Spherical Vs Extrudate Catalyst Carrier Pressure — What It Actually Is (And What It Is Not)

If you are loading a fresh hydrotreater, hydrocracker, reformer, or ebullating-bed residue HDS unit with a sulfided CoMo or NiMo catalyst, the choice of carrier shape (sphere, cylinder, trilobe, or quadrilobe) sets the floor on reactor pressure drop, catalyst effectiveness factor, mechanical strength, attrition resistance, and 10-year lifecycle cost. This guide walks through the Ergun equation applied to each shape, the Thiele modulus and effectiveness factor for diffusion-limited reactions, ASTM D4179 side crush strength data, ASTM D4058 attrition index data, packed-bed void fraction, reactor hot-spot risk, and the scale-up economics from 100 kg R&D pack to 50 t bulk order for Aluminaworld CC-BF01 / CC-BF02 / CC-CY01 / CC-TL01 / CC-TL02 / CC-EB01 / CC-AS01 catalyst carrier grades.

The catalyst carrier is the backbone of every refinery hydrotreater, hydrocracker, reformer, and residue HDS unit. The metal function (MoS2, WS2, NiMo, CoMo, Pt, Pd) does the chemistry, but the carrier does four jobs that determine whether the catalyst survives the 1 to 5 year service life: it provides the surface area where the active metal disperses; it forms the packed bed that holds the catalyst in place against gravity, vibration, and pressure fluctuation; it shapes the flow distribution that determines whether the bed runs uniformly or with hot spots; and it accepts the metal (V, Ni, Fe) and coke deposits without rapid pore plugging. The carrier shape (sphere, cylinder, trilobe, quadrilobe, or ring) is one of the three primary specification parameters along with alumina phase (gamma, eta, alpha) and porosity (5 to 12 nm mesopore, 50 to 80 percent open porosity).

Each shape has a different trade-off curve among activity (5 to 15 percent range across shapes), pressure drop (30 to 50 percent range), crush strength (factor of 3 to 5 range), attrition (factor of 5 to 10 range), and cost (factor of 2 range). The wrong shape costs 3 to 8 percent of reactor throughput per year of operation, which on a 50,000 bbl/day refinery hydrotreater at USD 70 per bbl gross margin is USD 4 to 10 million per year. The right shape pays back its cost differential in 3 to 6 months.

This guide compiles the engineering data, scale-up math, and Aluminaworld product specification for the seven carrier shapes most commonly supplied in 2026. The intent is to give a refinery process engineer, catalyst procurement specialist, or technical buyer the data they need to make a defensible shape selection for their next 5 to 50 t catalyst loading.

Reactor pressure drop is the first constraint in carrier shape selection. The Ergun equation relates the pressure drop per unit bed depth dP/L to the bed void fraction eps, the particle equivalent diameter dp, the fluid viscosity mu, the fluid density rho, and the superficial velocity u:

The first term (laminar, viscous contribution) scales as (1-eps)^2/eps^3 x 1/dp^2. The second term (turbulent, inertial contribution) scales as (1-eps)/eps^3 x 1/dp. For low velocities (laminar flow in the bed), the first term dominates and dP/L scales as 1/dp^2 - meaning a 50 percent smaller particle increases the bed pressure drop by a factor of 4. For high velocities (turbulent flow in the bed), the second term dominates and dP/L scales as 1/dp.

Spherical Vs Extrudate Catalyst Carrier Pressure — The Hidden Defect / Failure Mode

The carrier shape enters the Ergun equation through two terms: the equivalent spherical diameter dp (which is the particle diameter for spheres but a calculated equivalent for non-spherical shapes) and the packed-bed void fraction eps (which depends on the packing geometry of the shape).

The 4 to 6 percentage-point lower void fraction for cylinders vs spheres is the dominant driver of higher cylinder bed pressure drop. For the same reactor and superficial velocity, a cylinder bed has 30 to 45 percent higher dP/L than a sphere bed at the same nominal size. The trilobe and quadrilobe designs recover some of the lost void fraction by using the lobe geometry to open up the bed, but the practical pressure drop is still 15 to 25 percent above the sphere bed.

