KR970002035B1 - Process for oxidation of hydrocarbon utilizing partitioning oxidizing gas - Google Patents

Abstract

None.

Description

Oxidation of hydrocarbons using the distribution of oxidizing gases

1 is a test apparatus showing the movement of oxygen from an oxygen aqueous solution to a liquid hydrocarbon.

2 is a process flow diagram for large scale oxidation of hydrocarbons.

* Explanation of symbols for main parts of the drawings

A, B: Retaining container R ₁ : Reactor

H: heat exchanger C ₁ , C ₂ , C ₃ , C ₄ : column

The present invention relates to a process for improving the controlled oxidation of hydrocarbons. In particular, the present invention relates to the distribution of oxygen from aqueous solutions to hydrocarbons to be oxidized and the recovery of excess oxygen from oxidized hydrocarbons.

Controlled oxidation of hydrocarbons, in particular aliphatic and cyclic aliphatic hydrocarbons, represents an important industrial method for the preparation of many oxidized organic compounds including alcohols, aldehydes, ketones, carboxylic acids and the like. For example, cyclized hexane is useful as a feedstock to produce various products including cyclohexanol, cyclohexanone, adipic acid, e-hydroxycaproic acid and the like through partial oxidation. Such products can be supplied as intermediates in the manufacture of a wide variety of products such as hexanediol and caprolactam.

Other hydrocarbons are often oxidized in the form of oxidized products, including butane, hexane, cyclohexene, benzene, naphthalene and the like. Oxidation methods involving these and other hydrocarbons are well known to produce a significant portion of the chemicals on the market.

Unfortunately, the oxidation of controlled hydrocarbons, which generally occur at elevated temperatures, represents a severe stability product. Direct introduction of oxygen, either at the same concentration as atmospheric oxygen or higher than atmospheric oxygen, directly into hot, combustible liquids creates the risk of fire and explosion. This is particularly the case when the oxidation reaction takes place in the gas phase or when the apparatus used traps oxygenated hydrocarbon vapors in the reactor head space. In the latter case, air presents a much greater risk than pure air, since the explosive area is actually wider. The fact that highly unstable peroxides and hydroperoxides consisted of a significant portion of oxidation increases the inherent risks in these methods.

In a typical oxidation reaction, air is introduced into the base of the reactor as fine bubbles, and the gap is carefully detected for the presence of unreacted oxygen. In European patent application EP-A-0199 339, pure oxygen is used, and direct initial contact between oxygen and hydrocarbon is blocked by introducing oxygen under the aqueous solution layer in a fine injection form. The hydrocarbon to be oxidized is introduced into a vessel in which oxygen is dissolved above the aqueous solution layer. However, this method, even if the initial contact between oxygen and hydrocarbons is blocked by careful control of pure gaseous oxygen, is still present in the solution vessel, creating a very large risk of explosion.

The present invention relates to the direct introduction of oxidizing gases such as oxygen directly into hydrocarbons by first dissolving the oxidizing gas in water in a separate vessel and then distributing the gas to the hydrocarbon to be oxidized by contact of the aqueous oxygen solution with the liquid hydrocarbon. It has been found that many risks can be excluded. Under these conditions, oxygen is transported to the hydrocarbon under conditions that are substantially free of gaseous oxygen, which greatly increases the stability of the overall oxidation reaction.

Figure 1 shows the experimental setup, which is useful for demonstrating the transfer of oxygen from an aqueous oxygen solution to a liquid hydrocarbon. 2 shows a method of oxidizing a liquid hydrocarbon into oxidized products, which is used to distribute the oxidizing gas between an aqueous solution and the hydrocarbon to be oxidized. In addition, FIG. 2 shows a method for removing the excess oxygen remaining during the oxidation reaction by reverse distribution.

The oxidation of hydrocarbons is well known, and industrial methods have been widely practiced. Hydrocarbons, descriptions of oxidation processes in which catalysts are used and other details are described, for example, in the oxidation of hexanes, Berezin, et. Al., Pergamon Press, New York, ^ⓒ 1966. oxidation reaction Emanuel, Ed, Pergamon Press, the MacMilan Co., New York, ⓒ 1965); And US Patent No. 4,322,558; 3,933,930; 3,923,895; 3,937,735; 3,991,099; 3,681,447; 3,719,706; 3,761,517; 3,869,508; 3,965,164; 4,227,021; 4,263,453; 3,671,588; 3,932,513; 3,948,992; 3,987,115; 4,055,600; 4,098,817; 4,341,907; And 3,946,077 and the like.

