WO2019036119A1

WO2019036119A1 - Cyclohexylbenzene hydroperoxidation process and method for operating oxidation reactor

Info

Publication number: WO2019036119A1
Application number: PCT/US2018/039671
Authority: WO
Inventors: Bryan A. Patel; Jorg F.W. WEBER; Seth M. Washburn; Andrew R. Witt; Christopher L. Becker
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2017-08-18
Filing date: 2018-06-27
Publication date: 2019-02-21

Abstract

The present application relates to systems and methods for promoting safe operation of oxidation reactors to convert cyclohexylbenzene into cyclohexylbenzene-hydroperoxide, which may include operating the oxidation reactor so that (i) the electrical conductivity of the liquid-phase material in the reactor is greater than 50pS/m; and/or (ii) the concentration of cyclohexylbenzene in the vapor-phase headspace of the oxidation reactor is less than the lower flammability limit (LFL). Further disclosed herein are systems and methods for promoting safe ramp-up up of oxidation reactors to steady-state conditions.

Description

CYCLOHEXYLBENZENE HYDROPEROXIDATION PROCESS AND METHOD FOR OPERATING OXIDATION REACTOR

INVENTOR(S): Bryan A. PATEL, Jorg F.W. WEBER, Seth M. WASHBURN, Andrew R. WITT, Christopher L. BECKER

CROSS-REFERENCE OF RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S.S.N. 62/547,521, filed August 18, 2017, and is incorporated by reference in its entirety.

FIELD

[0002] This disclosure relates to systems and methods for operating oxidation reactors, particularly for oxidizing cycloalkylaromatic compounds (e.g., cyclohexylbenzene) to hydroperoxides (e.g., cyclohexylbenzene-hydroperoxide).

BACKGROUND

[0003] The production of phenol and/or cyclohexanone from cyclohexylbenzene (CHB) is an emerging technology, of particular interest because of the potential to co-produce cyclohexanone rather than acetone. CHB may be produced, for example, by direct alkylation of benzene with cyclohexene, or as disclosed in US 6,037,513, by contacting benzene with hydrogen in the presence of a catalyst. The CHB may then be oxidized to the corresponding hydroperoxide and the hydroperoxide cleaved to phenol and cyclohexanone using a catalyst. Depending upon need or demand, the phenol and cyclohexanone may each be taken as products, and/or the phenol can be hydrogenated to produce additional cyclohexanone, and/or the cyclohexanone can be dehydrogenated to produce additional phenol. Cyclohexanone is widely used to make caprolactam, which, in turn, is used for making nylon-6, a widely used polymer material. Phenol may be used to make a wide variety of chemical products, including bis-phenol A, polycarbonates, phenolic resins, and the like.

[0004] With respect to oxidation, a CHB-containing liquid and an C -containing gas (such as pure O2, air, and diluted air and O2) may be supplied to an oxidation reactor, where they are allowed to contact each other, such that the CHB is oxidized by O2 molecules either at the gas- liquid interface and/or in the liquid phase. The O2 is typically bubbled through the CHB- containing liquid, enabling absorption of O2 in the liquid and subsequent reaction to cyclohexylbenzene-hydroperoxide (CHB -HP). The unreacted O2 then emerges into the headspace region of the reactor before venting through an effluent line. The headspace will also typically contain low concentrations of CHB and other hydrocarbons in equilibrium, which may constitute a flammable mixture. [0005] As such, systems and methods for promoting safe operation of such oxidation reactors are needed.

SUMMARY

[0006] The present invention provides for systems and methods for promoting safe operation of oxidation reactors.

[0007] In one aspect, the present invention relates to processes for oxidizing CHB in an oxidation reactor to form CHB -HP. The oxidation reactor may be operated such that (i) the liquid electrical conductivity of the liquid mixture in the reactor is greater than 50pS/m; and/or (ii) the concentration of CHB in the vapor-phase headspace of the reactor is less than the lower flammability limit (LFL).

