Activation of Spent Bleaching Earth for Dehumidification Application

1,054 views

Published on

To circumvent the current pollution-prone disposal of the spent bleaching earth (SBE), an experimental program was conducted to recover the waste SBE and to use it for air dehumidification application. Waste SBE was obtained from the damping site of the oil industry, and the entrained oil was recovered via hexane extraction while the remaining hydrocarbons were oxidized with 30% H2O2 and heat at 550 oC. This reactivation procedure affords oil useful in other ole-chemical applications and active SBE for air dehumidification. For the purpose of adsorbent development, SBE regeneration was found to follow two routes, solvent extraction followed by oxidation using 30% H2O2 which retains the elasticity of the clay crucial in molding the adsorbents and thermal processing at 550 oC after molding. Experiments were carried out in batch system, and the effects of parameters including, activation temperature, contact time, The sorption characteristic of the adsorbent established two peaks when activated at 550 oC and 650 0C with a capacity of 27.07 and 26.63% respectively. The regenerated SBE proved to be a promising adsorbent for moisture since its sorption capacity was higher than that of clay (15%) which is commonly used as commercial desiccant.

Published in: Technology, Business
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,054
On SlideShare
0
From Embeds
0
Number of Embeds
4
Actions
Shares
0
Downloads
19
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

Activation of Spent Bleaching Earth for Dehumidification Application

  1. 1. WORLD ACADEMIC JOURNAL OF BUSINESS & APPLIED SCIENCES-MARCH-OCTOBER 2013 EDITION International Journal of Chemistry (IJC) OCTOBER 2013 VOL.1, No.8 Activation of Spent Bleaching Earth for Dehumidification Application John K. Mathaga 1 , Thomas F.N. Thoruwa 2 & Gerald K. Muthakia 3 1 Department of Chemistry, Kenyatta University, P.O. Box 43844-00100, Nairobi, Kenya Department of Engineering, Kenyatta University, P.O. Box 43844-00100, Nairobi, Kenya 3 Department of Chemistry, Kimathi University College of Technology, P.O. Box 657-1010,Nyeri, Kenya 2 Accepted 16 October 2013 Abstract To circumvent the current pollution-prone disposal of the spent bleaching earth (SBE), an experimental program was conducted to recover the waste SBE and to use it for air dehumidification application. Waste SBE was obtained from the damping site of the oil industry, and the entrained oil was recovered via hexane extraction while the remaining hydrocarbons were oxidized with 30% H2O2 and heat at 550 oC. This reactivation procedure affords oil useful in other ole-chemical applications and active SBE for air dehumidification. For the purpose of adsorbent development, SBE regeneration was found to follow two routes, solvent extraction followed by oxidation using 30% H2O2 which retains the elasticity of the clay crucial in molding the adsorbents and thermal processing at 550 oC after molding. Experiments were carried out in batch system, and the effects of parameters including, activation temperature, contact time, The sorption characteristic of the adsorbent established two peaks when activated at 550 oC and 650 0C with a capacity of 27.07 and 26.63% respectively. The regenerated SBE proved to be a promising adsorbent for moisture since its sorption capacity was higher than that of clay (15%) which is commonly used as commercial desiccant. Key Words: Activation; Spent Bleaching Earth; Dehumidification. 