Mixed-adsorption drying with material using zeolite is an option to improve product quality and energy efficiency of drying seeds. In this case, zeolite and seeds are mixed and fluidized by warm air as drying medium. The air will desorb water from seed, and at the same time, zeolite will adsorb vapor from air. Thus, the driving force of drying can be kept high. However, in Indonesia, the zeolite with high adsorption capacity is hardly found in market. This research studied the activation of natural zeolite using two different methods: by heating at 200-400oC, and  adding NaOH 0.5-2.0 N. Results showed that the adsorbing capacity of zeolite activated by 1.0 N NaOH is 0.170 gr water/gr dry zeolite. While, by heating at 300oC for 3 hours, is 0.140 gr water loaded/gr dry zeolite. With the performance, zeolite can be used for drying application.



Keywords: zeolite, fluidized, adsorption, drying, activatio

Djaeni, M

Kurniasari, L

Purbasari, A

Sasongko, SB

English

Diponegoro University Institutional Repository

Proceeding of the 1st International Conference on Materials Engineering (ICME) and 3rd AUN/SEED-Net Regional Conference on Materials (RCM) 25-26 November 2010, Yogyakarta Indonesia   Activation of Natural Zeolite as Water Adsorbent for Mixed-Adsorption Drying   Mohamad DJAENI1, Laeli KURNIASARI, Aprilina PURBASARI1, Setia Budi SASONGKO1 1Department of Chemical Engineering, Faculty of Engineering, Diponegoro University Jl Prof H. Soedharto, SH, Tembalang, Semarang Telp: 024 7460058  2Department of Chemical Engineering, Faculty of Engineering, Wahid Hasyim University Jl. Menoreh Tengah X / 22 Sampangan Semarang Phone: (024) 850568 Corresponding author: mzaini98@yahoo.com, lalei_kurniasari@yahoo.co.id, sbsemar@yahoo.com   Abstract: Mixed-adsorption drying with material using zeolite is an option to improve product quality and energy efficiency of drying seeds. In this case, zeolite and seeds are mixed and fluidized by warm air as drying medium. The air will desorb water from seed, and at the same time, zeolite will adsorb vapor from air. Thus, the driving force of drying can be kept high. However, in Indonesia, the zeolite with high adsorption capacity is hardly found in market. This research studied the activation of natural zeolite using two different methods: by heating at 200-400oC, and  adding NaOH 0.5-2.0 N. Results showed that the adsorbing capacity of zeolite activated by 1.0 N NaOH is 0.170 gr water/gr dry zeolite. While, by heating at 300oC for 3 hours, is 0.140 gr water loaded/gr dry zeolite. With the performance, zeolite can be used for drying application.  Keywords: zeolite, fluidized, adsorption, drying, activation   1. INTRODUCTION The drying is a process commonly used in post harvest treatment such us seeds.  The process is aimed to purify the product, prolong storage life of the product, reduce microbial activity, and saving transportation cost.  However, current drying process still deals with reducing product quality and high energy usage as well as low efficiency. In post harvest treatment, more than 70% of energy used in drying. This is quite big, thus the development of efficient drying with high product quality still the important issue [1]. Mixed adsorption drying using zeolite is a potential option to be developed. In this method, the seed and zeolite are mixed and fluidized by warm air. The air will evaporate water from product, and at same time, the zeolite will adsorb vapor from air. As consequence, the relative humidity of air can be kept low. In addition, adsorption process releases heat that can be used to increase sensible heat of drying air. Thus, the driving force of drying can be still high. Zeolite is alumino-silicate compound with tetrahedral bound linked by oxygen. Atom Al is negatif that can be netralized by cation. The exchangable cation affects the adsorption ability of zeolite. Beside that, the ability is also influenced by Si/Al ratio, surface area, and size of zeolite pore [2-4]. In Indonesia, the natural zeolite is available in market. Even, the potential of zeolite production is high [5]. However, adsorbing capacity of natural zeolite is too low rounding 0.7-0.9 gr water loaded/gr zeolite. In general, the natural zeolite contains organic and an-organic impurities, as well as having high Si/Al ratio. Additionally, the size of pore is not homogenous. For adsorbing water, it needs the size pore 3oA close to molecular diameter of water. Therefore, the activation process is required before using natural zeolite [6].   