Editing Ziegler–Natta catalyst (section)

==History==
The 1963 [[Nobel Prize in Chemistry]] was awarded to German [[Karl Ziegler]], for his discovery of first titanium-based catalysts, and Italian [[Giulio Natta]], for using them to prepare stereoregular polymers from [[propylene]]. Ziegler–Natta catalysts have been used in the commercial manufacture of various polyolefins since 1956. As of 2010, the total volume of plastics, elastomers, and rubbers produced from alkenes with these and related (especially Phillips) catalysts worldwide exceeds 100 million tonnes. Together, these polymers represent the largest-volume commodity plastics as well as the largest-volume commodity chemicals in the world.

In the early 1950s workers at [[Phillips Petroleum]] discovered that chromium catalysts are highly effective for the low-temperature polymerization of ethylene, which launched major industrial technologies culminating in the [[Phillips catalyst]]. A few years later, Ziegler discovered that a combination of [[titanium tetrachloride]] (TiCl<sub>4</sub>) and [[diethylaluminium chloride]] (Al(C<sub>2</sub>H<sub>5</sub>)<sub>2</sub>Cl) gave comparable activities for the production of polyethylene. Natta used crystalline [[Titanium trichloride|α-TiCl<sub>3</sub>]] in combination with [[triethylaluminium|Al(C<sub>2</sub>H<sub>5</sub>)<sub>3</sub>]] to produce first [[isotactic]] [[polypropylene]].<ref name=nattadanusso>{{cite book|editor1-first=G. |editor1-last=Natta|editor2-first= F.|editor2-last= Danusso |title=Stereoregular Polymers and Stereospecific Polymerizations|publisher= Pergamon Press|date= 1967}}</ref> Usually Ziegler catalysts refer to [[titanium]]-based systems for conversions of [[ethylene]] and Ziegler–Natta catalysts refer to systems for conversions of [[propylene]]. 

Also, in the 1960s, [[BASF]] developed a gas-phase, mechanically-stirred [[polymerization]] process for making [[polypropylene]]. In that process, the particle bed in the reactor was either not fluidized or not fully fluidized. In 1968, the first gas-phase fluidized-bed polymerization process, the Unipol process, was commercialized by [[Union Carbide]] to produce polyethylene. In the mid-1980s, the Unipol process was further extended to produce [[polypropylene]].

In the 1970s, [[magnesium chloride]] (MgCl<sub>2</sub>) was discovered to greatly enhance the activity of the titanium-based catalysts. These catalysts were so active that the removal of unwanted amorphous polymer and residual titanium from the product (so-called deashing) was no longer necessary, enabling the commercialization of [[linear low-density polyethylene]] (LLDPE) resins and allowed the development of fully amorphous copolymers.<ref>{{cite encyclopedia |encyclopedia=Handbook of Transition Metal Polymerization Catalysts |publisher=John Wiley & Sons |date=2010 |editor1-last=Hoff |editor1-first=Ray |edition=Online |pages=131–155 |doi=10.1002/9780470504437.ch6 |isbn=9780470504437 |last2=Mink |first2=R. I. |last3=Kissin |first3=Y. V. |first1=T. E. |last1=Nowlin |editor2-first=Robert T. |editor2-last=Mathers |chapter=Supported Magnesium/Titanium-Based Ziegler Catalysts for Production of Polyethylene}}</ref>

The fluidized-bed process remains one of the two most widely used processes for producing [[polypropylene]].<ref name="Technology Economics Program">{{cite book |url=http://www.magcloud.com/browse/issue/411008 |title=Polypropylene Production via Gas Phase Process, Technology Economics Program |date=2012 |publisher=Intratec |isbn=978-0-615-66694-5}}</ref>