Regeneration continuous

Oxidation of benzoin with concentrated nitric acid or by catalytic amounts of cupric salts in acetic acid solution, which are regenerated continuously by ammonium nitrate, yields the diketone benzil ... 

The catalytic cracking processes, as well as most other refinery catalytic processes, produce coke which collects on the catalyst surface and diminishes its catalytic properties. The catalyst, therefore, needs to be regenerated continuously or periodically essentially by burning the coke off the catalyst at high temperatures. 

The oxidation of an anthracene suspension in sulfuric acid conducted in the presence of cerium salts can serve as an example of mediated oxidation. In the bulk solution the Ce" ions chemically oxidize anthracene to anthraquinone. The resulting Ce ions are then reoxided at the anode to Ce". Thus, the net result of the electrochemical reaction is the oxidation of anthracene, even though the electrochemical steps themselves involve only cerium ions, not anthracene. Since the cerium ions are regenerated continuously, a small amount will suffice to oxidize large amounts of anthracene. 

In this example the XZ intermediate compound corresponds to the 2 N02 term, and the catalyst nitric oxide is regenerated continuously. 

In this process, propane, and a small amount of hydrogen to control coking, are fed to either a fixed bed or moving bed reactor at 950—1300° F and near atmospheric pressure. Once again the catalyst, this time platinum on activated alumina impregnated with 20% chromium, promotes the reaction. In either design, the catalyst has to be regenerated continuously to maintain its activity. 

Macrolides. Steliou, Hanessian, and co-workers- have prepared lactones and lactams in moderate to excellent yield by treatment of ro-hydroxy or ru-amino carboxylic acids with catalytic amounts of di-r -butyltin oxide in refluxing mesitylcne or xylene in a Dean-Stark apparatus for 12 24 hours. The method has the advantage of high dilution, since the tin reagent is regenerated continuously. As expected, yields arc low for medium-sized rings. 

Replacement of either one or two of the chlorines of carbon tetrachloride by fluorine can be achieved readily with antimony trifluoride containing some antimony pentachloride. The reaction stops after two chlorines have been replaced. The antimony trifluoride can be regenerated continuously from the antimony chloride by addition of anhydrous hydrogen fluoride ... 

The reactions are always accompanied by coke deposition on the catalyst, which causes catalyst deactivation, and the catalyst must be regenerated continuously. 

Type of operations Periodic regeneration Continuous Continuous (but not during transient) Continuous... 

The first treatment usually brings great satisfaction to the patient in terms of how the stretch marks feel they do not feel as deep, and the depressed atrophic base starts to fill out. Gradually, the atrophic base comes level with the surrounding skin, and in places its structure returns completely to normal. Regeneration continues throughout the following treatments. 

In the earlier instruments, the suppressor unit was a cation-exchange column of high capacity that had to be regenerated periodically. Newer suppressors contain ion-exchange membranes that can be regenerated continuously by flowing a solution of sulfuric acid over the outer membrane surface or by electrically generated acid. 

Membrane suppressors that can be regenerated continuously have also been developed for the ion-exclusion chromatography of weak acids. In IE, the primary contributor to the high eluent conductance is the hydrogen cation from the acid eluent. Membrane suppressors can reduce this background by exchanging the hydronium ion for tetrabutylammonium ion (TBA). This is shown in Table 8.2. 

Properties and Control. Early cupric chloride formations had slow etch rates and low copper capacity and were limited to batch operation. Regenerated continuous operation using modified formulations has brought useful improvements. Etch rates as high as 55 s for 1 oz copper are obtained from cupric chloride-sodium chloride-HCl systems operated at 130°F with conventional spray-etching equipment. Copper capacities are maintained at 20 oz/ gal and above. However, more recently, higher copper contents and adjusted chemistries at 125°F typically etch at 75 to 90 s for 1 oz copper. 

The determination of traces of inorganic disinfection by-products (IDBPs) in drinking water samples needs improved lower limit of detection. In order to achieve this, a new electrochemically regenerating continuously operating suppressor (DS-Plus suppressor. Model 335 suppressor module. Alltech Associates (Deer-field, IL)) has been tested and was foimd well applicable by Bose et al. [96]. 

Miscellaneous Processes.—Various types of reaction other than those discussed above have been investigated under PTC conditions, and only some recent instances are cited here. A ready debromination of 1,2-dibromides to alkenes (Equation 7) by aqueous iodide uses catalytic quantities of both a phosphonium salt (to transfer iodide ion) and iodide ion itself. The latter species is regenerated continuously by reduction of the halogen products with sodium thiosulphate in the... 

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