SE504578C2 - Tubular static mixer and its use in a process for producing hydrogen peroxide by the anthraquinone process - Google Patents

Abstract

The invention relates to a process for the production ofhydrogen peroxide by the anthraquinone process. A reaction mixture into which there are fed hydrogen or a hydrogencontaining gas and a working solution, i.e. an anthraquinone derivative in an organic solvent, is circulated via a tubular static mixing zone (9) which is continuous or comprises several parts, in order to hydrogenate the anthraquinone derivative in the presence of a solid catalyst, and by removing hydrogenated working solution (13) and gas (11) from the circulating reaction mixture (8). According to the invention, the reaction mixture (14) is circulated (8) via a catalyst-coated static mixing zone (9), where it is simultaneously both mixed and catalyzed.

Description

15 20 25 30 504 578 2 OH O R R ÛÛQ + 02 ___) ÛÛÛ + Hzoz.

OH 0 The working solution containing hydrogen peroxide is fed to the extraction step, in which the hydrogen peroxide is caused by extraction to pass from the working solution to an aqueous solution.

The extracted working solution is dried by removing excess water and recycled to the beginning of the cyclic process, i.e. to hydration. The aqueous solution of hydrogen peroxide obtained by extraction is purified and concentrated.

The hydrogenation described above is a demanding step in the anthraquinone process. High activity and high selectivity are required by the hydrogenation catalyst. The conversion and selectivity of the reaction in the hydrogenation step depend on the partial pressure of hydrogen, the temperature, the concentrations of the reactants, the catalyst and the flow conditions of the reaction apparatus. Secondary reactions can lower the quantity of the anthraquinone derivatives that form hydrogen peroxide. Both suspension reactors and fixed bed reaction devices have been used for the hydrogenation.

The suspended catalysts used have included porous so-called palladium black, palladium absorbed in a support (eg alumina, activated carbon) and Raney nickel. The porous catalyst is suspended and the hydrogen is dispersed in the working solution in, e.g. a mixing tank reactor or a tubular reactor. In a tubular reactor, the mixing is accomplished by the high linear velocity of the working solution. Typically, linear velocities are above 3 m / s and below 10 m / s in an open tube (U.S. Patent 4,428,923). Mixing has also been improved by the use as a reactor tube of an alternating converging and expanding tube (U.S. Patent 3,423,176, Kabisch et al.).

In addition, FI patent application 864 971 discloses a process of the type mentioned in the preamble, in which a reaction mixture containing hydrogen, working solution and a solid suspended catalyst is circulated in a tubular reactor system equipped with a static mixer. , which is continuous or composed of several parts. The pressure prevailing in the pipe system is below 15 bar and the temperature below 100 ° C. In this process, the working solution is circulated in the tubular reaction system at a flow rate lower than špm / s.

The contact and contact periods of the catalyst, working solution and hydrogen are important for the hydrogenation reaction.

By using a stationary solid catalyst in the hydrogenation, the contact period in the catalyst reaction can be shortened, thereby reducing the extent of secondary reactions. The absence of the expensive filtration step is a significant advantage of using a fixed catalyst bed instead of a suspended catalyst. Filtration can also be problematic technically, since the catalyst particles are small.

A suspended catalyst is left partially unused in the hydrogenation reaction, since it is in a hydrogen-free part of the process cycle for a large part of the time, e.g. in the circulation tank, or it can stick to the process cycle. A suspended catalyst is also more sensitive to sintering and mechanical abrasion.

In fixed bed reactors, carrier pellets and so-called honeycomb catalysts have been used (ßerglin et al., U.S. Patent 4,552,748). The support used has usually been active alumina, but other porous supports having a large specific surface area can also be used, e.g. Soy or activated carbon. A precious metal, usually palladium, has been absorbed as the active ingredient in the carrier. Only some kind of post-filtration for the separation, from the working solution, of particles removed from the bed is used in the fixed bed reactor before the oxidation step.

In fixed bed reactors, pellets (diameter usually 0.2 - 10 mm) arranged between screen cloths or nets are usually used. In pellets of this size, the transfer of material into and out of the deepest pores is slow, for which reason the active metal in the inner parts of these pellets remains unused in the reaction. Likewise, the pressure loss increases to a high level and channeling of the flows occurs in these freely packed catalyst beds. The reduction gas also tends to separate in the form of a separate phase, whereupon the hydrogenation rate decreases. Particular attention must be paid so that no catalytic toxins will pass into the working solution or into the reducing gas.

The s.k. The honeycomb catalyst is made of a cellular support structure that has parallel channels. The porous support is fixed in the form of a thin layer on the support structure and in addition a precious metal is absorbed therein. A reactor operating according to a principle such as this has the disadvantage of poor mixing of the hydrogen with the working solution and possible separation of the gas bubbles in the form of its own phase. Heat transfer from the inner parts of the honeycomb material remains poor, in which case the temperature therein may rise too high, a situation which increases the amount of undesirable by-products.

