Basic Inorganic Chemicals

Chemicals produced in bulk quantities and used primarily in subsequent industrial processes are termed as basic chemicals. Basic inorganic chemicals are, as the name indicates, non-carbon-based compounds, though carbon dioxide and inorganic carbonates are included under this category. Nearly 40% of the top 50 chemicals are basic inorganic chemicals [1]. Typically, seven of the top 10 chemicals produced worldwide are inorganic: sulfuric acid, nitrogen, oxygen, chlorine, phosphoric acid, ammonia, and sodium hydroxide. Nitrogen and oxygen are categorized under Industrial Gases, whereas ammonia is categorized under Fertilizer Products. The other four chemicals are considered Basic Inorganic Chemicals. Almost all of the inorganic chemicals are industrial products; that is, they are used in production of other chemicals and consumer products. For example, the largest use of sulfuric acid is in phosphate-based fertilizer production. Similarly, caustic soda (sodium hydroxide) and chlorine are used in the manufacture of organic chemicals and the pulp and paper industry.

2.2.2 Industrial Gases
Except for chlorine, which is considered a basic inorganic chemical, other industrially significant gases have their own distinct category. The most important of industrial gases are oxygen, nitrogen, hydrogen, and carbon dioxide. Oxygen and nitrogen are obtained from air primarily through cryogenic liquefaction and distillation. The use of nitrogen (and of hydrogen) is dominated by ammonia manufacture. Nitrogen is also used in enhanced oil recovery (EOR) and maintenance of inert atmosphere in processes, and the other significant application of hydrogen is in adjusting the carbon-to-hydrogen ratio in hydrocarbons, particularly transportation fuels. Pure oxygen is used in chemical manufacturing, including that of metals, and in medical applications. Carbon dioxide, as an industrial gas, is formed as a by-product of hydrogen manufacture. Its dominant use is in refrigeration, the food industry, and manufacturing chemicals. Figure 2.1 provides a very broad overview of the basic inorganic chemical and industrial gas products.

Figure 2.1 Major basic inorganic chemicals and industrial gases.

2.2.3 Basic Organic Chemicals and Petrochemicals
Almost all of the organic chemicals produced by the chemical industry are obtained from seven basic chemicals: methane, ethylene, propylene, butadiene, benzene, toluene, and xylene. Methane is the primary constituent of natural gas. Although some minor sources are available for the rest of the basic organic chemicals, they are invariably derived from petroleum, and chemicals derived from petroleum are collectively termed petrochemicals. Ethylene is the largest-volume organic chemical produced worldwide, followed by propylene. The largest use of these chemicals is in the manufacture of polymers, such as polyethylene, polypropylene, polybutadiene and rubbers, and polyesters (polyethylene terephthalate [PET] and polybutylene terephthalate [PBT]). The other important chemicals produced from these chemicals include ethylene oxide and vinyl chloride, propylene oxide and isopropyl alcohol, cyclohexane, toluene diisocyanate, and phthalic anhydride. Many of these derived chemicals are, in turn, used in manufacture of other organic compounds, including polymers such as polyvinyl chloride (PVC) and polyurethanes.

Figure 2.2 provides an overview of the basic organic chemicals and petrochemical products. The top level in the hierarchical representation shows the different sources of the basic chemicals. As mentioned previously, petroleum (crude oil) is the primary source for the chemicals; however, these chemicals, particularly methane, are also obtained from coal. The middle level in the figure shows the seven basic organic chemicals; methane is separate primarily to indicate that it is predominantly obtained from natural gas. The lower level provides a brief glimpse into the world of petrochemicals: the intermediates such as butadiene, ethylene dichloride, acrylonitrile, formaldehyde, and countless others that are precursors to a vast number of chemical products that go into objects used universally by practically every individual.

Figure 2.2 Overview of basic organic chemicals and petrochemical products.

