Selection Procedure for Parr Stirred Reactors
Parr has continued to expand its line of stirred reactors to give the user many new and additional choices when selecting a reactor for a specific set of operating conditions. New models have been added and the number of available options has been greatly expanded. But the selection process remains the same. It should start with the establishment of the Four Basic Specifications discussed below. Having set these requirements, the user can then identify a suitable Series group from the Stirred Reactors Selection Guide. A list of Standard Reactor Fittings is provided to confirm the basic capabilities included with each reactor. Finally, the Principal Options should be considered to establish the detailed specifications for specifying the reactor using the catalog number and ordering guide.
1. Establish your Four Basic Specifications
1. Maximum Operating Pressure
Parr offers a number of operating pressures. Vessels 600mL and under in volume are typically rated for 3000 psi, and vessels 1L or larger are typically rated for 1900 psi. We also offer 5000 psi versions of these sizes for those who need this combination of smaller size and higher pressure. Some pressure limits can be increased with custom designs. However, higher pressure vessels generally require thicker walls, which can make temperature control more difficult, and larger volume, high pressure vessels are heavier and more difficult to handle. We also have a line of 5100 Series Low Pressure Reactors which can handle pressures up to 150 psi with a glass cylinder or up to 1000 psi with a metal cylinder.
2. Maximum Operating Temperature
Traditionally, the choices here have been up to 350 °C for vessels with PTFE gaskets and up to 500 °C for flexible graphite (previously metal gaskets). Parr added the option of a self-sealing O-ring closure for general purpose vessels over a full range of volumes. These quick closing designs are limited to 225 °C, although this can be raised to 300 °C with special O-ring materials.
3. Vessel Size
Parr stirred reactors are offered in many sizes ranging from 25mL to 18.75 liters (5-gallon). It should be noted that these volumes refer to the free space in the vessel, and for safe operation the maximum liquid charge held in the vessel should not exceed two-thirds of the available free space in sealed batch operations. Generally, several vessel volumes are offered within most series, and reactor sizes can be reconfigured with conversion parts.
4. Material of Construction
Parr reactors are normally made of Type 316 Stainless Steel, but they can be made of other alloys as well.
The list of available materials of construction includes:
- Type 316/316L Stainless Steel
- Alloy 286
- Alloy 20
- Alloy 230
- Alloy 400
- Alloy 600
- Alloy 625
- Alloy B-2/B-3
- Alloy C-276
- Nickel 200
- Titanium Grades 2, 3, 4, & 7
- Zirconium 702 & 705
Other materials may be available upon request. The majority of organic reactions can be handled in a standard T316 Stainless Steel vessel, but other corrosion resistant alloys are available to provide vessels suitable for use with a wide range of corrosive acids, bases, salts and gases. Special alloy construction can be provided for both the internal parts of the vessel and the external valves and fittings. However, there are considerable cost savings if the user can accept standard external parts made of stainless steel instead of a special alloy.
There is more detailed information on special materials in the Materials of Construction section of this website.
2. Select Appropriate Series
3. Confirm Standard Fittings
A. Pressure Gage, analog type, which shows the pressure within the vessel at all times.
B. Liquid Sampling Valve for withdrawing liquid samples through the dip tube shared with the gas inlet valve. Incoming gas can be used to clear the dip tube between liquid samples.
C. Gas Release Valve to release gas from the reactor during or at the completion of a run.
D. Thermocouple or Thermowell for measuring the temperature within the vessel. In small reactors, a thermocouple encased in a metal probe extends directly into the vessel. In larger reactors, and vessels constructed of special alloys, the control thermocouple is inserted into a thermowell which extends to a point near the bottom of the vessel.
E. Internal Stirring System consists of a motor drive magnetically coupled to an internal stirrer shaft with attached turbine-type impeller(s).
F. Dip Tube
G. Safety Rupture Disc to protect the vessel and the operator from dangerous pressures beyond the rated limit for the vessel.
H. Gas Inlet Valve for charging gas into the reactor. This valve and the liquid sampling valve are connected to a dip tube which extends to the bottom of the vessel.
I. Guide or Foot Bearing with a PTFE bushing to support and stabilize lower stirrer shaft. (Not required with footless magnetic drive)
J. Cooling Coil
4. Specify Detailed Options
There are a number of options to be considered and selections to be made in order to complete the specifications for a reactor. You will need to choose from the following:
1. Sealing Style
Parr reactors may be provided with a flat gasket seal or an O-ring seal. Most commonly, a flat PTFE gasket is used. These are generally good for temperatures up to 350 °C. A graphite seal for temperatures up to 500 °C is used for high temperature systems.
O-ring seals allow for a convenient, boltless closure, but the material must be checked carefully against the intended process as there are many solvents and gases which attack O-rings.
Our typical O-ring seal is designed to be self-sealing at high pressures. However this design needs to be modified when the reactor is going to be operated at pressures below 20% of its high pressure rating.
