Basics Basics of
Basics Basics of Bio-Polyolefins Polyethylene H H | | — C — C — | | H H n Plastic Fuel Tank made from bio-PE (Photo: Courtesy Braskem) Ethylene H H \ / C ═ C / \ H H As it has almost become a habit, let’s start our ‘basics’ article with a look into Wikipedia: A polyolefin is a polymer produced from a simple olefin (also called an alkene with the general formula C n H 2n ) as a monomer. For example, polyethylene (C 2 H 4 )n (PE) is the polyolefin produced by polymerizing the olefin ethylene H 2 C=CH 2 . Polypropylene (PP) is another common polyolefin which is made from the olefin propylene. In some cases PE is produced as a copolymer using butene, hexene or octene as comonomer. Polyethylene Polyethylene or polythene (IUPAC name polyethene or poly(methylene)) is the most widely used plastic, with an annual production of approximately 80 million metric tons (2008). Its primary use is within packaging [1]. And in bioplastics MAGAZINE 01/2008 Dr. Thomas Isenburg wrote: Polyethylene is a plastic material that has been known for more than 100 years. It is found in millions of applications from simple film, through containers, to toys or technical components such as plastic fuel tanks for cars. Polyethylene was discovered by the chemist Hans von Pechmann in 1898. In 1933 polyethylene was successfully produced, at a pressure of 1400 bar and a temperature of 170°C, at the ICI laboratories. For a large scale industrial process these conditions were, however, difficult to produce and were highly energy intensive. In 1953 polymer chemistry saw a major breakthrough. The chemists Karl Ziegler and Giulio Natta succeeded in synthesising polyethylene from ethylene at normal pressure using catalysts. Ethylene So it all starts with ethylene… Ethylene is a chemical intermediate used to produce many different products, besides polyethylene (PE), for example polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polystyrene (PS) can be named. Its current world production capacity is around 115,000 tons per year, mainly (>98%) through the petrochemical route based on steam cracking (thermal pyrolysis) of petroleum liquids (naphtha, condensate, and gas oils) and natural gas feedstocks (ethane, propane, and butane). However, before the boom of petroleum started in the early 1950s, ethylene was produced from ethanol. Interestingly, the first report that was published in the literature about the catalytic dehydration of ethanol to ethylene dates from 1797. Applying the catalytic dehydration of ethanol to produce ethylene is again becoming more and more important. Especially in Brazil, with the building of large-scale plants motivated by the Brazilian sugarcane based ethanol competitiveness and by the low carbon footprint of the product obtained by this route. Just a few weeks before publication of this issue of bioplastics MAGAZINE Braskem started the manufacture of polyethylene on a large scale based on Brazilian renewable ethanol. 52 bioplastics MAGAZINE [05/10] Vol. 5
Article contributed by Antonio Morschbacker Responsible for Green Polymers Technology Braskem S.A. São Paulo, Brazil and Michael Thielen Ethanol We all know very well that bio-ethanol has been used as engine fuel since the beginning of the last century. In the mid 1970s, the Brazilian National Alcohol Program led to a significant increase in the Brazilian ethanol capacity. About thirty years later the United States started to grow their capacity very fast so that eventually they became the world leader in manufacture. With 23 billion liters (USA) and 21 billion liters (Brazil) in 2007 these two countries are currently by far the global leaders in ethanol production. In the meantime the Brazilian production reached 25 billion in 2009 and 28 billion estimated for 2010. Under optimal climate conditions, like in tropical regions, sugarcane is relatively inexpensive to grow. Sugarcane offers a high agricultural productivity and relatively simple harvest methods. The growing season for sugarcane (6 to 7 months) is longer than that of other crops. It is harvested year by year during at least four years with no necessity to plant it again during this cycle. The poor mechanical harvesting methods of about 10 years ago are much more efficient today and still do not emit carbon dioxide in consequence of the sugarcane burning. In Brazil, the water requirement for its production is to a large extent rainfed. The World Bank and the FAO have confirmed that Brazilian ethanol has not raised sugar prices significantly and that it is the only biofuel competitive with petroleum-based diesel or gasoline and which saves greenhouse gases [2]. And once again it needs to be explained: In Brazil the rainforests are in the north of the vast country, whereas most of the the sugarcane plantations are in the southeast. In addition, land and climate in the north – the rainforest area - aren’t appropriate for sugarcane production (see bM 04/2009). If a sugar source, mainly sugarcane juice and molasses (as in Brazil) and hydrolyzed starch from corn grains (as in the United States) is fermented, ethanol can be obtained. In some regions other crops can be used, such as potato, wheat, manioc, and sugar beets. The use of hydrolyzed cellulose and hemicellulose from low-cost biomass is a potential way to obtain cheaper ethanol but until now this technology is under development and its commercial production started at the end of the last year in a small unity [3]. To produce the ethanol through fermentation, sugar is extracted from sugarcane by crushing the raw cane with water to extract the sugars (mostly sucrose). In a similar Sugarcane (Photo: Courtesy Braskem) Braskem Green PE Plant (Courtesy Braskem - Photo by Mathias Cramer) bioplastics MAGAZINE [05/10] Vol. 5 53
