Geochemical study of maltenes from coal biodesulphurisation L. Gonsalvesh a,⇑ , M. Stefanova a , S.P. Marinov a , R. Carleer b , J. Yperman b a Institute of Organic Chemistry, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria b Research Group of Applied and Analytical Chemistry, CMK, Hasselt University, Agoralaan – gebouw D, B-3590 Diepenbeek, Belgium highlights Extracts of initial and biotreated coals are studied by geochemical proxies. Mature coal is less altered by treatments as biomarker pattern is slightly changed. Lignites are more susceptible to biotreatment especially with white rot fungus. Experimental data assign ‘‘light’’ degree of biodegradation during desulphurisation. article info Article history: Received 12 May 2014 Received in revised form 20 June 2014 Accepted 25 June 2014 Available online 14 July 2014 Keywords: Coal Desulphurisation Organic matter Geochemical proxies abstract The aim of the study is to examine by geochemical proxies the effect of biodesulphurisation on coal organic matter composition. Two Bulgarian and one Turkish low rank coals (R r = 0.20–0.46%) were analysed. Prior to biotreatments, the coals were demineralised and depyritised. The white rot fungi Phanerochaete chrysosporium – ME446 and the thermophilic and acidophilic archae Sulfolobus solfataricus – ATCC 35091 were used. After desulphurisations the samples were extracted with chloroform to recover bitumens. Maltenes (portion soluble in n-hexane) were prepared after asphaltenes precipitation. They were fractionated into aliphatic, aromatic and polar fractions and the first two were GC/MS studied. The following homologous series were registered: (i) n-alkanes, nC 12 –nC 32 , mainly long-chain homologues with ‘‘odd’’ members prevalence; (ii) n-alkan-2-ones; (iii) esters of n-fatty acids, nC 12 –nC 32 , with bimodal distributions; (iv) diterpenoids; (v) products of triterpenoids destruction and aromatisation; (vi) hopanoids. Results were quantitatively interpreted. All studied fractions of initial and biotreated samples were strongly dominated by n-alkanes, 60–90%, but patterns of distributions after desulphurisations were somewhat changed as shorter homologues had partly disappeared. Relative distribution of geochemically considered series depicted some peculiarities: (i) organic matter of higher mature coal was less attained by desulphurisation; (ii) lignite organic matter seemed to be more susceptible to biotreatment especially with P. chrysosporium culture. During S. solfataricus biodesulphrisation different series preserved their pattern of distribution while P. chrysosporium treatment strongly perturbed it. There were indications for coal organic matter oxidation assigned by polar biomarkers appearance. Tercyclohexanes were detected only in products of coals biotreated with S. solfataricus. The gradual changes in organic matter composition depicted by a scale adopted from petroleum exploration attested ‘‘light’’ biodegradation during coal biodesulphurisation. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The exploitation of all energy generating technologies invariably leads to some degree of environmental impact. The use of coal is not an exception. Combustion of sulphur-containing coals (fossil fuels) contributes to air pollution and causes operational problems during combustion. More importantly, the emission of SO 2 into the atmo- sphere during coal combustion is of serious ecological concern. Environmental legislation norms regarding sulphur emissions from coal combustion are already in place in many countries and under consideration in others. Therefore in the last years, in order to comply with the strict environmental requirements for coal combustion, desulphurisation of fossil fuels has become attractive. Thus, it is imperative to achieve high sulphur reductions accompa- nied by good coal combustion parameters. The native bacteria http://dx.doi.org/10.1016/j.fuel.2014.06.056 0016-2361/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: [email protected](L. Gonsalvesh). Fuel 135 (2014) 332–339 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel
Transcript
Fuel 135 (2014) 332–339
Contents lists available at ScienceDirect
Fuel
journal homepage: www.elsevier .com/locate / fuel
Geochemical study of maltenes from coal biodesulphurisation
http://dx.doi.org/10.1016/j.fuel.2014.06.0560016-2361/� 2014 Elsevier Ltd. All rights reserved.
