Catalyst Impregnation

By W.M. Zadorsky

1. Introduction

Many catalyst types are produced by impregnation. It consists in repeated dipping of porous support pellets into a solution containing a desired catalytic agent. The agent must be applied uniformly in a predetermined quantity to a preset depth of penetration. This is especially true of catalysts based on noble metals.

The liquid penetration into the pellets is hindered by air trapped in the pellet pores.

Various techniques like pressurizing, vacuum treatment, acoustic activation etc. are used to facilitate the impregnation process. They, however, are expensive and allow only limited control of absorption and penetration depth.

A simple, inexpensive, conserving, precise and rapid method to impregnate catalytic supports, such as activated carbon, alumina etc., is thus desired.

2. Project Description
2.1. Principle of Operation

The method eliminates vacuum or high pressure equipment and may require only minor, if any, modifications in the existing equipment. It relies on a simple three-step treatment of the catalyst support pellets directly before impregnation. The pretreatment removes all air trapped in the open pores and involves the following steps carried out in quick succession:

heating the catalyst pellets,
introducing a specific non-reactive gas, and
desorption of the gas.

It activates every open pore and results in their quick and complete filling during subsequent dipping.

2.2. Materials and Equipment

The non-reactive gas characteristics and the timing are unique to each support/catalyst impregnant system. This necessitates their tailoring to the system at hand. The gas will invariably be selected among those inexpensive and readily available ones.

Flexible modular units were developed that can be operated in a wide range of temperature, pressure etc. to process pellets of various materials and shapes. The compact modules allow a choice between superficial and deep impregnation, ensure precise control over the depth of penetration, and perform the drying step after dipping.

2.3. Process and Product Characteristics

The process offers waste reduction and improved utilization of catalytic agent. These advantages are due to a 30 to 35 % reduction in the catalytic agent consumption and to formation of finer catalyst grains.

The technology is highly versatile, for its performance is not dependent on pore size or void fraction of catalyst supports nor on physical and chemical properties of the employed media.

A 5 to 15 % increase in the catalyst activity may be achieved, depending on the catalyst type. Preset depth of deposition and uniform distribution of catalytic agent across pellet section is made possible.

The throughput rate of the dipping step may be increased by a factor of 2 to 100.

The process has been successfully implemented at several plants in the CIS.

3. Novelty

Although the process has been, on a limited scale, commercialized, some new and promising aspects of it were revealed by recent research. New and improved processes, for example those to be carried out in a fixed bed, may be patented.

4. Marketing

Catalysts are in ever growing demand worldwide. This is exemplified by the advent of automotive catalytic converters. On the other hand, the rare and precious metals are in short supply. The process meets the criteria of energy and materials conservation, engineering excellence and economic viability.

5. Applications

The process is well-suited for making catalysts of any type produced by dipping.

References

Problemy Khimii i Khimicheskoi Tekhnologii, 1991

Contact:
Prof.William Zadorsky
PEF&PCPC

Information supplied by the Author December 1998.  Page last updated: July 03, 2005