Iraqi Journal of Chemical and Petroleum Engineering 

 Vol.16 No.4 (December 2015) 11- 19 

ISSN: 1997-4884 

 
 
 
 

Esterification of Free Fatty Acid with High Chain Alcohol for 

Biodiesel Production Using Semi-Batch Reactive Distillation 
 

Wadood T. Mohammed and Marwa F. Abdul Jabbar* 

Chemical Engineering Department – College of Engineering – University of Baghdad 

*Chemical Engineering Department-College of Engineering-Al-Nahrain University 

 

Abstract 

   The esterification of oleic acid with 2-ethylhexanol in presence of sulfuric acid  as 

homogeneous catalyst was investigated in this work to produce 2-ethylhexyl oleate 

(biodiesel) by using semi batch reactive distillation. The effect of reaction temperature 

(100 to 130°C), 2-ethylhexanol:oleic acid molar ratio (1:1 to 1:3) and catalysts 

concentration (0.2 to 1wt%) were studied. Higher conversion of 97% was achieved 

with operating conditions of reaction temperature of 130°C, molar ratio of free fatty 

acid to alcohol of 1:2 and catalyst concentration of 1wt%. A simulation was adopted 

from basic principles of the reactive distillation using MATLAB to describe the 

process. Good agreement was achieved. 

   

Key Words: Biodiesel, Reactive distillation, Esterification, Homogeneous catalyst  

  

Introduction 

   Sustainable energy management is a 

major concern of the modern society. 

The increasing energy demand makes 

the implementation of sustainable fuels 

a crucial issue worldwide [1,2]. 

Biodiesel has become increasingly 

attractive because it is made from 

renewable sources and combines high 

performance with environmental 

benefits [3–5]. Unlike petroleum diesel 

that contains hydrocarbons, biodiesel 

consists of a mixture of monoalkyl 

esters of long-chain fatty acids. 

   Biodiesel has several advantages 

over petroleum diesel: it is safe, 

renewable, nontoxic and 

biodegradable; it contains no sulfur 

that effected lubricity prolongates the 

diesel engine life [2,5]. Biodiesel not 

only has a higher cetane number than 

petroleum diesel but also has a higher 

flash point, meaning better and safer 

performance and it generates less 

hydrocarbons, fewer carbon dioxide 

and fewer particles than petroleum 

diesel. Biodiesel can be blended with 

any amounts of petroleum diesel and 

defined by a “B” followed by the vol 

% of biodiesel [4]. The conventional 

biodiesel production process based on 

the use of alkaline catalyst, such as 

sodium hydroxide or sodium 

methoxide, for transesterification of 

triglyceride posed serious separation 

problem. The presence of water and/or 

free fatty acids (FFA) in the reaction 

system leads to saponification [6-8]. A 

homogeneous acid catalyst, such as 

sulfuric acid or hydrochloric acid can 

also be used [9,10], which does not 

produce soap and increase the fuel 

production. Meher et.al. suggested an 

alternative way to solve the FFA 

Iraqi Journal of Chemical and 
Petroleum Engineering 

 

University of Baghdad 
College of Engineering 



Esterification of Free Fatty Acid with High Chain Alcohol for Biodiesel Production Using Semi-Batch 

Reactive Distillation 

12                                       IJCPE Vol.16 No.4 (Dec. 2015)             -Available online at: www.iasj.net 
 

problem by using an acid catalyst. The 

esterification of FFA by methanol can 

be carried out before the 

transesterification of oil as shown in 

Eq. 1 [11]. Thus, valuable FFAs can be 

completely converted to biodiesel 

without being wasted. 

 

RCOOH + CH3OH = RCOOCH3 + 

H2O                                               ... (1) 

 

   There are five primary ways for 

making biodiesel: (i) direct use and 

blending of vegetable oil (ii) use of 

microemulsions with short-chain 

alcohols (iii) thermal cracking 

(pyrolysis) of vegetable oils (iv) 

transesterification of triglycerides 

catalyzed by bases, acids, or enzymes 

and (v) esterification of fatty acids 

with alcohols, using acid catalysts 

(H2SO4) or solid acids. 

   Usually, an alcohol excess is used for 

driving the reaction equilibrium 

towards the product side. This alcohol 

excess must be recovered in order to 

reutilize it and furthermore purify the 

biodiesel. The alcohol recovery 

process is generally carried out by 

distillation process, thus, the energy 

consumption, operating costs, 

equipment number and the production 

time increase. 

