te

ngversilogy

of Snomr conite htive. TFS)boubutiTH

The FTIR analyses of solvent-extraction components show that all of the fractions contain OH group, aromaticd aromatic ether oxygen group.

1. Introduction

in Chine total c824%,ric va(1.00el to beisturebecaus

Fuel Processing Technology 91 (2010) 783788

Contents lists available at ScienceDirect

Fuel Processing

e lsof energy consumption to removewater by evaporation drying, and thedried lignite is difcult to store. In addition, the high content of oxygenin lignite consumes a large amount of H2 for hydro-liquefaction oflignite. Therefore, in order to better use lignite, the lignite should haverstly effective dehydration and the high oxygen content of ligniteshould be utilized. From this point of view, the goal of the liquefaction oflignite should be to produce value added products, such as oxygen-contained chemical stocks.

Shengli (SL) lignite under different NaOH and methanol contents weredetermined. In order to avoid drying of lignite before liquefaction and tofurther decrease the drying cost, the effect of water on the liquefaction ofSL lignite with NaOHmethanol was investigated. Therefore, the rawlignite can be directly used for reaction without drying. The objective ofthis work is to investigate the effects of NaOH, methanol and watercontents on the liquefaction of SL lignite, which can facilitate thedevelopment of efcient lignite utilization.In order to elucidate the chemical structureused non-destructive reactionmethanolysisfound that the main reaction was hydrohydrogenation inwhichether linkageswere sp

Corresponding author. Tel.: +86 5552311552; fax:E-mail address: shhf@ahut.edu.cn (H. Shui).

0378-3820/$ see front matter 2010 Elsevier B.V. Aldoi:10.1016/j.fuproc.2010.02.014e of the large amount ofignite might bond withill lead to a large amount

yield should be studied. Little information about these is available inliterature based on our knowledge.

In thiswork, the liquefactionbehaviors of oneof theChinese lignites

energy consumption for drying. Water in lorganic oxygen by hydrogen bonding, whichwThere are abundant lignite resourcestons), which is approximately 13% of thas-received basis has high moisture (126%, average), relatively low net caloaverage), and low total sulfur contentsingly, lignite is treated as a low-grade fuin many countries. More than 30% molimit its use in direct coal liquefactiona (more than 130 billionoal reserve. Lignite on anaverage), high ash (16lue (32813854 kcal/kg,1.22%, average). Accord-red to supply electricitycontent in lignite might

were hydrogenated. This made the reacted coal nearly all soluble inpyridine except those from the high rank coals. All of those researchesindicated that methanolysis of lignite with NaOH can be used to breaklignite structure into oxygen-contained aromatic chemicals. But in ourpreliminary study [12], it was found that when the ratio of NaOH/SLlignite was at 1:1 on weight basis, the highest SL lignite conversion andproduct yield were obtained. From the economic point of view, theamounts of NaOH and methanol used should be signicantly reducedand the effect of water content on SL lignite conversion and productof coals, Ochi et al. [111]of coal with NaOH. Theylysis and simultaneouslit and aromatic products

2. Experimental

2.1. Lignite and r

SL lignite waground to 200 munder vacuum

+86 5552311822.

l rights reserved. 2010 Elsevier B.V. All rights reserved.

structure, carbonyl group anStudy on the liquefaction of Shengli ligni

Zhiping Lei a, Muxin Liu a, Hengfu Shui a,, Zhicai Waa School of Chemistry and Chemical Engineering, Anhui Key Laboratory of Coal Clean Conb School of Chemical Engineering and Technology, China University of Mining and Techno

a b s t r a c ta r t i c l e i n f o

Article history:Received 9 August 2009Received in revised form 1 February 2010Accepted 18 February 2010

