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Synthesis and performance analysis of oil palm ash (OPA) based adsorbent as a palm oil bleaching material
Journal of Cleaner Production 139 (2016) 1098e1104
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Short communication
Synthesis and performance analysis of oil palm ash (OPA) based adsorbent as a palm oil bleaching material Caleb Acquah a, b, Lau Sie Yon a, Zarina Tuah a, Ngu Ling Ngee a, Michael K. Danquah a, * a b
Department of Chemical Engineering, Curtin University, 98009 Sarawak, Malaysia Curtin Sarawak Research Institute, Curtin University, 98009 Sarawak, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 June 2016 Received in revised form 29 August 2016 Accepted 1 September 2016 Available online 3 September 2016
Bleaching is a vital step in crude palm oil (CPO) processing due to its importance for both decolourisation and removal of impurities present in the oil. The commonly used material for CPO bleaching is bleaching earth. However, there are associated environmental issues due to its disposal without pre-treatment, and the retention of significant quantities of oil during the bleaching process. It is therefore imperative to research into viable alternative bleaching materials which are economical, readily available and able to undergo successive regeneration while minimizing oil loss. The present work probed the performance of enhanced oil palm ash (OPA), as an alternate bleaching adsorbent. The performance of the bleaching process was investigated by engineering critical process parameters such as stirring speed, adsorbent dosage, regenerability and ash particle sizes. The effective particle size of OPA was determined to be 212 e300 mm, resulting in a maximum bleaching efficiency of 97.3%. A stirring speed of 800 rpm was optimal irrespective of the adsorbent particle size. In addition, a high adsorbent-to-CPO dosage ratio was identified to be effective for successive numbers of regeneration with less retention of oil. Indications from this analyses are that a higher bleaching performance can be obtained by optimizing relevant process conditions of OPA as an adsorbent. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Oil palm ash Bleaching Adsorbent Crude palm oil Optimization
1. Introduction Palm fruits are made up of exocarp (skin), mesocarp (which contain palm oil and water in fibrous matrix), endocarp (shell) and kernel (the seed containing oil and meal). Oil extracted from the mesocarp is known as the palm oil. Due to its health and nutritional value, palm oil has become an important vegetable oil in the global market, being the largest traded vegetable oil in the world (GarciaNunez et al., 2016; Norazlan et al., 2006; Xiao et al., 2016). The crude palm oil refining industry plays an important role in producing high purity and high stability palm oil products. Bleaching process is one of the most vital steps in crude palm oil processing as it is not only used for colour removal but also effectively removes the residual amounts of phospholipids, mucilage, oxidized tri-or partial acyl-glycerols as well as metal traces in ionisable and non-ionisable forms (Girgis, 2005). This absorption process has added significant operating cost to the crude palm oil processing industry (Norazlan et al., 2006). Basically, there are two
* Corresponding author. E-mail address: [email protected] (M.K. Danquah). http://dx.doi.org/10.1016/j.jclepro.2016.09.004 0959-6526/© 2016 Elsevier Ltd. All rights reserved.
methods available for palm oil refining and these are physical and chemical refining. Physical refining is more favourable because it has been proven to be more cost effective, efficient and requires only simple effluent treatment (Swern, 1982). Physical refining consists of two-step operations which are pre-treatment and deodorization. Palm oil industries produce a significant amount of empty fruit bunches (EFB), oil palm fibres, and oil palm shells as wastes (Islam et al., 2016; Ranjbar et al., 2016). The conventional method to discard these wastes is by incineration in the boilers as fuels for steam production in the oil palm mill. However, this method raises some environmental concerns due to the production of excessive amount of black soot during combustion and the production of large amounts of ash. Previous studies have shown the possibility of using OPA as a cement replacement material (Ahmad et al., 2008; Mujah, 2016), enhancement of soft soil conditions (Mujah et al., 2015), and as an adsorbent for the removal of zinc from aqueous solution (Zainudin et al., 2005). Nevertheless, a significant quantity of OPA is still disposed to landfills requiring large hectares of land; due to limited applications till date (Islam et al., 2016). Bleaching earth is one of the common bleaching materials used
C. Acquah et al. / Journal of Cleaner Production 139 (2016) 1098e1104
for bleaching process in palm oil industries. According to Loh and his team, bleaching earth is used to remove colour, phospholipids, oxidized products, metals and residual gums from the oil (Loh et al., 2007). However, it also absorbs approximately 20e40% by weight of oil during the process (Loh et al., 2013; Zainudin et al., 2005). This spent bleaching earth is disposed to landfills without pretreatment. Hence, to avoid the loss of significant amounts of oil and reduce the associated environmental impacts, the search for an alternate bleaching material, which is abundant in nature and can be regenerated for repeated use, has been a major research endeavour. This paper presents the synthesis and application of a low-cost bleaching adsorbent from oil palm ash (OPA) as a sustainable and viable alternative to bleaching earth, as shown in Fig. 1. The effects of key synthesis parameters such as stirring speed, morphology of adsorbent, adsorbent dosage, regenerability and ash particle sizes to yield an effective bleaching performance for the synthesized adsorbent (enhanced OPA) were investigated. It is anticipated that the outcome of this result will be of tremendous benefit to the palm oil refinery industry by enhancing reusability and recyclability of internally generated waste.
2. Experimental 2.1. Synthesis of adsorbent using oil palm ash OPA was obtained from Kirana Palm Oil Refinery in (Kuching, Sarawak) and sieved to obtain ashes with particulate size within
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the following ranges: <75 mm, 75e212 mm, 212e300 mm and 300e425 mm. Ashes with different particulate sizes were used to synthesize adsorbents in order to investigate the impact on the bleaching performance. The adsorbents were synthesized using the method proposed by Zainudin et al. (2005). The mass ratio of OPA to calcium hydroxide Ca(OH)2 used for the synthesis was 3:1. Briefly, a beaker was filled with 100 mL of deionized water and heated up to 65 C. 5 g of Ca(OH)2 was added to the water and stirred until the slurry reached 80 C. 15 g of OPA and 1 g of calcium sulphate (CaSO4) were added to constitute an OPA to Ca(OH)2 mass ratio of 3:1. The slurry mixture was well mixed and put inside a 100 C furnace for a 30 h hydration process. After the hydration process, the resulting slurry was filtered and dried in an oven at 200 C for 2 h.
2.2. Bleaching of crude palm oil Crude palm oil (CPO) in its' container was well shaken followed by the transfer of 150 mL of it into a beaker. The beaker was then heated to reach 100 C. 0.05 wt% of phosphoric acid was added to the CPO for degumming the mixture, followed by the addition of the synthesized adsorbent. The mixture was heated up to 150 C and stirred vigorously for 1 h. To study the effect of stirring speed on the bleaching performance; the stirring speed was varied between 200 rpm and 800 rpm while keeping other parameters constant. After the bleaching process was completed, the spent adsorbent was separated from bleached palm oil (BPO) by filtration
Fig. 1. Process cycle for sustainable generation and application of oil palm ash as a bleaching adsorbent in palm oil production.
