EP0812299A1

EP0812299A1 - Plant for producing hydrogen peroxide

Info

Publication number: EP0812299A1
Application number: EP96904143A
Authority: EP
Inventors: Henry Ledon
Original assignee: Chemoxal SA; Atofina SA
Current assignee: Arkema France SA
Priority date: 1995-02-28
Filing date: 1996-02-14
Publication date: 1997-12-17
Also published as: FR2730986A1; BR9607051A; AU4835096A; CN1176628A; FI973512A; NO973895L; FI973512A0; JPH11500997A; FR2730986B1; NO973895D0; US5902559A; CO4560351A1; NZ302323A; CZ269597A3; WO1996026898A1; CA2214087A1

Abstract

A plant for producing hydrogen peroxide by auto-oxidation of an anthraquinone derivative, including a catalytic hydrogenation vessel (1) supplied with hydrogen; an oxidising vessel (2) supplied with an oxygen-containing fluid, particularly air; an extractor (3) supplied with water; and means (7, 16, 19) for successively feeding a working solution containing at least one anthraquinone derivative dissolved in at least one organic solvent through the hydrogenation vessel (1), the oxidising vessel (2) and the extractor (3), then recirculating it to the hydrogenation vessel (1). Means (9, 26) are provided for diverting at least part of the working solution from the extractor (3) to the oxidising vessel (2) so that it by-passes the hydrogenation vessel (1). The plant is useful for producing hydrogen peroxide in situ in a paper pulp bleaching plant.

Description

Hydrogen peroxide production facility.

The present invention relates to an installation for the production of hydrogen peroxide according to the self-oxidation technique of an anthraquinone derivative, of the type comprising a catalytic hydrogenator supplied with hydrogen; an oxidizer supplied with a fluid containing oxygen, in particular air; an extractor supplied with water; and means for passing a working solution containing at least one anthraquinone derivative in solution in at least one organic solvent, successively into the hydrogenator, into the oxidizer and into the ex-tractor, then recycle it to the hydrogenator.

In what follows, the pressures indicated are relative pressures (or overpressures).

An installation as described above is conventionally implemented for the production of merchantable hydrogen peroxide solutions. An example of such an installation is presented in the work of Kirk Othmer, "Encyclopedia of Chemical Technology", 3rd edition, volume 17. For economic reasons (cf. Process Economics Report N ° 68B, Hydrogen Peroxide, March 1992, chapter VI, SRI international) essentially linked to transport and storage costs, these solutions must have the highest possible hydrogen peroxide concentration, ie a concentration greater than 35%, more generally a concentration of 60 % or 70% by weight.

In order to prepare these concentrated marketable hydrogen peroxide solutions, the process is carried out so as to recover, at the outlet of the extractor, a solution having the highest possible hydrogen peroxide concentration, while remaining outside the field explosive properties of working solutions / aqueous solutions of hydrogen peroxide. In this regard, patent application FR-A-2 228 717 indicates that the concentration of hydrogen peroxide of said aqueous solution leaving the extractor must not be greater than 600 g / 1, ie 50% by weight of hydrogen peroxide. A concentration in hydrogen peroxide greater than this value is described as being able to cause exploitative reactions.

In order to obtain highly concentrated aqueous solutions of hydrogen peroxide, the operating parameters of the self-oxidation installation mentioned above are adapted so as to allow the use of a working solution having, throughout the installation, a hydrogen peroxide equivalent as high as possible, for example a hydrogen peroxide equivalent greater than 11 g / 1, or even more. Thus, patent application FR-A-2,086,166 recommends the use of a working solution which can produce, after oxidation, an amount of the order of 16 g of hydrogen peroxide per liter. working solution. Thus, the equivalent hydrogen peroxide is at least 16 g / 1 at the inlet of the oxidizer. Conventional installations using a high hydrogen peroxide equivalent, however, have many drawbacks. Thus, they generally require the use of high oxidation temperatures. These temperatures are made necessary to avoid crystallization of the working solution having a high hydrogen peroxide equivalent. In this regard, reference may be made to "Engineering techniques", chapter "Hydrogen peroxide", J. 6020, which mentions that the oxidation temperatures must be between 60 and 80 ° C.

Another drawback encountered in these installations is that the working solution degrades rapidly.

In addition, these conventional installations are very sensitive to the presence of water, even in small quantities, which can accidentally be introduced either into the oxidizer or into the pipes connecting the oxidizer and the ex-tractor. At this level, water reacts with the oxidized working solution, which can cause explosive reactions.

