WO2017017524A1

WO2017017524A1 - Loop oxidation of toluene to benzoic acid

Info

Publication number: WO2017017524A1
Application number: PCT/IB2016/001171
Authority: WO
Inventors: Alain SCHOETERS
Original assignee: Synegis bvba
Current assignee: Synegis bvba
Priority date: 2015-07-29
Filing date: 2016-07-12
Publication date: 2017-02-02
Anticipated expiration: 2018-01-29

Abstract

A process of liquid phase oxidation of a hydrocarbon compound involving injection of pure oxygen into a hquid hydrocarbon in a reaction vessel while maintaining the atmosphere of the reaction vessel headspace outside the explosion triangle for the oxygen-hydrocarbon system.

Description

Loop Oxidation of Toluene to Benzoic Acid

BACKGROUND OF THE INVENTION

1. Field of Invention

[0001] Oxygen enriched gas is safely injected at high pressure into a liquid phase mixture of toluene, reaction initiators, promoters, a homogeneous catalyst and water using a loop reactor to produce benzoic acid.

2. Description of Related Art

Conventionally, air is the source of oxygen gas for a number of liquid-phase oxidation reactions. The air is conventionally delivered into the reactors via axial flow impellers which assist in mass transfer between the gas (oxygen) and the liquid reactants in the reaction vessel. However, since air also contains the inert nitrogen gas, the reactor vent gas contains significant amounts of unreacted solvent and reactants entrained in the gas as vapor. The recovery of such organic chemicals from the gas requires an extensive chemical treatment. Additionally, the concentration of oxygen in air limits the oxidation rate necessitating longer reaction times and larger reactors.

SUMMARY OF THE INVENTION

[0002] Oxidation of hydrocarbons with pure or a high-purity oxygen gas can be undertaken safely by using a loop reactor and a combination of inert materials in a flammable environment at specific reaction conditions. Additionally the method and apparatus of the invention reduces the amount of the vent gases from the reactor and results in a much lower loss of solvent and reactants. An oxygen distribution that keeps the oxygen level outside the explosive limits in the reactor system is set forth herein. The requirement of compression power from air compressors when using oxygen is completely eliminated. Reaction time is reduced, and smaller-sized or a fewer number of reactors are needed. This gives a net saving in terms of capital expenditure and operating costs.

[0003] The invention relates to a method of oxidizing toluene to obtain benzoic acid and a reaction vessel and associated mass transfer equipment.

[0004] The invention also relates to the recovery of the exothermic heat of the oxidation reactions. The reactor set up and reactor process conditions are additionally set to optimize the valorization of the thermal streams. Additionally, the invention also relates to the recovery of the homogeneous catalyst used in the oxidation reaction.

[0005] An embodiment of the invention is process of hquid phase oxidation of at least one hydrocarbon compound comprising:

a. providing a reaction system including a reaction vessel, an inlet to permit passage of gas into hquid contents of a reaction vessel, a circulation pump, piping connecting the circulation pump and reaction vessel in series to form a circuit, a separator for catalyst recycling, and a sparger, the reaction vessel containing:

i. a liquid phase mixture of the at least one hydrocarbon compound, a

homogeneous catalyst and water and

ii. a headspace including gaseous hydrocarbon, nitrogen and water b. injecting oxygen enriched gas through the sparger and inlet into the hquid phase mixture and

c. recycling the hquid phase mixture from a bottom portion of the reaction vessel to a top portion of the reaction vessel by operation of the circulation pump to afford oxidized hydrocarbon, and .

d. separating the catalyst from oxidized hydrocarbon with the separator

[0006] In a preferred embodiment, the process of the invention further comprises

e. setting a temperature and a pressure range of the contents of the reaction vessel, f. determining an explosion triangle for the set temperature and pressure range of the reaction vessel,

g. determining a headspace oxygen level corresponding to a point on the explosion triangle outside the explosion range, and

h. optionally monitoring the oxygen content of the headspace.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 shows a plan view of the loop reactor of the invention.

[0008] Figure 2 shows a detail view of a portion of the loop reactor of the invention.

[0009] Figure 3 shows a detail view of the gas and liquid injection and mixing shock zone of the loop reactor. DETAILED DESCRIPTION OF THE INVENTION

[0010] Oxidation of organic compounds for industrial production of chemicals can be divided into two main categories: gas-phase oxidation and liquid-phase oxidation. In the gas-phase oxidation, the reactants are oxidized in the gaseous state using either an oxygen-rich gas or air as an oxygen source. In the liquid-phase oxidation, the reaction is carried out in the liquid phase.