• Spheres (1.0 to 6 mm diameter): the highest-activity shape with the lowest pressure drop; preferred for fixed-bed hydrotreaters and ebullating-bed residue HDS.
• Cylinders / extrudates (1.0 to 3 mm D x 2 to 10 mm L): the lowest-cost shape with moderate activity and high crush strength; preferred for fixed-bed hydrocrackers and reformers where mechanical robustness matters more than the last 5 percent of activity.
• Trilobes and quadrilobes (1.0 to 3 mm outer diameter with three or four internal lobes): the highest mechanical-strength shape with intermediate activity and pressure drop; preferred for high-pressure (10 to 18 MPa) residue HDS, ebullating-bed internals, and graded-bed top layers.

Spherical Vs Extrudate Catalyst Carrier Pressure — Measured Numbers Across Grades

The characteristic diffusion length is the maximum distance a reactant molecule must travel from the bulk fluid to the center of the catalyst particle:

For dibenzothiophene (DBT) HDS at 350 C, 6 MPa, on a sulfided CoMo / gamma-alumina catalyst, the intrinsic rate constant is approximately k = 1 to 5 s-1 (volume basis) and the effective diffusivity is D_eff = 1e-9 to 5e-9 m^2/s (depending on the sulfur content of the feed and the extent of pore plugging). For a 1.5 mm particle:

Where Spherical Vs Extrudate Catalyst Carrier Pressure Earns Its Premium — Core Chemistry

The mechanical strength advantage of trilobes comes from the geometry of failure. A sphere fails under any contact load - any point on the sphere is the weakest point. A trilobe fails under bending along the lobe axis, which requires higher force because the three-lobe cross-section resists bending. For high-pressure reactors (10 to 18 MPa residue HDS) where the catalyst bed experiences significant stress from thermal cycling and pressure fluctuation, the trilobe is the engineering choice despite the higher cost.

Note the lower strength of eta-alumina spheres (CC-EB01) compared to gamma-alumina spheres (CC-BF01) at the same size. This is because eta-alumina has higher porosity (0.6 to 0.8 cc/g vs 0.4 to 0.6 cc/g for gamma) and the higher porosity comes at the cost of thinner pore walls and lower mechanical robustness. For fixed-bed service where mechanical strength is the limiting factor, gamma-alumina is preferred. For ebullating-bed or slurry-bed where activity is the limiting factor, the higher activity of eta-alumina offsets its lower mechanical strength.

Attrition is the third constraint, and it matters most for ebullating-bed and slurry-bed reactors. The ASTM D4058 test measures the weight loss of a catalyst sample after 30 minutes of rotation in a drum at 10 rpm, expressed as a percentage of the original sample weight.

Spherical Vs Extrudate Catalyst Carrier Pressure — Dosing Across Service Conditions

The FCC catalyst shape (microsphere at 60 to 80 microns, with 95 percent of particles in the 40 to 120 micron range) is fundamentally different from HDS / hydrocracker shapes (sphere, cylinder, trilobe at 0.8 to 6 mm) because the reactor engineering is fundamentally different. FCC is fluidized-bed; HDS / hydrocracker is fixed-bed. The two processes use different catalyst manufacturing routes (spray-drying for FCC, extrusion or oil-drop for fixed-bed) and different alumina feedstocks (pseudo-boehmite for FCC binder, gamma-alumina powder for fixed-bed carrier).

For buyers of FCC catalyst, the relevant specification parameters are different: particle size distribution (40 to 120 micron), attrition index (ASTM D5755, typically below 2 wt% per hour), activity (MAT, microactivity test, typically 60 to 80 percent conversion), and zeolite Y unit cell size (24.20 to 24.40 Angstrom, indicating the rare-earth exchange level). Aluminaworld does not currently supply FCC catalyst - our fixed-bed catalyst carrier portfolio (CC-BF01 through CC-AS01) is targeted at HDS, hydrocracking, reformer, and specialty chemical processes, not FCC.

Hydration Kinetics, Set Control, and Working Time

The choice of carrier shape for a new catalyst loading depends on the reactor type, the reaction exotherm, the target conversion, the operating pressure, and the budget. The decision tree below summarizes the engineering guidance.

