research article preparation and characterization of malaysian dolomites as a tar...

Hindawi Publishing CorporationJournal of EnergyVolume 2013 Article ID 791582 8 pageshttpdxdoiorg1011552013791582

Research ArticlePreparation and Characterization of Malaysian Dolomitesas a Tar Cracking Catalyst in Biomass Gasification Process

M A A Mohammed1 A Salmiaton1 W A K G Wan Azlina1

M S Mohamad Amran1 and Y H Taufiq-Yap2

1 Department of Chemical amp Environmental Engineering Faculty of Engineering Universiti Putra Malaysia43400 UPM Serdang Selangor Malaysia

2 Department of Chemistry Centre of Excellence for Catalysis Science and Technology Faculty of ScienceUniversiti Putra Malaysia 43400 Serdang Selangor Malaysia

Correspondence should be addressed to A Salmiaton mieengupmedumy

Received 18 December 2012 Accepted 29 April 2013

Academic Editor Johan E Hustad

Copyright copy 2013 M A A Mohammed et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Three types of local Malaysian dolomites were characterized to investigate their suitability for use as tar-cracking catalysts in thebiomass gasification process The dolomites were calcined to examine the effect of the calcination process on dolomitersquos catalyticactivity and propertiesThemodifications undergone by dolomites consequent to thermal treatmentwere investigated using variousanalytical methods Thermogravimetric and differential thermal analyses indicated that the dolomites underwent two stages ofdecomposition during the calcination process The X-ray diffraction and Fourier-transform infrared spectra analyses showed thatthermal treatment of dolomite played a significant role in the disappearance of the CaMg(CO

3)2phase producing the MgO-CaO

form of dolomite The scanning electron microscopy microphotographs of dolomite indicated that the morphological propertieswere profoundly affected by the calcination process which led to the formation of a highly porous surface with small sphericalparticles In addition the calcination of dolomite led to the elimination of carbon dioxide and increases in the values of the specificsurface area and average pore diameter as indicated by surface area analysis The results showed that calcined Malaysian dolomiteshave great potential to be applied as tar-cracking catalysts in the biomass gasification process based on their favorable physicalproperties

1 Introduction

Natural dolomite is the mineral form of the double carbonateof calcium and magnesium CaMg(CO

3)2 It occurs as the

major constituent of sedimentary formations in associationwith calcite CaCO

3 Dolomite was first described in 1791 as a

rock by the French engineer and mineralogist Deodat Gratetde Dolomieu (1750ndash1801) when he observed exposures in theDolomite Alps of Northern Italy [1] In Malaysia dolomiteis abundantly found in Perlis the northern part of PeninsularMalaysia and it is called ldquoBatu Reputrdquo by the local peopleThemain quarries of dolomite can be found in the surroundingsof ChupingCity in PerlisMalaysian dolomite is relatively softand easily crushed to fine powder It has a grayish color andwhen crushed to form the powder it becomes yellowish [2]

Dolomite in Malaysia is mainly used in the float glass andfertilizer industries for soil conditioning for use as buildingproducts in construction applications and to prepare roadsbefore paving with asphalt Dolomite also has the potentialto be used as a catalyst in certain chemical processes such asgasification and pyrolysis

Gasification and pyrolysis of biomass for the productionof fuel gas constitute one of the most promising processesfor clean energy based on the substitution of fossil fuel withrenewable energy moreover it decreases the global emissionlevels of carbon dioxide (CO

2) [3] Tar formation is a major

drawback when biomass is converted into syngas or fuel gasduring the gasification process The most common methodthat can effectively reduce the tar content in raw fuel gas isthermal and catalytic cracking These methods are preferred

2 Journal of Energy

P2

P1

P3

Figure 1 Dolomite quarries locations in Perlis State

because the gas is maintained at a high temperature Thisapproach has been intensively studied for more than twodecades because of its advantages including (1) conversion oftar into useful gases and (2) adjustability of the compositionof the gas product In a review of catalytic tar cracking bySutton et al [4] catalysts were divided into three distinctgroups namely (1) dolomite catalysts (2) alkali metal andother metal catalysts and (3) nickel catalysts Han and Kim[5] added a fourth group that is novel metal catalysts whichincludes Rh Pd Pt and Ru

The application of dolomite as a catalyst in biomassgasification has attracted the interest of many researchersand dolomite has been proved to have excellent tar-crackingcapacity because it is cheap easily replaceable and canincrease gas yield at the expense of the liquid productsHowever the main limitations of using dolomite catalystsare their low activity levels during reforming of the methanepresent in the product gas and their easy erosion andbreaking [4 10] The chemical composition and surface areaof dolomite varies with its source of supply Several researchgroups [6 8 9 11ndash13] have investigated a system of rawgas cleaning involving different types of dolomites suchas Spanish Swedish Finnish and Chinese dolomites ascatalysts for tar removal

