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Influence Of Near-critical Water On Organic Chemical Reactions

Posted on:2008-08-31Degree:MasterType:Thesis
Country:ChinaCandidate:H SunFull Text:PDF
GTID:2121360212489138Subject:Chemical processes
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Near-critical water (NCW), which stands for the pressurized liquid water under the condition of 180-350℃. As temperature and pressure goes to critical point, there is a dramatic increase in ionization constant. It is about three orders magnitude higher than that at ambient temperature and pressure, so NCW has a strong tendency to ionize and can act as an acid and/or base catalyst. Besides, it has excellent dissolve ability because of lower dielectric constant and appropriate density, which can dissolve organic substance to some extent to allow homogeneous reaction. As an environmentally benign medium, NCW can discard the use of large tons of catalysts and poisonous solvent. Meanwhile, it has good turnability, namely we can design the reaction medium according to different reaction system by turning temperature and pressure.As a reaction media, near-critical water has drawn increasing attention for acid or base catalyzed organic chemical reactions without any added acid or base and extensive research has been pursued on organic chemical reactions in NCW. However, little attention had been paid on the influence of NCW on organic reactions, which is important for studying the relationship between the reaction mechanism and the physical character of NCW.This work comprised:(a) The determination of the influence of NCW, as the reaction medium, on organic reaction;(b) The determination of the influence of NCW, as the reactant, on organic reaction;The task of this work was to study the influence of NCW on organic reactions. Our studies focus on two aspects: near-critical water as the reaction medium, and a small amount of NCW as the reactant.So we studied the hydrolysis of different vegetable oils in NCW, the influence of a small amount of NCW on the ester exchange reaction of butyl acetate with super critical methanol, and the influence of a small amount of NCW on thethermopolymerization reaction of linoleic acid.Non-catalyzed hydrolysis of olive oil, peanut oil, soybean oil, safflower oil in near-critical water was systematically determined in the temperature range from 170 ℃ to 240℃ and at pressure of 10 MPa. From the results, we can see that the vegetable oil hydrolysis in near-critical water is a typical self-catalyzed reaction. With a second-order kinetics equation, the activation energies evaluated were 41.8 kJ/mol for olive oil, 37.3 kJ/mol for peanut oil, 37.7 kJ/mol for soybean oil, and 31.2 kJ/mol for safflower oil. The activation energies of different vegetable oils have a close relationship with their iodine values. With the increase of iodine value, the activation energy of vegetable oil hydrolysis in near-critical water decreases.The influence of a small amount of NCW on the ester exchange reaction of butyl acetate with super critical methanol was investigated from 240℃ to 320℃. The results suggest that the rate decreases slowly with the additon of a small amount of water at 240℃, and decreases quickly with the additon of a small amount of water at 260℃-320℃. But, when the amount of NCW is larger, the rate of butyl acetate will increase with the increasing of water.The influence of a littlt NCW on the thermopolymerization reaction of linoleic acid was investigated in the temperature range from 280℃ to 320℃. And the results suggest that the addition of a small amount of water can slow down the reaction rate of linoleic acid, and has no obvious effect on the selectivity of dimer fatty acid. But a small amount of water can inhibit the decarboxylation of linoleic acid obviously.
Keywords/Search Tags:near-critical water, olive oil, peanut oil, soybean oil, safflower oil, non-catalyzed hydrolysis, kinetics, butyl acetate, super critical methanol, ester exchange reaction, linoleic acid, dimer fatty acid, thermopolymerization, decarboxylation
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