Propylene oxide is a highly significant organic compound raw material, currently ranking as the second-largest propylene derivative after polypropylene, surpassing acrylonitrile.
Currently, there are several industrial production methods for propylene oxide, including chlorohydrinization, co-oxidation, and direct oxidation (HPPO). The co-oxidation method can be further categorized into ethylbenzene co-oxidation and isobutane co-oxidation.
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Due to pressure from environmental regulations and industrial adjustments, chloroalcohol method has become challenging to completely eliminate pollution, leading to significant production capacity closures. The production gap will be filled by the co-oxidation and direct oxidation methods. Among these, HPPO has garnered widespread attention due to its simple process, minimal by-products, high product yield, and minimal pollution.
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Propylene oxide HPPO process filtration
The fundamental production principle of the hydrogen peroxide direct oxidation method involves a direct oxidation reaction occurring in a reactor under relatively mild conditions. In this process, propylene and hydrogen peroxide (H2O2) are used in a methanol/water mixture with the aid of a special titanium-silicon catalyst.
Currently, fixed-bed systems are predominantly used in HPPO (hydrogen peroxide direct oxidation) units. After the reaction, filters are required to capture broken or fine catalyst particles, in order to purify the reaction solution.
In the equipment provided by Feature-Tec, there are various filtration precision options ranging from 1μm to 100μm. The filtration precision largely determines the filtration method. Under the premise of dead-end filtration, metal membrane cartridges is an excellent choice for capturing micrometer-sized particles. Basket filters are suitable for capturing particles larger than 50μm.
In the new HPPO process, a suspended bed technology is employed. In this process, it is possible to intercept and reuse the catalyst that flows out with the reaction solution. Generally, fine catalyst particles have already become deactivated and lost their reusability, so a two-stage filtration approach is commonly used.
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Selfclear filtration system
The first-stage filtration employs the Selfclear filtration system, efficiently capturing large-diameter catalyst particles for recycling back into the reactor to sustain their participation in the reaction. Meanwhile, the finer, deactivated catalyst particles, along with the reaction liquid, proceed to the second-stage filtration, where they are intercepted and removed from the system.
In addition to the mentioned filter, Feature-Tec has also developed an integrated built-in filter for reaction and separation in the chemical industry. For example, in the BDO project's BYD reactor, Feature-Tec's filter is directly integrated within the reactor as the initial filtration stage. This structure enables the capture of active, large-diameter catalyst particles within the reactor. The finer, deactivated catalyst particles pass through the initial filtration stage and exit the reactor via the second-stage filter.
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The filter in the reactor
The filtration system consists of a primary catalyst recovery filter and a secondary spent catalyst filter. These filters are fully automated and can be regenerated through backwashing, minimizing maintenance costs. The primary catalyst recovery filter is designed to capture and reuse more than 80% of the catalyst that has not been deactivated. It significantly reduces the cost related to treat the spent catalyst as hazardous waste and also reduces the amount of new catalyst required.
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Application Program
In addition to catalyst filtration, it is important to filter methanol, propylene, and hydrogen peroxide in the feed system and circulating system. Filtration is necessary to ensure the purity of raw materials and to intercept corrosive substances in the pipeline.
The right filter is crucial in the production process of propylene oxide. It serves multiple purposes such as catalyst online separation and reuse, feed filtration and separation, circulating liquid filtration, process gas purification, final product filtration, and gas-liquid/liquid-liquid coalescence separation. The proper filtration system plays a key role in ensuring the production of high-quality end products.