[0008] In other aspects, the present invention relates to processes for ramping up (starting the process from no chemical reaction to a chemical reactor) an oxidation reactor to steady- state. In such case, the oxidation reactor is ramped up under oxidation conditions that include a temperature of less than 90°C. When sufficient CHB-HP is formed in the liquid reaction mixture to meet a liquid electrical conductivity threshold, the oxidation conditions are adjusted to steady-state oxidation conditions.

[0009] Additional features and advantages of the invention will be set forth in the detailed description and claims, as well as the appended drawings. It is to be understood that the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FTG. 1 is a simplified diagram illustrating a side view of operation of an oxidation reactor in accordance with some aspects of the present invention.

[0011] FIG. 2 illustrates the flammability characteristics of neat CHB at 238°C.

[0012] FIG. 3 illustrates the flammability characteristics of CHB at 105-125°C.

[0013] FIG. 4 illustrates liquid electrical conductivity of CHB and CHB/CHB-HP mixtures between 20-100°C.

[0014] FIG. 5 illustrates CHB conversion between 20-100°C.

[0015] FIG. 6 illustrates the liquid electrical conductivity of neat CHB and a mixture of neat CHB supplemented with an anti-static additive between 20-100°C. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] The present invention provides for processes for promoting safe oxidation of cyclohexylbenzene (CHB) to form cyclohexyl-1 -phenyl- 1 -hydroperoxide, otherwise referred to herein as cyclohexylbenzene-hydroperoxide (CHB-HP).

[0017] Such an oxidation reaction (and systems and apparatus for carrying out such a reaction) may, according to some embodiments, form an integral part of a larger overall process for the co-production of cyclohexanone and phenol from CHB produced by the alkylation or hydroalkylation of benzene. Such processes, in general, include the alkylation or hydroalkylation of benzene to form CHB, which in turn is oxidized to CHB-HP according to the example reaction detailed herein. The CHB-HP is then cleaved (e.g., using an acid catalyst) to form the desired cyclohexanone and phenol products. These antecedent and subsequent processes surrounding the oxidation reaction in such embodiments are described in greater detail following the below description of the oxidation reaction.

Oxidation of CHB

[0018] In the oxidation of CHB, CHB is converted to CHB-HP according to the following reaction:

[0019] The reaction is preferably carried out as a gas-liquid reaction, with the CHB in the liquid phase being contacted by an 02-containing gas. This may be accomplished, e.g., by passing the 02-containing gas through the liquid-phase reaction medium comprising the CHB (for instance, as in a bubble column reactor).

[0020] An oxidation catalyst is preferably supplied to the liquid phase reaction medium. The oxidation catalyst may be an N-hydroxy-substituted cyclic imide, such as any of the oxidation catalysts described in Paragraphs [0050] - [0054] of WO 2014/137623. A particularly suitable catalyst is N-hydroxyphthalimide (NHPI).

[0021] Oxidation further includes contacting the liquid-phase reaction medium 120 with an 02-containing gas, such as air and various derivatives of air, in the reactor 110. For example, a stream of pure O2, O2 diluted by inert gas such as N₂, pure air, or other 02-containing mixtures can be introduced into the reactor as gas inlet stream 112. The gas passes into the liquid-phase reaction medium 120, whereupon it will bubble up 122 through the reaction medium 120 and into vapor-phase headspace 130 of the reactor. Vapor-phase headspace 130 may include a mixture of unreacted O2, CHB and/or CHB-HP. The gaseous mixture may be drawn off as gas outlet stream 113. As O2 contacts liquid-phase reaction medium 120, the desired CHB-HP is formed in reaction medium 120, and may thereafter be drawn off from the reactor 110, e.g., via liquid outlet stream 114. Liquid outlet stream 114 may be drawn from the reactor 110 at any height along the reactor. The locations of such streams shown in FIG. 1 are not intended to be limiting. Optionally, the liquid feed may be provided to the oxidation reactor through a liquid distributor (not shown).

