Hydrogen sulfide is problematic in many types of systems including sewer water, produced water, and petroleum refineries. Natural gas plants can contain dangerous concentrations of hydrogen sulfide. A number of different chemicals can be used to either complex or oxidize hydrogen sulfide, with almost all of these reactions being pH dependent.
PureLine’s Greg Simpson, PhD., continues his evaluation of different chemicals and their reactivity with sulfide. In his most recent experiment, Dr. Simpson evaluates the reaction of THPS (Tetrakis hydroxymethyl phosphonium sulfate) to hydrogen sulfide along with chlorine dioxide compared to hydrogen sulfide.
THPS is a biocide that oxides rapidly to THPO (trishydroxymethylphosphine oxide), both effective biocides with low aquatic toxicity. Two experiments were conducted to evaluate THPS.
THPS Experiment 1
About 0.5 grams of sodium sulfide was dissolved in 4-L of DI water. Duplicate sulfide tests showed a sulfide concentration of 21 ppm. Small aliquots of 75% THPS were added, with the pH and the ORP being measured electronically every 30 seconds. Sulfide was measured several minutes after each addition of THPS. The plot of THPS added vs sulfide is shown in Figure 3. Although there was some reduction in sulfide, not all of the sulfide appeared to be complexed, or removed from solution.
THPS Experiment 2
THPS (1 mL) was dosed into 4-L of water. This equals 188 ppm. Then, aliquots of 0.5 g sodium sulfide in 100 mL DI water (850 ppm) were added. The response after the first addition of sulfide was rather unexpected, and so no further sulfide was added. The amount of sulfide added was well below the amount of THPS required to complex the sulfide. Therefore, a reading of zero sulfide was expected. Instead, the measurement was well above the upper limit of the test. This raises questions about claims that THPS acts as a sulfide scavenger. Instead, it may be that the reduction in sulfide observed in downhole applications occurs as a result of suppression of sulfate reducing bacteria.
While THPS does not appear to scavenge sulfide, there is evidence there is effectiveness on some form of iron sulfides. As Dr. Simpson further explains in his paper below, the combination of THPS with chlorine dioxide during hydraulic fracturing applications is promising.