In the process of the invention, the oxygen aqueous solution is preferably prepared first in a continuous manner. The oxygen is then transferred or distributed from the aqueous solution to the hydrocarbon to be oxidized, preferably at or below ambient temperature, by countercurrent distribution or apparatus. The dissolved oxygen-containing hydrocarbon is then heated to the temperature necessary for the oxidation reaction and transferred to the reaction vessel. After the reaction is carried out the product is separated from the unreacted hydrocarbon to be recycled. Preferably, most of the water used to provide the necessary oxygen is also recycled.

According to the method of the present invention, under a suitable process temperature and a pressure sufficient to dissolve the required amount of oxygen, the oxygen aqueous solution is prepared by dissolving air, oxygen enriched air, or oxygen in water. At least as a first approximation, it is well known that the solubility of a gas in a liquid is directly proportional to the pressure of the gas. Thus, at 10 bar pressure, it has oxygen solubility in water about 10 times higher than at 1 bar pressure. Thus, the solubility of oxygen at 1 bar pressure and 25 ° C., presented in Gmelin's Handbook of Inorganic Chemistry, Sauerstoff, 3d Ed., P.461, is approximately 0.04 g / l. At 10 bar the solubility will be approximately 0.4 g / l and at a pressure of 100 bar the solubility will be approximately 4 g / l.

As the temperature rises, the oxygen solubility in water decreases. Thus, the solubility of oxygen in air at 50 ° C. is reduced by about 30% from the value at 25 ° C. Thus, even if oxygen is derived from air, oxygen enriched air, or pure air itself, the temperature during the process of dissolving oxygen in water should be kept at the lowest possible value. The water temperature will therefore have to be maintained at ambient temperature, preferably below 70 ° C., more preferably at room temperature (25 ° C.) or below. The term oxygen, discussed below, refers to oxygen in a mixture containing air and oxygen enriched air, oxygen and one or more inert gases under reaction conditions in a pure state.

In order to supply the hydrocarbon with the desired amount of oxygen, approximately 2-10% by weight, the partial pressure of oxygen should be about 5 to about 200 bar, preferably 5 to about 100 bar, more preferably 7 to about 60 bar. The required pressure can be easily calculated or determined experimentally based on the existing process parameters such as the maximum design operating pressure and the desired operating range of the equipment used. The pressure of oxygen depends on the relative amount of water, the number of moving units and the equilibrium of oxygen between the water and the hydrocarbon with respect to the desired oxygen concentration hydrocarbon in the hydrocarbon. Based on a theoretical four stage distribution system and a volume flow rate of water 7.2 times greater than the volume flow rate of cyclized hexane, a partial pressure of about 830 psia will be required to provide approximately 5 mole percent oxygen to the cyclohexane. The necessary pressures for the different operating conditions are given in Table 1.

Dissolving oxygen in water can be carried out in any convenient way. For example, oxygen can be bubbled through water held in a storage tank under pressure. Oxygen can be introduced into the base of the filling tube, preferably with water introduced at the top of the tube, or injected by spraying into a tube filled with oxygen. The use of large volumes of oxygen and water is economical by utilizing a countercurrent dissolution process. Other methods of dissolving oxygen in water will be known to those skilled in the art.

The water used to dissolve oxygen can be fresh water, recycled water, or a combination of both. Preferably, most of the water in the process is recycled. The water may contain dissolved solids or organic substances that do not adversely affect oxygen dissolution or the oxidation reaction to be carried out. Recycled water can also be obtained from a clean back distribution system, which is used to remove unreacted oxygen from the oxidized product.

Basic substances such as alkali metal hydroxides, especially strong bases, are known to slow down the oxidation of hydrocarbons and should be removed. Furthermore, strong basic aqueous solutions can cause precipitation of transition metal catalysts, such as their oxides, hydroxides or hydroxides, and therefore can not only eliminate catalytic activity but also cause potential fouling problems.

Aqueous solutions containing significant amounts of dissolved inorganic salts should be removed when these salts are present in significant concentrations, reducing the solubility of oxygen in the solution. If the recycle material accumulates these substances for a long time in the process, it may be necessary to add a separation step to remove these substances, adjust the amount of recycled water, or periodically rerun the process using fresh water as the source of water. .

