Improving methane storage on wet activated carbons at various amounts of water

第40卷第4期燃料化学学报Vol. 40 No.42012年4月Joumal of Fuel Chemistry and TechnologyApr. 2012文章编号: 0253-2409(2012)04-0385-05Improving methane storage on wetactivated carbons at various amounts of waterMOHAMMAD JABER DARABI MAHBOUB, ALI AHMADPOUR, HAMED RASHIDI(Department of Chemical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad 9177948944, lran)Abstract: Different mesoporous activated carbons were prepared by both chemical and physical activation processes and wereexamined for methane uptake in the presence of water. Methane isotherms were obtained at wet condition by wetting samples withwater at mass ratio of water/carbon (R) close to 1.0. To compare, the amount of methane storage were also measured at drysituation.The maximum amount of methane stored was attained as 237 V/V at R= 1. 0 by hydrate formation :at the methane criticalpressure. In the next step, mass ratios of water/ carbon were changed to investigate various amount of water for metbane storageenhancement. Two other values of mass ratio of water/carbon (R=0.8 and 1.4) were selected and methane isotherms wereobtained at the same conditions. Maximum values of 210 and 248 V/V were reached for methane storage, respectively. It was alsoobserved that, in the pressure range lower than hydrate pressure, by increasing water ratio the hydrate formation pressure wasdecreased and methane uptake was much less than that of dry condition due to pore filling by water.Key words: methane storage; hydrate; isothemm; water; wettingCLC number: TE624. 4Document code: AIn recent years, natural gas ( with more thaninvestigated for stroing methane onto wet activated80% methane) has noticed considerable regard as acarbons is the combined utilization of ANG and NGHclean fuel for vehicles and transportation because oftechniques. In this method, hydrate formation playsvarious advantages such as abundant reserve, lowmajor role to enhance methane storage and for thisprice and clean fuel compared with the conventionalpurpose a mesoporous structure is required forfossil fuels1.2. Utilization of methane gas as a fueladsorbent. Methane molecules are trapped in cagesproduced less carbon dioxide and more water vapormade of water units that linked with each otherper energy unit than buming gasoline or diesel!'s.through hydrogen bonding. However, the formationAlthough methane is an appropriate fuel, it is difficultcondition of NGH is rigorous and its formation rate isto store due to its low density， therefore suitablelow[8.9]. Different research groups have conductedstorage method is necessary to use NG as vehicularexperiments with wet activated carbons to storefuel4). Four different techniques known for methanemethane. Perrin et al. investigated the storage of(or natural gas) storage namely liquefied natural gasmethane proposed by two patents dealing with(LNG), compressed natural gas ( CNG) , adsorbedmethane adsorption on wet activated carbons' 181.natural gas ( ANG) and natural gas hydrate (NGH)，They applied commercial carbons for storing methanehave been considered to improve the energyin the presence of water and isotherms for all samplesdensityS- 9. Among these methods, adsorbed naturalin both wet and dry conditions were obtained.gas on the porous materials have the advantage ofMethane storage of 227 V/V was attained for theiroperating at low pressure and room temperature,best sample at wet condition.allowing methane consumption comparable to theZhou et al. tried to achieve high gas adsorptionother conventional petroleum based fuels'by using moderate pressure and room temperatureMaximum storage pressure utilized in the ANG iscondition in microporous activated carbons producednormally in the range of 3.5 ~4.0 MPa and activatedfrom coconut shell. But， they found very lttlecarbons with deliverable capacities ranging from 70 toenhancement with wet activated carbons because pore150 V/V at room temperature and pressure of aroundsize and pore size distribution of carbon samples used3.5 MPa are appropriate adsorbents for thisin their experiments were quite inappropriate and mostpurpose135~]6]. The U. S. Department of Energyof the micropores were illed by water-19). Zhou et(DOE) has adjusted target of 180 V/V for methaneal. studied the influence of pore size distribution orstorage at 3. 5 MPa and ambient temperature[17].the adsorption in wet condition. They obtainedRecently, one of the latest methods that has beenmethane uptal中国煤化IvarcdcarbonsReceived date: 2011-11-08; Received in revised form: 2012-03-18.TYHCNMH GCorresponding author: Ali Ahmadpour. E-mail: ahmadpour@ um. ac. it.