[0022] To facilitate control of the temperature inside reactor 110, a portion of liquid outlet stream 114 and/or gas outlet stream 113 may be recycled to the reactor 110 via heat exchanger 116, alone or with fresh CHB stream 115.

[0023] To promote safe operation, the oxidation reactor may be operated in the absence of an ignition source. Additionally or alternatively, the concentration of CHB in the vapor-phase headspace of the oxidation reactor may be maintained at less than the lower flammable limit (LFL). The LFL is the lowest concentration of particular vapor component(s) (e.g., CHB) in air that can propagate a flame. Below the LFL, the air/CHB mixture is "fuel-lean".

[0024] In any embodiment, the oxidation reactor may be operated such that the concentration of CHB in the vapor-phase headspace of the oxidation reactor is greater than the upper flammable limit (UFL). The UFL is the highest concentration of a particular vapor component in air that is capable of flame propagation. Above the UFL, the mixture is "fuel- rich". LFL and UFL may be measured according to ASTM E681.

[0025] In any embodiment, the oxidation reactor may be operated such that the amount of O2 in the vapor-phase headspace is less than the limiting oxygen concentration (LOC). The LOC is the lowest O2 concentration for which flame propagation is possible for a particular mixture of O2 and flammable component(s). The LOC may be measured according to ASTM E2079.

[0026] The LOC within the oxidation reactor headspace may be controlled, for example, through O2 consumption during the oxidation reaction chemistry. For example, as the air bubbles rise through the reactor, O2 is transferred to the liquid reaction mixture and reacts, reducing the O2 concentration below the LOC. As such, it may be preferred to size the O2 delivery system to ensure sufficient O2 is consumed in the reactor. Additionally or alternatively, control systems may be used to maintain the reaction at the necessary conditions to ensure effective O2 consumption. Such controls may, for example, modulate reaction processes through control of temperature and NHPI concentration. In any embodiment, the concentration of O2 in the headspace can be controlled through adjustment of other components in the headspace. For example, inert gas(es) (e.g., nitrogen) may be supplied to the headspace to lower the O2 concentration.

[0027] That said, even O2 distribution and liquid mixing across the reactor cross-section is highly desired to maintain the O2 concentration below the LOC. In addition, the reaction kinetics for the desired reaction are relatively slow. Therefore, the under-utilization of O2 within the C -containing gas could lead to significant oxygen bypass as the C -containing gas is passed through the liquid-phase reaction medium. This could lead to build-up in O2 concentration in the vapor phase headspace, causing a combustion risk.

[0028] Generally speaking, the LFL, UFL and LOC vary with the oxidation reactor conditions (e.g., temperature, pressure, etc.).

[0029] For example, the diagram in Fig. 2 illustrates the flammability characteristics of neat CHB (238°C, 0 psig), which are conditions at which the CHB is sufficiently volatile to produce fuel-rich concentrations in the vapor-phase headspace. The flammability measurements for CHB were conducted according to ASTM E681 , producing data on the LFL (0.5 vol%) and UFL (5.4 vol%). The LOC (9 vol%) was measured according to ASTM E2079.

[0030] FIG. 3 shows a flammability diagram for typical CHB oxidation reactor process conditions (105-125°C, 0 psig). The flammability diagram of FIG. 3 is only possible above the flash point of CHB (97°C). The LFL (1 vol%) was measured according to ASTM E681. The LOC (10.5 vol%) was measured according to ASTM E2079. The UFL is not clearly defined because sufficiently high fuel concentrations in the vapor cannot be obtained in this temperature range.

[0031] In view of the foregoing, it may be preferable to operate at an O2 concentration below the LOC in the vapor-phase headspace (i.e., < 10.5 vol%). It may also be preferable to operate at an O2 concentration with a buffer margin below the LOC, such as < 8.5 vol%, or < 8 vol%, or < 7 vol% or < 6 vol%. In some cases, it may not be preferred to operate significantly below the LOC (e.g., < 5 vol%) because the oxidation reaction chemistry will produce unfavorable reaction byproducts and a lower yield of desired reaction products. In any embodiment, the preferred O2 concentration in the vapor-phase headspace is 5-8 vol%.

