Title of Invention

A PROCESS FOR THE PREPARATION OF A MIXTURE OF ALKYLPHENOLS

Abstract

This is an invention which relates to a process for the preparation of a mixture of alkylphenols. In the said process mixture of 2,6-dimethylphenol (2,6-xylenol) and o-methylphenol (o-cresol) is prepared using a mixed oxide catalyst. The process steps are: contacting a mixed oxide catalyst with a feed consisting of mixture of alkylating agent and a phenolic compound such as herein described at a weight hourly space velocity in the range of 1 to 5 at a temperature ranging between 250 to 400°C, at a pressure in the range of 14.7 to 150 psi, for a period ranging between 1 to 100 hrs and collecting the mixture of alkyl phenols products at a temperature ranging between -5 to +5°C by conventional methods.

Full Text

This is an invention which relates to a.process for the preparation of a mixture of alkylphenols. More particularly, it relates to the said process for the preparation of mixture of 2,6-dimethylphenol (2,6-xylenol) and o-methylphenol (o-cresol) using a mixed oxide catalyst. Alkylphenols are the compounds having the alkyl groups substituting or replacing a hydrogen either in the phenyl ring or in the OH group. Cresols, xylenols, anisole and trimethyl phenols are some of the important alkylphenols (for e.g. o-cresol used in the production of novolak resins, 2,6-xylenol used to manufacture polyphenylene oxide, epoxy resin and in special grade paints and 2,4,6-trimethylphenol serves as a component for the modification of polyphenylene oxide resins, etc.). Thus, these are industrially important chemical intermediates in the manufacture of plastics, special grade paints and a variety of chemicals. The stringent specifications and the demand of these chemicals necessitate the development of catalytic systems and the processes for their selective production. In the prior art, catalysts used for the alkylation reactions are ranging from ceramics, through zeolites to semi-conducting metal oxides and mixed metal oxides. US Patent 3,843,606 discloses the use of MgO as a highly active catalyst and British Patent 602,257 describes alumina as a suitable catalyst at lower temperatures. Polish Patent PL 159,203 describes the use of silica mixed with a metal oxide (where the metal is Mg, Fe, Cr, Sb, V etc.) to effectively convert phenol to 2,6-xylenol. US patent 4,371,714 describes a method for the alkylation of phenols using a crystalline zeolite, but with this catalyst - both cresols and xylenols are produced and no selectivity for 2,6-xylenol is observed. US patent 4,283,571 describes a method for the isomerisation of o-cresol to isomeric cresols on zeolite catalyst like ZSM-12. US patent 4,283,573 reported the formation of p-mono alkylphenols with long chain alcohols and phenols. Many other US patents like 4,197,413 and 4,205,189 describe the formation of alkylphenols mostly the cresols. The published literature reports the use of catalyst systems varying from alumina, metal oxides, zeolites and acidic catalysts. Most of these reported catalysts are not selective to 2,6-xylenol. MgO catalysts, promoted by the transition metal oxides and also multimetallic oxide catalysts are the ones by far providing the best conversions of phenol to 2,6-xylenol. The US Patent 4,933,509 claims 92.7% conversion of phenol with 76.9% selectivity to 2,6-xylenol over MgO catalyst and the US Patent 4,661,638 claims that the conversion could be improved to 97.0% by promoting MgO with Mn oxide. US patent 5,098,879 claims to achieve 100% conversion with 93% selectivity over MnO-K2O catalyst. US Patent 5,371,306 uses a multi metallic oxide to achieve 88.9% conversion and 63.5% selectivity, whereas Japanese Patent 10,113,561 which uses again a multimetallic oxide catalyst, claims 93% conversion and 97% selectivity. There are also variations to the processes such as batch reactors (Japanese Patent 10,113,561) and fluidised bed reactors (Japanese Patent 05,286,880). In all the above patents reported in this section, there are two main disadvantages: 1) The catalyst composition, particularly the active phase is not well defined and hence reproducibility will be a problem and 2) there is always para alkylation happening to the extent of atleast 4%, thus making the separtion of impurities as an essential unit process. Some of the important patents along with the operating conditions and other properties are given below: (Table Removed) The present invention provides a process wherein the catalyst used is a single phase based on Cu and Fe oxides having well defined spinel phase, whose preparation is disclosed here and it overcomes both the disadvantages existing for the other catalysts. Furthermore, the economy of the process is enhanced by the low cost of the catalyst, low operating temperature (around 350°C), high conversion of phenol, high selectivity to 2,6-xylenol, long operational cycle length and ease of regenerability. In our expending Indian Patent (2707/98) and US patent(Application No: 09/178, 576), we claim a process to make 2,6-xylenol with high selectivity for ortho alkylation (>95%) and least amount of side products, over a single phase ternary oxide system containing Co and Fe as metals. US patent 4,386,226 uses mixture of Fe2O3 (at least 87 wt.