FR2642412A1 - PROCESS FOR THE PREPARATION OF HYDROGEN PEROXIDE 1 - Google Patents

Abstract

The present invention relates to a process for the production of hydrogen peroxide by the anthraquinone process. Is circulated via a tubular static mixing zone 9 which is continuous or which comprises several parts, a reaction mixture into which is introduced hydrogen or a gas containing hydrogen and a shuttle solution, that is to say say an anthraquinone derivative in an organic solvent, in order to hydrogenate the anthraquinone derivative in the presence of a solid catalyst, and the hydrogenated shuttle solution 13 and the gases 11 of the circulating reaction mixture 8 are removed. In the invention, the reaction mixture 14 is circulated through a static mixing zone covered with catalyst 9, where it is simultaneously mixed and catalyzed.

Description

Process for the preparation of peroxide

of hydrogen (I).

  The present invention relates to a process for the preparation of hydrogen peroxide by the anthraquinone process, and more particularly to its partial process, namely hydrogenation. The present invention relates very specifically to a process in which a reaction solution is circulated, hydrogen or a gas containing hydrogen and a shuttle solution, that is to say a derivative of anthraquinone in a organic solvent, being brought into it via a tubular static mixing zone which is either continuous or consisting of several parts, in order to hydrogenate the anthraquinone derivative in the presence of a solid catalyst and the hydrogenated shuttle solution and the gases are removed from the circulating reaction mixture. Furthermore, the present invention relates to a tubular static mixer comprising one or more parts and the use of the mixer in the above-mentioned process. It is known that hydrogen peroxide can be prepared by the so-called anthraquinone process. In this process, an anthraquinone derivative is dissolved in a solvent comprising one or more constituents. The solution thus prepared is called the shuttle solution. In the preparation of hydrogen peroxide, the shuttle solution is first sent to the hydrogenation stage. During this step, the anthraquinone derivatives are hydrogenated, in the presence of a catalyst, into corresponding anthrahydroquinone derivatives. The hydrogenated shuttle solution is then directed to oxidation, during which oxygen or an oxygen-containing gas is introduced therein, a step in which the hydrogen peroxide

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  is formed in the solution. The main reactions of the anthraquinone process are shown below:

0 OH

Il Gm R + H2 catalvst> R

O OH

C H O

R

+ 02> + H202

  Ch O The shuttle solution which contains the hydrogen peroxide is sent to the extraction step, in which the hydrogen peroxide is subjected to extraction to pass from the shuttle solution into the aqueous solution. The extracted shuttle solution is dried to remove excess water and recycled at the start of the cyclic process, that is to say at hydrogenation. 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 for 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 in the reactor. Side reactions may reduce the amount of derivatives

  of anthraquinone which produce hydrogen peroxide.

  Suspension and fixed bed reactors were all

  two used for hydrogenation.

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  The suspended catalysts used include the so-called porous palladium black, the palladium absorbed in a support (for example of

  alumina, activated carbon), and Raney nickel.

  The porous catalyst is. suspended and the hydrogen is dispersed in the shuttle solution in, for example, a mixing vessel reactor or a tubular reactor. In a tubular reactor, mixing is carried out by the high linear speed of the shuttle solution. Linear velocities are commonly over 3 m / s and below 10 m / s in an open tube (US Patent 4,428,923). The mixture is also improved by the use as an reactor tube of an alternately convergent tube and

  divergent (US patent 3,423,176, KABISCH et al.).

  From patent document FI 864 971, a process of the type mentioned in the preamble is also known, in which a reaction mixture containing hydrogen, a shuttle solution and a solid catalyst in suspension is circulated in a network of tubular reactors equipped with a static mixer which is continuous or made up of several parts. The pressure existing in the network of tubes is below 15 bars and the temperature below 100 ° C. In the process, the shuttle solution is circulated in the network of reaction tubes to

  a flow velocity which is less than 3 m / s.

  The contact surfaces and the contact times of the catalyst, the shuttle solution and the hydrogen are important for the hydrogenation reaction. By using a stationary solid catalyst in the hydrogenation, the contact time in the catalytic reaction can be shortened, whereby the proportion of side reactions is reduced. The absence of the expensive filtration step is a significant advantage of using a fixed catalyst bed rather than a suspended catalyst. Filtration can also be problematic technically, since the

  catalyst particles are small.

