Modeling and Process Simulation of Biodiesel

Modeling and Process Simulation of Biodiesel Production from Soybean Oil using Cement Kiln Dust as a Heterogeneous Catalyst S. T. El-Sheltawy Chemical Engineering Department, Faculty of Engineering, Cairo University Cairo - Egypt [email protected]

Eslam G. Al-Sakkari Chemical Engineering Department, Faculty of Engineering, Cairo University Cairo - Egypt [email protected]

Mai Fouad Chemical Engineering Department, Faculty of Engineering, Cairo University Cairo - Egypt [email protected]

Abstract Due to the current depletion rate of fossil fuels, alternative energy sources should be produced to overcome this problem. One of these new alternatives is biodiesel which can compensate the shortage of liquid petro-diesel. This paper presents the production of biodiesel through heterogeneous catalyzed transesterification from soybean oil with methanol to oil molar ratio of 12:1 using cement kiln dust (CKD) as a catalyst at 65 C for 3 hours to produce about 51% conversion. A detailed process flow sheet to produce biodiesel at a rate of about 24 ton/day is developed. The design and sizing of a batch biodiesel reactor was performed and a control scheme was suggested.

Keywords Biodiesel, Heterogeneous Transesterification, Process design and Modeling

1. Introduction Renewable energy research has been receiving increased attention in recent years. Main reasons for this evolution are energy, economic and environmental security related concerns. It is reported that the present petroleum consumption is 105 times faster than the nature can create (Satyanarayana KG et al., 2011) and at this rate of consumption, the world's fossil fuel reserves will be diminished by 2050 (Demirbas 1

A., 2009 ). Apart from this, the fuel consumption is expected to rise by 60% or so in the next 25 years (Rittman RE, 2008). Since most of the transportation and industrial sectors need liquid fuels to drive the machinery and engines, more emphasis is needed on alternative fuel sources such as biodiesel. Biodiesel is composed of methyl or ethyl esters produced from vegetable oil or animal fat through transesterification reaction (Lin C. W. et al, 2015) and has fuel properties similar to diesel fuel (Babulal K. S., 2015). Biodiesel offers many benefits as it serves as alternative to petro-diesel, reduces greenhouse emissions and lower harmful gaseous emissions (Georgogianni KG et al., 2007) ( Hoekman SK., 2009) (Zaher F. A. et al, 2015). In transesterification the triglyceride molecules are broken into alkyl ester molecules (the biodiesel product) and glycerol (the by-product) by reaction with an alcohol in the presence of a catalyst (Pathak S., 2015). Methanol is the most commonly used alcohol, producing a biodiesel product which consists of methyl esters. Other alcohols, such as ethanol, may be used, but their use requires a modification in the production process (Siva S. et al., 2014). The reaction can be catalyzed by bases, acids, (Ejikeme P. M. et al, 2010) or enzymes (Lan T. T. B. et al, 2015) (Tuter M. et al, 2011). With soybean oils, sodium hydroxide and potassium hydroxide are the most commonly used base catalysts (Avinash K.A., 2006). The glycerol by-product is typically about 50% pure and contains excess methanol and catalyst (Andrade I. C. et al, 2015) (Nanda MR et al, 2014) (Xiao Y. et al, 2013). Due to the impurities, the glycerol by-product must generally be refined before commercial use in other industrial sectors (Saifuddin N., et al, 2014) (Surrod T. et al, 2011). Recovering the methanol leaves the glycerol at 80 to 90% pure and makes it more suitable as a marketable commodity (Isahak R. W. N. W. et al, 2015). After methanol recovery, most commercial biodiesel manufacturing companies are able to send the glycerol to a glycerol recovery/refining facility. Pure grades of glycerol (99.7%) can be used as raw material in other industrial sectors such as food products, cosmetics, toiletries, toothpaste, drugs, animal feed, plasticizers, tobacco, and emulsifiers industries (Hájek M. 2009). Most available literature suggests that methanol recovery following biodiesel production is an accepted and routine industrial practice among commercial producers (Dhar B. R. et al, 2009). Recovered methanol is typically returned to a raw material storage tank and reused for future fuel production (Singh A. et al., 2006). The initial biodiesel fuel product may contain small amounts of impurities. To remove the impurities, the biodiesel may be water washed or filtered to remove any residual catalyst and monoglycerides (Kiwjaroun C. et al., 2009). The resulting water wash and filter cake are wastes which have little or no commercial value and must be managed appropriately (Roman K., 2003) Another method of biodiesel is the heterogeneous catalyzed transesterification. The advantages of using heterogeneous catalysts are ease of separation, ability of reuse and fewer purification processes of biodiesel and the valuable byproduct glycerol (Lee J.S. et al, 2010). Another advantage of using solid catalysts is that they can catalyze both esterification and transesterification reactions (Yan S. et al, 2009). They can be categorized as basic and acidic solids (Singh Chouhan A.P. 2011). Examples of solid bases are metal oxides, mixed metal oxides and supported alkaline metal salts 2