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using Buchner funnel. The filtration process was carried out in the oven at 80 C for 22 h. Spent adsorbent was collected for regeneration. 2.3. Soxhlet extraction for adsorbent regeneration Soxhlet extraction was applied in the regeneration of spent adsorbents due to its simplicity and insolubility of the spent solid adsorbent in the solvent (hexane). Two boiling chips were added to a flat bottom flask and weighed. Hexane was then added into the flat bottom flask until it was half full, thereafter, the adsorbent was folded in a filter paper and placed inside a thimble before fixing it in the Soxhlet extractor to ensure the adsorbents do not spill over. A vertical condenser was connected above the Soxhlet extractor and two water pipes were connected to the inlet and outlet of the condenser for cooling. The hexane was heated to 200 C for extraction and the process was completed after 6e8 h. The extracted adsorbent slurry was dried in an oven at 105 C for 1 h to remove residual hexane solvent. The hexane was regenerated using rotary evaporator and collected with a condenser. 2.4. Adsorbent calcination for reuse The spent adsorbent was activated by calcinations before reuse. In this process, the adsorbent was placed in a crucible and heated. The furnace was set to a temperature of 400 C for 4 h in the furnace for calcinations to occur. The fume hood was turned on during calcinations to prevent inhalation of poisonous gases released during the process.
synthesized adsorbent (particulate size 75e212 mm) obtained using BET analysis are shown in Table 2. The characteristics of bleaching earth and acid activated bleaching earth (montmorillonte) are also presented for comparison. It can be observed that the raw oil palm ash has low BET surface area (22.9 m2/g), total pore volume (0.015 cm3/g) and average pore diameter (0.26 nm). After synthesis, the BET surface area of the resulting adsorbent of particulate size 75e212 mm increased slightly but still at a lower end, relatively. The total pore volume also increased slightly, while the average pore diameter increased significantly, implying that there was a structural change during the synthesis process. This structural change is as a result of the optimised hydration period to ensure complete pozzolanic reaction during the synthesis of the enhanced OPA adsorbent as previously established by Zainudin et al. (2005). Compared to bleaching earth and activated bleaching earth, the synthesized adsorbent had much lower BET surface area and total pore volume. The surface area of the adsorbent can be improved by reducing the particulate size to offer a large molecular interactive area during bleaching. However, increase in the pore diameter as observed was essential to enhance the convective mass transport required for a rapid bleaching process. SEM images of raw oil palm ash sample and synthesized adsorbents are shown in Fig. 2a and b respectively. In both cases, particles with uneven surface and non-uniform structure were observed. Agglomerates were formed on the surface of particles. The morphology of the synthesized adsorbent shows a porous matrix with large interstitial pores, confirming the increase observed for the average pore diameter. 3.2. Effect of ash particulate size on bleaching performance of adsorbent
2.5. Sample characterisation The chemical compositions of oil palm ash were determined using Shimadzu 1700 X-ray Fluorescence (XRF) Spectrophotometer. The surface morphologies of both the raw oil palm ash and the synthesized adsorbent were observed using a Scanning Electron Microscope (SEM). Brunauer-Emmett-Teller (BET) analysis was used to determine the surface area and pore characteristics of the oil palm ash and the synthesized adsorbents. 3. Results and discussion 3.1. Characterisation of raw oil palm ash and synthesized adsorbent Table 1 lists the chemical composition of the raw oil palm ash sample using XRF analysis. As shown in Table 1, the raw oil palm ash is mainly composed of Si-oxides, with minimal amounts of Al-, Feand Mg-oxides. Though the XRF analysis was performed with a raw palm oil ash sample of particulate size 75e212 mm, it does not affect the general compositional characteristics of the overall sample. Pore characteristics of the raw oil palm ash sample and the
Table 1 Chemical composition of the raw oil palm ash sample with particulate size 75e212 mm obtained via XRF analysis. Oxide
Percentage, %
Silicon oxide, SiO2 Aluminium oxide, Al2O3 Iron oxide, Fe2O3 Magnesium oxide, MgO Manganese dioxide, MnO2 Chromium oxide, Cr2O3 Rhodium oxide, Rh2O3 Ruthenium oxide, RuO2
86.44 6.49 4.08 1.51 0.10 0.69 0.41 0.29
Lovibond Model F was applied for colour analysis. Fig. 3a and b shows the colour indices of bleached palm oil (BPO) samples using 5 ¼ʺ and 1” glass cells, respectively. From Fig. 3a, the colour indices of ash particle with sizes of <75 mm, 75e212 mm, 212e300 mm and 300e425 mm, obtained using 5 ¼” glass cell, are 4 R, 4.4 R, 2.1 R and 4.3 R, respectively. This indicates that all the selected ash particle sizes are effective in bleaching crude palm oil as they meet the colour standard required by Palm Oil Refiners Association of Malaysia (PORAM), which is 20 R for 5 ¼” glass cell (PORAM, 2013). The ash particles with size 212e300 mm demonstrated the best bleaching performance, and this represents the optimal ash particle size range required to enhance the mass transfer through both particulate and interstitial pores of the adsorbent while maintaining the characteristic surface area required for effective adsorbentCPO interactions. The colour indices (using 5 ¼ʺ glass cell) of regenerated adsorbent samples with ash particle sizes of <75 mm, 75e212 mm, 212e300 mm and 300e425 mm are 3.4 R, 5.4 R, 3.4 R and 4.5 R, respectively. The regenerated samples also meet the industry standard, demonstrating the stability of the adsorbent particles for repeated use and the cost savings associated with it. The colour index for fresh CPO obtained using 1” glass cell test was 22 R. The percentage of colour reduction was determined using the result obtained from 1” glass cell as the colour of fresh crude palm oil (CPO) was too dark to be detected by 5 ¼ʺ glass cell. The percentage of oil bleached for each adsorbent sample was calculated and presented in Table 3. The colour reduction for regenerated adsorbents was generally slightly lower than fresh adsorbents, and this was due to the possible presence of traces of impurities retained in the particle pore which decreases the adsorption efficiency of the adsorbent. As mentioned earlier, the adsorbent with ash particle size 212e300 mm presented the optimal bleaching efficiency. These findings do not concur with the studies done by
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Table 2 Pore and surface characteristics of the raw oil palm ash sample, synthesized adsorbent with size 75e212 mm and bleaching earth with P/Po as relative pressure.