Keywords:LigniteLiquefactionNaOH

The behavior of liquefactionwater in lignite and the ecomethanol content andwateThe results show that SL lign99% at 300 C for 1 h respecparticipates in the reactiontetrahydrofuran soluble (THproduct yield increase for ayield and the product distriNaOHmethanol aremainly

j ourna l homepage: www.with NaOH/methanola, Xianyong Wei b

on and Utilization, Anhui University of Technology, Ma'anshan 243002, PR China, Xuzhou, 221116, PR China

hengli (SL) lignite with NaOHmethanolwas studied. Based on high content ofy of the process (amounts of NaOH used), the effects of NaOH concentration,tent on the liquefaction behavior of SL lignite were preliminarily investigated.as a good reaction activity, and its conversion and product yield reach 98% andly, when the ratio of SL lignite, NaOH and methanol is for 1 g:1 g:10 ml. NaOHhe increase of the amount of NaOH signicantly increases the amount offraction. Methanol plays a promotion role in the liquefaction, whichmakes thet 1623%. Water content has little effect on the SL lignite conversion, producton. Solvent-extraction components of liquefaction products of SL lignite withFS, toluene soluble (TS), hexane soluble (HS) andwater soluble fractions (WS).

Technology

ev ie r.com/ locate / fuproceagents

s used in this study. The SL lignite as received wasesh, stored under nitrogen atmosphere, and driedat 80 C overnight before use. The ultimate and

proximate analyses of the SL lignite are shown in Table 1. All solventsused were commercially pure chemical reagents and used as receivedwithout further purication.

2.2. Liquefaction

The liquefaction experiments were carried out in a 30 ml tubing

784 Z. Lei et al. / Fuel Processing Technology 91 (2010) 783788reactor shaken vertically. 1.0 g of the dried coal loaded with 1.0 gNaOH was charged into the reactor together with 10 ml of methanol.Before the liquefaction experiment, the reactor was sealed andushed 3 times with nitrogen followed by tuning the system to thedesired initial pressure of 0.1 MPa with nitrogen. The reactor, agitatedvertically at 120 rpm, was submerged into a eutectic salt bath asdescribed in detail elsewhere [13], which had been heated to thedesired temperature and maintained for 60 min. The pressure of theliquefaction at 300 C was about 13 MPa. Then, the reactor wasquenched to ambient temperature in a water bath before theoverhead pressure in the reactor was released slowly. The reactionmixture was removed by washing with methanol and separated bysolvent extraction.

2.3. Fractionation of liquefaction products

The liquefaction products were obtained by removing methanolthrough rotary evaporation. Then the reaction products were acidiedwith hydrochloric acid, washed with water, and ltrated until pH ofthe ltrate was at 7. The ltrate was extracted by ether and theproduct extracted by ether was dried by MgSO4. Then the watersoluble fraction (WS) was obtained by removing ether through rotaryevaporation followed by drying under vacuum at 50 C for 12 h. Solidproducts obtained by ltration were separated by Soxlet solventextraction with n-hexane, toluene, and tetrahydrofuran (THF) in turn.The n-hexane soluble, n-hexane insoluble/toluene soluble, tolueneinsoluble/THF soluble and THF insoluble fractions obtained weredened as hexane soluble fraction (HS), toluene soluble fraction (TS),THF soluble fraction (THFS) and THFI, respectively. The extractionprocedure on the liquefaction products is shown in Fig. 1.

The conversion of lignite (X) and product yield (Y) were calculatedas:

X wt:%;daf = mLignite 1Ad mTHFI 1ATHFI mLignite 1Ad

100

Y wt:%; daf = mWS + mHS + mTS + mTHFS mLignite 1Ad

100

where mLignite, mWS, mHS, mTS, mTHFS and mTHFI are the weight of SLlignite (g, daf), WS (g), HS (g), TS (g), THFS (g) and THFI (g),respectively. Ad and ATHFI are the ash contents of SL lignite and THFI(wt.%, d), respectively. All the reactions were duplicated to ensureaccuracy and the average errors were about 5%.

2.4. Products analyses

The reaction products were characterized by IR spectra using a PE-Spectrum One IR spectrometer at ambient temperature. In the IRmeasurements, the sample was mixed with KBr (sample/KBr: 1/100)

Table 1Proximate and ultimate analyses of the SL lignite sample.

