Industrial Chemistry: For Advanced Students - Mark A. Benvenuto 2015
Bisphenol A (so-called because the molecule incorporates two units of phenol and the carbon atoms from acetone) has been known for over a century, has had an industrial use since the 1950s and has been one of the top 100 chemicals produced globally for the past several decades. It has been used in the production of two broad categories of plastics and in food packaging plastics since shortly after the Second World War. Almost all bisphenol A finds use as monomeric material in plastics.
10.1 Method of production
Bisphenol A is produced from the reaction of two relatively simple, very inexpensive organic compounds, phenol and acetone, in a 2 : 1 molar ratio of phenol to acetone, as shown in Figure 10.1.
Both starting materials, phenol and acetone, are themselves made in what is sometimes called the cumene process or the Hock process, whereby benzene and propylene are reacted to form cumene (isopropyl benzene) at elevated temperature and pressure (generally 250 °C and 25—30 atm), then allowed to react with air, where the tertiary carbon—benzene bond is broken and combined with oxygen, yielding acetone and phenol. Indeed, this product mix can itself be used as a starting material for bisphenol A synthesis. Still, one can consider benzene and propylene as the ultimate refined, organic starting materials for bisphenol A. Both benzene and propylene are extracted from the crude oil.
Fig. 10.1: Bisphenol A synthesis.
The reaction proceeds with acid catalysis, often hydrochloric acid, and is considered a condensation reaction, as the oxygen from acetone and the two para-positioned hydrogen atoms from each phenol unite to form water as the by-product. Usually, an excess of phenol is used to ensure optimum yields. The reaction does not always run cleanly, with minor, organic by-products forming, such as ortho-substituted products, and thus the final desired material is distilled from the product mixture.
10.2 Volume of production annually
For the past several years, over two million tons of bisphenol A have been produced annually. The production of bisphenol A has been on or near this scale for at least the past 20 years; with major industrial production going back to the 1950s. In general, future production appears slated to stay at or about at the same level.
There are several major producers of bisphenol A, including Dow Chemical, Bayer Polymers, SABIC, and Sunoco (ICIS, 2014; IHS, 2014). A fuller list includes the following, a set of globally diverse companies:
1. Anhui Shanfu New Material Technology Co., Ltd. (Anhui Shanfu, 2014)
2. Bayer Material Science Bayer Material Science (2014)
3. Dalian CR Science Development Co., Ltd. (Dalian CR, 2014)
4. Dow Chemical (Dow Chemical, 2014)
5. Go Yen Chemical Industries Co., Ltd. (Go Yen, 2014)
6. Hexion Specialty Chemicals (Hexion Specialty Chemicals, 2014). Hexion claims at its website to be the world’s largest producer of thermosetting resins. Thus, bisphenol A should be a significant reactant and material needed for its resin production.
7. Jingjiang Concord Plastics Technology Co., Ltd. (Jingjiang Concord, 2014)
8. Oxford Lab Chem, India (Oxford Lab Chem, 2014)
9. SABIC (SABIC, 2014)
10. Shanghai Jorle Fine Chem. Co., Ltd. (Shanghai Jorle, 2014)
11. Sunoco (Sunoco, 2014)
12. Toronto Research Chemicals, Inc. (Toronto Research Chemicals, 2014)
10.3.1 Polycarbonate production
Almost all bisphenol A is utilized in the production of plastics. Perhaps the most simple is the production of what is called polycarbonate plastic, the reaction chemistry for which is shown in Figure 10.2. Polycarbonate, or PC, accounts for almost three-fourth of all bisphenol A use (ICIS, 2014; IHS, 2014).
Fig. 10.2: Production of polycarbonate from bisphenol A.
The co-product, or by-product, of this synthesis is 2 molar equivalents of hydrochloric acid, which can be reclaimed or neutralized with a base.
The co-monomer in the synthesis, phosgene, is the subject of Chapter 2. Because of the highly toxic nature of phosgene, and because large volumes are required for the production of polycarbonate plastic on an industrial scale, diphenyl carbonate can be used as a co-monomer, as shown in Figure 10.3.
Fig. 10.3: Production of polycarbonate from bisphenol A and diphenyl carbonate.
The by-product of polycarbonate production when diphenyl carbonate is used as the co-monomer is phenol. Interestingly, in one method, phenol is made into diphenyl carbonate by the addition of phosgene. This means that while phosgene can be eliminated from the final production of polycarbonate, it may still be a reactant in an earlier reaction.
