Mechanical strength is a core performance indicator for stable operation of industrial units. It reflects the catalyst's overall resistance to compression, abrasion and breakage, and directly affects bed pressure drop control, service life of catalysts and operational stability of units. The mechanical strength is jointly determined by material formula, preparation process, heat treatment conditions and on-site operating conditions.
- Material formula lays the foundation for catalyst mechanical strength. The purity and crystal stability of supports govern the compactness of the framework. Excessive impurities and improper particle size distribution will increase internal pore defects and weaken structural strength. Inappropriate proportion of binders and functional additives may lead to loose bonding between particles. Excess loading of active components will damage the original framework of supports and raise the risk of catalyst cracking.
- Forming and calcination processes are critical to the final mechanical strength. In extrusion, tabletting and other forming procedures, insufficient forming pressure, improper moisture content and excessive forming speed will result in low compactness, as well as internal micro-pores and micro-cracks. Low calcination temperature leads to incomplete solidification and loose structure. Excessively high temperature or rapid heating and cooling will cause grain distortion and thermal stress, greatly reducing the catalyst's resistance to impact and breakage.
- Operating conditions are the major cause of strength degradation. Long-term high pressure, frequent fluctuations in temperature and pressure, as well as thermal shock during unit start-up and shutdown generate alternating mechanical stress and propagate internal micro-cracks. Besides, erosion from high-velocity fluid, uneven gas flow, moisture and corrosive media, together with long-term coking, will damage the catalyst framework and cause particle abrasion and pulverization. This will further push up bed pressure drop and impair long-term stable operation of the unit.