Intermittent addition

The intermittent addition of chemical treatments by hand rather than continuous addition by use of a feed pump. 

The kinetic models are the same until the final stage of the solution of the reactor balance equations, so the description of the mathematics is combined until that point of departure. The models provide for the continuous or intermittent addition of monomer to the reactor as a liquid at the reactor temperature. 

Intermittent addition of biologically effective amounts of a control biocide. This means that the control biocide is dosed for a certain period of time, followed by a period of much lower or zero dosing. This cycle is repeated throughout the treatment. 

In comparison with a batch reactor, the gradual or intermittent addition of a reactant (say, B in A + B -> products, Figure 12.3(a)) in semibatch operation can result in improved control of T, particularly for a reaction with a large... 

Apparatus. The generator employed is shown in fig. 10. There are six important points. (1) The column. <4 is designed so that throttling is avoided it is at least 2 ft. long and surmounted by a reflux doublesurface water-condenser B. (2) A Perkin triangle (air-cooled), inserted between the down-condenser and the traps, enables any phosphorus oxychloride which distils to be removed. (3) It is convenient to have three traps, viz. C, ice and salt D, acetone and carbon dioxide E, liquid air. (4) The intermittent addition of the solid antimony trifluoride presents a problem. The mechanical solid feed... 

A solution of 3.0 g (0.0094 mole) of (cis)-4-phenylthio-L-proline hydrobromide in 25 ml of water is stirred, cooled to 5°C and 15 ml of 20% sodium carbonate are added. This mixture is treated with 2.0 g (0.011 mole) of D-3-acetylthio-2-methylpropionyl chloride in 5 ml of ether during the course of 10 min with the intermittent addition of 3.0 g of sodium carbonate to maintain the pH at 8.0 to 8.4). The mixture is stirred in the ice-bath for an additional hour, 25 ml of water are added and then a solution of 5 ml of concentrated hydrochloric acid in 25 ml of water. The strongly acid solution is saturated with sodium chloride and extracted with 50 ml of ethyl acetate (four times). The organic phases are combined, dried, filtered and solvent evaporated to give 3.8 g of a pale yellow viscous oil. The dicyclohexylamine salt following trituration with 15 ml of acetonitrile one obtains 2.4 g of colorless solid 1-[D-... 

Zirconium and hafnium trifluoracetylacetonates were prepared by Larsen, Terry, and Leddy, who measured some of their properties. They prepared these compounds by the dropwise addition of the ligand to an aqueous solution of the metal oxide chloride, using intermittent addition of sodium carbonate to maintain the proper pH. 

Semibatch operation involves the continuous or intermittent addition of monomer or other ingredients during polymerization. It is often employed in copolymerizations (Section 7.5) to minimize the drift of copolymer composition when the reactivities differ greatly. 

Flue gas leaving the cyclones contains a small r esidual concentration of catalyst and is passed through a Cottrell electrostatic precipitator recovered catalyst is returned to the regenerated-catalyst hopper. Catalyst losses for this type of unit have been reported to be within the range of 0.12 to 0.4 lb. per barrel of feed (232,233). The losses are compensated for by the intermittent addition of fresh catalyst. 

In the moving bed, gradients exist from top to bottom of the reactor with respect to both temperature and concentration of coke on the catalyst. The activity and coke concentration vary from particle to particle at a given level in the reactor because of the intermittent addition of fresh catalyst to replace losses due to attrition or intentional discard. However, a steady state exists with regard to time, so that all increments of the feed stock are exposed to the same cracking conditions and a uniform conversion is maintained. 

To eliminate the difficulties attending the intermittent addition of oxygen or air to the reacting steam and methane, the necessary combustion may be permitted to occur in a separate step and the resulting hot gaseous mixture is then passed directly to the catalyst for effecting the conversion. The process would thus be a step-wise one with the two steps carried out in succession as follows ... 

This phenomenon is often observed and is caused by the intermittent addition of small sample pulses into the illuminated region of the flow cell. As the sample concentration in the pulse tends to be different from the mean concentration inside the illuminated region, optical artefacts are formed along the radiation beam, which affects the measurements in a regular fashion. This leads to sinusoidal absorbance fluctuations superimposed on the main recorded signal (Fig. 4.13). As a constant frequency is involved, the related undulation can easily and efficiently be filtered out (see e.g., Ref. [4]). The signal-to-noise ratio, however, is adversely affected. 

Other variations on these three basic processes include intermittent addition of batches of one or more of the components and shot" addition. The latter has been used successfully to enhance the incorporation of water-soluble functional monomers such as sodium styrene sulfonate [14], This is added all at one time, i.e. as a shot , during the later stages of the polymerization, prior to con lete conversion of the main monomer. 

In Illustration 10.7 we consider how to meet the vast majority of the heat transfer requirements for operation of a semibatch reactor by a semi-autothermal mode of processing. By intermittent addition of a cold reactant stream to the hot contents of a well-stirred semibatch reactor, it is possible to maintain the system temperature within prescribed limits. 

Depending on the initial concentration, one can design different feed into reactors in order to obtain a higher yield, as shown in Figure 16.4. With two reactants, A and B, both with low concentration, the CSTR is the best choice. However, if the concentrations are high, depending on the residence time, the yield in the PFR will be higher. If the concentrations have different levels, one can use the schemes (c) and (d) with intermittent addition in several positions in the PFR reactor or many CSTR in series. 

Semibatch polymerization involves the continuous or intermittent addition of monomer (and/or initiator and/or chain transfer agent) to the polymerizing mixture during polymerization. The addition of monomer (and/or other ingredients) has in general the following beneficial effects ... 

---