Methane Adsorption on Chemically Modified Microwave Irradiated Palm Shell Porous Carbon

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1 Advanced Materials Research Submitted: ISSN: , Vol. 1043, pp Accepted: doi: / Online: Trans Tech Publications, Switzerland Methane Adsorption on Chemically Modified Microwave Irradiated Palm Shell Porous Carbon NASRI Noor Shawal 1,a*, HAMZA Usman Dadum 2,b, SAIDINA AMIN NorAishah 3,c, AHMED Murtala Musa 4,d, MOHAMMED Jibril 5,e and MOHD ZAIN Husna 6,f 1,2,4,5,6 Sustainability Waste-To-Wealth Unit, UTM-MPRC Oil and Gas Institute, Energy Research Alliance, Universiti Teknologi Malaysia, UTM Johor Bahru, Johor, Malaysia. 2,3,5 Chemical Engineering Department, Faculty of Chemical Engineering, Universiti Teknologi Malaysia, UTM Johor Bahru, Johor, Malaysia. 2,5 Chemical Engineering Programme, Abubakar Tafawa Balewa University, Tafawa Balewa Way, PMB 0248 Bauchi, Bauchi state, Nigeria. 1,4,6 Faculty of Petroleum and Renewable Energy Engineering, Universiti Teknologi Malaysia, UTM Johor Bahru, Johor, Malaysia. a noorshaw@petroleum.utm.my, b udhamza2@live.utm.my, c noraisha@cheme.utm.my, d muriahmed@yahoo.com, e mohammadjibril@gmil.com, f husnae@yahoo.com Keywords: CH 4 adsorption, ANG, microwave porous carbons, palm shell, Equilibria Abstract. Low-cost palm shell was used as a precursor for preparation of porous carbons via chemical impregnation with K2CO3 and microwave heating. Volumetric adsorption setup was used to measure the adsorption capacity of methane at K under pressure up to 4 bars. The methane adsorption data was modelled by Langmuir, Freundlich, and Dubinin Radushkevich (DR) isotherm equations. Langmuir and Freundlich models were found to have the best fit than DR isotherm. The kinetics of methane adsorption on the microwave porous carbon followed pseudosecond-order model equation. The highest methane adsorption capacity obtained was mmol/g at 4 bar and K. It was noticed that there is increase in adsorption with increased in initial pressure. The porous carbon displayed good adsorption characteristics for methane. Introduction Natural gas is receiving attention due its low price with less toxic gas emission compared to conventional fuels. Storage of natural gas with methane being the major component is important. Adsorbed natural gas (ANG) has advantage in methane storage over compressed natural gas (CNG) and liquefied natural gas (LNG). This is due to its low cost, energy efficiency, and safety [1]. Porous carbonaceous materials are good candidates for natural gas storage due to large surface area, large pore volume and low density [2]. Palm shell, which is a by-product of the palm oil processing industry, was used as a natural precursor for the production of the porous carbons. This could be important towards reducing environmental nuisance cause by these agricultural wastes. The aim of this study was to study adsorption equilibria of methane on K 2 CO 3 assisted microwave palm shell porous carbons for possible use as an ANG material. The adsorption data was fitted into Langmuir, Freundlich and Dubinin Radushkevich (DR) models. To understand the kinetics of methane adsorption, the experimental data are modelled by the pseudofirst-order equation and pseudosecond-order equation. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-09/05/16,13:33:38)