[0032] Flammability data for typical oxidation reactor process conditions (85-125 °C, 0-10 psig) is presented in Table 1 below. Because the flash point of CHB is 97°C, the mixture will not be flammable at 95°C (i.e., there is insufficient fuel in the vapor-phase headspace). However, given uncertainty in flash point measurements, a flash point of 90°C may be considered a practical lower bound.

Table 1

[0033] In oxidation reactors, one possible ignition source is static accumulation of charge in the liquid-phase reaction medium. Neat liquid hydrocarbons (e.g., neat CHB) have low electrical conductivity and may build up sufficient charge to lead to a discharge, which could ignite a flammable mixture. To mitigate charge buildup, it is preferred to maintain the liquid electrical conductivity of the liquid-phase reaction medium above a minimum threshold, such that it is not considered a "static accumulator" or "non-conductive" liquid. Electrical conductivity may be measured according to ASTM D2624. In any embodiment, the liquid electrical conductivity of the liquid-phase reaction medium is maintained above 50 picosiemens/meter (pS/m), or >100 pS/m, or >500 pS/m; or within a range from 50, or 100, or 500 pS/m to 1000, or 1500, or 2000, or 5000 pS/m.

[0034] The liquid electrical conductivity may be increased through conversion of CHB to a threshold concentration of CHB-HP. For example, FIG. 4 illustrates electrical conductivity at varying temperatures for neat CHB and CHB-HP/CHB mixtures. As shown, higher concentrations of CHB-HP lead to higher electrical conductivity. As such, it may be preferable to operate the oxidation reactor under conditions in which the liquid-phase reaction medium contains > 4 wt%, or > 8 wt%, or > 12 wt%, or > 16 wt% of CHB-HP, based upon the total weight of the liquid-phase reaction medium. More specifically, a mixture of 8 wt% CHB-HP in CHB has a conductivity of -80 pS/m at 20 °C, well below process temperatures. At process temperatures > 80°C, such a mixture has a conductivity >300 pS/m; or within a range from 200, or 300 pS/m to 500, or 1000 pS/m.

[0035] Additionally or alternatively, the liquid electrical conductivity may be increased via addition of an anti-static additive. For example, FIG. 6 illustrates electrical conductivity at varying temperatures for neat CHB and a mixture of neat CHB supplemented with 1 wppm of Stadis™ 450, an anti-static additive commercially available from Innospec Inc. As shown, the addition of the anti-static additive lead to higher electrical conductivity. As such, it may be preferable to operate the oxidation reactor under conditions in which the liquid-phase reaction medium contains > 0.1 wppm, or > 1 wppm, or > 10 wppm of anti-static additive, based upon the total weight of the liquid-phase reaction medium. More specifically, a mixture of CHB containing 1 wppm of Stadis™ 450 has a conductivity of 400 pS/m at 20°C, well below process temperatures. At process temperatures > 80°C, such a mixture has a conductivity >1000 pS/m.

[0036] In view of the foregoing, safe operation of the oxidation reactor may include one or more of the following: (i) low O2 concentration in the vapor-phase headspace (e.g., < 10.5 vol%); (ii) high liquid electrical conductivity in the liquid-phase reaction mixture (e.g., > 50 pS/m); and/or (iii) low CHB concentration in the vapor-phase headspace.

[0037] The reactor may be sized to ensure sufficient O2 is consumed in the reactor to achieve condition (i). Conditions (ii) and (iii) are primarily a function of reactor composition and temperature. For example, referring to FIG. 5, when a CHB oxidation reactor is operated below a temperature of 90°C (shown as a vertical dashed line, which is the effective lower bound of the flash point of CHB), the amount of CHB in the vapor-phase headspace is in the "fuel-lean" region. The diagonal dotted line shows the 50 pS/m liquid conductivity curve above which the liquid is conductive enough to avoid static build-up. As such, an oxidation reactor operating at any set of conditions in zone 500 will satisfy conditions (ii) and (iii). In zone 510, only condition (ii) is satisfied. In zone 520, only condition (iii) is satisfied. In zone 530, neither conditions (ii) or (iii) are satisfied.