%) and one other metal oxide (where metal is selected as As, Cd, Co, Hg, In, Ni, Pb, etc) for the title reaction. So far, there is no report in the literature on the use of copper ferrite systems for the preparation of xylenols, although there are few studies on Cu containing systems. Japanese Patent 07,835,061 describes a ferrite catalyst with a formula of MFe2O4, where few possibility of M = Ni, Cu, Cu-Zn were tried only to get a maximum conversion of 55.2%. European patent 785,180 discloses the use of Cu as promoter for the MgO catalyst to provide better yield of 2,6-xylenol. In yet another variation, European Patent 686,617 claims the production of 2,6-dialkylphenol from 2,4,6-trialkylphenol using a combination of CuCl2 and acetoxime as the catalyst. Thus a specific relation between copper and these phenolic systems seemed to exist. It is therefore desirable to provide a process for the preparation of a mixture of 2,6-xylenol and o-cresol using an ortho selective catalyst composite material which produces negligible amount of cresol and in particular p-cresol, not more than 0.5% other xylenols and at least is void of some of the drawbacks of the earlier processes. The inventors of the present invention have observed that the use of mixed metal oxide catalyst provided by the present invention removes some of the above mentioned drawbacks. The present invention invokes the idea of using a single phase ternary oxide with copper as a component of the catalyst and demonstrate the high activity to convert phenol and high selectivity to ortho alkylation and to produce 2,6-xylenol, in high yields. The objective of the present invention, therefore is to provide a process for the production of a mixture of alkylphenols more particularly, o-cresol and 2,6-xylenol in high selectivity and with superior activity of the catalyst for longer durations using an ortho alkylation catalyst. Another objective is to provide a process for the said improved catalyst that gives high conversion and high selectivity to 2,6-xylenols with low deactivation rates. Another objective is to provide an improved process for the preparation of the said improved catalyst, which need not necessarily be produced in situ. Accordingly, the present invention provides a process for the preparation of mixture of alkylphenols which comprises; characterised in that contacting a mixed oxide catalyst with a feed consisting of mixture of alkylating agent and a phenolic compound such as herein described at a weight hourly space velocity in the range of 1 to 5 at a temperature ranging between 250 to 400°C, at a pressure in the range of 14.7 to 150 psi, for a period ranging between 1 to 100 hrs and collecting the mixture of alkyl phenols products at a temperature ranging between -5 to +5°C by conventional methods. In one of the embodiments of the present invention the catalyst used has general formula: MANBFe2O4 wherein 'M' is a divalent metal such as cobalt, nickel, zinc, magnesium, copper, manganese and cadmium. 'N' is any divalent metal other than M. The values of A and B are such that A= 0 to 1 and B=l to 0 and A+B=1. The catalyst is characterized by the XRD pattern as given in Table-1. Table-l The observed'd' spacing and the relative intensity for various 'hkl' planes for CuFe2O4 (Table Removed) The catalysts are having a surface area of 20.0 to 40.0m2/g and a pore size varying from 10 to 50A°. In another embodiment, the alkylating agent used may be a lower alcohol such as methanol, or any other methylating agent such as dimethyl carbonate. In yet another embodiment, the phenolic compounds used may be such as phenol, methoxy benzene, o-cresol or methoxy cresols. In another embodiment, the ratio of phenolic compound to alcohol is varied from 1:7 to 1:3 (mol/mol). In still another embodiment, the space velocity of the reaction mixture is varied in the range of 1 to 5 WHSV (weight hourly space velocity, expressed in terms of g of feed per g of catalyst per hour). In a feature of the present invention, the catalyst is prepared as per the procedure which comprises preparing the solutions of the source of iron, a source of a divalent metal (copper), separating the undissolved solids from the solutions by conventional methods, mixing the solutions in the stoichiometric ratio, adding this reaction mixture to an alkali solution maintained at a temperature little over the ambient, further adjusting the pH of the solution in the range of 9 to 10, heating the mixture to a temperature ranging between 50 to 70 °C, digesting the mixture at this temperature for a period ranging between 1 to 2 h. to obtain the precipitate of the product, cooling the precipitate, washing with water to obtain the product, drying the product at temperature ranging between 80 to 100 °C for a period of 24 to 48 h, calcining the product at a temperature ranging between 200 to 500 °C for 10 to 48 h. The process of the present invention is described herein below with reference to following examples which are illustrative only and should not be considered to limit the scope of the present invention in any manner. Example-l This example describes a method of the preparation of catalyst material having copper alone at divalent metal position and iron alone at trivalent metal position. 