Preparation and characterization of a composite membrane based on the asphaltene component of coal

Mining Science and Technology( China)21(2011)407-411Contents lists available at ScienceDirectMining Science and Technology( China)ELSEVIERjournalhomepagewww.elseviercom/locate/mstcPreparation and characterization of a composite membrane basedon the asphaltene component of coaZhang Liying, Qin Zhihong, Li Xinyan, Chen Juan, Liu Peng. Wang XiaoyanSchool of Chemical Engineering and Technology. China University of Mining 6 Technology. Xuzhou 221116, ChinaARTICLE INFOABSTRACTArtide history:Asphaltene-ceramic composite membranes were fabricated from ceramic supports and an asphaltene6 October 2010omponent, which was obtained from the separation of coal to give a kind of new carbonaceous precursorin revised form 10 November 2010aterial Using SEM and thermogravimetric analysis to measure the microstructureAvailable online 12 June 2011asphaltene component allowed the porosity, permeability, and retention ratios to be determined. Thesults show that the asphaltene component can be regarded as a good carbon membrane precursoraterial because of its high carbon content and strong bonding capacity. when ceramic supports areKeywords:impregnated with asphaltene colloid the asphaltene easily combines with the support surface and formsa good carbonaceous film after carbonization. little of the asphaltene component permeates into theinternal pores of the ceramic support. although the number of coats applied to the substrate had littleaffect on the porosity of the asphaltene-ceramic composite membranes the permeability varied dependeod colloiding upon the number of times the substrate was treated. The way bubbles escape from the film, and thephenomenon of coalescence, as affected by different film thicknesses also seem closely related to thember of coats. a composite membrane carbonized at a fnal temperature of 600C is relatively denseand the permeability of fe(OH) colloid through it is very low. a membrane fired at 800C is porous andits permeability and retention of Fe(OHh colloid are 88 L/(m h MPa)and 85.3% respectively when thetrans-membrane pressure is 0. 22 MPa.o 2011 Published by Elsevier B V on behalf of China University of Mining Technology1 IntroductionThe precursor of the composite carbon membrane described inhis study is an asphaltene obtained by the separation of coal com-A carbon membrane is a kind of novel inorganic membrane that ponents using carbon disulfide/N-methyl pyrrolidone(CS2/NMP)xhibits superior stability compared to organic polymer membranes mixed solvent(6, 7 Other members of our group previously sepa-when in the presence of high temperatures, oxidative, or erosive rated eight different coal samples characterized by different originenvironments [1, 2 Carbon membranes are generally divided into and rank [8]. The results showed that bitumen could be separatednon-supported carbon membranes and supported carbon mem- from all the coal samples and that the production from the major-branes according to their different structures[3, 4). Generally speak- ity of the coal samples was greater than 10% The asphaltene com-ing non-supported carbon membranes are crisp and brittle. while ponent shows a strong bonding capacity even though undersupported carbon membranes are more suitable for practical appli- natural conditions the bond index GRI may be more than 80 191.cation[5]. The reason is that supported carbon membranes are made Furthermore, it is readily available and low in price. In summary,by coating the precursor onto a high strength and porous support asphaltene obtained from coal is a high value carbon membranematerial, which makes up for the lack of mechanical strength of precursor material worth developing.the membranes. the nature of the precursor. the film preparationThe bitumen obtained from coal separation is in the form of anethod, and carbonization conditions are key factors for the prepa- thick black asphalt sol. The bitumen particles with an averageration of high performance carbon membranes. Expanding the range diameter around 100 nm will disperse in a small amount of NMPof precursors and developing cheaper and better performing precur- solvent[10]. this asphalt sol can be directly coated onto a supportsor materials are currently prerequisites for future industrial appli body without a further treatment, or actually dissolving the parti-cation of carbon membranescles, which compensates for the poor solubility of the organicpolymer.In this paper the properties of asphaltene and the preparationprocess of an asphaltene-ceramic composite membrane areCorresponding author. Tel: +86 13852034193.described. The porosity of composite membranes is determinedE-mailaddress:qinzh1210@163.com(zQn).by the water-boill中国煤化工nd retention ratio1674-5264/5-see front matter o 2011 Published by Elsevier B V. on behalf of China University of Miningdoi:101016mst201105005THCNMHGng et aL/ Mining Saiof Fe(oH)3 colloid were determined using permeation devices and Table 2an atomic absorption spectrophotometer.