Isobutane oxidation

Abstract: The non-catalytic liquid phase oxidation of isobutane is initiated with 0.05 wt.% to 0.5 wt.% ditertiary butyl peroxide.

Description: The invention relates to the production of tertiary butyl hydroperoxide. More particularly, the invention relates to the liquid phase oxidation of isobutane with molecular oxygen to form tertiary butyl hydroperoxide. Most particularly, the invention relates to initiation of the oxidation reaction in the absence of catalyst. Tertiary butyl hydroperoxide is a starting material and an intermediate in the production of commercial chemicals. Tertiary butyl hydroperoxide is used in combination with molybdenum-containing catalysts to convert olefins to the corresponding epoxides. The epoxides are the monomer intermediates for polymeric materials. Because of the commercial utility, improvements in the process to produce tertiary butyl hydroperoxide continue. US-A-2,845,461 (D.L.E. Winkler et al.) teaches the non-catalytic, liquid phase oxidation of isobutane to form tertiary butyl hydroperoxide. The reaction is initiated with amounts of tertiary butyl hydroperoxide or ditertiary butyl peroxide. US-A-3,478,108 (H. R. Grane)teaches the liquid phase oxidation of isobutane with molecular oxygen. The induction period for the reaction is reduced by adding a small quantity of hydroperoxide from the previous run. US-A-3,907,902 (H. R. Grane)teaches a method of increasing the selectivity to tertiary butyl hydroperoxide in the liquid phase oxidation of isobutane. Selectivity is improved by the presence of small amounts of isopropyl alcohol, isobutyl alcohol and secondary butyl alcohol. EP 0 076 534 A1 discloses the preparation of tertiary butyl hydroperoxide by the direct oxidation of isobutane wherein the production thereof is enhanced by conducting the oxidation in a dense, supercritical phase reaction mixture at a temperature in excess of the critical temperature of the mixture at a pressure in excess of the critical pressure of the mixture. An improved method has been discovered for initiating the non-catalytic liquid phase oxidation of isobutane with molecular oxygen to produce tertiary butyl hydroperoxide. The reaction is carried out at an oxidation temperature of 125°C to 155°C and an oxidation pressure of 350 psia to 800 psia (2.4 to 5.5 MPa). In the improvement, an initial reaction mixture is formed consisting of 50 wt.% or more isobutane, 10 wt.% or more tertiary butyl alcohol and 0.05 wt.% to 0.5 wt.% ditertiary butyl peroxide. Molecular oxygen is added at oxidation reaction pressure and the initial reaction mixture is heated to reaction initiation temperature of 135°C to 155°C. As a result, a steady state reaction mixture containing 10 wt.% to about 16 wt.% tertiary butyl hydroperoxide is achieved in 2 hours to 5 hours. The liquid phase oxidation of isobutane may be carried out in a batch, semi-continuous or continuous reaction vessel. The reaction vessel effluent, comprising a portion of the steady state reaction mixture, is subjected to product separation. Product separation is carried out by distillation, extractive distillation, solvent extraction or any combination thereof. Tertiary butyl hydroperoxide is recovered as a separate product or more typically in a mixture with the oxidation reaction coproduct tertiary butyl alcohol. Unconverted isobutane is recycled to oxidation reaction vessel. The reaction vessel is preferably designed to facilitate the contacting of liquid isobutane with molecular oxygen and for removal of heat from the exothermic oxidation reaction. The oxidation reaction is preferably carried out in a reaction vessel with means for withdrawing heat from the exothermic reaction mixture. For larger reaction vessels, heat withdrawal means may comprise heat exchanger tubes providing a quench medium such as chilled, demineralized water. For smaller reaction vessels, heat withdrawing means may comprise a jacket carrying the quench medium. Means is provided for heating the initial reaction mixture from an initial temperature, e.g., ambient temperature, to the reaction initiation temperature of 135°C to 155°C. This means typically comprises a heat exchanger. Isobutane is passed through the tube side and high pressure steam is provided to the jacket. The heat exchanger may be positioned in the recycle line. During start up, isobutane is circulated between the reaction vessel and the product separation means with heat applied to the recycled isobutane. Once the reaction is initiated heating is terminated. This reaction initiation is indicated by reactor thermocouples showing a reaction exotherm within the reactor. A steady state reaction mixture is rapidly established containing 10 wt% or more tertiary butyl hydroperoxide in 2 hours to 5 hours. It has been known heretofore to initiate the reaction with ditertiary butyl peroxide. It has been discovered surprisingly, that the reaction is initiated preferably with 0.05 wt% to 0.1 wt%, more preferably 0.05 wt% to 0.08 wt%, and most preferably 0.08 wt% ditertiary butyl peroxide. Accordingly, the requirement for larger amounts of initiator has been eliminated. This invention is shown by way of the following non-limiting Example. EXAMPLE An initial reaction mixture was made up comprising isobutane, tertiary butyl alcohol and ditertiary butyl peroxide. The reaction mixture was heated to reaction temperature. Pure oxygen was then introduced. The steady state reaction mixture was sampled and analyzed for composition. The results of three trials is reported as follows: Steady State Run 1 Run 2 Run 3 Reaction Temperature 142°C 141°C 141°C Reaction Pressure 3.4 MPa (500 psia) 3.47 MPa (510 psia) 3.47 MPa (510 psia) Initial Composition isobutane 70 wt% 69.4 wt% 69.9 wt% t-butyl alcohol 18.3 wt% 29.8 wt% 30.0 wt% ditertiary butyl peroxide 11.7 wt% 0.08 wt% 0.1 wt% Steady State Composition isobutane 68.7 wt% 73.0 wt% 69.5 wt% t-butyl alcohol 13.8 wt% 12.3 wt% 13.2 wt% tertiary butyl hydroperoxide 15.6 wt% 13.2 wt% 15.9 wt%

Claims: A process for the non-catalytic liquid phase oxidation of isobutane with molecular oxygen to produce tertiary butyl alcohol and tertiary butyl hydroperoxide, at an oxidation reaction temperature of 125°C to 155°C and an oxidation reaction pressure of 2.4 to 5.5 MPa (350 psia to 800 psia), characterized by forming an initial reaction mixture consisting of 50 wt.% or more isobutane, 10 wt.% or more tertiary butyl alcohol, and 0.05 wt.% to 0.5 wt.% ditertiary butyl peroxide, adding molecular oxygen to the initial reaction mixture at the oxidation reaction pressure and heating to a reaction initiation temperature of 135°C to 155°C, thereby forming a steady state reaction mixture containing 10 wt.% to 16 wt.% tertiary butyl hydroperoxide in 2 hours to 5 hours. A process as claimed in Claim 1, wherein in the initial reaction mixture the amount of ditertiary butyl peroxide is 0.05 wt.% to 0.1 wt.%. A process as claimed in Claim 1, wherein in the initial reaction mixture the amount of ditertiary butyl peroxide is 0.05 wt.% to 0.08 wt.%. A process as claimed in Claim 1, wherein in the initial reaction mixture the amount of ditertiary butyl peroxide is 0.08 wt.%.

Inventors: MUELLER MARK ALLAN, SANDERSON JOHN RONALD, MUELLER, MARK ALLAN, SANDERSON, JOHN RONALD
Applicants: HUNTSMAN SPEC CHEM CORP, HUNTSMAN SPECIALTY CHEMICALS CORPORATION
Application year: 1995
Main classification: C07C27
IPC codes: C07C27, C07C407, C07C31, C07C29, C07C409