A pressure reactor, sometimes referred to as a pressure tube, or a sealed tube, is a chemical reaction vessel which can conduct a reaction under pressure. A pressure reactor is a special application of a

pressure vessel A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure. Construction methods and materials may be chosen to suit the pressure application, and will depend on the size o ...

. The pressure can be caused by the reaction itself or created by an external source, like hydrogen in catalytic transfer

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a Catalysis, catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or S ...

Advantages

A pressure reactor can offer several advantages over the conventional

round-bottom flask Round-bottom flasks (also called round-bottomed flasks or RB flasks) are types of Laboratory flask, flasks having spherical bottoms used as laboratory glassware, mostly for chemistry, chemical or biochemistry, biochemical work. They are typicall ...

. Firstly, it can conduct a reaction above the

boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liquid varies depending upon the surrounding envir ...

of a

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

. Secondly, the pressure can reduce the reaction volume, including the liquid phase, and in turn increase

concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', ''molar concentration'', ''number concentration'', an ...

and

collision frequency Collision frequency describes the rate of collisions between two atomic or molecular species in a given volume, per unit time. In an ideal gas, assuming that the species behave like hard spheres, the collision frequency between entities of specie ...

, and accelerate a reaction. Increase in temperature can speed up the desired reaction, but also speed up the

decomposition Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is e ...

reagent In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...

s and starting materials. However, pressure can speed up the desired reaction and only impacts decomposition when it involves the release of a gas or a reaction with a gas in the vessel. When the desired reaction is accelerated, competing reactions are minimized. Pressure generally enables faster reactions with cleaner reaction profiles. The above benefits from a pressure reactor has been shown in

microwave chemistry Microwave chemistry is the science of applying microwave radiation to chemical reactions. Microwaves act as high frequency electric fields and will generally heat any material containing mobile electric charges, such as polar molecules in a solvent ...

. E.g., if a

Suzuki Coupling The Suzuki reaction is an organic reaction, classified as a cross-coupling reaction, where the coupling partners are a boronic acid and an organohalide and the catalyst is a palladium(0) complex. It was first published in 1979 by Akira Suzuki, a ...

takes 8 hours at 80°C, it only takes 8 minutes at 140°C in a microwave synthesizer. The microwave effect is a controversial topic. Later experiments show some of these early reports to be artifacts and rate enhancement is strictly due to thermal effects. If a pressure reactor is engineered properly, it can meet 4 out of 12

green chemistry Green chemistry, also called sustainable chemistry, is an area of chemistry and chemical engineering focused on the design of products and processes that minimize or eliminate the use and generation of hazardous substances. While environmental che ...

principles *1, less solvent and cleaner reaction profile result in less waste *5, less solvent is needed *6, short reaction time can save up to 92 percent electricity and 200 gallons of cooling water per refluxed reaction *12, closed vessel can prevent releasing toxic gas and explosions.

Types of Pressure Reactors

Standard glass pressure reactor

Glass Pressure reactors are typically used when an operator needs to observe how a reaction takes place. Although the pressure ratings on these systems are lower than most metal pressure reactors, they are still an efficient set up for reaching responsible pressure limits. The ratings on glass vessels are directly related to the diameter of the vessel. The larger the diameter, the lower the allowable pressure. Integrated bottom valves can also impact the pressure ratings. A bottom valve on a glass vessel typically relates to a lower allowable working pressure. These are all variables determined by the process and parameters of each individual reaction. Glass pressure vessels can also be used in inert applications. These vessels are used in reactions included but are not limited to Hydrogenations, Polymerizations, Synthesis, Catalytic, petrochemical, crystallization, and so on. One of the drawbacks of a standard glass pressure reactor is the potential explosions due to hard-to-predict excessive internal pressure and lack of relief mechanism. However, with proper safety implementation provided by the manufacturer, the operator can perform most reactions in a safe manner.

Fisher-Porter tube

A Fisher-Porter tube or Fisher-Porter vessel is a glass pressure reactor used in the chemical laboratory. Manufactured by Andrews Glass Co. of Vineland NJ

Metal pressure reactor

Metal Pressure reactors are typically used for high pressure reactions. They have a much higher pressure rating than glass reactors. Although they have a higher pressure rating, they still have their own distinct flaws. One of which would be that metal vessels are more susceptible to corrosion. The material of construction (MOC) is particularly important during the design phase of a metal pressure reactor. The correct MOC can reduce or even eliminate the corrosion seen in the vessel but, depending on the material chosen, could increase the price of a system. Metal vessels are also much heavier and should be handled carefully when performing maintenance. Metal high pressure reactors are used in reactions included but are not limited to Hydrogenation, Polymerization, Synthesis, Catalytic, Petrochemical and so on. They are also used to perform research such as Upstream, Biomass, Biopolymer, Zeolite, etc. The drawbacks of a metal pressure reactor (bomb) are set-up, maintenance, and corrosiveness.

Microwave synthesizer

The drawbacks of a microwave synthesizer are solvent limitation

References

{{DEFAULTSORT:Pressure Reactor Laboratory equipment Laboratory techniques