   Reactive distillation (RD) is the 

process in which chemical reaction and 

separation are carried out 

simultaneously within a fractional 

distillation apparatus. It may be 

advantageous for liquid-phase reaction 

systems when the reaction must be 

carried out with a large excess of one 

or more of the reactants, when a 

reaction can be driven to completion 

by removal of one or more of the 

products as they are formed, or when 

the product recovery or by-product 

recycle scheme is complicated or made 

infeasible by azeotrope formation [12]. 

By continuous separation of products 

from reactants while the reaction is in 

progress, the reaction can proceed to a 

much higher level of conversion than 

without separation [13]. 

   The aim of this work is the study of 

the production of biodiesel by 

esterification of oleic acid with 2-

ethylhexanol in a reactive distillation 

column. The esterification of oleic acid 

using sulfuric acid as a catalyst has 

been investigated at different process 

conditions: temperature, oleic acid: 2-

ethylhexanol ratio, sulfuric acid 

concentrations. 

 

Experimental Section 

 

Materials 

   Oleic acid (98%) was supplied from 

Thomas baker, india. This acid is 

unsaturated fatty acid that jatropa oil 

which is inedible oil contains 44.8% of 

it. 2-ethylhexanol alcohol (99% from 

GC analysis) was maintained from 

ministry of science and technology as 

industrial alcohol. Since this alcohol is 

typically a waste alcohol from the 

manufacturing of butanol, this process 

makes sense from an economic 

viewpoint. Sulfuric acid as catalyst, 

ethanol and phenolphthalein for 

titration. 

 

Reaction Procedure 

   The reaction was carried out in a lab 

scale reactive distillation column that 

consists of a 250 ml flask equipped 

with oil bath to set up a constant 

reaction temperature, magnetic stirrer, 

condenser, and column distillation. 

The feed is charge into the flask in the 

bottom of the rectifying column that 

also used as a reactor and reboiler. 

Esterification of fatty acid is a 

reversible reaction and water is 

formed. Removal of water can drive 

the reaction equilibrium to the 

completion and therefore increase the 

conversion. The best solution is 

working at temperatures above 100°C, 

in a system with continuous water 



Wadood T. Mohammed and Marwa F. Abdul Jabbar 

 

-Available online at: www.iasj.net                    IJCPE Vol.16 No.4 (Dec. 2015)                                13 
 

removal. By removing water as by-

product, the equilibrium is shifted 

towards ester formation. The ester 

(biodiesel) will always be separated in 

the bottom of the reactive distillation 

column. Water is present as side 

product and typically is removed as top 

product due to its lower boiling point. 

5 ml of diluted solution was taken for 

the determination of unreacted acid. 

This was titrated against 0.1 KOH 

solution using phenolphthalein as 

indicator and 2 ml ethanol for dilution. 

Difference between the fresh acid 

reading and reading for reaction 

mixture was used for finding out the % 

yield of ester. 

 

Acid value = 
       

        
                   ... (2) 

 

X%= (1- 
             

           
)  100            ... (3) 

 

And the amount of catalyst used is 

normalized to the total amount of 

reactants: 

 

   In these equations, V, N and m.wt is 

volume, concentration and molecular 

weight of KOH, m is weigh of sample. 

X [%] is the conversion of the fatty 

acid, [Acid]initial and [Acid]final are the 

molar concentrations of fatty acid 

before and after reaction, Wcat [%] is 

the weight percent of catalyst used in 

reaction and Mcat, Macid and Malcohol are 

the amounts of catalyst, acid and 

alcohol, respectively. 

 

Simulation Process 

   To develop a mathematical model of 

reactive distillation for biodiesel 

production, mass balance as well as the 

thermodynamic equilibrium equations 

on each tray is written. The stages are 

counted from top to bottom as shown 

in Fig. (1). 

   The model is valid under the 

following assumptions: 

 

I. All the plates are equilibrium stages. 

II. Vapor phase is an ideal gas mixture. 

III. The reaction takes place only in the 

reboiler, therefore, rate of reaction just 

added for reboiler equation. 

IV. Constant operating pressure  

V. Vapor phase hold up is assumed to 

be negligible as compared to the liquid 

phase hold up on each stage. 

VI. The column was considered 

isothermal (temperature for all stages 

is the same) therefore energy balance 

not established. 