L. Gonsalvesh a,⇑, M. Stefanova a, S.P. Marinov a, R. Carleer b, J. Yperman b
a Institute of Organic Chemistry, Bulgarian Academy of Sciences, Sofia 1113, Bulgariab Research Group of Applied and Analytical Chemistry, CMK, Hasselt University, Agoralaan – gebouw D, B-3590 Diepenbeek, Belgium
h i g h l i g h t s
� Extracts of initial and biotreated coals are studied by geochemical proxies.� Mature coal is less altered by treatments as biomarker pattern is slightly changed.� Lignites are more susceptible to biotreatment especially with white rot fungus.� Experimental data assign ‘‘light’’ degree of biodegradation during desulphurisation.
a r t i c l e i n f o
Article history:Received 12 May 2014Received in revised form 20 June 2014Accepted 25 June 2014Available online 14 July 2014
The aim of the study is to examine by geochemical proxies the effect of biodesulphurisation on coalorganic matter composition. Two Bulgarian and one Turkish low rank coals (Rr = 0.20–0.46%) wereanalysed. Prior to biotreatments, the coals were demineralised and depyritised. The white rot fungiPhanerochaete chrysosporium – ME446 and the thermophilic and acidophilic archae Sulfolobus solfataricus– ATCC 35091 were used.
After desulphurisations the samples were extracted with chloroform to recover bitumens. Maltenes(portion soluble in n-hexane) were prepared after asphaltenes precipitation. They were fractionated intoaliphatic, aromatic and polar fractions and the first two were GC/MS studied. The following homologousseries were registered: (i) n-alkanes, nC12–nC32, mainly long-chain homologues with ‘‘odd’’ membersprevalence; (ii) n-alkan-2-ones; (iii) esters of n-fatty acids, nC12–nC32, with bimodal distributions; (iv)diterpenoids; (v) products of triterpenoids destruction and aromatisation; (vi) hopanoids. Results werequantitatively interpreted.
All studied fractions of initial and biotreated samples were strongly dominated by n-alkanes, 60–90%,but patterns of distributions after desulphurisations were somewhat changed as shorter homologues hadpartly disappeared. Relative distribution of geochemically considered series depicted some peculiarities:(i) organic matter of higher mature coal was less attained by desulphurisation; (ii) lignite organic matterseemed to be more susceptible to biotreatment especially with P. chrysosporium culture. DuringS. solfataricus biodesulphrisation different series preserved their pattern of distribution whileP. chrysosporium treatment strongly perturbed it.
There were indications for coal organic matter oxidation assigned by polar biomarkers appearance.Tercyclohexanes were detected only in products of coals biotreated with S. solfataricus. The gradualchanges in organic matter composition depicted by a scale adopted from petroleum exploration attested‘‘light’’ biodegradation during coal biodesulphurisation.
� 2014 Elsevier Ltd. All rights reserved.
1. Introduction
The exploitation of all energy generating technologies invariablyleads to some degree of environmental impact. The use of coal is notan exception. Combustion of sulphur-containing coals (fossil fuels)contributes to air pollution and causes operational problems during
combustion. More importantly, the emission of SO2 into the atmo-sphere during coal combustion is of serious ecological concern.
Environmental legislation norms regarding sulphur emissionsfrom coal combustion are already in place in many countries andunder consideration in others. Therefore in the last years, in orderto comply with the strict environmental requirements for coalcombustion, desulphurisation of fossil fuels has become attractive.Thus, it is imperative to achieve high sulphur reductions accompa-nied by good coal combustion parameters. The native bacteria
L. Gonsalvesh et al. / Fuel 135 (2014) 332–339 333
capable to reduce simultaneously inorganic and organic sulphurare of special interest. Results for 50–53% sulphur destruction withcalorific value preservation are announced, i.e. by Mishra et al. [1].
In general, there are two basic options for controlling sulphuremissions from thermal power plants, i.e. pre- and post-combustiontreatments. Several methods have been proposed to reduce sulphurcontent before coal combustion. The applied techniques includephysical, chemical and biological processes and usually most ofthe inorganic sulphur in fossil fuel can be easily removed. However,there is one portion, known as refractory organic sulphur, which isvery difficult to get rid of [2]. The current methods, which affectthe refractory part, operate under extremely invasive conditionsand produce considerable amount of CO2. Probably this is one ofthe reasons why coal biodesulphurisation has recently become tothe forefront of coal technology research as a method with potentialtoward organic sulphur removal. Briefly, biodesulphurisation isregarded as promising approach for production of environmentalfriendly fuels. Microbial coal desulphurisation offers many advanta-ges over physical and chemical processes [2–5]. The fact that aftertreatment energy and combustion characteristics of coal are slightlyaltered is of utmost importance [6–8]. However, it should be men-tioned that beside sulphur removal, biodesulphurisation treatmentscould affect coal organic matrix. It is revealed that some microorgan-isms are capable to oxidise and destroy coal organic matter [9,10].
