ARSENIC IN NATURAL-GAS - ANALYSIS AND CHARACTERIZATION OF PIPELINE SOLIDS BY H-1-NMR AND OTHER METHODS

Natural gas from the Abo gas field in New Mexico is known to contain a rsenic in the form of tertiary alkylarsines. Deposition of alkylarsine sulfides near the pressure regulation equipment in the transmission l ines may cause serious operational problems. H-1 NMR spectra of CDCl3 solutions of the pure compounds, trimethylarsine sulfide (TMAS), dimet hylethylarsine sulfide (DMEAS) and methyldiethylarsine sulfide (MDEAS) were measured. The signlet resonance of the CH3-group bonded to As is well separated in the three compounds: TMAS (1.83 ppm), DMEAS (1.74 p pm) and MDEAS (1.66 ppm). Based on this, a method for the analysis of the pipeline solids has been developed. Analysis of two samples indica te that the pipeline solids have the following composition, DMEAS (42. 8-46.0%), TMAS (35.4-36.3%), MDEAS (4.7-10.9%). The identification of the arsenic compounds obtained by the H-1 NMR method has been confirme d by GC-MS analysis of the pipeline solids. A study of the reaction, i n the gas phase, between TMA and sulfur-containing compounds (H2S or C H3SH) in the presence of potentially catalytic materials indicates tha t the presence of H2O and a metal (Fe or Cr) is necessary for the form ation of TMAS by the reaction of TMA with H2S.