2 176 Engineering and Innovative Materials III Experimental Methodology Materials. Raw Palm shell was obtained from Koperasi Kampung Jawi Johor Bharu Berhad, Malaysia. K 2 CO 3 was purchased from Merck, Germany. CH 4 was supplied by Megamount Sdn Bhd., Malaysia. Deionized water was used in preparation of the solution. Sorbent Preparation. The raw palm shell was washed several times with distilled water. The palm shells were then dried at C for 24 hrs in an oven and later sieved to size mm. The dried materials were loaded into a stainless steel tubular reactor and then heated in furnace. Heating rate of 10 0 C/min was selected to achieve carbonization temperature of C under nitrogen flow of 100 cm 3 /min for 2hrs. The resultant palm char was allowed to cool to room temperature while maintaining the inert environment throughout the period. For the impregnation process, the char was mixed with K 2 CO 3 solution in the ratio 1:1. The impregnation ratio defined as the dry weight of activation agent per weight of the char. The mixture of precursor and chemical solution was stirred at 85 C and 6 r.p.m for 2 h. It was then placed in an oven for 24 hours at C. The activation involves changing 10 g of impregnated sample into a high temperature quartz reactor. It was then pre-heated in microwave oven (Samsung ME0113M model) in flowing stream of nitrogen (200 cm 3 /min). The flow was then switch over to CO 2 at flow rate of 200 cm 3 /min. Power level of 400W was chosen from the power controller with irradiation time of 6 min. The resultant microwave palm shell activated carbon (MPAC) was washed thoroughly with 0.1 M hydrochloric acid and deionized water until ph is reach. CH 4 Adsorption Procedure. The sorbent CH 4 adsorption capacity was studied in a fabricated packed-bed adsorption system. The temperature of the system was maintained using a thermal insulated electric furnace. The pressure and temperature were monitored using digital pressure transducer (Autonics PSA/PSB series) and K type thermocouple. About 3 g of the adsorbent was charged into the adsorption column with glass wool and then placed in a furnace. The sorbent was then dried in-situ at C under nitrogen flow for 1 h. The cell was then evacuated using VE 215, 2 stage, ¼ HP vacuum pump. For each adsorption measurement, CH 4 was passed into the loading cell to reach the required initial pressure. The valve between the loading cell and the adsorption cell was open to allow the gas contact the adsorbent in the cell. It was allowed to reach equilibrium state i.e. condition at the temperature and pressure constant. The CH 4 adsorption capacity was obtained based on mass balance across the loading and adsorption cell [3]. Equilibria and Kinetics of CH 4 adsorption The adsorption kinetics shows the profiles of the adsorption capacity with time and it is necessary to identify the types of adsorption mechanism. Pseudo first order: A linear form of Lagergren pseudo-first-order model is given in this form: ln (q e q t ) = ln q e k t. (1) If the CH 4 adsorption obeys the pseudo-first-order model, the plots of ln (q e q t ) versus t should be linear [4]. Pseudosecond-Order Model: The linear form of pseudo-second order equation can be written as t/q t =(1/k 2 q e 2 ) + t/ q e. (2) Where; Where; K 1 (min -1 ) and K 2 (mmol/g min) are the rate constant of the pseudo-first and pseudo-second order model respectively. q t (mmol/g) denotes the amount of adsorption at time t while q e denotes the amount of adsorbed at equilibrium. The parameters can be determined experimentally from the slope and intercept of the plots. Isotherm. Adsorption isotherms describe adsorbate and adsorbent interaction; they are useful for adsorption data interpretation and prediction [1]. Three isotherms were applied in this research: Langmuir, Freundlich, and Dubinin Radushkevich (DR).

3 Advanced Materials Research Vol Langmuir Isotherm: The linear form of the Langmuir isotherm model is express as: 1/q = (1/q m K L ) X 1/P + 1/q m. (3) K L is the Langmuir constant that is dependent on temperature. If Langmuir isotherm is valid, linear plot of 1/q versus1/p is a straight line with slope (1/q m K L ) and intercept 1/q m. Where; q m Is the saturation limit (mmol/g), q is the amount adsorbed (mmol/g), P is the equilibrium pressure (bar) [5]. Freundlich Isotherm: The linear form of the Freundlich isotherm model is expressed as: ln q e = ln K F + (1/n)lnP. (4) A plot of ln (q e ) vs. ln (P) is a straight line which enables the constant K F and exponent 1/n to be determined. The magnitude of the exponent n gives an indication of the favourability of adsorption. Whereby, values n > 1 represent favorable adsorption condition [6]. The applicability of the adsorption isotherm models was validated using root mean square deviation (RMSD). RMSD = [1/n (q exp q P ) 2 ] 1/2. (5) Where n is the number of data points q exp (mg/g) and q p (mg/g) are the experimental and calculated adsorption capacity. The lower the RMSD value the better the estimated model performs. Dubinin Radushkevich (DR) isotherm model The linear form of DR is given as: lnq e = lnq s B D Ɛ 2. (6) Where qe is the amount of adsorbed at equilibrium (mmol/g); qs is the theoretical isotherm saturation capacity (mmol/g); B D = Dubinin Radushkevich isotherm constant (mol 2 /kj 2 ); Ɛ is the Polanyi potential which is related to the equilibrium pressure as follows: Ɛ = RTln[1+1/P e ]. (7) where R, T and P e represent the gas constant ( J/mol K), absolute temperature (K) and adsorbate equilibrium pressure (mmol/g) respectively. The constant B D gives the mean free energy, E, of sorption per molecule of the sorbate when it is transferred to the surface of the solid from infinity in the solution and can be computed using the relationship [7]. E = 1/Sqrt(2B D ). (8) Results and Discussion Methane Adsorption. The equilibrium data of methane adsorption at K and pressures up to 4 bars is given in Fig. 1. The methane uptake isotherm profile is of type 1 according to IUPAC classification of isotherms. Initially, there is drastic increase in methane uptake at lower pressure but then slowly increased with increase in pressure [6]. Appropriate linearized plots were created (not shown) base on the Langmuir, Freundlich, and DR. isotherm Eq. (3), (4) and (6). The slopes and intercept were used to obtain the isotherm parameters listed in Table 1.

