Hydrogen cycling, feed

Among the few quantitative data on ion exchange performance in the technical literature are those reported by Myers (18) of the Rohm and Haas Co. He reports experimental results using Amberlite IR-1 in the hydrogen cycle with a sodium chloride feed solution, giving both feed and effluent concentrations. 

Figure 5. The shaded region shows the domain of ethane yields obtained in several different steady-state experiments at different stages of deactivation of Catalyst 11. The curves show ethane yields obtained by cycling feed hydrogen concentration with different periods.

Figure 7. Instantaneous effluent compositions for feed hydrogen cycling with Catalyst II for nine sets of periods (t) and mean hydrogen feed rates (directly related to y see Equation 4)...

In the solvent extraction step thorium and uranium are co-extracted in the first cycle subsequent partitioning of thorium and uranium in the second cycle gives two decontaminating cycles to both products while using only five columns. For short-decayed thorium a reductant, sodium hydrogen sulfite, is continuously added to the feed streams of both cycles to decrease the effect of nitrite formed by irradiation. Without the sulfite addition, the nitrite formed by radiation decomposition of nitrates converts ruthenium to a solvent-extractable form. Acid deficiency in the second cycle feed is achieved by adding dibasic aluminum nitrate (diban). 

PoUowing further development (38), a two-cycle process has been adopted by industry. In the first concentration cycle, the clarified feed acid containing 100—200 mg/L U Og [1334-59-8] is oxidized, for example, with hydrogen peroxide or sodium chlorate [7775-09-9] to ensure that uranium is in its 6+ valence state is not extracted. Uranium is extracted with a solvent composed of 0.5 Af D2EHPA and 0.125 Af TOPO dissolved in an aUphatic hydrocarbon diluent. 

A flow diagram for the system is shown in Figure 5. Feed gas is dried, and ammonia and sulfur compounds are removed to prevent the irreversible buildup of insoluble salts in the system. Water and soHds formed by trace ammonia and sulfur compounds are removed in the solvent maintenance section (96). The pretreated carbon monoxide feed gas enters the absorber where it is selectively absorbed by a countercurrent flow of solvent to form a carbon monoxide complex with the active copper salt. The carbon monoxide-rich solution flows from the bottom of the absorber to a flash vessel where physically absorbed gas species such as hydrogen, nitrogen, and methane are removed. The solution is then sent to the stripper where the carbon monoxide is released from the complex by heating and pressure reduction to about 0.15 MPa (1.5 atm). The solvent is stripped of residual carbon monoxide, heat-exchanged with the stripper feed, and pumped to the top of the absorber to complete the cycle. 

Aside from the above reforming reactions, a small amount of feed components are converted to polymeric hydrogen deficient products which deposit on the catalyst as "coke." A coke buildup results in activity and selectivity loss which ultimately requires catalyst regeneration. In semi-regenerative operation, the coking rate is maintained at a low level to provide cycles of at least three to six months. In cyclic units, coking conditions are inherently much more severe so that frequent regenerations are required. 

Addition reaction of peroxide-generated macroalkyl radicals with the reactive unsaturation in MA is shown in reaction scheme 4. The functionalised maleic-polymer adduct (II, scheme 4) is the product of hydrogen abstraction reaction of the adduct radical (I, scheme 4) with another PP chain. Concomitantly, a new macroalkyl radical is regenerated which feeds back into the cycle. The frequency of this feedback determines the efficiency of the cyclical mechanism, hence the degree of binding. Cross-linking reaction of I occurs by route c ( scheme 4). 

Among the classes of feedstock processed in the hydrocracker the most highly aromatics feed are light cycle oils produced in the FCC unit Once formed by cyclization and the hydrogen transfer mechanism discussed above, they accumulate in the product due to the absence of a metal function in the FCC catalyst and adequate hydrogen in the process environment. They are typically sold as low-value fuel oil, or hydrotreated to reduce sulfur content and improve their quality as diesel blend stocks. Another approach to upgrade their value even further... 

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