(Moradi G., et al, 2015). Sulfated zirconia and tungstated zirconia are typical examples of acidic solids (Lopez el al. (2005). To make the production process more economical, researchers suggested new catalysts produced from wastes such as eggshell (Tan Y. H., et al, 2015) and cement kiln dust (Lin V.S. et al., 2009). They consist of some active metal oxides such as calcium oxide which has high catalytic activity for both esterification and transesterification. However, heterogeneous catalysis has some drawbacks and limitations (Granados et al., 2007). Mass transfer limitations of using solid catalysts in liquid phase reactions are important disadvantages of solid catalysts. These limitations are due to relatively viscous reaction medium and large reactants molecules (Claire M., 2008). Optimization of reactor parameters as well as factors affecting transesterification can reduce these limitations (H.V. Lee et al, 2011). This paper deals with the production of biodiesel from soybean oil using cement kiln dust (CKD) as a heterogeneous catalyst. It introduces a simulation for the production process and modeling of the biodiesel batch reactor.

2. Process Description The suggested process consists of 3 units; biodiesel production unit, biodiesel purification unit and glycerol purification unit. The coded flow sheet of this process is illustrated in Figure 1 while Table 1 presents the equipment used. Following is a brief description of the process.

2.1. Biodiesel Production Biodiesel is produced in an isothermal batch reactor that operates at 65 oC. Methanol is introduced to the reactor in excess with molar methanol to oil ratio of 12:1 (methanol to oil). The catalyst (CKD) is loaded with percentage of 3.5% of oil weight. Production is carried out through two batches with reaction time of 3 hours each. The conversion under such conditions was about 51%. After each batch the products are introduced to a filter press to remove solid catalyst from this mixture. The mixture is then cooled to improve separation efficiency of methyl ester and glycerol phases. The cooled phases are pumped to a separation tank to obtain two separate layers which are then oriented to purification sections to produce clean products of biodiesel and glycerol that match the required specifications.

2.2. Biodiesel Purification Biodiesel layer is purified through three steps. The first step is to remove excess methanol associated with this layer which measures 3% wt. of this layer. After methanol removal, ester layer is then cooled and washed with an equal volume of fresh water in a washing vessel to remove any methanol traces, glycerol content and catalyst suspended residues or leached oxides if found. This washing vessel is equipped with coalescer to remove suspended water droplets from the ester phase. The washing operation should be laminar to avoid emulsification. After washing, the ester stream is sent to a vacuum distillation column to separate purified biodiesel from unreacted oil. Biodiesel, obtained at the top of the column, is then cooled and pumped to an insulated storage tank. 3

2.3. Glycerol Purification After separation, the glycerol layer stream is directed to a distillation column to remove the excess methanol which is recycled after separation. The bottom product of the glycerol purification column is almost pure free of dissolved solids and suspended catalyst residues in it. The purified glycerol is then cooled and routed to a storage tank.

S-22 S-12

S-13

S-7 S-14 D-1

S-10 S-3

D-5

S-2 S-6

D-6 D-7

D-8

D-3

S-9 S-16

S-5

S-15

S-8

S-4

S-11

S-1

S-21 S-17

D-4

D-10 S-18 D-9

S-20

D-2

S-19

D-11

D-12

Figure 1 Biodiesel Production using CKD as Heterogeneous Catalyst Process Flow Sheet

Table 1 Biodiesel Production using CKD as Heterogeneous Catalyst Process Equipment Code D-1 D-2 D-3 D-4 D-5 D-6 D-7 D-8 D-9 D-10 D-11 D-12

Equipment Methanol Storage Tank Oil Storage Tank Reactor Filter press Separation Tank Methanol Distillation Column 1 Washing Vessel Biodiesel Column Filter press Methanol Distillation Column 2 Glycerol Storage Tank Biodiesel Storage Tank 4

