Anthraquinone process

Working Solution Composition. The working solution in an anthraquinone process is composed of the anthraquinones, the by-products from the hydrogenation and oxidation steps, and solvents. The solvent fraction usually is a blend of polar and aromatic solvents which together provide the needed solubiUties and physical properties. Once the solution has been defined, its composition and physical properties must be maintained within prescribed limits for achieving optimum operation. 

Interest has continued in on-site manufacture of hydrogen peroxide from the elements, particularly for remote sites located considerable distances from wodd-scale anthraquinone processes. However, no commercial-scale direct combination plants have been constmcted as of this writing. 

Dream reactions can be performed using chemical micro process engineering, e.g., via direct routes from hazardous elements [18]. The direct fluorination starting from elemental fluorine was performed both on aromatics and aliphatics, avoiding the circuitous Anthraquinone process. While the direct fluorination needs hours in a laboratory bubble column, it is completed within seconds or even milliseconds when using a miniature bubble column. Conversions with the volatile and explosive diazomethane, commonly used for methylation, have been conducted safely as well with micro-reactors in a continuous mode. 

It is anticipated that the new, environmentally friendly technology designed by Headwaters for H2O2 production will soon replace the current anthraquinone process because of the high activity, selectivity, and durability of the novel nanocatalyst. 

The alkylated anthraquinone process accounts for over 95% of the world production of H202, mainly because the it operates under mild conditions and direct contact of 02 and H2 is avoided. In this process, 2-alkylanthraquinone (the alkyl group is typically an ethyl, terf-butyl or amyl group) is dissolved in a mixture of a non-polar solvent (C9-Cn alkylbenzene) and a polar solvent [Trioctyl phosphate (TOP), or tetrabutyl urea (TBU) or diisobutyl carbinol (DIBC)] and then hydrogenated over a precious metal (Pd or Ni) catalyst in a three-phase reactor (trickle bed or slurry bubble column) under mild reaction conditions (<5bar, <80 °C) to generate 2-alkylanthrahydroquinone [1-3, 5], The latter is then auto-oxidized with air in a... 

The hydrogenation step in the anthraquinone process of AKZO-Nobel is an industrial realization of a monolithic reactor and includes a lot of pioneering work from the Anderson group (59-63). More examples of the use of monoliths can be found in Refs. 5 and 64. 

The current efficiency of Traube s method was pushed to 92% [94] with the introduction of pressurized electrolysis. In 1939, Rubio [93] developed another process for producing H202 by the reduction of 02 in 50% KOH using an active carbon cathode and a Ni anode, with no industrial success. Today, most H202 are produced chemically by the anthraquinone process, which is unsuitable for small-scale production [91]. Another electrochemical process involving 02 reduction on carbon-based cathodes developed by Dow Chemical [2,95] has found a marketplace for on-site production of alkaline H202 for pulp bleaching. 

Electrochemical methoxylations usually lead to acetals or ketals these must be distilled and/or hydrolzed [8] to give the target molecules. The resulting ketones or aldehydes are purified again. In the anthraquinone process of Hydro Quebec [9], some of the cru-denaphthoquinone is purified further, but most of the crude products is reacted with butadiene to yield tetrahydroanthraquinone, which is dehydrogenated to anthraquinone. 

The anthraquinone process was developed by Hydro Quebec [105]. The licensing of plants for several thousand tons per year is negotiated with potential customers. The pilot-plant performance has been published [106]. 

Of these processes, the first has only historical interest the plants which produced 15 000 t/a of hydrogen peroxide and 30 000 t/a of acetone were shut down in 1980. Only in the former States of the USSR are such plants still in use. The electrochemical oxidation process is also of limited importance. Over 95% of the hydrogen peroxide is produced with the anthraquinone process. Electrochemical... 

The anthraquinone process requires a complex solvent mixture ... 

Formation of byproducts - particularly during hydrogenation - complicates the anthraquinone process... 

In practice, the anthraquinone process is much more complicated than has been de.scribed above, in that byproducts such as 1,2,3,4-tetrahydroanthraquinone are formed, particularly in the hydrogenation step. These behave similarly to anthrahydroquinones, but their further hydrogenation leads to octahydroanthrahydroquinones which are unusable in this process. Other byproducts such as oxanthrones and anthrones can only be partially regenerated. These unusable byproducts have to be removed from the process. 

Nevertheless, peroxide is least stable in alkaline solutions and so the production of pure H2O2 from the mixture is difficult and again uncompetitive considering the anthraquinone process. But the... 

J. M. Campos-Martin, G. Blanco-Brieva, J. L. G. Fierro, Hydrogen peroxide syntliesis, an outlook beyond the anthraquinone process, Angew. Chem. Int. Ed. 45, 6962-6984 (2006). 

The oxidation of isopropanol process is used only in a few plants in Russia and the electrochemical processes are currently utilized only in a few plants in Western Europe because of the high operating costs due to the large use of electricity. Because of their minor importance in H202 production [126], they will not be discussed further. The anthraquinone process accounts for 95% of the H202 production. The direct reaction of H2 and 02 is a recent discovery, so it is not yet fully utilized [126], The reaction cycle is ... 

The anthraquinone process involves a reduction/oxidation cycle with 2— alkyl-anthrahydroquinone where H202 is produced during the oxidation portion of the cycle. The alkyl group on the anthraquinone is usually ethyl, although /-butyl, /-amyl, and sec-amyl have been used [108]. 

Presently, the investment cost is about half as much as the anthraquinone process for the production of H202, but operating costs are higher for the direct reaction however, improvements are being made and should make the direct reaction process an economic alternative in the near future [130]. 

Fig. 1 (a) Schematic representation of the "indirect" anthraquinone process for the production of hydrogen peroxide using 2-alkyl-anthraquinone (1) and 2-all lhydroan-thraquinone (2). (b) Schematic representation of the direct synthesis of hydrogen peroxide from H2 and O2 (route A). Other reactions that decrease the selectivity of direct synthesis reaction are decomposition of hydrogen peroxide (route B) to water and hydrogenation of hydrogen peroxide (route C) to water. 

In the anthraquinone process, an alkylanthraquinone is catalytically reduced to the corresponding hydroquinone with hydrogen the hydroquinone reacts with oxygen (air), becoming re-oxidized to the anthraquinone derivative, with the formation of hydrogen peroxide. 

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