Batch free time

FiG. 71. The effect of particle size on batch-free time at 1427 °C at equal grain sizes of sand, soda and limestone (Potts et al., 1944). 

FIG. 70. Relation between the batch-free times and inverse relative surface area of single-sized SiO grains (for composition and author refer to Fig. 68). 

Also called batch-free time (the glass is free of any crystalline materials of batch origin). 

The time required to completely dissolve the original batch is known as the batch-free time. Although the definition of the batch-free time is straightforward, determination of the exact time at which the last remaining trace of batch remains in the melt is difficult. In general, determination of the batch-free time is subject to a variety of errors, including prejudice on the part of the researcher. 

The overall glass composition is by far the most important factor in controlling the batch-free time. Simple oxide mixtures, such as those used to produce calcium aluminate glasses, often form eutectic mixtures which melt directly with very short batch-free times. Many non-silicate melts are very fluid at any temperature above the melting point of their components and rapidly dissolve all batch particles. Borate, phosphate, and germanate melts can be formed at much lower temperatures than are typically required for silicate melts. As a result, it is usually easier to decrease their viscosity by increases in temperature, e.g., an increase in temperature from 1000 to 1200 C is more easily attained than an increase from 1400 to 1600 C. 

In addition to the physical batch behavior, other information can be gathered as well. The temperature at which the batch begins to collapse can easily be seen, and also the batch free time can be determined and a comparative analysis can be made between different raw materials. When the whole glass forming process is observed from start to finish it provide a good idea of how a potential borate source can affect the melting process. 

Phenyl-l-dodecanamine 992,1026 A mixture of 28% aqueous ammonia (105 g, 1.72 moles) and 90% formic acid (88 g, 1.72 moles) is heated slowly to 160° in a 500-ml three-necked flask fitted with a dropping funnel, thermometer, and descending condenser. Water distils off. Then dodecanophenone (89.5 g, 0.344 mole) is added in one portion and the mixture is kept at 160-170° for 24 h. Ketone that distils over is returned to the batch from time to time. The resulting A-formyl amine is hydrolysed by boiling the reaction mixture with concentrated hydrochloric acid (120 ml) under reflux for 8 h. Then the solution is set aside for 12 h, after which it is treated with water (200 ml). The crystalline mass of amine hydrochloride is broken up, filtered off, and washed with cold water. Recrystallization from hot water gives a salt (76 g, 78%) which, when recrystallized from ethanol, has m.p. 115-116°. The free amine boils at 170-172°/l-2 mm and has D25 1.4903. 

FIGURE 13.12 Results of predictive control of for free radical polymerization of Am in semibatch operation. In batch mode, decreases monotonically in time. By computing conditions for isoreactivity (Equation 13.63c) constant during the reaction was achieved. By operating Am flow into the reactor in the flooded regime (Equation 13.63b), a predictable increase in during the semibatch reaction was achieved. Adapted with permission from Kreft T, Reed WF. Predictive control and verification of conversion kinetics and polymer molecular weight in semi-batch free radical homopolymer reactions. Eur Polym J 2009 45 2288-2303. 

The majority of thermal polymerizations are carried out as a batch process, which requires a heat-up and a cool down stage. Typical conditions are 250—300°C for 0.5—4 h in an oxygen-free atmosphere (typically nitrogen) at approximately 1.4 MPa (200 psi). A continuous thermal polymerization has been reported which utilizes a tubular flow reactor having three temperature zones and recycle capabiHty (62). The advantages of this process are reduced residence time, increased production, and improved molecular weight control. Molecular weight may be controlled with temperature, residence time, feed composition, and polymerizate recycle. 

A factor in addition to the RTD and temperature distribution that affects the molecular weight distribution (MWD) is the nature of the chemical reaciion. If the period during which the molecule is growing is short compared with the residence time in the reactor, the MWD in a batch reactor is broader than in a CSTR. This situation holds for many free radical and ionic polymerization processes where the reaction intermediates are very short hved. In cases where the growth period is the same as the residence time in the reactor, the MWD is narrower in batch than in CSTR. Polymerizations that have no termination step—for instance, polycondensations—are of this type. This topic is treated by Denbigh (J. Applied Chem., 1, 227 [1951]). 

Under poor operational conditions, tannin chemistry is a particularly forgiving form of internal treatment because it tolerates FW with significant variations in quality. It is capable of delivering clean, corrosion-free waterside surfaces in many types of boilers, despite low FW temperatures, high oxygen levels, and hardness ingress. It is especially suitable for use in smaller facilities that do not have the benefit of full-time, trained operators, and under on-off, batch process, or permanent low-fire circumstances. 

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