In addition, in order to reduce the risk of explosion in the oxidizer, it is necessary to use loose fillings (for example with a Raschig ring). These garnis¬ wise have good characteristics with regard to gas-liquid contacts, but they are of a high cost of implementation and occupy an important place in the oxidizer. Furthermore, these linings tend to retain solid impurities. Thus, during a restart, the installation is exposed to high risks of causing a sudden abrupt entry into the ex¬ tractor of a relatively large quantity of impurities, particularly metallic, which is dangerous in this part of the installation.

The object of the present invention is to overcome the drawbacks mentioned above.

More particularly, the object of the invention is to provide a plant for the production of hydrogen peroxide according to the auto-oxidation technique, which is particularly well suited from the point of view of investment, the cost of operation and safety in real industrial conditions. In particular, the object of the invention is to provide an installation allowing the production of hydrogen peroxide directly on the consumption site by certain installations such as installations for the manufacture of paper pulp.

To this end, the subject of the invention is an installation for producing hydrogen peroxide according to the self-oxidation technique of an anthraquinone derivative, of the aforementioned type, characterized in that provision is made for means for diluting the working solution from the hydrogenator.

According to particular embodiments, this installation may include one or more of the following characteristics:

- The dilution means include means for diverting part of the working solution from the extractor to the oxidizer without the latter passing through the hydrogenator; - the bypass means are adapted to drift to the oxidizer between 15 and 45% by volume of the working solution from the extractor;

- the bypass means are adapted to divert to the oxidizer a third by volume of the working solution from the extractor;

- The hydrogenator is suitable for producing a working solution as an output with a hydrogen peroxide equivalent of between 8 and 15;

- the equivalent hydrogen peroxide at the outlet of the hydrogenator is between 9 and 12;

- Means are provided for mixing the reduced working solution from the hydrogenator and the oxidized working solution coming directly from the extractor, as well as means for directing the mixture thus formed towards the oxidizer;

- the bypass means and the mixing means are adapted to obtain a working solution at the inlet of the oxidizer having a hydrogen peroxide equivalent of between 7 and 9; - the bypass means comprise a bypass line disposed between a line for recycling the oxidized working solution, which connects an outlet of the extractor to an inlet of the hydrogenator, and a line for supplying the oxidizer with solution working which connects an outlet of the hydrogenator to an inlet of the oxidizer;

- A heat exchanger is provided between the line for recycling the oxidized working solution and the line for supplying the oxidizer with the working solution and in that said bypass line is connected to the upstream recycling line. of the exchanger, and to the supply line downstream of the exchanger; - The oxidizer comprises an envelope containing gas-liquid contact means constituted at least in part by simple perforated trays or trays similar to distillation trays, or else by an organized packing, in particular a corrugated-cross packing.

The invention will be better understood on reading the description which follows, given solely by way of example and made with reference to the appended drawings in which: - Figure 1 schematically shows an installation for producing hydrogen peroxide in accordance to the invention; FIG. 2 schematically represents in perspective the general arrangement of a part of the oxidizer equipped with a corrugated-cross packing; and

- Figure 3 shows in exploded perspective the constitution of an element of the lining of Figure 2.

The installation shown in FIG. 1 comprises three main apparatuses in the form of columns: a catalytic hydrogen generator 1, a counter-current oxidizer 2, and a water extractor 3. It also includes numerous equipment associated with these three apparatuses , of which only some have been represented. Thus, a booster-condenser assembly 4 for recirculating the mixture gaseous containing hydrogen is associated with the hydrogenator. A filter 6, a pump 7, a heat exchanger 8, a mixer 9, a water cooler 10 are connected in series on a pipe 11 for supplying the oxidizer 2 with working solution connecting an outlet 12 of the hydro-generator 1 at an upper inlet 13 of the oxidizer 2. The installation further comprises a head condenser 14 and an air compressor 15 associated with the oxidizer; a pipe 16, as short as possible, connecting the base of the oxidizer 2 to that of the extractor 3; and a coalescer 18 and a pump 19 for recycling the working solution.

FIG. 1 also shows a line 20 supplying the hydrogenator with additional make-up gas, a line 21 supplying air to the compressor 15, a line 22 supplying the ex¬ tractor 3 in demineralized water, a pipe 23 for producing hydrogen peroxide, which leaves from the base of the extractor 3 and ends at an installation 24 consuming hydrogen peroxide at the same concentration, and a line 25 for recycling the working solution carrying the pump 19 and connecting an outlet of the coalescer 18 to the base of the hydrogenator 1, passing through the heat exchanger 8. A bypass line 26 is provided between the recycling line 25 and the mixer 9. It is tapped upstream of the exchanger 8 on the recycling line 25.

