed with water in order to remove the catalyst, excess methanol. Though it was dehydrated by adding 25% anhydrous sodium sulfate, there’s still residual water in it. Results of effect of water content in material on FAME conversion were shown in Fig 5. From the results, one can see that when water content was lower than 0.4%, the biodiesel conversion was higher than 94%, when water content was 0.2%, biodiesel conversion (95.6%) was a little higher than that of with no water in feedstock (95.1%). Biodiesel conversion decreased rapidly with the increase of water content when it was higher than 0.4%. Ester hydrolysis reaction will take place when there’s water in the feedstock.

The produced fatty acid could initiate saponification reaction with NaOH. According to the spatial structure of the reaction molecule, the resulting saponified products from the hydrolysis reaction will cover the carbonyl group, which makes it difficult for the alcohol oxygen group to attack the carbonyl group, thus hinders the transesterification reaction. Due to the formation of soap, the subsequent separation and purification of the washing process is easy to produce serious emulsification, which resulting in decreased conversion of methyl ester. On the other side, the soap can be used as a surface active agent to increase the area and phase solubility of alcohol and oil, so as to speed up the reaction rate and increase the conversion rate. Results of this study showed that the water content in feedstock should be less than

11

0.4%. 3.5 Effect of acid value on biodiesel conversion After pre-esterification, the feedstock still contains a small amount of free fatty acids. Results of effect of acid value on biodiesel conversion were shown in Fig 6. It can be seen from the chart that when the acid value was less than 2 mgKOH· g-1, biodiesel conversion changes small and it could be higher than 94%. When the acid value was higher than 2 mgKOH·g-1, biodiesel conversion decreased rapidly with the increase of the acid value of raw materials. The content of free fatty acid in raw materials is an important parameter influencing the transesterification reaction. In the alkali catalyzed process, if the acid value is too high, not only free fatty acids need consume more alkaline catalyst to neutralization, but also the saponification reaction will reduce alkali catalyst activity, increase the viscosity of the system, promote the formation of colloidal and makes the subsequent separation process produce serious emulsification, the separation of biodiesel becomes very difficult and reduce the conversion of biodiesel. Results of this study showed that the acid value of feedstock should be less than 2 mgKOH· g-1. When the reaction conditions were as follows: pulse-on-time and pulse-off-time for the two probes were 4s and 2s, respectively, rate of two peristaltic pumps 150mL/min, triglyceride to methanol molar ratio 1:8, NaOH 1.8%, initial temperature 25 oC, power of each probe was set 400 W and the power density was 400 W/L, the biodiesel conversion could reach 96.3%. 3.6 Kinetic study

12

Kinetics is a method to describe chemical reaction process quantitatively by mathematical equation. Through the study of chemical reaction dynamics, one could conclude how to control the reaction conditions and could improve the reaction velocity and prevent or slow side reaction speed. The transesterification of triglyceride with methanol yields fatty acid methyl esters (FAME, biodiesel) and glycerin (GL). diglycerides (DG) and monoglycerides(MG) were intermediates. The stepwise reaction and overall reaction were shown in equations (1)-(4), in which k1-k8 are the rate constants for each step. (1)

(2)

(3)

(4)

However, since the concentration of methanol is always used in excess amount and the concentrations of DG and MG are much smaller than that of methanol. The reactions (1)-(3) are negligible for the kinetic analysis. In addition, to analyze the reaction kinetics simply, transesterification reaction kinetics were studied based on the following hypothesis: (1) Only consider the transesterification of triglycerides, and ignore the side effects caused by other impurities. (2)The reaction rates for the transesterification of TG containing saturated and unsaturated fatty acids are the same. (3) The effect of saponification on the catalyst concentration was ignored. (4) The transesterification reaction was simplified as one step reversible reaction. (5) The rate of transesterification reaction under no catalyst conditions was ignored. 13

The positive reaction rate equation can be expressed by the following formula

-r = kC Aα CB β

(10)

Where CA is the concentration of TG mol/L,CB is the concentration of methanol mol/L, k is reaction rate constant mol·L-1·min-1，α is the reaction order of TG, β the reaction order of methanol. For the concentration of methanol was far too much, kCBβcould be regarded as constant K, the equation(10) could be transformed to equation(11): -r = K C Aα

(11)

where K = kCB β , assume the conversion rate of triglyceride was x，the initial TG is C A0 ，the TG concentration at anytime is CA.