It is known that biodesulphurisation is relatively new and aninsufficiently studied method for organic sulphur removal fromcoal. On the other side, it is a very attractive approach due to therelatively low costs, mild experimental conditions and the lack ofadditional pollutants. However, the current limitations and disad-vantages of microbial treatments (slow and difficultly controlledprocesses requiring grounding to very fine particle size) hinder theirindustrial application [11]. In order to promote coal biodesulphuri-sation for future industrial application, there is a requirement foradditional research with the target to increase desulphurisationrates without deterioration fuel calorific parameters.
Recently, a sequence of papers is published with results on sul-phur distribution in organic/inorganic forms in a set of biodesul-phurised coals [8,9,12–14]. In these studies, AtmosphericPressure-Temperature Programmed Reduction (AP-TPR) techniqueis applied. AP-TPR device coupled with different detection systems,i.e. Mass Spectrometry (MS) and Thermal Desorption Gas Chroma-tography/Mass Spectrometry (TD-GC/MS), offers opportunity totrack organic sulphur alterations as a result of the applied biotreat-ments. By AP-TPR ‘‘off-line’’ TD-GC/MS an improved organic sulphurinformation is obtained due to specific sulphur sorbent application.A broad range of sulphur-containing organic compounds areidentified and quantitatively interpreted. Consequently, the organicsulphur biotransformation mechanisms are clarified at a certain extent.
The aim of the present study is to examine the effect ofbiodesulphurisations on coal organic matter composition bygeochemical proxies. Extractable portions of coals and productsof their biotreatments are comparatively studied and someassumptions on organic matter changes are proposed.
2. Materials and methods
2.1. Samples and chemical- and biotreatments
Two Bulgarian and one Turkish low rank coal samples wereinvestigated. They were selected due to their high sulphur con-tents, i.e. organic sulphur, and their importance for the countryindustrial electricity production.
Bulgarian coal samples under consideration were:
– Pirin subbituminous coal from the ‘‘Pirin’’ coal mine, Rr = 0.46%[15] – code name P.
– Handly picked up Humovitrain of Maritza East lignite from the‘‘Trajanovo-North’’ mine, Rr = 0.20% [16] – code name M.
Turkish lignite under study was:
– Beypazari lignite from the ‘‘Cayirhan’’ mine, Rr = 0.38% [17] –code B.
Prior to biotreatments coal samples (<0.063 mm) were demi-neralised [18,19] and subsequently depyritised by diluted nitricacid (17%) for 3 h at room temperature [18,20,21]. These treat-ments were performed to receive mineral- and inorganic sul-phur-free coals and to focus our attention on the changes thatoccurred only with organic sulphur and organic coal matter as aresult of biodesulphurisation. Demineralised and depyritised sam-ples were assigned as APF (Ash and Pyrite Free) and were consid-ered as initial samples in this study. Further on, APF sampleswere subjected to biodesulphurisation.
The white rot fungi Phanerochaete chrysosporium – ME446 (PC)and the thermophilic and acidophilic archae Sulfolobus solfataricus– ATCC 35091(SS) were the used microorganisms. Biodesulphurisa-tion procedures were applied at the optimal conditions as describedin Gonsalvesh et al. [8]. Briefly, demineralised and depyritised coalsamples were added to the selected microorganism media with aratio of 3 g coal per 100 mL microorganism in a nutrient mediumrecommended by the suppliers. Thereafter, lab-scale, shake-flaskexperiments were carried out at the following conditions:
(i) PC – pH = 4.7 (at ambient temperature), temperature 30 �C,125 rpm shaking rate, 6 days duration.
(ii) SS – pH = 4 (at ambient temperature), temperature 70 �C,40 rpm shaking rate, 14 days duration.
To avoid any biomass contamination and to purge SO42�
by-products, biotreated coal samples were filtrated and washedwith 5% HCl (aq.) solution, and next with hot distilled water. Coalsamples were dried at 105 �C and subjected for proximate, ulti-mate and sulphur analysis as described in previous papers [8,12].