  A suspended catalyst remains partially unused in the hydrogenation reaction since for a large part of the time it is in a hydrogen-free part of the process cycle, for example in the tank

  circulation, where it can follow the process cycle.

  A suspended catalyst is also more sensitive

  sintering and mechanical wear.

  In fixed bed reactors, the support pellets and the so-called honeycomb catalysts

  have been used (BERGLIN et Ai., US patent 4,552,748).

  The support used is usually activated alumina, but other porous supports having a large specific surface can also be used, for example SiO2 or activated carbon. A noble metal, commonly palladium, has been absorbed as an active component in the support. Only a kind of post-filtration, for the separation of particles detached from the bed of the shuttle solution, is used in the fixed bed reactor before the step

oxidation.

  In the fixed bed reactor, pellets are commonly used (usual diameter 0.2-10 mm)

  deposited between sieve sheets or nets.

  In pellets as large as these, the transfer of material into and out of the deepest pores is slow, which is why the activated metal in the interior parts of the pellets remains unused in the reaction. Likewise, the pressure drop increases to a high degree, and the flow of flows occurs in these freely packed catalyst beds. The gas

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  The reducing agent also tends to separate in a phase of its own, in which the rate of hydrogenation decreases. Special attention must be paid so that no catalytic poison passes into the shuttle solution or the reducing gas. The so-called honeycomb catalyst consists of a cellular support structure having parallel channels. The porous support is fixed in a thin layer on the support structure, and moreover a noble metal is absorbed therein. A reactor operating according to such a principle has the disadvantage of a weak mixture of hydrogen with the shuttle solution and the possibility of separation of the gas bubbles in a phase of their own. The heat transfer from the inner parts of the honeycomb remains low, in which case the temperature can become too high, a situation which

  increases the amount of unwanted byproducts.

  One step limiting hydrogenation in fixed bed reactors is the passage of hydrogen from the gas bubbles into the shuttle solution. The rate of passage of hydrogen depends on the size of the bubbles of hydrogen in the shuttle solution. The smaller the bubbles in which the hydrogen is in the solution, the larger the total surface area of the interface between the shuttle solution and the gas phase. The mixing of hydrogen with the shuttle solution has been improved by the use of static mixers at a point before the fixed bed reactor (US Patent 4,428,922). In this way, the hydrogen is in small bubbles in the shuttle solution when entering the reactor, but as a result of the pipeline in the reactor, the dispersion of the gas is reduced. A premix reactor in which the shuttle solution is saturated with hydrogen also has

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  been used to some extent before hydrogenation (US patent

2,837,411).

  The object of the present invention is therefore to provide a method and an apparatus for the production of hydrogen peroxide by the anthraquinone method, in which the drawbacks of the methods and apparatuses of the prior art have been eliminated. The main features of

  the invention are given in the claims

attached.

  In the process according to the invention, a reaction mixture comprising hydrogen or a gas containing hydrogen and the shuttle solution is therefore caused to circulate in a tubular reactor network of constant diameter or alternately convergent and divergent, installed horizontally or vertically and equipped with a static mixer which is continuous or which comprises several parts and which is covered with a catalytic substance, the reaction mixture being simultaneously mixed and catalyzed in the mixer. The tubular reactor can simply be sized to be of such length that the hydrogen has time to react before reaching the outlet of the tubular reactor. Thus, it is not necessary for the reducing gas to circulate in

the reactor.

  The static mixer according to the invention comprises a support structure made of a metallic, ceramic, polymer or other corresponding material, to the surface of which a porous support is fixed. The support includes, for example, alumina, SiO2, silicates or activated charcoal. An active metal in the hydrogenation, for example palladium, platinum, rodium, nickel or a

  mixture of these, is absorbed in the support.

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  In the reactor according to the invention, a sufficient transfer of material between the gas and the liquid and a sufficient transfer of heat from the reaction mixture to the wall of the tube are carried out by means of static mixers, which have been described in

  following publications, for example: Chem.-Ing.-Tech.