[0038] In any embodiment, start-up of the oxidation reactor is conducted at a temperature of less than 90°C (e.g., 80-90°C) until there is sufficient build-up of CHB -HP in the liquid- phase reaction medium to raise the electrical conductivity above 50 pS/m. At this point, the reactor operating conditions may be adjusted to steady-state conditions (e.g., a temperature of 95-125°C). Oxidation reactor operating conditions for conversion of CHB to CHB-HP are further described in US 9,238,605, which is hereby incorporated by reference.

[0039] Reactor temperature may be controlled through a heat exchanger (i.e., cooler) operating external to the reactor in which reactor effluent is recycled to the reactor through the cooler and remixed to remove heat from the system. Variation in cooling water flowrate can be used to control reactor operating temperature.

[0040] In any embodiment, the temperature of the liquid-phase reaction medium, the electrical conductivity of the liquid-phase reaction medium, the concentration of cyclohexylbenzene in the vapor-phase headspace, and/or the concentration of O2 in the vapor- phase headspace may be monitored offline (e.g., sample-based testing) and/or real-time. Various detection and monitoring systems and methods are known in the art for this purpose. Supply of CHB to Oxidation Reaction

[0041] The CHB supplied to the oxidation step can be produced and/or recycled as part of an integrated process for producing phenol and cyclohexanone from benzene. In such an integrated process, benzene is initially converted to CHB by any conventional technique, including oxidative coupling of benzene to make biphenyl followed by hydrogenation of the biphenyl. However, in practice, the CHB is desirably produced by contacting benzene with hydrogen under hydroalkylation conditions in the presence of a hydroalkylation catalyst whereby benzene

[0042] Alternatively, CHB can be produced by direct alkylation of benzene with cyclohexene in the presence of a solid-acid catalyst such as molecular sieves in the MCM-22 family according to the following reaction:

[0043] US 6,730,625 and US 7,579,511, WO 2009/131769, and WO 2009/128984 disclose processes for producing CHB by reacting benzene with hydrogen in the presence of a hydroalkylation catalyst, the contents of all of which are incorporated herein by reference in their entirety.

[0044] The catalyst employed in the hydroalkylation reaction is a bifunctional catalyst comprising a molecular sieve, such as one of the MCM-22 type described above and a hydrogenation metal.

[0045] Any known hydrogenation metal may be employed in the hydroalkylation catalyst, specific, non-limiting, suitable examples of which include Pd, Pt, Rh, Ru, Ir, Ni, Zn, Sn, Co, with Pd being particularly advantageous. Desirably, the amount of hydrogenation metal present in the catalyst is from 0.05 wt% to 10.0 wt%, such as from 0.10 wt% and 5.0 wt%, of the total weight of the catalyst.

[0046] In addition to the molecular sieve and the hydrogenation metal, the hydroalkylation catalyst may comprise one or more optional inorganic oxide support materials and/or binders. Suitable inorganic oxide support material(s) include, but are not limited to, clay, non-metal oxides, and/or metal oxides. Specific, non-limiting examples of such support materials include: S1O2, AI2O3, ZrC , Y2O3, Gd203, SnO, SnC , and mixtures, combinations and complexes thereof.

