No-Solvent Oil-in-Water Analysis – A Robust Alternative to Conventional Solvent Extraction Methods

摘要

Most oil-in-water analysis methods for produced water require the oil to be extracted into an organic solvent priorrnto measurement. Many of the organic solvents used for extraction are either extremely flammable, hazardous tornhuman health or both. The chlorinated hydrocarbons are very expensive and must be either recycled or disposedrnof as hazardous waste. Volatile hydrocarbon solvents such as pentane and hexane are extremely flammable andrnpresent a serious fire and explosion risk. All major airlines and many helicopter services consider the risk sornserious that they will not transport flammable solvents.rnThe methodology presented here makes it possible to perform oil-in-water analyses by making measurementsrndirectly on the produced water sample. No organic solvents are required. The method is based upon the additionrnof a detergent surfactant to a produced water sample. The surfactant converts the dispersed oil in the samplerninto an optically clear microemulsion that is ideal for direct fluorescence measurements using the TD-500D Oil-in-rnWater Analyzer. The surfactant is safe to handle with a minimum of personal protective equipment and is onlyrnslightly flammable even under a direct flame. The US Department of Transportation does not consider it to be arnhazardous material. It can be shipped without hazardous identification labels and can be carried on commercialrnairlines and helicopters without declaration.rnTwo samples (“Background” and “OIW”) are collected to perform an analysis. The Background sample isrnuntreated produced water. It is filtered into a measurement cuvette through an ultra-filter to remove suspendedrnsolids and dispersed oil. Only water-soluble substances pass through the filter into the cuvette. The OIW samplernis collected into a bottle containing surfactant. The sample is then heated to the cloud point of the surfactant andrnallowed to cool until the cloudiness disappears. This converts the dispersed oil into a stable microemulsion. Therndispersed oil is located inside micelles that are small enough to pass through an ultra-filter. The converted OIWrnsample is then filtered into a cuvette. The TD-500D readings for the Background and OIW cuvettes are thenrnrecorded. The dispersed oil concentration is the calculated difference between the OIW and Backgroundrnreadings. The Background reading itself provides additional information. Since it is proportional to thernconcentration of fluorescent water-soluble organics in the produced water sample, the Background reading canrnbe used to track changes in the concentrations of these substances.rnThe TD-500D has two measurement channels, A and B. Channel A makes fluorescence measurements usingrnultraviolet light and is used when the highest sensitivity is required. Channel B uses visible light for reducedrnsensitivity and extended dynamic range. With the “No-Solvent” method, channel A detects most crude oils atrndispersed oil concentrations less than 1 ppm. The linear range is from 0 to at least 100 ppm. The dynamic rangerncan typically be extended to 750 ppm or greater with a non-linear calibration function. When the instrument is setrnto channel B, the “No-Solvent” method can measure dispersed oil concentrations up to 10,000 ppm, eliminatingrnthe need to dilute highly concentrated oil-in-water samples.