One step that limits hydrogenation in fixed bed reactors is the passage of hydrogen from a gas bubble into the working solution. The extent of the passage of hydrogen depends on the size of the hydrogen bubbles in the working solution. The smaller the bubbles in which the hydrogen is in the solution, the larger the total surface area at the interface between the working solution and the gas phase. The mixing of hydrogen with the working solution has been improved by using static mixers at a location before the fixed bed reactor (U.S. Patent 4,428,922). In this way, the hydrogen is in small bubbles in the working solution when it enters the reactor, but as a result of the channeling in the reactor, the distribution of the gas is weakened. 504 578 A premix reactor in which the working solution is saturated with respect to hydrogen has also been used at a site before the hydrogenation (U.S. Patent 2,837,411). The object of the present invention is thus to provide a method and an apparatus for producing hydrogen peroxide by the anthraquinone process, in which the disadvantages of previous methods and devices have been eliminated. The main features of the invention are defined in the appended claims.

Thus, in the process of the invention, an reaction mixture containing hydrogen or a hydrogen-containing gas and the working solution is circulated in a constant diameter tubular reactor system or alternating converging and expanding, which is installed horizontally or vertically and is equipped with a static mixer, which is continuous or composed of several parts, and is coated with a catalytic substance, the reaction mixture being simultaneously mixed and catalyzed in the mixer. The tubular reactor can be easily dimensioned to be so long that hydrogen has time to react before it reaches the end of the tubular reactor.

In this way, reducing gas does not have to be circulated in the reactor.

The static mixer according to the invention comprises a support structure of a metallic, ceramic, polymeric or other corresponding material, on the surface of which a porous support is fixed.

The carrier contains e.g. alumina, SiO 2, silicates or activated carbon. A metal, active in hydrogenation, e.g. palladium, platinum, rhodium, nickel or a mixture thereof, have been absorbed into the support.

In the reactor according to the invention a sufficient transfer of material between the gas and the liquid is achieved and a sufficient transfer of heat from the reactor mixture to the pipe wall by means of static mixers, which have been described in the following publications, for example: Chem.-Ing.- Tech. 52 (1980), 4, p. 285- 291; Chem. Eng. Prog. 82 (July 1986), 7, p. 42-48 and 20 (May-June 1986), 3, p. 147-154; Perry, R.H. and Chilton, C. H., Chemical Engineer's Handbook, 5, New York: McGraw-Hill (1973) Section 19, p. 22. Axial mixing is also minimized and the temperature and concentration profiles in the cross-sectional area of the pipe are made equal.

The reaction occurs in a thin catalyst layer of 5-300 μm on the surface of the mixer. Because the layer is thin, the proportion of yield-lowering secondary reactions will remain small, because the residence times of reagents and reaction products in the pores are short. Likewise, the catalytically active metal will be used effectively in the thin catalyst layer. Due to this, the catalyst layer according to the invention is more advantageous than a fixed bed of pellets.

In contrast to the honeycomb reactor according to US patent 4,552,748, in which the catalyst pieces form mutually parallel, equally long channels without any mixing effect, the structures according to the invention serve not only as fixing surfaces for the catalyst but also as mixers, the static mixer having catalyst coated flow pistons with each other in different directions, which effectively distribute the flow over the entire cross-sectional area of the reactor. No such effect occurs in the reactor of U.S. Patent 4,552,748, which requires separate mixers for distribution and dissolution of the hydrogen in the working solution.

In the present invention, it is absolutely essential that the reaction solution be mixed while it is being catalyzed, since it has been observed that the hydrogenation reaction is not as effective if the catalysis and mixing are carried out in different steps, as in U.S. Patent 4,552,748.

As a result of the mixing, the transfer of heat and material between the liquid and the catalyst surface takes place faster than in honeycomb structures consisting of straight, parallel channels. With the help of the catalyst, the linear velocities in the reactor can be reduced to below 3 m / s, because the static mixers distribute the hydrogen in the working solution even at lower linear velocities, 10 15 20 25 30 35 v 504 578 e.g. within the range 0.1 - 1.5 m / s. At these speeds, the pressure loss and the mechanical wear on the catalyst coating are small.

The catalyst activities in the static mixer according to the present invention remain virtually unchanged even for long periods. This is partly due to a relatively open flow, in which case excessive amounts of contaminants can not adhere to the catalyst surface, the flow rinses the channel walls clean. Likewise, the almost anhydrous liquid phase and the oxygen-free gas phase promote the maintenance of the activity of the metal. '__ The length of the reactor depends on the type of mixer used. As the channels in the static mixer are smaller, the geometric surface area of the mixer is larger, whereupon more catalyst layers per unit volume can be bonded, but at the same time the dynamic pressure loss in the mixer will be larger. In this way, an optimal size for the channels in the mixer can be produced.

By means of the invention a high hydrogen peroxide yield is obtained, calculated in proportion to the active metal. This is due, firstly, to the fact that all the catalyst is in the part of the reactor system in which the hydrogenation reaction takes place. Second, the thin catalyst layer is advantageous for the utilization of the active metal.

A more important advantage compared with the closest comparable inventions is the method of mixing the hydrogen and the working solution, advantageous in terms of the transfer of material and heat.