[0011] In the liquid-phase oxidation the reactants are dissolved in a solvent, which acts as the medium of reaction. Pure oxygen or oxygen-rich gas or air is dispersed into the reactors via one or more gas spargers. The oxygen-containing gas is broken into tiny bubbles providing a high interfacial area for mass-transfer between the gas bubbles and the reactants. As most of the liquid-phase hydrocarbon oxidation reactions are mass transfer- limited, an increased dispersion results in both faster and enhanced absorption and, therefore, in a higher reaction rate. The reaction is said to be homogeneous if the catalyst, in case of a catalytic reaction, is soluble in the solvent.

[0012] Heterogeneous reactions involve insoluble catalyst material, which is held as dispersion in liquid. The invention relates to a method of oxidizing toluene to obtain benzoic acid and a reaction vessel and associated mass transfer equipment.

[0013] An embodiment of the invention is a process of liquid phase oxidation of a hydrocarbon compound comprising:

a. providing a reaction system including a reaction vessel, an inlet to permit passage of gas into liquid contents of a reaction vessel, a circulation pump, piping connecting the circulation pump and reaction vessel in series to form a circuit, a separator for catalyst recycling, and a sparger, the reaction vessel containing:

i. a liquid phase mixture of the hydrocarbon compound and water and ii. a headspace including gaseous hydrocarbon and water,

b. injecting oxygen enriched gas through the sparger into the liquid phase mixture and c. recycling the liquid phase mixture from a bottom portion of the reaction vessel to a top portion of the reaction vessel by operation of the circulation pump, and d. separating the catalyst from oxidized hydrocarbon with the separator.

[0014] In a preferred embodiment, the process of the invention further comprises

e. setting a temperature and a pressure of the contents of the reaction vessel, f. determining an explosion triangle for the set temperature and pressure of the reaction vessel,

g. determining a headspace oxygen level corresponding to a point on the explosion

triangle outside the explosion range, and

h. optionally monitoring the oxygen content of the headspace.

[0015] Catalyst. The presence of a cobalt catalyst greatly catalyzes the rate of the oxidation of toluene. The presence of Co³⁺ ions is crucial to this catalytic process. The catalysts used commonly are Co (II) acetate or Co (II) octoate. The advantage of the octoate salt is its solubility in toluene. Therefore, the Co²⁺ must be oxidized to Co³⁺ for the catalyst steps of the oxidation to occur. Normally, the presence of oxygen is enough to oxidize the Co²⁺ to Co³⁺. However, Co²⁺ may be "pre-oxidized" into Co³⁺ with an acid, for example, peracetic acid.

[0016] The importance of not only the amount of Co³⁺, but also the ratio of Co³⁺/Co²⁺ is a factor in designing a reaction scheme. No initiation period is observed when a Co³⁺ catalyst is used for the oxidation, and the presence of benzoic acid also supports initiation.

[0017] The invention includes any process of producing benzoic acid disclosed elsewhere herein where at least one of the following is true: (1) cobalt octoate is present in the organic phase and/ or (2) cobalt acetate is present in the aqueous phase.

[0018] Toluene is oxidized at 140 to 200 °C, preferably 150 to 190 °C, more preferably 160 to 180 °C, and most preferably 170°C with oxygen in the presence of a cobalt octoate catalyst to form benzoic acid and water. The toluene solution of benzoic acid is then distilled to separate the benzoic acid from the mixture and return the toluene and other intermediates to the oxidation reaction. This reaction mechanism is radical and also forms some byproducts. Some of these can be recycled back to the reactor to further be oxidized into benzoic acid. The stoichiometry of the toluene oxidation reaction is provided below.

[0019] Toluene Oxidation Reaction E uation

Formula C₇H₈ 0₂ C₇i¾0₂ H₂0

MW 92.14 32.00 122.12 18.02 [0020] Molecular Weights of Reactants and Product

[0021] Side Products. The side products include: benzaldehyde, benzyl alcohol, benzyl benzoate, biphenyl, benzene, acetic acid, 2-methyl biphenyl, benzyl acetate, benzyl formate, acetophenone, acetone, and formic acid.

