ACETYLENE

Less than a quarter century ago, acetylene was the big organic chemical feedstock in both the United States and Europe. This original dependence on acetylene resulted from the synthetic organic chemicals industry's beginning in Europe as a derivative of coal coking for iron and steel. The carbon in coal was converted to calcium carbide, which, when treated with water, releases acetylene. Calcium carbide is a solid and thus easy to handle and ship long distances so long as it is kept from contact with air and water. The synthetic organic chemicals industry could thus be located either at the coal mine, the steel mill, or the marketing area.

Much of the industry's technical activity since World War II has been devoted to either winning acetylene from natural gas or oil fractions or to making from ethylene products that had historically been made from acetylene.

There are two basic reasons for this trend. The first is that it takes less energy to make ethylene than to make acetylene, whether from oil, from gas, or from coal. The second is that coal cannot compete with oil economically as a raw material for paraffinic hydrocarbons.

As a result, acetylene is declining in importance as a chemical raw material, peaking in total consumption early in the 1960's and going down currently in both relative and absolute terms.

The biggest uses for acetylene are for vinyl chloride (now being supplanted by oxychlorination of ethylene), polychloroprene (now almost totally converted to butadiene), acrylics (now moving toward propylene), vinyl acetate (continuing to rely on acetylene), and chlorinated solvents (moving toward ethylene).

As graphic proof of the decline of acetylene and the demise of coal as a source of chemicals, acetylene is no longer even listed in trade magazine tabulations of chemical feedstocks; in 1950, it provided more of the carbon in organic chemicals than any other raw material.

Consumption of acetylene for chemical purposes is currently below 400,000 tons per year, down almost 20 percent from its highs in the mid-1960's.

THE AROMATICS-BENZENE, TOLUENE, XYLENE,

NAPHTHALENE

In the early days of the synthetic organic chemicals industry, aromatics derived from coal were sufficient to meet chemical demand. Although these same aromatics could have been derived from oil, they were more valuable to the oil companies as gasoline components.

This situation has been changing since World War II and particularly rapidly in the past 10 years. Data showing these trends are summarized in table 7.

TABLE 7.-OIL VS. COAL SOURCES FOR AROMATICS (BILLIONS OF POUNDS)

The trend is particularly marked for benzene, which makes up more than three-fourths of the aromatic chemicals recovered from coal (toluene about 15 percent, xylenes about 3 percent). Hence, as demand for toluene and xylene has grown, users have had to turn to petroleum sources almost from the beginning.

Naphthalene is a special case. Its biggest use is in making phthalic anhydride (used to make plasticizers for vinyl plastics and to make polyester and alkyd resins). When demand for phthalic anhydride approached coal tar naphthalene supply limits, producers had two choices-naphthalene from oil or phthalic anhydride from ortho-xylene from oil. Time has shown the latter to be more economical, so naphthalene demand has slackened.

The aromatics are generated in an oil refinery primarily from catalytic reforming, which gives about five pounds of toluene and three pounds of xylenes for each pound of benzene. Since, as Table 7 shows, the demand for benzene is much higher than that for toluene or xylene, some of the toluene from the catalytic reforming is further processed by hydrodealkylation to benzene or by disproportionation processes to benzenes plus xylenes.

As future ethylene capacity is expected to be based on oil fraction cracking, much future benzene (another coproduct) will be derived from this source, thus obviating the need for additional hydrodealkylating capacity.

Benzene for chemical uses competes against benzene and the other aromatics for gasoline. As lead is removed from gasoline for air pollution control purposes, the demand for aromatics for gasoline will increase, and the competition against chemical uses will stiffen.

Benzene

The biggest outlet for benzene is styrene (from which are made polystyrene, ABS resins, and synthetic rubber). Other major uses are phenol (phenolic resins, caprolactam for nylon manufacture, chemical intermediates and surfactants), cyclohexane (also for nylon manufacture), aniline (dyestuffs), and maleic anhydride (polyester resins). Polystyrene has been growing at 12 percent per year for a decade, while ABS and SAN resins are relatively new, rapidly growing product lines. Nylon in fibers, on the other hand, is a sluggish market in terms of growth. Overall, benzene demand is expected to grow at about 5-10 percent per year.

Benzene production and consumption data are summarized in tables 8 and 9.

Toluene's applications are still relatively limited, particularly as compared to benzene. Only a small portion of the toluene available from catalytic reforming (less than 10 percent) is recovered as such with the rest going into gasoline.

More than half the toluene recovered is hydrodealkylated to benzene, with the rest going into explosives, solvents, polyurethanes, and other chemical intermediates. When benzene is in adequate supply, the hydrodealkylation operations are the first to be curtailed, with the toluene so released either not recovered from the reformate or returned to gasoline by blending. Hence, the key to toluene capacity is recovery process capacity.

Toluene production and consumption data are summarized in tables 10 and 11.

The xylenes are a mixture of three compounds very similar in physical properties but rather different chemically. The ortho isomer, as indicated earlier, is finding use as a raw material for phthalic anhydride in place of naphthalene. The para isomer is used to make terephthalic acid for polyester fibers. Mixed xylenes go into gasoline. Production data for xylenes are summarized in table 13.

SYNTHESIS GAS-HYDROGEN AND CARBON MONOXIDE

Synthesis gas is a mixture of hydrogen and carbon monoxide. It, like acetylene, was originally made from coal but is now derived almost totally from natural gas or liquid petroleum fractions such as naphtha. The synthesis gas itself is used directly to make methanol and oxo alcohols. Methanol in turn is used as a solvent and as a starting material for formaldehyde (from which a range of plastics is made) and other resins for fibers, coatings, films, and adhesives. Oxo alcohols are used to make detergents, plasticizers, and a number of additional chemical intermediates.

The hydrogen and carbon monoxide are also used separately to make products. The largest tonnage item is ammonia, source of most fertilizer nitrogen content. Other derivative products are nitric acid and urea.

Hydrogen is also used extensively as a desulfurizing agent and as a reducing agent in a very broad range of organic products.

The carbon monoxide gas is used to make acrylic acid, ethylene glycol, propionic acid, butanol, and acetic acid. Reacted with chlorine, it yields phosgene, important as a starting point for isocyanates used in urethanes and as a reagent for making pesticides, specialty chemicals, and the specialty plastic, polycarbonate.

There are no data on how much synthesis gas is made. Ammonia production, however, as the major outlet, is a good indicator; production statistics for it are listed in table 13.