The installation 24, which is located on the same site as the installation for producing hydrogen peroxide, can in particular be a pulp bleaching installation.

The hydrogen peroxide production installation includes many other equipment well known in the art and not shown, such as means regeneration of degraded products of the working solution, implementation of the catalyst, recovery of solvent, etc.

In operation, part of the oxidized working solution consisting of at least one anthraqui¬ nonic derivative and at least one organic solvent is introduced into the base of the hydrogenator 1 via the recycling pipe 25 connected to the discharge of the pump 19, and a stream of gas containing hydrogen is also introduced at the base of the hydrogenator. This gas stream consists on the one hand of the gas stream drawn off at the top of the hydrogenator, recirculated by the booster-condenser assembly 4, and on the other hand of make-up hydrogen arriving via line 20. This part of the oxidized working solution is thus partially reduced. The reduced solution, supported from the base of the hydrogenator by the pump 7 via the filter 6, therefore contains hydroquinone derivatives (for example 80% tetrahydroanthrahydroquinone and 20% anthrahydroquinone).

The anthraquinone derivative constituting the working solution is preferably chosen from the 2 alkyl 9.10 anthraquinones in which the alkyl substituent comprises from 1 to 5 carbon atoms, such as the methyl, ethyl, sec-butyl, tert-butyl radicals , tertio-amyl, iso-a yl, as well as the corresponding tetrahydro-5,6,7,8 derivatives, or among the dialkyl 9,10 anthraquinones in which the alkyl substituents, identical or different, comprise from 1 to 5 carbon atoms, such as methyl, ethyl and tert-butyl radicals, for example 1.3 dimethyl, 1.4 dimethyl, 2.3 dimethyl, 2.7 dimethyl, 1.3 diethyl, 2.7 ditertio-butyl, 2 ethyl 6 tert-butyl and the corresponding tetrahydro-5,6,7,8 derivatives. The organic solvent constituting the working solution is preferably a mixture of a non-polar compound and a polar compound. The non-polar compound is preferably chosen from petroleum fractions with a boiling point above 140 ° C. mainly containing aromatic hydrocarbons containing at least 9 carbon atoms, such as the isomers of trimethylbenzene, the isomers of tetramethylbenzene , tert-butylbenzene, isomers of methylnaphthalene, isomers of dimethylnaphthalene. The polar compound is preferably chosen from saturated alcohols preferably containing from 7 to 11 carbon atoms, such as diisobutylcarbinol, trimethyl-3,5,5 hexanol, iso-heptanol, esters of carboxylic acids such as methyl acetate cyclohexyl sold under the name "Sextate", hexyl acetate, butyl benzoate, ethyl heptanoate, esters of phosphoric acid such as tributyl phosphate, tri phosphate (2 ethyl butyl), tri phosphate (2 ethyl hexyl), tri phosphate (n-octyl), tetrasubstituted ureas such as tetra (n-butyl urea).

By "hydrogen peroxide equivalent" is meant the quantity of hydrogen peroxide, expressed in grams, that a liter of working solution is capable of supplying at the outlet of the oxidizer if the yield of this step is 100 %. This poten¬ tial mass concentration of peroxide corresponds to a molar concentration which is equal to the molar concentration of all of the reoxidizable anthrahydroquinone forms in the working solution. It depends on the one hand on the concentration in anthraquinone forms of the starting working solution, and on the other hand on the conditions of hydrogenation in the hydrogenator 1, as well as on possible dilutions of the solution reduced work.

In the present case, the hydrogenation is carried out at a temperature of between 50 and 70 ° C., with a pressure in the gaseous sky of the hydrogenator (pressure which regulates the flow of hydrogen) from 0.8 to 1.5 bar approximately, and the hydrogen peroxide equivalent at output 12 of the hydrogenator 1 is adjusted at a value of between 8 and 15 g / l approximately, and preferably between 9 and 12 g / l approximately, by adjusting the residence time in the hydrogenator, for a given concentration of anthraquinone forms.

The reduced working solution drawn from the hydrogenator is filtered at 6 to remove all traces of catalyst, then cooled at 8. It is then diluted, in mixer 9 with the complementary part of the partially oxidized working solution coming from bypass line 26 and whose hydrogen peroxide equivalent is close to zero. This complementary part of the working solution corresponds to approximately 15 to 45% by volume, and preferably to approximately one-third by volume of the total working solution coming from the extractor 3. This part of oxidized working solution is therefore directed directly to the oxidizer 2 without having passed through the hydrogenator 1. The flow rate in the bypass line 26 is adjusted so that the working solution obtained at the outlet of the mixer 9 has an equivalent hydrogen peroxide included between 7 and 9 approximately.

