Ratio, recycle

A Hquid-phase variation of the direct hydration was developed by Tokuyama Soda (78). The disadvantages of the gas-phase processes are largely avoided by employing a weakly acidic aqueous catalyst solution of a siHcotungstate (82). Preheated propylene, water, and recycled aqueous catalyst solution are pressurized and fed into a reaction chamber where they react in the Hquid state at 270°C and 20.3 MPa (200 atm) and form aqueous isopropyl alcohol. Propylene conversions of 60—70% per pass are obtained, and selectivity to isopropyl alcohol is 98—99 mol % of converted propylene. The catalyst is recycled and requites Htde replenishment compared to other processes. Corrosion and environmental problems are also minimized because the catalyst is a weak acid and because the system is completely closed. On account of the low gas recycle ratio, regular commercial propylene of 95% purity can be used as feedstock. 

From Allyl Alcohol. The reaction of allyl alcohol [107-18-6] with chlorine and water gives a mixture of glycerol m on ochl orohydrin s consisting of 73% 3-chloropropane-l,2-diol and 27% of 2-chloropropane-l,3-diol (57). In a recycle reaction system in which allyl alcohol is fed as a 4.5—5.5 wt % solution, chlorine is added at a rate of 7—9 moles per hour. The reaction time is about five seconds, the reaction temperature 50—60°C and the recycle ratio is 10—20 1. Under these conditions m on ochl orohydrin s have been obtained in 88% yield with 9% dichlorohydrins (58) (see Allyl ALCOHOL AND DERIVATIVES). 

Accordingly, the change in concentration (or in temperature) across the reactor can be made as small as desired by upping the recycle ratio. Eventually, the reac tor can become a differential unit with substantially constant temperature, while substantial differences will concurrently arise between the fresh feed inlet and the produc t withdrawal outlet. Such an operation is useful for obtaining experimental data for analysis of rate equations. 

Part of the effluent from a PER is returned to the inlet. The recycle ratio is R, fresh feed rate is Fq... 

Without recycle, washout occurs when D is greater than flmax, but recycle permits operation with D far greater than flmax- A family of curves is shown in Fig. 24-24 for concentrations of cell mass and nutrient at different recycle ratios. The distinct differences from Fig. 24-22 with no recycle are obvious. 

As can be seen for infinite recycle ratio where C = Cl, all reactions will occur at a constant C. The resulting expression is simply the basic material balance statement for a CSTR, divided here by the catalyst quantity of W. On the other side, for no recycle at all, the integrated expression reverts to the usual and well known expression of tubular reactors. The two small graphs at the bottom show that the results should be illustrated for the CSTR case differently than for tubular reactor results. In CSTRs, rates are measured directly and this must be plotted against the driving force of... 

Peclet number independent of Reynolds number also means that turbulent diffusion or dispersion is directly proportional to the fluid velocity. In general, reactors that are simple in construction, (tubular reactors and adiabatic reactors) approach their ideal condition much better in commercial size then on laboratory scale. On small scale and corresponding low flows, they are handicapped by significant temperature and concentration gradients that are not even well defined. In contrast, recycle reactors and CSTRs come much closer to their ideal state in laboratory sizes than in large equipment. The energy requirement for recycle reaci ors grows with the square of the volume. This limits increases in size or applicable recycle ratios. 

Pirjamali et al (1972) developed a correction procedure for interparticle gradients in recycle reactors. Their study involved recycle ratios n from 36 to 1000 (as defined in this book) that relates to their recycle ratio P... 

Georgakopoulos and Broucek (1987) investigated the effect of recycle ratio on non-ideality, both mathematically and experimentally. They investigated two cases from which the bypass case b was completely uninteresting, because total bypass of the catalyst bed could be avoided by feeding the makeup directly to the location of highest sheerfield, at the tip of the impeller blade. For their case a they showed on their Fig. 3. that from a recycle ratio of about 10 = 32 there was no observable falsification effect. This matched well the conclusion of Pirjamali et al. 

Select a volume V = 19.64 cm of catalyst to be charged both in the regular basket (case A) and in a basket (case B) that is half of the diameter of A. In cases A and B the AP and RPM are kept the same. In Cases A and C the volumetric recycle flow remains the same. In row 1 and 2 on Figure 7.2.1, if the diameter drops to half, the height must increase four times (for constant catalyst volume.) In row 4, L/dp increases four times as well. In row 5, for cases A vs B, if L/dp increases four times, has to drop to one quarter, hence u will be one half to maintain constant AP. In row 6, for u in A and B and flow cross section 1/4, the volumetric flow will be 1/8 and the recycle ratio also 1/8. In row 7, or u four times larger. 

This example shows again that if the recycle ratio is high, errors do not cause much of a problem. In reality, it is not the recycle ratio, but rather the high recycle flow and the very small concentration change through the catalyst bed that helps to cut the significance of mistakes. 

The check for homogeneous reactions should be done by repeating some experiments with different quantities of catalyst charge. For example, make measurements over 20, 40 and 80 cm of catalyst charges with proportionally increased makeup feed rates. Change the RPM to keep the recycle ratio constant (if possible) or the linear rate u constant. The measured catalytic rate should remain the same if nothing happens in the empty space. 

Solvent Extraction - Solvent extraction uses solvents to dissolve and remove aromatics from lube oil feed stocks, improving viscosity, oxidation resistance, color, and gum formation. A number of different solvents are used, with the two most common being furfural and phenol. Typically, feed lube stocks are contacted with the solvent in a packed tower or rotating disc contactor. Each solvent has a different solvent-to-oil ratio and recycle ratio within the tower. 

The volumetric flowrate into the plug flow is Uq and the feed concentration of A is C g- portion of A exiting from the reactor is fed back through a pump and mixed with the feed stream, referred to as R (i.e., the recycle ratio). The volumetric flowrate at the entrance of the reactor is u = UgCl + R). A balance at the mixing point M gives... 

Recycle ratio, vol/vol feed, % Yields Vacuum residue 10-100... 

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