Dolomite seems to have a significant potential to solve theproblems of high tar content in producer gas and will be ofsignificant benefit to the Malaysian economy and environ-ment Thus this work was aimed at studying the suitabilityof Malaysian dolomite for use as a tar-cracking catalyst inthe biomass gasification process To achieve this objectivethree types of local dolomites from different locations inPerlis State were prepared and characterized in terms oftheir properties using different analytical techniques suchas X-ray fluorescence (XRF) thermogravimetric analysis(TGA) X-ray diffraction (XRD) Fourier-transform infraredabsorption spectra (FTIR) nitrogen adsorption-desorptionand scanning electron microscopy (SEM)

2 Experimental

21 Materials Three types of natural Malaysian dolomite(P1 P2 and P3) were used and characterized in this studyDolomite samples were obtained from dolomite quarrieslocated in Perlis State on the northern part of PeninsularMalaysia (as illustrated in Figure 1) These samples wereprovided by Northern Dolomite Sdn Bhd Perlis UMPANGlobal Sdn Bhd Penang and Kangar Dolomite Sdn BhdKedah respectively The original samples were in the formof stones and had to be crushed and ground until theychanged to the powder form then they were subjected to sizeclassification using a Retsch Test Sieve (ASTM E11 200 120583)The dolomites were then calcined under nitrogen in a furnaceat 1000∘C for four hours The dolomite powders with particlesizes below 02mm for both the natural and the calcinedforms were used for characterization

22 Analysis

221 XRF Study The chemical composition of dolomiteswas estimated using wavelength-dispersive XXRF (WDXRFmodel BRUKER S8 TIGER) The fused-bead technique wasused to prepare the dolomite samples for XRF analysisSpecifically 05 g of sample was mixed with 50 g of spectra-flux LT-110 (Li

2B4O7= 665 LiBO

2= 335) and placed

in a platinum crucible The mixture was then fused attemperatures between 900 and 1250∘C and cast in a platinumcasting dish The samples were subjected to precise controlof the cooling process to ensure the reproducibility of theflat glass discs and to avoid cracking or crystallization Thesamples were then placed in an XRF instrument within nineminutes for analysis

222 Thermal Analysis To evaluate the thermal decompo-sition behavior of dolomites during the calcination processthermal analysis was carried out in a simultaneous thermo-gravimetric analyzer (model Mettler Toledo TGASDTA851)for both TGA and differential thermal analysis (DTG)Approximately 50mg of dolomite powder was placed in analumina crucible and weighed exactly The sample was thenplaced inside the furnace and programmed for continuousheating from room temperature to 1000∘C at a heating rateof 10∘Cmin under nitrogen flow at the rate of 100mLmin

223 XRD Analysis To examine the structural changesinduced by the calcination process the dolomite sampleswere characterized using a diffractometer-XRD system(model Shimadzu XRD6000) using Cu-K120572 (at wavelength15406 A) radiation fitted with a Cu filter on the secondaryoptics and operated under 40 kV power and 30mA currentThe scanning 2120579 range was from 20∘ to 90∘ at a scan rate of3∘min

224 FTIR Spectral Analysis FTIR spectra (model Perkin-Elmer 100 series) were used to confirm the structural trans-formation of the dolomites during the calcination process

Journal of Energy 3

Table 1 Analysis results of the compositions of dolomite ()

CompoundsMalaysian

dolomite (P1)This study

Malaysiandolomite (P2)This study


Chinesedolomite(Zhejiang)

[6]

Swedishdolomite(Sala)[6]

Indiandolomite(D01)[7]

Spanishdolomite(Malaga)

[8]

Finnishdolomite

[9]

SiO2 007 009 1537 135 221 018 mdash 25Al2O3 004 008 169 014 011 025 04 06Fe2O3 007 012 051 003 054 063 001 21CaO 300 320 230 3072 305 3024 306 266MgO 210 210 172 2012 202 2133 212 183K2O 0014 0026 0195 002 004 003 mdash mdashNa2O 0013 0013 0013 001 003 023 mdash mdashP2O5 0013 0017 0019 001 001 mdash mdash mdashMnO 001 0011 0013 0002 mdash 2133 mdash mdashSrO 0008 0009 0009 mdash mdash mdash mdash mdashTiO2 0006 0007 0015 000 001 018 mdash 03

0

001

002

003

004

005

20

40

60

80

100

0 100 200 300 400

TGDTG

500 600 700 800 900 1000

Wei

ght l

oss (

)

P1P2P3

dm

dT

(mg

s)

Temperature(∘C)

Figure 2 TG and DTG curves of Malaysian dolomites

The spectral data were used to identify the sample com-pounds by matching the fingerprints of the samples withthose in the database In addition the functional groupsand structural characteristics of a compound enable us toelucidate the possible structure types The spectrum range ofthe FTIR study was themid-infrared region which covers thefrequency ranges of 500ndash4000 cmminus1 at a resolution of 8 cmminus1

225 SEMAnalysis The surface andmicrostructure analysisof dolomites was carried out using an SEM instrument(model HITACHI S-3400N) The dolomite powder wasmounted onto the SEM stubs (layered with sticky car-bon tape) The stub was then placed in a sputter coater(EMITECH K550X) for five minutes for coating with goldto provide high reflectivity during the scanning process Thesamples were then placed at 40∘C in an oven before SEManalysis