C A = CA（ 0 1 − x)

(12)

Linearization of equation (11): −r = −

dC A d [ C A 0 (1 − x ) ] = − = C dt dt

A0

dx = K C A α （13） dt

Combination of equation (12) and (13)： dx K [C A 0 (1 − x )]α = k 2 [C A 0 (1 − x )]α = dt C A0

where k2 =

（14）

K C A0

ln

dx = α ln[C A0 (1 − x)] + ln k2 dt

Equation (15) showed that l n

dx dt

（15 ）

is linear related to ln[CA0 (1 − x)] , and from

equation (15) k2, K and could be got. So long as the content of fatty acid methyl esters in reaction was determined by experiment, the relationship between the concentration and the reaction time was determined, and the kinetic parameters could be determined. 3.6.1 Kinetic of dual-frequency counter-current pulsed ultrasound For a given reaction process, the reaction rate equation can be derived directly 14

from the reaction process, but the process of vast majority of reactions are still not clear, so kinetic experimental data should be obtained through experiment and then the kinetic equation could be fitted by the kinetic experimental data. For the transesterification reaction, the kinetic data are obtained through the experimental study. The conditions for the reaction are as follow: the pulse-on-time and pulse-off-time for the two probes were 4s and 2s, respectively, the rate of two peristaltic pumps 150 mL/min, triglyceride to methanol molar ratio 1:8, NaOH 1.8%, initial temperature 25 oC. The power of each probe was set 400 W and the power density was 400 W/L. Using cooling water control the temperature, transesterification was take out at 318, 328, 338 K using dual-frequency counter-current pulsed ultrasound of 20/28kHz simultaneous mode (SMM) . From Table 1, we can conclude that the transesterification reaction was pseudo-second order. At lower temperature, the rate constant K was lower and the reaction becomes kinetically controlled. At higher temperature, K was higher and the yield of the reaction depends on the interaction between the methoxide ion and triglyceride molecule. This interaction occurs at the interface between oil and methanol, and thus, is dependent on the convection in the system or mass transfer characteristics of the system [24].Under ultrasound irradiation, the droplet sizes of emulsions are very tiny, leading to an increase in the interfacial area between TG and methanol. Furthermore, the movement of reactant droplets in the emulsion would be vigorously agitated by ultrasonic jet. Therefore, triglyceride on the surface of the 15

droplets promptly reacts with methanol [25]. When the reaction rate constants at different temperatures were determined, the activation energy for the transesterification reaction could be calculated using the Arrhenius formula (16). ln K = −

Ea + ln A RT

(16)

where K is the reaction rate constant, Ea is the energy of activation, R is the gas constant, T is the absolute temperature, A is the frequency factor. As shown in Fig.8, the Arrhenius equation about the reaction rate and the reaction temperature (318-338K) could be written as:

ln K = −2179.6508 / T + 6.0795

R2=0.9995 (17)

Good linearity was observed between ln K and 1/T. The activation energy (Ea) was 18.122 kJ·mol-1. 3.6.2 Kinetic of single-frequency static pulsed ultrasound The kinetic of single-frequency static pulsed ultrasound (SSPU) was also studied. The reaction conditions were same as those for dual-frequency counter-current pulsed ultrasound (3.6.1) . The frequency was 28 kHz. From Table 2, we can conclude that the transesterification reaction was pseudo-second order. The Arrhenius equation about the reaction rate and the reaction temperature (318-338K) could be written as:

ln K = − 3132.9642 / T + 8.49047 ， R2=0.9563 (18) Good linearity was observed between ln K and 1/T. The activation energy (Ea) was 26.034 kJ·mol-1。

16

Freedman et al [26] studied the transesterification kinetics of soybean oil and reported that the energy activation Ea for the transesterification of oil with base catalyst was in the range of 33.6-84 kJ·mol-1. In our study, the energy activation Ea obtained by SMM and SSPU were 18.122 kJ·mol-1 and 26.034 kJ·mol-1, respectively. They are lower than the reported values, which means that biodiesel production intensified by ultrasound is easier to proceed. The Ea of SMM is lower than that of SSPU, which means that transesterification reaction intensified by SMM is easier to take place than SSPU. These results support the result that SMM is a better intensification method. 4. Conclusions

