Pressure reactor
Encyclopedia
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. The pressure can be caused by the reaction itself or created by an external source, like hydrogen in catalytic transfer hydrogenation
.
. Firstly, it can conduct a reaction above the boiling point
of a solvent
. Based on the Arrhenius equation
, the reaction rate can double for every 10 degree Celsius increase in temperature. In other words, for every 10 degree Celsius increase, reaction time can be shortened in half. Secondly, the pressure can reduce the reaction volume, including the liquid phase, and in turn increase concentration
and collision frequency
, and accelerate a reaction.
Increase in temperature can speed up the desired reaction, but also speed up the decomposition
of reagent
s and starting materials
. However, pressure can speed up the desired reaction and has no impact on decomposition. When the desired reaction is accelerated, the competing reagent decompositions are minimized. Pressure enables faster reactions with cleaner reaction profiles.
The above benefits from a pressure reactor has been shown in microwave chemistry
. E.g., if a Suzuki Coupling takes 8 hours at 80°C, it only takes 8 minutes at 140°C in a microwave synthesizer. 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
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).
The drawbacks of a metal pressure reactor (bomb
) are set-up, maintenance, and corrosiveness.
The drawbacks of a microwave synthesizer
are solvent limitation (it needs a polar solvent to absorb microwave energy), and localized overheat which causes decomposition
.
There is a new pressure reactor, called Q-Tube. It features a simple and safe pressure release and reseal mechanism which can prevent a glass pressure reactor from explosions and retain the solvent.
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
.
Advantages
A pressure reactor can offer several advantages over the conventional round-bottom flaskRound-bottom flask
Round-bottom flasks are types of flasks having spherical bottoms used as laboratory glassware, mostly for chemical or biochemical work. They are typically made of glass for chemical inertness; and in modern days, they are usually made of heat-resistant borosilicate glass...
. Firstly, it can conduct a reaction above the boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....
of a solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
. Based on the Arrhenius equation
Arrhenius equation
The Arrhenius equation is a simple, but remarkably accurate, formula for the temperature dependence of the reaction rate constant, and therefore, rate of a chemical reaction. The equation was first proposed by the Dutch chemist J. H. van 't Hoff in 1884; five years later in 1889, the Swedish...
, the reaction rate can double for every 10 degree Celsius increase in temperature. In other words, for every 10 degree Celsius increase, reaction time can be shortened in half. Secondly, the pressure can reduce the reaction volume, including the liquid phase, and in turn increase concentration
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
and collision frequency
Collision theory
Collision theory is a theory proposed by Max Trautz and William Lewis in 1916 and 1918, that qualitatively explains how chemical reactions occur and why reaction rates differ for different reactions. For a reaction to occur the reactant particles must collide. Only a certain fraction of the total...
, and accelerate a reaction.
Increase in temperature can speed up the desired reaction, but also speed up the decomposition
Chemical decomposition
Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction...
of reagent
Reagent
A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...
s and starting materials
Reagent
A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...
. However, pressure can speed up the desired reaction and has no impact on decomposition. When the desired reaction is accelerated, the competing reagent decompositions are minimized. Pressure enables faster reactions with cleaner reaction profiles.
The above benefits from a pressure reactor has been shown in microwave chemistry
Microwave chemistry
Microwave chemistry is the science of applying microwave irradiation 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 or conducting ions in a solid...
. E.g., if a Suzuki Coupling takes 8 hours at 80°C, it only takes 8 minutes at 140°C in a microwave synthesizer. 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
Green chemistry, also called sustainable chemistry, is a philosophy of chemical research and engineering that encourages the design of products and processes that minimize the use and generation of hazardous substances...
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
One of the drawbacks of a standard glass pressure reactor is the potential explosions due to hard-to-predcit excessive internal pressure and lack of relief mechanism.The drawbacks of a metal pressure reactor (bomb
Autoclave
An autoclave is an instrument used to sterilize equipment and supplies by subjecting them to high pressure saturated steam at 121 °C for around 15–20 minutes depending on the size of the load and the contents. It was invented by Charles Chamberland in 1879, although a precursor known as the...
) are set-up, maintenance, and corrosiveness.
The drawbacks of a microwave synthesizer
Microwave chemistry
Microwave chemistry is the science of applying microwave irradiation 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 or conducting ions in a solid...
are solvent limitation (it needs a polar solvent to absorb microwave energy), and localized overheat which causes decomposition
Chemical decomposition
Chemical decomposition, analysis or breakdown is the separation of a chemical compound into elements or simpler compounds. It is sometimes defined as the exact opposite of a chemical synthesis. Chemical decomposition is often an undesired chemical reaction...
.
There is a new pressure reactor, called Q-Tube. It features a simple and safe pressure release and reseal mechanism which can prevent a glass pressure reactor from explosions and retain the solvent.