Multi-cycle process

In multi Cycle processes, conditioning vessels are usually required between each solvent cycle, and an evaporator may also sometimes be introduced in order to keep the feed concentration to the second cycle at a low value and therefore economize in the size of the second-cycle extraction plant. 

Physical, thermal, and chemical stability in order to reduce operating costs, solid sorbents must demonstrate stability under flue gas conditions, adsorption operation conditions, and during the multi-cycle adsorption-regeneration process. In particular, stability in the presence of water vapor is essential for the sustainable performance of the solid sorbent. In addition to thermal properties of the solid sorbent, heat capacity and thermal conductivity are also important in heat transfer operations. 

The first multi-step process having a theoretical efficiency above 50% was proposed by Marchetti and Beni in 1970 [2]. This process became the Mark-1 process of the European Commission s Joint Research Center (JRC), Ispra, Italy. A large number of cycles with reasonably high efficiencies were designed after this Abanades and co-workers have recently made a compilation of the available thermochemical cycles that yielded about 280 cycles [67]. A large number of cycles are listed in references [2,4,67,95,97]. However only a few of these processes have exhibited potential for high overall efficiencies and technical feasibility. We discuss a few cycles that are presently under study and promising for practical implementation. 

Repeating the cycle (B) Electrostatic multi-duplication process... 

Figure 24,7 Amino add biosynthesis by transamination. ) Within a transaminase, the internal aldimine is converted into pyridoxamine phosphate (PMP) by reaction with glutamate in a multi step process not shown. (2) PMP then reacts with an a-ketoacid to generate a ketimine. (3) This intermediate is converted into a quinonoid intermediate (4), which in turn yields an external aldimine. (3) The aldimine is cleaved to release the newly formed amino acid to complete the cycle.

A further development of the Mopac process led to the KWU Cord process (Chemical—Oxidation—Reduction-Decontamination), a multi-cycle, low-concentration process which proved to be especially suitable for the decontamination of subsystems and full reactor systems (Wille and Sato, 1994). The principles of this process are shown in Fig. 4.52. A CoRD decontamination cycle starts with an oxidation step, using a dilute solution of permanganic acid the excess Mn04 is then reduced by addition of a dicarboxylic acid, thereby generating CO2. By further addition of the dicarboxylic acid up to a concentration of about 0.2%, dissolution of the oxides starts and the metal ions are retained in the solution as complex compounds. The whole process is conducted at about 95 C it does not require a fixed number of cycles, but can be repeated according to the final radiation dose... 

As pointed out by Professor Ramshaw (Ramshaw, 2005), this development was founded on an ICI patent flled in the 1980s in which it was suggested that elevated acceleration fields could intensify the operation of the multi-phase processes involved in an absorption heat pump cycle. He goes on to say ... 

Another tricky question arises when facing life cycles of multi-output processes. Inputs, outputs and the related environmental impacts must then be allocated to products. This can be done according to physical properties of the product flows (mass or energy flows). If this is not possible or not justifiable the usual way is to allocate according to the economic value of the products (prices). In our study, both mass and price allocation have been applied to highlight the influence of this allocation procedure on the outcome of the analysis. 

Table I shows the multi output process of the biodiesel from tallow model. Four processes have more than one economic output. For the life cycle of biodiesel from used vegetable oil only the two letter processes (transesterification and KOH-production) are relevant.

Examples of multi-disciplinary innovation can also be found in the field of environmental catalysis such as a newly developed catalyst system for exhaust emission control in lean burn automobiles. Japanese workers [17] have successfully merged the disciplines of catalysis, adsorption and process control to develop a so-called NOx-Storage-Reduction (NSR) lean burn emission control system. This NSR catalyst employs barium oxide as an adsorbent which stores NOx as a nitrate under lean burn conditions. The adsorbent is regenerated in a very short fuel rich cycle during which the released NOx is reduced to nitrogen over a conventional three-way catalyst. A process control system ensures for the correct cycle times and minimizes the effect on motor performance. 

ROMP is without doubt the most important incarnation of olefin metathesis in polymer chemistry [98]. Preconditions enabling this process involve a strained cyclic olefinic monomer and a suitable initiator. The driving force in ROMP is the release of ring strain, rendering the last step in the catalytic cycle irreversible (Scheme 3.6). The synthesis of well-defined polymers of complex architectures such as multi-functionaUsed block-copolymers is enabled by living polymerisation, one of the main benefits of ROMP [92, 98]. 

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