Abstract An investigation into the effects of temperature and two different cooling modes (i.e. controlled and natural) on the solvent crystallization of dihydroxystearic acid (DHSA) was carried out. The effects of operating temperature and the time on the crystal size distribution (CSD), purity and yield of crystallized DHSA were studied. The crystal purity and average crystal particle size increased with temperature, but the crystal yield decreased as the temperature increased. The controlled cooling crystallization process initially resulted in better crystal properties compared to natural cooling crystallization. However, towards the end of the crystallization process, only marginal differences in terms of crystal properties were observed. Effects of Temperature and Cooling Modes on Yield, Purity and Particle Size Distribution of Dihydroxystearic Acid Crystals 47

Abdullah

Baru 43650 Bandar

Ehsan Selangor Darul

Feng Ling

Gregory Koay

Luqman Chuah

Malaysia Robiah Ehsan

Malaysia Thomas

S Y Choong

Salmiah Ahmad

Selangor Darul Bangi

Sumaiya Zainal Abidin

Yunus

CiteSeerX

European Journal of Scientific Research 
ISSN 1450-216X Vol.33 No.3 (2009), pp.471-479 
© EuroJournals Publishing, Inc. 2009 
http://www.eurojournals.com/ejsr.htm 
 
 
Effects of Temperature and Cooling Modes on Yield, Purity and 
Particle Size Distribution of Dihydroxystearic Acid Crystals 
 
 
Sumaiya Zainal Abidin 
Faculty of Chemical and Natural Resources Engineering 
Universiti Malaysia Pahang, Lebuhraya Tun Razak, 26300 Gambang 
Kuantan, Pahang Darul Makmur, Malaysia 
 
Gregory Koay Feng Ling 
Mewah Oils & Fats Pte Ltd, 5, International Business Park, Singapore 609914 
 
Luqman Chuah Abdullah 
Department of Chemical and Environmental Engineering, Faculty of Engineering 
Universiti Putra Malaysia, 43400 UPM Serdang, Selangor Darul Ehsan, Malaysia 
Institute of Tropical Forestry and Forest Products (INTROP), Universiti Putra Malaysia 
43400 UPM Serdang, Selangor Darul Ehsan, Malaysia 
E-mail: chuah@eng.upm.edu.my 
Tel: +60-3-89472176; Fax: +60-3-89472180 
 
Salmiah Ahmad 
Advanced Oleochemical Technology Division, Malaysian Palm Oil Board 
43650 Bandar Baru Bangi, Selangor Darul Ehsan, Malaysia 
 
Robiah Yunus 
Department of Chemical and Environmental Engineering 
Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang 
Selangor Darul Ehsan, Malaysia 
 
Thomas S. Y. Choong 
Department of Chemical and Environmental Engineering 
Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang 
Selangor Darul Ehsan, Malaysia 
 
 
Abstract 
 
An investigation into the effects of temperature and two different cooling modes 
(i.e. controlled and natural) on the solvent crystallization of dihydroxystearic acid (DHSA) 
was carried out. The effects of operating temperature and the time on the crystal size 
distribution (CSD), purity and yield of crystallized DHSA were studied. The crystal purity 
and average crystal particle size increased with temperature, but the crystal yield decreased 
as the temperature increased. The controlled cooling crystallization process initially 
resulted in better crystal properties compared to natural cooling crystallization. However, 
towards the end of the crystallization process, only marginal differences in terms of crystal 
properties were observed. 
Effects of Temperature and Cooling Modes on Yield, Purity and Particle Size Distribution of 
Dihydroxystearic Acid Crystals 472 
 
Keywords: Crystallization; agglomeration; purification; dihydroxystearic acid; crystal 
size distribution 
 
