Apparatus for the production of hydrogen peroxide
United States Patent 11 1 Liebert et al.  
 [ Apr. 29, 1975 [5 APPARATUS FOR THE PRODUCTION OF 2.902347 9/1959 Cosby et al. 423/590 HYDROGEN PEROXIDE 2,966,398 12/1960 Jenney 260/369 X 3,231,251 l/l966 r Scheibel 23/2705 T 1 Inventors: Martin Liebert, Frankfurt; Heinz 3.663574 5/1972 Yamagishi et al. 23/283 x Delle; Gerhard K&#39;abisch, both of Rhemfelden of Germany Primary E.\&#39;aminer.l0seph Scovronek [73] Assignee: Deutsche Gold-und Assistant Examiner-Barry l. Hollander Silber-Scheideanstalt vormals Attorney, Agent, or F irmCushman, Darby &amp; Roessler, Frankfurt (Main), Cushman Germany Filed: Dec. 6., 1972 57 ABSTRACT [21] Appl&#39; 312516 The oxidation step in the anthraquinones process for Related U.S. Applicati Dat producing hydrogen peroxide is carried out in a plu- [62] Division of sen 18356], Sept. 24, 1971, Pat&#39; rality of stages in an apparatus arranged for separating NO- 3352335. gas and liquid phases. The hydroquinone containing working solution is conducted in each stage in parallel 521 [1.8. CI. 23/283; 23/260; 261/21 flew from bottom to top with one Oxygen Containing 51 1111. C1. B01f3/04; B01 j 1/00; COlb 15/02 2 The Stage with the highest hydrequinone concen- [58] Field 61 Search 23/283, 260, 270.5 T; nation in the Working Solution is led to the gas rniX- 423 5gg 5 9 590; 2 21; 2 0 3 9 ture most depleted in oxygen and the fresh gas mixture is introduced into the stage which contains the [56] References cu working solution poorest in hydroquinone.  
  UNITED STATES PATENTS 6 Claims, 3 Drawing Figures 2,180,888 11/1939 Underwood 261/21 WJEK/Nf awn/rm 3/ f r-&#34;2:17 I 3/4- Mail!- ..I L .2  
 APPARATUS FOR THE PRODUCTION OF HYDROGEN PEROXIDE This is a division of application Ser. No. 183.561, filed Sept. 24. 1971, now Us. Pat. No. 3.752.885.  
  The present invention is directed to an apparatus for the production of hydrogen peroxide by the anthraquinone process and is especially concerned with improving the oxidation step of this cyclic process.  
  It is known in this process to dissolve an anthraquinone derivative as the reactor carrier in a solvent and to hydrogenate in the presence of a catalyst the working solution obtained so that about 50 percent of the quinones are converted into the corresponding hydroquinones. In the oxidation step, the hydroquinone solution is treated with an oxygen containing gas whereby the quinone is reformed while simultaneously hydrogen peroxide is formed and then is isolated from the working solution. Most of the known process for isolating the H from the working solutions involve an extraction with water. By returning the working solution to the hydrogenation step and repeatedly rotating the in dividual steps there is obtained a cyclic process in which individual steps there is obtained a cyclic process in which hydrogen peroxide is synthesized in practical manner from the gases hydrogen and oxygen (from the air) with the reaction carrier dissolved in the working solution.  
  In carrying out the oxidation industrially, there is the problem chemically to carry out the synthesis as quantitatively as possible while avoiding breakdown reactions of the compounds of the working solution. In regard to carrying out the oxidation step industrially one is concerned with carrying out the reaction in an energy saving manner using the smallest possible apparatus.  
