Single step process for the oxidation of cyclohexane

Abstract

The present invention disclosed a single step process for the conversion of cyclohexane to adipic acid by using manganese oxide, tungsten oxide or Mn—WOx nano structure having improved yield and selectivity.

Claims

1. A single step process for conversion of cyclohexane to adipic acid, the process comprising: adding cyclohexane, a solvent and a catalyst to a reactor followed by charging oxygen with a pressure in a range of 0-30 bars at a temperature ranging from 100-125° C. under constant stirring for a period in a range of 5 to 6 hours to afford adipic acid, wherein the catalyst is Mn-WOx nanostructure, wherein the Mn-WOx nanostructure catalyst is in the form of a nanorod, a nanoseed or a fish bone structure, and wherein yield of adipic acid is in a range of 20-40%.

2. The process as claimed in claim 1, wherein said solvent is selected from acetonitrile, acetic acid, water or a mixture thereof.

3. The process as claimed in claim 1, wherein the Mn-WOx nanostructure catalyst is in the form of a fish bone structure.

4. The process as claimed in claim 1, wherein selectivity of the process towards adipic acid is in a range of 40 to 70%.

5. A process for the preparation of Mn with Tungsten oxide fish bone catalyst, the process comprising the steps of: a) dissolving sodium tungstate dihydrate, manganese (II) sulfate monohydrate and metal sulphates in a suitable solvent at a temperature ranging from 25-30° C. to form a solution; b) adjusting the pH of the solution of step (a) up to 0.5 to 5 by constant stirring for 30-50 mins; c) heating the solution of step (b) at a temperature ranging from 100-250° C. for a time period ranging from 24-72 hours; d) cooling the solution of step (c) up to 25-30° C. to afford Mn with Tungsten oxide fish bone catalyst.

6. The process as claimed in claim 5, wherein the metal sulphate is selected from sodium sulfate, potassium sulfate or a mixture thereof.

7. The process as claimed in claim 5, wherein the solvent is selected from water, an alcohol or a mixture thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: SEM images of Mn—WOx fish bone structure

(2) FIG. 2: XRD—pattern for Mn—WOx fish bone structure

(3) FIG. 3: SEM images of Mn—WOx nano seed structure

(4) FIG. 4: XRD—pattern for nano seed structure

(5) FIG. 5: UV-Visible spectra of (a) seeds and (b) fish bone structure

(6) FIG. 6: TEM images of Mn—WO.sub.4 nano rods and Mn—WOx fish bone structures

DETAILED DESCRIPTION OF THE INVENTION

(7) The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

(8) In view of the above, the present invention provides an economic, environment friendly, single step process for the oxidation of cyclohexane to adipic acid in presence of catalyst selected from manganese oxide, tungsten oxide or Mn—WOx nanostructure.

(9) In an embodiment, the present invention provides a single step process for the conversion of cyclohexane to adipic acid, wherein the process comprises addition of cyclohexane, solvent and catalyst to a reactor followed by charging oxygen with pressure in the range of 0-30 bars at a temperature ranging from 100-125° C. under constant stirring for a period in the range 5 to 6 hours to afford adipic acid.

(10) The catalyst is selected from manganese oxide, tungsten oxide or Mn—WOx nanostructure. In preferred embodiment, the catalyst is Mn—WOx nanostructure. In more preferred embodiment, the Mn—WOx nanostructure catalyst is in the form of nanorod, nanoseed or fish bone structure.

(11) The yield of adipic acid is in the range of 20-40%. In preferred embodiment, the yield of adipic acid is in the range of 35-40%. The solvent is selected from acetonitrile, acetic acid and water.

(12) The selectivity of the process of instant invention is in the range of 40 to 70%. In a preferred embodiment, the selectivity of the process of instant invention is in the range of 45 to 60%.

(13) In another embodiment, the present invention provides a process for the preparation of Mn with Tungsten oxide fish bone catalyst comprising the steps of: a) dissolving metal tungstate, manganese (II) sulfate monohydrate and metal sulphates in a suitable solvent at a temperature ranging from 25-50° C.; b) adjusting the pH of solution of step (a) upto 0.5-5 by constant stirring for 30-50 mins; c) heating the solution of step (b) at a temperature ranging from 100-250° C. for a time period ranging from 24-72 hours; d) cooling the solution of step (c) upto 25-30° C. to afford Mn with Tungsten oxide fish bone catalyst.

(14) In preferred embodiment, said metal tungstate is selected from sodium tungstate dihydrate.

(15) In another preferred embodiment, said metal sulphate is selected from sodium sulfate, potassium sulfate or mixture thereof.