 

 
Fig. 1, Scheme of semi-batch 

distillation column 

 

   The column was simulated assuming 

4 stages including the reboiler. The 

feed was introduced at the reboiler and 

the reaction took place in reboiler. The 

simulation was carried out by solving 

the system simultaneously using 

MATLAB program. 

   The determination of phase 

composition can be made by solution 

of material balance equations. The 

solution of material balance equations 

are derived for condenser, the column 

stages and reboiler as follow:- 

 

 

 



Esterification of Free Fatty Acid with High Chain Alcohol for Biodiesel Production Using Semi-Batch 

Reactive Distillation 

14                                       IJCPE Vol.16 No.4 (Dec. 2015)             -Available online at: www.iasj.net 
 

• For Condenser (k=1, i=1-4) 

 
      

  
 = 

                   

    
                  ... (5) 

 

• For Column (k=2,3and i=1-4) 

 
      

  
 = 

 

   
 (               + 

 

   
 

(                                           ... (6) 

 

• For Reboiler (k=N and i=1-4) 

 
      

  
 =  

                        

    
+Rate... (7)      

 

Where  

H is holdup, K is stage, i is component  

Equilibrium ratio (k=2 to N)  

 

     = 
       

∑        
 
   

                           … (8)  

 

Where  

αi  is the relative volatility 

x is composition of liquid phase 

y is composition of vapor phase  

 

   The UNIQUAC model was applied 

to consider the nonideal liquid- phase 

behavior. The degree of deviation from 

ideality in liquid phase is represented 

by γi (activity coefficient).  It was 

employed for the vapor–liquid 

equilibrium (VLE) calculations in 

MATLAB. 

   Activity coefficient consists of two 

terms, residual and combinatorial  

 

lnγi= ln  
 
 + ln   

                          ... (9) 

 

ln   
 
 = 1- Ji +ln Ji -5qi (1- 

  

  
 + ln 

  

  
)              

                                                    ... (10) 

 

ln   
  =    [ 1- ∑    

   

  
  ˗     ln 

   

  
 )]         

                                                    ... (11) 

 

 

Results and Discussion 

 

1- Effect of Mixing Speed 
   Fig. (2) illustrates the relationship 

between conversion of oleic acid with 

time at different mixing speeds (500-

900 rpm) using a homogeneous 

catalyst of concentration of 1wt%, 

reaction temperature of 130°C and 

oleic acid:2-ethylhexanol molar ratio 

of 1:1.  

   The results obtained here, showed 

that the conversion increased from 

91.78 to 96.55% for mixing speed of 

500 to 650 rpm respectively, then 

decreasing to 93.97% for mixing speed 

of 900 rpm. When the speed is higher 

than the desired one which gave high 

conversion, there was a negative effect 

because of the formation of very small 

droplet that behave as rigid drop, 

causing the molecules inside the drop 

could not move and transferred from 

center of drop to surface to be 

converted, therefore the reaction and 

conversion took place only on the 

surface which gave lower value. 

 

 
Fig. 2, Effect of mixing speed on 

conversion of oleic acid 

 

[Operating conditions:molar ratio of free 
fatty acid: alcohol was 1:1, reaction 

temperature 130°C and concentration of 

sulfuric acid 1wt%] 

 

 

 



Wadood T. Mohammed and Marwa F. Abdul Jabbar 

 

-Available online at: www.iasj.net                    IJCPE Vol.16 No.4 (Dec. 2015)                                15 
 

2- Effect of Molar Ratio of Alcohol 
to Free Fatty Acid 

   The most important parameter effect 

biodiesel production is molar ratio of 

alcohol to oil. For batch studies of 

conventional process the alcohol to oil 

ratio of feed has considered as an 

important factor for determining 

equilibrium constant and excess of 

alcohol used to shift the reaction to 

equilibrium. On contrast, reactive 

distillation used to overcome this 

problem since it reduce the need of 

excess alcohol and reduce the time by 

continuous removing of water instead 

of adding excess reactant.  

   For oleic acid and 2-ethylhexanol 

using homogeneous catalyst (H2SO4), 

Fig.(3) shows the effect of molar ratio 

of 2-ethylhexanol: oleic acid on the 

conversion of oleic acid at a constant 

temperature of 130°C, concentration of 

sulfuric acid of 1wt% and mixing 

speed of 650 rpm. lt can be clearly 

seen the activity profile, when the 

molar ratio increased from 1 to 2 the 

conversion was found to increase from 

78% to 97% after 20 min reaction time 

while for further increase in 2-

ethylhexanol ratio to 3, the conversion 

decrease to reach 93.40% after 2 h 

reaction time. 

