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Teaching of industrial organic chemistry.

This article outlines our successful approach to the teaching of industrial organic chemistry, which has been used for several years. Ideally, the student of industrial organic chemistry will already have a background familiarity with traditional alkane, alkene, and aromatic chemistry and terminology, together with an acquaintance with teh placing and transformation of the common functional groups by classical laboratory reactions. A basic grounding in general chemistry could be sufficient, but progress would be slowed as the tradional organic chemistry would have to be covered alongside the industrial material. An understanding of the terminology and the practical operating details of chemical operations could also provide a useful background, as has been previously discussed in this forum. [1]

Raw Materials

Sugars, starch, wood, fats and oils, and other plant sources were the predominant sources of the small-scale organic chemicals production during the 18th and 19th centuries. Ethanol and other fermentation products, coating resins, turpentine, and medications were among the products of this period. Coal became a dominant source fo organic chemicals in the mid-19th century, only to be supplemented and then surpassed from the beginning of the 20th century in volume of utilization by petroleum and natural gas.

Price and stability of supply have always been the major factors in the selection of raw materials for products in which raw material options exist. Benzene, for example, used to be obtained primarily by fractionation of the pyrolysis products of coal. [2] Now nearly all the supply is from petroleum, either by fractionation of aromatic crudes or by cracker operations designed to convert ethane, propane, or naphtha to aromatics. In the early days of the rubber industry, the sole source of the raw latex was from the coagulated sap of rubber trees such as Hevea braziliensis. In the 1940s when Western access to the rubber plantations was cut off, large acreages of the desert guayule shrub were planted for latex production in the US. At the same time, inexpensive and reliable petroleum-based technologies were developed. Gradually production of petroleum-based synthetic rubber grew at the expense of natural sources, until by 1973, only about 22% of US rubber was produced from natural latex. But, erratically increased petroleum prices and decreased reliability of petroleum supply since then has raised the proportion of rubber from natural sources back to 27% in the States and 37% globally. [3]

Today, despite the price and supply changes, some 90% of all organic chemicals, plastics and synthetic fibers are produced from petroleum and natural gas and the remainder from coal and plant sources. [4,5] This vast organic chemical industry still consumes only 10% of the total volume of petroleum and natural gas produced, the rest being consumed for transportation and other energy needs.

Nature of Petroleum

There is a common perception that the appearance, characteristics and composition of petroleum, as obtained from conventional wells, are fairly consistent. This is nto closely reflected in the reality (examples of which are shown in

[TABULAR DATA OMITTED]

Table 1). It can vary in colour from pale yellow to green to brown to black, and can be so viscous that it can set solid (pour point) at temperatures as high as 5[degrees]C or can be so fluid that it pours readily even at -13[degrees]C. It can have densities of only about three quarters that of water or can actually be more dense than water for heavy or asphaltic crudes. Some crudes may be so volatile that about one half of the crude is distilled by the time the distillate boiling point reaches 200[degrees]C, or be so involatile that they may have close to two-thirds of crude left as a residue even at boiling temperatures as high as 450[degrees]C. [6,7]

There are also heavy oils, for example near the Alberta-Saskatchewan border, where heating of the oil in place is necessary to lower the viscosity enough to allow recovery. [8] The tar sands, the largest deposits of which occur in northern Alberta and eastern Venezuela, [9] also require heat, usually in conjunction with surface mining, for the recovery of a useful synthetic crude from a complex matrix of fused aromatics. [10] Tar sands now provide some 12% of all the petroleum produced in Canada. Oil shales, while not comprising hydrocarbons in place like the other sources mentioned, nevertheless represent another large potential source of hydrocarbons. [11,12]

Distillation at very low temperatures (-95[degrees]C for methane separation), sometimes under pressure, is used to recover discrete fractions from natural gas (see Figure 1). Distillation at atmospheric pressure, or at reduced pressure for fractions of very high-boiling points, is used to obtain more discrete fractions from the original complex mixtures of hydrocarbons present in petroleum. Further details of the procedures used to isolate the various hydrocarbon fractions from petroleum are available, [7,13] and the physical details of how and why they operate make interesting discussion. Often it is possible to arrange a visit to a local refinery, where procedures can be seen first-hand.

Natural gas has a reputation of being a clean fuel. But it, like petroleum, is not so before the sulfides usually present are removed. [7] So sulfur removal usually precedes or follows fractionation of the natural gas (see Figure 2) or petroleum, depending on the sulfide content of the raw hydrocarbon being processed (see Table 1) and refinery site-specific details.

