Anaerobic degradation of methanethiol in a process for Liquefied Petroleum Gas (LPG) biodesulfurization

摘要: Due to increasingly stringent environmental legislation car fuels have be desulfurized levels below 10 ppm in order minimize negative effects on the environment as sulfur-containing emissions contribute acid deposition (‘acid rain’) and reduce amount of particulates formed during burning fuel. Moreover, low sulfur specifications are also needed lengthen lifetime exhaust catalysts. The research presented this thesis focuses biological desulfurization Liquefied Petrol Gas (LPG). Currently, LPG is mainly by physical-chemical methods that absorb volatile compounds present (mainly hydrogen sulfide thiols) into a strong caustic solution, whereafter thiols partially oxidized disulfides whilst dissolved discharged ‘spent sulfidic caustic’. Disadvantages method relatively high energy consumption production hazardous waste stream. As an alternative, new three-step biotechnological technology has been studied, produces elemental end-product from bio-conversion (H2S) methanethiol (MT). process involves: (i) extraction phase (bi)carbonate-containing solution; (ii) anaerobic degradation MT H2S, CO2 CH4 (iii) partial oxidation H2S sulfur. particles removed system sulfur-free alkaline water re-used process. can used for sulfuric or agricultural applications. In attention paid feasibility second step, i.e. treatment step first third already well described. Anaerobic appeared possible with variety (reactor) sludges sediments, both under methanogenic sulfate-reducing conditions. related dimethyl disulfide were degraded well, contrast ethanethiol propanethiol, which not anaerobically. biodesulfurization higher converted their corresponding oily skimmed off reactor solution sent disposal, e.g. incinerator. fifty percent inhibition concentration MT, propanethiol activity granular sludge methanol acetate was found between 6 mM (pH 7.2, 30°C). Hydrogen inhibited at concentrations mM, depending pH source inoculum. Dimethyl 2 mM. lab-scale upflow blanket (UASB) inoculated originating full-scale treating paper mill wastewater, up volumetric loading rate 17 mmol MT∙L-1∙day-1 7.0-7.5, 30°C, < 0.03 M total salts). inoculum sodium exceeding 0.2 M. Initially, MT-degrading archaea genus Methanolobus enriched reactor. Later, they outcompeted methanogens belonging Methanomethylovorans, small aggregates (10-100 μm) larger particles. Estuarine sediment Wadden Sea inoculate operated Na+ 0.5 maximum achieved amounted 37 8.2-8.4 22 8.9-9.1 (30°C). tests, no observed till 0.8 Na+. Methanosarcina mazei dominant methanogen, but after about 1.5 years continuous operation, taylorii became dominant, probably due shift 9.0 UASB mixture estuarine salt lake sediments Soap Lake (USA) Kalunda Steppe (Russia) it degrade 10, 13 (30°C, Na+) presence co-substrate. responsible oregonensis. Thiols novel directed aerobic bioreactor. Our shows here will react biologically produced (both 1-16 mM; 8.7 10.3; 30-60oC) form poly-sulfur compounds, polysulfide ions polysulfides. reaction S8 ring opening nucleophilic attack CH3S9-. depends bio-sulfur concentrations, temperature. activation determined 70 kJ·mol-1 16 10.3. CH3S9- ion unstable leads shorter-chain compounds. main end-products polysulfides (S32-, S42-, S52-), [(CH3)2S2, (CH3)2S3] H2S. Also long-chain [(CH3)2S4-7] trace amounts (μM level). Excess results complete methylation initially inorganic An increased molar MT/S ratio formation more (CH3)2S2 over (CH3)2S3. Flowsheet simulations reveal acceptable degree (i.e. less than treated product) recycle stream extractor column must 9. This means inocula (estuarine sediments) provide good opportunities applied