Preparation Of1-Chloropropane By Chlorination Of N-Propanol Using Ionic Liquids Catalysts

1-chloropropane is an important chemical raw material mainly usedfor the production of medicines, dyes, and other fine chemicals.Traditional production method is through reaction of n-propanol withconcentrated hydrochloric acid catalyzed by zinc chloride. This processhas some disadvantages, for example,(1) the reactant of concentratedhydrochloric acid contains large amounts of water which will adverselyaffect the reaction equilibrium, and decrease the yield of1-chloropropane.(2) Concentrated hydrochloric acid is inconvenient for transport andstorage and needs anti-corrosive equipments. In order to overcome thesedemerits, this article focuses on the exploration of new productionapproaches from the points of view of catalyst, chlorine sources, andreactor forms conducted at gas phase and liquid phases.(1) Ionic liquids are used here as the catalysts for the production of1-chloroprppane, considering their designability in structure and catalyticproperties by tuning the structure of cation or anion or substitute groups.Three different ionic liquids, namely [BMIM]Cl,[HPy]Cl, and[HMIM]Cl, are prepared and their structure and purity are analyzed interms of HNMR. These ionic liquids are of ease preparation, low cost,and thus suitable for industrial application. Besides, they show uniquecatalytic activity for both the hydrolysis of chloromethanes (e.g. carbontetrachloride and chloroform) and the reaction between alcohol andhydrochloride, leading to the production of chloroalkanes in a one pot reactor. Further, they are also good solvents for the absorption ofhydrogen chloride gas.(2)Effect of reactor form on the catalytic reaction betweenhydrochloride acid and1-propanol was studied. First, the reaction iscarried out in a reflux reactor at atmosphere pressure. The results showthat the catalytic performance of ionic liquid [BMIM]Cl is better than theconventional catalyst ZnCl2; higher temperature is helpful for the reactionalthough the temperature raising is limited due to the lower boiling pointof the reacting mixture. Secondly, the reaction is carried in a closedcylinder reactor, where the hydrogen chloride dissolved in ionic liquidreacts with n-propanol at elevated temperature and pressure. This methodcan effectively improve the reaction performance, since the ionic liquidacts as both catalyst and water absorbent to promote the reaction. At80°Cthe n-chloropropane yield is25%, while the yield at reflux reactor underthe same conditions is only16%.(3) With respect to the chlorine source, trichloromethane is used asthe source of hydrochloride for the chlorination of1-propanol, and theresult is compared with the reaction using hydrochloride directly. Using agas phase reaction in a fixed-bed reactor, we studied the synthesis of1-chloropropane and found the optimal conditions. The results show thatthe yield of1-chloropropane of97%and the conversion rate ofn-propanol of99%can be achieved at the following conditions, viz. with10%pyridine hydrochloride loaded on active carbon as catalyst, moleratio of n-propanol to trichloromethane of1:0.43, residence time2.5min,and the reaction temperature of220℃.