1.  Introduction 
In today’s world, natural ingredient derived from vegetable oil are widely used within the personal care 
segment. The personal care industry has shown great interests in hydroxyl fatty acids, which are useful 
intermediates in the synthesis of fine chemical products (Awang et al, 2001; Ismail et al, 2006). Palm 
based dihydroxystearic acid (DHSA) is one of the plant based hydroxyl fatty acids which can be 
produced from oleic acid via epoxidation with formic acid followed by hydrolysis of the epoxide 
(Awang et al, 1998; Koay et al, 2006) The presence of hydroxyl and carboxyl groups in DHSA 
provided various reaction sites for the preparation of many useful derivatives. Studies have shown that 
DHSA is suitable as thickener, gelling agent, binding agent, mechanical properties booster and pigment 
dispersion enhancer in the formulation of decorative cosmetics (Awang et al, 2001; Ismail et al, 2006). 
The crude waxy DHSA can be purified by employing solvent crystallization as the purification method 
in order to remove the imbedded impurities, such as octanoic and decanoic acids. 
In commercial crystallization, yield and purity are not the only important aspect but also the 
crystal size distribution (CSD). Industrial crystallization demands for narrow range of CSD and 
regularity which result in good storage and transportation properties, free flowing nature and pleasant 
appearance (Timms, 1985). The crystal properties are affected by the crystallization temperature and 
the initial cooling rate. Controlled cooling crystallization demands very low supersaturation rate and 
hence very low cooling rate in the early stage of crystallization. Natural cooling crystallization is the 
simplest with no temperature control, resulting in very high initial cooling rate when the temperature 
driving force (temperature gradient) is the greatest. 
The objectives of this work are to investigate the effect of (i) crystallization temperature, and 
(ii) initial cooling rate on yield, purity and CSD of the DHSA crystals. The information obtained will 
be useful for process control of the crystallization to produce crystals of desired properties. 
 
 
2.  Materials and Methods 
2.1. Equipment Operation 
The investigation into controlled cooling crystallization was carried out using a fabricated crystallizer, 
which can take up to 12 samples at any one time. The process flow diagram is shown in Figure 1. The 
temperature of the tank is controlled by balancing between pulse heating and cooling. The heating 
achieved via an in-line heater and the cooling is achieved via a chiller. The desired cooling rate and 
crystallization temperature can be activated through a programmable logical controller (PLC). The 
non-control cooling (natural cooling) crystallization was performed in a conditioned room with an 
ambient temperature of 24°C. 
473 Sumaiya Zainal Abidin, Gregory Koay Feng Ling, Luqman Chuah Abdullah, 
Salmiah Ahmad, Robiah Yunus and Thomas S. Y. Choong 
 
 
Figure 1: Process flow diagram of the fabricated controlled cooling crystallizer. 
 
 
 
2.2. Experimental Procedures 
Twelve beakers with 250g of crude DHSA each were melted in an oven to a temperature around 80°C 
for 24 hours to ensure complete melting and the destruction of all crystal memories. The molted DHSA 
was then mixed with ethanol at 1:1 w/v ratio, where the solution temperature was found to be around 
65°C. Before the samples were placed into the chamber, the crystallizer was preheated to the same 
temperature (65°) to ensure that there was no excess heat applied to the solutions which might 
contribute to solvent evaporation. The cooling rate was fixed at 0.6°Cmin-1. The temperature-time 
profiles were recorded every 5 minutes. The crystallization process was carried out for 12 hours. The 
crystals obtained were then segregated from the mother liquor through a vacuum filtration system. The 
filter media was of nylon fabric with 10μm pore diameter. The crystals were then transferred into petri 
dishes and dried in an oven at 50°C for 48 hours. For natural cooling crystallization, the 12 samples 
were placed in a conditioned room with an ambient temperature of 24°C for 12 hours. The time-
temperature profile was obtained by recording the temperature at 5 minutes interval for the first three 
hours and 30 minutes interval after that till the crystallization process ended. All experiments were 
carried out in triplicates and repeated twice to ensure consistency and reproducibility. 
 