[0022] Toluene is provided in a reaction vessel in liquid form. The reaction vessel is cylindrical and generally oriented vertically. As seen in Figure 1, loop reactor 10 includes reaction vessel 20 containing liquid hydrocarbon at fluid level 70 (alternate fluid levels shown) and headspace 25. Extending from a bottom portion of reaction vessel 20 is a lower pipe 30 connecting to a circulation pump 40. Extending upward from circulation pump 40 is pipe 50, into which other side pipes may be used to add other reaction constituents such as a catalyst (not shown). An upper return pipe portion 60 completes the flow circuit back to and connects with an upper portion of reaction vessel 20. Assembly 200 in Figs 1 and 3, includes nozzle 110, which provides turbulence to the liquid hydrocarbon, gas inlet 120, gas suction chamber 125, mixing shock zone 140 created by the collision of the free liquid jet 150 (containing mostly unreacted hydrocarbon) with gas 120 at fluid level 70. Much of the oxidation occurs at mixing shock zone 140. Multi-phase injector 180 (shown in Figs 2 and 3) includes diffuser 160 and draft tube 170 which together eject oxygen bubbles 190 together with partially oxidized hydrocarbon. The detail of assembly 200 is shown in Figure 3.

[0023] As shown in Figure 2, detail 100 of loop reactor 10 is shown. In line with upper return pipe portion 60 is nozzle 110. Fresh gas, for example air, oxygen enriched air, or pure oxygen, is injected at injector 120. Injector 120 can also be located in the upper return pipe portion 60. An inert gas, for example a heavy inert gas, preferably xenon, can also be injected via injector 120 into headspace 25 in order to decrease the effective headspace volume by displacing headspace gas (i.e., which contains oxygen) upward away from the surface of the liquid hydrocarbon. Gas recirculation loop 130 connects the headspace 25 with the upper return pipe 60. An atmospheric monitoring device 135 is connected in series with gas recirculation loop 130 to monitor the headspace 25 for an explosive condition. Before headspace 25 reaches an explosive condition, the injection of air, oxygen enriched gas or pure oxygen into the headspace 25 is reduced or stopped to ehminate the explosive condition. A high velocity mixing shock zone 140 (shown in Figs. 2 and 3) is created by a venturi jet mixer (nozzle 110) where a free liquid jet flow of liquid hydrocarbon 150 impacts an incoming gas (oxygen) 120. A sparger 75 may be located at various orientations relative to the hquid jet flow in order to introduce oxygen bubbles into the hquid and provide surface area for mass transfer. For example, as seen in Figure 1, sparger 75 may be attached to pipe 50 for oxygen bubble inlet at that point. In Figure 2, sparger 76 is attached to upper return pipe 60. In Figure 3, sparger 77 enters gas suction chamber 120 so that incoming oxygen bubbles enter inside free hquid jet 150. Spargers 75, 76 and 77 are equivalent components, however in different locations as indicated by different but related reference numerals. Other alternative locations for the sparger are possible. In one embodiment of the reactor, the incoming gas has a superficial velocity in the range of 6-12 cm/sec, preferably 7-11 cm/sec more preferably 8-10 cm/sec with a gas volume turnover of 1500-3500 Am³/h, preferably 2000-3000 AnrVh, more preferably 2200-2800 Am³/h. In one embodiment, the liquid superficial velocity is 7.5 cm/sec at a liquid turnover rate of 2158 AnrVh.

[0024] The pressure created by the jet mixer nozzle 110 circulates the reactor headspace in a range of about 2000-3500, preferably 2200-3200, more preferably 2400-3000 Am³/h, The jet mixer 110 operation generates a venturi effect that delivers a pressure difference between the reactor 20 and the gas chamber 125. The pressure difference is the driving force for the gas recirculation of the reactor headspace.

[0025] The gas flow rate in the gas circulation loop can be varied by increasing or decreasing recirculation liquid flow, the level in the reactor (referenced as dipping height of the jet mixer, as noted in the table below) or via a flow reducing control valve.

