Recycling Solid-phase condensation

The table shows that the process can eliminate volatile compounds much more efficiently than non-volatile substances. Volatiles, like toluene and chlorobenzene, are already efficiently removed by step (ii) alone. Toluene was no longer measurable at a detection limit of 0.4 ppm. The other volatile, chlorobenzene, was recovered at 5.5 % of the initial concentration after the extrusion step. After the post-condensation step, the amount of toluene in the final product was likely to be far below the limit of detection since the detection limit was already determined after the extrusion step. Chlorobenzene also could not be found above the limit of detection. These results show very impressively that a conventional recycling process (consisting of steps (i) and (ii)) for post-consumer PET removes volatile real-life contaminants very efficiently, for example solvents and fuel. An additional vacuum treatment during solid-phase post-condensation further decreases any level of volatile compounds in the final product. 

In continuous steam distillation, an insulated conveying system with superheated steam as carrier is used for providing a countercurrent flow of steam and pulverised plant material. During transport, the oil is transferred into the vapour phase and exits the system with the steam. A cyclonic vessel separates the gas phase from the solid phase. In the last step the gas phase (steam and oil) is condensed, the oil is separated using a Florentine flask and the water recycled to the boiler [27]. 

The process requires flow meters for the gas phase—air, butane, recycled gas, nitrogen, oxygen, steam—the liquid phase—condensed water, maleic acid—and the solids—catalyst recirculation from one reactor to the other. In total, there are 248 flow meters and, as shown in Table 6.6, most of these flow meters are dedicated to nitrogen and water. Only four flow meters monitor the product of interest—maleic acid. Figure 6.13 shows some of the major flow... 

Yakaiah, T., Venkat Reddy, G., Lingaiah, B. P. V., Shanthan Rao, P. and Narsaiah, B. 2005. Zr0Cl2 8H20 as a new solid phase and recyclable catalyst for an efficient Knoevenagel condensation under solvent-free microwave irradiation conditions. Indian J. Chem. 44B(6) 1301-1303. 

The injected fluids usually have a chemical composition that is different from that of the in situ reservoir fluids, particularly when steam has been separated from the liquid phase and only the separated water is re-injected. The steam phase will be enriched in non-condensable gases, whereas the separated water has a higher concentration of dissolved solids, but a lower gas content. Changes in the chemistry of the produced fluids are to be expected in all fields where re-injection of separated water has been applied. When the same water is recycled, successive steam loss will increase its salinity, which may in turn lead to scaling problems (see Amorsson, 2004). 

The COj species in the HT interlayer could be exchanged with OH ions by calcination at 723 K and hydration at room temperature. A spinel phase of Mg-Al mixed oxide obtained after the calcination transforms into the original layered structure during the hydration. This reconstruction is known as the memory effect of HT materials. The reconstructed HT catalyzed the Knoevenagel condensation of various aldehydes with nitriles in the presence of water [119]. The reconstracted HT also showed an aqueous Michael reaction of nitriles with a,p-unsaturated compounds. The layered double-hydroxide-supported diisopropylamine catalyzed the Knoevenagel condensation of aromatic carbonyl compounds with malononitrile or ethyl cyanoacetate [120]. This solid base could be recycled at least four times, and exhibited activity for aldol, Henry, Michael, transesterification, and epoxidation of alkenes. 

In the interfacial process, bisphenol A is dissolved in the aqueous sodium hydroxide phase of a two-phase system with methylene chloride. As phosgene is pumped into the mixture, the sodium chloride condensation by-product dissolves in the aqueous phase, and the growing polymer dissolves in the organic phase. A tertiary amine is used as the catalyst. When the reaction is complete, the methylene chloride solution is extracted with acid to remove basic components and then washed with water. The solvent is then flashed off and recycled, leaving the solid. 

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