  52 (1980), 4, pp. 285-291; Chem. Eng. Prog. 82 (July 1986), 7, pp. 4248, and 20 (May June 1986), 3, pp. 147-154; Perry, R. H. and Chilton, C.H., Chemical Engineer's Handbook, 5, New York: McGraw-Hill (1973) Section 19, p. 22. Likewise, the axial mixing is minimized and the temperature and concentration profiles - in the section

  tube cross-sections are uniform.

  The reaction takes place in a thin layer of 5-300 micron catalyst on the surface of the mixer. As the layer is thin, the proportion of secondary reactions reducing the yield remains low since the retention times of the reagents and reaction products in the pores are short. Likewise, the catalytically active metal is

  used effectively in the thin layer of catalyst.

  For this reason, the catalyst layer according to the invention is more advantageous than a fixed bed.

made up of pellets.

  Unlike the honeycomb reactor according to US Pat. No. 4,552,748, in which the pieces of catalyst form mutually parallel channels and of equal length without mixing effect, in the reactor according to the invention the structures thereof these serve not only as fixing surfaces for the catalyst but also as mixers, the static mixer having flow baffles covered with catalyst reciprocally in different directions, which effectively distribute the flow over the whole

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  of the cross section of the reactor. Such an effect does not exist in the reactor according to US Pat. No. 4,552,748 which requires separate mixers to disperse

  and dissolve the hydrogen in the shuttle solution.

  In the present invention, it is absolutely essential that the reaction solution is mixed while it is catalyzed, since it has been observed that the hydrogenation reaction is not as effective if catalysis and mixing are carried out. in different stages, as in the patent

US 4,552,748.

  Due to the mixture, the transfer of heat and material between the liquid and the surface of the catalyst is faster than in honeycomb structures consisting of parallel rectilinear channels. By means of the catalyst, the linear speeds in the reactor can be lowered below 3 m / s since the static mixers disperse the hydrogen in the shuttle solution even at low linear speeds, for example in the range 0.1- 1.5 m / s. At these speeds, the pressure drop and the mechanical wear of the catalyst deposit are slight. The activity of the catalyst in the static mixer according to the present invention remains almost unchanged even for long periods. This is due in part to a relatively large flow, in which important impurities cannot adhere to the surface of the catalyst, the flow making the walls of the channels clean by rinsing. Likewise, the almost anhydrous liquid phase and the oxygen-free gas phase facilitate the maintenance of the activity of the catalyst. The length of the reactor depends on the type of mixer used. When the static mixer channels are smaller, the geometric surface of the

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  mixer is larger, to which a larger layer of catalyst per unit volume can be bonded, but at the same time the dynamic pressure loss in the mixer becomes greater. So an optimal size can be found for the channels

of the mixer.

  By means of the invention, a high hydrogen peroxide yield is obtained as calculated as a function of the active metal. This is due, firstly, to the fact that all the catalyst is in the part of the reactor network in which the hydrogenation reaction takes place. In addition, a thin layer of catalyst is advantageous for the exploitation of the active metal. A greater advantage compared to the closest inventions lies in the method of mixing hydrogen and the shuttle solution, advantageous in terms of transfer of material and heat. Thus, uniform conditions are practiced, advantageous for the selectivity and the rate of hydrogenation reaction. By using a thin layer of catalyst, the active metal can be used effectively in hydrogenation and, in addition, the contact time between the reactants and the catalyst

  stays short, a factor that reduces the amount of under-

  products. The hydrogenation process according to the invention can be transposed to an industrial scale so that the reduction is carried out in its entirety within an advantageous pressure range. The pressure in the reactor is maintained in the range 1-15 bars, preferably 2-5 bars. The temperature of the shuttle solution is advantageously maintained in the range -60 ° C., for example in a small-scale hydrogenation using a cooling jacket

around the reactor.

  t2642412 The invention is described below in more detail with reference to the accompanying drawing, which schematically illustrates the hydrogenation process according to the invention. The hydrogenation stage comprises a circulation tank 1 into which the shuttle solution 14 to be hydrogenated is introduced by means of the pump 4. The shuttle solution is recycled in the circulation tank 1 by means of a pump 3 in the network of tubes 8 via a hydrogenation reactor 2 equipped with one or more static mixers 9 covered with a catalytic substance. The hydrogenation reactor 2 is equipped with a cooling jacket 6, but it is clear that the cooling can just as easily be arranged in another way. The shuttle solution 14 to be hydrogenated can also be introduced

  directly into the circulation tube network 8.