[0026] Explosion safety is a key factor in the design of pure-oxygen or oxygen-enriched gas oxidation system. Ideally 100% liquid filled reactor (with no head space) - eliminates headspace explosion potential. The loop recycles the reaction mixture, which eliminates need for propeller (CSTR) - a pump provides pressure to create a mixing shock zone. With the use of a loop and jet, the vacuum caused by the injection can recirculate headspace at a rate of 1000-3000 Am³/ hour. Monitoring speed of the O2 level in the head space is determined by the recirculation rate and limits the reaction rate (i.e., the oxygen flow rate) because a non-explosive mixture must be maintained in the headspace. In other words, the time to achieve a dangerous (explosive) mixture should be greater than the time to sample the headspace - hence the rate Hmiting factor is the headspace recycling rate. Additionally, an inert gas, such as xenon can be injected into the headspace. This heavy inert gas displaces potentially volatile headspace atmosphere and reduces effective headspace, and increases the turnover rate (sampling rate) thereby increasing the overall possible reaction rate.

[0027] Alternately, oxygen enters into the jet mixture nozzle 110 via a sparger which may be located in pipe 50 or directly at the nozzle 110. The sparger may be a porous sintered glass or metal disc to produce oxygen bubbles of a desired size to maximize reaction surface area and mass transfer. The oxygen injection pressure is sufficiently high such that there is always some zone containing 100% pure oxygen. The oxygen injection point is to be located in the mixing shock zone 140 loop reactor's jet mixer or in the upper return pipe portion 60. The mixing chamber has been designed to produce high turbulence, having a Reynolds Number (Re) greater than 2,000,000. [0028] Explosion safety is impacted by the Oxygen bubble size, bubble distribution & potential for coagulation of Oxygen bubbles. Potential ignition of an Oxygen bubble is quenched with the amount of liquid re-circulated. Free and dissolved water provides additional flegmatization effect on an oxygen bubble in liquid toluene. The chemistry & reaction kinetics are driven by oxygen partial pressure, oxygen bubble diameter (surface area available for mass transfer), and the oxygen solubility of toluene. Pressure and temperature have an effect on reaction kinetics.

[0029] The design of the reactor and oxygen injection system requires a consideration of not only safety concerns, but production of oxygen bubbles of proper size to maximize mass transfer, which has been determined to be 2 mm or less, for example 0.1-2 mm, 0.2-1.8 mm, or 0.5-1.5 mm. Such oxygen bubble sizes may be produced by a sparger or by the violence of the mixing shock zone 140 or by diffuser 160. Additionally an oxygen dippipe (not shown) can be used to introduce oxygen into the reaction mixture. The size of the oxygen dippipe will impact the hydraulic profile of the mixing shock zone in the mixing chamber of the jet mixer.

[0030] An embodiment of the invention includes a sparger mounted flush with the wall of the reaction vessel 20, not shown. In a preferred embodiment, the end of the sparger is above the fluid level in the reaction vessel. This design is proposed to eliminate the negative impact on the hydraulic profile of the mixing shock zone in the mixing zone of the jet mixer. The oxygen is injected in the downward flowing liquid.

[0031] In any embodiment, as an alternate to a sparger, an oxygen dippipe can be mounted as an insert into the nozzle 110. An oxygen dippipe could also be mounted as an insert into the upper return pipe portion 60. Such inserts can be of various diameters, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 inches or values in between. Spargers may also have similar diameters or other values.

[0032] The benzoic acid produced by the processes herein can be further processed to afford various dibenzoate compounds. Such dibenzoate compounds may be useful as plasticizers.

[0033] The invention is further illustrated by the following items.

1. A process of liquid phase oxidation of a hydrocarbon compound comprising:

a. providing a reaction system including a reaction vessel, an inlet to permit passage of gas into liquid contents of a reaction vessel, a circulation pump, piping connecting the circulation pump and reaction vessel in series to form a circuit, and a sparger, the reaction vessel containing: i. a liquid phase mixture of the at least one hydrocarbon compound, a homogeneous catalyst and water and

ii. a headspace including gaseous hydrocarbon, nitrogen and water b. injecting oxygen enriched gas through the sparger and inlet into the liquid phase mixture and

c. recycling the liquid phase mixture from a bottom portion of the reaction vessel to a top portion of the reaction vessel by operation of the circulation pump to afford oxidized hydrocarbon, and

d. separating the catalyst from oxidized hydrocarbon with the separator, hereh The process of item 1 , further comprising

d. setting a temperature and a pressure of the contents of the reaction vessel, e. determining an explosion triangle for the set temperature and pressure of the reaction vessel,