50.5 g of copper nitrate and 168.9 g of ferric nitrate were dissolved separately each in 52 and 160 ml of deionised water, respectively. These solutions were mixed together and added dropwise to an alkali solution containing 73 g of sodium hydroxide dissolved in 345 ml of water. The pH of the resultant mixture was adjusted to 10.2 by adding dilute alkali solution, if needed. The temperature of the precipitation was 50°C and aged for 8 h. The precipitated material after attaining the room temperature, was washed free of nitrate ions and alkali ions. The precipitate was dried at 100°C for 36 h and calcined at 500°C for 20 h in flowing air. The dried material was powdered and sieved to the size of ~15 mesh. This gives the catalyst Cu Fe204(~50g). Examples 2 to 8 describe the process for the preparation of mixtures of alkylphenols. Example-2 3 g of the catalyst material is pressed and crushed to particles of size 15 mesh and placed at the center of a reactor maintained at a constant temperature of 350 °C. The catalyst was activated for 12h in flowing air at 450°C. The feed containing phenol and methanol at a ratio of 1:7 (mol/mol) are fed in to the catalyst system at a space velocity of 1h-1. The effluent of the reactor was cooled by chilled water and the products collected after 5h (TOS=5h) were analyzed by GC, with a capillary column (25m Ultra-2, 0.32 mm diameter). The results are shown in Table-2. Table-2 (Reaction conditions: Mole ratio of Phenol:Methanol = 1:7; Temperature = 350°C; WHSV=lh-1;TOS = 5h) (Table Removed) Example-3 The feed (phenol and methanol) at 9 mole ratio varying between 1:3 and 1:7 was contacted over 3 g of catalyst at a space velocity lh-1. The temperature of the catalyst bed was maintained at 350°C. The effluent of the reactor was cooled by chilled water and the products were analyzed by GC, with a capillary column (25m Ultra-2, 0.32mm diameter). The results are shown in Table-3. Table-3 (Reaction conditions: Temperature =350°C; WHSV=1 h-1TOS=5h) (Table Removed) Example-4 This example shows the effect of space velocity on the product distribution and the activity of the catalyst. In order to investigate this, a set of experiments with the feed weight varied from 1 to 5 g per g of catalyst. The products are collected after cooling and analyzed for calculating the yields and selectivities. Table-4 includes the data of this study. Table-4 (Reaction conditions: Mole ratio of Phenol: Methanol =1:4; Temperature =350°C; TOS=5h) (Table Removed) Example - 5 This example shows the effect of temperature on selectivity of the product formation. The feed of phenol and methanol in the ratio of 1:7 was fed to a bed of catalyst maintained at temperatures ranging between 300-425°C. The products were collected at the outlet of the reactor and analyzed for the composition. The results are tabulated in Table -5. Table-5 (Reaction conditions: Mole ratio of Phenol: Methanol =1:7; WHSV=1 h'1; TOS=5h) (Table Removed) Example-6 The catalyst composite material of example 1 was contacted with a feed consisting of phenol and dimethylcarbonate in the mole ratio 1:2 and at a temperature of 350°C, WHSV=1. The product analysis is given in Table-6. A comparison is given with methanol as methylating agent. Table-6 (Reaction conditions: Temperature = 350°C; WHSV=lh'; TOS=5h) (Table Removed) Example-7 This example illustrates the effect of dilution of the feed using water. A feed consisting of a mixture of phenol, methanol and water is contacted on a catalyst composite material. The results are presented in Table-7. Table-7 (Reaction conditions: Temperature =350°C, WHSV=lh-1; TOS=5h). (Table Removed) Example 8 This example shows the activity of the catalyst with time on stream. About 3 g of catalyst was loaded in the reactor and the activation was carried out as described in the earlier examples. The feed consisting of phenol and methanol in the mole ratio 1:7 was passed over the catalyst at a temperature of 350°C, WHSV=1. The product was collected every 5 h and analyzed using gas chromatography as in previous cases. Table-8 (Reaction conditions: Mole ratio of phenol:methanol=l :7; Temperature=350°C; WHSV=lh-1) (Table Removed) Advantages The present study provides a catalyst composition with improved conversion of phenol, high selectivity of required 2,6-xylenol. Moreover, the unwanted p-alkylated products (other alkylates) and trimethylated phenols (others) are produced only in traces ( We Claim: 1. A process for the preparation of mixture of alkylphenols which comprises; characterised in that contacting a mixed oxide catalyst with a feed consisting of mixture of alkylating agent and a phenolic compound such as herein described at a weight hourly space velocity in the range of 1 to 5 at a temperature ranging between 250 to 400°C, at a pressure in the range of 14.7 to 150 psi, for a period ranging between 1 to 100 hrs and collecting the mixture of alkyl phenols products at a temperature ranging between -5 to +5°C by conventional methods. 2. A process wherein the mixed oxide catalyst consists of oxides of divalent metals selected from cobalt,nickel,zinc,magnesium,copper,manganese , cadmium and oxides of Fe. 3. A process wherein the alkylating agent used is selected from lower alcohols selected from methanol, or other methylating agents dimethyl carbonate. 4. A process wherein the ratio of phenolic compound to alkylating agent in the feed varies from 1:3 to 1:7 (mol/mol). 5. A process wherein the mixed oxide catalyst used is preferably copper ferrite. 6. A process for the preparation of mixture of alkylphenols as fully described herein with reference to the examples 2 to 8.

Documents:

1211-del-2000-abstract.pdf

1211-del-2000-claims.pdf

1211-del-2000-correspondence-others.pdf

1211-del-2000-correspondence-po.pdf

1211-del-2000-description (complete).pdf

1211-del-2000-form-1.pdf

1211-del-2000-form-19.pdf

1211-del-2000-form-2.pdf

1211-del-2000-form-3.pdf