(16) The mole ratio of Tungsten to Manganese is in the range of 0.1:0.005-0.1:0.1.

(17) The solvent of step (a) is selected from milli-Q water/alcohol/water-alcohol mixture.

(18) The single step process for the conversion of cyclohexane to adipic acid is as depicted in scheme 1 below. The scheme 1 shows cyclohexane to adipic acid over Mn—W Nano structures oxygen as an oxidant.

(19) ##STR00001##

Scheme: 1

(20) The following table 1 shows oxidation of cyclohexane to adipic acid for reaction conditions; catalyst amount: 50 Mg, Cyclohexane: 6 ml, Acetonitrile: 3 ml, Temperature: 125° C., Oxygen pressure: 30 bar, Time: 6 hours.

(21) TABLE-US-00001 TABLE 1 Conversion of Selectivity Selectivity of Yield of Yield of Sr. cyclohexane of ka oil adipic acid ka oil adipic acid No. Catalyst (%) (%) (%) (%) (%) 1 Tungsten oxide 42.7 13.26 55.64 5.70 23.91 fish bone alone 2 Tungsten 24.75 16.19 51.03 4.00 12.60 oxide alone 3 Manganese 40.69 1.79 58.70 0.73 23.16 oxide alone 4 Mn—WOx fish 63.33 7.48 59.1 4.74 37.4 bone structure 5 Mn—WO.sub.4 Nano 32.58 23.23 48.49 7.56 15.79 rods 6 Mn-WOx Nano 31.77 22.00 52.60 6.99 16.68 seeds

(22) The following table 2 shows catalyst and adipic acid yield over various Mn—W nanostructures. Reaction conditions; catalyst amount: 50 Mg, Cyclohexane: 6 ml, Acetonitrile: 3 ml, Temperature: 125° C., Oxygen pressure: 30 bar, Time: 6 hours.

(23) TABLE-US-00002 TABLE 2 Catalyst Yield in % W oxide 23.91 Mn oxide 23.16 Mn—WOx fish bone 37.40 Mn WO.sub.4 nano rods 15.79 Mn WOx nano seeds 16.68
From above data it is shown that Mn—WOx fish bone structure is giving high percentage of yield around 40% compared to other nano structures like rods, seeds. Fish bone structure is playing crucial for selective oxidation of adipic acid.

(24) FIG. 1 represents SEM images of Mn—WOx nanostructures [(a) and (b)] which are prepared from 7 mmol of Na.sub.2WO.sub.4. 2H.sub.2O using 1.8 mmol of Sodium and potassium salt and MnSO.sub.4.H.sub.2O, in case of Example 1.

(25) FIG. 2 represents XRD pattern of Mn—WOx nanostructures which are prepared from 7 mmol of Na.sub.2WO.sub.4. 2H.sub.2O using 1.8 mmol of Sodium and potassium salt and MnSO.sub.4.H.sub.2O, in case of Example 1.

(26) FIG. 3 represents SEM images [(a) and (b)] of Mn—WOx nanostructures which are prepared from 7 mmol of Na.sub.2WO.sub.4. 2H.sub.2O using 1.8 mmol of Na.sub.2SO.sub.4 Sodium and potassium salt, in case of Example 1. Different nanostructures of Mn—WOx are achieved by changing the reaction parameter, in case of Example 1.

(27) FIG. 4 represents XRD pattern of Mn—WOx nano seed structures which are prepared from 7 mmol of Na.sub.2WO.sub.4. 2H.sub.2O using 1.8 mmol of Sodium and potassium salt and MnSO.sub.4.H.sub.2O, in case of Example 1. Different nanostructures of Mn—WOx are achieved by changing the reaction parameter, in case of Example 1.

(28) FIG. 5 represent absorption spectra of Mn—WOx (a) seeds and (b) fish bone structure.

(29) FIG. 6 represent TEM images of Mn—WO.sub.4 nano rods structure [(a) to (c)] in case of Example 2 and Mn—WO fish bone structure [(d) to (e)] in case of Example 1.

EXAMPLES

(30) Following examples are given by way of illustration therefore should not be construed to limit the scope of the invention.

Example 1

Mn—W (Fishbone) Synthesis Procedure

(31) In a typical experiment, 7 mmol of Na.sub.2WO.sub.4. 2H.sub.2O, 1.8 mmol of Na.sub.2SO.sub.4 and 1.8 mmol of K.sub.2SO.sub.4 and MnSO.sub.4.H.sub.2O was used. Tungsten to Manganese mole ratio should be 1:0.01 0.1:0.005-0.1:0.1 were dissolved in milli-Q water at 25° C. Under constant stirring, pH of the solutions were then adjusted to 2.25. Then stirred at 30-50 minutes. The solution was added to Teflon-lined stainless steel autoclave and heated at 180° C. for 24 hours in a hot air oven and cooled to room temperature naturally. The products were collected by vacuum filtration and washed repeatedly with milli-Q water and ethanol and dried under vacuum at 60° C. for 5 hours. After this calcination was done at 550° C. for 4 hr.