1. Introduction Bleaching process, the third step in edible oil manufacture refers to the adsorptive cleansing of edible oils; simply, the purification stage (Patterson, 1992). In oil bleaching, many methods exist which include; hydrogenation, heat treatment at 220 oC, alkali treatment and oxidative bleaching. However, on an industrial scale, acid treated calcium Montemorillonites clay commonly referred to as bleaching earth (BE) is prioritized in removing a variety of undesired impurities which could otherwise impart colour, odour and taste to the refined product (Patterson, 1989). Normally, this method employs two techniques (Wambu et al., 2009) namely; The percolation method in which the oil is filtered through granular product of 250-200 μm (or 10-60 mesh) essentially at low temperatures whereby the coloring matter get adsorbed by the soil as the oil passes through or contact processes in which the oil is put in contact with finely ground clay of about 74 μm (or less than 200 mesh) for predetermined period of time to equilibrate. Filter pressing operation then separates the oil at temperatures in the range of 150- 300 oC. 312
  2. 2. WORLD ACADEMIC JOURNAL OF BUSINESS & APPLIED SCIENCES-MARCH-OCTOBER 2013 EDITION The impurities removed in this process includes chlorophyll, β-carotene (and their derivatives), residual soaps, fatty acids, phosphatides and trace metals (Pollard et al., 1993). Activated carbon is also periodically used in the admixture with virgin bleaching earth for the removal of trace quantities of polynuclear aromatic hydrocarbons (PAH) from edible oils (Larsson et al., 1987). These contaminants, some of which are suspected human carcinogens, are sufficient to be of concern to edible oil processors. Spent bleaching earth (SBE) on the other hand is the solid waste or the filter cake obtained from this process. It contains impurities adsorbed from the crude oil with considerable quantities of entrained oil that is quantified approximately 30 to 40% (Wachira et al., 2005). Direct landfills are the most common current mode of disposal particularly in Kenya which poses an acute environmental pollution. The re-use of SBE and the concomitant recovery of residue oil has been a recurrent focus of research in recent years (Mana et al., 2007, 2008, Wambu et al., 2009). SBE regeneration has been attempted by solvent extraction (Cheah and Lion, 2002). Solvent extraction followed by thermal processing (Boukerroi and Ouali, 2000), preliminary acid impregnation followed by thermal processing (Mana et al., 2007, Wang and Lin, 2000) and the product obtained reported to posses similar properties as virgin bleaching clays. The regenerated spent bleaching earth (RSBE) has then found numerous applications such as removal of basic dyes from aqueous solution (Mana et al., 2007), biological treatment and land farming, fuel supplements (Daido, 1987), toxic metals and organic group adsorption (Wambu et al., 2009, Mehmet et al., 2003), cement manufacture (Wachira et al., 2005) among others. Dehumidification is a process of water removal from the atmosphere which has wide application ranging from preservation of stored material, industrial processes, condensation prevention, humidity control in air-conditioned spaces such as offices and supermarkets among others (Zhang et al., 2005). This process is accomplished through refrigeration or absorption by liquid desiccants and /or adsorption by solid desiccants which maintains the relative humidity to the desired level. The inadequate electric power supply in most parts of the tropics and the high cost of fossil fuels favors the use of desiccant for dehumidification applications over refrigeration (Thoruwa et al., 2000). Dehumidification using desiccants is a process by which liquid or solid sorbent materials extract moisture from the surrounding air to the sorbents. Typically, the sorbent moisture content is a function of the relative humidity (RH) of the surrounding air as presented by Hamed (2003). The driving force for moisture absorption is the vapour pressure differential attributed to lower vapour pressure on the sorbents compared to the surrounding air. When exposed to low moisture content, low vapour pressure builds which results in attainment of equilibrium upon exposure to high RH environment thus removing water from air (Zhang et al., 2005). The cosmic limitation of high relative humidity has led to a wide acceptance of desiccant technology which has found new ventures in hospitals, hotels and supermarkets recently (Ahmed, 2005). More materials that are hygroscopic in nature are thus