226 Physical Properties Analysis The physical propertiesof the dolomites such as specific surface area total pore

volume and pore size distribution were obtained by mea-suring their nitrogen adsorption-desorption isotherm at 77Kusing a Quantachrome instrument (model Autosorb-1) TheBrunauer-Emmet-Teller (BET) surface area was estimatedfrom the adsorption-isothermdata using the relative pressure(119901119901119900) range of 10minus6 to 1 The total pore volume was assessed

by converting the amount of nitrogen gas adsorbed at relativepressure to the volume of liquid adsorbate The analyticalmethod consisted of three steps including dehydrationdegassing under low vacuum pressure and nitrogen gasadsorption at 77KThe resulting isothermwas analyzed usingthe BET adsorption method and the pore-size distributionswere derived by the Barrett-Joyner-Halenda (BJH) desorp-tion method

3 Results and Discussion

31 Chemical Composition of Dolomite The chemical com-positions of the various Malaysian dolomite samples whichwere determined using XRF analysis are listed in Table 1Themain contents of dolomite are CaO and MgO followed bylow levels of undesirable impurities such as SiO

2 K2ONa

2O

andAl2O3The chemical composition of P3 dolomite differed

significantly from that of P1 and P2 As shown in Table 1 thechemical composition analysis indicated that the CaO andMgO contents of the P1 and P2 dolomites were very closeto those of other types of dolomites whereas in the case ofP3 these contents were relatively low Furthermore P1 and P2had a much lower content of impurities than the other typesof dolomites whereas P3 had a higher level of impuritiesespecially silica (SiO

2 1537) and alumina (Al

2O3 169)

These impurities combine with CaO at elevated temperaturesto form a slag reducing the pore volume and the amount ofavailable active lime [7] Many research groups have reportedthat the chemical composition of dolomites play an importantrole when used as a catalyst for tar reforming in gasificationprocesses [6 8 9 11ndash13] Myren and others reported that amixture of silica and dolomite was not as effective as the same

4 Journal of Energy

01000200030004000500060007000

10 20 30 40 50 60 70 80 90 100

D

DDD D D D D D D D D D D D

++ + + Calcined

Natural

D+

+

2120579 (∘)

CaMg(CO3)2

MgOCaO

Inte

nsity

(cou

nts)

(a)

0

500

1000

1500

2000

2500

3000

10 20 30 40 50 60 70 80 90 100

D

DDDD DD D

DD DD

D D D D D

+

+ +++

Calcined

Natural

2120579 (∘)

D+

CaMg(CO3)2

MgOCaO

Inte

nsity

(cou

nts)

(b)

0

500

1000

1500

2000

2500

3000

10 20 30 40 50 60 70 80 90 100

Inte

nsity

(cou

nts)

Natural

Calcined

D

D DD

DD

DD

D D D D DD D D

++ +

+ +

∘

∘

∘

∙

∙

D+

CaMg(CO3)2

MgOCaO

SiO2

TiO2

Fe2O3

2120579 (∘)

(c)

Figure 3 XRD analysis before and after calcination (a) P1 dolomite (b) P2 dolomite and (c) P3 dolomite

amount of pure dolomite for tar cracking [14] In generaldolomites with the lowest content of CaO andMgO show thelowest tar cracking efficiency [6]

32 Thermal Decomposition of Dolomite To evaluate thethermal decomposition behavior of dolomites under calci-nation temperatures thermal analysis was conducted in asimultaneous TG-DTA analyzerThe thermal decompositioncharacteristics of dolomites with reference to the TGA andDTG curves are displayed in Figure 2 Dolomite is the min-eral form of the double carbonate of calcium andmagnesiumCaMg(CO

3)2 Under heating dolomite is often assumed to be

decomposed in two separate stages as follows [2 15]

First stage

CaMg(CO3)2(s) 997888rarr CaCO

3(s) +MgO(s) + CO2(g) (1)

Second stage

CaCO3(s) 997888rarr CaO

(s) + CO2(g) (2)

The first thermal decomposition stage occurs after 600∘C andis followed by the second stage after 800∘C From Figure 2

the observed weight loss below 600∘C for P1 P2 and P3was 459 342 and 124 respectively whereas the weightloss between 600 and 830∘C was 5577 4926 and 3984respectivelyThemainweight loss in the 600ndash830∘C range canbe attributed to the decomposition of the carbonates mineralthat exists in dolomite and the release of carbon dioxide asexplained by (1) Therefore the weight loss for P1 and P2 inthis temperature range was higher compared to that of P3due to the higher content of carbonates In Figure 2 the DTGcurves of the three types of dolomites show two peaks ForP1 the onset of the first peak begins at 600∘C reaches a max-imum at 7677∘C and ends at 7903∘C whereas the secondpeak begins at 7903∘C reaches a maximum at 8013∘C andends at 830∘C For P2 the first peak begins at 600∘C reaches amaximumat 7875∘C and ends at 8095∘Cwhereas the secondpeak begins at 8095∘C reaches a maximum at 8295∘C andends at 830∘C For P3 also the first peak begins at 600∘Creaches a maximum at 7875∘C but ends at 7993∘C whereasthe second peak begins at 7993∘C reaches a maximum at8196∘C and ends at 830∘C As shown in (1) and (2) thepeak at the lower temperature represents the decompositionof the dolomite structure with the release of carbon dioxidefrom the carbonate ion associated with the magnesium partof the structure accompanied by the formation of calcite

