W. Delgadomorales et al., ANALYSIS AND REMOVAL OF ARSENIC FROM NATURAL-GAS USING POTASSIUM PEROXYDISULFATE AND POLYSULFIDE ABSORBENTS, International journal of environmental analytical chemistry, 54(3), 1994, pp. 203-220
Natural gas from the large Abo gas field in southeastern New Mexico co
ntains arsenic (0.2 to 2.5 mug/L) in the form of trialkylarsines. A me
thod of analysis for arsenic which is based on the extraction of the a
lkylarsines into a saturated solution of potassium peroxydisulfate (PP
DS) followed by determination of total arsenic, as AsO4(3-), by hydrid
e generation-d.c. helium plasma emission spectrometry (HG-DCHPES) is d
escribed. The extraction of the alkylarsines was carried out by either
shaking IL gas samples with PPDS or sparging the gas in PPDS solution
s. Analytical results of acceptable precision can be obtained using ei
ther procedure. Temperature (24-45-degrees-C) or pH (1.10-4.10) had li
ttle effect on the As concentrations obtained by the sparging method.
The measured arsenic concentrations of natural gas samples stored in C
r-Mo steel cylinders decrease with time of storage (approximately 30%
in the first 4 weeks). A standard blend of trimethylarsine in CH4 (1 m
ole TMA in 10(6) moles of CH4), stored in nickel-containing steel cyli
nder, showed a similar decrease in As concentration with times. The me
asured arsenic concentrations increase when the temperature of a cylin
der of natural gas is heated indicating that part of the alkylarsines
may be present in a condensed or physically adsorbed form on the inner
walls of the cylinder. Scanning electron microscopy with X-ray microa
nalysis of the metal powders (Ni, Cr, Mo, Fe) contacted with TMA indic
ate that arsenic-rich solids also containing C and O are formed in the
case of Ni and Cr. This phenomenon may represent an additional factor
in the observed decrease in As concentration with time of storage. Po
lysulfides in solution form (Na2Sx) or solid (Na2S4) can quantitativel
y remove the trialkylarsines from natural gas.