This research studies the activation of natural zeolite Indonesia by NaOH and heating. The aim is to find activated zeolite for water adsobernt that can be used as air dehumidifier in dryer. In this work, the effect of NaOH concentration, time, temperature on the adsorbed water capacity are studied at various air condition. In doing so, the physical properties of activated zeolite involving size and homogenous of pore are analized using scanning electron micrograph (SEM).  2. EXPERIMENTAL METHOD Natural zeolite from local market Semarang was activated with two different methods: activation by heat, and NaOH 0.5-2.0 N. The aims are to remove the impurities, and form the homogenous pore size.  In activation by heat, natural zeolite was milled and screened to get the granule in the size of 1-2 mm. The granule was then weighed 25 grams and heated in autoclave at 200oC for 2 hours (see Fig. 1). The zeolite was then cooled in desicator. After that, the ability of zeolite for adsorbing water is evaluated in sorption-isotem tank (see Fig. 2) at various air condition during 2-3 days. The water loaded in zeolite was measured by weighing the zeolite before and after put in sorption-isoterm tank. While, the pore size of zeolite was Generated by Foxit PDF Creator © Foxit Softwarehttp://www.foxitsoftware.com   For evaluation only.Proceeding of the 1st International Conference on Materials Engineering (ICME) and 3rd AUN/SEED-Net Regional Conference on Materials (RCM) 25-26 November 2010, Yogyakarta Indonesia  analyized by SEM. The method was repeated for various activation time (2-5 hours) and temperature 300-500oC.             Fig. 1. Autoclave working at 200-500oC for zeolite activation  For activation by NaOH, natural zeolite was mixed with NaOH solution 0.5 and stirred under 60oC for 2 hours. The zeolite was then washed by water and dried at 110oC for 4 hours. The zeolite was cooled in desicator, and  the water loaded capacity was tested in sorptio-isoterm tank. The activated zeolite was also analyzed by SEM in order to know homogenity and size of pore. The process was repeated for NaOH 1.0-2.0 N, and mixing temperature 70-90oC.            Fig. 2. Sorption-isoterm tank  3. RESULT AND DISCUSSION 3.1. Activation by Heat Activation by heat aims to remove the organic impurities in zeolite pore. The thermal introduction can cause cation movement in which influences the pore size [4]. Table 1 presents the water loaded in the natural zeolite after activated by heat. In all cases, the capacity increases significantly. The best condition, can be reach at 300-4000C and heating time 3 hours, with capacity 0.137 gr  water/gr zeolite. At temperature below 300oC, the organic impurities cannot be totally removed. While upper 300oC, perhaps, the formation of pores size is too big (bigger than molecular diameter of water), so the water is not optimally adsorbed.  This result is also corresponding with Turkey’s  zeolite where the process activation is 300-400oC [7].   Table 1. Performance of zeolite activated by heating Temperature variation, oC, activation time 3 hour   200 300 400 500 gr water/gr zeolite 0.128 0.137 0.136 0.130 Activation time variation, hour,  temperature, 300oC   2 3 4 5 gr water/gr zeolite 0.130 0.137 0.136 0.135 Natural zeolite without activation 0.08-0.09 gram water/gram zeolite  3.2. Activation by NaOH Using NaOH silica ion, a componen formating the zeolite crystal is dilluted. This process reduces the Si/Al ratio, then the affinity of zeolite to water increases [8]. In addition, other ion is also substituted by Na+, so the pore  size of zeolite tends to be homogen in the form of homoionic [9]. With this condition, the pores of zeolite will have same size ranging 3-4 A called micropore in which is suitable for water adsorption. The higher micropore, higher water capacity will be obtained. Table 2 presents water loaded in zeolite activated by NaOH at different concentration and temperature. The water loaded in zeolite can reach 0.171 gr water/gr zeolite after activated for 2 hours under 70-80oC with NaOH 1.0 N. This improvement is quite significant, because natural zeolite can adsorb water 0.08-0.09 gram water/gr zeolite, only.  