Method for hydrogenating an anthraquinone compound

Chemistry of inorganic compounds – Oxygen or compound thereof – Peroxide

Reexamination Certificate

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C423S590000, C552S208000

Reexamination Certificate

active

06464954

ABSTRACT:

The present invention relates to a process for hydrogenating an anthraquinone compound or a mixture of two or more thereof by contacting the anthraquinone compound or the mixture of two or more thereof with a catalyst comprising, as active metal, at least one metal of transition group VIII of the Periodic Table of the Elements and a process for preparing hydrogen peroxide by the anthraquinone process comprising a hydrogenation step as defined above and the reaction of the anthraquinone compound obtained in this step with an oxygen-containing gas.
Virtually all of the hydrogen peroxide produced worldwide is prepared by the anthraquinone process.
The process is based on the catalytic hydrogenation of an anthraquinone compound to give the corresponding anthrahydroquinone compound followed by reacting the latter with oxygen to give hydrogen peroxide and subsequently removing the hydrogen peroxide formed by extraction. The catalyst cycle is closed by rehydrogenation of the reformed anthraquinone compound.
The basic reactions are summarized in the scheme below:
The anthraquinone compounds used are typically dissolved in a mixture of several organic solvents. The resulting solution is referred to as the working solution. In the anthraquinone process, this working solution is usually passed through the above-described process steps in a continuous manner.
The anthraquinone process is reviewed in Ullmann's Encyclopedia of Industrial Chemistry, 5th ed., vol. A13, pp. 447-456.
A particularly important step of the anthraquinone process is the hydrogenation step, in which the anthraquinone compound in the working solution is hydrogenated in the presence of a catalyst to give the corresponding anthrahydroquinone compound.
Said catalytic hydrogenation can be carried out in suspension or in a fixed bed in various reactor types. The relevant prior art is described in detail in EP-A-0 672 617, for example. This reference relates to a process of the subject type using a fixed-bed reactor comprising a catalyst bed having an open structure. It is suggested to use palladium on a support, such as activated carbon, aluminum oxide or silica gel, as a catalyst.
EP-A-0 102 934 describes another version of the anthraquinone process which likewise utilizes a fixed bed having a structure containing specific, parallel passages. According to this reference, useful active metals for the catalysts described therein include noble metals, eg. palladium, platinum, rhodium or mixtures thereof.
U.S. Pat. No. 4,428,923 describes an anthraquinone process which is carried out in suspension and utilizes a loop reactor and palladium black as a catalyst.
EP-A-0 778 085 and WO 96/18574 describe the use of Pd, Rh, Pt or Ru as active metals in a catalyst suitable for the anthraquinone process, where conventional materials, such as Al
2
O
3
or SiO
2
, are used as support materials for the catalysts described.
The prior art catalysts did not always meet the requirements for such catalysts, such as a high activity together with a high selectivity. Furthermore, it was not always possible to achieve sufficiently high space-time yields.
It is an object of the present invention to provide novel processes for hydrogenating an anthraquinone compound using catalysts previously not used for said hydrogenation.
We have found that this object is achieved, in one embodiment, by a process for hydrogenating an anthraquinone compound or a mixture of two or more thereof by contacting the anthraquinone compound or the mixture of two or more thereof with a catalyst to obtain an anthrahydroquinone compound or a mixture of two or more thereof, which comprises using a catalyst (catalyst 1) comprising at least one homogeneous compound of at least one metal of transition group VIII of the Periodic Table of the Elements alone or together with at least one metal of transition group I or VII of the Periodic Table of the Elements, deposited on a support in situ.
The present invention further provides a process for hydrogenating an anthraquinone compound as described above, which comprises using a catalyst (catalyst 2) comprising, as active metal, at least one metal of transition group VIII of the Periodic Table of the Elements, alone or together with at least one metal of transition group I or VII of the Periodic Table of the Elements, applied to a support, the support having a mean pore diameter of at least 50 nm and a BET surface area of at most 30 m
2
/g and the amount of active metal being from 0.01 to 30% by weight, based on the total weight of the catalyst, and the ratio of the surface areas of the active metal and the catalyst support preferably being<0.05.
The invention further provides a process for hydrogenating an anthraquinone compound as defined above, which comprises using a catalyst (catalyst 3) comprising, as active metal, at least one metal of transition group VIII of the Periodic Table of the Elements, alone or together with at least one metal of transition group I or VII of the Periodic Table of the Elements, in an amount of from 0.01 to 30% by weight, based on the total weight of the catalyst, applied to a support, from 10 to 50% of the pore volume of the support being macropores having a pore diameter of from 50 nm to 10,000 nm and from 50 to 90% of the pore volume of the support being mesopores having a pore diameter of from 2 to 50 nm, the sum of the pore volumes being 100%.
In another embodiment, the present invention provides a process for hydrogenating an anthraquinone compound as described above, which comprises using a catal)-st (catalyst 4) comprising, as active metal, at least one metal of transition group VIII of the Periodic Table of the Elements with at least one metal of transition group I or VII of the Periodic Table of the Elements, in an amount of from 0.01 to 30% by weight, preferably from 0.2 to 15% by weight, based on the total weight of the catalyst, applied to a support, the support having a mean pore diameter of at least 0.1
&mgr;
m, preferably at least 0.5
&mgr;
m, and a surface area of at most 15 m
2
/g, preferably at most 10 m
2
/g.
The invention further provides a process for hydrogenating an anthraquinone compound as described above, which comprises using as a catalyst (catalyst 5) a monolithic supported catalyst obtainable by sequentially heating in air and cooling down a support material in the form of a metal fabric or metal foil, followed by coating with an active component under reduced pressure, subsequent cutting and shaping of the coated support material and finally processing to give a monolithic supported catalyst, using, as active metal, at least one metal of transition group VIII of the Periodic Table of the Elements alone or together with at least one metal of transition group I or VII of the Periodic Table of the Elements.
Any metal of transition group VIII of the Periodic Table of the Elements can in principle be used as active metal. Platinum, rhodium, palladium, cobalt, nickel or ruthenium or a mixture of two or more thereof are preferably used as active metals, in particular ruthenium. It is in principle likewise possible to use any metal of transition group I and/or VII, preference being given to using copper and/or rhenium.
For the purposes of the present invention, the terms “macropores” and “micropores” are used as defined in Pure Appl. Chem. 45 (1976) p. 79, namely to describe pores whose diameter is above 50 nm (macropores) or from 2 nm to 50 nm (mesopores).
The active metal content is generally from about 0.01 to about 30% by weight, preferably from about 0.01 to about 5% by weight, especially from about 0.1 to about 5% by weight, in each case based on the total weight of the catalyst used, the preferred contents of the catalysts 1 to 5 being specifically reported in the discussion of these catalysts.
“Anthraquinone compound” encompasses in principle all anthraquinone compounds and the corresponding tetrahydroanthraquinone compounds suitable for use in the preparation of hydrogen peroxide. The preferred compounds which can be used are described briefly in the chapter

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