Toluene ratio

Laboratory studies indicate that a hydrogen-toluene ratio of 5 at the reactor inlet is required to prevent excessive coke formation in the reactor. Even with a large excess of hydrogen, the toluene cannot be forced to complete conversion. The laboratory studies indicate that the selectivity (i.e., fraction of toluene reacted which is converted to benzene) is related to the conversion (i.e., fraction of toluene fed which is reacted) according to ... 

Fig 5 shows the yield of MNT as a function of acid/toluene ratio for a MA of 27/55/18% nitric acid/sulfuric acid/water and a nitration time of 50 minutes at 30°... 

GL 1[ [R 1[ [R 3] [P la-d] When the fluorine-to-toluene ratio is increased, conversion increases in a linear fashion [38]. This basically means that transport resistance would most likely not prohibit using still higher fluorine contents, thereby further possibly increasing the productivity (space-time yield) of the reactor (Figure 5.19). 

The objective of this contribution is to investigate catalytic properties of zeolites differing in their channel systems in transformation of aromatics, i.e. toluene alkylation with isopropyl alcohol and toluene disproportionation. In the former case zeolite structure and acidity is related to the toluene conversion, selectivity to p-cymene, sum of cymenes, and isopropyl/n-propyl toluene ratio. In the latter one zeolite properties are... 

Fig. 44.6 Product inhibition in the ruthenium-catalyzed hydrogenation of cinnamaldehyde. Reaction conditions 0.1 mmol RuCI3, 0.5 mmol TPPTS, H20 Toluene ratio 5 mL 5 mL.

A combination of V2Os and Sn02 (weight ratio 70 30) is a reasonable catalyst at 300—360°C in giving about 50% yield, as has been shown by Lodaya et al. [190], The yield was measured at a 5—8% level of conversion and is hardly dependent on temperature in the given region. The optimal NH3/toluene ratio is 6. 

Ethyl bromide aromatics ratio — 3. Ethyl bromide toluene ratio — 2. 

Equations (4.37) to (4.42) involve eleven variables therefore five degrees of freedom must be specified. We assume constant purity of the fresh hydrogen, yH,2 = 0.95. The control structure fixes the fresh toluene flow rate Fj = 120 kmol/h and hydro-gen/toluene ratio at reactor inlet, yt,3/yH,3 =1/5. Specifying two additional variables, for example reactor volume Vand gas recycle flow rate FR, the mass-balance equations can be solved for six unknowns F2, FB, FT, FP, X and yHP. This is left as an exercise for the reader. 

Since the molar ratio of air/toluene required for complete combustion is 42.9, and under the given conditions the air/toluene ratio is only 25.93, the amount of air available is not adequate. 

In a typical reaction, a solution of alkyne in THF is cooled to —20°C for 5 min. An equimolar amount of the dialkylzinc is added in toluene (ratio of THF toluene = 1 3). After 15 min, 10 mol % of the ligand is added, followed by the aldehyde. HPLC analysis shows complete reaction usually within 18 h. Both electron-rich and electron-poor aldehydes have been used along with aromatic and aliphatic alkynes. Yields are normally 70-90% with ee being 65-85%. Once again the optimal ligand structure may involve variation of the amine substitution pattern. 

Isotopic distributions of toluene exchanged at 110° in runs with a deuterium/toluene ratio of 5.5 appear in Table XI. Detectable activity appeared after activation at 215°, was a maximum at about 330°, and then declined. Most runs on toluene were preceded by a run with 1-hexene and deuterium at 64°. Information on the hexene runs is contained in Fig. 10 and Tables IV, V, VII, and IX. The toluene run, 250, was followed by a run with hexene and runs 240, 247, and 10 were not connected with hexene runs. 

The data in Fig. 1 show a drastic loss of selectivity with increasing reaction temperature and conversion, indicating a great sensitivity of benzaldehyde towards consecutive transformations, but do not allow discrimination between the effect of temperature and conversion of toluene and oxygen. Therefore, experiments were carried out at isotemperature and isoflow rate with different amounts of the catalyst or the 02/toluene ratio in the feed. The results are summarized in Figures 4A and 4B, respectively. 

