The HPPO process, jointly developed by Evonik and Uhde, is the first commercially available process for propylene oxide (PO) production which uses hydrogen peroxide (H2O2) as an oxidizing agent, and which is free of co-products. Apart from the economic benefits, it also offers numerous other advantages when compared with current state-of-the-art processes. One major advantage is based on the investment costs which are significantly lower than those involved in processes with co-products.

Propylene oxide is a versatile bulk chemical with high growth rates and is mainly used as a precursor for the production of polyurethanes. The entire process has been newly developed, starting with a laboratory scale set-up, followed by several years of miniplant operation, and culminating mid-2008 with the successful start up of a large scale reference facility in South Korea with a capacity of 100,000 mt/a of propylene oxide. The process includes a new reactor design and process configuration with an optimized catalyst. The new technology is licensed by Evonik and Uhde. Uhde acts as the contracting and engineering partner for this technology, Evonik is responsible for the catalyst delivery and supplies H2O2 "over the fence" to the PO plant.

Main Applications

Propylene oxide (PO) is a colorless, highly reactive, low-boiling liquid and is now one of the most important chemical intermediates, especially for the polyurethane (PUR) and solvents industry. At present, more than 6 million metric tons of PO per year are produced worldwide. PO is a bulk chemical primarily used for the production of polyurethane precursors, namely polyether polyols, as well as for propylene glycol and glycol ethers. Polyurethanes are used in a wide range of applications, including automobile components, furniture upholstery and thermal insulation. Other propylene oxide derived products are used in the cosmetics and pharmaceuticals industry. At present, two thirds of PO output is used for the production of polyether polyols, followed by about 20 % for propylene glycols (PG), and about 15 % for other products such as propylene glycol ethers. To meet the demand for future production, a world scale plant with an annual capacity of approx. 300,000 mt/a is needed every year. It is expected that most of new plants will be based on the HPPO process after 2015.

Development

In 2001 Evonik and Uhde announced an exclusive partnership for the development of the new HPPO process. Evonik investigated the process and developed a catalyst optimized for this particular purpose, while Uhde contributed its expertise in process engineering and the design and construction of chemical and other industrial plants. At Evonik's site in Hanau-Wolfgang (Germany), experts from the two companies further optimised the process parameters in a miniplant which included all recycle streams and reflected the complete production process.  The rigorous thermodynamic model for the 100,000 mt/a plant was verified by means of the results achieved during extensive testing in the miniplant. These formed the basis for the development of the process design package (PDP) by Evonik-Uhde, and for all engineering documents provided to the customer by Uhde in a basic engineering package (BEP). The scale-up procedure from miniplant to a commercial-scale PO facility with a capacity of 100,000 mt/a was carried out in a single development step. An investigation of raw materials for new clients and validation of the PO product is also performed to meet the quality requirements of the processing industry.  As all conventional PO processes have one common disadvantage - for every tonne of PO more than two tonnes of co-products are produced for which there is lower demand - the main impulse for the development of a new process is obvious.
The advantages of the new HPPO technology are:

• co-product free
• efficient raw material consumption
• high-performance catalyst with long lifetime
• low investment cost

The new technology is licensed by Evonik and Uhde and the PO plants will be built by Uhde as the contracting and engineering partner for this technology. As the preferred supplier Evonik will supply H2O2 "over the fence" to the PO plant.

HPPO Process

HPPO stands for ‘Hydrogen Peroxide to Propylene Oxide', i.e. the production of propylene oxide (PO) using hydrogen peroxide as the oxidizing agent. The entire process, i.e. both the reactor design and the process parameters, were newly developed in conjunction with a specially optimized catalyst. The core component of the HPPO process is the oxidation reactor, a tube-bundle reactor packed with titanium silicalite catalyst, where H2O2 is used to oxidise the raw material propylene to propylene oxide. Methanol is used as the solvent. Subsequently, the unconverted educts, products, and solvent have to be separated from one another and reprocessed. The liquid reaction mixture is fed into a decompressing unit in which the unconverted propylene is recovered. In further separation units, the product is separated out and purified to meet the quality specifications.

Finally, the methanol solvent is separated from the water and fed back into the reactor. The process helps to conserve resources and to protect the environment thanks to the environmentally friendly H2O2 and the use of a highly selective catalyst. Water is formed as a by-product. The quality of the propylene oxide thus produced is suitable for applications that require the highest levels of polyurethane quality, as well as for other PO-derived products. On the one hand the shell-and-tube design of the reactor is used to bring the reaction liquid to flow through each of the several thousand catalyst-filled tubes, and on the other to remove the reaction heat. The reaction takes place at a pressure of approx. 30 bar and at temperatures well under 100°C. The new design and optimized process configuration guarantee good removal of reaction heat and provide almost ideal plug flow characteristics in each tube, resulting in very high propylene oxide selectivity. Reactor internals, such as distributors and collectors, were developed for this special application. In conjunction with optimized H2O2 quality (stabilizers, concentration), this reaction process ensures a long catalyst lifetime.

Successful Start-up And Outlook

In July 2008 the first ever commercial-scale HPPO plant was successfully started up under the supervision of Evonik and Uhde personnel in South Korea. After a short time of process parameter optimization the plant operated at full capacity and within specifications. Even greater economies of scale can be achieved using bigger single train plants with capacities of more than 300,000 mt/a. Global licensing will expand the number of potential customers to include those who have not had access to PO technology as yet. Uhde is not only the engineering partner and plant contractor, but, as the know-how provider and licensor, it also acts as a direct contact for the customer.