constantly investigated for their potential in low cost desiccant development. Traditionally, ceramic materials dominated the desiccant market (William and Lu, 2002). Clayey materials have unique properties that make them suitable for dehumidification application in that, they consists of closed packed regular alteration of Si-O and Al-O sheets with inter-lamellar spaces punctuating each set of the sheets which holds water molecules. Moreover, they are plenty available at low cost Mooney et al. (1952). Since SBE is essentially contaminated clay, and no work has been devoted in the past on the regeneration of SBE for dehumidification application, the current work reports the findings of the convenient route for the activation of the SBE for dehumidification application. 2. Material and Methods 2.1 Preparation of material Spent bleaching earth samples were collected from a damping site of the Kapa oil refineries an oil company which is about five kilometer from Nairobi. Samples were air-dried and stored in desiccators for regeneration 313
  3. 3. WORLD ACADEMIC JOURNAL OF BUSINESS & APPLIED SCIENCES-MARCH-OCTOBER 2013 EDITION experiments. 2.2 Heat Reactivation The air dried samples (10 g) were measured, placed in a crucible and transferred into a furnace where they were heat reactivated at temperatures of 550 oC for 12 hours (Al-zahrani and Alhamed, 1976). The heat reactivated spent bleaching earth was then cooled in a desiccators for 24 hours. The adsorbent development procedure were similar to those described by Thoruwa et al., 2000, where cool hydrocarbon free samples were sprayed with 20% of the net dry weight mixture of distilled water to form a hand paste. About 0.6 g of the paste formed was weighed and moulded into spherical balls of approximately 1cm in diameter. 2.3 Hexane Extraction Experiments Separate 5.0 g portions of the remaining air-dried spent bleaching earth (SBE) samples were weighed and placed in eight 1000 ml Erlen-Meyer conical flasks containing 5, 10, 15, 20, 25, 30, 35, and 40 ml of hexane solvent and the flasks labeled 1:1, 1:2 to 1:8 respectively to reflect the respective content ratios. The mixture in each flask was then magnetically stirred for 12 hrs. Upon completion of the extraction step, the solvent extract and the SBE were separated by suction filtration using Buchner funnel and residue designated hexane extracted spent bleaching earth (HESBE) (Wambu et al., 2009). The oil and hexane on the other hand were separated by the use of a Soxhlet apparatus and the percentage of the extracted oil (PEO) for each mixing ratio calculated by the following relation (Cheah and Lion 2002), PEO = M1 − M 2 × 100 M1 Where, M 1 is the mass of dry SBE before regeneration and M 2 is the weight of dry hexane regenerated SBE. The total oil content was also determined by total combustion method in a separate experiment by burning 5 g of the SBE sample at 1000 oC. The average of total weight loss of these samples was 45%. Loss on ignition for the virgin bleaching clay was found to be 14%. The average moisture content was also determined by oven drying 5 g of the SBE at 110 oC for 24 hours which recorded 6%. Thus, the average of the total oil content from the calculations was established as 25% (Folleto et al., 2002). The HESBE were oven dried at 80 oC for 3hrs and then allowed to cool in desiccators. The dry HESBE samples were then weighed and sprayed with doubly deionized water (DDW) to form a medium hard paste which was used in moulding spherical balls of approximately 1cm in diameter which were used as adsorbents (Tretiak and Abdallah, 2009). 2.4 Oxidation of the Hexane Residues The hexane residues (HESBE) obtained in the procedure 2.3 above were oven dried at 100 oC for 12 hours and transferred in desiccators to cool. 30.00 g of dry HESBE were weighed and transferred in a 1000ml beaker, 90 ml of 30% H2O2 solution was added and the content of the beaker warmed to temperatures of 80 oC. 15 ml increment of 30% H2O2 solution were added every time the reaction subsided until a total of 150 ml was consumed. The oxidized samples were then washed with DDW and the water removed by centrifugation (model 6000 series centurion at 600*10 RPM for 3 min) (Nebergell et al., 1995). The solid samples were then sprayed with DDW to form a moderately hard paste and moulded into spherical balls of about 1cm in diameter. 