Journal of Energy 5

5001000150020002500300035004000

Tran

smitt

ance

()

NaturalCalcined

Wavenumber (cmminus1)

(a)

Tran

smitt

ance

()

NaturalCalcined

5001000150020002500300035004000Wavenumber (cmminus1)

(b)

Tran

smitt

ance

()

NaturalCalcined


(c)

Figure 4 FTIR spectra before and after calcination (a) P1 dolomite (b) P2 dolomite and (c) P3 dolomite

and magnesium oxide The peak at the higher temperaturecorresponds to the decomposition of calcite with the releaseof carbon dioxide As shown in Figure 2 the decompositionprocess for P1 is initiated at lower temperatures comparedto the other types of Malaysian dolomites This probably isdue to its higher content of CaO as presented in Table 1These results are in agreement with the previous works byMcIntosh et al [15] and Gunasekaran and Anbalagan [7] Inaddition Farizul et al [2] have also found that the DTG plotof Malaysian dolomite shows two peaks at 7500 and 9300∘CThe temperature of the second peak is higher compared tothat in the present study which can be attributed to the partialpressure of carbon dioxide in the dolomite samples wherebythe temperature of the second peak increases with increasingpartial pressure of carbon dioxideThe peak temperature alsodepends on other procedural variables such as the heatingrate and the sample mass because these in turn influencethe actual atmosphere around the decomposing sample [15]As a result the thermal treatment process (calcination) ofdolomite produced a catalyst with very high activity due todisappearance of the CaMg(CO

3)2phase and producing of

the MgO-CaO form of dolomite

33 XRD Analysis The dolomites were characterized beforeand after calcination using XRD to analyze the effect ofcalcination on the dolomite structure The results are shownin Figure 3 The XRD patterns for natural dolomites showthat all peaks correspond to those of CaMg(CO

3)2(JCPDS

36-0426) All these peaks also have been observed in otherresearch works [3 7] indicating that the Malaysian dolomitesamples have almost the same properties as the otherdolomitesThe XRD pattern for calcined dolomites howeverchanges drastically compared to that of natural dolomitesNew dominant peaks which belong to CaO (JCPDS 04-0777)and MgO (JCPDS 87-0652) are observed Natural P3 sample(Figure 3(c)) on the contrary shows three additional peaksbetween 2120579 = 20∘ and 2120579 = 30∘ which are assigned to Fe

2O3

(JCPDS 26-1319) TiO2(JCPDS 71-1169) and SiO

2(JCPDS 83-

0539) occurring at 2120579 = 252∘ 267∘ and 28∘ respectivelyThechanges in the peaks illuminate the fact that calcination ofMalaysian dolomites results in the formation of the MgO-CaO form which is the active catalytic component in tarconversion

34 FTIR Spectral Analysis The typical transmittance FTIRspectra of the Malaysian dolomites before and after the cal-cination process are shown in Figure 4 The FTIR spectra forall natural dolomite samples indicate that the most prevalentcomponent present in dolomite is carbonate The carbonatemineral group (magnesium and calcium carbonates) showsa strong and broad band near 1412 cmminus1 whereas the othermain components of dolomite are clearly differentiated bycharacteristic bands near 872 and 724 cmminus1 [16] In the case ofP3 (Figure 4(c)) in addition to the band corresponding to thecarbonate group the FTIR spectra show a band at 1005 cmminus1

6 Journal of Energy

Natural P1

Natural P2

Natural P3

Calcined P1

Calcined P2

Calcined P3

Figure 5 SEM microphotograph of natural and calcined Malaysian dolomites

Table 2 Pore characteristics of the calcined dolomites

P1(this study)

P2(this study)

P3(this study)

Sala[6]

Zhejiang[6]

Malaga[8]

BET surface area (m2g) 1525 1685 616 73 51 12Pore volume (cm3g) 032 0104 009 009 003 007Average pore diameter (A) 416 233 215 496 269 144

referring to the presence of SindashO vibration of the silicatephase which is in agreement with the chemical analysis data

The FTIR spectra for dolomites after calcination clearlyshow the structural transformation of natural dolomite tocalcium andmagnesium oxides At this stage themain broadband at 1412 cmminus1 shifts to 1430 cmminus1 and the intensity ofthe band decreases showing the presence of calcium andmagnesium oxides [17] Moreover strong and intense bandsare observed at 3641 and 660 cmminus1 due to calcium oxide inaddition to the band at 540 cmminus1 attributable to magnesiumoxide The weak bands at 875 and 1005 cmminus1 for natural P3(Figure 4(c)) combine together to form a strong and broadband after calcination which can be attributed to the effectof impurities such as silicates on the dolomite structure at

elevated calcination temperatures Moreover another strongband is observed at 1144 cmminus1 for calcined P3 dolomite dueto the presence of silica whereas the intensity of the calciumoxide bond at 3641 cmminus1 is weak compared to the bands of thecalcined samples of P1 and P2 These results are in completeagreement with the results obtained from XRD analysis

