Synthesis Of Propylene Glycol Ether By Propylene Oxide On Solid Bases

Be called as the "universal solvent", propylene glycol ether which has two groups-alcohol ether and hydroxyl, owns very strong ability to dissolve. It is widely used in coating, inks, paints, printing, electronic chemicals, dyes, washing, and textile industry. Meanwhile, it is applied in chemical productions, such as the intermediates, raw materials and so on. Therefore, it's very vital for us to have the study on the synthesis of propylene glycol ether.Generally, propylene glycol ether (PM) was synthesized by the addition reaction of propylene and methanol. Traditionally, sodium alcohol, liquid acid, such as BF3, were used as homogeneous catalysts for the synthesis of PM. However, these catalysts suffered from limitations such as the requirement for a large excess of the strong base or acid, the disposal of the catalysts and much waste produced in the process. The solid base catalysts were efficient for the reactions with high selectivity and reactivity, done well for the catalyst and so on. Hence, in this paper, different types of solid base catalysts were prepared, and applied in the synthesis of PM.The main contents are as follows:1. The optimal reaction conditions for synthesis of PM is n(method):n(propylene oxide)= 5:1; the dose of the catalyst, 1-2%(wt); reaction temperature,120℃; reaction time,5h. Under the optimal reaction conditions, using ZnO (nano) catalyst, potassium salts were supported on metal oxide and metalloid oxide catalyst, respectively, the yield of PM was above 97%.2. Nano-ZnO catalyst was prepared by using zinc carbonate hydroxide as the precursor, under air, calcined for 5h, naon-zinc oxide was got. Due to the great disperse, small size, high surface area, OH- and Od- were dispersed extensively on the surface of catalyst and the basicity is improved. So, the catalyst was efficient for the reactions. Meanwhile, it was great for the reuse of catalyst that the conversion of PO and the selectivity of PPM didn't change when the catalyst was cycled many times. After the catalysts being reused 7 times, the yield of PM was above 99% and the selectivity for PPM was still about 97.1%. The reused catalyst had the same activity as the fresh catalyst. Perhaps the nano-znic oxide with high surface area and being well dispersed couldn't be poisoned by the product during the reaction process. On the other sides, Znic oxide was just a simple oxide, which the activity site wasn't lost during the whole process.3. Supported solid base catalysts using alkaline metal oxide as carriers. By rubbed and calcined under high temperature, KF, K2CO3 and KOAc were supported on CaO and MgO (pretreatment) respectively. For example,30% KF/CaO-500 was very efficient for the reaction, with the conversion of PO,99.7%, PPM:SPM=93.6:6.4, and the selectivity of PPM,97.4%. As the catalyst KF/MgO-400, the best selectivity of PPM was 97.8%. During Mg(OH)2 was emerged in the preparation of the catalyst,MgOH and OH- on the surface had great interaction with the great activity site, [Mg-OH…F-]. Meanwhile, a new compound salt, KMgF3 was emerged when the catalyst was calcined under the high temperature. Due to the new salt, the activity for catalyst was improved.4. Supported solid base catalysts using metalloid oxide as carriers. Al2O3, ZrO2, CeO2 were carried for preparation of the catalysts. Though the pretreatment temperature for catalysts were low, it's very efficient for the conversion of PO,99%. For example,30% K2CO3/ZrO2-300 done well in the reaction, because being burned under high temperature, K2CO3 was dispersed well on the carrier and the basic sites were showed enough. Meanwhile, part of K+ was embed the crystal lattice of ZrO2, and replaced the sites of Zr4+. Due to the electricity of Zr4+ stronger than K+, the density of electron cloud was improved and the basictity of catalyst became stronger. The catalyst KF/CeO2 showed good activity for the reaction. Maybe some new salt was produced when the catalysts were preparation.5. The reuse of supported solid base catalysts was done. Through the experiments, the results showed that the active sites of catalysts were covered by organic compound in the solution. Being reused 4 times, the catalyst was good for the reaction with the yield of PM about 97%. But the yield was just 31.9% when the catalyst was reused on the 5th times. When the catalysts were calcined under high temperature, the active sites showed again and had good activity with the yield of PM about 60.9% for the reaction. After being reused 3 times, the activity of reused catalyst, with the selectivity of PPM about 95%, was not changed in the reaction. In a word, the supported solid base for the synthesis of PM showed good recycling.