  The hydrogen is introduced through a line 12 into the network of hydrogenation circulation tubes at a point a little before the hydrogenation reactor 2, and the gases expelled are eliminated through a line 11, which is located in the section upper of the circulation tank 1. The hydrogenated shuttle solution is eliminated through a conduit 13 connected to the lower section of the circulation tank 1 and is supplied via a pump 5 and a post-filter 7 to oxygenation. The hydrogenation conversion can be influenced by adjusting the rate of hydrogen supply 12, the pressure in the reactor and

  the flow of liquid 8 through it.

  Example: In the series of small-scale experiments that are carried out, a shuttle solution is used which

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  contains 2-ethyl anthraquinone 100 g / l. A solvent is used which is a mixture of aromatic hydrocarbons with an organic phosphorus compound. Ten static mixers covered with a catalytic substance and having a length of 40 mm are available in the tubular reactor network, the length of the tubular reactor network being approximately 400 mm and its diameter of 39 mm, in which case the reaction mixture is efficiently distributed with respect to the cross section of the

  tube, the latter being mixed and at the same time catalyzed.

  A layer of about 50 micrometers of aluminum gamma oxide support is attached to the surface of the metallic static mixer. Palladium, in total approximately 0.5% by weight, is absorbed in the

aluminum oxide layer.

  The flow speed of the shuttle solution is approximately 2000 liters per hour, which corresponds to a linear speed of 0.5 m / s. The temperature is 50 ° C and the pressure at the inlet of the

reactor is 4.0 bars.

  Hydrogen is introduced into the reactor at liters / hour (normal pressure and temperature), only part of which is consumed in the reactor. The production of hydrogen peroxide in the

  reactor is on average 50 kg / (kg palladium) per hour.

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Claims (9)

  1) Process for the production of hydrogen hydroxide according to the anthraquinone process, by circulating a reaction mixture into which are introduced hydrogen or a gas containing   hydrogen (12) and a shuttle solution (14), i.e.   say an anthraquinone derivative in an organic solvent, via an oblong static mixing zone (2) which is continuous or consists of several parts, in order to hydrogenate the anthraquinone derivative in the presence of a solid catalyst, and by removing the hydrogenated shuttle solution (13) and the gases (11) from the circulating reaction mixture, characterized in that the reaction mixture (8) is mixed, while it is catalyzed, by circulating the reaction mixture via a zone of static mixture covered with catalyst (2, 9).   2) Method according to claim 1, characterized in that in the static mixing zone covered with catalyst (2, 9), maintaining a pressure of 1-15 bars, preferably 2-5 bars and maintaining a temperature below 100 C, preferably 40-60 C.   3) Process according to claim 1 or 2, characterized in that the reaction mixture (8) is circulated through the static mixing zone covered with a catalyst (2,9) at a speed of 0.1-1.5 m / s.   4) Static tubular mixer (9), comprising one or more parts, for the catalytic hydrogenation of a reaction mixture which contains hydrogen or a gas containing   hydrogen (12) and a shuttle solution (14), i.e.   say an anthraquinone derivative in an organic solvent, characterized in that the static mixer   (9) is covered with a solid catalyst. 13 2 2642412   ) Static mixer according to claim 4, characterized in that it is covered with a porous support in which a metal catalyzing the hydrogenation is absorbed.   : 5 6) Static mixer according to claim, characterized in that the thickness of the layer is at most approximately 300 micrometers and of   preferably at least 5 micrometers.   7) Static mixer according to claim 5 or 6, characterized in that the porous support consists of activated alumina, silica, silicate and / or activated carbon.   8) Static mixer according to any one   claims 4 to 7, characterized in that   palladium catalyzing the hydrogenation, platinum, rhodium and / or nickel is absorbed in the mixer (9). 9) Use of a static tubular mixer (9), comprising one or more parts, for the catalytic hydrogenation of an anthraquinone derivative in an organic solvent by means of hydrogen or of a gas containing hydrogen, the surface of the static mixer being covered with a layer of a porous support preferably of thickness at most 300 micrometers in which a metal   catalyzing the hydrogenation was absorbed.