BET surface area (m2/g) Total pore volume at P/P0 0.97349186 (cm3/g) Average pore diameter (nm)
Raw oil palm ash
Synthesized adsorbent
Montmorillonite activated with acid treatment (Tsai et al., 2002)
Bleaching earth (Hassan, 2006)
22.98 0.02 0.26
32.21 0.10 1.19
268 0.36 0.54
157 0.29 e
Girgis (2005). According to their studies, adsorbent with ash smaller particle size gives higher adsorption capability due to the shorter diffusion path of the colouring matter in the oil to the adsorbent surface. Adsorbent with smaller ash particle size has larger surface area but with reduced porosity. Whilst this enhances particle-oil interactions, the pores should be large enough to increase the adsorption and retention capacities without significantly compromising the surface area. It should be noted that the porous structure of ash particles depends on the composition of the ash. The ash used in this experiment was boiler ash consisting of empty fruit bunches (EFB), mesocarp fibres, and shells. The pore structure of the individual materials differed and potentially presents nonuniformity in the bleaching performance. 3.3. Effect of adsorbent dosage on bleaching performance In this section, the effect of oil palm ash adsorbent dosage on
bleaching performance is investigated to probe any possible variation in the optimal dosage due to physicochemical characteristics of the adsorbent. The ratios 1:08, 1:09, 1:10 and 1:11 were tested with results presented in Fig. 4. As mentioned by Wambu and co-worker, increasing the adsorbent loading increases the quantity of dye adsorbed as there is an increase in available adsorptive surface for interaction (Wambu et al., 2011). From Fig. 4, it can be observed that a further increase in the adsorbent dosage above the ratio 1:09 does not influence the colour of the bleached oil. This represents the partitioning concentration of oil coloured matter established at the equilibrium point for a fixed concentration of the bulk liquid phase and constant process conditions. This observation was in keeping with that reported by Ajemba and Onukwuli (2013). They reported that further increase in the adsorbent dosage does not increase in bleaching efficiency. This occurrence was because of the establishment of adsorption equilibrium between the adsorbent and the oil mixture, thus preventing further pigment removal. 3.4. Effect of adsorbent dosage on oil retention From the graph shown in Fig. 5, it can be observed that most of the residual oil obtained from the spent adsorbent is within the
Fig. 2. Surface morphology of (a) raw oil palm ash and (b) synthesized adsorbent at a magnification of 5000.
Fig. 3. Plot of colour indices against particulate size using (a) 5 1/400 glass cell and (b) 100 glass cell for bleached palm oil (BPO).
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Table 3 Percentage colour reduction using fresh and regenerated adsorbents. Ash particle size range (mm)
Percentage colour reduction (using fresh adsorbent) (%)
Percentage colour reduction (using regenerated spent adsorbent) (%)
<75 75e212 212e300 300e425
94.1 96.4 97.3 95
94.5 92.3 95.0 94.5
range of 23e50 wt % and this is acceptable. Zahrani and co-workers reported that the total oil content extracted from their spent adsorbent was 23 ± 2% of the weight of the spent clay (Al-Zahrani and Alhamed, 2000). According to Loh and his team, an average of 50 wt % residual oil is often extracted from spent adsorbents (Loh et al., 2007). The higher residual oil content observed for some of the results from Fig. 5 is due to the dissolution and entrapment of hexane solvent in the residual oil and not completely removed during the rotary evaporation process. It can also be observed that higher adsorbent dosage resulted in more oil retention, and this is due to poor accessibility of entrapped oil within the adsorbent matrix during evaporation. 3.5. Effect of stirring speed on bleaching performance Adsorbent with ash particle sizes 212e300 mm and 300e425 mm were used to study the effect of stirring speed on the bleaching
performance. The results are presented in Fig. 6a and b for analysis using 5 ¼ʺ and 1ʺ glass cells. From the results, it can be seen that stirring speed of 800 rpm demonstrated the best bleaching performance for both ash particle sizes, and this is due to improved interactions with the adsorptive surface of the adsorbent during mixing. From Table 4, it can be observed that the percentage of oil bleached increases with stirring speed. Enhanced mixing provides high fluidity in the bulk phase environment for improved intermolecular interactions between the adsorbent and the palm oil input. Under such conditions, the number of surface interactions between the adsorbent particles and the changing molecular units of palm oil per time is rapid, thus more palm oil molecules are exposed to the adsorbent surface. This shows that the stirring speed has a significant effect on the bleaching performance regardless of the ash particle size. In keeping the results from the colour test, the stirring speed of 800 rpm demonstrated the best bleaching performance. This result concurs with the finding of Rehman et al. (2012) and Devi et al. (2012). They reported that stirring enhances the contact between the adsorbent and the dye species. Another study conducted by Suyamboo and Perumal (2012) confirmed that the rate of diffusion of dye molecules from the bulk liquid to the liquid boundary layer surrounding the particle becomes higher with increasing stirring speed because of increase in turbulence which decreases the thickness of the liquid boundary layer. However, if the stirring speed exceeds beyond the effective conditions, the rate of adsorption will decrease, and this is attributed to a possible increase in the desorption tendency of oil molecules under turbulent conditions. This desorption tendency may be due to high mixing speeds which cause more energy input and higher shear forces, causing the bond between the oil and adsorbent to break.
Weight Percentage of Residual Oil (%)
Fig. 4. Colour results of BPO using a freshly synthesized adsorbent with different adsorbent to CPO ratio for the optimised adsorbent with ash particle size range of 75e212 mm was used.
70
FA
1st R
3rd R
4th R
2nd R
60 50 40 30 20 1:08
1:09 1:10 Adsorbent to CPO ratio
1:11
Fig. 5. Percentage weight of residual oil for different adsorbent to CPO ratios. Experiments were performed with adsorbent of ash particle size range of 75e212 mm.
Fig. 6. Colour index of bleached palm oil for different stirring speeds using (a) 1ʺ glass cell and (b) 5 ¼ʺ glass cell, respectively.