Table 2. Performance of zeolite activated by NaOH NaOH variaton, N; temperature 80 oC   0.5 1.0 1.5 2.0 gr water/gr zeolite 0.155 0.171 0.167 0.160 Temperature variation, oC; NaOH 1 N   60 70 80 90 gr water/gr zeolite 0.145 0.171 0.170 0.167 Natural zeolite without activation 0.08-0.09 gram water/gram zeolite    Generated by Foxit PDF Creator © Foxit Softwarehttp://www.foxitsoftware.com   For evaluation only.Proceeding of the 1st International Conference on Materials Engineering (ICME) and 3rd AUN/SEED-Net Regional Conference on Materials (RCM) 25-26 November 2010, Yogyakarta Indonesia  3.3. Scanning Electron Micrograph (SEM) Analysis Fig. 3 presents the zeolite pore analyzed by SEM. After activation, the pore of zeolite is opened and the crystal structure changes. The crystal size becomes smaller  as well as pore size enlarges. In addition, after activation, the pore size becomes more homogen in which increases water loaded capacity. In this case, activation by NaOH results the pore size more homogen than that of by heating.             a. Zeolite before activation             b. Zeolite activated by NaOH            c. Zeolite activated by heating  Fig. 3. Zeolite before (a) and after activated by NaOH (b) and heat (c)) 3.3. Adsorbing capacity  Table 3 depicts the water loaded in zeolite at different air condition. Results shows that the higher relative humidity, higher water loaded can be obtained. Conversely, higher temperature, lower water loaded. For synthetic zeolite, this behaviour is also similar [2,10-11].  High affinity casuses water loaded in zeolite is still higher. The affinity is affected by Si/Al ratio. Compare to another vapor adsorbent, the usage of zeolite is more beneficial, since it can adsorb water at low relative humidity.   Table 3. Water loaded in zeolite at different air condition Temperature 80 oC, activated by heating  Relative humidity, % 20 60 100 gr water/gr zeolite 0.040 0.087 0.101 Temperature 80 oC, activated by NaOH 1 N  Relative humidity, % 20 60 100 gr water/gr zeolite 0.056 0.106 0.131 Relative humidity, 100%, activated by heating  Temperature, oC 40 60 80 gr water/gr zeolite 0.130 0.109 0.101 Relative humidity, 100%, activated by NaOH 1 N  Temperature, oC 40 60 80 gr water/gr zeolite 0.161 0.142 0.131  4. CONCLUSION Activation of natural zeolite can be done by both heating and NaOH. Results showed that the porosity of zeolite activated by NaOH is higher and more uniform than that of by heat activation. The adsorbing capacity also corresponds to the result where after activation with 1.0 N of NaOH under 700C, the capacity of zeolite is 0.17 gr water/gr dry zeolite. While, the capacity of activated zeolite by heating at 300oC for 3 hours, is 0.14 gr water loaded/gr dry zeolite. The performance improvement is significant. Therefore, the both methods can be an option to find zeolite with high water capacity for mixed-adsorption drying.  Acknowledgements  This research was funded by DP2M, Directorate General of Higher Education Indonesia. The authors thank to Laboratory of Process Engineering, Department of Chemical Engineering, Diponegoro University for collaboration in performing the research.  REFERENCES 1. M. Djaeni, Energy Efficient Multistage Zeolite Drying for Heat Sensitive Products, PhD thesis of Wageningen University, The Netherlands, (2008). 2. F. C. Ozkan and S. Ulku, J.of Thermal Analysis and Calorimetry 94 (2008), 699-702. 3. M. S. Gruszkiewics, J.M. Simonson, T.D. Burchell, D.R.    Generated by Foxit PDF Creator © Foxit Softwarehttp://www.foxitsoftware.com   For evaluation only.Proceeding of the 1st International Conference on Materials Engineering (ICME) and 3rd AUN/SEED-Net Regional Conference on Materials (RCM) 25-26 November 2010, Yogyakarta Indonesia  Cole, Journal of Thermal Analysis and Calorimetry 81 (2005), 609-615. 4. M.W. Ackley, S. U. Rege, H. Saxena, J. Microporous and Mesoporous Materials 61 (2003), 25-42. 5. S. P. Senda, H. Saputra, A. Sholeh, M. Rosjidi, A. Mustafa A, BPPT (2006), (in Bahasa Indonesia) 6. N. Rosita, T. Erawati, M. Moegihardjo, Majalah Farmasi Airlangga Vol 4 No. 1 (2004), (in Bahasa Indonesia) 7. F.C. Ozkan, S. Ulku, 2005, J. of Microporous and Mesoporous Materials 77 (2005), 47-53. 8. D. Bonenfant, M. Kharoune, P. Niquette, M. Mimeault, R.  Hausler, R ; Science Tech. Advance Material 9, (2008), DOI 10.1088/1468-6996/9/1/013007  9. V. J. Inglezakis, C. D. Papadeas, M. D. Loizidou,  H.P. Grigoropoulou, Environmental Technology Vol 22 (2001), 75-82 10. M.B. Kim MB, Y.K.  Ryu, C.H. Lee, J. of Chem Eng Data 50, (2005), 951-955 11. J. Pires, M. B. Carvalho J. Mater.Chem 7(9),  (1997), 1901-1904    Generated by Foxit PDF Creator © Foxit Softwarehttp://www.foxitsoftware.com   For evaluation only.

Activation of Natural Zeolite as Water Adsorbent for Mixed-Adsorption Drying

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