2.3. Materials and Analytical Methods 
The product yield is determined by dividing the amount of product formed with the amount of raw 
material being used, in percentage value. The Gas chromatography (GC) analysis was carried out using 
a Hewlett-Packard HP-6860A Plus gaschromatograph (Palo Alto, CA). The DHSA samples had to 
undergo silylation process before being injected into the GC equipment. The silylation process was 
carried out by preparing the trimethylsilyl (TMS) derivatives of DHSA where 0.01g of DHSA was 
weighted into a vial followed with the insertion of 2 ml of N, Ndimethylformamide (DMF) and 1ml of 
Bis(trimethylsilyl)trifluoroacetamide (BTSFA). The vial was then vortexed for 30 seconds in order for 
the content to achieve homogeneous mixing before being incubated at 60°C for 30 minutes. The 
derivatives were allowed to cool down for a few minutes. About 1.5ml of the derivatives was then 
transferred into a 2 ml clear wide opening crimp vial laced with a very small amount of sodium 
sulphate anhydrous. The vial was sealed off and injection followed. The derivatives concoction was 
Effects of Temperature and Cooling Modes on Yield, Purity and Particle Size Distribution of 
Dihydroxystearic Acid Crystals 474 
 
separated on a non-polar column, HP-5 (Hewlett-Packard, 30 m × 0.25 mm × 0.25 µm) with helium as 
the carrier gas. 
The oven was programmed to hold at 150°C for one minute, followed by ramping from 150 to 
290°C at a rate of 10°C per minute. The final temperature was held at 290°C for 30 minutes. The 
injector and flame-ionization detector were set at 300°C. 
 
2.4. Crystal Size Distribution Analysis 
The crystal size distribution (CSD) analysis was carried out by determining the wet dispersion laser 
diffraction measurements using Malvern Instruments Mastersizer 2000 and Hydro 2000S particle size 
analyzer (United Kingdom). The equipment was set to process the particle size ranging from 0.020 to 
2000.000 µm. The Mie-Scattering analysis model was chosen for the measurement of the diffraction 
pattern. The principal was based on simultaneous multi angle detection of scattered light where the 
scattering behavior was strongly dependent on the particle size. In this analysis, the reflective index 
(RI) of the particle, DHSA, was 1.520 while the RI of the dispersant, water, was 1.330. The 
Mastersizer 2000’s operating procedures were set to record the background measurement for 20 
seconds followed by sample measurement for 20 seconds. A small amount of DHSA crystal samples 
were then inserted into the designated vessel containing water, where they were introduced into the 
dispersion module, until an adequate obscuration level was obtained and the laser obscuration was 
stable (± 0.2%). The ideal obscuration level ranged from 10.0 to 20.0. A total of three measurement 
cycles were carried out for each sample and the average value was taken as the final result. The crystal 
particles’ specific surface area, surface weighted and volume weighted mean diameters were 
determined along with the d(0.1)-, d(0.5)- and d(0.9)-cumulative undersize. 
 
 
3.  Results and Discussion 
3.1. Effects of Temperature on Controlled Crystallization of DHSA 
For controlled cooling, the samples in the crystallizer were cooled from 65°C to three different 
temperatures, i.e. 24, 26 and 28°C, respectively, as shown in Figure 2. The crystallization temperature 
was achieved within two hours of cooling. Sufficient amount of crystals needed for chemical and 
physical analysis were obtained after 4 to 6 hours form the initiation of the crystallization process. The 
cooling profiles were found to have similar patterns for all temperatures. 
 
Figure 2: Comparison on time-temperature profile for three crystallization temperatures 
 
 
 
475 Sumaiya Zainal Abidin, Gregory Koay Feng Ling, Luqman Chuah Abdullah, 
Salmiah Ahmad, Robiah Yunus and Thomas S. Y. Choong 
 
 
The percentage of crystals deposited from the solution versus the solute weight is presented in 
Figure 3. As expected, the crystal yields increased with time. At the end of the crystallization process, 
the yields are 35.8, 28.8 and 7.3% for temperature of 24, 26 and 28°C, respectively. Crystal yield 
increased remarkably as temperature decreased. For an increment of 2°C, the first sampling time was 
delayed for a least an hour as the growth of DHSA crystals were lower and slower at higher 
temperature. 
Figure 4 shows the average crystal size versus time, measured according to volume weighted 
mean diameter. As temperature increased, average crystal size increased. At the early stage of 
crystallization, the crystals attracted with each other, forming large crystals. As time elapsed, 
individual crystals developed. Consequently, average crystal size remained approximately constant till 
the end of the crystallization process. Obvious fluctuation occurred for crystallization at 28°C because 
of low crystal yield. Only from the 11th hour onwards that more crystals were formed and thus 
segregating among themselves into individual crystals and remained almost constant after that. 
 
