Title of Invention

An Improved process for the preparation of phenol

Abstract

An improved process for the preparation of phenol which comprises; reacting benzene with hydrogen peroxide in presence of a solid catalyst having molar composition! (where x varies from 0.003 to 0.2) and characterized by the X-ray diffraction pattern as herein described at a temperature ranging from room temperature to 80° c for a period of 15 min. to 4 hours, removing the solid catalyst from the reaction mixture by conventional methods, separating aqueous and organic layers and isolating &. recovering the phenol a conventional c'.t still at ion methods.

Full Text

This invention relates to an improved process for the preparation of phenol. More particularly, it relates to a single step catalytic process by which benzene can be oxidized in the presence of hydrogen peroxide and a catalyst to produce phenol, which is an important bulk chemical for the production of bisphenol A, aniline, phenolic resins, xylenols, ionexchangers etc. Conventionally, phenol is produced by decomposing cumene hydroperoxide where acetone is co-produced. Cumenehydroperoxide is obtained from cumene, which in turn is produced from isopropylation of benzene by propylene or isopropanol. The major drawback of this method is that it is a three step labour and energy intensive process requiring separations and purification at each step. Another drawback of the priorart process is low selectivity of the products at every step resulting in lower yield of phenol. In another priorart method (reported by A. Thangaraj, R. Kumar and P. Ratnasamy in a scientific journal Applied Catalysis, volume 57, year 1990 at page L-1) for the preparation of phenol by direct hydroxylation of benzene in the presence of titanium silicate (as described in copending Indian Patent No 175810), dilute hydrogen peroxide and a co-solvent like acetone, acetonitrile or methanol to homogenize the organic substrate and aqueous hydrogen peroxide under biphase system (one homogeneous liquid and one solid catalyst phase). The major drawback of this prioract method mentioned above is the lower efficiency of costly hydrogen peroxide. Another drawback of this method is that the product phenol is separated from solvent and unreacted substrate benzene. Yet another drawback of this method mentioned above is the use and handling of environmentally hazardous organic solvents like acetone, acetonitrile etc. In view of the above mentioned drawbacks and limitations of the priorart processes, it was found desirable during the course of the present research work leading to the present invention to develop a new process for the production of phenol through direct, single step catalytic hydroxylation of benzene, in high yield using solid catalyst in the absence of organic co-solvent. The main objective of the present invention is to provide an improved process for the preparation of phenol using a solid catalyst. Another object is to provide the process giving high yields with increased H2O2 efficiency. Yet another object is to provide a process which does not employ organic co-solvents thereby reducing the cost considerably. Accordingly, the present invention provides an improved process for the preparation of phenol which comprises; reacting benzene with hydrogen peroxide in presence of a solid catalyst having molar composition: xTiO2:(1-x)SiO2 (where x varies from 0.003 to 0.2) and characterized by the X-ray diffraction pattern as herein described at a temperature ranging from room temperature to 80 °C for a period of 15 min. to 4 hours, removing the solid catalyst from the reaction mixture by conventional methods, separating aqueous and organic layers and isolating & recovering the phenol a conventional distillation methods. The catalyst used is prepared by the process described and claimed in 175810 and has following X-ray diffraction pattern and infrared spectral data. Table 1 : X-ray diffraction data of the catalyst composite material titanium silicate (Table Removed) a: the 29 values may vary by ± 0.05 °. b: R.I. = Relative Intensity, vs = very strong, s = strong, m = medium and w = weak, and infrared spectral data which are presented in Table 2, Table 2: Infrared spectroscopy data of the catalyst composite material titanium silicate (Table Removed) a: VS = very strong, S = strong, M = medium and W= weak. In one of the embodiment of the present invention the catalyst used is solid titanium silicate molecular sieve. In another embodiment of this invention is the ratio of hydrogen peroxide to benzene (herein after referred as substrate) ranges between 1 : 0.5 to 10, preferrably 1 : 1 to 3. In yet another embodiment of the present invention the addition of hydrogen peroxide may be made before raising the temperature of the reaction mixture or added dropwise continuously or may be added after the reaction temperature is raised to 80 °C. The salient features of the present invention are that it is a single step heterogeneous catalytic process, which operates at relatively mild conditions (room temperature to 80 °C, atmospheric pressure) and makes use of non-hazardous solid catalyst leading to high yields of phenol with high efficiency of hydrogen peroxide utilization in the absence of any organic co-solvent resulting in easy separation of product and work-up. The time required for the oxidation of benzene is within a range of 15 min. to 4 hours and can be within a range of 1 to 1.5 hours under more preferable reaction conditions. Another feature of the present invention is that the hydrogen peroxide may be added to react with substrate in following ways: 1) hydrogen peroxide is first added to the reaction mixture and then the temperature is raised. 2) hydrogen peroxide is added continuously dropwise. 3) the reaction mixture is heated upto desired temperature and hydrogen peroxide is then added dropwize continuously. However, the most salient feature of the present process is that no organic solvent is required coupled with significantly higher product yield in relatively less reaction time and the process is absolutely free from hazardous organic solvents and is environmentally friendly. The process for the present invention is described with following examples which are illustrative only and should not be construed to limit the scope of the present invention in any manner. Example 1 This example illustrates the procedure for the oxidation of benzene. 