Steady state erosion by absorbents used in catalytic convertors

The test standard ASTM G76 outlines a “Standard Test Method for Conducting Erosion Tests by Solid Particle Impingement Using Gas Jets”. The test standard prescribes the use of Ø50 µm alumina (Al₂O₃) particles as erodent, that can impinge the reference material type 1020 steel specimen and generate a steady-state erosion (mg/min). This steady-state erosion rate is important to differentiate materials based on their ability to resist erosion. In this study, we will investigate if such a steady-state erosion rate can be achieved by replacing the alumina erodent with porous media used in catalytic conversions (see Figure 1). The goal is to differentiate the porous media based on its harshness towards 1020 steel. 

Figure 1. Porous media type erodent 1, 2 and 3 that was used in catalytic conversion process. 

These porous media or absorbents coated with catalysts are used for the industrial production of gasoline from low value feedstock, that can damage the inner surface of the reactor. As shown in Figure 2, these erodent have sizes way smaller than the 50 µm prescribed by the G76 standard for the alumina particle.

Figure 2. Particle size distribution for each of the three catalysts used as erodent in this study.

Porous media was used as erodent in Ducom Air Jet Erosion Tester. Ducom Air Jet Erosion Tester (see Figure 3) is compliant with G 76 and G 211-14. It is designed for erodent and specimens with varying size, shape and material properties. The tests are conducted in an environmentally safe enclosure. The user can choose to heat the closed system up to 1000 deg C.

Figure 3. Ducom Air Jet Erosion Tester with a temperature control to reach 1000 deg C. 

At first our erosion tester was validated using the G76 reference erodent (Alumina from Norton) and type 1020 steel. A steady-state erosion was recorded, that was according to G 76 (see Figure 4). It offers a safe level of confidence that our data can be reproduced on other erosion testers compliant with G 76. 

Figure 4. Typical evolution of mass loss over test time for a G76 test. Alumina and Type 1020 steel were used are erodent and target specimen, respectively.

The results from porous media erodent indicates a steady state increase in the mass loss of 1020 steel over a 16 min test duration. This phenomenon was observed for the erodent 1, 2 and 3 (see Figure 5). 

Figure 5. Evolution of mass loss of 1020 steel for erodent 1, 2 and 3.

The slope in this steady-state erosion was used to determine the total volume loss, that is used to determine the harshness of erodent 1, 2 and 3 against 1020 steel (see Figure 6).  The smaller size erodent 3 showed mild erosion compared to bigger size erodent 1 and 2. Note: Smaller size erodent have lower kinetic energy compared to bigger erodent (assuming that the density and angularity are the same), and erosion wear is proportional to kinetic energy. 

Figure 6. Total volume loss of 1020 steel against erodent 1, 2 and 3. 

Key Conclusions:

1. Porous media used in catalytic conversions show steady-state erosion on 1020 steel. 

2. Ducom Air Jet Erosion Tester that is designed according to G 76 was useful in selection of least erosive porous media, that can reduce wear of reactor materials.