Thus, uniform conditions are created, which are advantageous for the selectivity and speed of the hydrogenation reaction.

By using a thin catalyst layer, the active metal can be used efficiently in the hydrogenation and, moreover, the contact period between the reagents and the catalyst remains short, a factor which reduces the amount of by-products.

The hydrogenation process according to the invention can be used on an industrial scale, so that the reduction is carried out in its entirety within a favorable pressure range. The pressure in the reactor is maintained in the range 1-15 bar, preferably 2-5 bar. The temperature of the working solution is maintained within the advantageous temperature range 40-60% L e.g. during small-scale hydrogenation by cooling the reactor with a cooling jacket.

The invention is described below in more detail with reference to the associated drawing figure, which schematically shows the hydrogenation process according to the invention.

The hydrogenation step comprises a circulation tank 1, into which the working solution 14 to be hydrogenated is fed by means of a pump 4. The working solution is recirculated to the circulation tank 1 by means of a pump 3 in the pipe system 8 via a hydrogenation reactor 2, equipped with one or more static mixers 9 , coated with a catalytic material. The hydrogenation reactor 2 is provided with a cooling jacket 6, but it is clear that the cooling can also take place in another way. The working solution 14 to be hydrogenated can also be fed directly into the circulation pipe system 8.

Hydrogen is introduced from the pipe 12 into the hydrogenation circulation pipe system at a location slightly before the hydrogenation reactor 2 and the exhaust gases are removed through a pipe 11, which is in the upper part of the circulation tank 1. Hydrogenated working solution is removed through a pipe 13, connected to the lower part of the circulation tank 1 , and fed via a pump 5 and a post-filter 7 to oxygenation.

The hydrogenation conversion can be carried out by adjusting the feed rate of hydrogen 12, the pressure in the reactor and the liquid flow 8 thereby.

Example In a small scale batch experiment performed a working solution containing 2-ethylanthraquinone 100 g / l was used. The solvent used was a mixture of aromatic hydrocarbons and an organic phosphorus compound. Static mixers, coated with a catalytic material and having a length of 40 mm, had been installed in the tubular reactor system, the length of which was about 400 mm and the diameter 39 mm, in which case the reaction mixture was efficiently distributed in relation to the cross-sectional area of the pipe, mixed and at the same time catalyzed. A layer of about 50 microns of about 50 microns of porous gamma alumina support had been fixed to the surface of the metallic static mixer. Palladium, a total of about 0.5% by weight, had been absorbed in the alumina layer.

The flow rate of the working solution was approximately 2000 l / h, which corresponded to a linear velocity of 0.5 m / s. The temperature was SOWI and the pressure at the beginning of the reactor was 4.0 bar.

Hydrogen was fed into the reactor at 55 l / h (NTP), of which only a portion was consumed in the reactor. The production of hydrogen peroxide in the reactor averaged 50 kg / (kg palladium) per hour.

Claims (9)

10 15 20 25 30 35 504 578 1o Patent claim A process for producing hydrogen peroxide by the anthraquinone process by circulating a reaction mixture into which hydrogen or a hydrogen-containing gas (12) and a working solution (14) are fed, i.e. an anthraquinone derivative in an organic solvent, via an elongate static mixing zone (2), which is continuous or composed of several parts, in order to hydrate the anthraquinone derivative in the presence of a solid catalyst, and by removing hydrogenated working solution (13) and gas (II) ) from the circulating reaction mixture, characterized in that the reaction mixture (8) is mixed while being catalyzed, by circulating the reaction mixture via a catalyst-coated static mixing zone (2, 9). Process according to Claim 1, characterized in that a pressure of 1-15 bar, preferably 2-5 bar, is maintained in the catalyst-coated static mixing zone (2, 9), and a temperature is maintained which is below 100 ° C, preferably 40-60 ° C. Process according to Claim 1 or 2, characterized in that the reaction mixture (8) is circulated through the catalyst-coated static mixing zone (2, 9) at a speed of 0.1-1.5 m / s. Tubular static mixer (9), comprising one or more parts, for catalytic hydrogenation of a reaction mixture containing hydrogen or a hydrogen-containing gas (12) and a working solution (14), i.e. an anthraquinone derivative in an organic solvent, characterized in that the static mixer (9) is coated with a solid catalyst. A static mixer according to claim 4, characterized in that it is coated with a porous support, in which a hydrogenation-catalyzing metal is absorbed. 10 15 11 504 578 A static mixer according to claim 5, characterized in that the thickness of the coating is a maximum of about 300 μm and preferably at least 5 μm. Static mixer according to Claim 5 or 6, characterized in that the porous support is active alumina, silica, silicate and / or activated carbon. Static mixer according to one of Claims 4 to 7, characterized in that hydrogenation-catalyzing palladium, platinum, rhodium and / or nickel are absorbed in the mixer (9). Use of a tubular static mixer (9), comprising one or more parts, for the catalytic hydrogenation of an anthraquinone derivative in an organic solvent by means of hydrogen or a hydrogen-containing gas, the surface of the static mixer being coated with a preferably maximum 300 μm thick porous support layer, in which a hydrogenation-catalyzing metal is absorbed.