Propylene oxide (PO) is a colorless yet extremely flammable liquid derived from crude oil. PO is used in several industrial applications, but the majority is used to produce polyols which are the building blocks for polyether polyols (e.g., foams, coatings, adhesives) and propylene glycol (e.g., PET bottles, fibers, furniture).

There are several production processes currently available to manufacture PO. Some of these processes create co-products (e.g., chlorohydrin «CH-PO», styrene «SM-PO», and methyl tert-butyl ether «MTBE-PO») and others are derivative-free (e.g., hydrogen peroxide «HP-PO» and cumene «CU-PO»). Out of these processes, HP-PO is considered to have the smallest environmental footprint.

This Process Application Note is focused on HP-PO process monitoring of hydrogen peroxide (H₂O₂) online using an explosion proof process analyzer due to the hazardous production environment. Online analysis facilitates a high propylene oxide production yield while reducing costs with low feedstock consumption, as well as ensures a safe working environment for operators working in this highly hazardous process.

Propylene oxide (PO) is an important intermediate product for several markets because of its wide range of applications that are predominantly used in the polyurethane and solvent industries.

The global production of PO is more than 10 million tons per year [1]. This market is still growing and with it the need for a more cost efficient and environmentally friendly production process. PO production methods are available both with and without byproduct materials (Table 1). Depending on the market for these byproducts, one or more of these processes may be in major use globally at any time.

H₂O₂ present in a methanol solvent is used as the sole oxidizing agent and is the critical feedstock and key parameter to measure the complete conversion rate to PO. Thus, there is a high demand for accurate and robust online process monitoring throughout the whole HP-PO reaction process.

Considering the dangerous nature of this process, online measurement techniques are key for safety reasons. H₂O₂ can be accurately monitored in the effluent of the primary reactor using an online analysis solution designed for extremely hazardous areas (Figure 1). 

Additionally, analyzing the residual H₂O₂ concentrations in finishing reactor overheads upstream of the propene recovery section ensures that unreacted hydrogen peroxide is closely monitored for control measures after the epoxidation reactor (Figure 1).

Due to the hazardous environment at these production plants, strict safety precautions have to be implemented with all production and process equipment. The ADI 2045TI Ex proof (ATEX) Process Analyzer from Metrohm Process Analytics (Figure 2) complies to all electrical safety requirements and is specifically designed for high throughput processing in hazardous locations.

• Protection of company assets with built-in alarms at specified warning limits
• Accurate moisture analysis in hygroscopic sample matrix
• Safer working environment for employees (high temperature and pressures, autopolymerization, ATEX)
• Increased product yield with an optimized production process: more profitability