2.5 Sorption Determination of Adsorbents The sorption properties of the adsorbents obtained in procedure 2.4 above were determined through a method proposed by (Young, 1967). The spherical adsorbents were placed in an oven and dried for three hours at 110 oC. The temperature was increased to 200 oC and samples heated for three hours. The samples were then transferred into a muffle furnace and different batches fired at 300, 400, 500, 550, 600, 650 and 700 oC. These heat activated 314
  4. 4. WORLD ACADEMIC JOURNAL OF BUSINESS & APPLIED SCIENCES-MARCH-OCTOBER 2013 EDITION adsorbents were cooled in desiccators for the sorption determination. The sorption studies were carried out in sealed beakers where the samples were held by wire mesh above saturated solutions of LiCl, MgCl2, K2CO3, Mg(NO3)2, NaCl and KNO3 which provided 11.3, 32.78, 43.16, 52.89, 75.5 and 93.58% relative humidity (RH) environment respectively (Young, 1967). The same procedure was repeated using virgin bleaching earth adsorbents and results compared. 3. Results and Discussion 3.1 Regeneration of Spent Bleaching Earth The restoration of spent bleaching earth (SBE) for dehumidification application was found to involve three major steps: An extraction step to remove a majority of entrained oil, about 62.5% by weight of the entrained oil, an oxidation step to remove the majority (25%) of remaining carbonaceous adsorbates which are not removed by the preceding extraction step, and the heat reactivation to remove the rest of hydrocarbons (12.5%) and to open up the adsorption sites of the clay. In the present work, the results for all the three steps in the restoration of SBE for air dehumidification applications are provided and tabulated in tables 1 and 2. 3.1.1 Optimization of Hexane to Spent Bleaching Earth Mixing Ratio Results of table 1 below reports the amount of oil removed from the spent bleaching earth (SBE) by different SBE to hexane mixing ratios. From the results, it was apparent that more hexane in the media extracted more oil. There was an increase in the ability of extraction from the ratio of 1 g to 1 ml SBE to hexane which extracted about 22.5% as compared to 1g to 8 ml which extracted 25.1% of the entrained oil. For the restoration of SBE, a ratio of 1g SBE to 5ml hexane which extracted 24.8% was chosen as the activation ratio which compared with results obtained by (Kheang et al., 2006). The hexane was found to extract mainly the oil content of the SBE which was recording a total mass of around 25% by weight of the dry SBE samples. The Hexane residues could not be moulded into spherical balls since the residues did not mix well with the deionized water which was attributed to the remaining hydrocarbons which are hydrophobic, thus the need of the oxidation step. From the average results obtained above, the ratio of 1:5 (1 g SBE to 5 ml hexane) was chosen and used in the treatment of SBE in the solvent extraction step. Solvent extraction was done using a soxhlet extractor where the solvent was regenerated to minimize the regeneration cost. The solvent was replaced several times until the cloudiness disappeared from the content siphoned. Table 1. The Amount of Oil Removed by Different Ratios of Hexane from the SBE Ratio of SBE: Hexane Mass of the SBE used (M1) Mass of the SBE after extraction (M2) Difference mass in % of oil in the SBE 1:1 5.0001 3.8769 1.1232 22.5 1:2 5.0004 3.8452 1.1552 23.1 1:3 5.0006 3.7953 1.2053 24.1 1:4 5.0008 3.7758 1.2250 24.5 1:5 5.0000 3.7584 1.2416 24.8 1:6 5.0003 3.7524 1.2479 25.0 1:7 5.0004 3.7459 1.2515 25.1 1:8 5.0006 3.7428 1.2578 25.1 3.1.2 Solvent Oxidation of Hexane Residues Since hexane removed about 62.5% of the organic matter present in SBE samples, the hexane residues samples were oxidized with 30% H2O2 according to procedure given in claim of U.S. patent NO. 5,468,701, 1995, this oxidized about 25% by mass of the total organic matter in SBE. For the oxidation to be realized, it was necessary to raise the temperature of the mixture to 80 oC to initiate the oxidation process. This is because the process 315