  The chemical requirements are considered in a series of processes whose improvements consist, for example, in the production of extensively oxidation stable working solutions for example according to German Offenlegungsschrift 1,945,750 (Kabisch U.S. Application Ser. No. 69,151 filed Sept. 2, 1970) or in the mode of action of regenerating breakdown products formed by the oxidation for example according to German Pat. No. 1,273,499. However, the oxidation step in the large industrial plants for the anthraquinone process today also not only requires more energy than the rest of the apparatus put together, but it also requires proportionally by far the largest apparatus in the cycle. Therefore there has not been a lack of proposals for industrially improving the oxidation step.  
  Thus in the former BASF plant the oxidation of the hydrogenated working solution was carried out in four gasification towers arranged consecutively (CIOS Report File No. XXI-I5, File XXVll-84, File XXV-44). which are always gassed with a fresh N- -O mixture, which volumewise correspond about to the composition of air. The waste gas depleted in O by passage through the tower is recycled and by dosing with O is brought to the original composition.  
  At high contents of tetrahydroanthrahydroquinone derivatives in the working solution which cause a reduction in the oxidation rate, according to a proposal in Jenney U.S. Pat. No. 3,073,680 attention should be paid to the maintenance of specified bubble sizes and cross section load. Accordingly, the gas distributor should have pore openings of 0.15 to 0.40 mm. diameter and air is employed in the O N mixture dosed into the towers which are arranged consecutively and have a cross section load of 36-72 cubic meters/sq. meter X hour (cum/sq. m X 11).  
  Both described processes have the disadvantage that they are burdened with a large apparatus expenditure. It is also a disadvantage that with smaller pore openings in the gas distributor the gas bubbles becomes smaller whereby the separation of the foam formed causes difficulties and the means for gas distribution (for example frits) are easily clogged.  
  In another process described in Cosby US. Pat. No. 2,902,347 the oxidation is characterized by a countercurrent passage. The hydroquinone solution to be oxidized is fed to the head of a packed column and flows against the uprising air fed into the bottom of the column. The charging of this countercurrent is limited by a very low flood level. Furthermore, it has the disadvantage of very great apparatus expense because several columns are arranged consecutively if the working solution to be oxidized has a high tetra content. In the industrial carrying out of the cycling of the working solution for months at a time, however, there cannot be avoided the tetracontent of the working solution. For these reasons there have been proposed apparatus arrangements for the oxidation of the tetra system which are described repeatedly in the literature, for example. Chem. Age. 82. 895 (1958), Chem. and Ind. 1959 page 76, Chem. Process Eng. 40 No. 1. 5 (1959), Brit. Chem. Engng. 4, 88 (1959), and The Ind. Chemist 35, 9 (1959).  
 In the drawings,  
  FIG. 1 illustrates the old apparatus arrangement and process employing concurrent flow,  
  FIG. 2 illustrates one form of apparatus arrangement and process of the invention, and  
  FIG. 3 illustrates a preferred apparatus and process according to the invention.  
  Referring more specifically to FIG. 1 both towers l1 and 11a have a height of 18.3 meters and a diameter of 3.7 meters. The hydroquinone working solution is introduced via conduit 50 and conduit 52&#39;to the bottom of tower II and via conduit 50 and conduit 54 to the bottom of tower 11a. Air is similarly introduced via conduit 56 and conduit 58 to the bottom of tower 11 and via conduit 56 and conduit 60 to the bottom of tower 11a. The air and working solution are forced upward in parallel flow through a layer of packing. The working solution-waste gas mixture is fed either via conduit 62 to separator 12 or via conduit 64 to separator 12a where the gas and liquid are separated. The waste gas as shown goes via conduits 66, 68, 70, 72, or 74 to after provided activated carbon towers 13a or 13b, then via conduits 76 or 78 to activated carbon towers 130 or 13d. In the activated carbon towers, the waste gas is freed of residual solvent (working solution) and leaves via conduits 80 and 82. The residual working solution can then be recovered and reused. The oxidized working solution leaves the bottom of separator 12 via conduit 84 and separator 12a via conduit 86 and is pumped by pump 14 to the extraction step.  