Example 2

Mn—W Nano Rods Synthesis Procedure

(32) Mn—W Nanorods structure prepared by hydrothermal synthesis. 0.2M solution of Mn (NO.sub.3).sub.2.4 H.sub.2O and 0.2M solution of Na.sub.2WO.sub.4. 2H.sub.2O added in 50 ml of milli-Q water to a mixed solution of pH=6.7. Subsequently, the pH of the mixed solution was adjusted to 9.9 by adding appropriate amounts of 0.1 M HNO.sub.3 or 0.1 M NaOH and the mixtures were transferred to the autoclave and the temperature was raised from 20° C. to 180° C. at a rate of 5° C./min. The synthesis temperature was kept at 180° C. for 12 hours. Then collected catalyst was calcined at 500° C. for 6 hours.

Example 3

Oxidation of Cyclohexane

(33) Liquid phase oxidation of cyclohexane was carried out in 50 ml autoclave Parr reactor using 50 mg of catalysts, 3 ml of Acetonitrile solvent and 6 ml of cyclohexane which were introduced in to reactor. Oxygen was charged to 30 bars, and temperature maintained at 125° C. under stirring 550 RPM for 6 hours. After reaction, the mixture was cooled down to room temperature and the product was collected from reaction mixture, dissolved in 7:3 ratio of acetone and water. The product was analyzed through by HPLC connected with C18 column and 0.005M H.sub.2SO.sub.4 and water used as a mobile phase. The yield were calculated and normalized with respect to HPLC response factor. The reusability of the catalyst was tested for multiple cycles after recovering the catalyst and washing with acetone and then with water several times.

(34) The following table shows oxidation of cyclohexane to adipic acid for Reaction conditions; catalyst amount: 50 Mg, Cyclohexane: 6 ml, Acetonitrile: 3 ml, Temperature: 125° C., Oxygen pressure: 30 bar, Time: 6 hours

(35) TABLE-US-00003 Conversion of Selectivity Selectivity of Yield of Yield of Sr. cyclohexane of ka oil adipic acid ka oil adipic acid No. Catalyst (%) (%) (%) (%) (%) 1 Tungsten oxide 42.7 13.26 55.64 5.70 23.91 fish bone alone 2 Tungsten 24.75 16.19 51.03 4.00 12.60 oxide alone 3 Manganese 40.69 1.79 58.70 0.73 23.16 oxide alone 4 Mn—WOx fish 63.33 7.48 59.1 4.74 37.4 bone structure 5 Mn—WO.sub.4 Nano 32.58 23.23 48.49 7.56 15.79 rods 6 Mn—WOx Nano 31.77 22.00 52.60 6.99 16.68 seeds

Example 4

Self-assembling of WO.SUB.3 .and W.SUB.18.O.SUB.49 .Nanorods Networks Leading to Nanorods Bundles, Cocoon, Urchin, Fishbone and Few Other Patterns

(36) In a typical experiment 7 mmol of Na.sub.2WO.sub.4, 1.8 mmol of Na.sub.2SO.sub.4 and 1.8 mmol of K.sub.2SO.sub.4 were dissolved in milli Q water at room temperature. Under constant stirring, pH of the solutions was then adjusted by dropwise addition of diluted HCL. The solution color changes from colorless to light to darker yellow with decreasing pH. After stirring for additional 30 minutes, the solution was added to 30 ml of Teflon-lined stainless steel autoclave and heated at 180° C. for 24 hours in a hot air oven and cooled to room temperature naturally. The products (bluish green to light green color) were collected by vacuum filtration and washed repeatedly with milli Q water and ethanol and dried under vacuum at 60° C. for 5 hours.

Advantages of the Invention

(37) 1. Economical single step process for preparation of Adipic acid from cyclohexane. 2. Eco-benign production of adipic acid using oxygen as an oxidant over Mn—W nano structures in absence of production of any harmful gases like NO.sub.2 etc. 3. Catalyst synthesis strategy has the advantages that it is one step hydrothermal method, aqueous medium based and requires no surfactant or stabilizing agent or conventional template. Furthermore, it also affords self-assemble of 1D nanorods of Mn—WO into hierarchical fishbone type nanostructure. 4. The high percentage of yield of catalyst is obtained at very low temperature. 5. Decomposition of Adipic acid is avoided.