  5. 5. WORLD ACADEMIC JOURNAL OF BUSINESS & APPLIED SCIENCES-MARCH-OCTOBER 2013 EDITION involves bond breakage which is endothermic process thus requiring heat energy from the surrounding for activation. Once the reaction starts, the process is self satisfactory in terms of heat energy required since the energy released in the formation of the CO2 and H2O is enough for the process to proceed. The two processes recorded an organic matter content of 35% by weight of SBE. The results for the organic content oxidized by the H2O2 are given in the table 2 below. Table2. The amount of entrained hydrocarbons extracted by oxidation process Wt of the HESBE Wt of the oxidized HESBE Charge in mass % HC A 30.02 26.34 3.68 12.3 B 30.02 25.05 4.97 16.6 C 30.10 28.13 1.97 6.5 D 30.00 28.58 1.42 4.7 Key: HESBE-Hexane Extracts Residues HC- Hydrocarbon Wt- Weight Oxidized samples were then heat reactivated at temperatures of 550 oC. This process removed about 12.5% of the entrained organic compounds in the SBE which indicated that hexane and hydrogen peroxide reactivation process did not remove all the entrained organic matter. These results agreed with results presented by other studies (Wambu et al., 2009), who established that the SBE has an organic matter content of about 40%. The results obtained were confirmed by a parallel studies on the same sample through total combustion method in the determination of moisture and ash content as described in procedure 2.3. 3.1.3 Reactivation Procedure on Adsorbent Development For the purpose of dehumidification, spherical balls were made by preparing medium hard paste before and after each and every activation step. It was found that, before treatment, the spent bleaching earth could not mix with water to form the paste required for moulding the adsorbents since hydrocarbons are hydrophobic. The hexane extracted samples (HESBE) also did not mix with water to develop the medium hard paste for the adsorbent moulding. The heat reactivation alone at temperatures of 550 oC where the hydrocarbons present are oxidized to water and carbon (IV) oxide interfered with the elasticity of the SBE hence the moulding was not possible with these samples. The hydrogen peroxide step produced samples that could be mixed with water and moulded into desired shapes. The results presented in tables 1 and 2 above indicated that the solvent extraction and H2O2 oxidation process did not remove the entire entrained hydrocarbons from the SBE. Thermal processing was hence paramount in order to remove approximately 5% of the entrained HC after the two regeneration steps as well as reactivating the sorption sites of the adsorbent. 3.2 Sorption The results for the sorption at various processing temperature are summarized in table 3 and graphically by the figure 1 below. The balls regenerated at 100, 200, 300 and 400 oC were observed to be dark in colour which was attributed to the incomplete combustion of hydrocarbons after H2O2 oxidation step (Wachira et al., 2005). The results of samples processed at 100 oC and 200 oC were not included due to excessive wetting on the surface as well as cracking and spalling of these balls after exposing them to high humid environment. Samples processed at 300 oC and 400 oC recorded similar results upon exposure to high RH but their change in weight could be monitored as the phenomena was less compared to samples processed below 300 oC. This was associated to incomplete combustion of the hydrocarbons in these adsorbents which could have sealed the pores 316
