Working solution

Whoever you are, you will certainly find discussion with your fellow students one way to get the most out of the programme and you may well find it is a good idea to work on the more difficult problems together. The review problems, revision problems, and problems without worked solutions are ideal for this. In some cases I have given references to the original hterature so that you can find out more details of the various possible approaches for yourself if you want to. It isn t necessary to look up any of these references as you work through the programme. 

Although considered an active participant in the process cycle, the tetrahydroaLkylanthraquinone (10) may not be a significant part of the catalytic hydrogenation because, dependent on the concentration in the working solution, these could all be converted to the hydroquinone by the labile shift per equation 17 and not be available to participate. None of the other first- or second-generation anthraquinone derivatives produce hydrogen peroxide, but most are susceptible to further reaction by oxidative or reductive mechanisms. 

The chemical yield of hydrogen peroxide and the anthraquinone per process cycle is very high, but other secondary reactions necessitate regeneration of the working solution and hydrogenation catalyst, and the removal of organic material from the extracted hydrogen peroxide. 

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. 

Table 4. U.S. Hydrogen Peroxide Producers Working Solution Components...

The tray-free area can be decreased at intervals from top to bottom as the density differential between the aqueous phase and the working solution widens. This adjustment maintains a nearly constant depth of coalesced working solution beneath each tray. For this type extractor the distance between trays (spacings) is constant from top to bottom. Alternatively, the tray area can be held constant and the height of the coalesced layer beneath the tray permitted to vary, thus providing the needed pressure drop for flow. 

The alumina or sodium alurninosiHcate catalysts used to regenerate degraded working solutions lose activity with time as active soda sites are neutralized, but these too can be regenerated. 

High pressure Hquid chromatography (qv) (138) and coulometry can be used to detect and quantify anthraquinones and thek derivatives in a hydrogen peroxide process working solution. 

The text is deliberately concise. Each chapter is designed to cover the content of one 50-minute lecture, twenty-seven in all, and allows time for demonstrations and illustrative slides. A list of the slides, and a description of the demonstrations that we have found appropriate to each lecture, are given in Appendix 2. The text contains sets of worked case studies (Chapters 7, 12, 16, 20, 22, 24, 26 and 27) which apply the material of the preceding block of lectures. There are examples for the student at the end of the book worked solutions are available separately from the publisher. 

Each chapter is designed to provide the content of a 50-minute lecture. Each block of four or so chapters is backed up by a set of Case Studies, which illustrate and consolidate the material they contain. There are special sections on design, and on such materials as wood, cement and concrete. And there are problems for the student at the end of each chapter for which worked solutions can be obtained separately, from the publisher. In order to ease the teaching of phase diagrams (often a difficult topic for engineering students) we have included a programmed-learning text which has proved helpful for our own students. 

It has been shown that an increase in crystallizer residence time, or decrease in feed concentration, reduces the working level of supersaturation. This decrease in supersaturation results in a decrease in both nucleation and crystal growth. This in turn leads to a decrease in crystal surface area. By mass balance, this then causes an increase in the working solute concentration and hence an increase in the working level of supersaturation and so on. There is thus a complex feedback loop within a continuous crystallizer, illustrated in Figure 7.11. 

Blue-numbered questions have answers in Appendix 6 and fully-worked solutions in the Student Solutions Manual. 

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