C. Acquah et al. / Journal of Cleaner Production 139 (2016) 1098e1104 Table 4 Percentage oil bleached for different stirring speeds and adsorbent particulate size. Stirring speed Percentage of oil bleached (rpm) (using 212e300 mm) (%)
Percentage of oil bleached (using 300e425 mm) (%)
200 400 600 800
56.5 69.6 97.8 98.2
82.6 90.8 95.7 96.5
The results show that the adsorbent with ash particle size of 300e425 mm gives comparable bleaching performance to the adsorbent with ash particle size of 212e300 mm at the effective stirring speed. As presented in Table 4, the percentage of bleached oil for adsorbent with ash particle size 300e425 mm is 98.2% and that of the adsorbent with particle size 212e300 mm is 96.5%. As stirring increases, the effect of particle size differences within a narrow range becomes insignificant at the optimal stirring speed to enhance bleaching contacts on the adsorbent surface. 3.6. Effect of adsorbent dosage on maximum number of adsorbent regeneration The adsorbents used to form the adsorbent-CPO ratios of 1:08, 1:09, 1:10 and 1:11 were continuously used to bleach CPO and regenerated until the collected oil samples shows orange colour as an indication of a very weak bleaching power of the adsorbent. The percentage regeneration efficiency for each adsorbent ratio is calculated. From the colour test, it is found that the maximum number of regenerations for adsorbent-CPO ratio1:08 is 5, 1:09 is 5, 1:10 is 5 and 1:11 is 3. The trend shows that, a higher dosage of adsorbent results in a higher maximum number of regeneration. This trend is similar to the findings by Sun et al. (2009). They reported that, the higher the adsorbent amount used, the more colour is washed out, which indicates that a higher regeneration efficiency is achieved. This results from a higher number of available adsorption sites with increasing adsorbent quantity. In general, the fresh adsorbent (FA) demonstrated a better bleaching performance in all the scenarios. The bleached palm oil showed orange colour when the bleaching was performed using a 2nd regenerated adsorbent in all the cases. As it can be deduced from Fig. 7, the adsorbent (at adsorbent to CPO ratio of 1:11) lost its bleaching power after 3rd regeneration, and this was validated by the colour of the bleached palm oil being almost same as the crude palm oil. This shows that the bleaching process is more efficient with freshly synthesized adsorbent compared to regenerated adsorbent. Boey et al. (2011) discussed the adsorption capacity of
Fig. 7. Colour test result for frequency of adsorbent regeneration at 1:08, 1:09, 1:10 and 1:11 adsorbent to CPO ratio for ash particle size range of 75e212 mm.
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regenerated adsorbent. It was reported that as the number of regeneration increases, more carbonized residues are entrapped in smaller pores of the matrix, resulting in the loss of specific surface area and pore volume. This could be explained by a study carried out by Wambu et al. (2011). It was shown that the rate of dye uptake is higher for fresh adsorbents and decreases gradually after each regeneration due to accumulated traces of impurities found in the pores of the adsorbents. 4. Conclusion From the present study, it can be concluded that OPA shows great potential in palm oil bleaching. The performance is affected by OPA particle size, the stirring speed, and the adsorbent loading. The adsorbent with ash particle size of 212e300 mm demonstrated the best bleaching performance under both fresh and regenerated conditions. It was also observed that the bleaching performance was higher for fresh adsorbent and decreased with regeneration. The use of higher stirring speed was found to have a positive effect on the percentage of oil bleached. In the study, it was shown that higher stirring speeds gave higher percentage of oil bleached. However, speeds above the effective, 800 rpm, could result in low bleaching efficiency due to desorption. Increase in adsorbent dosage significantly increases the total number of regeneration. Under conditions of the experiment, the highest achievable number of regeneration was 5 and this was demonstrated by adsorbent to CPO ratios of 1:08e1:09. Higher adsorbent loadings resulted in higher oil retention. The results demonstrate that high palm oil bleaching performance can be obtained sustainably using low-cost adsorbent materials at optimal process conditions. Future studies would aim at performing an extensive physicochemical characterisation of the OPA material along with modelling of the adsorption characteristics with a suitable kinetic isotherm. Acknowledgement The authors would like to thank Curtin University, Sarawak for providing the financial support for this project through the final year project funding scheme. References Ahmad, M., Omar, R., Malek, M., Noor, N.M., Thiruselvam, S., 2008. Compressive strength of palm oil fuel ash concrete. In: Proceedings of the International Conference on Construction and Building Technology, Kuala Lumpur, Malaysia, pp. 297e306. Ajemba, R.O., Onukwuli, O.D., 2013. Adsorptive removal of colour pigment from palm oil using acid activated Nteje clay. Kinetics, equilibrium and thermodynamics. Physicochem. Probl. Miner. Process. 49, 369e381. Al-Zahrani, A., Alhamed, Y., 2000. Oil removal from spent bleaching clay by solvent extraction. J. Environ. Sci. Health Part A 35, 1577e1590. Boey, P.-L., Ganesan, S., Maniam, G.P., 2011. Regeneration and reutilization of oilladen spent bleaching clay via in situ transesterification and calcination. J. Am. Oil Chem. Soc. 88, 1247e1253. Devi, B.V., Jahagirdar, A., Ahmed, M., 2012. Adsorption of chromium on activated carbon prepared from coconut shell. Adsorption 2, 364e370. Garcia-Nunez, J.A., Ramirez-Contreras, N.E., Rodriguez, D.T., Silva-Lora, E., Frear, C.S., Stockle, C., Garcia-Perez, M., 2016. Evolution of palm oil mills into biorefineries: literature review on current and potential uses of residual biomass and effluents. Resources. Conserv. Recycl. 110, 99e114. Girgis, A.Y., 2005. Reuse of discarded deactivated bleaching earth in the bleaching of oils. Grasas Aceites 56, 34e45. Hassan, S.N., 2006. Recovery of Spent Bleaching Clay for Reuse in Water Treatment (Thesis). Faculty of Chemical and Natural Resources Engineering, Universiti Teknologi Malaysia. Islam, M.M.U., Mo, K.H., Alengaram, U.J., Jumaat, M.Z., 2016. Mechanical and fresh properties of sustainable oil palm shell lightweight concrete incorporating palm oil fuel ash. J. Clean. Prod. 115, 307e314. Loh, S.K., Choo, Yuen May, Ngan, M.A., 2007. Residual Oil from Spent Bleaching Earth (SBE) for Biodiesel and Biolubricant Applications, Malaysian Palm Oil Board. Ministry of Plantation Industries and Commodities, Malaysia. Loh, S.K., James, S., Ngatiman, M., Cheong, K.Y., Choo, Y.M., Lim, W.S., 2013.
