Recycling integrated

Ignea C, Cvetkovic I, Loupassaki S, Kefalas P, Johnson C, Kampranis S, Makris A (2011) Improving yeast strains using recyclable integration cassettes, for the production of plant... 

The overall strategy for the hierarchical procedure is as follows. First, the six pretreatment methods are compared in terms of energy requirements. Then, the implementation of a direct recycle integration strategy is analyzed. The pretreatment options are then combined with conversion configurations and analyzed via process simulation. Next, a separation step based on conventional distillation is implemented. Finally, reactor fixed costs are estimated for some options to complete the analysis. Figure 2.2 summarizes the overall methodology. 

Most HCl consumed foi the production of EDC and methyl chloride is recycled acid generated in an integrated process and therefore does not affect net supphes of HCl. The exclusion of HCl consumption for EDC and methyl chloride production gives a better indication of net HCl supply. This figure gives only an order of magnitude of net HCl available for captive consumption and sales. 

Urea is dehydrated to cyanamide which trimerizes to melamine in an atmosphere of ammonia to suppress the formation of deamination products. The ammonium carbamate [1111-78-0] also formed is recycled and converted to urea. For this reason the manufacture of melamine is usually integrated with much larger facilities making ammonia and urea. 

Mechanical Mills with Mir Classifiers. To improve the end fineness and achieve a sharper topsize cutoff point, many mechanical impact mills are fitted with integral air classifiers (Fig. 13). These can be driven separately from the mill rotor or share a common drive. The material to be ground is introduced into the mill section of the machine, where impact size reduction takes place. The airflow through the machine carries the partially ground product to the air classifier, which is usually some form of rotating turbine. The speed of rotation determines which particle size is internally recycled for further grinding and which is allowed to exit the machine with the airflow. Machines are available up to 375 kW and can achieve products with essentially all material <20 fim. 

The feedstocks to the styrene process are ethylbenzene and superheated steam, and a typical unit produces hydrogen, small amounts of light hydrocarbons and carbon dioxide as gaseous products, and a Hquid product stream containing 95% + styrene and minor amounts of toluene, benzene, and other aromatics. In an integrated plant, the benzene can be recycled to the ethylbenzene unit, while the other by-products usually are consumed as fuel for the highly endothermic process. 

Oxychlorination of ethylene to dichloroethane is the first reaction performed in an integrated vinyl chloride plant. In the second stage, dichloroethane is cracked thermally over alumina to give vinyl chloride and hydrogen chloride. The hydrogen chloride produced is recycled back to the oxychlorination reactor. 

Oxychl orin ation of ethylene has become the second important process for 1,2-dichloroethane. The process is usually incorporated into an integrated vinyl chloride plant in which hydrogen chloride, recovered from the dehydrochlorination or cracking of 1,2-dichloroethane to vinyl chloride, is recycled to an oxychl orin a tion unit. The hydrogen chloride by-product is used as the chlorine source in the chlorination of ethylene in the presence of oxygen and copper chloride catalyst ... 

FIG. 12-95ii Strong-Scott flash dryer with integral coarse-fraction classifier to separate undried particles for recycle. (Bepex Cotp.)... 

Air separator Vow (N-S) Similar shape to hydrocycloue, hut higher included angle. Internal impeller induces recycle within classifier. 0.5 to 7.5 2 mm to 38 im to 2100 4 to 500 Used where solids must be kept dry, such as cement grinding. Air classifiers may be integrated into grinding mill structure. 

In the last few years, Idemitsu commercialized a 5000 metric ton/year integrated reaction and separation process in SCR isobutene, as shown in Rig. 22-24. The reaction of isobutene and water takes place in the water phase and is acid catalyzed. The product, sec-butanol, is extracted into the isobutene phase to drive the reversible reaction to the right. The. s c-butanol is then recovered from the isobutene by depressurizing the SCR phase, and the isobutene is recompressed and recycled. 

The differential reactor is the second from the left. To the right, various ways are shown to prepare feed for the differential reactor. These feeding methods finally lead to the recycle reactor concept. A basic misunderstanding about the differential reactor is widespread. This is the belief that a differential reactor is a short reactor fed with various large quantities of feed to generate various small conversions. In reality, such a system is a short integral reactor used to extrapolate to initial rates. This method is similar to that used in batch reactor experiments to estimate... 

Another view is given in Figure 3.1.2 (Berty 1979), to understand the inner workings of recycle reactors. Here the recycle reactor is represented as an ideal, isothermal, plug-flow, tubular reactor with external recycle. This view justifies the frequently used name loop reactor. As is customary for the calculation of performance for tubular reactors, the rate equations are integrated from initial to final conditions within the inner balance limit. This calculation represents an implicit problem since the initial conditions depend on the result because of the recycle stream. Therefore, repeated trial and error calculations are needed for recycle... 

As can be seen for infinite recycle ratio where C = Cl, all reactions will occur at a constant C. The resulting expression is simply the basic material balance statement for a CSTR, divided here by the catalyst quantity of W. On the other side, for no recycle at all, the integrated expression reverts to the usual and well known expression of tubular reactors. The two small graphs at the bottom show that the results should be illustrated for the CSTR case differently than for tubular reactor results. In CSTRs, rates are measured directly and this must be plotted against the driving force of... 

---