2.2. Fractionation and GC/MS study
Samples (�4 g) were extracted for 6 h with 50 ml chloroformreflux at 70 �C and stirred for bitumens isolation. Total chloroformextracts were separated into maltenes (portion soluble in n-hex-ane) and asphaltenes (precipitates). The latter were prepared bybitumen precipitation in n-hexane (1:100, v/v). Maltenes werefractionated by mini-SiO2 column (100 � 10 mm) into neutrals(n-hexane eluent), aromatics (dichloromethane, DCM eluent) andpolars (acetone eluent).
The first two fractions were subjected to a GC/MS study. HP6890 GC system plus HP 59763 MS detector operated in EI modewith ionisation energy 70 eV instrument was used. Scanrange was from 45 to 750 Da. Capillary column HP-5MS(30 m � 0.25 mm � 2.25 lm) with He as carrier gas was used. Fordata quantification deuterated n-dodecane, C12D26, was added asa standard. Homologous series were tracked by characteristic ionfragments, i.e. m/z 85 – for n-alkanes; m/z 83 – for cyclic alkanes;m/z 58 – for n-alkanones; m/z 191 – for hopanes (H); m/z 123 – forditerpenoids (Di-T); m/z 217 – for steranes; m/z 203, 218 – for trit-erpenoids (Tri-T); and m/z 74, 88, 102 – for esters of fatty acids.
3. Results and discussion
To be successful one biodesulphurisation process appropriatemicrobial culture must be selected depending on the coal charac-
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teristics. It should also be known that each microbial culture selec-tively removes one definite type of sulphur, i.e. organic or inor-ganic. Therefore it is advisable the choice of microbial culture todepend firstly or mainly on sulphur type prevalence. Coal inorganicsulphur microbial removal has been described in numerous studies[9,22–40]. The most studied microorganism for depyritisation isthe mesophilic and acidophilic lithotroph (an organism that useinorganic compounds, such as hydrogen sulphide, elemental sul-phur, ammonium and ferrous iron, as reducing agents for biosyn-thesis and chemical energy storage) Thiobacillus ferrooxidans,growing at 30–35 �C and pH 2.0–2.5 [9,11,22,27–31,38–42].Depending on the coal type and experimental conditions, over90% of pyritic sulphur has been removed [28,29,31,39–41].
Inasmuch as there are well developed industrial techniques(comprising mainly physical processes) for inorganic sulphurremoval, we believe that it is much more important to developand study biodesulphurisation towards organic sulphur removal.Therefore microbial cultures, i.e. PC and SS, which have been previ-ously found to be effective towards organic sulphur elimination[14,34,37] are applied in our current and previous studies [8,12].The biotreatments are performed on mineral- and inorganic sul-phur-free coal in order to enhance the organic sulphur removal,i.e. its accessibility by the microorganisms, and in order to focusour research on the changes that occur with organic sulphur as aresult of biodesulphurisation [8]. We agree that applied in the cur-rent study demineralisation and depyritisation chemical treat-ments are not acceptable for industrial application. However, weused these treatments (lab scale) only in order to obtain ash- andpyrite-free sample which on the other hand can be achieved byindustrially relevant methods.
Characteristics of the studied coals and products of biotreat-ments are presented in Table 1. In all biotreated coals, decreasesin the sulphur contents were registered. At the same time the mag-nitudes for the higher heating values (HHV) calculated by theChanniwala equation [43] were relatively preserved. These obser-vations fulfilled the main goal of the desulphurisation – to carryout sulphur reduction without caloric values alteration.
Inasmuch as coal biodesulphurisation is under concern in thecurrent study, although in a slightly different aspect focused onthe organic matrix, the effects of biodesulphurisation on coal com-position cannot be omitted and should be deeper discussed. Ourprevious paper [8] demonstrated that higher biodesulphurisationeffect is attained for APF coal samples treated with PC. Maximumtotal sulphur (St) biodesulphurisation of 24.2% is found in the caseof M-APF-PC coal sample, and 24.1% for P-APF-PC coal. Maximumorganic sulphur (So) biodesulphurisation with PC is achieved forthe same coal samples: M-APF-PC (22.0%) and P-APF-PC (23.8%).In the case of B-APF-PC coal, St biodesulphurisation is relativelylower (10.3%) and is much more effective towards pyritic sulphur(Sp) removal (71.1%). With regards to SS treatment, maximum St
and So biodesulphurisation effects of 16.9% and 18.3%, respectively,
ad – air dried; daf – dry ash free; HHV – higher heating value.
are determined for B-APF-SS coal sample. Supplemental informa-tion on qualitative/quantitative changes in sulphur forms andorganic sulphur functionalities can be found in previous articles[8,12]. It is worth to mention the insignificant effects of the PCand SS biotreatments on the heating value (HHV) of the samples.