Figure 3: Comparison of DHSA yield for three crystallization temperatures. 
 
 
 
Figure 4: Comparison of average crystal size for three crystallization temperatures. 
 
 
 
However, higher crystallization temperature produced purer DHSA crystals, as shown in Figure 
5. Nevertheless, the increase of purity over the crystallization time was relatively small, 90.1 to 91.7, 
92.5 to 93.9 and 94.1 to 94.7% for temperatures of 24, 26 and 28°C, respectively. Earlier, it was 
established that the crystallization temperature of 24°C yielded crystals of lower average particle size. 
Crystals with smaller particle size has higher probability of entrapping mother liquor (Saito et al, 
Effects of Temperature and Cooling Modes on Yield, Purity and Particle Size Distribution of 
Dihydroxystearic Acid Crystals 476 
 
2000), thus compromising the overall product purity, which was what exactly happening as the 
temperature decreased from 28 to 24°C. 
 
Figure 5: Comparison of crystal purity for three crystallization temperatures. 
 
 
 
3.2. Controlled Cooling Crystallization versus Natural Cooling Crystallization 
To investigate the effect of initial cooling rate on the crystal properties, the crystallization temperature 
of 24°C was selected. Figure 6 shows the temperature-time profile for the natural cooling and the 
controlled cooling modes. The cooling rate of the natural cooling was much faster than the controlled 
cooling, thus resulting in steeper temperature reduction. After the 200th minutes, the ambient 
temperature for both cooling conditions converged (Figure 6). 
 
Figure 6: Comparison of temperature-time profile for two cooling modes. 
 
 
477 Sumaiya Zainal Abidin, Gregory Koay Feng Ling, Luqman Chuah Abdullah, 
Salmiah Ahmad, Robiah Yunus and Thomas S. Y. Choong 
 
 
Figure 7: Comparison of yield for two cooling conditions. 
 
 
 
Figure 7 shows the yield from controlled and natural cooling crystallization. At the initial stage, 
very little crystals were formed for both cooling modes. The yield for the controlled cooling increased 
substantially after 6 hours. There was initially a big difference in yields between the controlled and 
cooling modes. However, as the crystallization proceeded, the yields for both cooling modes were 
almost the same at the end of the crystallization process. The purity of the crystals as shown in Fig. 8 
demonstrated only a small difference within the 12-hours crystallization time. The purity of crystals 
from controlled cooling crystallization was from 90.1 to 91.7% while for natural cooling was from 88.2 
to 89.8%. It was therefore important to have good control in the early stage of crystallization as this 
would produce crystals with higher purity. Controlled cooling produced slightly higher purity crystals 
compared to natural cooling mode. 
 
Figure 8: Comparison of product purity for two cooling conditions. 
 
 
Effects of Temperature and Cooling Modes on Yield, Purity and Particle Size Distribution of 
Dihydroxystearic Acid Crystals 478 
 
Figures 9 (a-d) show the CSD from two different cooling modes. Comparisons were made on 
the CSD from the sixth hour onwards as amount of nuclei formed before sixth hour was rather 
insignificant. At the sixth hour (Fig 9(a)), natural cooling yielded CSD curve which skewed to the 
right, and controlled cooling yielded balanced a unimodel CSD curve. The median crystal size for 
controlled cooling is 167μm; the median crystal size for natural cooling is 348μm. This was because 
uncontrolled cooling occurred during the initial stage of natural cooling (Fig. 6), contributing towards 
uncontrolled crystal sizes distribution. Through proper control of temperature, the broadness of the 
CSD curve could be narrowed. From the eighth hour onwards, both modes produced unimodel CSD 
curve. The median data showed that the controlled cooling produce slightly smaller crystals and 
narrower CSD curve compared to natural cooling. However, the difference between crystals produced 
using the two different cooling modes is only marginal at the end of crystallization process. 
 
