https://doi.org/10.15255/KUI.2007.002
Published: Kem. Ind. 57 (3) (2008) 101–108
Paper reference number: KUI-02/2007
Paper type: Professional paper
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The Use of Demulsifiers for Separating Water from Anthracene Oil

N. Zečević

Abstract

The main feedstocks for the production of oil-furnace carbon black are different kinds of liquid hydrocarbons. The quality and utilization of oil-furnace carbon black mainly depends on the type of liquid hydrocarbons contained in the oil feedstocks. In practice, both carbochemical and petrochemical oils are used as feedstock sources. Carbochemical oils are fractions obtained during coal tar distillation. Anthracene oil is one of these oils. Depending on the conditions of distillation, coal tars contain up to w = 18 ∙ 10–2 highly aromatic fractions, which can be used as carbon black feedstock. The sulphur fraction of these oils can vary between w = 0.5 and 0.7 ∙ 10–2, depending on the origin of the coal. The availability of carbochemical oils obtained from coal tar is largely dependent on the production of coke used in the manufacture of steel. The quantities available today are insufficient to satisfy the demand for carbon black feedstock. In addition, in highly industrialized countries, production of carbochemical oils is declining. Although, carbochemical oils are preferred in terms of efficiency, petrochemical oils are more important in terms of quantities available, particularly in the production of furnace blacks. These are residual oils resulting either from catalytic cracking processes or from the production of olefins in steam crackers using naphtha or gas oil as raw material. Nevertheless, the choice of carbon black feedstock is not determined merely by price and efficiency, but also by specific quality criteria. However, due to their origin, the feedstocks are mixtures of a large number of individual substances and are, therefore, not easy to characterize. More than 200 different components have been recorded in the range detectable by gas chromatography. Some important components of carbon black feedstock are listed in table 1.1 An important parameter for the evaluation of carbon black feedstock is density, since it increases with increasing aromaticity. It is also used for determination of the Bureau of Mines Correlation Index (BMCI),2 which is obtained either from density and midboiling point, or from density and viscosity for those feedstocks which cannot be distilled completely. This index is used by the carbon black industry as an important criteria for feedstock evaluation. The sulphur fraction in feedstocks should not exceed w = 2.5 ∙ 10–2, because a higher content greatly affects the quality of carbon black, pollutes the atmosphere, and accelerates corrosion of the facility. The maximum sulphur content in the typical hydrocarbon feedstock is w = 1.2 ∙ 10–2.3 A very important factor of hydrocarbon feedstock is the fraction of alkaline earth metals, especially sodium and potassium. The maximum sodium fraction may be w = 20 ∙ 10–6, while the maximum potassium fraction is w = 2 ∙ 10–6. The maximum fraction of asphalthenes is w = 15 ∙ 10–2. Asphalthenes, determined as pentane- insoluble matter, provide indications concerning the possibility of grit formation. Another very important factor is the temperature range of distillation, which should be low enough, because the hydrocarbon feedstock must evaporize before entering the hot region of the reactor. The viscosity, the pour point, and for safety reasons, the flash point determines the handling properties and storage conditions of the feedstock. In addition, the water fraction in the hydrocarbon feedstock is one of the most important factors. The water fraction in hydrocarbon feedstock influences the handling properties of the same. The maximum water fraction in hydrocarbon feedstock may be w = 2.0 ∙ 10–2, and desirably below w = 1.0 ∙ 10–2. A higher water fraction represent a considerable impact on the financial construction. Also, it is very difficult to manipulate such feedstock, especially unloading, and in the production of oil-furnace carbon black. Namely, every water fraction higher than w = 2.0 ∙ 10–2 in the hydrocarbon feedstock, causes the phenomenon of cavitations. In the oil-furnace carbon black plant of Petrokemija d. d. Kutina, the storage tank TK48003, was filled with 800 tons of anthracene oil. The average water fraction in the tank was w = 1010–2. It was impossible to manipulate in the process of production, because the mentioned water fraction caused the cavitations effect. Therefore, it was necessary to decrease the water fraction to below w = 2.0 ∙ 10–2, which will be satisfactory for production. As the water and anthracene oil formed a homogeneous emulsion (similar density at all temperatures), it was impossible to manage decanting the water from the anthracene oil. Additionally, it was impossible to manage evaporation of the water from the oil by heating the whole emulsion, because the flash point of anthracene oil is in the temperature range of T = 100 to 105 °C. Distillation of the whole emulsion of 800 tons was also impossible, because there was no distillation column adequate for separating the water from the anthracene oil. Thus, the use of different demulsifiers proved as a potential solution for separating the homogeneous mixture of anthracene oil and water. Namely, demulsifiers are a special type of high molecular tensides and organic solvents, which serve for separation the water from different hydrocarbons. The most common use is in emulsions with “lighter” hydrocarbons, especially when the density is not above ρ = 0.850 g cm–3. Since the density of anthracene oil ranges from ρ = 1.05 to 1.09 g cm–3, it was necessary to customise the conditions of application, and to choose the most adequate demulsifier for the separation of water from anthracene oil. Therefore, we experimented with different kinds of demulsifiers in cooperation with the companies TEH PROJEKT KEMO d. o. o. and KEM PROJEKT d. o. o. In laboratory conditions, we tested five different demulsifiers with different concentrations, and their efficiency in separating the water from anthracene oil. We then chose the most adequate demulsifier, which was applied on an industrial level.

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Keywords

anthracene oil, demulsifier, emulsion, separation, water