3. Summary of Material and Energy Balances According to the experimentally obtained conversion of 51%, the daily amount of oil needed for producing biodiesel at a rate of 24 ton/day is about 47 tons. The required catalyst amount is 1.65 tons which represents a percentage of 3.5% of the introduced oil weight. As the methanol to oil molar ratio equals 12:1, the methanol is provided to the plant at a rate of 19 ton/day. Table 2 summarizes the conditions and component compositions in each stream of the process flow sheet shown in figure 1. To obtain the compositions of streams leaving distillation columns general NRTL thermodynamic model was chosen. It may be observed that the flow rates of streams S-1 to S-5 are higher than all other streams as they are for charging and discharging the biodiesel batch reactor. After cooling, the excess methanol and unreacted oil can be recycled to be reused to minimize the process cost and render the process profitable. Heat integration between hot and cold streams could be applied to minimize the operating cost of heating and cooling. Waste washing water could be used as a source of heat for the batch reactor. Table 2 Summary of Material Balance and Conditions of Process Streams Stream Oil Methanol CKD Biodiesel Glycerol Water Flow rate kg/hr Temperature oC Pressure kPa Stream Oil Methanol CKD Biodiesel Glycerol Water Flow rate kg/hr Temperature oC Pressure kPa Stream Oil Methanol CKD Biodiesel Glycerol Water Flow rate kg/hr Temperature oC Pressure kPa

S-1 1 0 0 0 0 0 23500 25 atm. S-9 0.4886 0 0 0.51088 0.00052 0 1964 200 atm. S-17 0 0.8607 Traces 0 0.1393 0 725.4687 25 atm.

S-2 0 0 1 0 0 0 825 25 ----------S-10 0 0 0 0 0 1 2182.222 25 atm. S-18 1 0.8607 0 0 0.1393 0 725.4687 25 atm.

S-3 0 1 0 0 0 0 9500 25 atm. S-11 0 0 0 0 0.00047 0.99953 2183.243 80.7 atm. S-19 0 0 0 0 1 0 101.1 290 110

S-4 0.340429 0.243063 0.02439 0.355898 0.036219 0 33825 65 atm. S-12 0.4833 0 0 0.5167 0 0 1962.979 80.7 atm. S-20 0 0 0 0 1 0 101.1 30 atm. 5

S-5 0.34894 0.249139 0 0.364796 0.037125 0 33000 65 atm. S-13 0.000003 0 0 0.999997 0 0 1003 208 10 S-21 0 1 0 0 0 0 624.4 61.5 90

S-6 0.474 0.03 0 0.4955 0.0005 0 2024.527081 25 atm. S-14 0.000003 0 0 0.999997 0 0 1003 30 atm. S-22 0 1 0 0 0 0 685.13 60.28 atm.

S-7 0 1 0 0 0 0 60.73 47.5 50 S-15 0.99993 0 0 0.00007 0 0 959.6 415 20

S-8 0.4886 0 0 0.51088 0.00052 0 1964 288 60 S-16 0.99993 0 0 0.00007 0 0 959.6 30 atm.

4. Quality Control of Produced Biodiesel and Glycerol Quality of products should be tested continuously to match the standard specifications. Table 3 illustrates the required specs of both petro-diesel and biodiesel. Table 3 Specs of both Petroleum diesel and Biodiesel Diesel (Biodiesel Handling and Use Guide, 2009) Fuel Property Fuel standard Higher Heating Value Btu/gal Lower Heating Value Btu/gal Kinematic Viscosity cSt. @ 40 oC Specific Gravity kg/l @ 15 oC Carbon, wt% Hydrogen, wt% Oxygen, wt% Sulfur, wt% Boiling Point oC Flash Point oC Cloud Point oC Pour Point oC Cetane Number

Diesel

Biodiesel

ASTM D975 137640 129050 1.3-4.1 0.85 87 13 0 0.0015 max 180-340 60-80 -35 to 5 -35 to -15 40-55

ASTM D6751 127042 118170 4.0-6.0 0.88 77 12 11 0.0-0.0024 315-350 100-170 -3 to 15 -5 to 10 48.65

5. Modeling of Biodiesel Batch Reactor The principle equation of material balance for a certain system is: (1)

For a batch reactor with no in or out flows, the equation is reduced to: (2)

