Buffering processes-systems

Process-flow control and buffer-gas control have been discussed under Variable Nozzles and Buffer-Gas System respectively. Speed is usually self-controlled by a matching speed-sensitive load such as a compressor or a pump. If the load is an induction or svn-chronous generator feeding into a stable ac system, the system frequency fixes the speed. Otherwise, the speed can be controlled by a conventional governor. 

Many geochemical processes occur in which a fluid remains in contact with a gaseous phase. The gas, which could be the Earth s atmosphere or a subsurface gas reservoir, acts to buffer the system s chemistry. By dissolving gas species from the buffer or exsolving gas into it, the fluid will, if reaction proceeds slowly enough, maintain equilibrium with the buffer. 

Ziegler et al. (120) have recently reported the control of pH of an aqueous solution contacted with SCF CO2. Using NaOH and buffers, the system pH was maintained in the 6.2-1.% range, a range suitable for protein processing. An extension of this study would be to control the pH of aqueous solutions contacted with SCF NH3, thereby increasing the utility of SCF NH3 as an antisolvent for aqueous solutions. 

The buffer process is an equilibrium reaction and is described by an equilibrium constant expression. For acids, the equilibrium constant is represented as K, the subscript a impl)ring an acid equilibrium. For example, the acetic acid/sodium acetate system is described by... 

The frequency distributions of pH as shown in Fig. 8.3 and the ionic composition of three representative lakes (see Fig. 8.4) demonstrate a considerable input of sulfuric acid also into neutral waters, where the buffering process is resulting lastly in increased levels of salt content, after reactions with carbonate and with silicate minerals of soil and weathering bedrock. By exhaustion of these initially reacting buffers, the pH-values decrease sharply, and with subsequent acidic conditions, A1 and Fe become follow-up buffers. The Al-hydroxide system is already known to exist in soft-water lakes after rain acidification and was described in an extensive body of literature. The Fe(OH)x buffering system was known to be present in acidified soils (Ulrich 1981), but was not explicitly described to exist in lakes with pH 2-4. 

The intermediate storage has an important role in improving operating efficiency of batch processing systems. It increases the variability of the system and reduces the process uncertainties. Over a long time horizon, it can also buffer the effects of equipment and batch failures when it is sized adequately. 

The effect of the pH on the rate of polymerization has been investigated to some extent. Thus, Powers [150] carried out the polymerization in the presence of aqueous ammonia while Chatelain buffered the system at pH 7 [154]. Liegeois [155] observed that the initiation of the emulsion polymerization of vinyl chloride parallels the rate of decomposition of the persulfate ion (at various reactor pressures below the vapor pressure of the system). In the pH range from 3 to 9, as the rate of decomposition of the persulfate ion increases, the rate of initiation of the polymerization also increases. Thus it would seem that the pH of the system does have an effect on the rate of conversion. Yet since the process can take place in acidic, neutral, or basic media, the choice of the pH to be used does not appear to be very critical. 

D.-M. He, I. Kaleem, S.-Y. Qin, D.-Z. Dai, G.-Y. Liu, C. Li, Biosynthesis of glycyrrhetic acid 3-O-mono-P-D-glucuronide catalyzed by p-D-glucuronidase with enhanced bond selectivity in an ionic liquid/buffer biphasic system. Process Biochem. 45 (2010) 1916-1922. 

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