Primary endothermic reaction

The remaining unoxidized hydrocarbons react endothermically with steam and the combustion products from the primary reaction. The main endothermic reaction is the reforming of hydrocarbon by water vapor ... 

Rain unaffected by human activity contains mostly weak acids and has a pH of 5.7. The primary acid present is carbonic acid, H2C03, a weak acid that results when atmospheric carbon dioxide dissolves in water. The major pollutants in acid rain are strong acids that arise from human activities. Atmospheric nitrogen and oxygen can react to form NO, but the endothermic reaction is spontaneous only at the high temperatures of automobile internal combustion engines and electrical power stations ... 

Prior to the chemical reaction of the silane with the silanol-groups on the sUica surface, the silane molecule has to make contact with the sUica surface by adsorption. Then the chemical reaction of silica with an alkoxy-silyl moiety of the coupling agent takes place in a two-step, endothermic reaction. The primary step is the reaction of alkoxy-groups with silanol-groups on the silica filler surface [4]. Two possible mechanisms are reported ... 

The SR reactors are well suited for long periods of steady-state operation. The high endothermicity of the primary SR reaction results in reactor performances limited by heat transfer more than by reaction kinetics. Consequently, the reactors are designed to promote heat exchange and tend to be large and heavy [22]. 

Therefore, in the case of chemical induction the primary (spontaneous) reaction mechanism always includes at least a single endothermic stage, in which chemical energy is accumulated. 

In some cases a plant may have a pre-reformer. A pre-former is an adiabatic, fixed-bed reactor upstream of the primary reformer. It provides an operation with increased flexibility in the choice of feed stock it increases the life of the steam reforming catalyst and tubes it provides the option to increase the overall plant capacity and it allows the reformer to operate at lower steam-to-carbon ratios166. The hot flue gas from the reformer convection section provides the heat required for this endothermic reaction. 

Reaction (1) is the primary reforming reaction and is endothermic. Reaction (2) is the water-gas shift reaction and is exothermic. Both these reactions are limited by thermodynamic equilibrium. The overall reaction is endothermic and hence requires that additional fuel be combusted to supply heat. The conventional steam reformer is a fired furnace containing catalyst-filled tubes. The hydrocarbon and steam mixture is processed in the catalyst-filled tubes while external burners heat the tubes. Nickel supported on a ceramic matrix is the most common steam reforming catalyst. 

Fuel Requirement. Most of the fuel used in a steam reforming plant is required to sustain the following highly endothermic reaction in the primary reforming furnace ... 

Endothermic Reactions An endothermic reaction process is generally easier to bring to a safe state if an out-of-control situation is detected. Discontinuing the heat input is usually the primary line of defense to stop the operation. In this regard, the endothermic reaction is inherently safer than an exothermic reaction. 

The products of these endothermic reactions, which are not necessarily primary products, can be equilibrated by the water-gas shift reaction (4) and methane-steam reactions (5) and (6) ... 

Two primary methods of manufacturing formaldehyde from methanol are used today. The first uses silver as a metal catalyst in its reactions. In earlier years, facilities used a copper catalyst in this process. The simultaneous reactions involved in the metal catalyst process occur at essentially atmospheric pressure and 600-650 °C (Gerberich et al. 1980). Approximately 50-60% of the formaldehyde produced using the metal catalyst process is formed during an exothermic reaction the remainder is formed from an endothermic reaction. The overall yield for this process is 86-90% formaldehyde. The domestic licensors for this process include Borden Chemical Company and Davy Powergas, Inc. (Gerberich et al. 1980). 

The key components of a chemical energy transmission system or a chemical heat pipe are a primary energy source to provide heat, an input catalyst reactor where in an endothermal reaction energy is stored in newly created products, and an output catalyst converter, where the reverse exothermal chemical reaction helps to extract the stored heat for further consumption. 

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