Alkylation Of Phenol With Methanol Over Various Catalysts

C-alkylation (mainly Ortho-alkylation) of phenol with methanol has gained considerable attention for many years as the products are widely used in variety of applications. For example, O-cresol and 2,6-xylenol (poducts of C-alkylation), are extensively used as chemical intermediates in the synthesis of pharmaceuticals, agrochemicals(herbicides), resins, antioxidants, special grade paints, polyphenylene oxide (PPO) and various other fine chemicals.Since the first report of alkylation of phenol with methanol in the 1940s, many kinds of materials have been investigated as catalysts for the reaction, including various zeiolites and metal oxides (hydrotalcites, pure and mixed metal oxides, phosphates and spinel oxides so on). Among them, some solid bases, mixed metal oxides and spinel oxides show relatively good catalytic performance. However, the catalytic properties, especially the selectivity and stability, are still unsatisfied for practical applications. Furthermore, some basic problems such as the nature of active center, reaction mechanism are still unclear.In this work, various catalyst systems, including transition metals introduced iron catalysts, prepared by co-precipitation and impregnation methods, and the catalytic performance was investigated for alkylation of phenol with methanol. The catalysts were characterized by means of XRD, BET, TPD and TPR etc. in order to build a relationship between the structure, acid-base properties, redox properties of the catalysts and the catalytic performance. Meanwhile, the nature of active center and the reason for deactivation were also discussed. The main experimental results and conclusions are as follows:1. Vapor phase C-alkylation of phenol with methanol over transition metals introduced iron catalysts catalystsTransition metals introduced iron catalysts were prepared by an co-precipitation procedure and the catalytic performance of vapor phase C-alkylation of phenol with methanol was investigated. The co-precipitation procedure show relatively good catalytic properties , Meanwhile, the reaction conditions have considerable effect on the catalytic performance. Transition metals source has considerable effect on the catalytic performance. When W,Zr is used as the transition source, the catalyst exhibits the best catalytic performance. Additionally, combined with some related references and various characterization results, Additionally, iron can be partly reduced during the reaction, which might be the main reason for the decrease in the catalytic performance. Additionally, combined with some related references, it can be proposed that a synergic interaction between relatively strong Lewis acid sites and adjacent base sites should be responsible for the high ortho-selectivity of the catalyst.2. Vapor phase Ortho-selective alkylation of phenol with methanol over Fe/Zr catalystsThe gas phase ortho-selective alkylation of phenol with methanol was investigated over a series of iron oxide prepared by co-precipitation method. The types of Fe/Zr have considerable effect on the catalytic performance. The whole show relatively good catalytic properties. Among them, the Fe/Zr with a ratio of Fe/Zr =100/ 0.5 exhibits the best catalytic performance. Both the acidic amount and strength of Fe/Zr increase gradually when the ratio of Fe/Zr increases from 100/0.5 to 100/2.0, With further increase the content of Zr, the basicity of Fe/Zr samples increase gradually Therefore, it can be conclude that the change of composition and structure of the catalysts could result in the change of the acidity and basicity , thus considerably affect the catalytic performance of the catalysts.For the Fe/Zr = 100/0.5 sample, the reaction conditions have considerable effect on the catalytic performance. Increasing the reaction temperature and decreasing the weight hourly space velocity could result in an increase in the phenol conversion and the 2,6-xylenol selectivity. Combined with the related references and various characterization results, it is proposed that the existence of relatively weak acid sites are responsible for the formation of o-cresol, whereas the relatively strong acid sites are in favor of 2,6-xylenol.Additionally, combined with the related references XRD,TPR and TPD characterization results, it is proposed that a slight decrease in the catalytic activity of Fe/Zr catalysts could be ascribed to the decrease in the strength of Lewis acid which originated from the part reduction of Fe³⁺ into Fe²⁺ during the reaction.The gas phase ortho-selective alkylation of phenol with methanol was investigated over a series of potassium supported on the Fe/Zr prepared by an impregnation procedure. The results show that the weaker acid sites favors the formation of o-cresol and anisole, whereas the stronger acid sites favors the 2,6-xylenol. Meanwhile, the coexistence of the stronger acid sites and the relatively weak (or medium) basic sites of the cobalt chromites catalysts is benefit to the increase in the catalytic activities of the ortho-selective alkylation of phenol with methanol。The gas phase ortho-selective alkylation of phenol with methanol was investigated over a series of zinc supported on the Fe/Zr sample prepared by an co-precipitation procedure. The results show the introduction of suitable amount of zinc (Zn/Zr = 1.0) could improve the selectivity of 2,6-xylenol.