Bed volume

Fig. 8. Representation of measurement of elution volume, as a function of sample volume (a) <2% of bed volume, (b) >2% and (c) >2% and giving a plateau region which has the same concentration as the iajected sample A represents the inflection poiat. See text.

To escape aggregative fluidization and move to a circulating bed, the gas velocity is increased further. The fast-fluidization regime is reached where the soHds occupy only 5 to 20% of the bed volume. Gas velocities can easily be 100 times the terminal velocity of the bed particles. Increasing the gas velocity further results in a system so dilute that pneumatic conveying (qv), or dilute-phase transport, occurs. In this regime there is no actual bed in the column. 

The bed level is not weU defined in a circulating fluidized bed, and bed density usually declines with height. Axial density profiles for different CFB operating regimes show that the vessel does not necessarily contain clearly defined bed and freeboard regimes. The sohds may occupy only between 5 and 20% of the total bed volume. 

Rinse. When transfer of the required volume of regenerating solution to the column has been completed, a small amount of regenerating solution occupies space immediately above the resin bed, between resin particles in the bed, and within the resin particles. It must be displaced with water before the column can be returned to the adsorption step. Rinsing should begin at the same flow rate as used during regeneration and continue at that rate until a volume of water equal to 1—2 bed volumes has been used. After that, the flow rate is increased to the rate normally used during the adsorption step, and continued at that rate until the effluent is of satisfactory quaHty, as deterrnined by pH, conductivity, or resistivity. The water need not be at an elevated temperature unless the process stream is above ambient temperature. 

Design nd Operation. The destruction efficiency of a catalytic oxidation system is determined by the system design. It is impossible to predict a priori the temperature and residence time needed to obtain a given level of conversion of a mixture in a catalytic oxidation system. Control efficiency is determined by process characteristics such as concentration of VOCs emitted, flow rate, process fluctuations that may occur in flow rate, temperature, concentrations of other materials in the process stream, and the governing permit regulation, such as the mass-emission limit. Design and operational characteristics that can affect the destmction efficiency include inlet temperature to the catalyst bed, volume of catalyst, and quantity and type of noble metal or metal oxide used. 

From surface area to volume ratio considerations, the internal area is practically all in the small pores. One gram of the adsorbent occupies 2 cm as packed and has 0.4 cnP in small pores, which gives a surface area of 1150 m /g( or about 1 mi per 5 lb or 6.3 miVft of packing). Based on the area of the annular region filled with adsorbate, the solute occupies 22.5 percent of the internal pore volume and 13.5 percent of the total packed-bed volume. 

This important dimensionless group is the volumetric capacity of the bed for the sorbable component divided by the concentration of the sorbable component in the feed. The stoichiometi ic capacity of the bed for solute is exactly equal to A empty bed volumes of feed (to saturate the sorbent at the feed concentratiou) plus a fraction of a bed volume of feed to fill the voids outside and inside the particles. Alternatively, we also obtain Eq. (16-124) using the dimensionless transition variables for concentrations [Eq. (I6-II)], but now the partition ratio in the first term of Eq. (16-124) pertains to the transition and is given by... 

Here is the porosity of die bed, which is equal to die difference between the bed volume and the volume of particles, divided by the bed volume. It can... 

Chelex can be regenerated by washing in two bed volumes of IM HCl, two bed volumes of IM NaOH and five bed volumes of water. 

Volume of voids + volume of solids, i.e. total bed volume)... 

A contact time of 60 seconds is considered a minimum in choosing a bed volume. A larger volume may be considered, as it will extend the bed life and thus extend the cycle time between bed change outs. Assuming a minimum contact time of 60 seconds, any combination of vessel diamc ter and bed height that satisfies the following is acceptable ... 

A process scale application of Sephacryl S-100 is demonstrated by the polishing of a pharmaceutical in a system of three BPSS columns giving a final bed volume of 2500 liters (Fig. 2.9, page 51). 

Column Bed volume (ml) Column dimensions [diameter (cm) x length (cm)] Column fittings Column materials" (Tube/Frit) Maximum operating pressure (kPa) Maximum linear velocity (cm/hr)... 

FIGURE 2.9 Industrial fractionation by SEC using Sephacryl S-lOO in three BPSS columns (L = 30 cm, i.d. = 140 cm) to give a total bed volume of 1500 liters. Courtesy of R. Hersberg. (Reproduced by permission of Amersham Pharmacia Biotech.)... 

Column Column dimension (i.d. X L) (cm X cm) Bed volume (ml) Column materials° (Tube/Frit) Column fittings (inlet/outlet) Theoretical plates (N/m) Maximum operating pressure/flow rate (kPa)/(ml/hr)... 

Maximum bed volumes and bed heights require packing equipment. ... 

The diameter of the column is selected from the volume of sample that is to be processed. As a rule of thumb the maximum productivity is obtained at a sample volume of 2-6% of the bed volume in preparative gel filtration on a 50-/rm chromatographic medium (Hagel et al., 1989). Thus, the required column diameter is calculated from the bed volume needed to cope with the sample volume and the column length needed to give the resolution desired. 

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