Propylene Oxide (PO) Production Filtration

Overview of Propylene Oxide Production

Propylene oxide (PO), also known as propylene epoxide or methyloxirane, is a critical intermediate for polyether polyols, propylene glycol, and various chemical derivatives. Today, PO has surpassed acrylonitrile to become the second-largest propylene derivative after polypropylene.

Industrial PO production routes include:

• Chlorohydrin process
• Co-oxidation processes (ethylbenzene or isobutane routes)
• Hydrogen Peroxide to Propylene Oxide (HPPO) direct oxidation process

Due to increasing environmental regulations and structural industry adjustments, chlorohydrin technology is being phased out. Capacity gaps are primarily filled by co-oxidation and HPPO processes. Among them, HPPO is gaining strong industry acceptance due to its simplified process, minimal by-products, high yield, and near-zero environmental burden.

Filtration Requirements in HPPO Process

HPPO Process Overview

The HPPO process is based on the direct oxidation of propylene with hydrogen peroxide (H₂O₂) in a methanol/water solvent system. The reaction occurs under relatively mild conditions using a titanium–silicalite (TS) catalyst.

After the reaction, solid catalyst fines and fragments must be removed to:

• Prevent downstream equipment fouling
• Maintain solvent purity
• Stabilize product quality
• Enable catalyst reuse where applicable

Catalyst Filtration in Fixed-Bed HPPO Systems

Filtration Objectives

• Capture broken or fine catalyst particles
• Protect downstream separation and purification units
• Maintain reaction liquid cleanliness

Recommended Filtration Solutions

• Cartridge filters or basket strainers downstream of the reactor
• Filtration ratings typically range from 1 µm to 100 µm, depending on catalyst particle size and breakage behavior

Selection Guidelines

• Sintered metal membrane cartridges for stable micron-level filtration and consistent pore structure
• Basket strainers for coarse particle removal above 50 µm

Catalyst Recovery in Slurry-Bed HPPO Processes

New-generation HPPO processes increasingly adopt slurry-bed reactor designs, where catalysts are suspended in the reaction medium.

Two-Stage Catalyst Filtration Strategy

Stage 1 – Catalyst Recovery Filtration

• Automatic backwashing filters intercept larger, active catalyst particles
• Recovered catalyst is returned to the reactor for continued reaction
• More than 80% of non-deactivated catalyst can be effectively reused

Stage 2 – Spent Catalyst Removal

• Fine, deactivated catalyst particles are captured by secondary filtration units
• Spent catalyst is discharged as solid waste

Key Advantages

• Fully automatic operation
• Regenerable filter elements via backwashing
• Reduced catalyst consumption
• Lower solid waste disposal costs
• Improved overall process economics

Both primary recovery filters and secondary spent catalyst filters are typically designed as fully automatic filtration systems, minimizing operator intervention and maintenance frequency.

Feedstock and Circulating System Filtration

In addition to catalyst management, filtration is required across multiple process streams:

• Methanol filtration – removal of corrosion products and particulates
• Propylene filtration – protection of catalysts and reactors
• Hydrogen peroxide filtration – prevention of catalyst poisoning
• Circulating solvent filtration – control of accumulated solids and by-products

These filtration steps ensure raw material purity and protect critical equipment throughout the HPPO process.

Role of Filtration in PO Production

Proper filtration system selection plays a critical role in propylene oxide production, supporting:

• Online catalyst separation and reuse
• Feedstock purification
• Circulating solvent cleanup
• Process gas purification
• Final product polishing
• Gas–liquid and liquid–liquid coalescence

Well-designed filtration solutions directly contribute to process stability, catalyst efficiency, environmental compliance, and high-quality PO production.