  6. 6. WORLD ACADEMIC JOURNAL OF BUSINESS & APPLIED SCIENCES-MARCH-OCTOBER 2013 EDITION in addition to incomplete reactivation of the sample. The adsorbents processed at temperatures’ beyond 500 oC recorded minimum wetting and water dripping as well as high solidity maintenance as they did not crack or spall. This was ascribed to the complete combustion of the hydrocarbons from the host material, hence opening the adsorption sites and ameliorated the adsorption of water molecules on the adsorbent. The water sorption results indicated two peaks at 550 oC and 650 oC for all the samples tested. The increased moisture sorption when processed between the temperatures of 300 oC to 400 oC was imputed to the excessive surface wetting of the samples due to incomplete processing. The adsorption peak observed on the adsorbents reactivated at 550 oC compared well with other findings (Tretiak and Abdallah, 2009), however the peak at 650 oC was not in literature for solid desiccants but agreed with findings of Wambu et al., (2009) whose study reported a peak on the same material on copper adsorption when reactivated at 700 oC. The first peak is attributed to the de-hydroxylation of γ-aluminium trihydoxides to γ-alumina which is a more porous matrix structure upon calcinations, in addition to the complete combustion of the hydrocarbons which results in a large moisture exchange surface area. The second peak at 650 oC accounts for the formation of ρ-alumina (Wambu et al., 2009), another product of calcinations of trihydroxides of aluminium which is characterized by high surface area that ameliorates the sorption. The conversion of the aluminium trihydroxides to alumina on calcinations proceeds via partial dehydroxylation that begins at temperatures of 225 oC converting gibbsite to Boehmite with a loss of water followed by conversion of Boehmite to alumina from 525 oC. Al(OH)3(s) AlO(OH)(s) + H2O(l) 2Al(OH)3 (s) Al2O3( s) + 3H2O(l) This explains the increase on adsorption from 300 oC. The lower moisture sorption at 700 oC was as a result of the conversion of the active alumina to relatively inert α-alumina in the range of 700 oC - 1000 oC. Table 3. The amount of water adsorbed in % per dry weight of the sample 300 400 500 550 600 650 700 VBE 31.54 22.32 24.11 24.01 17.79 27.64 22.19 RSBE 21.32 21.87 21.85 27.07 14.64 26.63 21.91 Temp oC Key: VBE- Virgin bleaching earth RSBE- Regenerated bleaching earth Figure1. Sorption curves representing the Effect of processing temperature on RSBE and VBE adsorbents on sorption capacity 317
  7. 7. WORLD ACADEMIC JOURNAL OF BUSINESS & APPLIED SCIENCES-MARCH-OCTOBER 2013 EDITION 4. Conclusions The challenge for oil manufacturing industries in the environmental field is to identify and devise methods for utilizing the spent bleaching earth. With a growing concern for the safe disposal of this material, the current study has shown that the waste spent bleaching earth has the potential of removing water from the air and thus can be utilized in desiccant manufacture. The reactivation efficacy of different conditions investigated showed that solvent oil extraction followed by 30% H2O2 oxidation and thermal treatment at 550 oC are the most effective in spent bleaching earth reactivation for this application. Thermal treatment alone was found not viable due to its effect on elasticity of the material. Solvent extraction by hexane was found to extract oil which could be utilized in other applications such as bio-diesel; detergent and soap manufacture thus maximizing on the components of the waste. However, the water sorption capacity for the material (27.07) was very low as compared to commercially available desiccants (40-45%) and thus more research need to be conducted on the material in order to enhance its sorption efficiency. Acknowledgements I would like to appreciate Kenyatta University for the partial scholarship and a place that afforded me to carry out the research. Credit goes to technical staff of food science department of Jomo Kenyatta University of Science and Technology for their support on sorption studies. References 1. Ahmed, M.H. (2005). Experimental Investigation on the Adsorption/Desorption Processes using Solid Desiccant in an Inclined-Fluidized Bed. J of Renewable Energy; 30: 1913-1921. 