35 Scanning Electron Microscopy (SEM) Analysis As illus-trated in Figure 5 the SEM micrographs of the calcineddolomites are significantly different from those of thedolomites before calcination The SEMmicrographs of natu-ral dolomites show a rough and disordered surface with low-porosity grains whereas the surfaces of calcined dolomitesshow clusters of tidy and porous grains confirming thethermal decomposition

Journal of Energy 7

05

1015202530354045

1 15 2 25 3 35

P1P2P3

400 A150 A

50 A

40 A

LogD

dAd

logD

Figure 6 Pore size distribution of calcinedMalaysian dolomites119863pore diameter (A) 119860 BET surface area (m2g)

36 Surface Area and Total Pore Volume Analysis The BETsurface area the BJH pore volume and the average poresize for calcined Malaysian dolomites are summarized inTable 2 A comparison of the surface area and pore volume(17ndash3000 A) shows that P1 and P2 dolomites have the highestsurface area and pore volume compared to P3 and otherpublished dolomitesThis is possibly due to the highCaO andMgO contents in P1 and P2 dolomites and the lower contentsof impurities such as SiO

2 K2O Na

2O and Al

2O3 Slag is

produced when these impurities combine with CaO at hightemperatures leading to a reduction in both the pore volumeand the amount of available active lime [18] The surfaceproperties apart from the chemical composition of dolomiteare the most important factors for selecting dolomite as thecracking catalyst in many thermochemical processes

The pore size-distribution curves of the calcined Malay-sian dolomites are shown in Figure 6 The pore-size distribu-tion of P1 and P2 dolomites differs from that of P3 The poresizes of P1 and P2 dolomites are mainly in the 400 A regionwhereas the major pore size of P3 is in the 150 A region

4 Conclusions

The natural Malaysian dolomites after undergoing thermaltreatments at high temperatures (1000∘C) produced activateddolomite which could be used as a cracking catalyst inthe biomass gasification process Malaysian dolomites P1and P2 contained higher amounts of CaO and MgO withlower amounts of SiO

2 K2O Na

2O and Al

2O3 compared to

P3 and other dolomites (Table 1) The DTG curves showedtwo stages of decomposition during the calcination pro-cess The first thermal decomposition occurred after 600∘Cfollowed by the second step after 800∘C The XRD andFTIR results confirmed the structural transformation ofnatural dolomite to the calcium and magnesium oxideform and the results of the BET and BJH analyses showedthat P1 and P2 dolomites had higher surface areas andpore volumes compared to P3 and other types of dolomitesThis suggests that P1 and P2 dolomites have great potential for

use as tar-cracking catalysts The most important factors thatcontribute to the selection of dolomites with highly efficienttar-cracking capacity are calcination balance and chemicalcomposition in additional to geometrical surface area andaverage pore diameter

Acknowledgments

The authors would like to thank Northern Dolomite SdnBhd UMPAN Global Sdn Bhd and Kangar Dolomite SdnBhd for their support in providing the dolomites samplesThe work was financed by the Department of Chemicaland Environmental Engineering Faculty of EngineeringUniversiti Putra Malaysia

References

[1] W L Roberts T J Cambell and G E Rapp Encyclopedia ofMinerals Van Nostrand-Reinhold New York NY USA 2ndedition 1990

[2] H K Farizul P C Goh DM S N Suhardy HM D Irfan andS Saiful Azhar ldquoDolomite as a rawmaterial in fertilizer produc-tionrdquo in Proceedings of the AEESEAP International ConferenceN A Rahim Ed pp 4ndash8 Kuala Lumpur Malaysia 2005

[3] G Hu S Xu S Li C Xiao and S Liu ldquoSteam gasificationof apricot stones with olivine and dolomite as downstreamcatalystsrdquo Fuel Processing Technology vol 87 no 5 pp 375ndash3822006

[4] D Sutton B Kelleher and J R H Ross ldquoReview of literature oncatalysts for biomass gasificationrdquo Fuel Processing Technologyvol 73 no 3 pp 155ndash173 2001

[5] J Han andHKim ldquoThe reduction and control technology of tarduring biomass gasificationpyrolysis an overviewrdquo Renewableand Sustainable Energy Reviews vol 12 no 2 pp 397ndash416 2008

[6] Q Z Yu C Brage T Nordgreen and K Sjostrom ldquoEffects ofChinese dolomites on tar cracking in gasification of birchrdquo Fuelvol 88 no 10 pp 1922ndash1926 2009

[7] S Gunasekaran and G Anbalagan ldquoThermal decomposition ofnatural dolomiterdquoBulletin ofMaterials Science vol 30 no 4 pp339ndash344 2007

[8] P Perez P M Aznar M A Caballero J Gil J A Martın andJ Corella ldquoHot gas cleaning and upgrading with a calcineddolomite located downstream a biomass fluidized bed gasifieroperating with steam-oxygen mixturesrdquo Energy and Fuels vol11 no 6 pp 1194ndash1197 1997

[9] P Simell E Kurkela P Stahlberg and J Hepola ldquoCatalytic hotgas cleaning of gasification gasrdquo Catalysis Today vol 27 no 1-2pp 55ndash62 1996