Chemicals from Petroleum

Petroleum-derived products are generally referred to as petrochemicals. Over 90% of all petrochemicals are obtained by one or several chemical conversions from the same seven basic building blocks of the petrochemical industry: methane, ethylene, propylene, [C.sub.4] fraction, benzene, toluene, and xylene (see Table 2). Of these, ethylene alone is used in the production of petrochemicals and consumer products comprising about one half of the total mass of petrochemical output (see Tables 3 and 4). For this reason, ethylene regularly nears the top of the organic chemicals list in terms of annual volume of production, both in Canada and the States with about 100 kilogram per capita produced in these countries. It is exceeded only by sulfuric acid, nitrogen, and oxygen in a ranked list of all chemicals produced. With the inclusion of methane, which is not a petrochemical product, four of these building block chemicals, methane, ethylene, propylene, and benzene all appear on the list of the 10 largest volume organic chemicals. No less than five of these 10 are ethylene or its derivatives, eg. ethylene dichloride, vinyl chloride, ethyl-benzene, and styrene. Finally, no less than eight of the 20 largest volume chemicals produced are organic. An additional three, ammonia, nitric acid, and ammonium nitrate, while not organic, are nevertheless derived from hydrocarbons and are therefore petrochemicals, as explained below.

Petrochemicals, despite their hydrocarbon origins, may not always be recognized as organic. The bulk of ammonia and carbon black, for example, are made from methane and air hence are classed as petrochemicals (equations 1-3). Yet they are hardly 'organic'. Carbon black was the first petrochemical, having

[CH.sub.4] + [O.sub.2] + [4N.sub.2] + [H.sub.2.O] [right arrow] [CO.sub.2] + [3H.sub.2] + [4N.sub.2] 1

[3H.sub.2] + [N.sub.2] catalyst/[right arrow]pressure [2NH.sub.3] 2

[CH.sub.4] + [O.sub.2] [right arrow] C + [2H.sub.2.O] 3

been produced from natural gas since 1872. [15] Sometimes even nitric acid and ammonium nitrate, derived from ammonia and hence also indirectly from methane, are also classed as petrochemicals.

Isopropyl alcohol, produced from propylene in 1920 by Standard Oil, N.J., was the first petrochemical requiring more than one step (equations 4,5). [16]. By 1925,

[CH.sub.3.CH]=[CH.sub.2] + [H.sub.2.SO.4] [right arrow] [CH.sub.3.CH(OSO.sub.3.H)CH.sub.3] 4

[CH.sub.3CH(OSO.sub.3.H)CH.sub.3] + [H.sub.2.O] [right arrow] [CH.sub.3.CH(OH)CH.sub.3] + [H.sub.2.SO.sub.4] (dilute) 5

it was being produced by this method on the scale of 68 tonnes per year, and in the US alone today on the scale of 647 kilotonnes per year, about four orders of magnitude larger than this early beginning.

With some 3,000 discrete petrochemicals currently in production, it is only possible in an outline such as this to briefly survey the alternative routes to one common large-volume product. This will be sufficient to demonstrate that while some commercial chemical processes are operated using classical laboratory synthetic routes, others employ chemistry and procedures that would be awkward or impractical to carry out in the laboratory.

Vinyl chloride, the monomer used for the large-scale production of poly(vinyl chloride), PVC, was initially prepared by adding hydrogen chloride to acetylene (equation 6). But, with the decline in price of ethylene

HC=CH + HCl [right arrow] [H.sub.2.C]=CHCl 6

relative to energy intensive acetylene as a petrochemical feedstock through the 1960s and 1970s, vinyl chloride production based on ethylene rapidly took over.

In this route to vinyl chloride, chlorine was initially added to ethylene to yield ethylene dichloride (1,2-dichloroethane, equation 7). When ethylene

[CH.sub.2]=[CH.sub.2] + [2Cl.sub.2] [right arrow] [CH.sub.2.Cl-CH.sub.2.Cl] 7

dichloride is thermally cracked, vinyl chloride is formed by the loss of hydrogen chloride (equation 8). Markets for hydrogen choloride are limited, so for an

[CH.sub.2.ClCH.sub.2.Cl catalyst/[right arrow][Delta] [CH.sub.2]=CHCl + HCl 8

intervening period, the ethylene chloride process which produced hydrogen chloride, and the acetylene process which consumed it were operated side by side.