As the amount of the catalyst increases (Fig. 4A) the conversion of toluene does not follow a nearly linearly increase as expected for a first order rate equation of hydrocarbon depletion (the low hydrocarbon conversion indicates pseudo-differential conditions with respect to hydrocarbon axial profile), because the concentration of oxygen also affects the reaction rate. This is confirmed in Fig. 4B showing the dependence of the conversion of toluene on the Oa/toluene ratio in the feed. The rate of toluene depletion thus is not limited by the rate of adsorption of the hydrocarbon, but probably by the consecutive steps of oxidation. 

The selectivity to benzaldehyde shows a maximum with respect to the increase in contact time. The initial slight increase derives from the fact that the decrease in the Oi/toluene ratio along the axial direction of the catalytic bed (caused by the catalytic reaction) causes an increase in the selectivity to benzaldehyde (Fig. 4B), but the further increase in contact time leads to further consecutive oxidation of benzaldehyde with a consequent lowering of the se-... 

Fig. 4 Effect of amount of catalyst (A, left) and O /toluene ratio in the feed (B, right) on the catalytic behavior of V3-HMS at 400 C and 500°C, respectively.

The results on the effect of temperature, contact time and methanol to toluene ratio on the isomer composition of xylenes on K2.5 salt are given in Table 3. It is seen that selectivity of p-xylene decreases with increase in the temperature whereas the selectivity of m-xylene increases, obviously, due to the isomerization. As contact time increases p-xylene selectivity increases. It is also found that the p-xylene selectivity increases with increasing methanol to toluene ratio. As methanol to toluene ratio increases the catalyst surface will be saturated with more of alkylating species which offers hindrance to the approach of the aromatic substrate and thereby resulting in the preferential alkylation at para position. In conclusion,it may be suggested that high Bronsted acidity is responsible for high para selectivity found in heteropolyoxometallates. 

Effect of temperature, contact time and methanol to toluene ratio on xylene isomers on K2.5H0.5PW 12O40. 

Carbon and hydrogen balance closures were achieved during the experiment. The typical mass balance during the experiment is shown in Figure 9. The effects of various parameters such as temperature, pressure, H2/Toluene ratio, and space velocity on the selectivity of the R11/AI2O3 at supercritical condition were investigated. The selectivity was more significantly affected by space velocity than any other variable tested. 

The hydrogen-to-toluene ratio at the reactor inlet should be 5 1. 

If production rate and hydrogen/toluene ratio at the reactor inlet (yns/yta) are set, Eqs. 13.30 to 13.34 have two degrees of freedom. Hence, two design variables must be specified, but not any combination is feasible. Douglas (1988) considers reactor conversion and purge composition as design variables and optimises the economic potential. We use his results (X = 0.78, Y p - 0.424) as a starting point. 

Next we will examine potential controlled and manipulated variables. There are five potential controlled variables production (Fb), hydrogen/toluene ratio (yns/yn), pressure, purge composition (ynp). and conversion (X). However, some of them might be left uncontrolled. For example, conversion control is difficult, because of dead-time associated with a PFR. Moreover, it requires on-line composition analyser, which is not available or expensive. For these reasons, it would be desirable to develop a control structure in which controlling the reactor inlet temperature would be sufficient. 

The remaining manipulated variable (set-point of the furnace duty) can be used to control either the conversion or the hydrogen/toluene ratio. Both controlled variables seem to be important. Low conversion means more utility consumption for separation, while high conversion affects reaction selectivity. Low hydrogen/toluene ratio leads also to undesirable by-products. 

Without control, hydrogen/toluene ratio deviates considerably from the optimal value (Fig. 13.34a). Controlling purge composition (CS3, CS4) reduces the variability, but it is still bellow target at higher production rates. 

Figure 13.35 Conversion vs. reactor volume, for fixed hydrogen / toluene ratio and different values of the gas recycle flow rate...

Figure 13.38 presents the results of the dynamic simulation. Large production increase or decrease can be easily achieved, while the product purity is held on specification. Reaction selectivity remains high, so that the production of heavies is minimised. The constraint related to hydrogen / toluene ratio is satisfied most of the time. Note that the reactor design is such that the operation point is on the upper stable branch in Fig. 13.35. In contrast, if the design is on the unstable branch, close to the turning point, then operability problems appears (Bildea et al., 2002).

Hydrogen make-up hydrogen/toluene ratio kept on setpoint with the fresh hydrogen feed. 

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