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Enhancement of palm oil refinery wasteeSpent bleaching earth (SBE) into bio organic fertilizer and their effects on crop biomass growth. Ind. Crops Prod. 49, 775e781. Mujah, D., 2016. Compressive strength and chloride resistance of grout containing ground palm oil fuel ash. J. Clean. Prod. 112, 712e722. Mujah, D., Rahman, M.E., Zain, N.H.M., 2015. Performance evaluation of the soft soil reinforced ground palm oil fuel ash layer composite. J. Clean. Prod. 95, 89e100. Norazlan, M., Aziz, A., Kamal, M., 2006. Process Design in Degumming and Bleaching of Palm Oil (Thesis). Universiti Teknologi, Malaysia, pp. 1e158. PORAM, 2013. Standard Specifications for Processed Palm Oil. Accessed from: http://econ.mpob.gov.my/economy/exporters/PORAM%20STANDARD.htm (Last accessed on: 29.08.16.). Ranjbar, N., Behnia, A., Alsubari, B., Birgani, P.M., Jumaat, M.Z., 2016. Durability and mechanical properties of self-compacting concrete incorporating palm oil fuel ash. J. Clean. Prod. 112, 723e730. Rehman, R., Abbas, A., Mahmud, T., Salman, M., Akbar, S., 2012. Thermodynamical and mechanistic studies of direct Red-28 dye adsorption on syzygium cumini stem. J. Chem. Soc. Pak. 34, 1156. Sun, K., Jiang, J.C., Xu, J.M., 2009. Decolorization and chemical regeneration of
granular activated carbon used in citric acid refining. Bull. Chem. Soc. Ethiop. 23, 29e36. Suyamboo, B.K., Perumal, R.S., 2012. Equilibrium, thermodynamic and kinetic studies on adsorption of a basic dye by Citrullus lanatus rind. Iran. J. Energy Environ. 3, 23e34. Swern, D., 1982. Bailey's Industrial Oil and Fat Products, fourth ed. John Wiley and Sons, Inc, New York. Tsai, W., Chen, H., Hsieh, M., Sun, H., Chien, S., 2002. Regeneration of spent bleaching earth by pyrolysis in a rotary furnace. J. Anal. Appl. Pyrolysis 63, 157e170. Wambu, E.W., Muthakia, G.K., Shiundu, P.M., 2011. Kinetics and thermodynamics of aqueous Cu (II) adsorption on heat regenerated spent bleaching earth. Bull. Chem. Soc. Ethiop. 25. Xiao, J., Wang, W., Wang, K., Liu, Y., Liu, A., Zhang, S., Zhao, Y., 2016. Impact of melting point of palm oil on mechanical and water barrier properties of gelatinpalm oil emulsion film. Food Hydrocoll. 60, 243e251. Zainudin, N.F., Lee, K.T., Kamaruddin, A.H., Bhatia, S., Mohamed, A.R., 2005. Study of adsorbent prepared from oil palm ash (OPA) for flue gas desulfurization. Sep. Purif. Technol. 45, 50e60.
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Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
Short communication
Synthesis and performance analysis of oil palm ash (OPA) based adsorbent as a palm oil bleaching material Caleb Acquah a, b, Lau Sie Yon a, Zarina Tuah a, Ngu Ling Ngee a, Michael K. Danquah a, * a b
Department of Chemical Engineering, Curtin University, 98009 Sarawak, Malaysia Curtin Sarawak Research Institute, Curtin University, 98009 Sarawak, Malaysia
a r t i c l e i n f o
a b s t r a c t
Article history: Received 13 June 2016 Received in revised form 29 August 2016 Accepted 1 September 2016 Available online 3 September 2016
Bleaching is a vital step in crude palm oil (CPO) processing due to its importance for both decolourisation and removal of impurities present in the oil. The commonly used material for CPO bleaching is bleaching earth. However, there are associated environmental issues due to its disposal without pre-treatment, and the retention of significant quantities of oil during the bleaching process. It is therefore imperative to research into viable alternative bleaching materials which are economical, readily available and able to undergo successive regeneration while minimizing oil loss. The present work probed the performance of enhanced oil palm ash (OPA), as an alternate bleaching adsorbent. The performance of the bleaching process was investigated by engineering critical process parameters such as stirring speed, adsorbent dosage, regenerability and ash particle sizes. The effective particle size of OPA was determined to be 212 e300 mm, resulting in a maximum bleaching efficiency of 97.3%. A stirring speed of 800 rpm was optimal irrespective of the adsorbent particle size. In addition, a high adsorbent-to-CPO dosage ratio was identified to be effective for successive numbers of regeneration with less retention of oil. Indications from this analyses are that a higher bleaching performance can be obtained by optimizing relevant process conditions of OPA as an adsorbent. © 2016 Elsevier Ltd. All rights reserved.
Keywords: Oil palm ash Bleaching Adsorbent Crude palm oil Optimization
1. Introduction Palm fruits are made up of exocarp (skin), mesocarp (which contain palm oil and water in fibrous matrix), endocarp (shell) and kernel (the seed containing oil and meal). Oil extracted from the mesocarp is known as the palm oil. Due to its health and nutritional value, palm oil has become an important vegetable oil in the global market, being the largest traded vegetable oil in the world (GarciaNunez et al., 2016; Norazlan et al., 2006; Xiao et al., 2016). The crude palm oil refining industry plays an important role in producing high purity and high stability palm oil products. Bleaching process is one of the most vital steps in crude palm oil processing as it is not only used for colour removal but also effectively removes the residual amounts of phospholipids, mucilage, oxidized tri-or partial acyl-glycerols as well as metal traces in ionisable and non-ionisable forms (Girgis, 2005). This absorption process has added significant operating cost to the crude palm oil processing industry (Norazlan et al., 2006). Basically, there are two
* Corresponding author. E-mail address: [email protected] (M.K. Danquah). http://dx.doi.org/10.1016/j.jclepro.2016.09.004 0959-6526/© 2016 Elsevier Ltd. All rights reserved.
methods available for palm oil refining and these are physical and chemical refining. Physical refining is more favourable because it has been proven to be more cost effective, efficient and requires only simple effluent treatment (Swern, 1982). Physical refining consists of two-step operations which are pre-treatment and deodorization. Palm oil industries produce a significant amount of empty fruit bunches (EFB), oil palm fibres, and oil palm shells as wastes (Islam et al., 2016; Ranjbar et al., 2016). The conventional method to discard these wastes is by incineration in the boilers as fuels for steam production in the oil palm mill. However, this method raises some environmental concerns due to the production of excessive amount of black soot during combustion and the production of large amounts of ash. Previous studies have shown the possibility of using OPA as a cement replacement material (Ahmad et al., 2008; Mujah, 2016), enhancement of soft soil conditions (Mujah et al., 2015), and as an adsorbent for the removal of zinc from aqueous solution (Zainudin et al., 2005). Nevertheless, a significant quantity of OPA is still disposed to landfills requiring large hectares of land; due to limited applications till date (Islam et al., 2016). Bleaching earth is one of the common bleaching materials used
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for bleaching process in palm oil industries. According to Loh and his team, bleaching earth is used to remove colour, phospholipids, oxidized products, metals and residual gums from the oil (Loh et al., 2007). However, it also absorbs approximately 20e40% by weight of oil during the process (Loh et al., 2013; Zainudin et al., 2005). This spent bleaching earth is disposed to landfills without pretreatment. Hence, to avoid the loss of significant amounts of oil and reduce the associated environmental impacts, the search for an alternate bleaching material, which is abundant in nature and can be regenerated for repeated use, has been a major research endeavour. This paper presents the synthesis and application of a low-cost bleaching adsorbent from oil palm ash (OPA) as a sustainable and viable alternative to bleaching earth, as shown in Fig. 1. The effects of key synthesis parameters such as stirring speed, morphology of adsorbent, adsorbent dosage, regenerability and ash particle sizes to yield an effective bleaching performance for the synthesized adsorbent (enhanced OPA) were investigated. It is anticipated that the outcome of this result will be of tremendous benefit to the palm oil refinery industry by enhancing reusability and recyclability of internally generated waste.
