Synthesis of hydrogen peroxide

Details Synthesis of hydrogen peroxide Synthesis of hydrogen peroxide

1998-06-29

2002-01-29

Padmanabhan, Sreeni (Department: 1621)

Chemistry of inorganic compounds

Oxygen or compound thereof

Peroxide

C423S584000, C423S589000, C423S590000, C568S326000, C568S332000

Reexamination Certificate

active

06342196

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the synthesis of hydrogen peroxide, and more particularly, to the synthesis of hydrogen peroxide without the use of an organic solvent.
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.
It is, therefore, very desirable to develop reactants and processes for the synthesis of hydrogen peroxide that minimize or eliminate the use of organic solvents.
SUMMARY OF THE INVENTION
In general, the present invention provides a method for synthesizing hydrogen peroxide, comprising 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).
A liquid-liquid phase envelope is preferably formed in the functionalized anthraquinone-carbon dioxide systems of the present invention at relatively moderate pressures. The operating pressure at which the analogs of anthraquinone (and preferably the analogs of hydroquinone) are reacted in carbon dioxide is preferably no greater than approximately 5000 psi. More preferably, the operating pressure is no greater than approximately 3000 psi. Even more preferably, the operating pressure is no greater than approximately 2500 psi. Most preferably, the operating pressure is no greater than approximately 1500 psi. The operating pressure at which the analogs of anthraquinone are reacted with hydrogen (and, preferably, the operating pressure at which the analogs of hydroquinone are reacted with oxygen) is preferably chosen such that it is above the cloud point curve (and, preferably, above the maximum of the cloud point curve) in the liquid-liquid phase envelop (or liquid-fluid phase envelope when operating at supercritical conditions). In the region above the cloud point curve, single-phase behavior is observed.
The operating temperature of the present reactions is preferably between approximately 0° C. and approximately 100° C. The operating temperature of the present reactions is more preferably between approximately 20° C. and approximately 40° C. Most preferably, the operating temperature of the present reactions is approximately 25° C. (room temperature).
Preferably, the CO
2
-philic functionalized anthraquinones and the corresponding hydroquinones of the present invention exhibit reactivity similar to the 2-alkyl anthraquinone and hydraquinones used in the current commercial synthesis of hydrogen peroxide. Indeed, the kinetic rate constants calculated for the oxygenation of the functionalized anthraquinones of the present invention were found to be approximately ten time greater than anthraqinone. The use of CO
2
-philic groups to increase the solubility of a molecule in carbon dioxide is also discussed in U.S. Pat. No. 5,641,887, the disclosure of which is incorporated herein by reference.
In general, the analog of anthraquinone preferably has the formula:
At least one of R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, and R
8
(corresponding to the 1, 2, 3, 4, 5, 6, 7, and 8 carbons on the anthraquinone ring structure) is a modifying group or functional group that is miscible/souble in carbon dioxide. Attachment of one or more such CO
2
-philic groups to anthraquinone results in an analog of anthraquinone that is miscible/soluble in carbon dioxide. In that regard, R
1
, R
2
, R
3
, R
4
, R
5
, R
6
, R
7
, and R
8
are preferably, independently, the same or different, H, R
C
or R
S
R
C
, wherein R
S
is a connector or a spacer group and R
C
is a fluoroalkyl (fluorinated alkyl) group, a fluoroether (fluorinated ether) group, a silicone group, an alkylene oxide group, a phosphazene group or a fluorinated acrylate group. At least one of R
1
, R
2
, R
3
, R
4

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-2835119