Reactions liquid-phase

The equilibrium conversion can be increased by employing one reactant in excess (or removing the water formed, or both). b. Inerts concentration. Sometimes, an inert material is present in the reactor. This might be a solvent in a liquid-phase reaction or an inert gas in a gas-phase reaction. Consider the reaction system... 

Increasing the pressure of irreversible vapor-phase reactions increases the rate of reaction and hence decreases reactor volume both by decreasing the residence time required for a given reactor conversion and increasing the vapor density. In general, pressure has little effect on the rate of liquid-phase reactions. 

For liquid-phase reactions, the effect of pressure on the selectivity and reactor volume is less pronounced, and the pressure is likely to be chosen to... 

Having considered reactor temperature and pressure, we are now in a position to judge whether the reactor phase will be gas, liquid, or multiphase. Given a free choice between gas- and liquid-phase reactions, operation in the liquid phase is usually preferred. Consider the single reaction system from Eq. (2.19) ... 

Clearly, in the liquid phase much higher concentrations of Cfeed (kmol m ) can be maintained than in the gas phase. This makes liquid-phase reactions in general more rapid and hence leads to smaller reactor volumes for liquid-phase reactors. 

By contrast, if the reactor is continuous well-mixed, then the reactor is isothermal. This behavior is typical of stirred tanks used for liquid-phase reactions or fluidized-bed reactors used for gas-phase reactions. The mixing causes the temperature in the reactor to be effectively uniform. 

CH2C1 CH2C1. Colourless liquid with an odour like that of chloroform b.p. 84 C. It is an excellent solvent for fats and waxes. Was first known as oil of Dutch chemists . Manufactured by the vapour- or liquid-phase reaction of ethene and chlorine in the presence of a catalyst. It reacts with anhydrous ethano-ales to give ethylene glycol diethanoate and with ammonia to give elhylenediamine, these reactions being employed for the manufacture of these chemicals. It burns only with difficulty and is not decomposed by boiling water. 

This is illustrated in Figure 17.1. The energies of the van der Waals complexes are a better description of the separated species for describing liquid-phase reactions. The energies of the products separated by large distances are generally more relevant to gas-phase reactions. 

Catalytic esterification of alcohols and acids in the vapor phase has received attention because the conversions obtained are generally higher than in the corresponding liquid-phase reactions (7). 

Material and energy balances are based on the conservation law, Eq. (7-69). In the operation of liquid phase reactions at steady state, the input and output flow rates are constant so the holdup is fixed. The usual control of the discharge is on the liquid level in the tank. When the mixing is adequate, concentration and temperature are uniform, and the effluent has these same properties. The steady state material balance on a reacdant A is... 

Gas-Film Coefficient Since the gas film is not affected by the liquid-phase reaction, one of the many available correlations for physic absorption may be apphcable. The coefficient also may be found directly after elimination of the hquid-film coefficient by employing a solution that reacts instantaneously and irreversibly with the dissolved gas, thus cancehng out any backpressure. Examples of such systems are SO2 in NaOH and NH3 in H2SO4. 

Liquid phase reactions involving optically active species. 

In chemical laboratories, small flasks and beakers are used for liquid phase reactions. Here, a charge of reactants is added and brought to reaction temperature. The reaction may be held at this condition for a predetermined time before the product is discharged. This batch reactor is characterized by the varying extent of reaction and properties of the reaction mixture with time. In contrast to the flasks are large cylindrical tubes used in the petrochemical industry for the cracking of hydrocarbons. This process is continuous with reactants in the tubes and the products obtained from the exit. The extent of reaction and properties, such as composition and temperature, depend on the position along the tube and does not depend on the time. 

A second order, liquid phase reaction, A + B —> C, is to be performed in a single-stage CESTR. Given the following data ... 

The definition of Kp obviously applies to tlie reaction of Eq. (4.6.1). Assuming that a K value is available or calculable, this equation may be used to detennine the partial pressures of the participating components at equilibrium. For liquid phase reactions, K is given approximately by... 