The pattern that emerges is: spheres dominate fixed-bed service (highest activity, lowest pressure drop, acceptable crush strength at 1.5 to 2.5 mm); trilobes dominate high-pressure (10 to 18 MPa) residue HDS and hydrocracker service (highest crush strength, acceptable pressure drop); cylinders are the budget choice for naphtha and mild hydrotreating (lowest cost, acceptable activity); ebullating-bed and slurry-bed demand spheres (the only shape that survives the ebullating motion); guard beds and bed supports use large alpha-alumina spheres (6 to 12 mm, no active phase needed).

1. Step 1: Raw material (pseudo-boehmite or alumina hydrate): 30 to 40 percent of cost at all scales
2. Step 2: Forming (extrusion, oil-drop, or roll): 25 to 35 percent at all scales, but rejects 20 to 50 percent of input material depending on shape complexity
3. Step 3: Calcination (energy for 450 to 1400 C sintering): 15 to 25 percent, scales with volume
4. Step 4: QC and packaging: 5 to 10 percent at all scales, but per-kg cost is much higher at small scale
5. Step 5: Overhead (R&D amortization, sales, freight): 10 to 20 percent, scales non-linearly

• Spheres (CC-BF01): dP/L = 6.0 kPa/m x 12 m = 72 kPa (10.4 psi) total bed pressure drop
• Cylinders (CC-CY01): dP/L = 8.3 kPa/m x 12 m = 100 kPa (14.5 psi) total bed pressure drop
• Trilobes (CC-TL01): dP/L = 7.2 kPa/m x 12 m = 86 kPa (12.5 psi) total bed pressure drop

Procurement Specification — What to Demand on the COA

For procurement of a 5 t order, the freight from Qingdao to a typical Asian port (Singapore, Jakarta, Manila, Mumbai, Dubai) is USD 80 to 150 per ton; to a European port (Rotterdam, Hamburg, Genoa) is USD 250 to 400 per ton; to a US Gulf port (Houston, New Orleans) is USD 400 to 600 per ton. CIF (cost-insurance-freight) pricing is available on request for all major destinations.

The 10-year total cost of ownership (TCO) for catalyst carrier in a 50,000 bbl/day ULSD hydrotreater depends on three cost drivers: the initial fill cost (the catalyst cost at first loading), the replacement fill cost (the catalyst cost at each subsequent loading after deactivation), and the operating cost differential (the energy cost from pressure drop, the activity penalty from less effective shape, and the maintenance cost from fines generation or hot spots).

• Sphere (radius R): L = R (distance from surface to center) = d/2 for diameter d. For reaction-diffusion analysis, the standard form uses L = d/6.
• Cylinder (radius R, half-length L_cyl): L = min(R, L_cyl). For a 1.5 mm D x 4 mm L cylinder, L = 0.75 mm = d/4. For a long cylinder (L_cyl >> R), L approaches d/6.
• Trilobe (outer diameter d_o, internal lobe diameter d_l): L is between d_o/6 and d_o/5, depending on the lobe thickness. For a 1.5 mm trilobe with 0.5 mm lobes, L is approximately d_o/5 to d_o/6 = 0.30 mm.
• Quadrilobe: similar to trilobe, L = d_o/6 to d_o/7 for the same outer diameter.

Storage, Shelf Life, and Inventory Hygiene

For buyers who do not have on-site lab capability, Aluminaworld offers pre-shipment QC at the Zibo factory with a buyer-witnessed sampling protocol: the buyer or buyer's representative visits the factory, takes a stratified sample from 10 percent of the bags (or 20 bags minimum), and the sample is analyzed in Aluminaworld's ISO 17025 certified lab with the buyer present. The lab issues a buyer-witnessed CoA that is binding on the supplier. The cost of the witness protocol is USD 2,000 to 5,000 per visit plus travel, and the lead time extends by 3 to 5 days.

Seven procurement and engineering mistakes recur in the catalyst carrier market. Avoiding these mistakes can save 3 to 12 months of reactor underperformance, USD 100,000 to 1 million in catalyst replacement, or a forced reactor shutdown.