[10] L Wang C L Weller D D Jones and M A Hanna ldquoCon-temporary issues in thermal gasification of biomass and itsapplication to electricity and fuel productionrdquo Biomass andBioenergy vol 32 no 7 pp 573ndash581 2008

[11] A Orio J Corella and I Narvaez ldquoPerformance of differencedolomites on hot raw gas cleaning from biomass gasificationwith airrdquo in Proceedings of Conference on Developments inTher-mochemical Biomass Conversion pp 1144ndash1150 Banff Canada1996

[12] J Delgado M P Aznar and J Corella ldquoBiomass gasificationwith steam in fluidized bed effectiveness of CaO MgO andCaOminusMgO for hot raw gas cleaningrdquo Industrial amp EngineeringChemistry Research vol 36 pp 1535ndash1543 1997

8 Journal of Energy

[13] V Vassilatos G Taralas K Sjostrom and E Bjornbom ldquoCat-alytic cracking of tar in biomass pyrolysis gas in the presence ofcalcined dolomiterdquo Canadian Journal of Chemical Engineeringvol 70 no 5 pp 1008ndash1013 1992

[14] C Myren C Hornell E Bjornbom and K Sjostrom ldquoCatalytictar decomposition of biomass pyrolysis gas with a combinationof dolomite and silicardquo Biomass and Bioenergy vol 23 no 3 pp217ndash237 2002

[15] R M McIntosh J H Sharp and F W Wilburn ldquoThe thermaldecomposition of dolomiterdquo Thermochimica Acta vol 165 no2 pp 281ndash296 1990

[16] V Ramasamy V Ponnusamy S Sabari S R Anishia and SS Gomathi ldquoCondensed matter structural mechanical andthermal propertiesrdquo Indian Journal of Pure and Applied Physicsvol 47 pp 586ndash591 2009

[17] D O Kevin and T A R R C Jackson ldquoA guide to identifyingcommon inorganic fillers and activators using vibrational spec-troscopyrdquo Internet Journal of Vibrational Spectroscopy vol 2 pp1ndash11 1998

[18] R K Chan K SMurthi andD Harrison ldquoThermogravimetricanalysis of Ontario limestones and dolomites I Calcinationsurface area and porosityrdquo Canadian Journal of Chemistry vol48 no 19 pp 2972ndash2978 1970

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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

2 Journal of Energy

P2

P1

P3

Figure 1 Dolomite quarries locations in Perlis State

because the gas is maintained at a high temperature Thisapproach has been intensively studied for more than twodecades because of its advantages including (1) conversion oftar into useful gases and (2) adjustability of the compositionof the gas product In a review of catalytic tar cracking bySutton et al [4] catalysts were divided into three distinctgroups namely (1) dolomite catalysts (2) alkali metal andother metal catalysts and (3) nickel catalysts Han and Kim[5] added a fourth group that is novel metal catalysts whichincludes Rh Pd Pt and Ru

The application of dolomite as a catalyst in biomassgasification has attracted the interest of many researchersand dolomite has been proved to have excellent tar-crackingcapacity because it is cheap easily replaceable and canincrease gas yield at the expense of the liquid productsHowever the main limitations of using dolomite catalystsare their low activity levels during reforming of the methanepresent in the product gas and their easy erosion andbreaking [4 10] The chemical composition and surface areaof dolomite varies with its source of supply Several researchgroups [6 8 9 11ndash13] have investigated a system of rawgas cleaning involving different types of dolomites suchas Spanish Swedish Finnish and Chinese dolomites ascatalysts for tar removal

Dolomite seems to have a significant potential to solve theproblems of high tar content in producer gas and will be ofsignificant benefit to the Malaysian economy and environ-ment Thus this work was aimed at studying the suitabilityof Malaysian dolomite for use as a tar-cracking catalyst inthe biomass gasification process To achieve this objectivethree types of local dolomites from different locations inPerlis State were prepared and characterized in terms oftheir properties using different analytical techniques suchas X-ray fluorescence (XRF) thermogravimetric analysis(TGA) X-ray diffraction (XRD) Fourier-transform infraredabsorption spectra (FTIR) nitrogen adsorption-desorptionand scanning electron microscopy (SEM)

2 Experimental

21 Materials Three types of natural Malaysian dolomite(P1 P2 and P3) were used and characterized in this studyDolomite samples were obtained from dolomite quarrieslocated in Perlis State on the northern part of PeninsularMalaysia (as illustrated in Figure 1) These samples wereprovided by Northern Dolomite Sdn Bhd Perlis UMPANGlobal Sdn Bhd Penang and Kangar Dolomite Sdn BhdKedah respectively The original samples were in the formof stones and had to be crushed and ground until theychanged to the powder form then they were subjected to sizeclassification using a Retsch Test Sieve (ASTM E11 200 120583)The dolomites were then calcined under nitrogen in a furnaceat 1000∘C for four hours The dolomite powders with particlesizes below 02mm for both the natural and the calcinedforms were used for characterization

22 Analysis

221 XRF Study The chemical composition of dolomiteswas estimated using wavelength-dispersive XXRF (WDXRFmodel BRUKER S8 TIGER) The fused-bead technique wasused to prepare the dolomite samples for XRF analysisSpecifically 05 g of sample was mixed with 50 g of spectra-flux LT-110 (Li