Preferably the water used should be neutral or slightly acidic and may contain an effective amount of the specific oxidation catalyst when an oxidation catalyst is required. Oxidation catalysts are well known to those skilled in the art and are generally salts or complexes of metals, especially transition metals or heavy metals such as cobalt, chromium, manganese, vanadium, aluminum, lead, tin and copper and the like. Numerous examples of such catalysts are given in the references cited above. Because many of these catalysts are at least to some extent soluble in water, such water supplied to provide oxygen can also provide a catalyst feed to the hydrocarbons.

Oxygen distribution from the aqueous oxygen solution to the hydrocarbon to be oxidized is carried out in such a way as to maximize the liquid-liquid surface area by contacting the two liquids. Preferably the two liquids are contacted in the filling tube by countercurrent flow at ambient temperature and below. In general, due to the large solubility of oxygen in hydrocarbons, the efficient transfer of the actual amount of oxygen from the water-soluble to the non-aqueous phase occurs easily with the degree of migration limited by the distribution coefficient of oxygen in the two liquids at the contact temperature. Furthermore, the concentration of oxygenated hydrocarbons can be increased by circulating a larger volume of water than cyclohexane. The term substantial amount as used herein relates to a theoretically movable amount wherein at least 10 percent of the substantial part is.

The distribution of oxygen over the hydrocarbon is carried out and then the hydrocarbon is heated to the desired oxidation temperature. When catalysts are utilized in oxidation, the catalysts may be added before or after reaching the desired temperature, or may be partitioned from the aqueous phase into hydrocarbons as set out above.

Unlike the solubility in water, the inherent stability factor in the present invention is the solubility in many hydrocarbons, in particular cyclohexane, which increases with increasing temperature. Thus, the solubility of oxygen in cyclohexane under atmospheric pressure is 12.3, 12.4, and 12.7 (× 10 ⁻⁴ ) mole percent at 283.5 ° K, 297.6 ° K, and 313.1 ° K, respectively. This provides an additional stability factor because solutions saturated with oxygen in hydrocarbons at room temperature can be unsaturated by increasing temperature, so oxygen readily leaks and forms vapors.

The oxidation method itself is general in general. After the oxidation reaction has been carried out, the product is separated and purified in a conventional manner.

Suitable hydrocarbons for the process of the present invention are aliphatic hydrocarbons such as benzene, toluene and other lightweight aromatic hydrocarbons, in particular butane, pentane, hexane, isooctane and the like, more preferably cyclopentane, cyclopentene, cyclopentanol, cyclohexane, cyclohexene And cycloaliphatic, cyclohexanol, methyl-cyclohexane, dimethyl-cyclohexane. Most preferred is cyclohexane.

The invention will now be described with reference to the drawings and embodiments.

This discussion should in no way be construed as limiting the scope of the invention. Useful modifications of the claimed method will be made by those skilled in the art. All such modifications are foreseen within the scope of the present invention.

Example 1

A convenient way of distributing oxygen from aqueous solution to hydrocarbons was determined by the following experiment. Regarding FIG. 1, cyclohexane was introduced into vessel F ₁ and then all the dissolved oxygen was removed with nitrogen gas for 12 hours. Cyclohexane vapor was removed from the nitrogen flow outlet by trap (T ₁ ) and returned to the vessel. The pressure did not increase above atmospheric pressure except for the small amount of back pressure generated by the apparatus itself for 12 hours after the introduction of distilled water into the vessel F ₂ .

During each test, water was drawn from the vessel F ₂ to the holding vessel A by means of a pump and from the holding vessel A to the upper layer of the distribution tube C ₁ via the valve V ₁ . The distribution tube C ₁ was a glass tube 25.0 cm in length and unfilled. At the same time, cyclohexane was drawn into the cyclohexane inlet of the distribution pipe by pump P ₂ through valve V ₂ . Cyclohexane containing molten oxygen was left in the tube with an overflow device (D ₁ ). Through the vertical plane of the 1/8 tube, water entered the tube, descended along the cyclohexane in the form of droplets without touching the tube wall, and then left in the tube through the valve (V ₃ ) into the holding vessel (B). In the holding container B, water was removed by the overflow device D ₂ . The height of the water / cyclohexane interface (I) was adjusted by adjusting the height of (D ₂ ). The flow rates of cyclohexane and water were measured periodically. The vapor spaces of the vessels (A) and (B) were kept to a minimum. All types of water vapor were carefully removed from the tube (C ₁ ). Vessel C received water from which all the released oxygen flowed out. At regular intervals, the oxygen content of the water in vessels (A) and (B) was measured using an Orion O ₂ electrode (Model No. 970800) and Orion Digital Ionalzer (Model No. 501). The data obtained from several tests are summarized in Table 1 below.