[0047] The effluent from the hydroalkylation reaction (hydroalkylation reaction product mixture) or from the alkylation reaction (alkylation reaction product mixture) may contain some polyalkylated benzenes, such as dicyclohexylbenzenes (DiCHB), tricyclohexylbenzenes (TriCHB), methylcyclopentylbenzene, unreacted benzene, cyclohexane, bicyclohexane, biphenyl, and other contaminants. Thus, typically, after the reaction, the hydroalkylation reaction product mixture is separated by distillation to obtain a C6 fraction containing benzene, cyclohexane, a C12 fraction containing CHB and methylcyclopentylbenzene, and a heavies fraction containing, e.g., CI 8s such as DiCHBs and C24s such as TriCHBs. The unreacted benzene may be recovered by distillation and recycled to the hydroalkylation or alkylation reactor. The cyclohexane may be sent to a dehydrogenation reactor, with or without some of the residual benzene, and with or without co-fed hydrogen, where it is converted to benzene and hydrogen, which can be recycled to the hydroalkylation/alkylation step.

[0048] Depending on the quantity of the heavies (liquid, or fraction that has a higher boiling point than the fraction being removed) fraction, it may be desirable to either (a) transalkylate the CI 8s such as DiCHB and C24s such as TriCHB with additional benzene, or (b) dealkylate the CI 8s and C24s to maximize the production of the desired monoalkylated species.

[0049] Transalkylation with additional benzene is desirably effected in a transalkylation reactor, which is separate from the hydroalkylation reactor, over a suitable transalkylation catalyst, such as a molecular sieve of the MCM-22 type, zeolite beta, MCM-68 (see US 6,049,018), zeolite Y, zeolite USY, and mordenite. The transalkylation reaction is desirably conducted under at least partially liquid phase conditions, which suitably include a temperature in the range from 100°C to 300°C, a pressure in the range from 800 kPa to 3500 kPa, a weight hourly space velocity from 1 hr¹ to 10 hr¹ on total feed, and a benzene/dicyclohexylbenzene weight ratio in a range from 1 : 1 to 5 : 1. [0050] Dealkylation is also desirably effected in a reactor separate from the hydroalkylation reactor, such as a reactive distillation unit, at a temperature of 150°C to 500°C and a pressure in a range from 15 to 500 psig (200 to 3550 kPa) over an acid catalyst such as an aluminosilicate, an aluminophosphate, a silicoaluminophosphate, amorphous silica- alumina, an acidic clay, a mixed metal oxide, such as WOx/ZrC , phosphoric acid, sulfated zirconia and mixtures thereof. Desirably, the acid catalyst includes at least one aluminosilicate, aluminophosphate or silicoaluminophosphate of the FAU, AEL, AFI and MWW family. Unlike transalkylation, dealkylation can be conducted in the absence of added benzene, although it may be desirable to add benzene to the dealkylation reaction to reduce coke formation. In this case, the weight ratio of benzene to poly- alkylated aromatic compounds in the feed to the dealkylation reaction can be from 0 to 0.9, such as from 0.01 to 0.5. Similarly, although the dealkylation reaction can be conducted in the absence of added hydrogen, hydrogen is desirably introduced into the dealkylation reactor to assist in coke reduction. Suitable hydrogen addition rates are such that the molar ratio of hydrogen to poly-alkylated aromatic compound in the total feed to the dealkylation reactor can be from 0.01 to 10.

[0051] The CHB freshly produced and/or recycled may be purified before being fed to the oxidation step to remove at least a portion of, among others, methylcyclopentylbenzene, olefins, phenol, acid, and the like. Such purification may include, e.g., distillation, hydrogenation, caustic wash, and the like.

Cleavage of CHB-HP Resulting from Oxidation Reaction

[0052] In any embodiment, at least a portion of the cyclohexyl-1 -phenyl- 1 -hydroperoxide decomposes in the presence of an acid catalyst in high selectivity to cyclohexanone and phenol according to the following desired cleavage reaction:

[0053] The cleavage product mixture may comprise the acid catalyst, phenol, cyclohexanone, CHB, and contaminants.

