Abstract

Trace level estimation of bio-ethanol / butanol in aqueous fermented sugars by headspace-gas chromatography (GC-HS)

Author(s): Anju Chopra, Dheer Singh, A.K.Tewari, Ravi Sahai, M.P.Singh, M.B.Patel, B.Basu

Ethanol is used as liquid biofuel either as such or blendedwith gasoline. Bio-ethanol production fromsugars,which is at the advancedR&D stage, is being produced by the fermentation of monosaccharides generated fromthe hydrolysis of celluloses and hemicelluloses.Alot ofwork is being done byvarious laboratoriesworldwide formonitoringthe bio-ethanol concentration produced frombiomass by gas chromatographywith flame ionization detector (GC-FID).Aqueous fermentation supernatant containing both volatile and non-volatilematerials is directlyinjected to the injector port ofGC. The non-volatile residues,which are comingfromthe biomass, remain in the injection port and lead to fouling of the injector.These residues undergo thermal degradation and enter into theGCcolumn,which leads to erroneous results. In the present work, amethod has been developed by Headspace Gas Chromatography (GC-HS) for the estimation of ethanol content in fermented broth, without injectingthe aqueous solution inthe injection port. In thismethod, headspace autosampler vaporizes the fermentation supernatant and the vapor of analytes is injected in the injection port ofGC. The effect of aqueousmatrix,which influences the vapour pressure in the headspace, is alsominimized byaddition of inorganic salt. The concentration of salt has beenoptimizedtomaximize the alcohol content in the headspace. The quantitation has been performed against isopropanol internal standard using FIDdetector. The same method has been applied for the estimation of butanol concentration and separation of ethanol andbutanolhas also beenoptimizedon amidpolar PEG based stationary phase. The developed methodwill be used for simultaneous estimation of ethanol and butanol concentration in fermented sugarswithout anymatrix interferences. The detection limitof boththe alcohols has beenfoundtobe10ppm. Thismethod has been found to be an excellent substitute of theNRELmethod,whichcan estimate ethanol in the range 0.1%to 5%.