The flow rate ratio is based on the volume ratio.

The unit of oxygen partial pressure is psia.

The flow rate unit of water and cyclohexane is ml / min.

All units of oxygen are ppm. The supply amount of O was measured in the container A, and the release amount of O was measured in the container B.

The contact time between falling droplets and the cyclohexane phase, in seconds.

As can be seen in Example 1, even at atmospheric pressure, 26 to about 31% water soluble oxygen can be partitioned into cyclohexane. In particular, this distribution is relatively inefficient and is achieved using unfilled tubes and short contact times. It will be expected that the use of filling or baffle tubes will result in a lot of transport.

2 shows the process flow diagram for large scale oxidation of hydrocarbons such as cyclohexane. The constituent materials are conventional and well known to those skilled in the art. Typically, stainless steel, clad or glass-clad equipment is desirable to minimize corrosion. In particular due to the high pressure used in tubes (C) and (C), high aspect ratios are preferred for process tubes because the minimized diameter provides a high stability limit and at the same time enables economical use of construction materials. In general, all tubes and reactors R will be filled with typical filling materials, ie balls, sheet-shaped braces, spirals, etc., but tray tubes and unfilled tubes can be used in theory.

During operation, water is supplied to the supernatant of the oxygen solution tube C through the valve V under pressure. This water can be fresh water from line L via valve V or can produce partially or completely recycled water as described below. Pure oxygen, oxygen diluted with inert gas, oxygen diluted with air, or oxygen under atmospheric pressure is pressurized by the pump P and supplied to the tube C through the valve V. Both the pressure and flow rate of oxygen can be adjusted by dissolving the desired mole percent oxygen in water. Oxygen loaded water exits the pipe through line (L) and enters distribution pipe (C) through pump (P). The liquid hydrocarbon is pressurized in the pump P and fed to the pipe C through the valve V. Backflow Flow Conditions Backflow conditions are established due to the difference in specific gravity, and lighter oxygen-loaded hydrocarbons are discharged through the conduit line (L), while oxygen-free water is passed through the line (L) below the hydrocarbon / water interface I. Discharged. In the case of hydrocarbons heavier than water, the inlet and outlet points of the various flows will have to be reversed. In the case of hydrocarbons that are solid at ambient temperature, this tube must be heated to a temperature sufficient to keep the hydrocarbons in the liquid state.

In line (L), the oxygen rich hydrocarbons may enter another distribution tube to enrich more oxygen or may be degassed in tube (C), as shown. An important requirement of the present invention is that the system must be maintained at a suitable pressure to capture oxygen in solution without the formation of a vapor phase. For this reason it is wise to bear with a tube (C) which is at a slightly higher pressure than the tube (C). Similarly, the pressure drop occurring in the process line must be taken into account.

It is most preferable that the degasification reaction due to the lack of pressure does not occur, so that the tube (C) becomes an excessive safety structure. All recovered gases are released into the atmosphere, flared or preferably pressurized by pump P and recycled to line C through line L to solution tube C. Oxygen-rich hydrocarbons are metered to the reactor (R) via valve (V). Reactor R is operated at a suitable oxidation temperature, such as 100 ° C to 200 ° C. Heat exchanger (H) is used to provide the necessary heat to initiate the reaction and may provide additional heat or remove heat from the reactor as required by the reaction.

In general, the oxidation reaction is promoted in the presence of a suitable catalyst by an amount of about 0.01 to about 100 ppm. Due to the flexibility of the system, this catalyst can be added at one or more locations. For example, this catalyst can be added to the inlet via lines S and valves V as an aqueous solution or as a melt in a suitable solvent.

Preferably, all solvents used will be one of the reaction products. When cyclohexane is oxidized, you may use cyclohexanol, cyclohexanone, or a mixture of these products as such a solvent. Otherwise, the catalyst may be introduced into line L via line S and valve V prior to the distribution of oxygen from water to hydrocarbon, or via line S and valve V prior to oxidation. It can be added by injecting into line (L).