Where

(3) (4)

The limiting reactant in the present study is the oil as the methanol is introduced to the reaction medium in high excess. The final rate form is as follows: (5) 6

Based on statistical analysis, the Eley-Rideal model was found to best fit the obtained experimental. Substituting with the rate formula in the previous equation, the following equation is obtained: (6)

Applying material balance calculations on this liquid reactive system, the following relations result: (7) (8) (9) (10)

For simplification, rate equation could be approximated to a power law model. After performing a statistical analysis, the closest power law model to Eley-Rideal model is the first order model with respect to oil concentration and contains reverse reaction part. Equation 11 represents the suggested first order model. (11)

So triglyceride concentration gradient with respect to time may be calculated using equation 12. (12)

Using relations from 7 to 10 and substituting in equation 12, a relation between conversion and time can be obtained in a form of differential equation. This relation is at a temperature of 65 oC. To have a general relation at any reaction temperature Arrhenius form could be used to represent the rate constants of forward and backward reactions. Equation 13 shows the relation between rate of reaction and conversion gradient with respect to time. (13)

At steady state this equation is still applicable then equation 14 appears (14)

On subtracting equation 14 from equation 13 the linearized equation of material balance can be described by equation 15 7

(15)

The linearized rate equation takes the form presented by equation 16 (16)

Substituting with 16 in 15 and applying Laplace transformation, equation 17 is obtained. (17)

Where

and

To obtain an equation that relates the amount of heating fluid and the conversion or reaction temperature, energy balance on this isothermal batch reactor should be performed. Equation 18 can be a general representative energy balance equation of this system. (18)

This general equation may be represented mathematically by equation 19 (19)

Where ΔHrxn, V, U, Th and T represent the standard heat of reaction, reactor volume, overall heat transfer coefficient, heating fluid temperature and temperature inside reactor respectively Linearization of this equation leads to equation 20 (20)

Substituting with equation 16 in equation 20 and performing Laplace transformation (21)

Where As the heat transferred to the reactor is obtained from the heating fluid (steam), thus equation 22 could be deduced from equation 20. (22)

Where λst and mst are the latent heat and flow rate of steam used for heating reaction medium. Substituting with 16 in 22, tidying and rearranging the equation, performing Laplace transformation and substituting with equation 17 this leads to equation 23. (23) 8

Where The relation between conversion and heating fluid flow rate is shown by equation 24. (24)

Where

6. Reactor Design Table 4 summarizes reactor sizing and design. It presents the suggested dimensions of the reactor, heating jacket and agitator. The power of motor and steam needed for the reaction are also mentioned. Table 4 Summary of Biodiesel Batch Reactor Design Parameter Volume (theoretical) Height Diameter Impeller type Agitator diameter Distance between reactor bottom and agitator Speed (after scaling up) Power Width Height (from reactor bottom) Steam flow rate

Value Reactor 38 4.75 3.65 Agitator Rushton Turbine 1.5

Units

--------(m)

0.75

(m)

73 55 Jacket 0.075 1.15 446.5

(rpm) (hp)

(m3) (m) (m)

(m) (m) (kg/hr)

7. Reactor Control Reaction extent could be controlled by controlling reaction temperature which can be controlled by manipulating heating fluid flow rate using a PID controller. The transfer function relating heating fluid flow rate and reaction temperature equals . A proportional controller can be used to control the level inside reactor during discharge. Figure 2 shows the control scheme of the reactor.

9

TT

TC LT

m LC

Figure 2 Control Scheme of Biodiesel Batch Reactor

8. Conclusion This paper introduced a simulation of a suggested process for biodiesel production from soybean oil using CKD as a heterogeneous catalyst. Reaction conditions are: 65 o C reaction temperature, 12:1 oil to methanol molar ratio and catalyst loading of 3.5% wt. The conversion obtained at these conditions was 51%. Reactor products are filtered to remove solid catalyst then they are allowed to be separated in a separation tank. After separation each layer is purified to produce pure biodiesel and glycerol that meet the desired specs. To maximize process profitability, excess methanol and unreacted oil were recycled. Modeling of reactor showed that temperature of reaction is related to the heating fluid (steam) flow rate with a simple transfer function. Design and sizing of the reactor are presented as well as the control scheme used to control temperature inside the reactor in order to control conversion and level during reactor discharging. This study also includes the use of heat integration principles and searching for a reasonable method to increase the catalytic activity of CKD. Since the present process is more expensive and less feasible than the conventional homogeneous process thus more study should be performed aiming at decreasing its cost and making it more competitive.

