Today, propylene oxide (PO) is usually extracted from propylene and hydrogen peroxide using the modern, economical HPPO process. The propylene oxide extracted in this way is primarily used for the production of polyurethane pre-products, which are in turn used for diverse products such as foams, insulating materials, expanding foams, paints, coatings and adhesives. HPPO plants usually have an upstream plant for the manufacture of hydrogen peroxide, which is sometimes even operated by another owner who exclusively supplies "over the fence". This is ideal, because unlike with other processes, there are practically no by-products that have to be processed or marketed. For this reason, and because of the very high yields attainable of approx. 95%, this process is more environmentally-friendly, and also requires less investment.
Generally speaking, hydrogen peroxide is manufactured in a cycle – the AO-process – consisting of the alternating hydrogenation and oxidation of an anthraquinone derivative. The first stage, hydrogenation, takes place using a catalyst (e.g. palladium) at moderate pressures of 2 to 4 bar. The catalyst is then filtered out again. A catalyst is not required for oxidation at 2 to 8 bar. The now dissolved hydrogen peroxide in the so-called working solution is then extracted with water. Following extraction and drying, the working solution is fed back into hydrogenation, which completes the cycle.
The hydrogen peroxide is dissolved in methanol for further processing to HPPO and used as an oxidising agent for oxidising propylene to propylene oxide. This enables high-grade conversion to propylene oxide (PO) in the main reactor. Following separation of the extracted raw propylene oxide, the subsequent process chain usually involves a refinement reactor, the removal of O₂, water glycol separation, as well as methanol recovery and purification. At the end of the process steps, the propylene oxide is then removed in the last distillation stage from the high boilers.

HPPO technology requires reliable process monitoring throughout the entire reaction process. Precise recording of the process parameters is crucial, not least for low energy and raw material consumption and a maximum yield. KROHNE's portfolio includes all of the instrumentation for diverse measuring tasks, starting with robust pressure transmitters for measuring process pressure and hydrostatic level measurements and magnetic level indicators, through to electromagnetic flowmeters for complex HPPO applications that rely on high accuracy. The innovative verification tool OPTICHECK is available for many of our measuring systems, and can be used to easily manage commissioning, verification and monitoring of KROHNE measuring devices as well as device setting without process interruption, both in the field and remotely.