本文的英文电子版由Elsevier 出版社在ScienceDirect.上出版( htp://www. seiencedirect. com/scicnce/journal/18725813)。386燃料化学学报第40卷at various water to carbon mass ratios ( R) andphysical activation techniques.maximum amount of storing was obtained a1 Experimental30 mmol/g for a carbon sample named BY-1C .preparation and charactrization ofNajbi et al. examined natural gas storage in dry andwet conditions on three commercial activated carbonsactivated carbons Four activated carbons werenamed NC120， Picazine and Sigma. In theirprepared from coconut shell by the application of bothinvestigations on these three different ACs， achemical and physical activation processes. In brief,maximum methane storage of 180 V/V was.raw material was sieved to uniform size in the rangeachieved21of1.0 ~2.0 mm and was activated by ZnCl2 as aIn most previous studies, methane storages werechemical agent with various mass ratios of ZnCl,/rawobtained with constant water/ carbon ratio close to 1.matereial. The sample was placed in a boat inside aThere is not enough investigation on the variousrotary furmace and kept under nitrogen flow ofamount of water for methane storage at the wet300 mL/min until the temperature was reachedcondition. Only Celzard et al. and Zhou et al.800 C. After that, N2 gas was switched to CO2 as aexamined various amounts of water to increasephysical agent for a certain time. After finishing thmethane uptake and they reported various ratios asexperiments and cooling samples to the ambientoptimums for different adsorbents1. Besides, theytemperature, they washed several times withhave not performed good comparison among thehydrochloric acid and distillated water to remove allresults due to applying various amounts of water forthe remained chemicals. Samples were then dried for24hat110Cinanoven.diverse activated carbons.In the present work,we have investigatedBy using an automatic adsorption instrument( Micromeritics,Autosorb-1C )，N2 adsorptionmethane adsorption on wet activated carbons madefrom coconut shell and examined three differentisotherms of samples were measured at 77 K toamounts of water/ carbon ratio equals to0.8, 1. 0 anddetermine BET, mesoporous surface areas, total porevolumes ,micropore volumes and mean pore1.4 for all samples to improve methane storage and toobtain the better amount of water. Activatd carbonsdiameters. Table 1 shows different conditions used inwere also prepared by the combined chemical andthe preparation of ACs and major charactristics foreach sample. .Table 1 Different preparation conditions and characteristic of samplesSarmple(R)(water CO2 flow Temp. Carbonization Soaking Agr/ Average pore Total pore volume Packing density/catbon) (mL min~) 1/Ctimet/h timet/h (m°.g") diameterd/nm v/(cm’.g") ρ/(cm'.g- )L30073021548 .3. 4231.3240.437200002 1003. 3361.7520.402L113.51 5852. 985.1.183 .0.414L15151 6403. 1311. 2480. 6041. 2Density measurement The density ofunder vacuum condition at 243 ~247 K (by the helpactivated carbon is a very important parameter in ANGof dry ice bath) for 2h to remove any air or gasesapplications , as higher packing density leads to higherwhich trapped inside the AC porous structure. Twomethane uptake in the limited vessels. Packingpressure sensors and a thermocouple were used todensities of samples were measured in a small stainlessmeasure pressure and temperature of the bed. Asteel cylinder by applying the pressure of aboutthermostatic device could adjust the temperature to be335 kg .cm~It had been shown that pressure叩toconstant at about 2 C ( bath with N, N Dimethyl550 kg. cm-2 did not affect methane uptake of theAniline at its melting point) and also all the apparatussamples at dry condition4was isolated in that constant temperature. For each1.3Methane srorage instruments Eachadsorbent sample, the methane uptake was measuredactivated carbon sample was weighted and placed intoby loading methane into the vessel up to 8 MPa. Thea high pressure stainless steel vessel and degassed atquantity of loaded methane was determined by the220 C for 10 h to remove any impurity and thenpressure decr中国煤化Iducer and thecooled to room temperature. In the next step, watercharging ratYHCNMH Gneedle valve.was added to the carbon powder. For uniformFinally, the mumber or moles oI meunane really storeddistribution of water， the sorbent bed stayedin the sample holder was obtained by the applicationuntouched for 1 h and then sample was degassed again.