- 期刊
自臺產二甲苯中對二甲苯之分離
Separation of p-XyLene from Xylene Fraction of Taiwan Petroleum
摘要
中國石油公司臺灣油礦探勘處苗栗煉油廠所產粗二甲苯，經用Udex法萃取，萃出物中含二甲苯90-95%，其中11.5%為對二甲苯。分餾得135-140℃餾分53%，內含對二甲苯16.6%，間二甲苯55%。為有效提取對二甲苯，於二甲苯原料中摻加四氯化碳(CCI_4)，使與對二甲苯生成共結晶物，分離析出，然後熔化，蒸去四氯化碳，便得濃縮之對二甲苯，方法簡單，收率亦高。共結晶分離對二甲苯之收率與四氯化碳用量、結晶冷卻溫度、二甲苯中對二甲苯之含量均有關。於-75°C溫度，以四氯化碳摻入二甲苯中共結晶，當用量在80%以上時，對二甲苯之收率達98%以上，濃度為40-50%；如不用四氯化碳時，其收率為86.2%。將溫度增高至-65°, -55°, -46°C，對二甲苯之收率減低，其濃度則隨結晶溫度之增高而增加，約45-58%。在-75°C析出之對二甲苯結晶中(已除去四氯化碳)，間二甲苯之含率不受四氯化碳摻入量之影響，均在35%左右。其濾液除去四氯化碳後，冷卻至-75°C再結晶，晶體中含間二甲苯69%，而含對二甲苯甚少。如用較高濃度，含40.2%對二甲苯之二甲苯為原料時，所得對二甲苯之結晶產率與用低濃度者相似，惟濃度則稍高。共結晶析出之對二甲苯，於-50°, -30°, -20°, -10°, 0°, 5°, 10°C浴中，按次反復再結晶，約90%對二甲苯可萃出成高濃度產品。如68%對二甲苯798gm.，反復再結晶後，380.5gm. (68.7%)均變成98%，存於10°C結晶體中。加用四氯化碳與否，對此項再結晶並無影響。將46.8%對二甲苯，冷卻至-50°C，生成之結晶用部分熔化法濃縮提純，所得7°C結晶體中，含對二甲苯92.4%，收率49.0%。又曾試用一次再結晶法濃縮對二甲苯，所得產品濃度與用部分熔化法者相若，惟收率則降低甚多。含對二甲苯11.5%之原料二甲苯中，直接投入乾氷冷卻，可得濃度46%之對二甲苯18.6%。
關鍵字
無資料並列摘要
The crude oil produced in Taiwan contains considerable amount of xylenes. They are important raw materials for synthesizing organic chemicals. In order to make them available, the xylene fraction was first concentrated to 90-95 % purity by Udex process using diethylene glycol as solvent. Of which about 11.5% was p-xylene. Attempts were made to separate p-xylene from the isomeric mixture by co-crystallizing with carbon tetrachloride. The effects of operating conditions on the yield and concentration of p-xylene were studied. For co-crystallization, carbon tetrachloride was added into crude xylenes. The mixture was then cooled until co-crystals of p-xylene and carbon tetrachloride formed. After filtration, the crystals were melted and distilled off the carbon tetrachloride. p-Xylene of higher concentration was obtained. The yield of crystals was increased with the amount of carbon tetrachloride used and decreased at higher temperature, Cooling to -75°C, using 0.8 times of carbon tetrachloride, the concentration of resulted p-xylene was 40-50% and rate of recovery was over 98%. However, refining by crystallization without adding carbon tetrachloride at the same temperature, the rate of recovery of p-xylene was only 86.2%. The concentration of xylene in the crystals was increasee to 45-58% at -65° to -46°C. The amount of m-xylene in the concentrated p-xylene separated at 75°C was about 35% which was not affected by the addition of carbon tetrachloride. The filtrate was distilled to drive off carbon tetrachloride and then recrystallized at -75°C. The crystal thus obtained contained 69% of m-xyiene with only small amount of p-xylene. Under the same operating conditions, if the concentration of p-xylene in the crude xylene was increased to 40.2%, the rate of recovery of p-xylene was almost same as that of using lower concentrations. But the concentration of p-xylene obtained was slightly increased. In order to concentrate the p-xylene thus produced to higher concentration, it was recrystallized by partial melting and direct cooling respectively. Among which the partial melting method offered the most satisfactory results. p-Xylene of 46.8% purity was cooled to -50°C and refined by partial melting. The concentration of p-xylene in the crystaIs obtained at 7°C was 92.4%. Yield was 49.0%. Recrystallizing 798gm. of p-xylene of 68.8% purity succesively at different temperatures, 380.5gm. of p-xylene of 98% purity was recovered from the crystals of 10°C fraction. In this process, it was not advantageous to adopt carbon tetrachloride co-crystallization. The concentration of p-xylene produced by recrystallizing once was similar to that of using partial melting method. However, the yield was only half of the latter. On direct cooling the crude xylene containing 11.5% p-xylene by adding solid carbon dioxide, only 18.6 percent of 46% p-xylene was obtained.