[TABULAR DATA OMITTED]

To have to operate two processes to the same product was awkward, however, and the continually increasing price differential between ethylene and acetylene prompted a search for more direct ways to use the hydrogen chloride byproduct from the cracking of ethylene dichloride. Over a century ago, Deacon found that it was possible to oxidize hydrogen chloride catalytically by heating it with air (equation 9). Isolation of the chlorine from this process was a problem, since

[TABULAR DATA OMITTED]

4HCl + [O.sub.2] [CuCl.sub.2]/[right arrow]heat [2H.sub.2.O] + [2Cl.sub.2] 9

cooling the system formed liquid water which reacted with and consumed the chlorine product (equation 10). However, it was discovered that if ethylene was

[Mathematical Expression Omitted] 10

included as a component of the Deacon reaction under the right conditions, it reacted with the chlorine, as it formed, to yield ethylene dichloride and water which were then easily phase-separated after condensation (equation 11). The hydrogen chloride derived product was then combined with the chlorine addition product for cracking in accord with Equation 8. This reaction, which required inclusion of an extra step in the vinyl chloride production sequence did,

4HCl + [O.sub.2] + [CH.sub.2]=[CH.sub.2] [CuCl.sub.2]/[right arrow]heat [2H.sub.2.O] + [CH.sub.2.ClCH.sub.2.Cl] 11

however, permit use of byproduct hydrogen chloride with ethylene rather than acetylene. Many other examples of parallel and varied routes to the same petrochemical product exist, the development of each motivated by the vagaries of feedstock pricing, by the development of more efficient processes, or from environmental considerations. [4,7,17]

Organic Chemicals from Wastes

One does not require a discrete hydrocarbon stream to produce organic chemicals. Whey residues from cheese-making can be used to make lactic acid from the lactose content, or to make sweeteners or yeast. [18] Molasses is used to make several amino acids, or yeast biomass via aerobic fermentation processes. (equation 12), and to make ethanol via anaerobic fermentation with yeast (equation 13).

[C.sub.6.H.sub.12.O.sub.6] + [O.sub.2] + yeast nutrients/[right arrow] yeast biomass + [CO.sub.2] 12

[C.sub.6.H.sub.12.O.sub.6] yeast/[right arrow] [2CH.sub.3.CH.sub.2.OH] + [2CO.sub.2] 13

Immobilized yeast cells in a column can even produce ethanol directly, by passage of a sugar solution through the column. [19]. Lactose immobilized on glass beads can convert lactose in milk, poorly tolerated by many individuals, to the better tolerated mixture of galactose and glucose (equation 14). [20]

[Mathematical Expression Omitted] 14

The rather indiscriminant organic substrates provided by sewage sludge, or municipal solid waste can yield substantial quantities of methane on anaerobic decomposition (equation 15). [21] The methane produced can be used to supply much of the

Biomas + moisture methanogenic/[right arrow]bacteria [CH.sub.4] + [CO.sub.2] 15

energy requirement of a well-run integrated sewage treatment plant, and can contribute to town gas supplies. Methane produced in moist landfill sites is generally lost to the ambient air. But, buried perforated pipe networks operating under reduced pressure are being put in place, or are planned for some landfills to capture a fraction of the gas produced.

There are several examples of organic products employing waste sulfite liquor, a waste stream which has been used to produce ethanol, lactic acid, fumaric acid, propionic acid, and yeast or fungal protein by various fermentation processes. [22] But the isolation of vanillin in a series of chemical steps with yields of about 15% on the initial calcium lignosulfonate content (equation 16) recovered from waste sulfite liquor, has to be one of the more elegant examples. [23]

[Mathematical Expression Omitted] 16

Vanilla beans from Madagascar, from which natural vanilla extract is made, sell for US$81 per kg. [23] Based on

[TABULAR DATA OMITTED]

the 3 to 4% content, this vanillin sells for US$2000 to $2700 per kg. Vanillin, from waste sulfite liquor, sells in bulk for about US$16 per kg. [24] It is the main flavour ingredient in synthetic vanilla extract, as well as a flavour component of many commercial food products. To recover a valuable product such as this, from a pulping waste stream, represents an excellent example of the adage 'what is one man's waste stream is another man's feedstock'.