f. determining a headspace oxygen level corresponding to a point on the explosion triangle outside the explosion range, and

g. monitoring the oxygen content of the headspace. The process of item 1, further comprising contacting a cobalt-containing catalyst with the liquid phase mixture. The process of item 3, wherein the cobalt-containing catalyst is selected from the group consisting of cobalt octoate and cobalt acetate. The process of item 4 wherein cobalt octoate is present in the organic phase and cobalt acetate is present in the aqueous phase. The process of any preceding item, wherein the temperature is from about 140 to about 200 °C. The process of any preceding item, wherein the temperature is from about 150 to about 190 °C. The process of any preceding item, wherein the temperature is from about 160 to about 180 °C. The process of any preceding item, wherein the temperature is about 170 °C. The process of any preceding item, further comprising injecting an inert gas into the headspace. The process of item 10 wherein the inert gas is xenon. The process of any preceding item, wherein the sparger produces oxygen bubbles having a size of 0.1-2 mm. The process of any preceding item, wherein the oxygen enriched gas is pure oxygen. The process of any preceding item, wherein the hydrocarbon is toluene. The process of any preceding item, wherein the oxidized hydrocarbon is benzoic acid. A plastic mass or plastic article including the benzoic acid produced by any preceding item. A plastic mass or plastic article including a reaction product of the benzoic acid produced by the process of any of items 1-15. A method of plasticizing a plastic mass comprising combining the benzoic acid produced by the process of any of items 1-15. A dibenzoate reaction product of the product of any of items 1-15. 20. A method of plasticizing a plastic mass comprising combining a dibenzoate reaction product of the product of any of items 1-15 with the plastic mass.

[0034] Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and illustrative examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

CLAIMS Claims

1. A process of liquid phase oxidation of a hydrocarbon compound comprising:

a. providing a reaction system including a reaction vessel, an inlet to permit passage of gas into liquid contents of a reaction vessel, a circulation pump, piping connecting the circulation pump and reaction vessel in series to form a circuit, and a sparger, the reaction vessel containing:

i. a liquid phase mixture of the at least one hydrocarbon compound, a

homogeneous catalyst and water and

ii. a headspace including gaseous hydrocarbon, nitrogen and water

b. injecting oxygen enriched gas through the sparger and inlet into the liquid phase mixture and

d. separating the catalyst from oxidized hydrocarbon with the separator, hereh

2. The process of claim 1, further comprising

a. setting a temperature and a pressure of the contents of the reaction vessel, b. determining an explosion triangle for the set temperature and pressure of the reaction vessel,

c. determining a headspace oxygen level corresponding to a point on the explosion

triangle outside the explosion range, and

d. monitoring the oxygen content of the headspace.

3. The process of claim 1, further comprising contacting a cobalt-containing catalyst with the liquid phase mixture.

4. The process of claim 3, wherein the cobalt-containing catalyst is selected from the group consisting of cobalt octoate and cobalt acetate.

5. The process of claim 4 wherein cobalt octoate is present in the organic phase and cobalt acetate is present in the aqueous phase.

6. The process of any preceding claim, wherein the temperature is from about 140 to about 200 °C.

7. The process of any preceding claim, wherein the temperature is from about 150 to about 190 °C.

8. The process of any preceding claim, wherein the temperature is from about 160 to about 180 °C.

9. The process of any preceding claim, wherein the temperature is about 170 °C.

10. The process of any preceding claim, further comprising injecting an inert gas into the

headspace.

11. The process of claim 10 wherein the inert gas is xenon.

12. The process of any preceding claim, wherein the sparger produces oxygen bubbles having a size of 0.1-2 mm.

13. The process of any preceding claim, wherein the oxygen enriched gas is pure oxygen.

14. The process of any preceding claim, wherein the hydrocarbon is toluene.

15. The process of any preceding claim, wherein the oxidized hydrocarbon is benzoic acid.

16. A plastic mass or plastic aiticle including the benzoic acid produced by any preceding claim.

17. A plastic mass or plastic article including a reaction product of the benzoic acid produced by the process of any of claims 1-15.

18. A method of plasticizing a plastic mass comprising combining the benzoic acid produced by the process of any of claims 1-15.

19. A dibenzoate reaction product of the product of any of claims 1-15.

20. A method of plasticizing a plastic mass comprising combining a dibenzoate reaction product of the product of any of claims 1-15 with the plastic mass.