高酸原油热处理脱酸研究
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2o04 Petroleum Science V_01.1 NO.3 Thermal Treatment for Decreasing the Acidity of Crude Oil Shen Haiping,Wang Yuzhang and Li Rui (Research Institute ofPetroleum Processing,Beijing 100083,ChinaJ Received November l 5.2oo3 Abstract:Highly acidic crude oil is thermally soaked to investigate how the temperature and time involved affect the removal of organic acid in feedstock.Experimental results indicate that thernlal treatment is an effective approach to decreasing acidity and the acid removal rate reaches 80%.Temperature is one of the main factors that determine the acid removal reaction.When the temperature ranges from 420。C to 440。C.the acid removal rate increases with the rise of the reaction temperature,but the increase slows down gradually.At the reaction temperature below 440。C.山e long reaction time favors the acid remova1.The cracking and polymerization of hydrocarbon molecules take place so that the properties of the crude oil change at the same time when the highly acidic crude is thermally treated.
Key words:Highly acidic crude,naphthenic acid,acid removal,thermal treatment,visbreaking
1.Introduction Acidic components in crude oil typically include naphthenic acids,other carboxylic acids,inorganic acids,phenols,mercaptans,and so on.Naphthenic acids and other organic acids generally refer to petroleum acids。over 90%of which is naphthenic acid. so naphthenic acid is a generic term used to identifv a mixture of organic acids present in petroleum feedstocks.Research on the structure of petroleum acids shows that most of these acids in crude oil are calboxylic acids that include various naphthenic acids, a small part of aliphatic carboxylic acids and basic calboxylic acids. Petroleum carboxylic acid,similar to the organic calboxylic acid,possesses a strong acidity,which can react with amine.alcohol and base.and is severely corrosive to meta1.Phenol and mercaptan are weak in acidity and their corrosivity is relatively weak. Since the acidic crude oilis corrosive to the refinery equipment,it is hard for refineries to process it with toml acid number(TAN1 over 1 mgKOH/g.In order to reduce the corrosivity of the acidic crude oil,some caustic bases are added to neutralize the acidic components.The naphthenic acid will react with the caustic base to produce soap,which results in the emulsion of the crude and causes difficulties in desalting and dewatering.The salt content in the crude oil willinfluence,and bring about difficulties to.the downstream processing.Another approach is to use the anticorrosive alloy metal,which is expensive and will increase the refining cost.It is currently impractica1. especially in the near future,for new anticorrosive
materials to be used in the existing refinery equipment. The third is to add a corrosion inhibitor to the crude oil. which will influence the downstream processing and decrease山e activity and life of the catalyst.The fourth. which is the most widely used way,is to blend the highly acidic crude oil with the low acidic crude oi1 tO ease the corrosivity.T|lis is limited by the crude supply and crude storage tanks. The removal of acid in crude oil can be accomplished by several methods involving physical adsorption, solvent extraction and chemical conversion,etc.(Saul and Willarn、1 999;Guido and David,2000;Ramesh and Thomas,2000).In the Research Institute of Petroleum Processing r PP). simple thermal treatment was adopted to remove acid in crude oil.In this paper,it is investigated how acid removal of acidic crude is influenced by thermal treatment conditions.
2.1 Apparatus The experiments ale carried out in a continuous visbreaking pilot plant.Visbreaking is mild thermal cracking normally used to reduce viscosities and pour—points of oil.The pilot plant process is shown in Fig.1.The feedstock is pumped into the preheater and heated to the reaction temperature,and then thermally treated in the soaker under the operating conditions.
2.2 Feedstocks The feedstocks for the experiments ale two types of highly acidic heavy oils whose properties ale shown in1'ab1e 1.
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