10.3.2 Epoxy resin production
Epoxy resins account for almost all of the remaining use of bisphenol A, comprising roughly 20% of total annual demand (ICIS, 2014; IHS, 2014). While several different kinds of epoxy resins exist, bisphenol A and epichlorohydrin are used to produce almost all of the epoxy resin that is commercially used. The simplified reaction chemistry is shown in Figure 10.4.
Fig. 10.4: Epoxy resin formation from bisphenol A and epichlorohydrin.
While the product is drawn as if it were simply one repeat unit in a polymer, the ratio of starting materials that make epoxy resins can be varied to adjust the final molecular weight, or molecular weight distribution, of the end product. Often, when a higher epichlorohydrin:bisphenol A ratio is used, the products are low molecular weight materials, sometimes called pre-polymers. As the ratio shifts to greater amounts of bisphenol A, the molecular weight or weight distribution of the product increases. These are considered to be linear polyether polymers.
Epoxy resins find numerous uses in a variety of consumer end products. Coatings, electric laminates, paving, and flooring are all examples. Perhaps the best known consumer end-use is that some adhesives are used for epoxy resins and glues.
10.4 The controversy
Bisphenol A continues to be a controversial material in terms of its use in food packaging plastics, because of its apparent role as an estrogen mimic, and because it is sometimes difficult to determine how much of a food contact material can enter into the food with which it comes into contact (for example, how much plastic wrap enters into food that is microwaved when still in the wrapper?). Calls have already been made to ban all use of bisphenol A, but the industry is mature and developed enough that this does not seem likely to occur.
Some products now produced without bisphenol A advertise this fact subtly, as shown in Figure 10.5. The figure shows a polycarbonate bottle, inverted, showing the resin identification code (RIC) of 7, and under the RIC recycle triangle the lettering “BPA FREE,” both molded into the plastic.
Fig. 10.5: BPA free beverage bottle.
10.5 Recycling and reuse
Any recycling with respect to bisphenol A is for the end product plastics into which it has been added or made, and not for the material itself. Thus, this form of reuse becomes part of the larger recycling programs instituted throughout different countries (BPA, 2014; Polycarbonate Recycling, 2014).
Anhui Shanfu New Material Technology Co., Ltd. Website. (Accessed 18 May 2014, as: http://www.chem-shanfu.com/english.asp).
Bayer Material Science. Website (Accessed 18 May 2014, as: http://www.materialscience.bayer.com/GlobalwebsiteInformation/Search-result.aspx?qwaw=bisphenol+A&gs=1).
Dalian CR Science Development Co., Ltd. Website. (Accessed 18 May 2014, as: http://dlchuanrong.cn).
Dow Chemical. Website. (Accessed 18 May 2014, as: http://www.dow.com/products/).
Go Yen Chemical Industries Co., Ltd. Website. (Accessed 18 May 2014, as: http://goyenchemical.com/english/main.php?method=products).
Hexion Specialty Chemicals. Website. (Accessed 18 May 2014, as: http://www.transaction-information.com/hexion-fact-sheet).
ICIS. Website. (Accessed 10 January 2014, as: http://www.icis.com/resources/news/2008/01/14/9092025/chemical-profile-bisphenol-a/).
IHS. Website. (Accessed 9 January 2014, as: http://www.ihs.com/products/chemical/planning/ceh/index.aspx).
Jingjiang Concord Plastics Technology Co., Ltd. Website. (Accessed 18 May 2014, as: http://jingjiang-concord.en.ywsp.com/).
Oxford Lab Chem, India. Website. (Accessed 18 May 2014, as: http://www.oxfordlabchem.com/price_list.html).
The Polycarbonate/Bisphenol A (BPA) Global Group. Website. (Accessed 9 January 2014, as: http://plastics.americanchemistry.com/Product-Groups-and-Stats/PolycarbonateBPA-Global-Group ).
Polycarbonate Recycling. Website. (Accessed 9 January 2014, as: http://www.azom.com/article.aspx?ArticleID=7963).
SABIC Website. (Accessed 18 May 2014, as: http://www.sabic.com).
Shanghai Jorle Fine Chem. Co., Ltd. Website. (Accessed 18 May 2014, as: http://www.jorle.com.cn).
Sunoco. Website. (Accessed 18 May 2014, as: http://www.sunocoinc.com).
Toronto Research Chemicals, Inc. Website. (Accessed 18 May 2014, as: http://www.trc-canada.com).