Length‐to‐Diameter Ratio of Extrudates in Catalyst Technology: III. Catalyst Breakage in a Fixed Bed

Abstract

A correlation is demonstrated to predict the reduction in the mean length‐to‐diameter ratio of catalyst extrudates by breakage due to stress in a fixed bed. The stress can be caused either by the reactor load or it can be externally applied as in the bulk crush strength measurement. The strength characteristic of particular interest here is the extrudate bending strength characterized by the Euler‐Bernoulli modulus of rupture. The balance of the bending strength to the applied stress leads to a new dimensionless group. Extrudates in a fixed bed start to break above a specific critical stress, and their mean length‐to‐diameter ratio then becomes linearly proportional to this dimensionless group to the power one‐third.

Predicting Catalyst Extrudate Breakage Based on the Modulus of Rupture

“…Beeckman 18 shows that the aspect ratio of the catalyst in balance with the load force can be described by:…”

“…Table 1 shows catalyst properties and derived stress properties that allow to calculate the reduction in aspect ratio during compression in the bulk crush strength measurement. Adapted from Beeckman et al 2017 18 …”

“…Each data-point is a separate measurement with fresh catalyst from the beginning. Adapted from Beeckman et al 2017 18 Please click here to view a larger version of this figure.…”

“…Breakage due to stress in a fixed bed The method outlined above is so far only available in the literature as described in Beeckman 18 . For the bulk crush strength, it is important to follow the standard operating protocol as outlined in ASTM D7084-04 17 for reason of repeatability.…”

“…The catalyst fines are screened out from the catalyst sample and weighed while the bulk of the catalyst sample is riffled to obtain a representative sample to accurately measure the aspect ratio. While the standard bulk crush strength test procedure focusses on the amount of fines that is created in order to gauge catalyst strength, this manuscript focusses on the reduction of the aspect ratio after breakage as a function of the load, see also Beeckman 18 .…”