  It has been found that the energy requirements and the apparatus yield of the oxidation step while retaining the parallel flow from the bottom to the top according to FIG. 1 can be substantially improved if there is employed, for example. in the oxidation stage, a column provided with obstruction or packing, in which column the hydrogenated working solution and the oxidation gas, air or an oxygen containing gas are led in parallel or concurrent flow from bottom to top in several columns or sections divided in such a way that the section with the highest hydroquinone concentration is provided with the least oxygen concentration and conversely. If more than two sections are provided as the hydroquinone concentration goes up from section to section the oxygen concentration goes down.  
  FIG. 2 shows in schematic fashion one method of carrying out the invention. The working solution to be oxidized is fed with the help of pump 88 via conduit 90 to the bottom of packed column 21 and then flows from the top of column 21 via conduit 92 to the bottom of packed column 22 and next flows from the top of column 22 via conduit 94 to the bottom of packed column 23. The oxidation gas-fresh gas, e.g., air, is first introduced via conduit 96 to the bottom of tower 23 in which the hydroquinone concentration is the lowest and flows in parallel with the working solution in tower 23 from bottom to top through a packed layer. At the top of each column the gas-liquid mixture is separated by suitable obstructions such as that at 100. The exhaust gas from tower 23 is led via conduit 102 to the bottom of tower 22 and finally via conduit 104 to the bottom of tower 21 where the gas which is now greatly depleted in oxygen is reacted with the fresh working solution which contains the highest hydroquinone concentration. The waste gas leaves the top of tower 21 via conduit 106.  
  The oxidized working solution is led from the top of tower 23 via conduit 108 to the buffer feed vessel 24 of the extraction step.  
 - A preferred form of the invention which is distinquished by an especially simple apparatus construction in the new oxidation system is shown schematically in FIG. 3. The hydrogenerated working solution flows into the bottom of upper section 31 of the packet oxidation tower and then flows from the top of section 31 to the bottom of section 32 and next flows from the top of section 32 to the bottom of section 33 of the tower. The oxidation-fresh gas is first fed via conduit 33a into section 33 in which the working solution is extensively oxidized and flows in parallel flow from bottom to top, for example, through a packed layer, with the liquid introduced via conduit 33b. In the upper part of the section, there is provided a device 34a suitable for gasliquid separation. This upper section is also so designed volumewise that it can serve as the buffer or feed vessel of the subsequent extraction step. The liquid can be led off to the extraction step through conduit 35. The exhaust gas from section 33 enters section 32 via conduit 32a and subsequently via conduit 31a enters section 31 through which it is again led from bottom to top in parallel flow with fresh hydroquinone solution introduced via conduit 31b and the waste gas depleted of oxygen finally leaves the oxidation tower via conduit 36. The liquid leaving section 31 at the upper end goes via conduit 32b into section 32 and from there, as already mentioned, goes via conduit 33b into section 33. The schematically indicated apparatus for phase separation always shown in the upper part of each section in FIGS. 2 and 3 (FIG. 3 indicated at 34a, 34b and 34c) can be situated either outside or inside the true apparatus or sections. Preferably, it is placed inside whereby it is well suited as phase separation apparatus of known components, for example, cyclones working according to the principle of Ter Linden.  
  The number of individual apparatus which preferably are composed as sections of an oxidation tower depends upon various degrees of influence, for example, of speed of oxidation and tetra content of the working solution, reaction temperature, pressure, oxygen content of the gas feed. Since air is the preferred oxidation gas for carrying out the process of the invention, the number of apparatus (i.e., sections) ranges between 2 and 6, especially between 2 and 4. Of course, by using a larger number of sections the advantages specified below are increased. However, in such a case there is also an increased apparatus expense.  
