07 January 2011 00:00 [Source: ICB]
With oil supplies coming under ever more pressure, innovative chemists are finding new uses for alternative feedstocks
Developing new C1 technologies using gas, coal-derived synthesis gas (syngas) or methanol as alternatives to petroleum-based feedstocks may offer attractive opportunities to reduce reliance on petroleum derivatives for production of important petrochemical commodities.
Syngas and methanol, which can be produced conveniently from either natural gas or coal, may play an increasingly important role as interesting new C1-based technologies for manufacture of several important petrochemicals continue to emerge.
Low gas prices in the US stemming from abundant supplies of shale gas, dwindling ethane supplies in the Middle East and low coal prices in China are all factors that may accelerate innovation in C1-based chemical routes to commodity chemicals.
Increasing the use of C1-based technologies derived from natural gas for chemical production also offers an opportunity to reduce the carbon footprint of the chemical derivatives. Use of coal or gas-derived methanol can also decrease dependence on imported petroleum in petroleum-poor regions or countries, particularly in countries such as China, India and even the US.
Production processes for commodity petrochemicals that partially or completely replace conventional feedstocks with syngas or methanol have therefore received increased attention recently. Five important high-volume petrochemicals that are being impacted by this trend include monoethylene glycol (MEG), paraxylene (PX), styrene, light olefins and ethanol.
Henan Coal Chemical and Tongliao Jinmei Chemical Industry, both Chinese, are understood to be jointly developing a coal to MEG process. Several 200,000 tonne/year plants are already under construction in China and are planned to start up in the third quarter of 2011. This new MEG technology is a complete departure from the conventional ethylene-based route and is believed to involve initial preparation of dimethyl oxalate via oxidation of carbon monoxide (CO) with methyl nitrite, followed by hydrogenolysis of the dimethyl oxalate to MEG. In the last step, methanol is liberated and recycled to make additional methyl nitrite by reaction with nitric oxide and oxygen. Thus, the only feedstocks consumed are CO, hydrogen and oxygen. This process, if proven, could have a significant impact on world trade for this important commodity chemical.
Some of the new process technologies might soon be capable of exerting a noticeable impact on petroleum consumption
Although this technology has been demonstrated only at the bench-scale level, if the claims of high selectivity are borne out in pilot tests, the costs of production and feedstock savings could be improved significantly over conventional SM processes.
Saudi Arabia's SABIC and Netherlands-headquartered Lummus Technology announced late in 2010 plans to jointly develop a new route to paraxylene (PX) that involves methylation of toluene with methanol:
This technology has been designed around a proprietary SABIC catalyst. While details of this catalyst have not been revealed by the developers, a scan of recent SABIC patents in this area indicates that the catalyst is based on phosphorous modified ZSM-5 zeolites.
Previous catalysts reported in the literature for this conversion tended to deactivate quickly. The SABIC phosphorous-modified zeolites appear to significantly extend the life of such catalysts. Lummus has indicated that this type of process may provide a unique debottlenecking option for aromatic complexes. Typically, toluene is disproportionated to both xylenes and benzene. The SABIC/Lummus approach would allow toluene conversion to just xylenes.
Replacing NGL and petroleum-based hydrocarbon feedstocks, such as ethane, propane, liquefied petroleum gas (LPG) and naphtha, with methanol for production of light olefins such as ethylene or propylene represents an even more significant potential for reducing petroleum-based feedstocks for chemical manufacture.
Direct methanol to olefins as well as related indirect processes via dimethyl ether intermediate have been under development for more than 30 years by companies such as US groups Mobil and UOP, Norway's Norsk Hydro, German group Lurgi and China's DICP. The processes all use variations of zeolite-type catalysts that were initially examined in the 1980s for production of gasoline from methanol.
The significant advantage of starting from methanol, particularly when compared with conventional steam crackers, is that the yield of light olefins, particularly ethylene and propylene, is considerably higher than achievable from petroleum-based naphtha crackers.
This not only minimizes the production of lower-valued higher olefins, but also substantially decreases the complexity of the downstream separation and purification portions of the process design.
Unlike naphtha cracking, the methanol-based processes provide considerable flexibility in the olefin slate of products that can be achieved by modification of both catalyst composition and operating conditions. The UOP/Hydro technology, usually referred to as MTO (methanol-to-olefins), produces an ethylene-rich mixture of olefins. The Lurgi technology referred to as MTP (methanol-to-propylene) can produce propylene primarily or even exclusively.
The Chinese technology, developed by a consortium of companies (DICP, SYN, Sinopec and LPEC) has recently been commercialized by Shenhua in Baotou, in Inner Mongolia. In this process, nearly 3.5m tonnes of coal is converted to 300,000 tonnes of ethylene and 300,000 tonnes of propylene, all of which is converted to the corresponding polyolefins. US group Dow and France's Total have recently independently expressed intentions to commercialize coal-to-olefins (CTO) plants in China.
US group Celanese has recently announced its intention to build one, or possibly two, 400,000 tonne/year CTO plants in China using newly developed, proprietary conversion technology.
While the specifics of this new technology have not been released, Celanese has stated that this technology leverages its long experience in acetyls chemistry and is based on a direct route to ethanol. The company claims this new technology has advantages over fermentation techniques. Celanese has stated that industrial applications such as ethyl acetate (etac) will be the initial focus, although other applications can be envisioned easily, thus opening the possibility for a variety of petrochemicals ultimately being produced from coal or gas-derived C1 chemistry.
Each of the examples above is at different stages of development, so their ultimate commercialization is by no means assured. Nevertheless, they clearly illustrate that some of the new process technologies utilizing syngas and methanol feedstock in place of more conventional petroleum-based feedstocks might soon be capable of exerting a noticeable impact on petroleum consumption used for petrochemical manufacture.
George Intille is a principal at Nexant and can be reached at firstname.lastname@example.org. Jeffrey Plotkin is a vice president at Nexant and can be reached at email@example.com. In 2010, Nexant published reports on coal to MEG, methanol to olefins, styrene and aromatics which provide additional details concerning the C1-based processes technology and production economics discussed in this article.
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