   As the alcohol to acid molar ratio 

varies to reach three orders of 

magnitude, dehydration to ethers is a 

potentially unwanted side reactions, 

the formation of alkene which cause 

decrease in conversion were occured. 

Also further increasing in alcohol led 

to disturbing the stoichiometric of 

alcohol to acid and accordingly 

decreases in reaction rate. As well as 

the molar ratio of alcohol to acid 

increased, the catalyst was diluted by 

excess of alcohols this also led to 

decreased conversion. 

 

 

 

 

 
Fig. 3, Effect of Acid:Alcohol molar 

ratio on oleic acid conversion 

 

[Operating conditions: reaction 

temperature 130°C, concentration of 

homogeneous catalyst 1wt%    (H2SO4) 

and mixing speed 650 rpm] 

3- Effect of Reaction Temperature 
   Fig. (4) illustrates the variation of 

conversion with time at different 

reaction temperatures of 100, 110 120 

and 130°C to enhance the separation of 

water. 

   It has been observed as the 

temperature increase, the conversion 

increase from 93.34% at 100°C to 

reach 96.55% at 130°C after 10 min 

reaction time with constant molar ratio 

of oleic acid:2-ethylhexanol of 1:2 and 

catalyst amount of 1wt%.  

   Since the esterification reaction is 

endothermic, increasing the reaction 

temperature led to increasing 

conversion. The high temperature 

cause increase in activity of molecules 

which mean more molecules have 

more energy, therefore the probability 

of molecules to react increased.  



Esterification of Free Fatty Acid with High Chain Alcohol for Biodiesel Production Using Semi-Batch 

Reactive Distillation 

16                                       IJCPE Vol.16 No.4 (Dec. 2015)             -Available online at: www.iasj.net 
 

Fig. 4, Effect of temperature on oleic 

acid conversion  

 

4- Effect of Catalyst Concentration 
   The amounts of catalyst also play a 

role on the conversion of the 

esterification reaction but less effect 

than temperature and molar ratio. The 

varying amount of catalysts was 

studied in this work at the following 

reaction conditions: ratio of alcohol to 

fatty acid 2:1 , temperature 130°C and 

mixing speed of 650 rpm during 120 

min of reaction time.  

  The results are displayed in Fig.(5) 

and shows that reaction was highly 

depend on presence of catalyst which 

accelerate the reaction. it gave 59.13% 

after 120 min. Conversely, in the 

presence of acid catalysts, a different 

results were observed. Therefore the 

conversion increased to reach 86% and 

97% when the reaction catalyzed by 

0.2wt% and 1wt% sulfuric acid 

respectively after 60 min. The increase 
in catalyst concentration considerably 

shortened the time needed to reach the 

reaction equilibrium. This in 

agreement with Kusmiyati and 

Sugiharto A., 2010, who studied the 

effect of concentration of sulfuric acid 

on esterification of oleic acid with 

methanol and showed that further 

adding of catalyst amount above 1wt% 

did not lead the conversion to increase 

significantly [14]. Since sulfuric acid 

absorbs some of the water formed by 

reacting with it to form solvated ions, 

thus reducing the amount of free water 

in the system therefore the best 

concentration achieved was 1wt%. 
 

 
Fig. 5, Effect of homogeneous catalyst 

concentration on oleic acid conversion 

 

[Operating conditions: reaction 

temperature 130°C, molar ratio of 2-

ethylhexanol:oleic acid 2:1 and mixing 

speed 650 rpm] 
 
Testing of Biodiesel Obtained 

from Oleic Acid 

   Biodiesel obtained from oleic acid 

was analyzed by ASTM (American 

Standard for Testing Material). Table 

(1) shows biodiesel from this 

experiment 

 

Table 1, Petroleum diesel vs. biodiesel 

Recent 

work[16]  

Diesel 

[15] 

Biodiesel  

[15] 
Fuel properties 

100 
60–80 

 

