Sulfur dioxide interface reaction

Because at 80°C, S — 0.5, and at 100°C no sulfochlorination at all takes place, the process is run between 35 °C and 40°C. The selectivity also depends on the molar ratio of sulfur dioxide to chlorine. Provided that there is a fine dispersion of the reacting gases in the alkane for a molar ratio of 3, the selectivity approaches 0.98 (Fig. 5). Sufficient turbulence in the reaction medium (supported by additional mechanical energy) means that the sulfochlorination itself proceeds at the gas-liquid interface. 

Two disparate translation methods are investigated for the measurement of sulfur dioxide. Both involve interaction with an aqueous solution. In the first, collected S(IV) is translated by the enzyme sulfite oxidase to which is then measured by an enzymatic fluorometric method. The method is susceptible to interference from i CWg) efforts to minimize this interference is discussed. The second method involves the translation of SO2 into elemental Hg by reaction with aqueous mercurous nitrate at an air/liquid interface held in the pores of hydrophobic membrane tubes. The liberated mercury is measured by a conductometric gold film sensor. Both methods exhibit detection limits of 100 pptv with response times under two minutes. Ambient air measurements for air parcels containing sub-ppbv levels of SO2 show good correlation between the two methods. 

S. M. Ramasamy and H. A. Mottola, Repetitive Determination of Sulfur Dioxide Gas in Air Samples by Flow Injection and Chemical Reaction at a Gas-Liquid Interface. Anal. Chem., 54 (1982) 283. 

The XPS results indicated that there were about 3-5 at. % sulfur and 27-47 at. % oxygen incorporated onto the sulfur dioxide plasma treated LDPE substrate surfaces (Table 1). The sulfur atomic concentration reached a maximum at about 50 A from the sample surface (0 = 30°) right after the plasma treatment (Figure 3). (The uncertainty of the XPS multiplex scan for atomic concentration analysis is believed to be 0.5-1.0 at. %.) The sulfur-containing species diffused into the bulk of the polymer (> 100 A) as shown from the XPS data collected eleven days after the plasma reaction. This phenomenon is due to the mobility of the polymer surface. s After the sulfur dioxide plasma modification, the hydrophilic sulfonyl groups on the LDPE backbone diffuse away from the polymer surface toward the bulk of the material so that a lower surface energy can be attained. Because the air/LDPE interface has a low surface tension, thermodynamic equilibrium favors a hydrophobic surface. As a result, the sulfur atomic concentrations in the top 100 A of the substrates decreased with time as the sulfonyl groups diffused away from this surface layer. 

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