9. References -

-

-

-

-

Avinash .A. K., (2007) "Biofuels (alcohols and biodiesel) applications as fuels for internal combustion engines", Progress in Energy and Combustion Science Vol. 33, 233–271 (39 pages) Andrade I. C., Moreno E. A., Cantor J. F. S., Fajardo C. A. G. and Sodré J. R., (2015) "Purification of glycerol from biodiesel production by sequential extraction monitored by 1H NMR" Fuel Processing Technology, Vol. 132, 99-104 (6 pages) Babulal K. S., Pradeep A. and Muthukumar P., (2015) "Experimental Performance and Emission Analysis of C.I Engine Fuelled with Biodiesel" International Journal of Innovative Research in Science, Engineering and Technology, Vol. 4, No. 2, 133-138 (6 pages) Claire M., (2008) "Evaluation of Heterogeneous Catalysts for Biodiesel Production" Ph.D Thesis, School of Chemical Engineering and Advanced Materials, Newcastle University, p 612. Demirbas A., "Global renewable energy projections" Energy sources 2009, Part B, 4, 212224.

11

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

Dhar B. R. and Kirtania K., (2009) "Excess Methanol Recovery in Biodiesel Production Process using a Distillation Column: a Simulation Study" Chemical Engineering Research Bulletin Vol. 13, 55-60 (6 pages) Ejikeme P. M., Anyaogu I. D., Ejikeme C. L., Nwafor N. P., Egbuonu C. A. C., Ukogu K. and Ibemesi J. A. (2010) "Catalysis in Biodiesel Production by Transesterification ProcessesAn Insight" E-Journal of Chemistry, Vol. 7, No. 4, 1120-1132 (13 pages) Georgogianni K.G., kontominas M.G., Tegou E., Avloitis D., Gergis V (2007) "Biodiesel Production: Reaction and Process Parameters of Alkali-Catalyzed Transesterification of Waste Frying Oils", Energy and Fuels, Vol. 21, 3023-3027 (5 pages) Granados, M.L., Poves, M.D.Z., Alonso, D.M., Mariscal, R., Galisteo, F.C., MorenoTost, R., Santamaría, J., Fierro, J.L.G., (2007) "Biodiesel from sunflower oil by using activated calcium oxide" Applied Catalysis B: Environmental, Vol. 73, 317-326 (10 pages) Hájek M. and Skopal F. (2009) "Purification of the Glycerol Phase after Transesterification of Vegetable Oils", 44th International Petroleum Conference, Bratislava, Slovak Republic Hoekman S.K., (2009) "Biofuels in the US - Challenges and Opportunities" Renewable Energy, Vol. 34, 14-22 (9 pages) Isahak R. W. N. W., Ramli Z. A. C., Ismail M., Jahim J. M. and Yarmo M. A. (2015) "Recovery and Purification of Crude Glycerol from Vegetable Oil Transesterification", Separation & Purification Reviews, Vol. 44, No. 3, 250-267 (18 pages) Kiwjaroun C., Tubtimdee C. and Piumsomboon P (2009) "LCA studies comparing biodiesel synthesized by conventional and supercritical methanol methods" Journal of Cleaner Production, Vol. 17, No. 2, 143-153 (11 pages) Lan T. T. B. and Hoa P. N. (2015) "Lipase Catalysis for Transesterification Produces Biodiesel Using Coconut Oil as Main Raw Material Source" Biological and Chemical Research, Volume 2015, 258-267 (10 pages) Lee H.V., and R. Yunus., (2011) "Process optimization Design of Jatropha-based Biodiesel Production Using Response Surface Methodology" Fuel Processing Technology (92) 24202428 (9 pages) Lee J.S. and Saka S. (2010) "Biodiesel production by heterogeneous catalysts and supercritical technologies: review" Bioresource Technology, Vol. 101, No. 7, 191–200 (10 pages) Lin C. W. and Tsai S. W. (2015) "Production of biodiesel from chicken wastes by various alcohol-catalyst combinations" Journal of Energy in Southern Africa, Vol. 26, No. 1, 36-45 (10 pages) Lin V.S. , Cai Y , Kern C. , Dulebohn J. I. , Nieweg J.A. , (2009) "Solid catalyst system for biodiesel production" Patent No. WO2009058324 A1, Univ. Iowa State Res. Found Inc, USA. Lopez, D., Goodwin, J., Bruce, D., and Lotero, E. (2005), "Transesterification of triacetin with methanol on solid acid and base catalysts" Applied Catalysis, A: General, Vol. 295, 97105 (9 pages) Moradi G., Davoodbeygi Y., Mohadesi M. and Hosseini S., (2015) "Kinetics of transesterification reaction using CAO/AL2O3 catalyst synthesized by sol-gel method" The Canadian Journal of Chemical Engineering, Vol. 93, No. 5, 819–824 (6 pages) Nanda MR, Yuan Z, Qin W, Poirier MA and Chunbao X. (2014) "Purification of Crude Glycerol using Acidification: Effects of Acid Types and Product Characterization" Austin Journal of Chemical Engineering, Vol. 1 No. 1: 1004 Pathak S., (2015) "Acid catalyzed transesterification" Journal of Chemical and Pharmaceutical Research, Vol. 7, No. 3, 1780-1786 (7 pages) Rittman R.E., (2008), "Opportunities for Renewable Bioenergy Using Microorganisms" Biotechnology and Bioengineering, Vol.100, 203-212 (10 pages)

