Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
2002-03-14
2004-06-15
Wong, Edna (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
C204S157900
Reexamination Certificate
active
06749727
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of hydrogenation of alkyl anthraquinones and/or alkyl hydroanthraquinones in the presence of a catalyst. More specifically, the present invention relates to a hydrogenation method of a working solution in a hydrogen peroxide production process utilizing an anthraquinone method.
2. Description of the Prior Art
In industrial scale, hydrogen peroxide is mainly produced by an anthraquinone process. In this method anthraquinones which are dissolved in an appropriate organic solvent, are used as a reaction media. The organic solvent is usually a mixture of several organic solvents. The solution obtained by dissolving the anthraquinones in the organic solvent is called “a working solution”.
The anthraquinones (AQ) in the working solution are subjected to reduction with hydrogen (hereinafter referred to as “the hydrogenation”) in the presence of a catalyst (reaction 1) to produce corresponding anthrahydroquinones (AHQ).
Thereafter the anthrahydroquinones are oxidized with air or with an oxygen-containing mixture of gases to convert the anthrahydroquinones into the anthraquinones again (reaction 2). In this oxidation step one mole of hydrogen peroxide is formed per one mole of oxidized anthrahydroquinone.
Hydrogen peroxide produced into the working solution after the above mentioned process steps is usually separated from the working solution by extraction with water.
The working solution from which hydrogen peroxide has been separated is returned to the reduction step again, thereby forming a cyclic process. This process can produce hydrogen peroxide substantially from hydrogen and air, and hence it is an extremely efficient process.
The alkyl anthrahydroquinones (AHQ) and the alkyl anthraquinones (AQ) are subjected to a number of secondary reactions during the cyclic process. Hydrogenation of the aromatic nuclei of the alkyl anthraquinones yields alkyl tetrahydroanthrahydroquinones (THAHQ's or “tetra”) (see reaction 3). THAHQ's have an ability to produce hydrogen peroxide by the repetition of the reduction and oxidation like the alkyl anthraquinones.
If “tetra” formation is not suppressed during hydrogenation or “tetra” is not dehydrogenated, an equilibrium is reached, in which the hydroquinone charged to the oxidizer consists exclusively of 2-alkyl-5,6,7,8-tetrahydroanthrahydroquinone (THAQ). Such a system is called an “all-tetra” system. Even in the all-tetra system it is essential to maintain a certain equilibrium between AQ:s and THAQ:s in order to avoid the formation of further by-products.
The cyclic Riedel-Pfleiderer or BASF process forms the technological basis for all modern AQ processes. The processes are described for example in
Ullman's Encyclopedia of Industrial Chemistry
, vol. A 13, pp. 447-457 (VCH, Weinheim, 1989). Developments include improvement of the individual process steps, use of stable working solutions, and use of selective hydrogenation catalysts.
The basic principles of the process are:
Hydrogenation. From the storage tank or hydrogenation feed tank, the working solution enters the hydrogenator where it is hydrogenated in the presence of a suspended, supported, or fixed-bed catalyst. If a suspended catalyst (e.g., palladium black or Raney nickel) or a supported catalyst (e.g., palladium) is used, the hydrogenation step includes a main filtration stage which retains the catalyst and allows it to be returned to the hydrogenator.
Oxidation. Before the hydrogenated working solution that contains hydroquinone can be fed to the oxidation step, it must pass through a safety filtration stage. This is particularly important because the hydrogenation catalysts used in the AQ process (palladium and Raney nickel) also catalyze the decomposition of hydrogen peroxide. Even a small amount of these catalysts in the oxidation and extraction steps would lead to considerable loss of hydrogen peroxide and serious disturbances. During the oxidation step, the hydrogenated working solution is gassed with air and/or oxygen. Dissolved hydroquinones are oxidized to quinones, and hydrogen peroxide is formed.
Extraction and Recovery of the Working Solution. The oxidized working solution is then treated with water to extract hydrogen peroxide. The working solution leaving the extraction unit must be adjusted to a specific water content before being returned to the hydrogenation step. Free water taken up by the working solution during extraction is separated and the water content is adjusted to the desired level in the drier.
Hydrogen Peroxide Concentration. Crude aqueous hydrogen peroxide from the extraction stage (H
2
O
2
concentration 15-35 wt %) is fed into the crude product storage tank via a prepurification unit. From the crude product storage tank, aqueous hydrogen peroxide goes to the concentration unit where it is distilled. Here, hydrogen peroxide is freed from most of its impurities and concentrated to the commercial concentration of 50-70 wt %; it is then collected in a storage container.
Auxiliary Processes. A number of additional processes are required to maintain the AQ operation. For example, to maintain hydrogenation activity, part of the catalyst is removed, regenerated in the catalyst regeneration area, and returned to the hydrogenator. To compensate for quinone and solvent losses, working solution is periodically made up with anthraquinone and solvent.
Hydrogenation Step
The hydrogenation step is the most important step of modern AQ processes. Quinone decomposition products that cannot be regenerated into active quinone are formed during this step. New hydrogenation catalysts and hydrogenation reactors have been developed that deviate totally from the BASF principle. Here, design of the hydrogenator depends largely on the type of catalyst used.
Four typical reactors for the three usual catalyst systems (suspended, supported, and fixed-bed catalysts) are discussed.
BASF Hydrogenation Step. The hydrogenation step in the BASF plant uses a Raney nickel catalyst at a slight excess pressure of approximately 0.2 MPa and at 30-36° C. Because Raney nickel is sensitive to oxygen, the working solution from the extraction or drying and purification steps cannot be fed directly into the hydrogenator. This working solution still contains residual hydrogen peroxide and must pass over a decomposition catalyst (e.g., supported Ni—Ag), together with a fraction of the hydrogenated working solution (which also contains hydroquinone), to remove hydrogen peroxide completely:
The solutions are passed through the precontact column and collected in the hydrogenator feed tank. The working solution is then pumped into the stirred vessel reactor and is gassed with hydrogen in the presence of Raney nickel. Periodic addition of small amounts of hydrogenation catalyst from the catalyst feed tank allows a constant rate of hydrogen conversion in the hydrogenator. Hydrogenated working solution is collected in the oxidizer feed tank through the internal filters in the stirred vessel, thus exploiting the excess pressure in the reactor. The solution is then led into the oxidation step via the safety filter. A side stream of hydrogenated working solution is withdrawn and recycled to the precontact column.
When the concentration of Raney nickel in the hydrogenation reactor reaches a certain limit, the content of the reactor is drained into the catalyst separator. Raney nickel settles to the bottom, and catalyst-free supernatant is pumped back to the hydrogenator.
A significant disadvantage of Raney nickel as catalyst is its limited selectivity, i.e., the ratio of hydroquinone formation to “tetra” formation. BASF largely eliminated this by pretreating the catalyst with ammonium formate.
Alternatives were subsequently suggested for pretreating Raney nickel (e.g., nitrites, amines, and aldehyde solutions).
The pyrophoric properties of Raney nickel also require more stringent safety procedures when handling the material. Raney nickel is still used today in some AQ plants, but palladium cataly
Aksela Reijo
Paloniemi Juhani
Birch & Stewart Kolasch & Birch, LLP
Kemira Chemicals Oy
Wong Edna
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