100–170 

 
Flash point °C 

9659.5 
1.3–4.1 

 
1.9–6.0 

Kinematic 

viscosity 

(mm/s)@40°C 

0.859 56.9 56.. 
Density g/ml 

@30°C 

-10 
-35 to –

15 

-15 to 10 

 
Pour point °C 

-7 
-15 to 5 

 

-3 to 12 

 
Cloud point °C 

198 
188-

343 
182-338 

Boiling point 

°C 

0.136    
Carbon 

residue% 

 

 



Wadood T. Mohammed and Marwa F. Abdul Jabbar 

 

-Available online at: www.iasj.net                    IJCPE Vol.16 No.4 (Dec. 2015)                                17 
 

Simulation Results  

   The predicted results from the 

simulation model of batch reactive 

distillation could be utilized to 

speculate the composition of reactants 

and products to compare them with 

experimental work. 

   Figs. (6) to (8) displaying the 

composition change with time for oleic 

acid with homogeneous catalyst at 

various conditions of temperature and 

molar ratio of alcohol to FFA with 

constant concentration of catalyst   
(1wt %). 

   There are simple differences between 

theoretical and experimental results. 

   The main deviation due to non 

ideality of a system which ignored in 

the experiment but considered for 

theoretical study. 

   Fig. (6) shows a decrease in mole 

fraction of oleic acid with time, which 

approached nearly zero within 5 min, 

this is due to the fact that is converted 

to biodiesel after the reaction reached 

its suitable conditions.  

       

 
Fig. 6, mole fraction of oleic acid and 

its biodiesel 

 

[Operating conditions: molar ratio 

alcohol: acid was 2:1, reaction 

temperature 130°C and concentration 

of homogeneous catalyst wt 1% 

(H2SO4)] 

 

 
Fig. 7, mole fraction of oleic acid and 

its biodiesel 

 

[Operating conditions: molar ratio of 

alcohol:acid was 2:1, reaction 

temperature 100°C and concentration 

of homogeneous catalyst 1wt% 

(H2SO4)]   

   This result was in a good agreement 

with experimental results as shown in 

the figure. While for biodiesel, the 

mole fraction in still increased for both 

experiment and simulation, but 

simulation gave lower fraction as a 

result of water presence. At 

temperature 100°C at the same ratio of 

alcohol: acid of (2:1) very good 

agreement shown in Fig. (7). 

Composition for theoretical and 

experimental reaches 0.45 and 0.48 

biodiesel, respectively after 120 min. 
 

 
Fig. 8, mole fraction of oleic acid and 

its biodiesel 



Esterification of Free Fatty Acid with High Chain Alcohol for Biodiesel Production Using Semi-Batch 

Reactive Distillation 

18                                       IJCPE Vol.16 No.4 (Dec. 2015)             -Available online at: www.iasj.net 
 

[Operating conditions: molar ratio 

alcohol:acid was1:1, reaction temperature 

130°C and concentration of homogeneous 

catalyst 1wt% (H2SO4)] 

 

Conclusions 

1- The influence of various parameters    
reaction was studied and shown that 

the best conditions for biodiesel 

production were molar ratio of 1:2, 

temperature 130°C and catalyst 

amount of 1wt% which give higher 

conversion 96.55% after very short 

time of 10 min reaction. 

2- Reversible reaction not occurs 
because of continuous removal of 

water during reaction and shifts it to 

equilibrium. Stochiometeric ratio is 

enough to give high conversion, 

since it reach 88.91% at time 2 h 

while reached 97.68% for ratio 1:2 

at the same time and may be obtain 

higher conversion for low ratio if 

we use high temperature but cannot 

rise temperature because sulfuric 

acid is dangerous and cause 

crackling when added to mixture 

therefore we prefer high ratio and 

low temperature when using 

sulfuric acid as catalyst.  

3- The most parameter effect on 
esterification is molar ratio then 

temperature while amount of 

catalyst has very small effect on 

biodiesel production.   

 

Nomenclature 

C: concentration of KOH solution, 

mole/l. 

mwt.: molecular weight of KOH, 

g/mole. 

V: volume of KOH solution, ml. 

M: weight of sample, g. 

X: conversion, dimensionless. 

γ
 
 : Combinational term for activity 

coefficient  

  
 : Residual term for activity 

coefficient 

 

 

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Wadood T. Mohammed and Marwa F. Abdul Jabbar 

 

-Available online at: www.iasj.net                    IJCPE Vol.16 No.4 (Dec. 2015)                                19 
 

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