2. Mounting Style
Parr reactors may be provided with a moveable vessel mounting or fixed head mounting.
In the moveable vessel style the complete vessel assembly (only the head in the one gallon or larger) is removed from the heater for charging, product recovery, and vessel cleaning.
In the fixed head style the head remains in the mounting and the reactor heater then cylinder drop away to open the vessel. This is useful for users who wish to leave inlet and feed lines, discharge and vent lines, condensers, and similar head connections undisturbed between runs. The head is easily removable if desired, by sliding the head out of its slot on the stand.
3. Support Stand
Parr stirred reactors are most commonly mounted on a bench top stand for sizes of 2 liter or smaller. Vessels 1 liter or larger may be mounted on either moveable carts or fixed floor stands. Care should be taken to check stand dimensions with the available space at the user’s facility.
4. Stirrer Type
Parr reactors have a magnetic drive equipped for most low to moderate viscosity fluids and light slurries. Drives with higher coupling torque and more powerful motors are available for higher viscosity applications.
Also, many reactors require a lower support bracket to stabilize the stirring shaft. In applications with abrasive particles or heavy mixing, a “footless” magnetic drive with a larger diameter shaft may be provided.
5. Cooling Coil”
An internal cooling coil can be installed in all reactors (except the Micro sizes) to remove the heat of a reaction and/or to cool the vessel at the end of a run. In some reactors a cooling coil is furnished as a standard fitting. In others, a coil can be added as an option in either serpentine style or alternately in a spiral style for selected models. For the micro sizes, with their limited dimensions, a cold finger may be added as an option
6. Gage and Rupture Disc Ranges
The pressure gage range must be selected to provide the resolution desired, while having a range high enough to handle the maximum pressure the reactor will undergo. One would be tempted to simply get a gage with the largest range possible, but this can reduce the resolution to unacceptable levels. One good rule of thumb for good resolution is to operate with the gage at half of its maximum range.
The rupture disc is most commonly matched to the Maximum Allowable Working Pressure of the vessel, ensuring the disc will burst before reaching a pressure beyond the MAWP range. Care must be taken not to take the vessel above 90% of its burst pressure under normal operation. This will help protect the disc from the effects of repeated pressure cycles.
7. Controller Options
Parr controllers are typically set up to control temperature, but may also be set up with digital displays of pressure, stirring speed, secondary temperature and other displays and controls.
These may be set up with data logging via PC as well. For more information on these options, see the “Controller Section” of this catalog.
ASME, CE, CHINA, and PARR Certifications are available for users who require these recognized quality assurance certifications.
9. Custom Options
A wide range of custom options such as special openings in the head or cylinder, high viscosity stirrers, windows, special valves, heaters or jackets, explosion proof wiring, and volume modifications are available.
Various accessories, such as glass or PTFE liners, condensers, catalyst holders, and alternate stirrers are available to further adapt these reactors to the individual user’s applications.
Detailed information for these and other options can be found on the Stirred Reactors Accessories Page of this website.
The User's Responsibility
All Parr reactors and pressure vessels are designed and manufactured with great care to ensure safe operation when used within their prescribed temperature and pressure limits. But… the basic responsibility for safety when using this equipment rests entirely with the user; who must:
1. Select a reactor or pressure vessel which has the capability, pressure rating, corrosion resistance and design features that are suitable for its intended use. Parr engineers will be glad to discuss available equipment and material options with prospective users, but the final responsibility for selecting a reactor or pressure vessel that will perform to the user’s satisfaction in any particular reaction or test must rest with the user — not with Parr.
In exercising the responsibility for the selection of pressure equipment, the prospective user is often faced with a choice between over or under-designed equipment. The hazards introduced by under-designed pressure vessels are readily apparent, but the penalties that must be paid for over-designed apparatus are often overlooked.
Recognizing these criteria, Parr reactors and pressure vessels are offered in several different styles, each designed for convenient use in daily operation within certain temperature and pressure limits, using gaskets, closures and other elements carefully selected for safe operation within the limits specified for that design. But in order to preserve the validity of these designs, all temperature and pressure limits must be observed, and no attempt should be made to increase these limits by making alterations or by substituting components which are not recommended by Parr Instrument Company.
2. Install and operate the equipment within a suitable barricade, if required, with appropriate safety accessories and in full compliance with local safety codes and rules.
All standard Parr pressure vessels are provided with either a suitable relief device or a means to attach one (typically in the form of a plugged opening). When a pressure vessel is delivered without a pressure venting device, it is the customer’s responsibility to provide pressure relief in order to protect the operator and the equipment from destructive high pressures. If you need more information or need help in selecting a proper relief device, please contact Parr Instrument Company.
3. Establish training procedures to ensure that any person handling the equipment knows how to use it properly.
4. Maintain the equipment in good condition and establish procedures for periodic testing to be sure the vessel remains structurally sound.