Toxic H2S Gas Research Articles

Deposition of CuInS2 Thin Films Using Copper- and Indium/Sulfide-Containing Precursors through a Two-Stage MOCVD Method

Copper indium disulfide (CuInS2; CIS) films were deposited on various substrates by two-stage metal-organic chemical vapor deposition (MOCVD) at relatively mild conditions, using Cu- and In/S-containing precursors without toxic H2S gas: first, a pure Cu thin film was prepared on glass or indium/tin oxide glass substrates by using a single-source precursor, bis(ethylbutyrylacetato)copper(II) or bis(ethylisobutyrylacetato)copper(II); second, on the resulting Cu film, tris(N,N-ethylbutyldithiocarbamato)indium(III) was treated to produce CIS films by a MOCVD method at 430 degrees C. In this process, their thicknesses and stoichiometries were found to be elaborately controlled on demand by adjusting the process conditions. The optical band gap of the stoichiometric CIS film was about 1.41 eV, which is in the near-optimal range for harvesting solar radiation energy.

Removal of hydrogen sulfide by sulfate-resistant Acidithiobacillus thiooxidans AZ11

Toxic H2S gas is an important industrial pollutant that is applied to biofiltration. Here, we examined the effects of factors such as inlet concentration and space velocity on the removal efficiency of a bacterial strain capable of tolerating high sulfate concentrations and low pH conditions. We examined three strains of Acidithiobacillus thiooxidans known to have sulfur-oxidizing activity, and identified strain AZ11 as having the highest tolerance for sulfate. A. thiooxidans AZ11 could grow at pH 0.2 in the presence of 74 g l(-1) sulfate, the final oxidation product of elemental sulfur, in the culture broth. Under these conditions, the specific sulfur oxidation rate was 2.9 g-S g-DCW (dry cell weight)(-1) d(-1). The maximum specific sulfur oxidation rate of A. thiooxidans AZ11 was 21.2 g-S g-DCW(-1) d(-1), which was observed in the presence of 4.2 g-SO4(2-) l(-1) and pH 1.5, in the culture medium. To test the effects of various factors on biofiltration by this strain, A. thiooxidans AZ11 was inoculated into a porous ceramic biofilter. First, a maximum inlet loading of 670 g-S m(-3) h(-1) was applied with a constant space velocity (SV) of 200 h(-1) (residence time, 18 s) and the inlet concentration of H2S was experimentally increased from 200 ppmv to 2200 ppmv. Under these conditions, less than 0.1 ppmv H2S was detected at the biofilter outlet. When the inlet H2S was maintained at a constant concentration of 200 ppmv and the SV was increased from 200 h(-1) to 400 h(-1) (residence time, 9 s), an H2S removal of 99.9% was obtained. However, H2S removal efficiencies decreased to 98% and 94% when the SV was set to 500 h(-1) (residence time, 7.2 s) and 600 h(-1) (residence time, 6 s), respectively. The critical elimination capacity guaranteeing 96% removal of the inlet H2S was determined to be 160 g-S m(-3) h(-1) at a space velocity of 600 h(-1). Collectively, these findings show for the first time that a sulfur oxidizing bacterium has a high sulfate tolerance and a high sulfur oxidizing activity below pH 1.

Preparation of In2S3Thin Films by MOCVD Using Single Source Precursors: Tris(N,N-ethylbutyldithiocarbamato)indium(III) and Tris(2-ethylpiperidinedithiocarbamato)indium(III)

The ternary chalcopyrite semiconductor CuInSe2 (CIS) or related Cu(In,Ga)Se2 (CIGS) are well known materials for high efficiency thin film solar cells. In case of CIGS absorber film prepared through chemical bath deposition method, photovoltaic conversion efficiency was reported to be higher than 19%. Such high efficiency has been reached with a CdS buffer layer processed in a wet chemical bath and the CdS has been found to be best suited as a buffer layer material. However, cadmium is toxic and has a negative effect on environment. Therefore, there have been many studies to find replacement materials for cadmium sulfide. The possible candidates for the cadmium free solar cells are ZnS, In2S3, ZnSe, InxSey. Among these materials, In2S3 is nontoxic and exhibits optical and electrical properties similar to those of CdS. Also, In2S3 thin film deposited by ALCVD using In(acac)3 and H2S was reported to be an n-type semiconductor and was found to properly function as a buffer layer for the heterojunction solar cells. For the preparation of In2S3 thin films without using toxic H2S gas, various single source precursors suitable to the MOCVD process are possible. Among them, the precursors containing dialkyldithiocarbamate ligands with non-symmetrical structure are interesting since they were found to have better thermal properties compared to symmetrical ones. In this work, two single source precursors, tris(N,Nethylbutyldithiocarbamato)indium(III) and tris(2-ethylpiperidinedithiocarbamato)indium(III) (designated as In(ebdtc)3 and In(epdtc)3, respectively) were synthesized with high purity and yield. Using them, In2S3 thin films were successfully grown on various substrates, such as glass, ITO glass, and CIGS film through MOCVD process. Experimental Details

Sulfur Plant Operations in Jay and Flomaton Fields

Summary Jay field sour-oil and Flomaton field sour-condensate production facilities are owned jointly and operated by Exxon in the northwest-Florida/south-Alabama area. They have provided extensive experience with sulfur plant operations and maintenance. Experience with different sulfur plant designs is discussed along with sulfur catalyst problems such as coking, sulfur condensation, thermal degradation, and sulfaction. Sulfur plant maintenance, surveillance, and safety also are addressed. Introduction The Jay field, discovered in 1970 and unitized in 1974, is in Florida's northwest panhandle.1 This sour-oil field producing from the dolomitized Smackover carbonate is producing 109,500 BOPD (corresponding to the permitted fieldwide SO2 emissions) with associated sweet-gas volumes of 140 MMcf/D. The full wellstream off-gas contains 10% H2S and 3% CO2. Nine separate crude-stabilization, sour-gas-treating, and sulfur-recovery plants have been designed and built to achieve a minimum 96% sulfur recovery as required by the State of Florida. The Flomaton sour-gas condensate field, 10 miles northwest of the Jay field in southern Alabama, produces from the Norphlet sandstone formation. This nonunitized field was discovered in 1968 and produces 2,600 B/D of stabilized condensate and 15 MMcf/D of sweet gas. The full wellstream gas contains 10% H2S and 40% CO2, for which the State of Alabama requires a sulfur recovery of 91%. Operation of the Jay field treating facilities has provided experience in straight-through sulfur plants with various reheat designs such as acid-gas reheat burners, indirect reheat using steam, and hot-gas bypass reheat. The Flomaton sulfur plant uses a split-flow design because of the high CO2 content of its acid gas. This paper reviews these sulfur plant operations including initial operating problems and solutions; sulfur plant maintenance procedures such as the annual plant turnaround activities, refractory repairs, and sulfur-boiler inspections; and daily operational surveillance and sulfur recovery testing for regulatory compliance. Sulfur plant safety procedures, emergency shutdowns, and operator-training programs for processing of toxic H2S gas also are described.