1.0 g of the catalyst composite material titanium silicate was slurried in 20 g water and 10 g of benzene. 5 g of aqueous hydrogen peroxide (containing 30 wt % hydrogen peroxide, H2O2) were added in the glass pot reactor (100 ml. capacity) under stirring. The reaction mixture was heated up to 60 °C with constant stirring. The reaction was continued for 2 hours and then the reaction mixture was cooled to room temperature and the products were analyzed by capillary gas chromatograph using fame ionisation detector. Benzene conversion was 90 wt % with 95% phenol selectivity, the remaining 5 % being parabenzoquinone. Example 2 This example illustrates the effect of reaction time on the hydroxylation of benzene to phenol. 1.0 g of the catalyst composite material titanium silicate, was slurred in 20 g water the 10 g of benzene and 5 g of aqueous hydrogen peroxide (containing 30 wt % hydrogen peroxide, H2O2) were added in a glass pot reactor (100 ml. capacity) under stirring. The reaction mixture was heated up to 60 °C with constant stirring. Small aliquots of the products were collected at different time intervals. The total reaction time was 3 h. The products were analyzed by capillary gas chromatography using fame ionisation detector. The results are recorded in Table 3. Table 3 : Effect of reaction time on the conversion and hydroxylation of benzene with HbOa over catalyst titanium silicate selectivity in the composite material (Table Removed) Example 3 This example illustrates the effect of continuous addition of hydrogen peroxide (30 wt % aqueous) during 2 hours for the hydroxylation of benzene and phenol selectivity. 10 g benzene, 20 g water and 1 g of catalyst composite material titanium silicate were mixed in a batch reactor. The reaction was heated to 60 °C with constant stirring and hydrogen peroxide was added continuously at a rate of 3.0 ml / hour for 2 hours. The reaction mixture was cooled to room temperature and products were analyzed by gas chromatography (GC). The results are presented in Table 4. (Table Removed) Example 4 This example describes the effect of different substrate (benzene) to H2O2 molar ratios on the conversion and phenol selectivity. 1.0 g of the catalyst composite material, titanium silicate was slurred in 20 g water the 10 g of benzene and 5 g of aqueous hydrogen peroxide (containing 30 wt % hydrogen peroxide, H2O2) were added in a glass pot reactor (100 ml. capacity) under stirring. The reaction mixture was heated up to 60 °C with constant stirring. The reaction was continued for 2 hours and then the reaction mixture was cooled to room temperature and the products were analyzed by capillary gas chromatography using fame ionisation detector. The results are recorded in Table 5. Table 5 : Effect of various substrate : H2O2 ratios on the oxidation of benzene over catalyst composite material titanium silicate (Table Removed) It is observed from the Table 5 that in higher substrate to H2O2 molar ratios hydrogen peroxide efficiency is more. Example 5 This example illustrates the effect of temperature on the conversion, hydrogen peroxide and phenol selectivity in the oxidation of benzene. 1.0 g of the catalyst titanium silicate was slurred in 20 g water the 10 g of benzene and 5 g of aqueous hydrogen peroxide (containing 30 wt % hydrogen peroxide, HaOa) were added in a glass pot reactor (100 ml. capacity) under stirring. The reaction mixture was heated up to 60 °C with constant stirring. The reaction was continued for 2 hours and then the reaction mixture was cooled to room temperature and ':he products were analyzed by capillary gas chromatography using fame ionisation detector. Results are tabulated in Table 6. Table 6 : Effect of temperature on the activity and selectivity of benzene oxidation over catalyst composite material titanium silicate (Table Removed) It is evident from the Table 6 that with increase in temperature although the reaction rate increases, H2O2 selectivity drops down. Example 6 This example illustrates the comparative and controlled experiment in the absence of solvent (the method of the present invention) and in the presence of different solvents (conventional or priorart method) on the hydroxylation of benzene to phenol. The reaction procedure adopted was the same as described in Example 1. The solvents were acetone, acetonitrile, methanol and ethanol. The results, recorded in Table 7, clearly demonstrate that the process of the present invention without using any organic solvent results in very high conversion and selectivity, and thereby very high yield of *, phenol, in comparison to what obtained using solvents conventionally. (Table Removed) WE CLAIM : 1. An improved process for the preparation of phenol which comprises; reacting benzene with hydrogen peroxide in presence of a solid catalyst having molar composition: xTiO2 : (1-x)SiO2 (where x varies from 0.003 to 0.2) and characterized by the X-ray diffraction pattern as herein described at a temperature ranging from room temperature to 80 °C for a period of 15 min. to 4 hours, removing the solid catalyst from the reaction mixture by conventional methods, separating aqueous and organic layers and isolating & recovering the phenol a conventional distillation methods. 2. An improved process according to claim 1 wherein benzene to hydrogen peroxide mole ratio is in range of 1 : 0.5 to 18. \ I/O 3. An improved process as claimed in claims 1 & 2, wherein the ratio of the catalyst to benzene ranges between 5 wt % to 20 wt %. 4. An improved process for the preparation of phenol substantially as herein described with reference to the examples.

Documents:

266-del-1997-abstract.pdf

266-del-1997-claims.pdf

266-del-1997-complete specification (granted).pdf

266-del-1997-correspondence-others.pdf

266-del-1997-correspondence-po.pdf

266-del-1997-description (complete).pdf

266-del-1997-form-1.pdf

266-del-1997-form-2.pdf