Synthesis of hydrogen peroxide

Details Synthesis of hydrogen peroxide Synthesis of hydrogen peroxide

2000-04-28

2003-12-02

Langel, Wayne A. (Department: 1754)

Chemistry of inorganic compounds

Oxygen or compound thereof

Peroxide

Reexamination Certificate

active

06656446

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the synthesis of hydrogen peroxide, and more particularly, to the synthesis of hydrogen peroxide in which the use of organic solvents is reduced or eliminated.
BACKGROUND OF THE INVENTION
Hydrogen peroxide (H
2
O
2
) is often considered to be a “green” material, in that it is increasingly used to replace chlorine-containing reagents in paper bleaching and in water purification. For this reason, as well as others, hydrogen peroxide production is estimated to increase steadily through the beginning of the next century.
The production of hydrogen peroxide is a mature process in that the general procedure has not changed appreciably in twenty years. Indeed, recent research publications in the area of hydrogen peroxide synthesis are somewhat scarce. Typically, hydrogen peroxide is generated in a two-step process, wherein hydrogen is first reacted with a 2-alkyl anthraquinone (usually 2-ethyl or 2-amyl anthraquinone) in an organic solvent to produce the corresponding tetrahydroquinone (2-alkyl tetrahydroquinone) The reaction is catalyzed by a simple palladium-on-alumina catalyst. Conditions for this reaction are typically 30 to 70° C. with hydrogen pressures up to 300 psi. Given the nature of the reactants, the reactor contains three phases (gas, liquid, and solid catalyst) and previous work has shown that the reaction is completely mass transfer limited, such that the rate of the reaction is essentially the rate at which hydrogen diffuses into the liquid phase. Partly as a result of this inefficiency of hydrogen use, side reactions (hydrogenation of one or both of the aromatic rings) also occur, and byproducts build up during repeated cycling of the anthraquinone. These byproducts must periodically be removed and treated. The organic solvent employed is typically a mixture of an aromatic (a good solvent for the anthraquinone) and a long-chain alcohol (a good solvent for the hydroquinone).
The second step of the process involves oxidation of the hydroquinone, regenerating the anthraquinone and producing hydrogen peroxide. Here the catalyst is retained in the first reactor, and the solution of alkyl anthraquinone, alkyl tetrahydroquinone and organic solvent (the working solution) is transferred to the second reactor, where the hydroquinone is reacted with oxygen (as air or oxygen). This reaction is uncatalyzed. Similar to the first reaction, the second reaction is mass transfer limited by the rate at which oxygen can diffuse from the gas to liquid phases. Finally, the hydrogen peroxide is stripped from the organic solvent via liquid-liquid extraction with water and sold as an aqueous mixture (usually 30 to 50%).
Because the final step in the production of hydrogen peroxide involves a liquid-liquid extraction between aqueous and organic phases, the final product is contaminated to some extent by the organic phase. Given that H
2
O
2
is promoted as a green reagent for paper production, and is also used in water purification, the organics in the final product must be minimized. Significant effort is thus made to strip the organic contaminants from the product.
Although approximately 95% of the world's hydrogen peroxide is produced via the anthraquinone process described above, a number of other synthetic routes exist. For example, from the 1960's to the 1980's, Shell maintained several hydrogen peroxide production plants that employed a free-radical initiated oxidation of a secondary alcohol (isopropanol) for the generation of hydrogen peroxide. These plants were closed, however, in the early 1980's because they could not compete economically with the well-known anthraquinone route to hydrogen peroxide production. The primary disadvantages to the use of secondary alcohol oxidation are that (a) one has to distill a complex mixture of hydrogen peroxide, water, residual alcohol, and the ketone byproduct of the reaction to purify the hydrogen peroxide product, and hot hydrogen peroxide is a safety hazard; and (b) the required reaction temperature for this process is rather high, 100 to 150° C., also a safety hazard. During the 1980's, Arco Chemical explored the use of another secondary alcohol, phenethyl alcohol, for use in the production of hydrogen peroxide. This secondary alcohol exhibited better reactivity than isopropanol, but that process suffers from similar disadvantages to the isopropanol process described above.
Arguably, the ideal synthetic route for producing hydrogen peroxide would be one that employs the simple reaction of hydrogen plus oxygen, yet which could also run safely. Clearly, a mixture of hydrogen and oxygen can pose a serious safety hazard, one fact that has prevented such a technology from being scaled up and commercialized to date. On the other hand, production of hydrogen peroxide from only oxygen and hydrogen would represent the most efficient (and thus the most inexpensive) and cleanest method by which to generate the product.
Indeed, a number of research groups throughout the world have been investigating a more direct route to the production of hydrogen peroxide, that is, via the direct reaction of hydrogen and oxidation. The keys to a successful process include (a) maintaining safe operating conditions, (that is, preventing explosion), (b) generating hydrogen peroxide continuously and at high rates (to satisfy economic constraints), and (c) preventing decomposition of the hydrogen peroxide product once it is formed. To date, attempts to develop a commercially viable synthetic route to hydrogen peroxide via the direct route of hydrogen and oxidation have met with very limited success.
It remains, therefore, very desirable to develop reactants and processes for the synthesis of hydrogen peroxide.
SUMMARY OF THE INVENTION
A method for synthesizing hydrogen peroxide using a CO
2
-philic anthraquinone is described in U.S. patent application Ser. No. 09/106,480, filed Jun. 29, 1998, U.S. Pat. No. 6,342,196, and entitled SYNTHESIS OF HYDROGEN PEROXIDE, assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference. That method comprises generally the steps of:
synthesizing an analog of anthraquinone that is miscible with (in the case of a liquid analog) or soluble in (in the case of a solid analog) carbon dioxide;
reacting the analog of anthraquinone with hydrogen in carbon dioxide to produce a corresponding analog of tetrahydroquinone; and
reacting the analog of tetrahydroquinone with oxygen to produce the hydrogen peroxide and regenerate the analog of anthraquinone.
Preferably, the regenerated analog of anthraquinone is recycled for future use.
The step of synthesizing an analog of anthraquinone that is miscible in carbon dioxide preferably comprises the step of attaching to anthraquinone at least one modifying or functional group that is relatively highly soluble in CO
2
(“CO
2
-philic”). The miscibility/solubility of the resulting analogs of anthraquinone are several orders of magnitude greater at the operating pressures of the present invention than the solubility of 2-alkyl anthraquinone in carbon dioxide at pressures equal to or below 5000 psi. Alkyl-anthraquinones used in the commercial synthesis of hydrogen peroxide do not exhibit appreciable solubility in carbon dioxide at pressures below 5000 psi. In that regard, a number of studies have explored the solubility of alkyl-functional anthraquinones in carbon dioxide and found generally that the system exhibits solid-fluid phase behavior with maximum solubilities of approximately 10
−2
mM. See, for example, Joung, S. N., Yoo, K. P.,
J. Chem. Eng. Data
, 43, 9 (1998). Coutsikos, P., Magoulos, K., Tassios, D.,
J. Chem. Eng. Data
, 42, 463 (1997). Swidersky, P., Tuma, D., Schneider, G. M., J.,
Supercrit. Fl
., 9, 12 (1996). ibid, 8, 100 (1995).
Preferably, the CO
2
-philic functionalized anthraquinones and the corresponding hydroquinones exhibit reactivity similar to the 2-alkyl anthraquinone and hydroquinones used in the current commercial synthesis of hydrogen peroxide.

Affiliated with

Also associated with

Rating

Synthesis of hydrogen peroxide does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Synthesis of hydrogen peroxide, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Synthesis of hydrogen peroxide will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3095935