Biodesulphurized low rank coals appraisal: Initial, treated, their bitumens and solid residues S.P. Marinov a , M. Stefanova a, ⁎, L. Gonsalvesh a , V. Groudeva b , P. Gadjanov c , R. Carleer d , J. Yperman d a Institute of Organic Chemistry, Bulgarian Academy of Sciences, bl. 9, Sofia 1113, Bulgaria b Sofia University “St. Kl. Ohridski”, Faculty of Biology, D.Tzankov, 8, Sofia 1164, Bulgaria c Technical Uniersity of Sofia, Thermal and Nuclear Power Eng. Dept., Sofia 1756, Bulgaria d Hasselt University, CMK, Research Group Appl. Anal. Chem., Agoralaan- gebouw D, B-3590 Diepenbeek, Belgium abstract article info Article history: Received 13 June 2011 Received in revised form 27 July 2011 Accepted 28 July 2011 Available online 20 September 2011 Keywords: Coal Sulphur Biodesulphurization AP-TPR/MS Low rank high sulphur containing Bulgarian coals are biodesulphurized on laboratory scale. Treatment of Maritza East lignites by bacteria Pseudomonas putida B2 (PP) attained 44% total desulphurization, while biodesulphurization of Bobov dol subbituminous coal by Acidothiobacillus ferrooxidans F3 (AFe) demonstrated 14%. The caloric values were slightly altered, 0.8% for lignites and 4.7% for subbituminous coal. Bitumens from the initial and biotreated coals and fractions of their neutral oils are studied. For subbituminous coal treated by AFe F3 bacteria increase in polar diterpenoids is registered by GC/MS. Concerning the set of polar diterpenoids produced during lignites treatment by PP B2 their relative contents are comparable with the ones for initial lignites. GC/MS analyses of soluble products from both coals did not give any information for sulphur containing compounds. Temperature programmed reduction coupled “on-line” with mass spectrometry (AP-TPR/MS) and its “off- line” TD-GC/MS version are used for sulphur tracking in solid residues after bitumen extraction. Quantitative interpretation of TD-GC/MS profiles revealed changes in organic sulphur compounds, elemental sulphur and SO 2 . Results gave us ground to conclude that AFe F3 bacteria decrease pyritic sulphur content and slightly oxidize coal organic matter while PP B2 bacteria influence lignite organic matter and also affect pyritic sulphur. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Clean coal utilization is an actual challenge concerning higher energy consumption and global ecological impact. During coal combustion sulphur is emitted as SO x and contributes to air pollution and acid rains. Sulphur is present in coal mainly as inorganic, i.e. pyritic and organic forms. Contents of these dominating sulphur types account more than 80%. Pyritic sulphur occurs as finely disseminated and randomly distributed crystals in coal mineral matter whereas the organic sulphur is presented as an integral part of the coal matrix covalently bounds to its complex structure. By application of different desulphurization procedures it is difficult to attain simultaneously high organic sulphur removal and moderate coal destruction. The last one reflected a decrease in coal energy value and thus considered less suitable for energy production. One possibility to prevent environment from sulphur oxides is to reduce sulphur content in fuel before combustion. Biodesulphuriza- tion is one of the promising methods for production of environmental friendly fuels. Microbial coal desulphurization offers many advantages over conventional physical and chemical treatments and energetic value of coal is slightly altered. Biological processes are based on coal treatment by microorganisms and are performed under mild conditions without harmful products. Biodesulphurization carried out at appropriate conditions promoted the oxidative conversion of the reduced forms of sulphur in water soluble, easy washed-out compounds. Acidothiobacillus ferrooxidans (AFe) and Pseudomonas putida (PP) are widespread microbial cultures used in coal biodesulphurization [1,2]. AFe is effective only in the pyritic sulphur removal while PP microorganism is capable to decrease organic sulphur as well [3,4]. There are scanty studies on the changes in extracted organic products (bitumen) from coals desulphurized by the above men- tioned bacteria [5–7]. An investigation on sulphur transformations in solid residues after bitumen extraction totally misses. By additional information for the organic soluble components, light will be shed on microorganisms' application and mechanisms of their activity. It will contribute to improve our knowledge for biodesulphurization processes as well. The aim of the present study is to appreciate sulphur types changes in biotreated coal samples by AFe and PP bacteria. The distribution of Fuel Processing Technology 92 (2011) 2328–2334 ⁎ Corresponding author. E-mail address: maia@orgchm.bas.bg (M. Stefanova). 0378-3820/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fuproc.2011.07.022 Contents lists available at SciVerse ScienceDirect Fuel Processing Technology journal homepage: www.elsevier.com/locate/fuproc