Condenser temperature choices

The purpose of the glass tube condenser is to condense virtually all the input gas s H2S04(g) as sulfuric acid during the gas s passage up the glass condenser tubes. The next four subsections describe condenser temperatures chosen to achieve this purpose. 

The temperature of the input process gas must be higher than the sulfuric acid dew point of the gas. Otherwise, sulfuric acid will condense in and corrode the process gas input flue and the upstream gas heat exchanger. The input flue gas temperature is typically 270-290 °C. This temperature is usually kept 20-30 °C above the acid dew point, which increases with increasing feed gas SO2 concentration. 

The output process gas temperature is chosen so that the gas contains very little uncondensed H2S04(g). Specifically, it is chosen so that the H2S04(g) vapor pressure of the condensing acid at the top of the condensing tube is 2 x 10 bar, which is equivalent to 2 X lO volume% H2S04(g) in the gas. The output gas temperature is typically 110 °C. 

Output cooling air temperature must be lower than the process gas input temperature. This ensures that the process gas is being cooled over the whole length of the glass condenser tubes. However, the process gas must not be so cool that sulfuric acid mist condenses homogeneously inside the glass tubes (Schoubye, 1993). This restricts exit cooling air temperature to above 190 °C. 

The sensible heat in this warmed exit cooling air is not wasted. It is recovered by using it for combustion and heating duties around the plant. 

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During the course of exploratory experimentation involved in the preparation of 8-242pU203, some limited oxygen potential measurements over Pu02-X fluorite phase were made at 1750 and 2050 K. The transpiration method was used for this study because, for a given temperature, the composition of the condensed phase can be fixed by appropriate choice of oxygen potential (via H2/... 

Table I. It is probable that all the indicated yields can be improved. However, using these data as a criterion, it appears that the chloral can be replaced by its hydrate or alcoholate and that a moderate excess of fluorobenzene favors the reaction. There is one report that aluminum chloride brings about this condensation (34), but here, as with DDT, the choice condensing agents are concentrated sulfuric acid (with or without the addition of oleum), and chlorostflfonic acid (84). A moderate temperature and prolonged stirring, which must also be vigorous, increase the yield.

As discussed in Section 7.1.4, polymer-bound acetoacetates can be used as precursors for the solid-phase synthesis of enones [33], For these Knoevenagel condensations, the crucial step is to initiate enolization of the CH acidic component. In general, enolization can be initiated with a variety of catalysts (for example, piperidine, piperidinium acetate, ethylenediamine diacetate), but for the microwave-assisted procedure piperidinium acetate was found to be the catalyst of choice, provided that the temperature was kept below 130 °C. At higher reaction temperatures, there is significant cleavage of material from the resin. 

Darzens reaction of (-)-8-phenylmethyl a-chloroacetate (and a-bromoacetate) with various ketones (Scheme 2) yields ctT-glycidic esters (28) with high geometric and diastereofacial selectivity which can be explained in terms of both open-chain or non-chelated antiperiplanar transition state models for the initial aldol-type reaction the ketone approaches the Si-f ce of the Z-enolate such that the phenyl ring of the chiral auxiliary and the enolate portion are face-to-face. Aza-Darzens condensation reaction of iV-benzylideneaniline has also been studied. Kinetically controlled base-promoted lithiation of 3,3-diphenylpropiomesitylene results in Z enolate ratios in the range 94 6 (lithium diisopropylamide) to 50 50 (BuLi), depending on the choice of solvent and temperature. ... 

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