HPPO Process Technology a Novel Route to Propylene Oxide Without Coproducts

sustainability/ Industry perspective GREEN CHEMISTRy FRANZ SCHMIDT, MAIK BERNHARD, HEIKO MORELL, MATTHIAS PASCALy* *Corresponding author Evonik Industries AG, Advanced Intermediates – Innovation, Rodenbacher Chaussee 4, 63457 Hanau-Wolfgang, Germany Matthias Pascaly HPPO Process Technology A novel route to propylene oxide without coproducts KEYWORDS: HPPO process, propylene oxide, hydrogen peroxide, titanium silicalite. The common industrial technologies for the conversion of propylene to propylene oxide have been Abstract compared with a special focus on the direct oxidation using hydrogen peroxide. The HPPO process is an economically and ecologically superior technology since there are no market dependencies of other coproducts and water is the only waste product. The catalyst used in this process is a partly titanium substituted silica based zeolite called TS-1. The article summarizes the most important information concerning the HPPO process. INTRODUCTION approximately 7 Mt/a in the year 2010 at a production capacity of approximately 8 Mt/a. Based on a total The oxidation of organic compounds is of vital importance market growth of around 5 % per year, the expected for the chemical industry. Besides basic oxidation reactions values for demand and capacity in 2015 are nearly such as bleaching processes (e.g. paper or laundry) also at 9 and 10 Mt/a respectively. The growing markets are in oxidation reactions of chemicals are important: Epoxides Asia and potentially in the Middle East (1). - especially ethylene and propylene oxide – are among the There are several industrial routes to produce propylene major chemicals. Replacement of traditionally used halide- oxide, of which the chlorohydrin process (CH) is the based oxidants (chlorine) by hydrogen peroxide provided a oldest one (2). Other indirect oxidation processes new route to the desired oxidized products. Past demand for coupled with coproducts are propylene oxide / styrene hydrogen peroxide was due to the replacement of a monomer (PO/SM) and propylene oxide / methyl chlorine bleaching step in the paper industry or the tert-butyl ether (PO/MTBE) (3). Newer technologies are introduction of percarbonates as bleaching agent in based on an oxidation without a coproduct. One of detergents. Today, the newly developed HPPO (hydrogen- these technologies is the propylene oxide cumene peroxide-to-propylene-oxide) process is one of the largest (PO/CU) process developed by Sumitomo (4). However, consumers of hydrogen peroxide for the epoxidation of the most promising way is the oxidation of propylene with propylene yielding propylene oxide on a titanium doped zeolite without any coproducts. Also in this case, the oxidative potential of hydrogen peroxide allows the replacement of traditionally used chlorine-based oxidants enabling a novel environmentally more benign process. This article provides an overview on the HPPO technology which is now state of the art for the industrial production of propylene oxide. The article touches the catalyst TS-1, the propylene oxide reaction as well as the process conditions. Furthermore, a future perspective is given, based on the market situation and in comparison to other processes. PROPYLENE OXIDE MARKETS AND PRODUCTION PROCESSES Figure 1. Development of PO-technologies (* data based on (1) Propylene oxide ranges on place eleven of all organic and Evonik’s own estimates). chemicals being produced with a total demand of Chimica Oggi - Chemistry Today - vol. 32(2) March/April 2014 31 hydrogen peroxide (HPPO), independently developed by Evonik/TKIS (ThyssenKrupp Industrial Solutions AG) and BASF/Dow Chemical, respectively. Figure 1 shows the percentaged PO production capacity of the different processes in the past and an estimated future trend (1). In recent years, the PO production technology is observed to shift away from the formerly standard chlorohydrin route. This shift takes place in favor of the HPPO process. However, the majority of the propylene oxide is currently still produced via the Chlorohydrin (CH) route (Figure 2). This process is performed generally in two-steps. In the first step, intermediately generated hypochlorous acid reacts with propylene resulting in two kinds of propylene chlorohydrins. These chlorohydrins are subsequently dehydrochlorinated by calcium hydroxide or sodium hydroxide. Beside the aspired propylene oxide 2.1 tons CaCl2 and 0.1 tons 1,2-dichloropropane are obtained as byproducts per ton propylene oxide. This is the main disadvantage of this process. For process optimization Figure 2. Reactions of the industrial relevant propylene oxide Ca(OH)2 can be replaced by NaOH. Subsequently the producing processes. generated NaCl is converted to NaOH and Cl2 via