4 Amount adsorbed, q (mmol/g) 178 Engineering and Innovative Materials III Fig. 1. CH 4 adsorption isotherm plot On the basis of the RSMD and R 2 value, it was found P (bar) that the Langmuir and Freundlich isotherm model fits the experimental data better than the DR model (Table1). Previous studies show that Langmuir [1] and Freundich [2] isotherms fit methane adsorption data satisfactorily. Table 1. CH 4 adsorption isotherm parameters Isotherm Constants RSMD R 2 Freundlich n K F (mmol/g) Langmuir q m (mmol/g) K L (bar -1 ) D-R K d x10 7 (mol 2 /J 2 ) q s (mmol/g) E (J/mol) Kinetics. The linearized methane adsorption kinetic plots (not shown) using eq. (1 and 2) were used to obtained kinetic constants and R 2 (Table 2). The calculated values of methane adsorbed on the MPAC porous carbon varied with the experimental values. Hence, the pseudofirst-order equation was not appropriate to describe the methane adsorption on the activated carbon. This is confirmed by low R 2 values. In the pseudosecond-order model, the calculated values are close with the experimental values with higher R 2 values also. This shows that second order mechanism is predominant. Similar observation was reported on adsorption of methane anthracite-based porous carbon [6]. qe, exp. qe, Fred. qe, Lang. qe, DR. Sample Table 2. Kinetic model parameters for adsorption of CH 4 on MPAC Initial Press. q e, exp Pseudo-first order Pseudo-second-order q e, cal k 1 R 2 q e, cal k 2 R MPAC

5 Advanced Materials Research Vol Conclusions The adsorption equilibrium data of methane adsorption on the microwave palm shell porous carbon were obtained at K and at pressures up to 4 bar. The MPAC sorbent recorded highest CH 4 uptake of mmol/g CH 4 /g adsorbent at 4 bar, K. The adsorption experimental data correlated well with Langmuir and Freundlich isotherm with R 2 > The kinetics of the adsorption process followed pseudo-second-order model based on the correlation coefficients values. The equilibrium and kinetic study conducted shows that porous carbon derived from palm shell via K 2 CO 3 assisted microwave heating is a potential material for methane adsorption and storage applications. Acknowledgment The authors acknowledge and appreciate the financial support provided by the ministry of education Malaysia through University Teknologi Malaysia (UTM), Johor, Malaysia, to fully undertake this research under the University Research Grant (URG) Q.J H79. References [1] J. S. Sren scek-nazzal, W. Kamin ska, B. Michalkiewicz, Z.C. Koren: Production, Characterization and Methane Storage Potential of KOH-Activated Carbon from Sugarcane Molasses. Industrial Crops and Products. Vol. 47 (2013) [2] M. Delavar, A.A. Ghoreyshi, M. Jahanshahi & N. Nabian: Comparative experimental study of methane adsorption on multi-walled carbon nanotubes and granular activated carbons, Journal of Experimental Nanoscience, 9:3 (2014), [3] R. Maryam, F. Shohreh; Mehrdad G.; M.M. Ali: Study of Methane Storage and Adsorption Equilibria in Multi-Walled Carbon Nanotubes. Iran. J. Chem. Chem. Eng. Vol. 27, No.3, [4] Z. Shahryari, A.S. Goharrizi, M. Azadi: Experimental study of methylene blue adsorption from aqueous solutions onto carbon nano tubes. Int J of Water Res.& Environ Eng. Vol.2 (2) (2010), p [5] N.S. Nasri, U.D. Hamza, N.S. Ismail, M.M Ahmed, R. Mohsin: Assessment of Porous Carbons Derived from Sustainable Palm Solid Waste for Carbon Dioxide Capture. J of Cleaner Prod. 71 (2014), p [6] J. Luo, Y. Liu, C. Jiang, W. Chu, W. Jie and H. Xie: Experimental and Modeling Study of Methane Adsorption on Activated Carbon Derived from Anthracite. J. Chem. Eng. Data 56 (2011), p [7] L. Cavas: Comment on Equilibrium sorption isotherm studies of Cd(II), Pb(II) and Zn (II) ions detoxification from waste water using unmodified and EDTA-modified maize husk. Electronic Journal of Biotechnology, Vol 11 (2), 2008.

6 Engineering and Innovative Materials III / Methane Adsorption on Chemically Modified Microwave Irradiated Palm Shell Porous Carbon /

CO 2 Adsorption Equilibria on a Hybrid Palm Shell-PEEK Porous Carbons

CO 2 Adsorption Equilibria on a Hybrid Palm Shell-PEEK Porous Carbons A publication of CHEMICAL ENGINEERING TRANSACTIONS VOL., Guest Editors: Petar Sabev Varbanov, Jiří Jaromír Klemeš, Sharifah Rafidah Wan Alwi, Jun Yow Yong, Xia Liu Copyright, AIDIC Servizi S.r.l., ISBN