Proximate analysis wt.% Ultimate analysis wt.%, daf

Ad Vdaf Mad C H O N S

18.3 49.5 20.6 67.95 4.50 24.78 0.98 1.29*By difference.and themixturewas pressed into a pellet. The liquid product (HS)wasdetermined by lm coating method on KBr crystal plate. Theelemental analysis was carried out in Elementar Vario EL III.

3. Results and discussion

3.1. Effect of the ratio of NaOH/SL lignite

In order to reduce the amount of NaOH used and improve theeconomy of the liquefaction of SL lignite with NaOHmethanol, effectsof the NaOH/SL lignite ratio on the conversion of SL lignite andliquefaction product yield were investigated and the results areshown in Figs. 2 and 3. The liquefaction was carried out at 300 C for1 h with a 10 ml methanol addition and a varied amount of NaOH. Itcan be seen that the conversion of SL lignite was only 8% withoutNaOH addition. With the increase of NaOH/SL lignite ratio theconversion of SL lignite increased signicantly. From Fig. 2 it can beseen that the conversion of SL lignite increased almost linearly withthe NaOH/SL lignite ratio up to 1.When the NaOH/SL lignite ratio got 1(1 g NaOH addition), the conversion of SL lignite reached to 98%. Thismay suggest that NaOH participates in the reaction system, whichagrees with Masataka's nding [1].

Fig. 3 shows the effect of the NaOH/SL lignite ratio on theliquefaction product yield and distribution. From Fig. 3, it can be seenthat the liquefaction product yield markedly increased with theincrease of the NaOH/SL lignite ratio. The products yield was alwayshigher than the conversion of SL lignite as shown in Fig. 2, indicatingthe effect of the combination of methanol with SL lignite. The solvent-extraction components of the liquefaction product of SL lignite withNaOH are mainly THFS and TS. The amounts of HS and WS are small.With the increasing of the NaOH/SL lignite ratio, the amount of THFSsignicantly increased from 5% to 79%, and the amount of WS+HS+TS increased rstly, then stabilized at about 17%. This suggests thatthe amount of the small molecular weight product in SL lignitestructure is small.

3.2. Effect of methanol content

It is clear so far that NaOH plays signicant role in the liquefactionof SL lignite with NaOHmethanol. Masataka Makabe [1] suggestedthat NaOH reacted with methanol to produce H2, which could be usedfor coal hydrogenation. Accordingly the amount of methanol isimportant for increasing lignite conversion and product yield in theliquefaction of SL lignite with NaOHmethanol. Then the effects of theamount of methanol on SL lignite conversion and product yield shouldbe investigated and the results are shown in Figs. 4 and 5. In allexperiments the amounts of SL lignite and NaOH used were 1 g,respectively.

From Fig. 4 it can be seen that the amount of methanolinsignicantly affects the conversion of SL lignite. Without methanoladdition, the conversion of SL lignite reached about 83%. It suggeststhat NaOH plays about 83% of the role on the liquefaction of SL lignitewith NaOHmethanol. The main reaction of SL lignite with NaOHmethanol is hydrolysis and SL lignite probably has more etherlinkages. With the increasing of the amount of methanol from 0 to10 ml, the conversion of SL lignite slightly increased from 83% to 98%.From the results above it can be concluded that methanol plays asmall part (up to 15%) of the role during the liquefaction of SL lignitewith NaOHmethanol. Then the role of the production of H2 from thereaction of NaOH with methanol for lignite conversion should benegligible.

Fig. 5 shows the effect of the amount of methanol on theliquefaction product yield and distribution. Without methanoladdition, product yield was about 74% and main products wereTHFS, WS and TS. The difference between yield and conversion is

probably due to the evolution of gases during reaction [9] and also the

uefa

785Z. Lei et al. / Fuel Processing Technology 91 (2010) 783788material losses during product extractionmay affect the product yield.Fig. 5 shows that product yield was somewhat irregular withmethanol addition and the amounts of THFS, TS and HS signicantlyincreased with the addition of methanol, but the amount of WS

