Reaction, coupled exothermic

A bidirectional fixed-bed reactor for coupling exothermic and endothermic reactions. 

Enzymatic catalysis lowers AG to accelerate the reaction rate, but does not affect the AG° that controls the position of equilibrium. However, cells also have an elegant ability to overcome an unfavorable equilibrium by coupling an endothermic reaction with exothermic ATP hydrolysis. For example, the reaction of acetate with coenzyme A (CoASH) giving acetyl CoA is uphill by about 7 kcal/mol. The hydrolysis of ATP to ADP and phosphate is downhill by about the same amount. By coupling these two reactions shown below for acyl-CoA synthetase, the cell achieves a total AG° of almost 0 for a ATgq of about 1. The phosphorylation of acetate by ATP improves the leaving group for the second reaction with CoASH. There are many enzymes whose catalytic process remains a mystery enzymes still have much to teach us about reaction mechanisms. 

Batteries exposed to certain abusive conditions may experience thermal runaway - a series of coupled exothermic chemical reactions involving metallic lithium, lithium dithionite and possibly sulfur, resulting in the formation of sulfides. At the elevated temperatures resulting from these reactions, these products may further react with the carbon in the cathode to form carbon dioxide (CO2) and carbon disulfide (CS2). Carbon... 

Multiple steady-state behavior is a classic chemical engineering phenomenon in the analysis of nonisothermal continuous-stirred tank reactors. Inlet temperatures and flow rates of the reactive and cooling fluids represent key design parameters that determine the number of operating points allowed when coupled heat and mass transfer are addressed, and the chemical reaction is exothermic. One steady-state operating point is most common in CSTRs, and two steady states occur most infrequently. Three stationary states are also possible, and their analysis is most interesting because two of them are stable whereas the other operating point is unstable. 

As mentioned, membrane micro-reactors are very interesting systems to be studied in case external mass transfer limitations could not be ignored (such as for high-flux Pd-based membranes) and when different steps need to be coupled (coupling exothermic and endothermic reaction is an example). However, more research is required before being... 

In electrocatalysis, the electromotive force supplied by the electrical power supply is the source of the energy necessary to drive an unfavorable reaction, as in electrochemical water splitting into H2 and O2. In a thermal reaction, an exothermic reaction can be coupled to an endothermic one to drive the latter to... 

When catalyst is introduced on to the walls of the second flow path, a catalytic wall reactor is formed, as shown in Figure 7.3c. This design has enormous potential for directly coupling exothermic reactions (such as steam reforming) and exothermic reactions (such as catalytic combustion of fuel cell anode off-gas), which are then only separated by the few hundred micrometer metal foils between the two coatings. 

Gas-solid exothermic and endothermic reaction coupling (Ramaswamy et al., 2006)... 

As an example consider a second-order reaction Here the suitable coupling between pex and V, over and above the couphng due to the compressibility of the system (the equation of state triangle in Fig. 15.3), comes from the fact that on decreasing V the number of reactions per unit time increases as V for fixed total number of particles. For an exothermic (endothermic) reaction this effect leads to increased (decreased) production of heat as V decreases, and consequently to temperature and pressure changes, in addition to those due to compression. For first-order reactions coupling can be achieved through the temperature dependence of rate coefficients. 

The majority of ethylbenzene (EB) processes produce EB for internal consumption within a coupled process that produces styrene monomer. The facility described here produces 80,000 tonne/yr of 99.8 mol% ethylbenzene that is totally consumed by an on-site styrene facility. As with most EB/styrene facilities, there is significant heat integration between the two plants. In order to decouple the operation of the two plants, the energy integration is achieved by the generation and consunption of steam within the two processes. The EB reaction is exothermic, so steam is produced, and the styrene reaction is endothermic, so energy is transferred in the form of steam. 

Another crosslinking mechanism, leading to the formation of H-crosslinks, is shown in Scheme 6. Secondary macroradicals can decay, moving along the polymeric chain, via disproportion (Scheme 6, Reaction 11) or coupling (Reaction 12). Both reactions are exothermal (AH = — 260kJ/mol and — 313kJ/mol for Reactions 11 and 12, respectively). 

To a suspension of a tinc-copper couple in 150 ml of 100 ethanol, prepared from 80 g of zinc powder (see Chapter II, Exp. 18), was added at room temperature 0.10 mol of the acetylenic chloride (see Chapter VIII-2, Exp. 7). After a few minutes an exothermic reaction started and the temperature rose to 45-50°C (note 1). When this reaction had subsided, the mixture was cooled to 35-40°C and 0,40 mol of the chloride was added over a period of 15 min, while maintaining the temperature around 40°C (occasional cooling). After the addition stirring was continued for 30 min at 55°C, then the mixture was cooled to room temperature and the upper layer was decanted off. The black slurry of zinc was rinsed five times with 50-ml portions of diethyl ether. The alcoholic solution and the extracts were combined and washed three times with 100-ml portions of 2 N HCl, saturated with ammonium chloride. 

The coupling reaction is very exothermic. The reaction temperature can be controlled by the rate of addition of 4-iodoanisole. 

The palladium-catalyzed cross-coupling of alkenylsilanols has been extensively studied with respect to the structure of both the silicon component and the acceptor halide. The preferred catalyst for coupling of aryl iodides is Pd(dba)2 and for aryl bromides it is [allylPdCl]2. The most effective promoter is tetrabutylammonium fluoride used as a 1.0M solution in THF. In general the coupling reactions occur under mild conditions (room temperature, in 10 min to 12 hr) and some are even exothermic. 

The couplings of reactive iodides (with electron-withdrawing groups) were exothermic. However, the reaction temperature can be modulated by the slow addition of iodides last. These protocols are suitable for larger scale applications as well. 

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