POonly Routes Several Approaches for Sustainable Alternatives

Alternative routes that do not produce sizeable quantities of coproducts and that do not use chlorine-based chemistry have already been, or will be, implemented at the commercial level. In April 2003, Sumitomo Chemical commercialized the first "PO-only" plant in Japan, which produces PO by oxidation of propene with cumyl hydroperoxide (the latter being obtained by hydroperoxidation of cumene) without a significant formation of coproducts. Nowadays, the plant located at the Chiba factory, a joint venture between Nihon Oxirane Co and Lyondell, produces around 200 000 tons of PO/year. A second plant was started in May 2009 in Saudi Arabia, a joint project with Saudi Arabian Oil Co.

This process is a variant of the PO/SM process that uses cumene instead of ethylbenzene and recycles the coproduct cumyl alcohol via dehydration to a-methyl-styrene and hydrogenation back to cumene (the latter two steps can be combined into a single hydrogenolysis step). Cumene hydroperoxidation technology is well-known for its use in phenol and acetone production.

Much attention has been directed recently towards processing approaches based on the epoxidation of propene using hydrogen peroxide (HP) as the oxidant. In principle, this technology can employ commercial HP, HP produced in an integrated facility or even that generated by the direct combination ofhydrogen and oxygen (for an overview of the different technologies for H P production see the review published by Fierro et al. [4]). Recently developed technologies include:

• liquid-phase epoxidation with conventionally produced HP (HPPO: hydrogen-

peroxide-propene-oxide);

• liquid-phase epoxidation with in situ generated HP (in situ HPPO).

The estimate for the future PO production market share indicates that by 2012 roughly 18% of all PO production will be based on HPPO technology, corresponding to a total capacity of almost 1.5 million-tons per year, 15% will be based on PO/TBA technology, 29% on PO/SM technology, 34% on CHPO technology and 4% on the Sumitomo cumene/PO process. Current PO production capacities are mainly located in Europe, North America and Asia; there are a few small-capacity plants in the Middle East. However, this region is of interest with regards to the natural gas reserves and the new routes of natural gas transformation, such as the methanol-to-olefins, methanol-to-propene and propane dehydrogenation routes. In fact, nowadays propene is produced mainly in steam-cracking units of naphtha and in FCC plants; 97% of the propene is of oil-based origin, while only 3% is gas-based. In the next few years, this ratio is expected to shift in favor of natural gas.

New approaches under investigation include the direct oxidation of propene with molecular oxygen, eventually in the presence of hydrogen:

• direct oxidation of propene with oxygen (DOPO: direct-oxidation-propene-oxide);

• hydro-oxidation of propene with oxygen and hydrogen (HOPO: hydrogen-oxygen-

propene-oxide).

Several companies are working on the direct oxidation of propene; for instance Lyondell is operating a pilot plant in Newtown Square, PA, and intends to commercialize the technology by 2010. Shell Chemical is also working on a direct route to PO production, based on variations of the gold and silver catalysts it uses to make ethene oxide.

Table 6.1 summarizes the newly developing PO production processes.

Evidently, PO synthesis is a compendium of industrial chemistry. In fact, the different approaches and technologies used nowadays for PO synthesis are emblematic not only of the limitations and drawbacks that have burdened the chemical industry, but also of how the discovery of new catalysts and catalytic technologies may lead to the development of more economical and more sustainable processes. Furthermore, it is an example of how the oxidation of an organic substrate can be achieved through quite different approaches, with various oxidants (organic hydroperoxides, HP, molecular oxygen) and catalyst types, either in the liquid or in the gasphase (Figure 6.2). However, in all the recently developed technologies, the discovery and use of a new heterogeneous catalyst has been the turning point for the successful commercial implementation of the corresponding process.

6.2 PO-only Routes: Several Approaches for Sustainable Alternatives j 325 Table 6.1 Summary of newly developing PO production processes.

Technology Oxidant Catalyst: main active component

HPPO and in situ HPPO

H2O2 (by the anthraquinone

TS-1

(BASF/Dow/Solvay, Degussa/

route)

Uhde, Lyondell)0

HPPO and in situ HPPO (Lyondell,

H2O2 (by direct liquid-phase

Pd/Pt-TS-1

BASF, Degussa/Headwaters,

oxidation of H2)

Tosoh Co, Hoechst)

DOPO (Lyondell, Olin, BASF, Dow)

O2

Ag-CaCO3

HOPO (Dow, Nippon Shokubai,

H2O2 (by gas-phase oxidation

Au-Ti silicate

BASF, Dow, Bayer)

ofH2)

aFirstly developed by EniChem.

aFirstly developed by EniChem.

Figure 6.2 Summary of the various technologies for PO production.
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