2.2.4 Fertilizer Products
Fertilizer industries are vital components of a nation’s economy; however, the significance of fertilizer products cannot be measured merely by the economic value they add. The sustainability of food production is critically dependent on the availability of fertilizers. In that sense, fertilizer production is the most important endeavor of the chemical industry. Fertilizer products utilize the basic inorganic and organic chemicals and industrial gases as described earlier. Fertilizer products belong primarily to one of the two major classes: nitrogenous fertilizers and phosphatic fertilizers. Nitrogenous fertilizers include products such as ammonium nitrate, ammonium sulfate, and urea; phosphatic fertilizers include ammonium phosphates and superphosphates. Figure 2.3 provides an overview of the fertilizer products that are indispensable for satisfying the food demands of the ever-increasing human population.

Figure 2.3 Overview of fertilizer products.

Phosphatic fertilizers are based on phosphoric acid formed by reacting the raw material phosphate rock with sulfuric acid, a basic inorganic chemical, as previously mentioned. Nitrogenous fertilizers are based on ammonia, which itself is formed from the industrial gases nitrogen and hydrogen. Most fertilizer products available in the market are characterized by a three-number label, with the numbers representing the elemental content with respect to nitrogen, phosphorus, and potassium (N-P-K).3 The desired level of potassium in the particular product is obtained by blending appropriate quantity of potash (generally potassium chloride, though the term potash is variously used to refer to potassium carbonate, hydroxide, chloride, or oxide [1]) into the product.

3. The numbers for P and K actually refer to the percentages of P2O5 and K2O, respectively.

2.2.5 Polymer Products
Polymers are among some of the most useful and valuable products of the chemical industry. In general, polymer products are classified as plastics and resin products or as rubber products. A plastic material is defined as a solid, high-molecular-weight, polymerized organic substance and typically involves liquid-phase manufacturing or processing of the material [2]. Plastic and resin products include chemicals such as polyolefins (polyethylene/polypropylene), polyesters (PET, PBT), polyamides (nylons), and formaldehyde-based resins. Rubber products are, similarly, polymers having a high molecular weight, but in contrast to plastic and resin products, they exhibit elastic behavior and often are called elastomers [1]. Rubber products include synthetic rubber, latex, nitrile, silicone, and other rubbers.

The polymer product sector is inevitably linked to the basic organic chemicals and the petrochemicals. Most of the polymers are formed either through addition reactions (involving addition of the monomer molecule to the polymer chain) or condensation reactions (involving reaction groups belonging to two different monomer units). Most of the polyolefins, such as polyethylene, polypropylene, and PVC, are formed through the addition polymerization reactions. Such polymers typically soften and melt without decomposition upon heating and can be resolidified into new forms without losing their polymer characteristics. These polymers are called thermoplastics [1]. Phenolic resins, such as phenol-formaldehyde resins, and polyesters, such as PET, are formed by condensation reactions. These polymers are characterized by strong chemical bond crosslinking of units. They typically decompose upon heating and, unlike thermoplastics, cannot be reconstituted upon cooling. Figure 2.4 shows some of the important polymer products. The figure offers only a brief glimpse into the world of polymers and does not include several other products of equal significance.

Figure 2.4 Classification and examples of polymer products. ABS, acrylonitrile-butadiene-styrene; LDPE, low-density polyethylene; HDPE, high-density polyethylene; PBT, polybutylene terephthalate; PET, polyethylene terephthalate; PVC, polyvinyl chloride; SBR, styrene butadiene rubber.

The polymer sector of the chemical industry includes the manufacture not only of the polymer (polyester, for example) but also of fibers and filaments based on these polymers. Polymers are highly versatile chemicals with remarkable properties that allow them to be shaped into thin films, flexible nets, rigid furniture, cloth, and countless other products that make them so ubiquitous in modern society.

2.2.6 Pharmaceutical Products
The pharmaceutical sector of the chemical industry involves the manufacture of (1) uncompounded medicinal compounds and (2) pharmaceutical formulations (tablets, ointments, etc.) that can be administered as doses. As with the fertilizer product sector, the significance of this sector goes beyond the mere monetary value to the economy. Pharmaceutical products are generally produced in much smaller quantities than other products previously described. However, these are value-added products that command a substantially higher price. The products also have a much more complex structure than the simple chemicals discussed earlier.

2.2.7 Other Chemical Products
Although the majority of chemical products can be classified as industrial products (products used for other industrial processes), a significant fraction of the chemical industry output consists of products used directly by the consumers. These include soaps and detergents, perfume and cosmetics, flavors, pesticides, paints, inks, and so on.