Liquid shortening process

Some typical applications in SFE of polymer/additive analysis are illustrated below. Hunt et al. [333] found that supercritical extraction of DIOP and Topanol CA from ground PVC increased with temperature up to 90 °C at 45 MPa, then levelled off, presumably as solubility became the limiting factor. The extraction of DOP and DBP plasticisers from PVC by scC02 at 52 MPa increased from 50 to 80 °C, when extraction was almost complete in 25 min [336]. At 70 °C the amount extracted increased from 79 to 95 % for pressures from 22 to 60 MPa. SFE has the potential to shorten extraction times for traces (<20ppm) of additives (DBP and DOP) in flexible PVC formulations with similar or even better extraction efficiencies compared with traditional LSE techniques [384]. Marin et al. [336] have used off-line SFE-GC to determine the detection limits for DBP and DOP in flexible PVC. The method developed was compared with Soxhlet liquid extraction. At such low additive concentrations a maximum efficiency in the extractive process and an adequate separative system are needed to avoid interferences with other components that are present at high concentrations in the PVC formulations, such as DINP. Results obtained... 

The problems encountered in the catalytic transfer of highly hydrophilic anions from aqueous solutions into the organic phase can be countered by the use of anhydrous solid salts the organic reactant is dissolved in the organic solvent or, if liquid, may be used neat. Solid liquid two-phase reactions using ammonium salts have widespread application (see, for example, the many examples cited in later chapters) frequently with shortened reaction times, lower reaction temperatures, and higher yields [e.g. 66, 67] and are generally superior to solidrliquid reactions catalysed by crown ethers [68]. The process is particularly useful in base-initiated reactions with fluorides, hydroxides or carbonates. 

At high liquid flowrates, the liquid gradient on the tray can become excessive and lead to poor vapour distribution across the plate. This problem may be overcome by the shortening of the liquid flow-path as in the case of the double-pass and cascade trays. The whole design process is discussed in Volume 6. 

Process intensification also offers substantial improvements to those sectors of the chemical industry in which time to market plays a crucial role, e.g., the fine chemical and pharmaceutical sectors. Ramshaw (35) discussed how process intensification could shorten the time to market in case of a low-tonnage pharmaceutical process. The idea consists in developing a continuous lab-scale process and using it directly as the commercial-scale process. One must not forget that liquid flow of only 1 milliliter per second means, in continuous operation, circa 30 tons per year, which is quite a reasonable capacity for many pharmaceuticals. 

Absorption of a component of a gas stream into a liquid is a common practice in the chemical industry to affect cleanup of vent gases, conduct chemical reactions, purify products, or to recover products from process streams. The enhanced mass transfer capability of RPBs provides the opportunity to perform absorption processes in smaller equipment, to lower inventories, to shorten startup and shutdown times, and to lower pressure drop (48). Figure 8 provides a visual comparison of the size of a conventional absorber tower next to three RPBs that handle the equivalent gas and liquid flows (9). 

This plant will use the high-pressure Shortened Liquid Phase (SLP) process developed by DSM. Melamine produced with the SLP process has the same quality as melamine produced in the gas phase (or low pressure) process. The new technology is a result of DSM s further development of a process acquired from MCI (Melamine Chemical Industries) in 1997. The SLP process is expected to increase efficiency by 25%. It is also expected to enable the plant to reach a level of cost-effectiveness similar to a 100,000 tonnes/year production facility. The new process requires only 3 or 4 processing steps, in contrast to the 10 steps in conventional processes115,231. The process employs the same raw materials as the low-pressure urea process, but the final melamine recrystallization step is eliminated. The company may be able to make 99% purity melamine without recrystallization114. 

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