2. Experimental 2.1. Synthesis of adsorbent using oil palm ash OPA was obtained from Kirana Palm Oil Refinery in (Kuching, Sarawak) and sieved to obtain ashes with particulate size within
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the following ranges: <75 mm, 75e212 mm, 212e300 mm and 300e425 mm. Ashes with different particulate sizes were used to synthesize adsorbents in order to investigate the impact on the bleaching performance. The adsorbents were synthesized using the method proposed by Zainudin et al. (2005). The mass ratio of OPA to calcium hydroxide Ca(OH)2 used for the synthesis was 3:1. Briefly, a beaker was filled with 100 mL of deionized water and heated up to 65 C. 5 g of Ca(OH)2 was added to the water and stirred until the slurry reached 80 C. 15 g of OPA and 1 g of calcium sulphate (CaSO4) were added to constitute an OPA to Ca(OH)2 mass ratio of 3:1. The slurry mixture was well mixed and put inside a 100 C furnace for a 30 h hydration process. After the hydration process, the resulting slurry was filtered and dried in an oven at 200 C for 2 h.
2.2. Bleaching of crude palm oil Crude palm oil (CPO) in its' container was well shaken followed by the transfer of 150 mL of it into a beaker. The beaker was then heated to reach 100 C. 0.05 wt% of phosphoric acid was added to the CPO for degumming the mixture, followed by the addition of the synthesized adsorbent. The mixture was heated up to 150 C and stirred vigorously for 1 h. To study the effect of stirring speed on the bleaching performance; the stirring speed was varied between 200 rpm and 800 rpm while keeping other parameters constant. After the bleaching process was completed, the spent adsorbent was separated from bleached palm oil (BPO) by filtration
Fig. 1. Process cycle for sustainable generation and application of oil palm ash as a bleaching adsorbent in palm oil production.
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using Buchner funnel. The filtration process was carried out in the oven at 80 C for 22 h. Spent adsorbent was collected for regeneration. 2.3. Soxhlet extraction for adsorbent regeneration Soxhlet extraction was applied in the regeneration of spent adsorbents due to its simplicity and insolubility of the spent solid adsorbent in the solvent (hexane). Two boiling chips were added to a flat bottom flask and weighed. Hexane was then added into the flat bottom flask until it was half full, thereafter, the adsorbent was folded in a filter paper and placed inside a thimble before fixing it in the Soxhlet extractor to ensure the adsorbents do not spill over. A vertical condenser was connected above the Soxhlet extractor and two water pipes were connected to the inlet and outlet of the condenser for cooling. The hexane was heated to 200 C for extraction and the process was completed after 6e8 h. The extracted adsorbent slurry was dried in an oven at 105 C for 1 h to remove residual hexane solvent. The hexane was regenerated using rotary evaporator and collected with a condenser. 2.4. Adsorbent calcination for reuse The spent adsorbent was activated by calcinations before reuse. In this process, the adsorbent was placed in a crucible and heated. The furnace was set to a temperature of 400 C for 4 h in the furnace for calcinations to occur. The fume hood was turned on during calcinations to prevent inhalation of poisonous gases released during the process.
synthesized adsorbent (particulate size 75e212 mm) obtained using BET analysis are shown in Table 2. The characteristics of bleaching earth and acid activated bleaching earth (montmorillonte) are also presented for comparison. It can be observed that the raw oil palm ash has low BET surface area (22.9 m2/g), total pore volume (0.015 cm3/g) and average pore diameter (0.26 nm). After synthesis, the BET surface area of the resulting adsorbent of particulate size 75e212 mm increased slightly but still at a lower end, relatively. The total pore volume also increased slightly, while the average pore diameter increased significantly, implying that there was a structural change during the synthesis process. This structural change is as a result of the optimised hydration period to ensure complete pozzolanic reaction during the synthesis of the enhanced OPA adsorbent as previously established by Zainudin et al. (2005). Compared to bleaching earth and activated bleaching earth, the synthesized adsorbent had much lower BET surface area and total pore volume. The surface area of the adsorbent can be improved by reducing the particulate size to offer a large molecular interactive area during bleaching. However, increase in the pore diameter as observed was essential to enhance the convective mass transport required for a rapid bleaching process. SEM images of raw oil palm ash sample and synthesized adsorbents are shown in Fig. 2a and b respectively. In both cases, particles with uneven surface and non-uniform structure were observed. Agglomerates were formed on the surface of particles. The morphology of the synthesized adsorbent shows a porous matrix with large interstitial pores, confirming the increase observed for the average pore diameter. 3.2. Effect of ash particulate size on bleaching performance of adsorbent
2.5. Sample characterisation The chemical compositions of oil palm ash were determined using Shimadzu 1700 X-ray Fluorescence (XRF) Spectrophotometer. The surface morphologies of both the raw oil palm ash and the synthesized adsorbent were observed using a Scanning Electron Microscope (SEM). Brunauer-Emmett-Teller (BET) analysis was used to determine the surface area and pore characteristics of the oil palm ash and the synthesized adsorbents. 3. Results and discussion 3.1. Characterisation of raw oil palm ash and synthesized adsorbent Table 1 lists the chemical composition of the raw oil palm ash sample using XRF analysis. As shown in Table 1, the raw oil palm ash is mainly composed of Si-oxides, with minimal amounts of Al-, Feand Mg-oxides. Though the XRF analysis was performed with a raw palm oil ash sample of particulate size 75e212 mm, it does not affect the general compositional characteristics of the overall sample. Pore characteristics of the raw oil palm ash sample and the
Table 1 Chemical composition of the raw oil palm ash sample with particulate size 75e212 mm obtained via XRF analysis. Oxide
Percentage, %
Silicon oxide, SiO2 Aluminium oxide, Al2O3 Iron oxide, Fe2O3 Magnesium oxide, MgO Manganese dioxide, MnO2 Chromium oxide, Cr2O3 Rhodium oxide, Rh2O3 Ruthenium oxide, RuO2
86.44 6.49 4.08 1.51 0.10 0.69 0.41 0.29
Lovibond Model F was applied for colour analysis. Fig. 3a and b shows the colour indices of bleached palm oil (BPO) samples using 5 ¼ʺ and 1” glass cells, respectively. From Fig. 3a, the colour indices of ash particle with sizes of <75 mm, 75e212 mm, 212e300 mm and 300e425 mm, obtained using 5 ¼” glass cell, are 4 R, 4.4 R, 2.1 R and 4.3 R, respectively. This indicates that all the selected ash particle sizes are effective in bleaching crude palm oil as they meet the colour standard required by Palm Oil Refiners Association of Malaysia (PORAM), which is 20 R for 5 ¼” glass cell (PORAM, 2013). The ash particles with size 212e300 mm demonstrated the best bleaching performance, and this represents the optimal ash particle size range required to enhance the mass transfer through both particulate and interstitial pores of the adsorbent while maintaining the characteristic surface area required for effective adsorbentCPO interactions. The colour indices (using 5 ¼ʺ glass cell) of regenerated adsorbent samples with ash particle sizes of <75 mm, 75e212 mm, 212e300 mm and 300e425 mm are 3.4 R, 5.4 R, 3.4 R and 4.5 R, respectively. The regenerated samples also meet the industry standard, demonstrating the stability of the adsorbent particles for repeated use and the cost savings associated with it. The colour index for fresh CPO obtained using 1” glass cell test was 22 R. The percentage of colour reduction was determined using the result obtained from 1” glass cell as the colour of fresh crude palm oil (CPO) was too dark to be detected by 5 ¼ʺ glass cell. The percentage of oil bleached for each adsorbent sample was calculated and presented in Table 3. The colour reduction for regenerated adsorbents was generally slightly lower than fresh adsorbents, and this was due to the possible presence of traces of impurities retained in the particle pore which decreases the adsorption efficiency of the adsorbent. As mentioned earlier, the adsorbent with ash particle size 212e300 mm presented the optimal bleaching efficiency. These findings do not concur with the studies done by
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Table 2 Pore and surface characteristics of the raw oil palm ash sample, synthesized adsorbent with size 75e212 mm and bleaching earth with P/Po as relative pressure.