2. Al-zahrani, A.A. and Alhamed, Y.A., (1976). Regeneration of spent bleaching clay by calcinations cum-acid treatment. Journal of Indian Institute of Chemical Engineering. 3 (38, n): 71-75 3. Cheah, K.Y., and Lion, S.W., (2002) “Regeneration of Spent Bleaching Clay.” Malaysia Palm Oil Board, Kaula Lumpur, Malaysia. 4. Daido, M. (1987). A Recovery and Re-Use System for Fatty Oils from By-Products & Waste Materials of Vegetable Oil Production. Conservation and Recycling; 10: 273-278. 5. Folleto, E.L., Alves, C.A., Sganzrla, L.R. and Porto, M.L. (2002). ‘Regeneration and Utilization of Spent Bleaching Clay.’ Latin American Applied Research; 32: 205-208. 6. Hamed, A.M. (2003). Desorption Characteristics of Desiccant Bed for Solar Dehumidification/ Humidifier Air Conditioning System. Journal of renewable Energy; 28: 2099-2111 7. Kheang, L.S., Cheng, S.F., Choo, Y.M., and Ngan, M.A. (2006). A Study of Residual Oils Recovered from Spent Bleaching Earth: Their Characteristics and Applications. American Journal of Applied Sciences; 3 (10): 2063-2067. 8. Larsson, B.K., Eriksson, A.T., and Cervenka, M., (1987). Polycyclic Aromatic Hydrocarbonsin Crude and Deodorized Vegetable Oils. J. Am. Oil Chem. Soc., 64, 365-370. 9. Liu, Y.F. and Wang. R.Z. (2003). Pore Structure of New Composite Adsorbent SiO2.xH2O.yCaCl2 with High Uptake of Water from Air. J of Science in China Series; E 46(5): 551-559. 10. Mana M., Ouali M.S., and De Menorval L.C. (2007). Removal of Basic Dyes from Aqueous Solutions with a Treated Spent Bleaching Earth. J of Colloid Interface Science 307(1): 9-16. 11. Mana M., Ouali, M.S., Lindheimer, M. and Menorval, L.C. (2008). Removal of Lead from Aqueous Solutions with a Treated Spent Bleaching Earth. . Journal of Hazard Mater; 159(2-3): 358-364. 318
  8. 8. WORLD ACADEMIC JOURNAL OF BUSINESS & APPLIED SCIENCES-MARCH-OCTOBER 2013 EDITION 12. Mehmet, M., Kizilcikli, I., Bicer, O. and Tuncay, M. (2003). ‘Removal of MCPA from Aqueous Solutions by Acid Activated Spent Bleaching Earth. ’ Journal of Environmental Science; 38(6): 813-827. 13. Mooney, R.W., Keenan, A.G. and Wood, L.A. (1952) Adsorption of Water Vapour by Montmorillonite. II. Effect of Exchangeable Ions and Lattice Swelling as Measured by X-Ray Diffraction. Journal of the American Chemical Society, 74: 1371-1374. 14. Nebergell, R.S., Kucharz, C.J. and Taylor, d.R., (1995). Process for Regenerating Acid-Activated Bentonite Clays and smectite Catalysts. U.S Patent NO. 5,468,701. 15. Patterson, H.B.W., (1992). Bleaching and Purifying Fats and Oil: theory and Practice. American Oil Chemists’ Society Press. 16. Patterson, J.W. (1989). Industrial Waste Reduction. Environ Science technology; 23: 1032-1038. 17. Pollard, S.J.T., Sollars, J.C., and Perry R. (1993). The Reuse of Spent Bleaching Earth: A Feasibility Study in Waste Minimization for the Edible Oil Industry. Journal of Science Direct; 45: 53-58. 18. Thoruwa, T.F.N., and Ben-Abdullah, N., (1988). Moisture Sorption Characteristics of Solid Clay Supported CaCl2 CSAE paper No. 88-407. 19. Tretiak and Abdallah (2009). Sorption and Desorption Characteristic of Packed Bed of Clay-CaCl2 Desiccant Particles. Journal of Solar Energy; 1861-1870. 20. Wachira, J.M., wa Thiong’o J.K., and Muthakia, G.K. (2005). Low Cost Pozzolana Based Cement from Industrial and Agricultural Waste Materials, J. of civ. Eng. Research and Practice. 2(1): 15-21. 21. Wambu, E., Muthakia, G.K., Wa-Thiongo, J.K. and Shiundu, P.K. (2009). “Regeneration of Spent Bleaching Earth and its Adsorption of Copper (II) ions from aqueous solution.” Journal of Applied 22. Wang. I. H., and Lin C.I., (2000) “Kinetics of Heat Regeneration of Spent Bleaching Clay”, Journal of Chemical Engineering. Japan; 33 (3): 522-525 23. William, J.L., and Lu, N. (2002). Water Vapor Sorption Behavior of Smectite-Kaolinite Mixtures. Clay and Clay Minerals, vol 50, No 5, 553-561. 24. Zhang, X.J., Sumathy, Y.J., and Wang, R.Z. (2005). Parametric Study on the Silica-Gel Calcium Chloride Composite Desiccant Rotatory Wheel Employing Fractal BET Adsorption Isotherm, Journal of Energy; 29: 37-51. 319

×