Information for the coal organic matter alterations during treat-ments can be received by geochemical proxies. Extractable por-tions (chloroform bitumens) represented negligible parts of coalorganic matter – 0.8–2.3% (Table 2). Nevertheless they suppliedvaluable information for the products compositions. Balances ofbitumens separations in maltenes/asphaltenes fractions and subse-quent maltenes fractionations into neutrals, aromatics and polarsare gathered in Table 2. Contents of GC/MS registered homologousseries, calculated in lg/g Corg are listed in Table 3.
Yields of the bitumens from SS treatment were systematicallylower comparing to APF and PC samples. Maltene fractional compo-sitions were similar (Table 2). Higher molecular and polyfunctionalcomponents, i.e. polars and asphaltenes, were dominant in allsamples under consideration. In such circumstances, portions ofneutrals/aromatics represented �20–30% of the analysed samples.
Information for lignite biomarkers and techniques of MS track-ing can be found in a previous paper and in a special volumedevoted to coal biomarkers [44]. The registered in the currentstudy biomarker assemblages (see Table 3) determined certain dif-ferences in biomarker compositions of the samples. Generally ourdata supported the facts that Matritza East coal is lignite, predom-inantly composed of conifer parent vegetation, Beypazari lignite byangiosperm coal-forming vegetation, while Pirin coals are moremature as angiosperm progenitors are already aromatised anddestructed.
The biomarker assemblages were mainly comprised by linearand cyclic compounds some of them functionalised in the formsof ketones, phenols and esters. Inasmuch as n-alkanes were pre-vailing in the analysed mixture they will receive a special attentionand will be discussed later on. Considering n-alkanones distribu-tions, the long chain ‘‘odd’’ numbered members, i.e. nC27, nC29,were dominant which is typical for higher plants waxes [45].
A peculiarity of the samples compositions was the presence ofseries of fatty acid methyl esters (in the range of nC14–nC30, max-imising at the ubiquitous nC16 and nC18) and ethyl esters (in therange of nC12–nC34, with strong ‘‘even’’ carbon numbered domi-nance with two maxima, again at ubiquitous nC16 and at nC28).Fatty acid ethyl esters are not unusual as they are found in somecoals and geological sediments [46]. Long chain fatty acids arecharacteristic for epicuticular waxes of higher plants and ethylesters presence is attributed to bacterial activity in the depositionenvironments. Besides methyl and ethyl esters some short chainpropyl esters of nC12, nC14 and nC16 were also observed in thetracked chromatograms. In the coal extracts such esters have notbeen yet described. Their presence cannot be rendered to the bio-treatments since they were registered in the APF samples as well.
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Sesquiterpenoids are natural products present in resins andessential oils of higher plants. In combination with diterpenoidsthey serve to tag plant resins in the geological record and con-nect them with a certain class of plant input [47]. The precursorsof the most sesquiterpanes are common components ofessential oils and resins and can occur as saturated, unsaturated,aromatic and functionalised derivatives. Cuparene and cadalenesesquiterpenoids were registered in all samples in contents <1%.One polar sesquiterpenoid, cuparol, was resolved in P-APF-SSsample.
The diterpenoids in the samples under study were assigned tothe abietane, pimarane and phyllocladane structural groups. Aro-matised abietane hydrocarbon, i.e. simonellite, was determinedas well. All these compounds were in huge amounts in M-APF sam-ple indicating its conifer vegetation progenitors [48]. The samplesalso contained polar diterpenoids consisting of ferruginol and abie-taketone, i.e. abieta-8,11,13-trien-7-one [49]. The latter com-pounds are considered as oxidation products with the endmember abietic acid.
Triterpenoids and their polar analogues are characteristics forangiosperm vegetation in the paleomire. They were highly abun-dant in B-APF sample. Inasmuch as P-APF sample was slightly moremature, angiosperm progenitors were already aromatised and des-tructed. Two main pathways of functionalised coal precursor rear-rangement are maintained [50]: (i) loss of ring with des-Atriterpenoid formation and subsequent aromatisation; (ii) progres-sive aromatisation with the skeleton intact. It is known that pro-gressive aromatisation of triterpenoids starts soon after burial,probably via microbial mediation. The end products of diagenesisare alkylated picene and chrysene derivatives. In our study severalspecies were found that could be regarded as the end productsfrom destruction of higher plants triterpenoids preserving olean-ane, ursane or lupane skeleton. Registered triterpenoid structures
Table 3Homologue series and compounds contents, in lg/g Corg.
were not specific for a distinct plant family. They simply provedan abundance of angiosperm paleovegetation in the paleorealm,especially in the case of Beypazari sample.