2B4O7= 665 LiBO

2= 335) and placed

in a platinum crucible The mixture was then fused attemperatures between 900 and 1250∘C and cast in a platinumcasting dish The samples were subjected to precise controlof the cooling process to ensure the reproducibility of theflat glass discs and to avoid cracking or crystallization Thesamples were then placed in an XRF instrument within nineminutes for analysis

222 Thermal Analysis To evaluate the thermal decompo-sition behavior of dolomites during the calcination processthermal analysis was carried out in a simultaneous thermo-gravimetric analyzer (model Mettler Toledo TGASDTA851)for both TGA and differential thermal analysis (DTG)Approximately 50mg of dolomite powder was placed in analumina crucible and weighed exactly The sample was thenplaced inside the furnace and programmed for continuousheating from room temperature to 1000∘C at a heating rateof 10∘Cmin under nitrogen flow at the rate of 100mLmin

223 XRD Analysis To examine the structural changesinduced by the calcination process the dolomite sampleswere characterized using a diffractometer-XRD system(model Shimadzu XRD6000) using Cu-K120572 (at wavelength15406 A) radiation fitted with a Cu filter on the secondaryoptics and operated under 40 kV power and 30mA currentThe scanning 2120579 range was from 20∘ to 90∘ at a scan rate of3∘min

224 FTIR Spectral Analysis FTIR spectra (model Perkin-Elmer 100 series) were used to confirm the structural trans-formation of the dolomites during the calcination process

Journal of Energy 3


CompoundsMalaysian





[6]




[8]

Finnishdolomite

[9]


0

001

002

003

004

005

20

40

60

80

100

0 100 200 300 400

TGDTG

500 600 700 800 900 1000

Wei

ght l

oss (

)

P1P2P3

dm

dT

(mg

s)

Temperature(∘C)









2 K2ONa

2O




2O3 169)


4 Journal of Energy

01000200030004000500060007000

10 20 30 40 50 60 70 80 90 100

D


++ + + Calcined

Natural

D+

+

2120579 (∘)

CaMg(CO3)2

MgOCaO

Inte

nsity

(cou

nts)

(a)

0

500

1000

1500

2000

2500

3000

10 20 30 40 50 60 70 80 90 100

D

DDDD DD D

DD DD

D D D D D

+

+ +++

Calcined

Natural

2120579 (∘)

D+

CaMg(CO3)2

MgOCaO

Inte

nsity

(cou

nts)

(b)

0

500

1000

1500

2000

2500

3000

10 20 30 40 50 60 70 80 90 100

Inte

nsity

(cou

nts)

Natural

Calcined

D

D DD

DD

DD

D D D D DD D D

++ +

+ +

∘

∘

∘

∙

∙

D+

CaMg(CO3)2

MgOCaO

SiO2

TiO2

Fe2O3

2120579 (∘)

(c)






First stage


3(s) +MgO(s) + CO2(g) (1)

Second stage


(s) + CO2(g) (2)



Journal of Energy 5

5001000150020002500300035004000

Tran

smitt

ance

()

NaturalCalcined


(a)

Tran

smitt

ance

()

NaturalCalcined


(b)

Tran

smitt

ance

()

NaturalCalcined


(c)






3)2(JCPDS


2O3


2(JCPDS 83-



6 Journal of Energy

Natural P1

Natural P2

Natural P3

Calcined P1

Calcined P2

Calcined P3



P1(this study)

P2(this study)

P3(this study)

Sala[6]

Zhejiang[6]

Malaga[8]






Journal of Energy 7

05

1015202530354045

1 15 2 25 3 35

P1P2P3

400 A150 A

50 A

40 A

LogD

dAd

logD



2 K2O Na

2O and Al

2O3 Slag is



4 Conclusions


2 K2O Na

2O and Al

2O3 compared to



Acknowledgments


References













8 Journal of Energy











FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Journal of Energy 3


CompoundsMalaysian





[6]




[8]

Finnishdolomite

[9]


0

001

002

003

004

005

20

40

60

80

100

0 100 200 300 400

TGDTG

500 600 700 800 900 1000

Wei

ght l

oss (

)

P1P2P3

dm

dT

(mg

s)

Temperature(∘C)









2 K2ONa

2O




2O3 169)


4 Journal of Energy

01000200030004000500060007000

10 20 30 40 50 60 70 80 90 100

D


++ + + Calcined

Natural

D+

+

2120579 (∘)

CaMg(CO3)2

MgOCaO

Inte

nsity

(cou

nts)

(a)

0

500

1000

1500

2000

2500

3000

10 20 30 40 50 60 70 80 90 100

D

DDDD DD D

DD DD

D D D D D

+

+ +++

Calcined

Natural

2120579 (∘)

D+

CaMg(CO3)2

MgOCaO

Inte

nsity

(cou

nts)

(b)

0

500

1000

1500

2000

2500

3000

10 20 30 40 50 60 70 80 90 100

Inte

nsity

(cou

nts)

Natural

Calcined

D

D DD

DD

DD

D D D D DD D D

++ +

+ +

∘

∘

∘

∙

∙

D+

CaMg(CO3)2

MgOCaO

SiO2

TiO2

Fe2O3

2120579 (∘)

