Analyzing the quality of crude oil with an elementary instrument
Crude oil is a term that has been given to the raw, unprocessed oil obtained from the earth. It is a fossil fuel that is formed due to compression of a wide range of organic matter under heated conditions. They vary in colour from clear to dark black and in viscosity from water to hard solids. The most important points that make crude oil one of the most valuable assets is that it contains a lot of energy in them. The fractions that are obtained from crude oil like gasoline, diesel fuel, naphtha, petrol and so on are used as fuel for utilizing this stored energy. The second most interesting characteristic of crude oil is that it can take up many different forms, from gases that are lighter than air to liquids to solids like tar or wax.While crude oil contains high amounts of hydrocarbons, it also contains water, chloride salts and other impurities.
A desalting process can remove many of the impurities. This process involves the addition of water to dissolve the salts and other impurities from the crude oil feedstock. The mixture is then separated; the water goes to an industrial wastewater treatment facility and the refined petroleum is developed into different petroleum products. The desalting process removes the majority of chloride salts, which if present in the oil at high temperatures can form hydrochloric acid. The hydrochloric acid formed can readily corrode equipment throughout the refining process. As a result, the desalting process is crucial to crude oil refining. Organic chlorides are also present in crude oil as chloroform and chlorobenzene. While these compounds are generally not present naturally, the oil can be adulterated when additives, cleaning solutions or chemicals for oil recovery are used. As a result, refineries typically do not accept crude oil that contains more than 5 parts per million (?g/g) of organic chloride.
Naphtha is a derivative of crude oil which is collectively described as a family of volatile liquid hydrocarbon mixtures. Naphtha is a major component of gasoline and other fuel types Chlorides are frequently occurring contaminants in naphtha and crude oil, often exceeding concentrations of 3 ppm (mg/L). To minimize corrosion and scaling, chloride levels should be kept below 1 ppm. Chlorides can be detected and monitored in naphtha and crude oil through a reduction with sodium biphenyl and subsequent potentiometric titration. Organic chlorides are determined through potentiometric titration per Standard Method ASTM D4929. This method utilizes a sodium biphenyl reduction of the organic chlorides to yield inorganic chlorides. The chlorides are then extracted from the petroleum sample into an aqueous phase and titrated with silver nitrate.
An oil and natural gas supplier was looking to determine the concentration of chloride in naphtha and crude oil. The supplier wanted to follow the Standard Test Method ASTM D4929-99 for the determination of chloride in crude oil; this method approves the use of a silver-silver chloride billet-type electrode. For this application, Hanna Instruments recommended the HI902C Automatic Titration System with the HI5110 glass body ORP Half-Cell Electrode for Argentometric Titration. The HI5110 has a silver ring as part of the indicating electrode. This silver ring is also known as a “silver-billet”. Since the method uses organic solvents as part of the sample preparation, it is necessary to have chemically compatible materials including glass body electrodes.
For the reference the double junction glass body HI5311 Reference Half-cell is recommended. The titration is then performed with a known volume of a prepared naphtha or crude oil sample that is titrated potentiometrically with a standard solution of silver nitrate. This titration results in a precipitation reaction of silver chloride from the silver nitrate titrant and the chloride present in the sample. The method also requires a blank titration to be performed, which is used to determine the exact volume of titrant that is consumed by the reagents, excepting the naphtha sample. Electrode preparation is a critical step in this method. It is necessary to coat the silver billet before performing both the blank and sample titrations, as it is the sensing element for the reaction. Coating the silver billet prevents any imperfections in the silver-halide coating, which can lead to erratic ORP recommended.
Prior to analysis, the electrode is filled with 3.5M KCl HI7082 Electrolyte Solution. The silver billet electrode is first soaked in sodium hypochlorite, rinsed with deionized water, and polished with fine grit sandpaper. The electrode is then placed in a saturated potassium chloride solution and an alternating voltage is applied for intervals of several seconds. The reference electrode is then emptied of the aqueous KCl electrolyte and filled instead with aqueous 1M KNO? HI7072 Electrolyte Solution. Following this procedure crude oil can be analyzed in a very affordable way and also the titrator produces quick, precise, and consistent results with a very minimal amount of manpower.
Pavithra Manayil
Applications Specialist
Web: www.hannaindia.in