  In the apparatus (sections) in which the liquid-gas mixture always is led in parallel flow from bottom to top in order to provide thorough inner mixing there can be provided suitable obstructions. These obstructions, for example, can be bubble caps or grids. Packing can also be employed in their place. Preferably there is used packing having dimensions of abaout 15 to mm., especially of 25 to 50 mm. The height of the layers in which an exchange of materials in the phases occurs is designated as the effective height. Collectively the effective height of all sections in a given case composited to a column, should amount to 8 to 25 meters, especially 10 to 18 meters. Surprisingly, it was found that the process of the invention, despite the smaller effective height of the apparatus, can be carried out so that in a composite column, the sections can employ very high liquid cross sectional loads namely 10 to 55 cum/sq. m X 11, especially 15 to 35 cu.m/sq. m X I1. This results in an especially good apparatus yield, which is connected to further advantages. The stated load limits again depend upon many factors (composition, tetra content, viscosity, surface tension and ca pacity of the work solution, size of the packaging, oxidation temperature, pressure, etc.), especially, however, they depend upon the amount of oxygen containing gas necessary for the oxidation. lf air is employed as the oxidizing gas in the invention process then the gas cross sectional load (based on the free, unfilled column cross section) of 370 to 2,050 normal cubic meters/sq. meter X hour, especially 550 to 1,300 N cu.m/sq. m X h. The cross sectional loads are at least twice as high as in the previously known processes.  
  The process of the invention can be carried out at normal pressure or increased pressures of 1 to 7 atmosphere absolute. The temperature can also be varied within wide limits, for example from 20 to C. Since a high temperature increases the rate of oxidation and permits high cross sectional loads on the one hand but on the other hand, cause increased breakdown of product formation, temperatures in the range of 45 to 75 C. are preferred.  
  The process of the invention can be employed for the oxidation of all known working solutions used in the anthraquinone process. The process is especially suitable for working solutions which employ as reaction carriers alkyl anthraquinone, 2-methyl anthraquinone, 2-butyl anthraquinone, 2-isopropyl anthraquinone, 2- sec., amyl anthraquinone, l, 3 dimethyl anthraquinone, 2, 7-dimethyl anthraquinone and mixtures of these as well as their partially nuclear hydrogenated derivatives, e.g., the tetrahydro anthraquinones such as 2-ethyl tetrahydro anthraquinone. As quinone solvents there can be used for example aromatic hydrocarbons such as tctramethyl benzene, t-butylbenzene, diphenyl, naphthalene, diethyl benzene, utetrahydronaphthalene, xylene, methyl naphthalene, mixtures of aromatic hydrocarbons boiling at l85205C., as hydroquinone solvents there can be used for example. phosphates or phosphonat&#39;es such as trioctyl phosphate, tributyl phosphate, triamyl phosphate, dioctyl phenyl phosphonate. trihexyl phosphate and tridecyl phosphate. alcohols such as octanol-2, esters such as methyl cyclohexyl acetate. Working solutions of this type contain stable components and therefore permit high cross sectional loads, high oxidation rates and high temperatures whereby especially favorable apparatus yields results.  
  The most substantial advantages of the process of invention in comparison to the known ways of carrying out the oxidation steps are summarized below:  
  1. Lower apparatus expense, i.e,, lower investment cost.  
  2. Lower energy requirements. i.e., lower operation costs.  
  3. Lowerliquid holdup in the apparatus; which corresponds to a short residence time of the working solution in the apparatus, which is synonymous with a lowering of decomposition product formation.  
  4. The system makes possible the oxidation of working solutions with high tetra contents,  
  5. High cross sectional loads for gas and liquid which are at least twice as high as in known processes; accompanying this there are industrially favorable apparatus yields at degrss of oxidation which are over 97 percent frequently even over 99 percent.  
  6. Cessation of operation disturbances by clogging of the gasification candle and/or strong form development.  
 7. Cessation of intermediate closing of gas and liquid.  
  ln the following comparison examples two typical working experiments are described which are carried out according to the known process (FIG. 1, Example 1) and according to the process of the invention (FIG. 3, Example 2). By the illustrative examples the advantages of the process of the invention are made evident. The process of the invention, however, is not limited to the illustrative form selected.  