Generally, the flow of oxidized hydrocarbons contains from 1 to about 15 weight percent, more particularly from about 3 to about 8 weight percent oxygen saturation product. Treatment of oxidized hydrocarbons can be carried out in a variety of ways. For example, in (R), the outlet flow (L) can be delivered to tube (C) after the decomposition of peroxides and hydroperoxides by reaction with caustic agents or by some other suitable method. Otherwise, the oxide may be fractionally distilled prior to or after decomposition of the peroxide and hydroperoxide. In the case of cyclohexane, the hot boiling fraction containing, for example, cyclohexanone and cyclohexanol (both compounds have some solubility in water) is the residue delivered to tube (C), mostly cyclohexane May be removed from the process at this moment.

Another alternative is to treat the (R) effluent oxide in a conventional manner, bypassing completely in tubes (C) and (C). However, all residues, i.e., unreacted oxygen, can be removed by back-distribution in tubes (C) and (C) resulting in greater safety downstream in reactor (R).

Fresh water enters the tube C through the valve V, for example into the tube C via the line L, and finally exits the tube C through the line L. In addition, fresh water is added to both tubes and in each case is discharged through or near the bottom of each tube.

In addition, the water in line (L) may be dissolved oxygen saturated with hydrocarbons; Molten oxygen saturation products; Predominantly mono- and dibasic organic acids; And a minimum amount of catalyst. This water may be recycled to the tube C through the valve V, where this water may comprise, for example, 10-25% or more of the total water in the system. Through proper balance of fresh water inlet valves (V) and (V), the system must quickly equilibrate for the concentration of the various system components in the aqueous stream. A portion of the water soluble stream, for example, may be recovered periodically or continuously in lines (C) or (C) to deoxygenate this drawn stream and send water, which is actually free of hydrocarbons, to tubes C and C. In addition, the water used to remove unreacted oxygen can be degassed in the tube (C) by a decrease in pressure and then used as a source of molten organic acid via line (L).

Claims (19)

A method of partially oxidizing a hydrocarbon with an oxide containing an oxidized hydrocarbon product using an oxygen molecule as an oxidant, comprising: a) preparing an oxygen aqueous solution in a separate vessel; b) contacting the aqueous oxygen solution with the liquid hydrocarbon to be oxidized such that the actual amount of oxygen is transferred from the aqueous phase to the hydrocarbon phase; And c) oxidizing the oxygen-containing hydrocarbon at an elevated temperature. The method of claim 1, wherein the aqueous liquid solution is prepared by dissolving oxygen in water at a pressure of about 5 bar to 200 bar. The method of claim 1 wherein the movement of oxygen occurs in the tube under conditions of backflow. 3. The method of claim 2 wherein the movement of oxygen occurs in the tube under conditions of backflow. The method of claim 1 wherein the oxygen free water formed during step (b) is recycled in step (a). The method of claim 2 wherein the oxygen free water formed during step (b) is recycled in step (a). 4. The method of claim 3 wherein the oxygen free water formed during step (b) is recycled in step (a). 5. The method of claim 4, wherein the oxygen free water formed during step (b) is recycled in step (a). The method of claim 1 wherein step (b) occurs at ambient temperature. 5. The method of claim 4 wherein step (b) occurs at ambient temperature. The method of claim 1 wherein step (b) occurs at a higher temperature than step (a). A method of partially oxidizing a hydrocarbon with an oxide containing an oxidized hydrocarbon product, using an oxygen molecule as an oxidant, comprising: a) preparing an oxygen aqueous solution in a separate vessel; b) contacting the aqueous oxygen solution with the liquid hydrocarbon to be oxidized to transfer the actual amount of oxygen from the aqueous phase to the hydrocarbon phase; And c) oxidizing the oxygen containing hydrocarbon at elevated temperature; And d) partitioning oxygen between the mentioned product and water to remove all unreacted oxygen from the product of step (c) in a countercurrent manner. 13. The method of claim 12, wherein the water mentioned in step (d) is fresh water. 13. The process according to claim 12, wherein the water mentioned in step (d) is process water deoxygenated. 13. The process of claim 12 wherein the oxygen-enriched water produced in step (d) is recycled in step (a). The process of claim 13, wherein the oxygen-enriched water produced in step (d) is recycled in step (a). The method of claim 14, wherein the oxygen-enriched water produced in step (d) is recycled in step (a). 13. The process of claim 12 wherein the peroxide and hydroperoxides contained in the product of step (c) are decomposed before removing the unreacted oxygen of step (d). 13. The peroxide and hydroperoxides contained in the product of step (c) are decomposed and the resulting mixture is separated into hydrocarbon and hydrocarbon oxide parts having only the hydrocarbon part treated according to step (d). How to.

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