Several catalyst molding processes
In industrial production, some catalysts are in powder form, some catalysts are in column form, some are in spherical form, and some are in flake form, and in the actual catalyst preparation process, the process of different types of catalyst preparation is also very different.
Catalyst molding process is a unit operation process in which all kinds of powders, granules, solutions or molten raw materials are aggregated with each other under a certain pressure to make solid catalyst particles of a certain shape, size and strength.
The molding process strengthens the characteristics of the multiphase reaction process, which affects the activity, selectivity, flow resistance and other properties of the catalyst.
Catalyst molding process is an indispensable process in catalyst production, which has a certain impact on catalyst mechanical strength and performance.
However, not all catalysts need forming process.
So, which catalysts need to be prepared by forming process?
1
According to the catalytic reaction and device requirements, the catalyst should be formed to provide the catalyst with suitable shape, size and mechanical strength, and to give full play to the catalyst’s activity and selectivity, and to prolong the catalyst’s service life;
2
Catalyst particle size, shape, surface properties and other characteristics determine the fluid dynamics operating conditions in the reactor, the productivity of the reactor and the selectivity of the catalytic process, to reduce the pressure drop generated by the fluid flow, to prevent the occurrence of grooves, to obtain a uniform fluid flow.
Common molding processes are the tabletting process, the extrusion process, the spraying process, and the balling process.
Several different molding processes are introduced:
Tabletting process: The tabletting process is a widely used catalyst molding process, which is mostly applied to the molding of powdered catalysts obtained by the precipitation method.
Low-temperature shift catalysts are prepared using the tablet molding process. Tablet forming equipment mainly includes rotary tablet press or ring press.
Characteristics of the tabletting process
High strength
Uniform size
Smooth surface
Uniform particle shape
Suitable for fixed bed reactors
Low capacity and complex equipment
Specific surface area and pore structure change
Pressure increases, average pore size and total pore volume decreases, pore distribution averages out
Cautions
NOTICE
The raw material powder molded by tablet press must be mixed well in ball mill or powder mixer first, and some materials also need to be pre-pressing and granulating to adjust the stacking density and fluidity of the materials.
Extrusion process: Extrusion molding is the use of pistons or screw rods to force mud-like materials from the plastic film with a certain diameter extrusion, and cut into a certain length of the strip (also called columnar) catalyst. The strength of the catalyst depends on the plasticity of the material and the type and amount of binder added.
Extrusion molding is generally carried out in horizontal cylindrical containers, and the extrusion process is divided into four steps: conveying, compressing, extruding and cutting of raw materials.
Characteristics of extrusion process
Low strength (can be sintered for reinforcement)
Fine powder, large amount of binder, easy to extrude strip molding
High amount of binder, shrinkage after drying, difficult to maintain shape
High amount of binder, easy to extrusion molding
Suitable for materials with good shape (aluminum glue, etc.)
or powder with binder.
Spraying process: Spraying process is a molding method to make micro-spherical catalysts from suspension or paste materials by using spray drying principle.
Characteristics of spray process
Most of the fluidized bed catalysts use this method
Particle diameter and particle distribution are well adjusted
No crushing after drying, shortening the process
Rolling ball process: Rolling ball process is to put the dry powder into the rotary tilting turntable, slowly sprayed into the binder, due to the action of capillary suction, the wetting of the local powder first bonded to become a very small particle size particles to become the nucleus, with the continued movement of the turntable, the nucleus grows up to become a round ball.
Characteristics of rolling ball process
Uniform particle size
Regular shape
Mechanical strength is not high
Rough surface
Fine powder, high mechanical strength after molding, but difficult to form a ball
The binder quantity is small to form the ball for a long time, when the quantity is large to cause multi-cells, difficult to form the ball
Add the number of turntable and tilt, particle size down, turntable deep, large particle size
