Anthrahydroquinone autoxidation

The first commercial-scale anthrahydroquinone autoxidation process in the United States was put into operation by E. I. du Pont de Nemours Co., Inc. (Memphis, Tennessee) in 1953, followed by EMC Corporation (West Virginia), LaPorte Chemicals, Ltd. (U.K.), Degussa (Germany), Mitsubishi-Gas Chemical Co. (Japan), and others. 

In the former USSR, there reportedly are two technologies in use one is old anthrahydroquinone autoxidation technology and the other is closed-loop isopropyl alcohol oxidation technology. Production faciUties include several smaller, 100-150-t/yr isopropyl alcohol oxidation plants and a larger, 15,000-t/yr plant, which reportedly is being expanded to 30,000-t/yr. Differences in this technology as compared to the Shell Chemical Co. process are the use of oxygen-enriched air in the oxidation step and, catalytic reduction of the coproduct acetone back to isopropyl alcohol per equation 21. 

Nitrogen Compound Autoxidation. CycHc processes based on the oxidation of hydrazobenzene and dihydrophenazine to give hydrogen peroxide and the corresponding azobenzene—phenazine were developed in the United States and Germany during World War II. However, these processes could not compete economically with the anthrahydroquinone autoxidation process. 

This electrolytic process technology is no longer used because of the extensive and continuous electrolyte purification needs, the high capital and power requirements, and economic inabiHty to compete with large-scale anthrahydroquinone autoxidation processes. 

Figure 1.3 Anthrahydroquinone autoxidation process for the manufacture of aqueous hydrogen peroxide.

Figure 18.2 Simplified block diagram of anthrahydroquinone autoxidation (AO).

The mechanism of hydroquinone autoxidation likely proceeds by a radical chain pathway. Kinetic studies carried out under relevant reaction conditions support a second-order rate law for the reaction, rate =Ar[QH2] [Oj], with an apparent activation energy of = 15 kcal/mol [21]. Based on these kinetic findings, as well as DFT studies [22], anthrahydroquinone autoxidation has been proposed to occur through initial, rate-limiting, direct H-atom abstraction from the hydroquinone species by O2 (Eq. (14.2)). The semiquinone species then react readily with triplet O2 (Eq. (14.3)), and hydroperoxy radical, HO2, has been proposed to act as a radical chain carrier (Eq. (14.4)). 

In the autoxidation step of the AO process, the 2H /2e reduction of O2 to HjOj is coupled to the uncatalyzed oxidation of anthrahydroquinone to anthraquinone. A variety of 2-alkylanthraquinones have been reported, but 2-ethylanthraquinone... 

An important redox equilibrium exists between anthrahydroquinone A and tetra (Eq. (14.9)). Because tetra is more readily reduced than the parent anthraquinone, this equilibrium lies almost entirely to the right. Thus, if tetra formation is not suppressed, eventually all the hydroquinone species present in the oxidation process will consist of the reduced form of tetra. Because the analogous tetra hydroquinone is oxidized more slowly, the autoxidation step will slow down significantly. 

The capability of anthrahydroquinone derivatives to afford corresponding anthraquinones and HjOj in the course of autoxidation, through decomposition of intermediate HP (Eq. 14.9), consti-mtes a basis for the main industrial process of the hydrogen peroxide production (the Riedl-f eiderer process) [22]. 

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