Preparation Of Low-toxic Coal Tar Pitch And Study Of Physical And Chemical Properties

Coal tar pitch is a kind of greatly valuable raw material, which was used widely in road construction and building sealant. Coal tar pitch is irreplaceable when applicated as the electrode of the smelting aluminium and the new carbon material.However, the application of coal tar pitch is limited strictly in recent years for the carcinogenic of the polycyclic aromatic hydrocarbons (PAHs) and the harmfulness to the environment. Considering the harmfulness of the coal tar pitch, it's necessary to do some pre-processing work to reduce the carcinogenic of coal tar pitch for the worker's health and environment. This is a very urgent and significant work, especially for China where the product of coal par pitch is growing greatly.The article aims to reduce carcinogenic PAHs of coal tar pitch, principally benzo[a]pyrene (BaP) which is worldwidly considered as a strong carcinogen.Four different modifiers are choosed in the experiment to react with coal tar pitch in different conditions which emphasis on the change of temperature, reaction time and the quantity of cross linking agents. The modifiers include polystyrene (PS), epoxy resin (EP), Paraformaldehyde (PA) and benzaldehyde (BA). The selected modifiers show the tangible result on the BaP decreasing rate.47.41%reduction on BaP in modified coal tar pitch with 30%PS at 300℃for 5h is achieved;53.45%reduction on BaP in modified coal tar pitch with 20%EP at 200℃for 40mins is achieved;75.86%reduction on BaP in modified coal tar pitch with 5%PA at 110℃is achieved; 47.42%reduction on BaP in modified coal tar pitch with 15%BA at 140℃for 3h is achieved; The BaP equivalency content which is representative of the carcinogenic of coal tar pitch is reduced from 2.94%to 1.68%,1.47%,1.42%and 1.75%respectively. The properties of the modified coal tar pitch including soft point (SP) and penetration et al changes more or less. The content ofβresin which represent for the adhesion of the coal tar pitch increases a lot.The modified coal tar pitch by PA, whose BaP decreasing rate is the maximum, is studied by IR spectra and toxicological safety evaluation test. The analysis of IR spectra indicates that the mechanism of the reaction between PA and PAHs in coal tar pitch is positive ion-typed condensation polymerization catalyzed by acid. The result of toxicological safety evaluation test shows that, the crude coal tar pitch possesses, while the modified coal tar pitch doesn't show mutagenicity...