Fig. 1. Extraction procedure for the liqslightly decreased compared to that without methanol. These resultssuggest that the main reaction is SL lignite hydrolysis by NaOH andhigher molecular weight products (such as THFS) may be split andtransformed to lowermolecular structure (such as TS, HS), whichmaybe caused by the hydrogenation of H2 produced from the NaOHreaction with methanol [1]. It can be concluded that the mainreactions of SL lignite with NaOHmethanol are the splitting of the SL

Fig. 2. Effect of the NaOH/SL lignite ratio on SL lignite conversion; 300 C, 1 g SL lignite,10 ml methanol, 1 h.lignite structure by NaOH and the hydrogenation of liquefactionproducts, which play about 85% and 15% role, respectively.

3.3. Effect of water content

ction product of SL lignite with NaOH.SL lignite has a good activity with NaOHmethanol and is one ofthe feasible liquefaction coals with NaOH as mentioned above. Inorder to probe the possibility of direct liquefaction of lignite withoutdehydration and drying pre-treatment, the liquefaction experimentsof SL lignite with water were carried out. The results are shown inFigs. 6 and 7.

Fig. 3. Effect of the NaOH/SL lignite ratio on the liquefaction product yield of SL lignite;300 C, 1 g SL lignite, 10 ml methanol, 1 h.

reaction. It suggests that hydrogenation reaction takes place in the

molecular weight productHS.Fig. 8 shows the FTIR spectra of HS, TS and THFS fractions,

Fig. 4. Effect of methanol content on SL lignite conversion; 300 C, 1 g SL lignite and 1 gNaOH, 1 h.

786 Z. Lei et al. / Fuel Processing Technology 91 (2010) 783788Fig. 6 shows that the conversion of SL lignite slightly increasedwith addition of water in the absence of methanol and reached to asteady value of 86% with increasing the amount of water from 0.1 mlto 0.5 ml, which is about equal to the SL lignite moisture contentsbetween 10% and 50%. Under the existence of methanol (10 ml) the SLlignite conversion signicantly increased for about 15%, then slightlydecreased and reached to a steady value of 95% with increasing theamount of water from 0.1 ml to 0.5 ml. These results clearly show thatNaOH and methanol play mayor and promoting roles respectively inthe lignite liquefaction with NaOHmethanol.

It can be seen from Fig. 7 that the addition of water slightlychanges the product yield and distribution in the presence or absenceof methanol. The addition of water slightly increased the percentageof TS+HS+WS, which suggested that the addition of water couldslightly promote the transformation of THFS to lower molecularweight products such as TS, HS and WS. It clearly demonstrates thatthe addition of water does not affect the SL lignite conversion andproduct yield in the presence or absence of methanol. This maysuggest that for the liquefaction of SL lignite with NaOH, there is noFig. 5. Effect of methanol content on product yield; 300 C, 1 g SL lignite and 1 g NaOH,1 h.liquefaction of SL lignite with NaOH. It is important to note that thesulfur content in HS was four times than that of SL lignite itself,suggesting that sulfur in SL lignite could be transformed into a lowerneed to dry the lignite before use, which can signicantly improve theeconomy of this process. Further work has been carried out in ourlaboratory.

3.4. Characteristics of SL lignite liquefaction products

Table 2 shows the ultimate analysis of products of SL lignite whichreacted with NaOHmethanol. The products were obtained at 1 g SLlignite reaction with 1 g NaOH and 10 ml methanol. It can be seen thatcarbon and hydrogen contents and the H/C ratio of all the liquefactionproducts signicantly increased compared with those of SL ligniteitself (as shown in Table 1), showing hydrogen addition during

Fig. 6. Effect of water content on SL lignite conversion; 300 C, 1 g SL lignite, 1 g NaOH,1 h.comparedwith that of SL lignite. The band near 3400 cm1 is assigned

Fig. 7. Effect of water content on reaction product yield; 300 C, 1 g SL lignite, 1 g NaOH,1 h.