  Unless otherwise indicated all parts and percentages are by weight.  
 EXAMPLE 1 a as the reaction carrier 90 grams of 2-ethyl tetrahydroanthraquinone plus grams of ethyl anthraquinone per liter. The solvent consisted of a mixture of 75 volume percent of aromatic hydrocarbons (boiling range l85-205C) and 25 volume percent tri (2- ethylhexyl) phosphate. The flow of the working solution through the cyclic apparatus amounted to 130 cu. meters/hour, In the hydrogenation step the working solution was hydrogenated to the extent that there was formed a working solution having an amount of hydroquinone corresponding to an H 0 equivalent of about 9.45 kg/cu.m. The working solution was led through an oxidation tower (analogous to lower 11 in FIG. 1) which was filled with 25 X 25 mm. ceramic Raschig rings, and had an effective of height of 20 meters and a diameter of 3.7 meters. Together with the working solution there was fed into the bottom of the column 5,000 normal cubic meters of air/hour (pressure at the bottom of the column 3.0 atmospheres absolute; pressure at the top of the column 1.5 atmospheres absolute), in which a mean temperature of 54C. prevailed. In this manner of operation there was produced a 98.1% overall oxidation in which the 0 content of the waste gas amounted to 6 percent and a current requirement of 0.44 kilowatt/kg H 0 was measured as the share for the air compresser.  
 EXAMPLE 2 260cu.m/h of a working solution having the same composition and hydroquinone content as in example 1 was fed through an oxidation tower according to FIG. 3 together with l0,000 normal cu. m. of air/h, This tower also had a diameter of 3.7 meters and was divided into three sections which together had an effective height of only 15 meters. At the same pressure and temperature conditions as in Example 1, there was obtained an overall oxidation of 98.3% and the 0 content of the waste gas was below 5.9% and there was a current requirement of 0.36 kilowatt/kg. H 0 measured as the share for the air compressor.  
 What we claim is:  
  1. In an apparatus for forming hydrogen peroxide by the cyclic anthraquinone process employing a working solution comprising a column for hydrogenating the working solution and a separate column for oxidizing the working solution and wherein liquid flows from the bottom to the top of said separate column. the improvement comprising column means for oxidizing the working solution made of a plurality of vertically disposed, vertically aligned column sections including a first lower section and a second upper section, conduit means for introducing an oxygen containing gas to the bottom portion of said first section, conduit means for conducting working solution lowest in hydroquinone concentration and separated from the top portion of said second section into the bottom portion of said first section, cyclone means in the top portion of said first section for separating gas and working solution, conduit means connected to the top of said first section for removing the separated working solution, extractor means for removing hydrogen peroxide from the working solution, conduit means for returning the working solution to the hydrogenation means of the cyclic process, conduit means for leading the gas separated from the top of said first section to the bottom of said second section, conduit means for introducing working solution to the bottom of the second section, cyclone means in the top portion of said second section for separating gas and working solution and conduit means for removing gas from the top portion of said second section.  
  2. An apparatus according to claim 1 wherein there are 2 to 6 of said sections in the oxidizing column, each section above the bottom section containing conduit means in the bottom portion for introducing gas from the top portion of the next lower section and each sec-.  
 tion below the top section containing separate conduit means in the bottom portion for introducing working solution from the top portion of the next higher section, conduit means for introducing gas into the bottom portion of the lowermost section, conduit means for introducing working solution into the bottom portion of the topmost section and cyclone means for separating gas from working solution in the top portion of each section, conduit means for passing working solution out of 6. An apparatus according to claim 1, wherein there is provided obstruction means in the bottom of the sections in the oxidizing column and both the conduit means for introducing the working solution at the bottom of each section and the conduit means for introducing gas at the bottom of each section have their inlet to each section below said obstruction means to provide thorough mixing of the working solution and gas.