• Fluidize uniformly in air or hydrocarbon vapor at 0.3 to 0.5 m/s superficial velocity, which requires a narrow particle-size distribution centered on 60 to 80 microns (Geldart Group A powder). Particles smaller than 20 microns entrain with the product vapor and are lost to the cyclone; particles larger than 200 microns do not fluidize properly and segregate to the bottom of the bed.
• Resist attrition over thousands of circulation cycles at high temperature, which requires a hard, spherical particle without edges or lobes that would chip under impact. The FCC catalyst attrition index is typically 1 to 3 wt% per hour in the ASTM D5755 (jet cup) test - much higher than fixed-bed catalyst because the test simulates the high-velocity impact of cyclones.
• Have high activity and selectivity for the cracking reaction, which is achieved by spray-drying a slurry of pseudo-boehmite (the binder) and zeolite Y (the active component, typically 20 to 40 wt% of the catalyst) into microspheres that are then calcined at 500 to 600 C to convert the pseudo-boehmite to gamma-alumina binder.

• BET surface area: 200 to 260 m2/g
• Pore volume: 0.45 to 0.55 cc/g
• Particle size: 2.3 to 2.8 mm
• ASTM D4179 side crush: 80 to 140 N per bead (avg 110 N)
• ASTM D4058 attrition: 0.02 to 0.04 wt percent

Total Cost of Ownership — Why Premium Pays for Itself

The extrusion method produces extrudates with uniform cross-section but less perfect sphericity (the ends are flat from the cutting step). The crush strength is higher than oil-drop spheres (50 to 90 N for 1.5 mm cylinder) and the attrition is higher (0.10 to 0.20 wt percent) because of the flat ends and edges. The cost is lower than oil-drop because of the higher throughput (extrusion is continuous, not batch) and the simpler raw material (no acid or base required). The extrusion method is the preferred route for cost-driven fixed-bed HDS and hydrocracker service.

The roll method (also called the "pelletizing" or "agglomeration" method) is used to make irregular-shaped catalyst carrier, typically in the 2 to 8 mm size range. The process starts with a dry alumina powder (typically alpha-alumina or calcined alumina) mixed with a binder (water, molasses, or starch at 5 to 10 wt percent). The mixture is fed onto an inclined rotating pan or disk, and the rolling action agglomerates the powder into irregular pellets. The pellets are screened to size, dried, and calcined.

The math: a 5-10% longer service life plus lower thermal-cycling spalling plus reduced replacement-frequency combine to deliver 12-25% lower TCO over a single cell-stack replacement cycle, even before the safety/insurance argument for eliminating thermal-shock microcracks. The 8-15% raw-material premium pays back 1.5-2.5x over the first cycle.

Related Products & Technical Resources

We supply activated alumina, molecular sieve, and alumina-ceramic products as part of a broader specialty adsorbent catalog. The full datasheet for this grade includes additional grain-size distributions, customer-specific blend recommendations, and pilot-plant support. Talk to our technical team if your application has unusual thermal-cycling, mechanical-load, or chemical-feed constraints.

• Activated Alumina — gamma-Al2O3 adsorbent for CO2, H2S, and fluoride removal.
• Molecular Sieve — 3A / 4A / 5A / 13X grades for PSA, TSA, and drying service.
• Alumina Powder — high-purity Al2O3 powders for general industrial use.
• Aluminum Hydroxide — ATH flame retardant grade.
• Reactive Alumina Low-Soda for Castable and Burned-Magnesia Bonding
• MCFC CO2 Removal: Activated Alumina vs Carbon Molecular Sieve
• Adsorbent Bed Pressure Drop: Ergun Equation Design Guide

Next Steps — Get a Sample or Talk to Our Engineers

For samples, COAs, or application-specific blend recommendations, reach out to the Aluminaworld technical team. We hold stock of the relevant grade in our Zibo warehouse with same-week dispatch for trial orders, and we can also produce custom recipes for OEMs and EPCs with multi-ton annual demand.

Contact: WhatsApp +86 13325222240 (preferred for fast reply) or email barry@aluminaworld.com. Trial orders ship FOB Qingdao in 7-10 days; full-container shipments in 15-25 days depending on grade and customization.