[0054] The acid catalyst can be at least partially soluble in the cleavage reaction mixture, is stable at a temperature of at least 185°C and has a lower volatility (higher normal boiling point) than CHB. Acid catalysts preferably include, but are not limited to, Bronsted acids, Lewis acids, sulfonic acids, perchloric acid, phosphoric acid, hydrochloric acid, p-toluene sulfonic acid, aluminum chloride, oleum, sulfur trioxide, ferric chloride, boron trifluoride, sulfur dioxide, sulfur trioxide, and solid acid catalysts such as zeolites. Sulfuric acid and solid acids are preferred acid catalysts.

[0055] The cleavage reaction can take place in a cleavage reactor in direct or indirect fluid communication with the oxidation reactor or the oxidation reactor system. The cleavage reactor can be operable to transport a portion of the contents through a cooling device and return the cooled portion to the cleavage reactor, thereby managing the exothermicity of the cleavage reaction. Alternatively, the reactor may be operated adiabatically. Cooling coils operating within the cleavage reactor(s) can be used to at least a part of the heat generated. Separation and Purification

[0056] The cleavage product mixture may comprise one or more contaminants. In embodiments disclosed herein, the processes further comprise contacting at least a portion of a contaminant with an acidic material to convert at least a portion of the contaminant to a converted contaminant, thereby producing a modified product mixture. Detailed description of the contaminant treatment process can be found, e.g., in WO 2012/036822A1, the relevant content of which is incorporated herein by reference in its entirety.

[0057] At least a portion of the cleavage product mixture may be subjected to a neutralization reaction. Where a liquid acid such as sulfuric acid is used as the cleavage catalyst, it is highly desirable that the cleavage reaction product mixture is neutralized by a base, such as an organic amine (e.g., methylamine, ethylamine, diamines such as methylenediamine, propylene diamine, butylene diamine, pentylene diamine, hexylene diamine, and the like) before the mixture is subjected to separation to prevent equipment corrosion by the acid. Desirably, the thus formed amine sulfate salt has a boiling point higher than that of CHB.

[0058] The neutralized cleavage reaction product mixture can then be separated by methods such as distillation. In one example, in a first fractionation column after the cleavage reactor, a heavies fraction comprising the amine salt is obtained at the bottom of the column, a side fraction comprising CHB is obtained in the middle section, and an upper fraction comprising cyclohexanone, phenol, methylcyclopentanone, and water is obtained.

[0059] The separated CHB fraction can then be treated and/or purified before being delivered to the oxidizing step. Since the CHB separated from the cleavage product mixture may contain phenol and/or olefins such as CHB, the material may be subjected to treatment with an aqueous composition comprising a base as described above for the second fraction of the oxidation product mixture and/or a hydrogenation step as disclosed in, for example, WO 2011/100013A1, the entire contents of which are incorporated herein by reference.

[0060] In one example, the fraction comprising phenol, cyclohexanone, and water can be further separated by simple distillation to obtain an upper fraction comprising primarily cyclohexanone and methylcyclopentanone and a lower stream comprising primarily phenol, and some cyclohexanone. Cyclohexanone cannot be completely separated form phenol without using an extractive solvent due to an azeotrope formed between these two. Thus, the upper fraction can be further distillated in a separate column to obtain a pure cyclohexanone product in the vicinity of the bottom and an impurity fraction in the vicinity of the top comprising primarily methylcyclopentanone, which can be further purified, if needed, and then used as a useful industrial material.

Uses of Cyclohexanone and Phenol

[0061] The cyclohexanone produced through the processes disclosed herein may be used, for example, as an industrial solvent, as an activator in oxidation reactions and in the production of adipic acid, cyclohexanone resins, cyclohexanone oxime, caprolactam, and nylons, such as nylon-6 and nylon-6,6.

[0062] The phenol produced through the processes disclosed herein may be used, for example, to produce phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and/or plasticizers.

Claims

1. A process comprising:

(a) providing a liquid feed comprising cyclohexylbenzene to an oxidation reactor, thereby forming a liquid-phase reaction medium and a vapor-phase headspace in the oxidation reactor;

(b) contacting the liquid-phase reaction medium with an oxygen-containing gas under oxidation conditions to form cyclohexylbenzene-hydroperoxide in the liquid-phase reaction medium; and

(c) operating the oxidation reactor such that at least one of the following conditions is met:

(i) the liquid electrical conductivity of the liquid-phase reaction medium is greater than 50pS/m; and/or

(ii) the concentration of cyclohexylbenzene in the vapor-phase headspace is less than the lower flammability limit (LFL).