11

-

-

-

-

-

-

-

-

-

-

Roman K., (2003) "From the Fryer to the Fuel Tank", third edition Chapter 6, p59-72, Joshua Tickell, New Orleans, Louisiana. Saifuddin N., Refal H. and Kumaran P. (2014)"Rapid Purification of Glycerol by-product from Biodiesel Production through Combined Process of Microwave Assisted Acidification and Adsorption via Chitosan Immobilized with Yeast" Research Journal of Applied Sciences, Engineering and Technology Vol. 7 No. 3 593-602 (10 pages) Satyanarayana K.G., Marino A.B., Vergas J.V.C., (2011) "A review on microbale, a versatile source for sustainable energy and materials", Int. J. Energy Res., Vol. 35, 291-311 (21 pages) Singh, A.; He, B.; Thompson, J.; van Gerpen, J., (2006) Process optimization of biodiesel production using different alkaline catalysts. Appl. Eng. Agr., Vol. 22 No. 4, 597-600 (4 pages) Singh Chouhan A.P. and Sarma A.K. (2011) "Modern heterogeneous catalysts for biodiesel production: A comprehensive review" Renewable and Sustainable Energy Reviews, Vol. 15, 4378–4399 (22 pages) Siva S., Marimuthu C. (2014)"Production of Biodiesel by Transesterification of Algae Oil with an assistance of Nano-CaO Catalyst derived from Egg Shell" International Journal of Chem. Tech. Research, Vol. 7, No. 4, 2112-2116 (5 pages) Surrod T. and Pattamaprom C. (2011) "Purification of Glycerin By-product from Biodiesel Production Using Electrolysis Process" The Second TSME International Conference on Mechanical Engineering, Krabi, Thailand Tan Y. H., Abdullah M. O., Hipolito C. N., Taufiq-Yap Y. H., 2015 "Waste ostrich and chicken eggshells as heterogeneous base catalyst for biodiesel production from used cooking oil: Catalyst characterization and biodiesel yield performance" Applied Energy, Vol. 160, 5870 (13 pages) Tuter M. , Akdere C. , Yerlikaya C. and Sirkecioğlu A. (2011) "The Evaluation of Fusel Oil Fraction for Lipase Catalyzed Alcoholysis of Hazelnut Oil", Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, Vol. 33, No. 6, 521-528 (8 pages) Xiao Y., Xiao G. and Varma A. (2013)"A Universal Procedure for Crude Glycerol Purification from Different Feedstocks in Biodiesel Production: Experimental and Simulation Study" Industrial & Engineering Chemistry Research, Vol. 52 No. 39, 14291–14296 (6 pages) Yan S., Salley S. O. and Simon Ng K.Y. (2009) "Simultaneous transesterification and esterification of unrefined or waste oils over ZnO-La2O3 catalysts" Applied Catalysis A: General, Vol. 353, No. 2, 203–212 (10 Pages) Zaher F. A. and Soliman H. M., (2015) "Biodiesel production by direct esterification of fatty acids with propyl and butyl alcohols" Egyptian Journal of Petroleum

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