第4期Mohammad Jaber Darabi Mahboub et al:. Improving methane storage ......387_of Van der Waals equation of statel18,2. Thethis particular temperature and pressure range. In theexperimental charging process onto wet activated low pressure range, the methane storages increasecarbons was carried out ina set-up shown in Figure 1.”rapidly ilustrating adsorption of methane moleculesinside the micropores. By increasing pressure, therates of gas uptake decrease and slowly reach theoplateau at the high pressures.The above AC samples were then wetted by thedeionized water with a water/carbon mass ratio ( R)of 1.0 and new isotherms were measured at the same一conditions. Figure 3 shows methane uptakes for wetactivated carbons with R = 1. 0. The first part ofisotherms shows classical physisorption related toadsorption inside the pores before critical pressure and白bhydrate formation occurring. In comparison with th|adry situation, before the hydrate formation pressure,the isotherms indicate much lower methane uptake inthe wet condition than that of dry due to the presenceof water inside the pores. Secondly, with increasingpressure, at the critical pressure, hydrate is formeda: methane gas cylinder; b: gas loading cell;inside the mesopores and the methane uptake increasesC: valves; d: pressure transducers;rapidly ( creating stepwise at isotherms) and becomese: N,N dimethyl aniline bath;much higher than that measured at dry condition. Thisf: sample holder; g: high vacuum pumpjump corresponds to the formation of the hydrate2 Results and discussionwithin the large pores. On the other hand, with the2.1Methane storage at wet and dryincreasing of pressure to higher values, the methaneconditions Methane isotherms were collected atadsorptions in some pores which do not contain2C and up to the pressure of 8 MPa for both dry andenough water to form hydrate, provid positive slopeswet conditions. Methane uptakes were first measuredat the end of the isotherms.for all AC samples at dry condition and the isotherms240are shown in Figure 2.200 t80 r60 F60ξ 140个20 t--L780 t00 t40-●- L1I一1-L740 tFigure 3 Methane uptakes of activated carbons listed inPressure p/MPaTable 1 at2 C and wetted with a constantwater/carbon mass ratio = 1.0Figure 2 Methane isotherms for activatedcartbons at dry condition at 2 C2.2 Effect of water amounts on methaneThe applicable unit for gas storage purposes isstorage In the previous section ，methane uptakesusually defined as the STP volume of methane storedwere studied at the ratio of water/ carbon equal toper unit volume of the storage vessel ( V/V )，1.0. To achieve. maximum amount of methanestorage, two d」中国煤化工ratios of0.8therefore the amount of methane adsorbed in moles pernd 1.4 wer(YHC N M H Ge mentionedgram of adsorbent have been converted to V/V unitactivated carbon samples. Figure 4 shows isothermsafter applying ACs bulk densities. As in Figure 2for these samples with different wetting ratios.shown the data points are typically type I isotherms atMeanwhile, for comparison the dry isotherms were388燃料化学学报第40卷also illustrated. All isotherms present the similar shape pores would be filled by water and resulted in lowto those in Figure 3. The bhydrate formation pressure is hydrate formation!2)seen to be different depending on the activated carbonTable 2 Methane storage values withsample. Based on the above results, a large amount ofdifferent amounts of watermethane is observed to be stored in activated carbonscontaining higher amounts of water. Table 2 showsDry conditin R=1.4 R=1.0 R=0.8Sample(V/V(V/V) (V/V)(VV)the amounts of methane uptake at wet and dry166248210L7conditions. Researches by other groups indicated that16822622085L8wetting more than the saturation value (R>Rm) leads3319761L1Hto very low methane storage, because most of the3819820258L152525(sampleL7sampleL8ξ 200s 200so F-.... dry.... dry...