The working solution obtained at the outlet of the mixer 9, consisting for example of the mixture of about two-thirds of solution having been partially reduced in the hydrogenator and of about a third of solution coming in oxidized form directly from the extractor

3 is then cooled in 10 to a temperature of the order of 35 to 40 ° C. The pressure of the gaseous overhead of the oxidizer is maintained at a value between 2 and

4 bars. The essentially reduced working solution, resulting from the mixture at 9, is thus oxidized at 2, the oxidizer head fluid being partially condensed at 14.

The hydrogen peroxide formed by the oxidation reaction is withdrawn from the base of the oxidizer, in an amount per unit volume of the oxidized working solution equal to the product of the hydrogen peroxide equivalent equivalent to l input 13 of the oxidizer by the efficiency of the oxidizer. This liquid is sent directly via line 16, thanks to the difference in driving pressure, to the base of the extractor 3, which operates a little above atmospheric pressure. In the extractor is carried out a liquid-liquid extraction by means of demineralized water introduced at the top of the extractor. A water-hydrogen peroxide solution is drawn from the base of the latter, the hydrogen peroxide concentration of which is adjusted to the value necessary for its direct use in the installation consom¬ matrix 24. In the example considered, where the installation 24 is a pulp bleaching installation, the hydrogen peroxide concentration is chosen to be less than 15% by weight, for example between 5 and 12% by weight.

The working solution separated from the hydrogen peroxide is withdrawn from the top of the extractor 3, freed from the droplets of aqueous phase which it has entrained in the coalescer 18. Part of this solution is sent by the pump 19 to the heat exchanger 8, in which it heats up, and from there recycled to the base of the hydrogenator 1. The other part is sent to the mixer 9 via the bypass line 26.

The oxidizer 2 comprises an outer casing containing an organized lining, or simple perfo¬ res trays or trays of the type of distillation trays, that is to say each with a liquid guard, bubbling orifices for the gas rising through this guard, and means for lowering the liquid from one tray to the next, or a combination of an organized lining and such trays. The organized packing, if there is one, is preferably of the so-called "corrugated-cross" type.

FIG. 2 illustrates the general arrangement of the current part of the oxidizer containing such a lining. This main part essentially comprises a cylindrical shell 27 in which are stacked packing elements 28 of generally cylindrical shape.

Each element 28, of the "wavy-cross" type, comprises a packet of strips 29 having a general rectangular shape and wavy obliquely, the waves preferably having a triangular profile. The direction of inclination of the waves is reversed from one strip to the next, as can be seen in FIG. 3.

All the slats of the same element are arranged in parallel vertical planes and have the same height. On the other hand, their length, or horizontal dimension, increases from a minimum value, for one extreme lamella, to a maximum value for the middle lamella, then decreases again to the same minimum value, for the other extreme lamella. Thus, when all the strips are pressed against each other, an element 28 of generally cylindrical shape is obtained, the outline of which has been indicated in FIG. 2.

On each face, each strip has wave peaks 30 and wave troughs 31 defining a multitude of inclined channels.

The peaks of waves of one face of a strip touch those of the opposite face of the strip adjacent to you, forming a multitude of crossing points; these favor the distribution and the bringing into contact of fluids. In addition, for the same purpose, each element 28 is angularly offset by 90 ° relative to the following, as seen in Figure 2, and each strip has a multitude of perforations, not shown. The installation as described here uses a hydrogenator 1 having a high efficiency. Since only part of the working solution (approximately 2/3 by volume) is treated in the hydrogenator, the dimensions of the latter can be reduced compared to the hydrogenators of installations in which all of the solution work is covered in this one. Furthermore, the working solution introduced into the hydrogenator has a fairly high concentration of anthraquinone forms, which allows easy hydrogenation. This makes it possible to obtain a hydrogen peroxide equivalent of between 8 and 15.