数mof carbonizationtemperature ('C/min)cyclestempera2. Experimental042.3,4600.700.8002.1. Materials and equipmentsAsphalt sol was obtained from separation of Pingdingshan coal, 2.6. Determination of porosity and permeabilityHigh-tech Materials Co, Ltd, and were 15 mm in diameter andThe porosity and permeability of the ceramic support were3 mm thick. The instrumentation used included an STA409C type measured by using water-boiling and a permeation device [111DTA/ DSC-TG thermal analysis instrument (NETZSCH Company, The same procedure was applied to the composite membrane.Germany ), an $-3000N scanning electron microscope, and a tube Using the formula 121carbonization furnace from the Xuzhou jinchang Mechanical andElectrical Equipment Co, Ltd. The penetration assessment devicewas homemade and a tSA-990 SUPER AFG-type tSa-990 atomicA·t△Pabsorption spectrophotometer from the Beijing Puxi General where is the water permeability. L/(m h MPa): A the area of themembrane, m2: v the volume of water that passed through themembrane, L; t the time, h; and, AP is the trans-membrane pres-2. 2. Proximate and ultimate analysissure, MPa it was possible to determine the permeability of thesamples.The proximate and ultimate analysis of the raw coal and asphaltene samples are recorded in Table 12.7. Preparation of fe(oH)] gel and the determination of retentionrano2.3. Microscopic structure of asphalteneGel was prepared according to the chemical reactionAn asphalt film supported on the surface of quartz was made by FeCl]+ 3H20=Fe(OH)3(gel)impregnation. The film forming properties and microstructure ofThe preparation was performed by800 mL of distilledthe asphaltene sol were examined. The microscopic morphology water into a large beaker and boilingmL of FeCl3 solutionthe film was observed using a scanning electron microscope after (30 / L) was added and the mixturefor an additionaldrying 24 h under natural air.2 min a red-brown, Fe(OH)3, colloid was then obtained. the retention ratio, r. of thebrane toward Fe(OH) colloid2. 4. Thermal properties of asphaltenewas determined by mixing a known volume of the original colloidal solution with an equal volume of freshly prepared hydrochloricA STA409C type DTA/DSC-TG thermal analysis instrument was acid (3 mol/L)stirring. This solution was allowed to stand for 24hsed to measure the thermal properties of the solid asphaltene. before the testing( this procedure dissolved the Fe(OH) in the oriThe conditions were: heating rate, 10C/min: final temperature.ginal colloidal with the hydrochloric acid). This same procedure900C; nitrogen flow rate, 100 mL/ minwas applied to the filtrate that had passed through the membrane.After this the Fe*concentrations in both the original colloidalsolution and in the filtrate were determined using a TSA-9902.5. Carbon membrane preparationSUPER AFG TSA-990 atomic absorption spectrophotometer. Theresults are indicated by Co and C. The retention ratio, R, of the com-The concentration of the asphalt sol obtained from separation of posite membrane is given bythe following way. a piece of ceramic substrate was dipped into R=co-cx100%the asphaltene sol at a uniform rate of 2 cm/ min and soaked for5 min before being slowly removed. This same operation was per-formed once more on the coated ceramic after first drying at room 3 Results and discussiontemperature for 1 h In this way two, three, or four-coat carbonmembranes could be prepared. The composite membrane was 3.1. sEM photosdried under natural conditions for 12 h before carbonization to remove the solvent. Table 2 shows the carbonization conditions.The microscopic morphology and structure appear as shown inNote that N2 was used as protective gas to isolate the sample from Fig. 1 when the asphaltene colloid is used for coating the surface ofquartz. Fig. 1a shows that the coating is uniform and denseat that temperature for 10 min before the stove power was shut off. (excluding cracks). There is a layer of fine asphaltene particles be-leaving the N2 flow on, while the temperature dropped to 450 C. neath the cortex. Fig 1b shows that these particles are uniform insize and that the particle size is about 500 nm the particles are inTable 1the form of small balls formed from the fine asphaltene colloidalProximate and ultimate analysis of the raw coal and asphaltene(byparticles, the original diameter of which is 100 nm. the colloidalparticles coalesce with each other as the solvent evaporates duringthe drying pre15130.37031.6568.3584。