This particular waste stream utilization has become such an important factor in the operation of the few pulp mills practising this process that it actually affects the choice of tree stand to be used for pulping. Softwoods, in which the lignin has a higher guaiacyl content (17a) amenable to conversion to vanillin, are preferred to hardwoods, which have a higher syringaldehyde (17b) content which is not convertible to vanillin.

[Mathematical Expression Omitted] 17

The Ontario Paper Company at Thorold, Ont., produces thousands of tonnes of vanillin annually by this process, enough to supply some 60% of the world market.

Concluding Comments

I hope this brief outline of a framework for industrial organic chemistry, plus the few conventional and non-conventional examples given, provides some incentive to incorporate further applied material into chemistry programmes. It is anticipated that topics such as these would generally be taken at the post secondary level, although an occasional example that catches the eye of the high-school instructor could probably be introduced at this level for enrichment. Further background material for this most interesting instructional area is available from the references cited throughout. With the heady years of rapid development of the low cost petroleum-based organic chemicals industry of the 1950s, 1960s, and 1970s now passed, we are entering an era of change in which the industry and the instructor are going to be hard pressed to keep up with the more varied feedstock sources which are bound to be developed in the coming decades.

References

[1] M.B. Hocking, Canadian Chemical News 42 (3), 21, Mar. 1990.

[2] L.E. Swabb, Jr., Science 199, 619, Feb. 10, 1978.

[3] S. Stinson, Chemical and Engineering News 68 (21), 45, May 21, 1990.

[4] H.A. Witcoff and B.G. Reuben, Industrial Organic Chemicals in Perspective, John Wiley and Sons, Toronto, 1980.

[5] R.S. Wishart, Science 199, 614, Feb. 10, 1978.

[6] Riegel's Industrial Chemistry, J.A. Kent, ed., Reinhold Book Corporation, New York, 485, 1962.

[7] M.B. Hocking, Modern Chemical Technology and Emission Control, Springer-Verlag, New York, 1985.

[8] A. Verma and S.M. Farouq Ali, Canadian Chemical News 37, (11), 10, Dec. 1985.

[9] L. Bridges, Science Affairs 9 (3), 4, 1976.

[10] M.B. Hocking, J. Chemical Education 54, 725, 1977.

[11] M. Atwood, Chemtech 3, 617, Oct. 1973.

[12] D.L. Klass, Chemtech 5, 1, Aug. 1975.

[13] Kirk-Othmer Concise Encyclopedia of Chemical Technology, E. Graber, A. Klingsberg, and P.M. Siegel, editors, John Wiley and Sons, Toronto, 851-860, 1985.

[14] Chemical and Engineering News, 68 (25), 34, June 18, 1990.

[15] R.N. Shreve, Chemical Process Industries, McGraw-Hill, Toronto, 124, 1967.

[16] G.T. Austin, Shreve's Chemical Process Industries McGraw-Hill, Toronto, 747, 1984.

[17] F.A. Lowenhein and M.K. Moran, Faith, Keyes and Clark's Industrial Chemicals, John Wiley and Sons, Toronto, 1975.

[18] R. Greene, Chemical Engineering 65, 78, Apr. 10, 1978.

[19] Canadian Chemical Processing 65 (1), 18, Feb. 1981.

[20] N. Basta, Chemical Engineering 89, 55, Apr. 9, 1982.

[21] J. Coombs, Chemistry and Industry, London 233, Apr. 4, 1981.

[22] J.C. Mueller, Fermentation of Wastes, BC Research Guidelines, 1, Oct. 1975.

[23] D. Craig and C.D. Logan, Method of Producing Vanillin and Other Useful Products, Canadian Patent 615,552 to Ontario Paper Co. Ltd., Feb. 28, 1961.

[24] Chemical Marketing Reporter, New York 236 (26), 42, Jun. 25, 1990.

M.B. Hocking, FCIC, obtained his early education in Edmonton, earned a BSc from the University of Alberta in 1959 and took his PhD in organic chemistry from the University of Southampton, England. He then spent a period of eight years as an industrial research chemist. He is now associate professor at the University of Victoria where he oversaw the introduction and has chaired its Environmental Studies Programme. He participates in the Cooperative Education Programme and teaches primarily in the areas of industrial and environmental chemistry.
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Author:Hocking, Martin B.
Publication:Canadian Chemical News
Date:Mar 1, 1991
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