to the OH stretchingmode [14,15]. It is obvious that the band intensityof the OH stretching mode for THFS was much stronger than that forTS and HS, suggesting the presence of more phenol group in THFS,which is consistent with the higher oxygen content in THFS comparedto that in HS and TS (see Table 2). The bands between 3000 and2800 cm1 are assigned to the aliphatic CH stretching vibrationmode and used to measure the aliphatic hydrogen content [1419].Fig. 8 shows that the intensities of aliphatic CH stretching modes ofHS were higher than those of THFS and TS. The band near 1600 cm1,1500 cm1 and 1450 cm1 was assigned to aromatic ring stretching

[5] Masataka Makabe, Koji Ouchi, Effect of pressure and temperature on the reactionof coal with alcoholalkali, Fuel 60 (1981) 327329.

Table 2Ultimate analysis of the products of SL lignite reacted with NaOHmethanol.

Ultimate analysis (wt.%, daf)

C H O N S H/C

HS 77.89 9.15 7.11 0.66 5.18 1.41TS 76.83 7.91 13.09 1.39 0.78 1.24THFS 71.50 6.42 19.28 1.60 1.20 1.08

*By difference.

787Z. Lei et al. / Fuel Processing Technology 91 (2010) 783788vibration modes [20]. Fig. 8 shows that the order of intensities ofaromatic ring stretching vibration modes was THFSNTSNHS, whichagreed with the elemental analysis data in Table 2. The band near1610 cm1, which was assigned to aromatic ring streching vibrationmodes, moved from 1610 cm1 in HS to 1640 cm1 in TS and THFS,and indicated more poly-aromatic or heterocyclic compounds in TSand THFS [21,22]. This is supported by the appearance of the carbonylvibration band at 1710 cm1 [23,24] for TS and THFS. The bands near1300 cm1, 1260 cm1 and 1220 cm1 for THFS, which wereassigned to CO (phenol), CarOCar, CO (alcohol) and CarOCalstructures respectively, were much stronger than those for TS and HS,suggesting the presence of more phenol and/or ether groups in THFS,corresponding to the higher oxygen content in THFS compared to thatin HS and TS (see Table 2). All the results above indicate that theliquefaction products have a large number of polar functional groups,such as OH group, aromatic structure, carbonyl group and aromaticether oxygen group, which cannot be obtained from petroleum and itsderivatives. Liquefaction products partially reserve the oxygenfunctional groups of SL lignite. The further separation and utilizationof the liquefaction products are now under investigation in ourlaboratory.Fig. 8. FTIR of SL lignite and extracted components of liquefaction products (HS, TS andTHFS).[6] Koji Ouchi, Hiroshi Ozawa, Masataka Makabe, Hironori Ltoh, Dissolution of coalwith NaOHalcohol: effect of alcohol species, Fuel 60 (1981) 474476.

[7] Masataka Makabe, Koji Ouchi, Solubility increase of coals by treatment withethanol, Fuel Processing Technology 5 (1981) 129139.

[8] Fanor Mondragon, Masataka Makabe, Hironori Itoh, Koji Ouchi, Solubilities ofTaiheiyo (Japan) coal in a series of alcohols, Fuel 60 (1981) 996997.

[9] Koji Ouchi, Shinya Hosokawa, Kazuhiro Maeda, Hironori Itoh, Coal hydrogenolysisin the presence of NaOH, Fuel 61 (1982) 627630.

[10] Fanor Mondragon, Ryuji Kamoshita, Takashi Katoh, Hironori Itoh, Koji Ouchi, Coalliquefaction by the hydrogen produced from methanol: 2. Model compoundstudies, Fuel 63 (1984) 579585.

[11] Yoshihide Ozaki, Masatake Makabe, Hironori Itoh, Takashi Katoh, Koji Ouchi, Coalliquefaction by the hydrogen produced from methanol, 4. Effect of catalystspecies, Fuel Processing Technology 14 (1986) 145153.

[12] Z.P. Lei, M.X. Liu, H.F. Shui, Z.C. Wang, X.Y. Wei, Behavior of supercriticalmethanolysis reaction of Shenli lignite, Modern Chemical Industy (Chinese) 29(2009) 1215.