BET surface area (m2/g) Total pore volume at P/P0 0.97349186 (cm3/g) Average pore diameter (nm)
Raw oil palm ash
Synthesized adsorbent
Montmorillonite activated with acid treatment (Tsai et al., 2002)
Bleaching earth (Hassan, 2006)
22.98 0.02 0.26
32.21 0.10 1.19
268 0.36 0.54
157 0.29 e
Girgis (2005). According to their studies, adsorbent with ash smaller particle size gives higher adsorption capability due to the shorter diffusion path of the colouring matter in the oil to the adsorbent surface. Adsorbent with smaller ash particle size has larger surface area but with reduced porosity. Whilst this enhances particle-oil interactions, the pores should be large enough to increase the adsorption and retention capacities without significantly compromising the surface area. It should be noted that the porous structure of ash particles depends on the composition of the ash. The ash used in this experiment was boiler ash consisting of empty fruit bunches (EFB), mesocarp fibres, and shells. The pore structure of the individual materials differed and potentially presents nonuniformity in the bleaching performance. 3.3. Effect of adsorbent dosage on bleaching performance In this section, the effect of oil palm ash adsorbent dosage on
bleaching performance is investigated to probe any possible variation in the optimal dosage due to physicochemical characteristics of the adsorbent. The ratios 1:08, 1:09, 1:10 and 1:11 were tested with results presented in Fig. 4. As mentioned by Wambu and co-worker, increasing the adsorbent loading increases the quantity of dye adsorbed as there is an increase in available adsorptive surface for interaction (Wambu et al., 2011). From Fig. 4, it can be observed that a further increase in the adsorbent dosage above the ratio 1:09 does not influence the colour of the bleached oil. This represents the partitioning concentration of oil coloured matter established at the equilibrium point for a fixed concentration of the bulk liquid phase and constant process conditions. This observation was in keeping with that reported by Ajemba and Onukwuli (2013). They reported that further increase in the adsorbent dosage does not increase in bleaching efficiency. This occurrence was because of the establishment of adsorption equilibrium between the adsorbent and the oil mixture, thus preventing further pigment removal. 3.4. Effect of adsorbent dosage on oil retention From the graph shown in Fig. 5, it can be observed that most of the residual oil obtained from the spent adsorbent is within the
Fig. 2. Surface morphology of (a) raw oil palm ash and (b) synthesized adsorbent at a magnification of 5000.
Fig. 3. Plot of colour indices against particulate size using (a) 5 1/400 glass cell and (b) 100 glass cell for bleached palm oil (BPO).
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Table 3 Percentage colour reduction using fresh and regenerated adsorbents. Ash particle size range (mm)
Percentage colour reduction (using fresh adsorbent) (%)
Percentage colour reduction (using regenerated spent adsorbent) (%)
<75 75e212 212e300 300e425
94.1 96.4 97.3 95
94.5 92.3 95.0 94.5
range of 23e50 wt % and this is acceptable. Zahrani and co-workers reported that the total oil content extracted from their spent adsorbent was 23 ± 2% of the weight of the spent clay (Al-Zahrani and Alhamed, 2000). According to Loh and his team, an average of 50 wt % residual oil is often extracted from spent adsorbents (Loh et al., 2007). The higher residual oil content observed for some of the results from Fig. 5 is due to the dissolution and entrapment of hexane solvent in the residual oil and not completely removed during the rotary evaporation process. It can also be observed that higher adsorbent dosage resulted in more oil retention, and this is due to poor accessibility of entrapped oil within the adsorbent matrix during evaporation. 3.5. Effect of stirring speed on bleaching performance Adsorbent with ash particle sizes 212e300 mm and 300e425 mm were used to study the effect of stirring speed on the bleaching
performance. The results are presented in Fig. 6a and b for analysis using 5 ¼ʺ and 1ʺ glass cells. From the results, it can be seen that stirring speed of 800 rpm demonstrated the best bleaching performance for both ash particle sizes, and this is due to improved interactions with the adsorptive surface of the adsorbent during mixing. From Table 4, it can be observed that the percentage of oil bleached increases with stirring speed. Enhanced mixing provides high fluidity in the bulk phase environment for improved intermolecular interactions between the adsorbent and the palm oil input. Under such conditions, the number of surface interactions between the adsorbent particles and the changing molecular units of palm oil per time is rapid, thus more palm oil molecules are exposed to the adsorbent surface. This shows that the stirring speed has a significant effect on the bleaching performance regardless of the ash particle size. In keeping the results from the colour test, the stirring speed of 800 rpm demonstrated the best bleaching performance. This result concurs with the finding of Rehman et al. (2012) and Devi et al. (2012). They reported that stirring enhances the contact between the adsorbent and the dye species. Another study conducted by Suyamboo and Perumal (2012) confirmed that the rate of diffusion of dye molecules from the bulk liquid to the liquid boundary layer surrounding the particle becomes higher with increasing stirring speed because of increase in turbulence which decreases the thickness of the liquid boundary layer. However, if the stirring speed exceeds beyond the effective conditions, the rate of adsorption will decrease, and this is attributed to a possible increase in the desorption tendency of oil molecules under turbulent conditions. This desorption tendency may be due to high mixing speeds which cause more energy input and higher shear forces, causing the bond between the oil and adsorbent to break.
Weight Percentage of Residual Oil (%)
Fig. 4. Colour results of BPO using a freshly synthesized adsorbent with different adsorbent to CPO ratio for the optimised adsorbent with ash particle size range of 75e212 mm was used.
70
FA
1st R
3rd R
4th R
2nd R
60 50 40 30 20 1:08
1:09 1:10 Adsorbent to CPO ratio
1:11
Fig. 5. Percentage weight of residual oil for different adsorbent to CPO ratios. Experiments were performed with adsorbent of ash particle size range of 75e212 mm.