electrolysis. This step reduces the salt load of the waste water, but increases investment and production costs achieved by Shell´s SMPO process using a heterogeneous due to additional power consumption and required TiO2/SiO2 catalyst offering a more efficient catalyst purification of NaCl prior electrolysis (2). separation in the epoxidation step (6). An alternative is the so called Lummus process using Due to the above mentioned drawbacks, intensive tert-butyl hypochlorite and water to form tert-butanol research was performed to develop coproduct free routes and the propylene chlorohydrins (5). These chlorohydrins for the production of propylene oxide. For example, in the are converted to propylene oxide using NaOH and the Bayer-Degussa-process perpropionic acid is used as resulting NaCl is electrolyzed to NaOH and Cl2. Therefore, oxidation agent (6). This process offers a high selectivity to a total recycling to build up the required HOCl-carrier propylene oxide and an efficient recycling of propionic (tert-butyl hypochlorite) is possible. The drawback is the acid. But a high price of H2O2 at the time of development slower formation rate of propylene chlorohydrins using prevented the commercialization of this process. tert-butyl hypochlorite. The breakthrough regarding a direct oxidation and The other industrially used propylene epoxidation therefore a coproduct-free method was achieved by ENI processes can be divided into coproduct-producing (PO/ in the 1980s (7). Using a novel titanium silicalite-1 (TS-1) SM and PO/MTBE) and coproduct-free (PO/CU and HPPO) catalyst the direct oxidation of propylene with hydrogen processes and offer the opportunity of being chlorine free peroxide was enabled without further oxidation agents (8). (Figure 2). In the PO/SM and the PO/MTBE routes a Evonik and TKIS improved this process by developing a precursor is used which is oxidized by readily available air special TS-1 catalyst quality using an optimized process or molecular oxygen. The intermediate hydroperoxide technology. On this basis, the HPPO process could be transfers the oxygen to the propylene resulting in developed and finally commercialized. This coproduct- propylene oxide and a primary coproduct, which is usually free process offers high specific propylene oxide yields, an alcohol. The challenge using the coproduct routes is to resulting in low feedstock consumptions. A long catalyst achieve a high selectivity for PO and receive an lifetime is achieved by moderate reaction conditions additional benefit from selling the coproduct. which are enabled by the high-performance TS-1 During the last few years several processes were catalyst. Since the HPPO process is a stand-alone- developed using acetaldehyde, isobutane, isopentane, technology, the product is independent from offering cyclohexane, ethyl benzene and cumene as precursors coproducts on the market. Contrary to the chlorohydrin leading to different secondary coproducts (Table 1) (6). route the HPPO-process enables an environmentally However, all of these processes suffer from the need to friendly production due to a totally closed solvent and process the coproduct, preferentially by obtaining a credit for supplementing it in the PO production costs. Therefore, only the PO/SM and PO/MTBE process yielding styrene monomer and methyl tert-butyl ether as coproduct are currently economically feasible (1). Nevertheless, high amounts of styrene (690 kta) and MTBE (830 kta) produced as coproducts in a world scale PO-plant (300 kta) need to be traded and the risk of an oversupply with Table 1. Summary of possible precursors used for propylene oxide production via styrene and MTBE could reduce the efficiency indirect epoxidation routes with coproduct. of such processes. An optimization was 32 Chimica Oggi - Chemistry Today - vol. 32(2) March/April 2014 feedstock cycle and the complete absence of chlorine. interconnected channel system of straight and sinusoidal Compared with the other state-of-the-art technologies, channels with pore diameters of 5.1 – 5.6 Å (8). Important the HPPO-process offers lower investment costs and is the avoidance of non-tetrahedral coordinated titania energy consumption. Furthermore, an additional benefit (TiO2) which is supposed to promote side reactions. can be achieved by recovering valuable byproducts like The ratio of framework incorporated titanium to extra- propylene glycol which is obtained in the range framework species of titanium is a crucial factor for the of 30 kg/t propylene oxide. catalytic performance of the catalyst and can be All these improvements meet the standard of a modern tailored via the synthesis route. Therefore, the choice of sustainable process for propylene oxide and lead to the raw materials and the right parameters during catalyst startup of the first

Load more