[13] Z.C. Wang, H.F. Shui, Y.N. Zhu, J.S. Gao, Catalysis of SO42/ZrO2 solid acid for theliquefaction of coal, Fuel 88 (2009) 885889.

[14] D.W. Kuehn, R.W. Snyder, A. Davis, P.C. Painter, Characterization of vitriniteconcentrates. 1. Fourier Transform infrared studies, Fuel 61 (1982) 682.

[15] Z.C. Wang, H.F. Shui, D.X. Zhang, J.S. Gao, A comparison of FeS, FeS+S and solidsuperacid catalytic properties for coal hydro-liquefaction, Fuel 86 (2007) 835.

[16] M. Sobkowiak, E. Reisser, P. Given, P. Painter, Determination of aromatic andaliphatic CH groups in coal by FT-i.r.: 1. Studies of coal extracts, Fuel 63 (1984)1245.

[17] J.T. Senftle, D. Kuehn, A. Davis, B. Brozoski, C. Rhoads, P.C. Painter, Characterizationof vitrinite concentrates: 3. Correlation of FT-i.r. measurements to thermoplasticReferences

[1] Masataka Makabe, Yasuo Hirano, Koji Ouchi, Extraction increase of coals treatedwith alcoholsodium hydroxide at elevated temperatures, Fuel 57 (1978)289292.

[2] Masataka Makabe, Sachihide Fuse, Koji Ouchi, Effect of the species of alkali on thereaction of alcoholalkalicoal, Fuel 57 (1978) 801802.

[3] Masataka Makabe, Koji Ouchi, Structural analysis of NaOHalcohol treated coals,Fuel 58 (1979) 4347.

[4] Masataka Makabe, Koji Ouchi, Reaction mechanism of alkalialcohol treatment ofcoal, Fuel Processing Technology 2 (1979) 131141.4. Conclusions

SL lignite has a good reaction activity with NaOHmethanol. Theconversion of SL lignite and product yield reached to 98% and 99% at300 C for 1 h respectively, when the ratio of SL lignite, NaOH andmethanol was at 1 g:1 g:10 ml. The main products were THFS (about70%) and TS (about 15%).

During the liquefaction, NaOH participated in the reaction andplayed the main role (up to 85%). The conversion of SL ligniteincreased almost linearly with the NaOH/SL lignite ratio up to 1. Theconversion of SL lignite and product yield reached about 83% and 74%in the SL lignite reaction with NaOH, respectively. Methanol played apromotion role in the liquefaction of SL lignite with NaOH. Methanoladdition leaded to the conversion of SL lignite and product yieldincreased for about 15% and 25%, respectively. Water content(between 10% and 50%) insignicantly affected the conversion of SLlignite and product yield.

Liquefaction products (THFS, TS and HS) contained OH group,aromatic structure, carbonyl group and aromatic ether oxygen, andthe contents of polar function groups followed the order ofTHFSNTSNHS.

Acknowledgements

The authors express their grateful appreciation for the nancialsupport from the National High Technology Research and Develop-ment Program of China (863 Program 2007AA06Z113), the NaturalScientic Foundation of China (20876001, 20776001), and the StateKey Laboratory of Coal Conversion (Grant No. 09-904). Authors arealso appreciative for the nancial support from the ProvincialInnovative Group for Processing & Clean Utilization of Coal Resource.and liquefaction behaviour, Fuel 63 (1982) 245.

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the i.r. spectrum of coal, Fuel 62 (1983) 742.[21] Y.X. Zhao, X.Y. Sun, Spectrum Identify of Organic Molecule Structure, Science

Publisher, Beijing, 2003 in Chinese.

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788 Z. Lei et al. / Fuel Processing Technology 91 (2010) 783788

Study on the liquefaction of Shengli lignite with NaOH/methanolIntroductionExperimentalLignite and reagentsLiquefactionFractionation of liquefaction productsProducts analyses

Results and discussionEffect of the ratio of NaOH/SL ligniteEffect of methanol contentEffect of water contentCharacteristics of SL lignite liquefaction products

ConclusionsAcknowledgementsReferences