Thanks to the mixing carried out in the mixer 9, the oxidizer 2 is supplied with a working solution of which the hydrogen peroxide equivalent is between 7 and 9. The relatively low value of this equivalent compared to the values used in the installations known limits the temperature in the oxidizer without risk of crystallization of the solution. By the way, the low temperature in the oxidizer leads to a low partial pressure of organic vapor in the gaseous sky (for example less than 2600 Pascals and preferably less than 1300 Pascals). The mixture thus contained in the oxidizer then has characteristics suf¬ ficiently distant from the explosive conditions. The same advantages are found in the pipe 16 as well as the extractor 3, in which the concentration of species which can form hydrogen peroxide in the presence of water, or the concentration of hydrogen peroxy¬ is limited. Although a "corrugated-cross" packing as described above is relatively ineffective from the point of view of the division of the rising gas into fine bubbles, it is suitable in the installation described, from the point of view of the exchange gas-liquid like that of security. Indeed, because the oxidizer works in a temperature range (35 to 40 ° C approximately at the top, 45 to 50 ° C approximately at the base) significantly lower than the usual temperature range in peroxide production plants of hydrogen which function according to the auto-oxidation technique of an anthra¬ quinone derivative, the risk of explosion in the oxidizer by contact of oxygen with solvent vapors is considerably reduced, even at the base of the oxidizer. The essential advantage which results from the use of such a cross-corrugated packing resides in the fact that it has much less tendency to retain solid impurities than the loose packings usually used in one oxidizer. The above remarks also apply to the use of plates promoting gas-liquid contact in the oxidizer 2.

It should also be noted that, for the same effi¬ ciency, the "corrugated-cross" packings like the trays occupy a smaller volume than the loose packings, which makes it possible to reduce the dimensions of the oxidizer. In addition, in the case of trays, one can optimize the reaction at each level of the oxidizer by a judicious choice of the spacings between the trays. The relatively low oxidation temperature also brings, as another advantage, the possibility of using oxygen-enriched air, or even pure oxygen, in the safety, in order to reduce the time. of stay of the solution in the oxidizer. Indeed, when the residence time is longer in short, the dimensions of the apparatus can be further reduced, and the quantity of degraded products of the working solution is reduced.

The installation described here uses a bypass of the recycling line for the dilution of the reduced working solution from the hydrogenator. It is also possible to use any other suitable device.

Claims

CLAIMS 1.- Installation for the production of hydrogen peroxide according to the self-oxidation technique of an anthraquinone derivative, of the type comprising a catalytic hydrogenator (1) supplied with hydrogen; an oxidizer (2) supplied with a fluid containing oxygen, in particular air; an extractor (3) supplied with water; and means (7, 16, 19) for passing a working solution containing at least one anthraquinone derivative in solution in at least one organic solvent, successively in the hydrogenator (1), in the oxidizer (2 ) and in the extractor (3), then recycle it to the hydrogenator (1), characterized in that means (9, 26) are provided for diluting the working solution from the hydrogenator (1) ).

2.- Production installation according to revendi¬ cation 1, characterized in that the dilution means comprise means (26) for bypassing towards the oxidizer (2) part of the working solution from the extractor (3) without it passing through the hy¬ drogenator (1).

3.- Production installation according to revendi¬ cation 2, characterized in that the means (26) of bypass are adapted to drift to the oxidizer (2) between 15% and 45% by volume of the working solution from the extractor (3).

4.- Production installation according to revendi¬ cation 2, characterized in that the bypass means (26) are adapted to drift to the oxidizer (2) a third by volume of the working solution from the extractor ( 3).

5.- production installation according to any one of the preceding claims, characterized in that the hydrogenator (1) is adapted to produce in output a working solution with a peroxy¬ equivalent of hydrogen between 8 and 15.

6.- Production installation according to claim 5, characterized in that the equivalent hydrogen peroxide at the outlet of the hydrogenator (1) is between 9 and 12.

7.- Production installation according to any one of the preceding claims, characterized in that means (9) are provided for mixing the reduced working solution from the hydrogenator (1) and the solution oxidized work directly from the extractor (3), as well as means (11) for directing the mixture thus formed towards the oxidizer (2).

8.- Production installation according to claim 7, characterized in that the bypass means (26) and the mixing means (9) are adapted to obtain the inlet (13) of the oxidizer ( 2) a working solution having a hydrogen peroxide equivalent of between 7 and 9.

9.- Production installation according to any one of claims 2 to 8, characterized in that the bypass means comprise a bypass line (26) disposed between a line (25) for recycling the oxidized working solution , which connects an outlet of the extractor (3) to an inlet of the hydrogenator (1), and a line (11) supplying the oxidizer (2) in working solution which connects an outlet (12) from the hydrogen generator (1) to an inlet (13) of the oxidizer (2).

10.- Production installation according to claim 9, characterized in that a heat exchanger (8) is provided between the line (25) for recycling the oxidized working solution and the line (11) of supply of the oxidizer (2) in working solution and in that said bypass line (26) is connected to the recycling line (25) upstream of the exchanger (8), and to the supply line (11) downstream of the exchanger (8).

11.- Production installation according to any one of the preceding claims, characterized in that the oxidizer (2) comprises an envelope containing gas-liquid contact means constituted at least in part by simple perforated plates or similar plates to distillation trays, or else by an organized packing, in particular a cross-corrugated packing (28).