Recycling Schemes

Gas is produced to surface separators which are used to extract the heavier ends of the mixture (typically the components). The dry gas is then compressed and reinjected into the reservoir to maintain the pressure above the dew point. As the recycling progresses the reservoir composition becomes leaner (less heavy components), until eventually it is not economic to separate and compress the dry gas, at which point the reservoir pressure is blown down as for a wet gas reservoir. The sales profile for a recycling scheme consists of early sales of condensate liquids and delayed sale of gas. An alternative method of keeping the reservoir above the dew point but avoiding the deferred gas sales is by water injection. 

Introduction Reactive distillation is a unit operation in which chemical reaction and distiUative separation are carried out simultaneously within a fractional distillation apparatus. Reactive distillation may be advantageous for liqiiid-phase reaction systems when the reaction must be carried out with a large excess of one or more of the reactants, when a reaction can be driven to completion by removal of one or more of the products as they are formed, or when the product recoveiy or by-product recycle scheme is complicated or macfe infeasible by azeotrope formation. 

The goal in any salt recycle system is to keep the system as simple as possible and to use compatible reagents for each of the steps processing, recovery, and reprocessing. In evaluating potential recycle schemes, these two considerations will play an important role. 

The Vinyloop process is based on the selective dissolution of PVC used in composites applications like cable insulation, flooring, tarpaulins, blisters, etc. After removal of insoluble parts like metals, rubber or other polymers, the PVC is reprecipitated with all additives by introduction of a non-solvent component whieh will form with the seleetive solvent an azeotropie mixture. By using typical conditions, the process is able to reeover a pure PVC eompound powder ready for use without any additional treatment like melt filtration or a new pelletisation (speeific characteristics of the powder are average diameter of 400 microns and bulk density above 600 kg/ eub.m). All the solvents used are eompletely reeyeled and reused. PVC compounds recovered in the Vinyloop process can be reused in a closed-loop recycling scheme... 

Our task was to develop a feasible synthesis for diamino resorcinol. From several possibilities [1-4] the resorcinol and anihne were chosen as starting materials. The diazotated aniline was coupled with resorcinol among basic conditions giving 4,6-bisphenylazo resorcinol. Hydrogenation of the latter resulted in diamino resorcinol and aniline, which could be recycled (scheme 14.2). This chemistry is well known [5-13] therefore, the research work focused on finding the optimal parameters and catalyst and finally on elaborating a process for scale-up. 

Since, based on the historical data, complete kinetic regioselectivity was unlikely to be achieved, our attention was focused on the possibility of a demethylation followed by an N-methylation recycle (Scheme 6.15). Unfortunately, the attempted... 

Table 2 Summary of existing collection and recycling schemes [7]...

Figure 9-21 shows an MCFC network. The arrangement of stacks in series, as well as a unique recycle scheme, allows an MCFC network to meet all the requirements of an MCFC power system, while achieving high efficiency. 

Two ASPEN (Advanced System for Process Engineering, public version) simulations compare the performance of conventional and networked fuel cell systems having identical recycle schemes and steam bottoming cycles. Each simulated system was composed of three MCFC stacks operating at the same temperature and pressure. The Nemst potential of each MCFC in both systems was reduced by 0.3 volts due to activation, concentration and ohmic voltage... 

The minor products are formed by hydrolysis of the first formed imidazole carboxamidines and recyclization (Scheme 62). 

Irradiation (254nm) of l-(o-cyanobenzyloxy)-2-arylbut-2-enes (Ar = Ph, />-Tol, />-anisyl) leads via a [2+2] cycloaddition, followed by the cleavage of the azetine ring and recyclization (Scheme 19), to the annulated 2,7-dihydroox-epine derivatives <1994BCJ1769>. 

Another approach to polymer/catalyst separation is to replace the use of costly wasteful solvents with a procedure that produces little to no waste, and requires no catalyst modification. These switchable polarity solvents (SPS), as developed by Jessop and coworkers, are able to utilize the reaction of secondary amines with C02 to reversibly form carbamate salt ionic liquids (Scheme 8.10) [66]. Upon the completion of the polymerization reaction, EtBuNH (Et = ethyl, Bu = n-butyl) is added to dissolve the polymer/catalyst mixture. The subsequent bubbling of C02 through this solution results in a precipitation of the polymer product, such that the purified polymer can be isolated by simple filtration. The catalyst can then be recovered by distilling the amine/carhamate mixture, and the entire system can (in theory) be recycled (Scheme 8.11). 

Olefin metathesis can be very useful in the CM mode, as shown in the synthesis of insect phere-mones.46 In the first example for the synthesis of the peach twig borer pheromone 23, an excess of 1-hexene was used to increase the yield of the desired product. However, both of the other products could be recycled (Scheme 28.17). In the second example, CM was used to change the ester groups of meadowfoam oil (24) through cleavage of the alkenes rather than ester bonds. The sequence resulted in the synthesis of the mosquito pheromone (25) (Scheme 28.18). 

Oxazole N-oxides having a 4-methyl substituent are attacked by acetic anhydride to yield 4-acetoxyoxazoles (equation 21). The combined action of benzoyl chloride and potassium cyanide leads to compounds of the Reissert type, e.g. (177). The reaction of 4-methyloxazole Yoxides with phenyl isocyanate gives 5-hydroxy-4-methylene-l-phenyl-4,5-dihy-droimidazoles by cycloaddition, extrusion of carbon dioxide and recyclization (Scheme 12) with 4-phenyloxazole JV-oxides the reaction takes a different course, yielding imi-dazooxazolidinones (Scheme 13). 

Dimroth rearrangement of neutral heterocyclic bases is also possible. For example, the adenine derivative 775 heated in NaOH produces 6-ethylaminoadenine 777 (91%), hypoxanthine 778 (2%), and 1-ethylhypoxanthine 779 (2%). The minor products are formed by hydrolysis of the first formed imidazole carboxamidine 776 and recyclization (Scheme 87). 

Reaction of deprotonated 1,2-diazetines 155 with ketones containing an acidic methylene group affords dihydropyr-idazine derivatives 156 via a sequence of ring opening and recyclization (Scheme 78) <2006S2885, CHEC-III (8.01.10.1)85>. 

Ideally, typical production considerations, such as cost of the chemicals and the technological issues (temperature level, reaction rates etc.) should also be taken into account. Especially, any use of costly auxiliary agents that cannot be recycled or production of by-products that require their disposal needs to be avoided. In this respect, the most favorable recycling procedure would be self-contained, that is, the regeneration is only carried out with molecular hydrogen and the BNH waste. To date, none of the proposed recycling schemes fulfill all of these requirements. 

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