Hopanes and steranes are widely used as coal biomarkers sup-plying additional information for microbial activity and deposi-tional environment. Their relative contents in the analysedsamples were low especially those of steranes. Nevertheless theywere all tracked by their specific fragments. Concerning hopanes(neutral fraction), all steric isomer were identified (see Fig. 1).Hopane distributions of lignite samples were dominated by bb ste-reo isomers. Unsaturated C30 hop-22(29)-ene (diploptene) wasespecially abundant in the Beypazari samples. A particular featurewas the presence of C32–C34 benzohopanes. These compounds havenot been identified till now in Bulgarian coals. A possible explana-tion for their appearance could be the bond cleavage of their link-age to the coal matrix or improved accessibility as a result ofapplied chemical- and biotreatments. Ketohopanes, i.e. 17a(H)-Trisnorhopan-21-one, C27, were in a considerable amount in thearomatic fractions of all samples and were an indication for theproceeding of oxidation process during deposition.
The careful GC/MS examination of M-APF-SS aliphatic fractionshowed tricyclohexane presence, M+.248, m/z 83, 100% (Fig. 2).Subsequent SIM m/z 248 tracking of all products of SS treatmentregistered differently arranged three cyclohexane rings structures.The following contents were calculated, in lg/g Corg: 8.8 for P-APF-SS, 56.0 for M-APF-SS and 0.2 for B-APF-SS. Experimental data giveus ground to speculate that during biotreatment by SS covalentbonds were splitted and tricyclohexanes were formed.
In Fig. 3 the different GC/MS tracked series are expressed inrel.% from the total amounts listed in Table 3. All GC/MS registeredcompounds are typical coal biomarkers [51]. n-Alkanes werehighly abundant in all samples and represent 60–90 rel.%. Theywere taken under consideration in all calculations of the rel.% butare not shown in Fig. 3 as they would completely dominate thepresentations with loss of relevancy. Some series, i.e. sesquiterpe-noids and steranes, were in very low amounts, <1%, and are notincluded in Fig. 3 as well.
Based on the relative distribution of homologous series deter-mined by geochemical proxies (see Fig. 3) two main commentscould be expressed: (i) organic matter of the higher mature coalP-APF was less affected by desulphurisation. The patterns of distri-butions for P-APF, P-APF-SS and P-APF-PC were mostly similar.Only some small increase in oxygen-containing homologues, i.e.n-alkanones, ketotriterpenoids and ketohopanes, was observedwhich might be an indication for oxidation processes; (ii) Ligniteorganic matter was more susceptible to biotreatment, especiallywith PC culture. During SS biodesulphrisation different compoundgroups almost preserved their pattern of distribution compared to
Fig. 1. Hopane elution regions of B-APF sample and products of PC and SS biodesulphrisation treatments tracked by m/z 191 (H – hopane; BH – benzohopane; 1,2,3-triterpenes M+ 410, C30H50; 4-diploptene; 5-diaromatic triterpane M+ 374, C28H38).
Fig. 2. TICs of M-APF (A) and M-APF-SS (B) samples.
336 L. Gonsalvesh et al. / Fuel 135 (2014) 332–339
APF samples (except keto-TT for P-APF-SS sample, linear esters forM-APF-SS sample, etc.) while PC treatment strongly disturbed it. Itis a bit astonishing that due to PC treatment of M-APF sample diter-penoids almost disappeared as it is well known that these speciesprotect from microbial decay ([52] and references therein). How-ever, it has been already revealed that some microorganisms, par-ticularly fungi and bacteria, involved in coal biodesulphurisation,are capable of biodegradation and convert some coals into liquidor water-soluble states [11,53–58]. The greatest effect in this fieldhas been seen for low-rank, highly oxidised coals, which are chem-ically close to wood.