2. The process of claim 1, wherein the contacting comprises bubbling the oxygen- containing gas through the liquid-phase reaction medium.

3. The process of claim 2, wherein both conditions (i) and (ii) are met.

4. The process of any one of claims 1 -3 , wherein the concentration of oxygen in the vapor- phase headspace is less than a limiting oxygen concentration (LOC).

5. The process of claim 4, wherein the LOC is 10.5 vol%.

6. The process of claim 4 or claim 5, wherein the LOC is between 5 to 8 vol%.

7. The process of any one of claims 4-6, wherein at least a portion of the oxygen- containing gas is vented from the vapor-phase headspace.

8. The process of any one of claims 4-7, wherein an inert gas is introduced into the vapor- phase headspace to maintain the concentration of oxygen in the vapor-phase headspace below the LOC.

9. The process of claim 8, wherein the inert gas is nitrogen.

10. The process of any one of claims 1-9, wherein at least one of the temperature of the liquid-phase reaction medium, the liquid electrical conductivity of the liquid-phase reaction medium, the concentration of cyclohexylbenzene in the vapor-phase headspace, and the concentration of oxygen in the vapor-phase headspace are monitored real-time.

11. The process of any one of claims 1-10, wherein the temperature of the oxidation reactor is adjusted to achieve one or more of the conditions (i) and (ii).

12. The process of any one of claims 1-11, wherein the temperature of the oxidation reactor is controlled by recycling at least a portion of the liquid-phase reaction medium through a heat exchanger.

13. The process of any one of claims 1-12, wherein the oxidation conditions include a temperature of less than 90°C.

14. The process of any one of claims 1-12, wherein the oxidation conditions include a temperature between 85-125°C.

15. The process of any one of claims 1-12, wherein the oxidation conditions include a temperature between 105-125°C.

16. The process of any one of claims 1-15, wherein the liquid electrical conductivity of the liquid-phase reaction medium is maintained greater than 50pS/m by controlling the amount of cyclohexylbenzene -hydroperoxide in the liquid-phase reaction medium.

17. The process of any one of claims 1-16, wherein the liquid-phase reaction medium contains greater than 4 wt% of cyclohexylbenzene-hydroperoxide, based upon the weight of the liquid-phase reaction medium.

18. The process of any one of claims 1-17, wherein the liquid-phase reaction medium contains greater than 0.1 wppm of an anti-static additive, based upon the weight of the liquid-phase reaction medium.

19. The process of any one of claims 1-18, wherein the LFL is 0.25 vol %.

20. A process for ramping up an oxidation reactor to steady-state, the process comprising:

(b) contacting the liquid-phase reaction medium with an oxygen-containing gas under oxidation conditions that include a temperature of less than 90°C to form cyclohexylbenzene-hydroperoxide, wherein at least a portion of the cyclohexylbenzene-hydroperoxide accumulates in the liquid-phase reaction medium;

(c) monitoring the liquid-phase reaction medium until a liquid electrical conductivity threshold is met; and

(d) adjusting the oxidation conditions to steady-state oxidation conditions after the liquid electrical conductivity threshold is met.

21. The process of claim 20, wherein the liquid electrical conductivity threshold is 50pS/m or greater.

22. The process of claim 20 or claim 21 , wherein the liquid electrical conductivity threshold is met by increasing the concentration of cyclohexylbenzene-hydroperoxide in the liquid phase reaction medium.

23. The process of any one of claims 20-22, wherein the concentration of oxygen in the vapor-phase headspace is less than 10.5 vol%. The process of any one of claims 19-23, wherein the steady-state oxidation conditions include a temperature between 105-125°C.