HH中国煤化工 ace layer do not combined into bAsphaltene 7.05-rces acting on them5401Rather theyCN MHGthe action of surfaceL Zhang et al. Mining Science and Technology( China)21(2011)407-411(a) Asphaltene surface(1000x)b)Asphaltene particles(10000x)Fig. 1. Scanning electron micrographs of an asphaltene coating on a quartz surfacetension [13]. As solvent continues to evaporate the cortex may fabricated under different carbonization temperatures, again com-shrink and form localized cracks. After charring these cracks will pared with their supportsdisappear as the small spheres melt at the high temperature.Table 3 and Fig 3 show that for a final carbonization temperature of 600C the percentage decline of porosity and permeability3.2. TG-DTG curveare both larger. A minimum appears at 800C for the compositemembrane, which results from the pyrolysis and condensationFig. 2 shows the TG-DTG curves of the asphaltene. As can be reaction of the asphaltene. Increasing the temperature aboveseen from the TG curve, the mass of the asphalt declines steadily 600C causes the pyrolysis of asphaltene to continue and a signif-at temperature ranging from 25 to 900C. This indicates that the icant high-temperature polycondensation appears at 700Cdecomposition of bitumen is accompanied by release of some (Fig. 2). More pores then appear in the asphalt film carbonized atmaterial during the process. The residual carbon constitutes 67% 800C, which results in greater porosity and permeability of theof the sample at a temperature of 900 C. The DTG curve of the asphalt film. However, the number of coating cycles has less effectasphaltene contains multiple peaks that can be divided into several on porosity when coating more than twice, while the permeabilitystages:(1)from 25 to 170C the main process is removal of water changes significantly as the number of coats changes. The maxi-and the maximum rate of dehydration occurs at 1106C.(2)From mum penetration occurs on a three-coat composite membrane.170 to 360C NMP and adsorbed gas are evolved. the maximum The reason may be that the film formed on the support surface israte for this process occurs at 2524C. (3)From 360 to 600C ther- relatively thin if it is coated twice so the gases, and tar steam, pro-mal decomposition occurs and CHA H2, unsaturated hydrocarbons, duced during carbonization can escape without forming bubblesand tar vapor outgas from the asphaltene[ 14]. The maximum for Therefore, coating twice results in a dense carbon film Coatingtween 600 and 900C is slow and represents mainly the release port. Although the gas and tar vapor of a four-coat film producedof secondary gases, such as H2 and CH4 [14]. A smaller peak ap- during carbonization can escape from the film in the form of bubpears at 700C, which may be due to a polycondensation of asphal- bles pores created by the bubbles coalesce when the thick filmtene that speeds up the mass releasemelts and carbonizes. Hence, the four- coat composite membraneis relatively dense, too. The only thickness appropriate for the for-3.3. Porosity and permeabilitymation of a porous film is the three-coat one.The reason the porosity of the composite membrane is lowerthan that of ceramic support is that the surface and pore walls ofThe porosity and water permeability data for nine composite the ceramic support are covered, or filled in, by asphalt duringFig. 3a shows the percentage decline in porosity of the composite the dip-coating: the composite membrane pore size is smaller.membranes obtained under different carbonization temperatures, from the escape of gas and tar vapor during carbonization, the restcompared with their supports, as a function of the number of coats. of the residual carbon will continue to fill the original pores. ThusFig- 3b shows the relationship between coats and the percentage the pore structure is more uniform than that of the ceramic sup-decline in pure water permeability of the composite membranesport. the decrease in composite membrane porosity increases theresistance to liquid flow and thus a corresponding decrease in100composite membrane permeability occurs. Fig 3 shows that thepercentage decline in porosity of the composite membranes, com-pared to the support, ranges from 6.0% to 8.5%. the decline in permeability of the composite membrane is from 79% to 88% Thisndicates that the bitumen sol permeated into the pores of the sup-port only a little during dip-coating while the bitumen forms a filmon the surface of the support thus causing a relatively small changein porosity but a bigger change in permeability. The surface film2524°Cafter carbonization forms a correspondingly dense or porous film10.6Caccording to the form of the gas and tar vapor escaping from theL100300500film. as well as theer.T°C)cortex composite中国煤化工 allow for separa-tion while beingthe supports areCNMH Gurned off so thatFlg. 