Exothermic heat

Section 6 2 Hydrogenation of alkenes is exothermic Heats of hydrogenation can be... 

Finding the End Point by Monitoring Temperature The reaction between an acid and a base is exothermic. Heat generated by the reaction increases the temperature of the titration mixture. The progress of the titration, therefore, can be followed by monitoring the change in temperature. 

Stea.ming Retjuirements. The steaming of fixed beds of activated carbon is a combination of thermal swing and displacement purge swing. The exothermic heat released when the water adsorbs from the vapor phase is much higher than is possible with heated gas purging. This cycle has been successhiUy modeled by equiUbrium theory (128). 

Another useful reaction is the reaction of water with isocyanate to generate CO2 and urea groups which modify the polymeric stmcture. This vigorous reaction is also a prime source of exothermic heat to drive equation 3 to completion. 

The highly exothermic nature of the butane-to-maleic anhydride reaction and the principal by-product reactions require substantial heat removal from the reactor. Thus the reaction is carried out in what is effectively a large multitubular heat exchanger which circulates a mixture of 53% potassium nitrate [7757-79-1/, KNO 40% sodium nitrite [7632-00-0], NaN02 and 7% sodium nitrate [7631-99-4], NaNO. Reaction tube diameters are kept at a minimum 25—30 mm in outside diameter to faciUtate heat removal. Reactor tube lengths are between 3 and 6 meters. The exothermic heat of reaction is removed from the salt mixture by the production of steam in an external salt cooler. Reactor temperatures are in the range of 390 to 430°C. Despite the rapid circulation of salt on the shell side of the reactor, catalyst temperatures can be 40 to 60°C higher than the salt temperature. The butane to maleic anhydride reaction typically reaches its maximum efficiency (maximum yield) at about 85% butane conversion. Reported molar yields are typically 50 to 60%. 

Fresh butane mixed with recycled gas encounters freshly oxidized catalyst at the bottom of the transport-bed reactor and is oxidized to maleic anhydride and CO during its passage up the reactor. Catalyst densities (80 160 kg/m ) in the transport-bed reactor are substantially lower than the catalyst density in a typical fluidized-bed reactor (480 640 kg/m ) (109). The gas flow pattern in the riser is nearly plug flow which avoids the negative effect of backmixing on reaction selectivity. Reduced catalyst is separated from the reaction products by cyclones and is further stripped of products and reactants in a separate stripping vessel. The reduced catalyst is reoxidized in a separate fluidized-bed oxidizer where the exothermic heat of reaction is removed by steam cods. The rate of reoxidation of the VPO catalyst is slower than the rate of oxidation of butane, and consequently residence times are longer in the oxidizer than in the transport-bed reactor. 

Copper naphthenate added to the resin at levels between 100—200 ppm effectively extends gel and cure characteristics, resulting in a reduction in exothermic heat (Eig. 7). Copper additives are used widely in commercial laminating resins to modify process exothermic effects. a-Methylstyrene [98-83-9] substituted for styrene at levels of 5—8% has also been used effectively in resins cured at above ambient temperatures. The inhibitor 2,5-di-/-butyIhydroquinone exerts significant exotherm suppression at levels of 200—400 ppm and is useful in high temperature mol ding processes. 

Potassium siUcates are manufactured in a manner similar to sodium siUcates by the reaction of K CO and sand. However, crystalline products are not manufactured and the glass is suppHed as a flake. A 3.90 mole ratio potassium siUcate flake glass dissolves readily in water at ca 88°C without pressure by incremental addition of glass to water. The exothermic heat of dissolution causes the temperature of the solution to rise to the boiling point. Lithium sihcate solutions are usually prepared by dissolving siUca gel in a LiOH solution or mixing colloidal siUca with LiOH. 

Both the fermentation of hexose sugars to ethanol and carbon dioxide and the oxidation of ethanol to acetic acid are exothermic (heat yielding) processes (see Sugar). The first reaction is expressed as foUows ... 

The first reactor in series in the Arco, lEP, and Phillips processes is adiabatic (vessel filled with catalyst). The exothermic heat of reaction is removed in a pump-around loop where a portion of the reactor contents are taken from the reactor, pumped through an external exchanger, cooled, and returned to the reactor. 

Hydration at Ordinary Temperatures. Pordand cement is generally used at temperatures ordinarily encountered in constmction, ie, from 5 to 40°C. Temperature extremes have to be avoided. The exothermic heat of the hydration reactions can play an important part in maintaining adequate temperatures in cold environments, and must be considered in massive concrete stmctures to prevent excessive temperature rise and cracking during subsequent cooling. 

Dichloroethane is produced by the vapor- (28) or Hquid-phase chlorination of ethylene. Most Hquid-phase processes use small amounts of ferric chloride as the catalyst. Other catalysts claimed in the patent Hterature include aluminum chloride, antimony pentachloride, and cupric chloride and an ammonium, alkaU, or alkaline-earth tetrachloroferrate (29). The chlorination is carried out at 40—50°C with 5% air or other free-radical inhibitors (30) added to prevent substitution chlorination of the product. Selectivities under these conditions are nearly stoichiometric to the desired product. The exothermic heat of reaction vapori2es the 1,2-dichloroethane product, which is purified by distillation. 

If the addition of liquid to the tank causes an average endothermic or exothermic heat of solution, q J/kg (Btii/lb) of m eiip, it may be included by adding q,/co to both the numerator and the denominator of the left side. The snbscrmt 0 refers to the makeup. 

In the case of HCl absorption, a shell-and-tube heat exchanger often is employed as a cooled wetted-waU vertical-column absorber so that the exothermic heat of reaction can be removed continuously as it is released into the liquid film. 

Differential scanning calorimetry (DSC) Onset temperature of exotherms, heat of reaction... 

Potential System with sufficient exothermic (heat evolving) capacity... 

Adsorption onto a solid is always accompanied by a liberation of heat. For physical adsorption, this exothermic heat of adsorption is always greater than the heat of condensation of the adsorbate. 

Because the reaction is exothermic, heat must be removed from the reactor to keep the temperature from increasing out of control. The heat transfer rate of removal is ... 

A typical method of preparation of 5- and 7-ply plywood panels is by pressing at room temperature and the simultaneous use of a one-step exothermic heat gluing/ monomer curing technique. Prior to monomer impregnation, all veneer samples were conditioned at room temperature. The assembly was compressed to 1.03 MPa (150 psi) between steel plates in a hydraulic press, and the steel plates fastened with a pair of bolts and nuts at both ends. 

The main route to ethylene oxide is oxygen or air oxidation of ethylene over a silver catalyst. The reaction is exothermic heat control is important ... 

Polymers obtained by the bulk technique are usually pure due to the absence of a solvent. The purity of the final polymer depends on the purity of the monomers. Heat and viscosity are not easily controlled, as in other polymerization techniques, due to absence of a solvent, suspension, or emulsion medium. This can be overcome by carrying the reaction to low conversions and strong agitation. Outside cooling can also control the exothermic heat. 

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