Biodiesel production from soybean oil deodorizer distillate intensified by dual-frequency counter-current pulsed ultrasound and the kinetics were studied.Effect of different modes including single-frequency, dual-frequency of sequential mode (SQM) and simultaneous mode (SMM) on biodiesel were studied with the reactants in a counter-current state. Results indicated that the biodiesel conversions enhanced by single-frequency were lower than those enhanced by dual-frequency. For dual-frequency, the biodiesel conversions of SMM were higher than those of SQM. The biodiesel conversion of the combination of 20/28 kHz is the highest. The effects of 20/28 kHz simultaneous mode (SMM) on biodiesel production were studied and 8:1 was the optimal methanol to triglyceride molar ratio, 1.8% was the optimal catalyst content, the water content in feedstock should be less than 0.4%, the acid value of feedstock should be less than 2 mgKOH•g-1, the biodiesel conversion could

17

reach 96.3%. The kinetics of SMM and SSPU were studied and results showed that the transesterification reaction was pseudo-second order and the energy activation obtained by SMM and SSPU were 18.122 kJ•mol-1 and 26.034 kJ•mol-1, respectively. These results showed that transesterification reaction intensified by SMM is easier to take place than SSPU. Acknowledgements

This work was supported by Jiangsu Key Lab of Biomass-based Green Fuels and Chemicals (No: JSBGFC13003), Six Talent Peaks Project of Jiangsu Province (No:XNY-012(2015) and XNY-010(2015)), Independent Innovation Fund of Agricultural Science and Technology of Jiangsu Province (No: CX(15)1009), Huaian Key Research and Development Project (Modern Agriculture) (No:HAN2015003), Colleges

and

universities

in

Jiangsu

Province

Natural

Science

Fund(No:13KJD550001), Science and technology project of Huaiyin Institute of technology(No: 15HGZ008), Jiangsu province science and technology plan (BY2015051-03), Open project of Jiangsu Provincial Engineering Laboratory for Biomass Conversion , Process Integration (No: JPELBCPL2014004) , The Ministry of science and Technology Spark Program (No: 2013GA690267, 2014GA690218, 2014GA690163, and 2015GA690288).

18

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Figure caption

Fig.1. The schematic of the ultrasound reactor Fig.2. Effect of different ultrasound modes on biodiesel conversion Fig.3. Effect of methanol to triglyceride molar ratio on biodiesel conversion Fig.4. Effect of catalyst content on biodiesel conversion Fig.5. Effect of water content in material on on biodiesel conversion Fig.6. Effect of acid value on biodiesel conversion Fig.7. Effect of temperature and time on biodiesel conversion for SMM Fig.8. Relationship between lnk1 and 1/T for SMM Fig.9. Effect of temperature and time on biodiesel conversion for SSPU Fig.10. Relationship between lnk1 and 1/T for SSPU

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Table 1 Kinetics equations, rate constants and reaction orders of transesterification reaction intensified by SMM Temperature

K Kinetics equations

α /mol· L-1·min-1

/K 318

ln

dx = 1.7198ln[C A0 (1 − x )]+0.4279 dt

0.4602

1.7198

328

ln

dx = 2.0384 ln[C A 0 (1 − x )]+0.6445 dt

0.5715

2.0384

338

ln

dx = 1.7078 ln[C A0 (1 − x)]+0.8346 dt

Table 2

0.6912

1.7078

Kinetics equations, rate constants and reaction orders of transesterification reaction intensified by SSPU

Temperature

K Kinetics equations

α /mol· L-1·min-1

/K 318

ln

dx = 1.6448ln[C A0 (1 − x )]-0.1237 dt

0.2651

1.6448

328

ln

dx = 1.5703 ln[C A 0 (1 − x )]+0.0725 dt

0.3226

1.5703

338

ln

dx = 1.6433ln[C A 0 (1 − x )]+0.4228 dt

0.4579

1.6443

34

► Biodiesel

production intensified b y dual-frequency counter-current pulsed

ultrasound. ►The conditions of dual-frequency ► The kinetics of SMM

counter-current pulsed ultrasound.

and SSPU were studied and compared.

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