- R=0.8--●-- R=0.8一R=1.050上)0789Pressure P /MPaPressure p /MPa50 rsample L1Isample LI5多20000 t50 t100.. dry-●一dry--●- R=0.8- -8- R=1.0- R=1.4a- R=1.489;789Pressure p MPaFigure 4 Methane uptakes of AC samples with different amounts of water3 Conclusionsperformance in terms of methane uptakes among otherThe present study shows that hydrate formationvalues of R. According to the results, for L7 sampleinside the pores of activated carbons plays major role( with higher average pore diameters) , the amounts ofin enbancement of methane storage. The resultsmethane storage are 210， 237, and 248 V/V forindicate that before the hydrate formation pressure ,water/carbon ratio equals to0.8, 1.0, and 1.4,the methane uptakes are much less than that of dryrespectively.condition due to the presence of water which f1l andAcknowledgementsblocks the majority of the porosity. After the hydrateThe authors are grateful to Chemical engineeringformation ,isotherms show stepwise increaseindicating the high methane storage. With theresearch Lab. of Ferdowsi University of Mashhad forincreasing water/ carbon mass ratio studied, theproviding some facilities. Also, special thanks touptakes of methane increase. The condition withShahid Hash「 中国煤化工sppring thiswater/carbon mass ratio of 1. 4 ilustrates the bestproject."YHCNMH GReferences[1] LEJS, JHUNG s H, YOONJ w, HWANG Y K , CHANGJ s. Adsorptio of methane on porous metal carboxylates[J]. J Ind Eng Chem,第4期Mohammad Jaber Darabi Mahboub et al: Improving methane storage ......3892009, 15(5): 674-676.temperature on pore textures and methane storage ability[J]. carbon, 2004, 42( 14): 2855-2866.3] ESTEVES IA AC, LOPES M ss, NUNES P MC , MOTAJP B. Adsorption of natural gas and biogas components on activated carbo[J].Sep Purif Technol, 2008, 62(2): 281-296.4] SENKOVSKA I . KASKEl s. High pressure methane adsorption in the matal-organic franeworks Cu3( btc)2, Zn(bdc)zdabco, and CrgF(H2O)20( bdc);[J]. Microporous Mesoporous Mater, 2008, 112(1/3): 108-115.5] BAGHERI N, ABEDI J. Adsoption of methane on com cobs based activated carbon[J]. Chem Eng Res Des, 2011, 89( 10) : 2038-2043.6] LINO P, MAIONE B, AMORESE C. Modeling and predictive control of a new injection system for compressed natural gas engines[J].Control Eng Pract, 2008, 16( 10): 1216-1230.7] SZARGUT I, sZCZYGIEl 1. Uilization of the ceryogenic energy of liquid natural gas (LNG) for the production of elctrcity[J]. Energy,2009, 34(7): 827-837.8] KIMN, LeEe JH, CHO Ys, CHUN W. Formation enhancement of methane hydrate for natual gs tansport and stonge[J]. Energy, 2010,35(6): 2717-2722.9] GANI H, MANTEGHIAN M，RAHMI MOFRAD H. Effet of mixed compounds on methane bhydrate formation and disciation rates andstorage capacity[J]. Fuel Process Technol, 2007, 88(9): 891 -895.[10] YANGXD, ZHENGQR, GU A z, LU X S. Experimental studies of the performance of adsorbed natural gas storage system duringdischarge[J]. Appl Thermal Eng, 2005 , 25(4); 591-601.[11] PUPIER O, GOETZ V, FISCAL R. Effet of cycling operations on a adsorbed natural gas storage[J]. Chem Eng Process: ProcessIntensification, 2005. 44(1): 71-79.[12] SALEHI E, TAGHIKHANI v, GHOTBI C, NEMATI LAY E, AHOIAEI A. Theoretical and experimental study on the adsorption anddesorpion of mechane by granular activated carbon at 25C[J]. J Nat Gas Chem, 2007, 16(4): 415-422.[13] GUAN C, suf, ZHAOX s, WANG K. Methane storage in a template-syntbesized carboa[J]. Sep Purif Technol, 2008, 64(1): 124-126.[14] ARIYADEJWANICH P, TANTHAPANICHAKOON w, NAKAGAWA K, MUKAI S R, TAMON H. Preparation and characterization ofmesoporous activated carbon from waste tires[J]. Carbon, 2003, 41(1): 157-164.[15] ZHU z, UI A, YAN L, LIU F, ZHANG Q. Preparation and characterization of highly mesoporous spherical activated carboas fromdivinylbeazene-dcrived polymer by ZnCl2 activation[J]. J Colloid Interface Sci, 2007, 316(2): 628-634.[16] ZHOU H, 2HU s, HONMA I, SEKI K. Mecthane gas storage in self ordered mesoporous catbon (CMK-3)[J]. Chem Phys Ltt, 2004, 396(4/6):252 - 255.[17] MA s. Gas adsorpion pplications of porous metal - organic frameworks[J].Pure Appl Chem, 2009. 81(12): 235-225.[18] PERRIN A, CELZARD A, MARECHE J F, FURDIN G. lmproved methane storage capacity by sorption on wet active catbons[J]. Carbon,2005 , 42(7): 1249-1256. .[19] zHOUL, u M, SUN Y, zHoU Y. Effect of moisture in microporous activated carbon on the adsorptio of methane[J]. Carbon, 2001, 39(5): 73.776.[20] ZHOU Y, DAI M, zHOUL, SUN Y, sU W. Storage of methane on wet activated catbon: Infuence of pore size distributioa[J]. Carton,2004. 42(8/9): 1855-1858.[21] NAJIBI H, CHAPOY A, TOHIDI B. Methane/ naural gas storage and delivered capacity for activated carbons in day and wet conditions[J].Fuel, 2008, 87(1): 7-13.[22] CELZARD A, MARECHE I F. Optimal weting of active carbons for methane bydrate fomatio[J]. Fuel, 2006, 85(7/8): 957-966.[23] LOZANO-CASTELLO D, CAZORLA-AMOROS D, LINARES-SOLANO A, QUINN D F. Infuence of pore size distribution on methanestorage at relatively low pressure: Preparation of activated carbon with optimum pore size[J]. Carbon, 2002, 40(7): 989-1002.中国煤化工MYHCNMHG.