(c)






First stage


3(s) +MgO(s) + CO2(g) (1)

Second stage


(s) + CO2(g) (2)



Journal of Energy 5

5001000150020002500300035004000

Tran

smitt

ance

()

NaturalCalcined


(a)

Tran

smitt

ance

()

NaturalCalcined


(b)

Tran

smitt

ance

()

NaturalCalcined


(c)






3)2(JCPDS


2O3


2(JCPDS 83-



6 Journal of Energy

Natural P1

Natural P2

Natural P3

Calcined P1

Calcined P2

Calcined P3



P1(this study)

P2(this study)

P3(this study)

Sala[6]

Zhejiang[6]

Malaga[8]






Journal of Energy 7

05

1015202530354045

1 15 2 25 3 35

P1P2P3

400 A150 A

50 A

40 A

LogD

dAd

logD



2 K2O Na

2O and Al

2O3 Slag is



4 Conclusions


2 K2O Na

2O and Al

2O3 compared to



Acknowledgments


References













8 Journal of Energy











FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















4 Journal of Energy

01000200030004000500060007000

10 20 30 40 50 60 70 80 90 100

D


++ + + Calcined

Natural

D+

+

2120579 (∘)

CaMg(CO3)2

MgOCaO

Inte

nsity

(cou

nts)

(a)

0

500

1000

1500

2000

2500

3000

10 20 30 40 50 60 70 80 90 100

D

DDDD DD D

DD DD

D D D D D

+

+ +++

Calcined

Natural

2120579 (∘)

D+

CaMg(CO3)2

MgOCaO

Inte

nsity

(cou

nts)

(b)

0

500

1000

1500

2000

2500

3000

10 20 30 40 50 60 70 80 90 100

Inte

nsity

(cou

nts)

Natural

Calcined

D

D DD

DD

DD

D D D D DD D D

++ +

+ +

∘

∘

∘

∙

∙

D+

CaMg(CO3)2

MgOCaO

SiO2

TiO2

Fe2O3

2120579 (∘)

(c)






First stage


3(s) +MgO(s) + CO2(g) (1)

Second stage


(s) + CO2(g) (2)



Journal of Energy 5

5001000150020002500300035004000

Tran

smitt

ance

()

NaturalCalcined


(a)

Tran

smitt

ance

()

NaturalCalcined


(b)

Tran

smitt

ance

()

NaturalCalcined


(c)






3)2(JCPDS


2O3


2(JCPDS 83-



6 Journal of Energy

Natural P1

Natural P2

Natural P3

Calcined P1

Calcined P2

Calcined P3



P1(this study)

P2(this study)

P3(this study)

Sala[6]

Zhejiang[6]

Malaga[8]






Journal of Energy 7

05

1015202530354045

1 15 2 25 3 35

P1P2P3

400 A150 A

50 A

40 A

LogD

dAd

logD



2 K2O Na

2O and Al

2O3 Slag is



4 Conclusions


2 K2O Na

2O and Al

2O3 compared to



Acknowledgments


References













8 Journal of Energy











FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Journal of Energy 5

5001000150020002500300035004000

Tran

smitt

ance

()

NaturalCalcined


(a)

Tran

smitt

ance

()

NaturalCalcined


(b)

Tran

smitt

ance

()

NaturalCalcined


(c)






3)2(JCPDS


2O3


2(JCPDS 83-



6 Journal of Energy

Natural P1

Natural P2

Natural P3

Calcined P1

Calcined P2

Calcined P3



P1(this study)

P2(this study)

P3(this study)

Sala[6]

Zhejiang[6]

Malaga[8]






Journal of Energy 7

05

1015202530354045

1 15 2 25 3 35

P1P2P3

400 A150 A

50 A

40 A

LogD

dAd

logD



2 K2O Na

2O and Al

2O3 Slag is



4 Conclusions


2 K2O Na

2O and Al

2O3 compared to



Acknowledgments


References













8 Journal of Energy











FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















6 Journal of Energy

Natural P1

Natural P2

Natural P3

Calcined P1

Calcined P2

Calcined P3



P1(this study)

P2(this study)

P3(this study)

Sala[6]

Zhejiang[6]

Malaga[8]






Journal of Energy 7

05

1015202530354045

1 15 2 25 3 35

P1P2P3

400 A150 A

50 A

40 A

LogD

dAd

logD



2 K2O Na

2O and Al

2O3 Slag is



4 Conclusions


2 K2O Na

2O and Al

2O3 compared to



Acknowledgments


References













8 Journal of Energy











FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















Journal of Energy 7

05

1015202530354045

1 15 2 25 3 35

P1P2P3

400 A150 A

50 A

40 A

LogD

dAd

logD



2 K2O Na

2O and Al

2O3 Slag is



4 Conclusions


2 K2O Na

2O and Al

2O3 compared to



Acknowledgments


References













8 Journal of Energy











FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















8 Journal of Energy











FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of





















FuelsJournal of







Advances in



Journal of


Renewable Energy





RotatingMachinery


EnergyJournal of

















research article preparation and characterization of malaysian dolomites as a tar...

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