It has been already mentioned in the discussion that n-alkanesamount up to 60–90% of the samples under consideration. In
Table 4 they are divided into short-chain (nC15–nC20), mid-chain(nC21–nC25) and long chain (nC26–nC33) homologues. CPI valueswere calculated (Table 4) and they reflected ‘‘odd’’ homologuesprevalence over ‘‘even’’ ones. The ‘‘odd’’ numbered n-alkanes, i.e.nC27, nC29, nC31, strongly dominated all distributions and CPI val-ues were >1. Obviously, the biotreatments resulted in a partialdecrease in the contents of the short- and mid-chain homologuesand in a relative increase in the long ones. This observation wasnot valid only for M-APF-SS sample characterised with the highestn-alkanes reduction among SS biotreated coals. For this sample anincrease in short- and mid-chain homologues of 7 rel.% was calcu-lated at the expense of long ones. Apparently, desulphurisationaction of SS on M-APF sample is different from the one on the other
Fig. 3. Homologous series expressed in rel.%.
Table 4n-Alkane distributions, in rel.% and CPI values.
Subbituminous coal Pirin Humovitrain of Maritza East lignite Beypazari lignite
L. Gonsalvesh et al. / Fuel 135 (2014) 332–339 337
two coal samples. Similar trend has been observed in a previousstudy as well [8]. However, reasonable explanation for that cannotbe provided at the current stage of the research.
Coal biotreatment has been recently studied by Fabianska et al.[10,59]. They applied geochemical proxies to assess products fromPolish coals and embedded sediments biodesulphurised byT. ferrooxidans and Thiobacillus thiooxidans. Their results indicatedthat microbial desulphurisation could significantly affect organicmatter of Miocene lignite as lower molecular weight fraction ofthe extracts was changed and biodegraded. Distribution ofn-alkanes and aromatic hydrocarbons were strongly affected bythe process. The cited authors found several trends in the extractcompositions of biotreated coal and compared them with thechanges in organic matter of biodegraded fossil materials, i.e.petroleum, asphalts, etc. They assessed the observed gradualchanges in organic matter compositions by a scale adopted frompetroleum exploration [59,60]. Based on this scale and on the factthat all studied by us extracts were dominated by n-alkanes, butpatterns of distributions after biotreatments were changed asshorter homologues partly disappear, it can be stated that theextract compositions in our case attest ‘‘light’’ degradation of coalorganic matter. However, it cannot be expected that all coal sam-ples will obey the same effects of biotreatments as far as the pro-cess is influenced by a lot of factors, i.e. rank, maceralcompositions, parent vegetations, mineral matter, etc. Moreoverapplied strain types and experimental conditions are of utmost
importance. Even though in our study some tendencies for PCand SS biotreated coals have been pointed out and discussed.
4. Conclusions
In order to track the influence of biotreatments on the coalorganic matter composition maltenes from low rank coals wereevaluated by geochemical proxies. During the study of the extractfractions the following trends have been found:
– decrease in extracts yields after S. solfataricus treatments;– decrease in lighter n-alkane homologues contents;– hint for coal organic matter oxidation assumed from the
increase in polar biomarkers amounts, i.e. n-alkanones, ketotrit-erpenoids and ketohopanes;
– covalent bond cleavage with tercyclohexane formation after S.solfataricus treatments;
– organic matter of the higher mature coal P-APF has been lessattained by desulphurisation as pattern of biomarkers distribu-tion was not notably affected;
– lignite organic matter has been more susceptible to biotreat-ment, especially with P. chrysosporium culture, since biomarkerspatterns of distribution after biodesulphurisation werechanged and products of triterpenoids aromatisation and degra-dation became the dominant components in the studiedfractions;
338 L. Gonsalvesh et al. / Fuel 135 (2014) 332–339
– appearance of some biomarkers in the extracts could bereferred to bond cleavage of their linkage to the coal matrix orto the improved accessibility due to applied chemical- andbiotreatments.
Generally, our data revealed that the applied biodesulphurisa-tion do not alter significantly coal matrix. The observed gradualchanges evaluated by a scale adopted from petroleum explorationhave attested ‘‘light’’ biodegradation during desulphurisation.
Acknowledgements
The study was supported within the framework of Cooperationagreement for joint supervision and award of a doctorate betweenHasselt University, Belgium and Bulgarian Academy of Sciences(BAS). Jan Czech is especially acknowledged for GC/MS analyses.The authors are also grateful to Prof. Y. Yürüm, Dr. G. Dinler-Doganay and Dr. A. Dumanli for the biotreatment assistances, donein the frame of Project collaboration between IOCH-BAS andSabanci University.
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