Study On Extraction, Composition And Distribution Of Phenolic Compounds In Low Temperature Coal Tar From Shanbei Region

Shanbei (Northern Shaanxi province) is a major coal-producing region in China. Shanbei coals are mainly non caking coals and weakly caking coals both with high volatile matter. Low temperature carbonization industry (semicoke) was established in local. Low temperature coal tar, as a main by-product of semicoke production, contains abundant normal alkanes, alkenes, alkyl-aromatic hydrocarbon and phenolic compounds, and the content of phenolic compounds can reach up to 20～30%. Low temperature coal tar in Shanbei region has been used for bad fuel oil or been sold directly for a long time. Nowadays, pilot projects such as full fractions hydrogenation and delayed coking-hydrogenation of low temperature coal tar are being established in Shanbei region, but there are problems with mechanism, process et, al. remain to be solved. Phenolic compounds are hazardous substances to hydrogenation oil for they can increase the hydrogen consumption as well as the carbon residual, foul smell, discoloration, corrosion, bad combustion conditions and other negative effects. Meanwhile, phenolic compounds are important chemical raw materials. Therefore, extraction of phenolic compounds from low temperature coal tar is not only conducive to the quality of hydrogenation oil but also can get high value-added chemical materials.L-tar and H-tar of low temperature coal tar from Shanbei region were investigated in this article. Soda wash method and precipitation method were used to extract the phenolic compounds from low temperature coal tar. The composition and distribution of phenolic compounds in crude phenols were investigated and column chromatography was used to separate the crude phenols. Firstly, The basic properties of low temperature coal tar were obtained referring to the analysis methods of petroleum products and coking products.The dehydration method of low temperature coal tar was discussed through toluene azeotropic distillation. Five fractions were gained from low temperature coal tar by atmospheric distillation in<170℃,170-240℃,240～270℃,270～300℃,>300℃respectively. Soda wash method and precipitation method were used to extract the phenolic compounds from the middle three fractions. The process condition of soda wash method was optimized by orthogonal experiment considering three factors and four levels. The results showed that soda wash method was better than precipitation method. The composition and distribution of phenolic compounds in crude phenols, soda washed oil(middle three fractions)and<170℃,>300℃fractions were analyzed by gas chromatography/mass spectrometry (GC/MS), fourier transform infrared spectrometer (FTIR) and thermogravimetric analyzer coupled with fourier transform infrared spectrometer(TG-FTIR). The separation of 170～240℃crude phenols by silica gel column chromatography and alumina column chromatography was studied. Low-rank phenols and high-rank phenols were received respectively.In silica gel column chromatography, there was phenol single compound in the elution fraction under the heptane:ethyl acetate 1:10 eluent.