A chemical reactor is an essential production device for the synthesis of molecules in batches.
When a molecule is synthesized chemically, such tank is called a “reactor”.
When a molecule is synthesized for biotech, such a tank is called a “bioreactor” or a “fermenter”.
The word « boiler » is used for reactors used in distillation processes, either for vegetal extraction, or organic synthesis.
A reactor is defined by :
A volume capacity, 1 liters to 40,0000 liters, depending of batch size to produce,
A material, that must resist the solvents used, and also corrosion due to molecules produced during reactions,
A temperature program, usually between -20 and +150°C, occasionally at lower temperatures (often down to -100°C) for so-called “cryogenic” reactors, or even at higher temperatures (often up to +300°C) usually used for distillation of heavy products.
Reactors are sometimes built and installed in order to produce one specific molecule according to one given process.
Reactors are more often built so to be general-purpose in order to produce at request different molecules according to varying processes within vast temperature and pressure ranges.
A reactor may be equipped with :
- a thermal or fluid jacket
- leak-proof jacket over insulation
- observation window
- man- or fist-hole
- temperature sensor
- level detector
- inner baffles
- safety and discharge valves
- spray balls
- various nozzles
A chemical reactor undergoes, at various moments of its use, a gaz inerting process, a control of its pressure, or of vaccuum, of its temperature, or a safety valve :
The reactor sky, above the reactive liquid phase is mainly composed of an inert gas : nitrogen. Depending of conditions of temperature and pressure, the reactor’s sky may include the gas phase of some solvents that are present within the reactor : VOC (Volatile Organic Components).
The reactor’s sky inerting process has 2 purposes :
Preventing the presence of atmospheric oxygen which could trigger a parasitic reaction.
Avoiding the presence of a combustive in a permanent explosion risk zone. The inside of a reactor is often classified as a zone 0 according to the ATEX standard.
A reactor is inerted by injecting unpressurized nitrogen, or even pressurized nitrogen.
Pressure control :
In most cases, a high pressure inside of the reactor is achieved by heating the reactive liquids, which leads to the evaporation of solvents within a confined volume.
It may be necessary, in certain operations at low temperature, or in absence of an organic solvent, to increase the pressure by injecting inert gas.
In this case, the duct bringing in the nitrogen for the inerting is equipped of a control valve linked to a maesure of the sky’s pressure.
The reactor’s pressure is also controlled in the case of liquid-gas operations : this is the case of hydrogenation and phosgenation.
Vaccuum control :
Vaccuum is achieved in a reactor by conecting it to a vaccuum network or to a specific vacuum pump.
Only partial vacuum can be achieved, pressure in the reactor is necessarily limited by partial pressure or pressures of solvents present in the vessel.
Also, if the vacuum is created by a liquid ring pump, the level of vacuum is limited by the liquid ring’s partial pressure. This is why it is important to cool the liquid ring at the lowest possible temperature.
Vaccuum is controlled through a control loop that uses the indications of an absolute pressure sensor of the inside of the reactor and a control valve on the vacuum line upwards from the vacuum pump.
Temperature control :
The reaction mass temperature can be controlled by circulating a fluid in the thermal jacket of the vessel.
Two control technologies can be used: direct injection of a service fluid in the thermal jacket, or circulating a “monofluid” inside of a single loop (see description of the Energy Module technology).
Thermal jacket construction technologies are the following :
- Classical “double envelop”, in which the fluid circulates with a laminar mode. This technology of thermal jacket can be improved by the addition of coiled baffles or injection channels
- “Half-coil”, made of half pipes welded upon the internal or external surface of the reactor wall, on the heads and shell of the vessel, or even with more complex-shaped tubings. The thermal fluid is circulated in the half–coils with a turbulent mode, more efficient in terms of heat exchange.
- “Matressing”, which consists of an extra layer of sheet metal on the inside or outside of the reactor wall, and seam-welded, then expanded by pressurized hydro-forming. This technology is not suitable for reactors, and must be reserved for tanks that do not have any particular thermal performances, or simply for maintaining a certain temperature.
In any case, the heat exchange surface between the thermal jacket and the reactor itself is necessarily limited by the size of the reactor’s shell and heads.
In order to improve the thermal efficiency of the reactor, additional exchange surface can be added by using so-called “candles”, or internal heat exchangers hanging from the top head of the reactor.
Safety valve :
The reactor is dimensionned, built and approved according to a Maximum Service Pressure (MSP) value, defined by its usage.
Safety devices protect the reactor in case of accidental use, or of use at a pressure exceeding the Maximum Service Pressure : rupture disks or safety valves, or both simultaneously.
The safety valve must be tared at MSP value, it consists in a discreet valve which must be cleaned and re-tared after opening.
A rupture disk is also designed to break at MPS value, and must be, of course, replaced after breakage.
These safety devices that protect a pressure vessel compliant with the European Directive DESP 97/23/CE must also be compliant with the same directive according to the same vessel category, or above.
Thus, safety valves are usually CE approved in category IV in order to adapt to every need.