Homogeneous reactions are those in which the reactants, products, and any catalysts used form one continuous phase (gaseous or liquid). Homogeneous gas phase reactors are almost always operated continuously, whereas liquid phase reactors may be batch or continuous. Tubular (pipeline) reactors arc normally used for homogeneous gas phase reactions (e.g., in the thermal cracking of petroleum of dichloroethane lo vinyl chloride). Both tubular and stirred tank reactors are used for homogeneous liquid phase reactions. 

Pipeline reactor for gaseous or liquid phase reactions Turbulent 1 or 2 six-element modules... 

The liquid phase reaction of ethylene with carbon monoxide and oxygen over a Pd VCu " catalyst system produces acrylic acid. The yield based on ethylene is about 85%. Reaction conditions are approximately 140°C and 75 atmospheres ... 

Typical liquid-phase reaction conditions for the chlorination of benzene using FeCls catalyst are 80-100°C and atmospheric pressure. When a high benzene/Cl2 ratio is used, the product mixture is approximately 80% monochlorobenzene, 15% p-dichlorobenzene and 5% o-dichlorobenzene. 

Similar to the alkylation and the chlorination of benzene, the nitration reaction is an electrophilic substitution of a benzene hydrogen (a proton) with a nitronium ion (NO ). The liquid-phase reaction occurs in presence of both concentrated nitric and sulfuric acids at approximately 50°C. Concentrated sulfuric acid has two functions it reacts with nitric acid to form the nitronium ion, and it absorbs the water formed during the reaction, which shifts the equilibrium to the formation of nitrobenzene ... 

A heterogeneous catalyst is one that is in a different phase from the reaction mixture. Most commonly, the catalyst is a solid that increases the rate of a gas-phase or liquid-phase reaction. An example is the decomposition of N20 on gold ... 

A heterogeneous catalyst is a catalyst present in a phase different from that of the reactants. The most common heterogeneous catalysts are finely divided or porous solids used in gas-phase or liquid-phase reactions. They are finely divided or porous so that they will provide a large surface area for the elementary reactions that provide the catalytic pathway. One example is the iron catalyst used in the... 

Consider the liquid-phase reaction of a diacid with a diol, the first reaction step being... 

At extreme pressures, liquid-phase reactions exhibit pressure effects. A suggested means for correlation is the activation volume, A Vaco Thus,... 

Example 11.6 Suppose the liquid-phase reaction is A -b B Products = kaibi... 

Solution The liquid-phase reaction has the form C + A P, which we assume to be elementary with rate constant k. Suppose there are J trays in the column and that they are numbered starting from the bottom. Figure 11.4 shows a typical tray and indicates the notation. Since the... 

Measurements Using Liquid-Phase Reactions. Liquid-phase reactions, and the oxidation of sodium sulfite to sodium sulfate in particular, are sometimes used to determine kiAi. As for the transient method, the system is batch with respect to the liquid phase. Pure oxygen is sparged into the vessel. A pseudo-steady-state results. There is no gas outlet, and the inlet flow rate is adjusted so that the vessel pressure remains constant. Under these circumstances, the inlet flow rate equals the mass transfer rate. Equations (11.5) and (11.12) are combined to give a particularly simple result ... 

The overall driving force for mass transfer is AT = Pg—Pi, where Pi is the concentration of oxygen in the liquid phase expressed as an equivalent partial pressure. For the experimental conditions, T/ 0 due to the fast, liquid-phase reaction. The oxygen pressure on the gas side varies due to the liquid head. Assume that the pressure at the top of the tank was 1 atm. Then Tg = 0.975 atm since the vapor pressure of water at 20°C should be subtracted. At the bottom of the tank, 1.0635 atm. The logarithmic mean is appropriate AT =1.018 atm. Thus, the transfer rate was... 

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