2. TG-DTG curves of the asphaltene.L Zhang et aL Mining Science and Technology(china)21(2011)407-411Porosity and permeability of support and composite membranesCarbonization Sample Number Support Composite membrane Supporttemperature(C) number of coats porosity porosityx10-5Lpem h bilay foposite membrane porosity0-L/(m?'hMPa))041903852.972.7623456789234234230.4160412206042203952.782.4104210.3910.41603912.2104143.92(a)9(b)■600℃8700℃800℃a328420oating timesCoating timeFig 3, Percentage decline in porosity and permeability versus number of coating times. (a) Porosity, and(b) permeability3. 4. Retention of fe(oH)3 colloid by the composite membraneity of Fe(OH)3 colloid through it is very low. a membranemade at 800C is porous, however. The permeability andThe size of the Fe(OH)3 colloidal particles is between 10-andtention of Fe(OH) colloid for a twice coated composite10 m[15]. The ceramic support has almost no rejection towardmembrane fired at 800C are 88 L/(m h MPa)and 85.3%this sized particle. The filtrates obtained after passing the fe(OH)3respectively when the trans-membrane pressure issuspension through composite membranes 1, 4, and 7 were color-0.22 MPaless and transparent. This shows that the asphaltene-ceramicomposite membranes have a good retention capacity for nano-particles. The retention rate, R, of membrane number 7 for atransmembrane pressure of 0.22 MPa was 85.3% and the filtration Acknowledgmentsrate was 88 L/(m2h MPa). The permeability of composite mem-We express our appreciation to the National Natural Sciencebranes 1 and 4 was less than 3 L/(m h MPa)in both cases owing Foundation of China( Nos. 50874108 and 50921002) the Naturalto the more dense carbonaceous cortex of these samples. The result Science Foundation of Jiangsu Province(No BK2007038), the Funindicates that membranes 1 and 4 are unsuited for evaluation by damental Research Funds for the Central Universities(NoFe(OH)a colloid retention and that some other characterization 2010LKHX01)and the Open Fund of Key Laboratory of Coal Processmethods should be tried in the futureand Clean Utilization of Ministry of Education( No. CPEUKF08-06)for their financial support.4. Conclusions(1)The asphalt component from separation of coal is a goodprecursor for preparing carbonaceous composite mem- [1] Wei w Liu SQ, Wang TH. You LB, Hu HQ, Preparation of carbon membranebranes because of its high residual carbon content andstrong adhesion to the surface of a support, which allows 2) Lu zH. Du J U XH, Tao aY, Zhou xx ing SL Review on the preparation andit to form a uniform carbonaceous layer.Chinese(2)Dip coated ceramic supports showed little permeation of[3] Wei w, Qin GT, Hou SD. Carbon membrane and its application in thebitumen into the internal pores. Asphaltene colloid is easilyenvironmental field. Technol Equip Environ pollut Control 2004: 5 (7): 8 [incombined with the support surface to form a good quality [4] Song CW, Wang TH, Qju JS, Qu XC, Cai TC. Progress of preparation of carboncarbonaceous filtering surface after carbonizationmembranes. Chem Ind Eng Prog 2003: 22(9): 61 [in Chinese(3)The number of coating cycles has little effect on composite 5I Zhang wD Preparation and applications of high strength coal-based tubularmembrane porosity but the permeability changes signifiChinesel.cantly for a different number of coats. Maximum penetration [6] Qin ZH, Zhang D, Hou CL, Jiang C, Sun H Group separation of all-componentsoccurs for the three-coat composite membrane. The waybubbles escape from the film and changes in coalescence (7 Qin ZH. The solubilization behavior of organic matter in coals and inbuilt statecaused by the film thickness are closely related to the numniversity of Mining and Technologyber of coats中国煤化工(4)A composite membrane prepared at a final carbonization[8 Gong T Allanalysis oftemperature of 600oC is relatively dense and the permeabilCNMHG University of Minias andL Zhang et aL/ Mining Science and Technology(China)21(2011)407-411[91 Qin ZH, Wei XY. Sun H Jiang C, Zhou M, Hu Gz et al. New method and its [12] Xu NP Xing wH. Zhao y]. Inorganic membrane technology and applications.ts from coal. InBeijing: Chemical Industry Press: 2003. p 35-7 in Chinese].chnology Association. The 20th venue technology of China Association 2005 [13 Gu tR, Zhu BY u wL Surface chemistry. Beijing: Science Press: 1994[14] Zhang sQ Wu GG. Coal chemistry. Xuzhou: China University of Mining andTechnology Press: 2004. p. 112-14 lin Chineseinbuilt state structural model. J China Univ Min Technol [151 Zhejiang University general chemistry teaching and research. General2008:37(4):43-9| in ChineseemIstry. Beijing: Higher Education Press: 2002. p 315 [in Chinesel.[11]Huang ZT. Zeng ZH, Zhong BK. Pang XS. Wang LF. Inorganic membraneechnology and applications. Beijing: China Petrochemical Press: 1999. p. 114-中国煤化工CNMHG