PAR-5400 Continuous Flow Tubular Reactors

Tubular reactors are always used in a continuous flow mode with reagents flowing in and products being removed. They can be the simplest of all reactor designs. Tubular reactors are often referred to by other names:

• Pipe reactors
• Packed-bed reactors
• Trickle-bed reactors
• Bubble-column reactors
• Ebulating-bed reactors

Single-phase flow in a tubular reactor can be upward or downward. Two-phase flow can be co-current up-flow, counter-current (liquid down, gas up) or, most commonly, co-current down-flow.

Tubular reactors can have a single wall and be heated with an external furnace or they can be jacketed for heating or cooling with a circulating heat transfer fluid. External furnaces can be rigid, split-tube heaters or be flexible mantle heaters.

Tubular reactors are used in a variety of industries:

• Petroleum
• Petrochemical
• Polymer
• Pharmaceutical
• Waste Treatment
• Specialty chemical

Tubular reactors are used in a variety of applications:

• Carbonylation
• Dehydrogenation
• Hydrogenation
• Hydrocracking
• Hydroformulation
• Oxidative decomposition
• Partial oxidation
• Polymerization
• Reforming

   

   

  Tubular reactors may be empty for homogenous reactions or packed with catalyst particles for heterogeneous reactions.  Packed reactors require upper and lower supports to hold particles in place. Uppermost packing is often of inert material to serve as a pre-heat section. Pre-heating can also be done with an internal spiral channel to keep incoming reagents close to the heated wall during entry.

  It is often desirable to size a tubular reactor to be large enough to fit 8 to 10 catalyst particles across the diameter and be at least 40-50 particle diameters long. The length to diameter ratio can be varied to study the effect of catalyst loading by equipping the reactor with spools to change this ratio.

  Temperature is typically controlled by thermocouples located on the outer wall of an externally heated tubular reactor. A moveable internal thermocouple is often employed to observe the temperature changes occurring as the reaction proceeds through the reactor.

   

  Series 5400 Continuous Flow Tubular Reactors
  Model	5401	5402	5403	5404
  Size	3/8 in	1/2 in	1 in	1.5 in
  OD/ID (in)	0.38/0.28	0.50/0.37	1.9/1.0	2.0/1.5
  OD/ID (mm)	9.5/7.0	13/9.4	48/25	51/38
  Heated Length (in)	6, 12, 24	6, 12, 24	12, 24, 36	12, 24, 36
  Max. Tubular Reactor Pressure (psi)	3000	3000	5000	3000
  Max. Temperature (C)	550	550	550	350
  Support Spools	No	No	Yes	Yes
  Spiral Pre-Heat	No	No	Yes	Yes
  # Ports in Top Head	1	1	4	4
  # Ports in Bottom Head	1	1	4	4
  Internal Thermocouple	Yes	Yes	Yes	Yes

   

We can furnish either a fixed internal thermocouple in each zone or a single movable thermocouple that can be used to measure the temperature at points along the catalyst bed. External thermocouples are typically provided for control of each zone of the heater. 

Gas Feed Systems

Various gas feeds can be set up and operated from a Gas Distribution Panel. In order to deliver a constant flow of gas to a reactor, it is necessary to provide gas at a constant pressure to an electronic Mass Flow Controller. This instrument will compare the actual flow rate delivered to the set point chosen by the user, and automatically adjust an integral control valve to assure a constant flow. Care must be taken to size these controllers for the specific gas, the flow rate, and the pressure of operation. A mass flow controller needs a power supply and read-out device, as well as a means of introducing the desired set point.

When ordering mass flow controllers, you will need to specify:

1. Type of gas to be metered (e.g. N2, H2, CH4)

2. Maximum operating pressure of the gas (100 or 300 bar) 3. Maximum flow rate range in standard ccs per minute (sccm) 4. Pressure for calibration of the instrument

Mass flow controllers are available for use to 1500 psi and to 4500 psi. Considerable savings can be obtained if the mass flow controller is to be used only to 1500 psi.

The schematic below depicts the installation of a mass flow controller for the introduction of gas to a continuous-flow reaction system. Such installations can be enhanced with the addition of a by-pass valve for rapid filling.

A purge line can also be added. It is typically used for feeding nitrogen or helium to remove air before reaction or to remove reactive gases before opening the reactor at the end of a run. The purge line includes a shut-off valve, metering valve, and a reverse-flow check valve.

Chemical feed pumps are our recommendation for continuous feeding of liquids when the desired flow rate is greater than 2 liter per hour. Here we will try to help you find a suitable pump. We will need to know the type of liquid; the minimum, typical, and maximum desired feed rate; the maximum operating pressure; and any special operating considerations such as explosion proof operation or corrosion possibilities.

Back Pressure Regulators

In addition to supplying gases to a reaction through electronic mass flow controllers, the reactor is kept at a constant pressure by installing a Back Pressure Regulator (BPR) downstream of the reactor. This style of regulator will release products only when the reactor pressure exceeds a preset value.

When a BPR is used in conjunction with mass flow controllers, the user is assured that a constant flow of gas is passing through a reactor, which is being held at a constant pressure. This provides for the highest degree of control and reproducibility in a continuous-flow reactor system.

Cooling Condensers

It is often desired to cool the products of the reaction prior to handling them. For this purpose, tube-and-shell heat exchangers are available to act as the cooling condensers. An adaptation of our standard condensers provides an excellent design. Descriptions and available sizes are found in the 4500 Catalog, Stirred Reactors and Pressure Vessels.

Gas/Liquid Separators

Tubular reactors operating in continuous-flow mode with both gas and liquid products will also require a Gas/Liquid Separator for smooth operation. The separator is placed downstream of the reactor, often separated from the reactor by a cooling condenser. In the separator vessel, liquids are condensed and collected in the bottom of the vessel. Gases and non-condensed vapors are allowed to leave the top of the vessel and pass on to the back pressure regulator. It is important to operate the BPR with a single fluid phase to prevent oscillation of the reactor pressure.

The gas/liquid separator can be sized large enough to act as a liquid product receiver that can be manually drained periodically. Many of the non-stirred pressure vessels listed in our 4500 catalog are ideally suited for use as gas/liquid separators. Vessels of 300, 600, 1000, or 2000 mL are commonly chosen.

Control and Data Acquisition Systems

A variety of solutions exist to meet the needs of system operators. System accessories such as heaters, mass flow controllers, and pumps can be obtained with individual control packages to create a manual, distributed control system. Each of the various controllers that are equipped with an output signal can be incorporated into a PC-based data acquisition system.