Figure 9: (a) CSD curve for natural and controlled cooling at the sixth hour. (b) CSD curve for natural and 
controlled cooling at the eighth hour. (c) CSD curve for natural and controlled cooling at the tenth 
hour. (d) CSD curve for natural and controlled cooling at the twelfth hour. 
 
 
0
2
4
6
8
10
12
1 10 100 1000 10000
V
o
lu
m
e,
 %
Crystal Size, micron
Controlled Cooling
Natural Cooling
 
 
0
2
4
6
8
10
12
1 10 100 1000 10000
V
ol
um
e,
 %
Crystal Size, micron
Controlled Cooling
Natural Cooling
(a) (b) 
 
0
2
4
6
8
10
12
1 10 100 1000 10000
V
ol
um
e,
 %
Crystal Size, micron
Controlled Cooling
Natural Cooling
 
0
2
4
6
8
10
12
1 10 100 1000 10000
V
ol
um
e,
 %
Crystal Size, micron
Controlled Cooling
Natural Cooling
(c) (d) 
  
 
 
4.  Conclusion 
Three operating temperatures were studied for the crystallization of DHSA. The crystal yield was 
found to be very sensitive to the operating temperature. The yield dropped substantially from 36% at 
24°C to 7% at 28°C. Higher operating temperature produced crystals of higher purity and bigger size. 
479 Sumaiya Zainal Abidin, Gregory Koay Feng Ling, Luqman Chuah Abdullah, 
Salmiah Ahmad, Robiah Yunus and Thomas S. Y. Choong 
 
 
Both yield and purity from natural cooling were slightly lower compared to the controlled cooling. 
Although initially the yield for the natural cooling mode was much lower than the controlled cooling, 
the quantity of crystals for natural cooling mode increased as time elapsed. At the end of crystallization 
process, the two different cooling modes produced crystals on similar quality and quantity. 
 
 
References 
[1] Awang, R., Ahmad, S. and Ghazali, R. (2001). “Properties of sodium soap derived from palm-
based dihydroxystearic acid” Journal of Palm Oil Research 13(2): 33-38. 
[2] Ismail Z., Ahmad S., Ismail R., Rigano L. 2006. “The advantages of palm-based dihydroxy 
stearate in deodorant sticks” Journal of Dispersion Science and Technology 27, pp. 463-467. 
[3] Roila, A., Salmiah, A. and Kang, Y. B. 1998. “Preparation of dihydroxy fatty acid from oleic 
acid” Malaysian Patent 9804456. 
[4] Koay G.F.L., Abdullah L.C., Yunus R., Thomas Choong S.Y., Siwayanan P., Ahmad S. 2006. 
“Crystallization of dihydroxystearic acid produced from commercial grade palm oil based crude 
oleic acid employing isopropyl alcohol as solvent” International Journal of Engineering and 
Technology. 3, pp.115-124. 
[5] Timms R.1985. PORIM Palm and Palm Kernel Oil Processing Course Monograph, Malaysian 
Palm Oil Board, Kuala Lumpur, p.10. 
[6] Saito N., Yokota M., Fujiwara T., Kubota N. 2000. “Liquid inclusions in crystals produced in 
suspension crystallization” Chemical Engineering Journal 79(1), pp. 53-59. 
 


Effects of Temperature and Cooling Modes on Yield, Purity and Particle Size Distribution of Dihydroxystearic Acid Crystals

http://citeseerx.ist.psu.edu/viewdoc/download;jsessionid=48948DA5D4E3EDC480BAF93E62AF4911?doi=10.1.1.1044.9841&rep=rep1&type=pdf

Effects of Temperature and Cooling Modes on Yield, Purity and Particle Size Distribution of Dihydroxystearic Acid Crystals

Abstract

Similar works

Full text

Available Versions

CiteSeerX