Fig. 6. Colour index of bleached palm oil for different stirring speeds using (a) 1ʺ glass cell and (b) 5 ¼ʺ glass cell, respectively.
C. Acquah et al. / Journal of Cleaner Production 139 (2016) 1098e1104 Table 4 Percentage oil bleached for different stirring speeds and adsorbent particulate size. Stirring speed Percentage of oil bleached (rpm) (using 212e300 mm) (%)
Percentage of oil bleached (using 300e425 mm) (%)
200 400 600 800
56.5 69.6 97.8 98.2
82.6 90.8 95.7 96.5
The results show that the adsorbent with ash particle size of 300e425 mm gives comparable bleaching performance to the adsorbent with ash particle size of 212e300 mm at the effective stirring speed. As presented in Table 4, the percentage of bleached oil for adsorbent with ash particle size 300e425 mm is 98.2% and that of the adsorbent with particle size 212e300 mm is 96.5%. As stirring increases, the effect of particle size differences within a narrow range becomes insignificant at the optimal stirring speed to enhance bleaching contacts on the adsorbent surface. 3.6. Effect of adsorbent dosage on maximum number of adsorbent regeneration The adsorbents used to form the adsorbent-CPO ratios of 1:08, 1:09, 1:10 and 1:11 were continuously used to bleach CPO and regenerated until the collected oil samples shows orange colour as an indication of a very weak bleaching power of the adsorbent. The percentage regeneration efficiency for each adsorbent ratio is calculated. From the colour test, it is found that the maximum number of regenerations for adsorbent-CPO ratio1:08 is 5, 1:09 is 5, 1:10 is 5 and 1:11 is 3. The trend shows that, a higher dosage of adsorbent results in a higher maximum number of regeneration. This trend is similar to the findings by Sun et al. (2009). They reported that, the higher the adsorbent amount used, the more colour is washed out, which indicates that a higher regeneration efficiency is achieved. This results from a higher number of available adsorption sites with increasing adsorbent quantity. In general, the fresh adsorbent (FA) demonstrated a better bleaching performance in all the scenarios. The bleached palm oil showed orange colour when the bleaching was performed using a 2nd regenerated adsorbent in all the cases. As it can be deduced from Fig. 7, the adsorbent (at adsorbent to CPO ratio of 1:11) lost its bleaching power after 3rd regeneration, and this was validated by the colour of the bleached palm oil being almost same as the crude palm oil. This shows that the bleaching process is more efficient with freshly synthesized adsorbent compared to regenerated adsorbent. Boey et al. (2011) discussed the adsorption capacity of
Fig. 7. Colour test result for frequency of adsorbent regeneration at 1:08, 1:09, 1:10 and 1:11 adsorbent to CPO ratio for ash particle size range of 75e212 mm.
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regenerated adsorbent. It was reported that as the number of regeneration increases, more carbonized residues are entrapped in smaller pores of the matrix, resulting in the loss of specific surface area and pore volume. This could be explained by a study carried out by Wambu et al. (2011). It was shown that the rate of dye uptake is higher for fresh adsorbents and decreases gradually after each regeneration due to accumulated traces of impurities found in the pores of the adsorbents. 4. Conclusion From the present study, it can be concluded that OPA shows great potential in palm oil bleaching. The performance is affected by OPA particle size, the stirring speed, and the adsorbent loading. The adsorbent with ash particle size of 212e300 mm demonstrated the best bleaching performance under both fresh and regenerated conditions. It was also observed that the bleaching performance was higher for fresh adsorbent and decreased with regeneration. The use of higher stirring speed was found to have a positive effect on the percentage of oil bleached. In the study, it was shown that higher stirring speeds gave higher percentage of oil bleached. However, speeds above the effective, 800 rpm, could result in low bleaching efficiency due to desorption. Increase in adsorbent dosage significantly increases the total number of regeneration. Under conditions of the experiment, the highest achievable number of regeneration was 5 and this was demonstrated by adsorbent to CPO ratios of 1:08e1:09. Higher adsorbent loadings resulted in higher oil retention. The results demonstrate that high palm oil bleaching performance can be obtained sustainably using low-cost adsorbent materials at optimal process conditions. Future studies would aim at performing an extensive physicochemical characterisation of the OPA material along with modelling of the adsorption characteristics with a suitable kinetic isotherm. Acknowledgement The authors would like to thank Curtin University, Sarawak for providing the financial support for this project through the final year project funding scheme. References Ahmad, M., Omar, R., Malek, M., Noor, N.M., Thiruselvam, S., 2008. Compressive strength of palm oil fuel ash concrete. In: Proceedings of the International Conference on Construction and Building Technology, Kuala Lumpur, Malaysia, pp. 297e306. Ajemba, R.O., Onukwuli, O.D., 2013. Adsorptive removal of colour pigment from palm oil using acid activated Nteje clay. Kinetics, equilibrium and thermodynamics. Physicochem. Probl. Miner. Process. 49, 369e381. Al-Zahrani, A., Alhamed, Y., 2000. Oil removal from spent bleaching clay by solvent extraction. J. Environ. Sci. Health Part A 35, 1577e1590. Boey, P.-L., Ganesan, S., Maniam, G.P., 2011. Regeneration and reutilization of oilladen spent bleaching clay via in situ transesterification and calcination. J. Am. Oil Chem. Soc. 88, 1247e1253. Devi, B.V., Jahagirdar, A., Ahmed, M., 2012. Adsorption of chromium on activated carbon prepared from coconut shell. Adsorption 2, 364e370. Garcia-Nunez, J.A., Ramirez-Contreras, N.E., Rodriguez, D.T., Silva-Lora, E., Frear, C.S., Stockle, C., Garcia-Perez, M., 2016. Evolution of palm oil mills into biorefineries: literature review on current and potential uses of residual biomass and effluents. Resources. Conserv. Recycl. 110, 99e114. Girgis, A.Y., 2005. Reuse of discarded deactivated bleaching earth in the bleaching of oils. Grasas Aceites 56, 34e45. Hassan, S.N., 2006. Recovery of Spent Bleaching Clay for Reuse in Water Treatment (Thesis). Faculty of Chemical and Natural Resources Engineering, Universiti Teknologi Malaysia. Islam, M.M.U., Mo, K.H., Alengaram, U.J., Jumaat, M.Z., 2016. Mechanical and fresh properties of sustainable oil palm shell lightweight concrete incorporating palm oil fuel ash. J. Clean. Prod. 115, 307e314. Loh, S.K., Choo, Yuen May, Ngan, M.A., 2007. Residual Oil from Spent Bleaching Earth (SBE) for Biodiesel and Biolubricant Applications, Malaysian Palm Oil Board. Ministry of Plantation Industries and Commodities, Malaysia. Loh, S.K., James, S., Ngatiman, M., Cheong, K.Y., Choo, Y.M., Lim, W.S., 2013.
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