Oxidative process concepts

Braun A M, Jakob L, Oliveros E (1993) Advanced Oxidation Processes - Concepts of Reactor Design, J Water SRT-Aqua 42, No. 3 166-173. 

Air-Based Direct Oxidation Process. A schematic flow diagram of the air-based ethylene oxide process is shown in Figure 2. Pubhshed information on the detailed evolution of commercial ethylene oxide processes is very scanty, and Figure 2 does not necessarily correspond to the actual equipment or process employed in any modem ethylene oxide plant. Precise information regarding process technology is proprietary. However, Figure 2 does illustrate all the saUent concepts involved in the manufacturing process. The process can be conveniently divided into three primary sections reaction system, oxide recovery, and oxide purification. 

Based upon the concepts of the adsorption of the anode reaction product, the share of the anodic curve, on which the carbamide oxidation processes is reflected as a wave, can be explained. It may be assumed that the adsorption of the reaction product inhibits the direct oxidation of carbamide. To verify this conclusion, the anode was polarized to the electrolysis product formation potential, and the reverse sweep was stopped before the electrolysis product was reduced at the electrode. Then the carbamide oxidation process was completely inhibited on the subsequent forward sweep, and the curve exhibited only a current increase at the chlorine ion oxidation potential. 

Recent work in our laboratories has confirmed the existence of a similar pathway in the oxidation of vindoline in mammals (777). The availability of compounds such as 59 as analytical standards, along with published mass spectral and NMR spectral properties of this compound, served to facilitate identification of metabolites formed in mammalian liver microsome incubations. Two compounds are produced during incubations with mouse liver microsome preparations 17-deacetylvindoline, and the dihydrovindoline ether dimer 59. Both compounds were isolated and completely characterized by spectral comparison to authentic standards. This work emphasizes the prospective value of microbial and enzymatic transformation studies in predicting pathways of metabolism in mammalian systems. This work would also suggest the involvement of cytochrome P-450 enzyme system(s) in the oxidation process. Whether the first steps involve direct introduction of molecular oxygen at position 3 of vindoline or an initial abstraction of electrons, as in Scheme 15, remains unknown. The establishment of a metabolic pathway in mammals, identical to those found in Strep-tomycetes, with copper oxidases and peroxidases again confirms the prospective value of the microbial models of mammalian metabolism concept. 

In an attempt to illustrate in a simple way the general concept of the doping process in polymers, let us consider the p-doping (oxidation) process of polypyrrole. In the undoped state, polypyrrole is a poor electronic conductor with an energy gap of 3.2 eV between the conduction band (CB) and the valence band (VB) ... 

Microbial biofuel cells were the earliest biofuel cell technology to be developed, as an alternative to conventional fuel cell technology. The concept and performance of several microbial biofuel cells have been summarized in recent review chapters." The most fuel-efficient way of utilizing complex fuels, such as carbohydrates, is by using microbial biofuel cells where the oxidation process involves a cascade of enzyme-catalyzed reactions. The two classical methods of operating the microbial fuel cells are (1) utilization of the electroactive metabolite produced by the fermentation of the fuel substrate " and (2) use of redox mediators to shuttle electrons from the metabolic pathway of the microorganism to the electrodes. ... 

Several recent contributions concerning the participation of lattice oxygen in selective oxidation processes have appeared and fully agree with the above concepts. They will be discussed in more detail below. 

First we will review the basic concepts of kinetics (Section B 4.1), discussing in detail reaction order (Section B 4.2) and reaction rate constants (Section B 4.3) with emphasis on the practical aspects of determining them for oxidation processes. This lays the foundation for the discussion of which operating parameters influence the reaction rate and how (Section B 4.4). These influences are illustrated with results from current publications, with special emphasis on analyzing the common and apparently contradictory trends. 

Researchers at Degussa AG focused on an alternative means towards commercial application of the Julia-Colonna epoxidation [41]. Successful development was based on design of a continuous process in a chemzyme membrane reactor (CMR reactor). In this the epoxide and unconverted chalcone and oxidation reagent pass through the membrane whereas the polymer-enlarged organocatalyst is retained in the reactor by means of a nanofiltration membrane. The equipment used for this type of continuous epoxidation reaction is shown in Scheme 14.5 [41]. The chemzyme membrane reactor is based on the same continuous process concept as the efficient enzyme membrane reactor, which is already used for enzymatic a-amino acid resolution on an industrial scale at a production level of hundreds of tons per year [42]. 

ANALYSIS OF THE ACTIVE OXYGEN CONCEPT FROM MODERN POSITIONS OF OXIDATION PROCESSES... 

Analysis of the Active Oxygen Concept from Modern Positions of Oxidation Processes 7... 

It has even been proposed to give up the separation of the gas chambers.156-158 Then one has to completely rely on selective catalytic activity of electrocatalysts to activate reduction or oxidation processes. In Ref.158 considerable power densities have been achieved in this way. This single chamber fuel cell concept might be indeed relevant for reduced temperature application. 

Cyclic artificial photosynthetic systems (Fig. 11) include an oxidation process complementary to the reduction reaction. For light-driven reductive syntheses of valuable chemicals or for the removal of environmental pollutants the concept of utilizing a sacrificial electron donor can be adapted. Yet, for the application of artificial photosynthetic systems as fuel generation devices, several basic criteria must be met by the complementary oxidation process ... 

The indirect internal reformer (HR) is situated within the cell stack in separate reforming channels, where only the reforming reaction takes place. This concept features energetic coupling with the exothermic oxidation process. The main advantage is that no external heat exchanger is required, as the separator plate between HR and anode channel fulfills this function. The HR can be seen as an external reformer operating at fuel cell temperature. 

Initial experimentation aimed at demonstrating the principle feasibility of the appealingly simple adsorptive Claus process concept described in the previous section yielded promising results indicating excellent harmonization between the catalytic and adsorptive processes for a commercial titanium oxide-based catalyst and a 3A zeolite adsorbent, respectively [30], The amounts of water vapor adsorbed... 

Roginskil s concepts of catalyst modification may potentially be of considerable importance in clarifying the basic concepts of the inextensive oxidation process. The practical utilization and verification of this theory has been tested only in a limited number of cases (98,218). 

Vogel F, Hare J, Hug A, Rohr von PR (2000) The Mean Oxidation Number of Carbon (MOC)-A Useful Concept for Describing Oxidation Processes, Wat. Res. 34,... 

Advanced Oxidation Processes (AOPs) Principles. Reaction Mechanisms, Reactor Concepts... 

---