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An overview of the chemicals industry in the united states

The number of environmental regulations that the chemical industry must comply with is so extensive that specialized consulting firms have been formed to aid the industry in handling them. The emissions from a chemical process can be related to the specific process.

A plant manufacturing a resin might be expected to emit not only the resin being manufactured but also some of the raw material and some other products which may or may not resemble the resin. A plant manufacturing sulfuric acid can be expected to emit sulfuric acid fumes and SO2. A plant manufacturing soap products could be expected to emit a variety of odors. Depending on the process, the emissions could be any one or a combination of dust, aerosols, fumes, or gases.

The emissions may or may not be odorous or toxic. Some of the primary emissions might be innocuous but later react in the atmosphere to form an undesirable secondary pollutant. A flowchart and material balance sheet for the particular process are very helpful in understanding and analyzing any process and its emissions.

In any discussion of the importance of emissions from a particular process for an area, several factors must be considered— 1 the percentage of the total emissions of the area that the particular process emits, 2 the degree of toxicity of the emissions, and 3 the obvious characteristics of the source which can be related to either sight or smell.

Air pollutant emissions from these various processes must be controlled. Sulfuric acid is one of the major inorganic chemicals in modern industry. The aerosol mists are particularly damaging to paint, vegetation, metal, and synthetic fibers. Other processes producing acids, such as nitric, acetic, and phosphoric acids, can be expected to produce acid mists from the processes themselves an overview of the chemicals industry in the united states well as various toxic and nontoxic gases.

The particular process must be thoroughly studied to obtain a complete listing of all the specific emissions. The major acids produced are hydrochloric, hydrofluoric, nitric, phosphoric, and sulfuric. The emissions and usual control methods for the various acid and manufacturing processes are shown in Table 31.

  • Several mercury cell chloralkali plants in Japan have been converted to diaphragm cells to eliminate the poisonous levels of methyl mercury found in fish;
  • Chemical products are used in many common household products such as soaps, detergents, and cleaners.

Major bases and caustics produced by the chemical industry are calcium oxide limesodium carbonate soda ashand sodium hydroxide caustic soda. The emissions and usual control methods for the various bases and their manufacturing processes are shown in Table 31.

The PO4 in the rock may then be reacted with sulfuric acid to produce normal superphosphate fertilizer. Over 100 plants operating in the United States produce approximately a billion kilograms of phosphate fertilizer per year. The particulate and gaseous fluoride emissions cause greatest concern near phosphate fertilizer plants.

Fertilizer production is dependent on the production of phosphates and nitrates. Phosphate rock preparation generates some dry particulate matter during drying, grinding, and transferring of the rock. These emissions are controlled by wet scrubbers and baghouses. The atmospheric emissions and control methods for the production processes are shown in Table 31. Ammonium nitrate fertilizer is produced by the neutralization of nitric acid with ammonia.

The primary emission is the dust or fume of ammonium nitrate from the prill tower. The material is of submicron size and, therefore, highly visible. Control is usually performed by a wet scrubber followed by a mist eliminator. Air pollutants can be emitted from several sites in Figure 31.

There is also water pollution and the opportunity for water-to-air emissions of compounds, such as slurries and gypsum ponds that contain scrubber waste. The reactor and ammoniator-granulator produce emissions of gaseous ammonia, gaseous fluorides such as hydrogen fluoride HF and silicon tetrafluoride SiF4as well as particulate ammonium phosphates.

These are commonly combined and passed through primary and secondary scrubbers. Exhaust gases from the dryer and cooler also contain ammonia, fluorides and PM, which are usually combined and passed through cyclones and primary and secondary scrubbers. The PM emissions and low ammonia and fluoride concentrations from product sizing and material transfer operations are controlled in this manner.

Exhaust streams from the reactor and ammoniator-granulator pass through a primary scrubber, in which phosphoric acid is used to recover ammonia and particulate. Exhaust from the dryer, cooler and screen first are sent to cyclones for PM recovery, and next to primary scrubbers.

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Materials collected in the cyclone and primary scrubbers are recovered and returned to the process. The exhaust is sent to secondary scrubbers, where recycled gypsum pond water serves as a scrubbing liquid to control the emissions of F-compounds.

The scrubber effluent recirculates to the gypsum pond. Primary scrubbing equipment at fertilizer plants commonly includes venturi and cyclonic spray towers, with impingement scrubbers and spray-crossflow packed bed scrubbers serving as secondary controls. Mainly to recover ammonia, primary scrubbers often use phosphoric acid of 20 to 30 percent as scrubbing liquor.

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Secondary scrubbers generally use gypsum and pond water for F control. Although this is the general configuration, any combinations and variations of the set-up exist, e. Existing plants are equipped with ammonia recovery scrubbers on the reactor, ammoniator-granulator and dryer, and particulate controls on the dryer and cooler. Emission control efficiencies for ammonium phosphate plant control equipment generally range from 94 to 99 percent for ammonium, 75 to 99.

Both processes emit chlorine to the atmosphere from various streams and from handling and loading facilities.

If the chlorine concentration is less, the usual practice is to scrub the vent gases with an alkaline solution. Mercury is emitted from the mercury cell process from ventilation systems and by-product streams.

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Control techniques include 1 condensation, 2 mist elimination, 3 chemical scrubbing, 4 activated carbon adsorption, and 5 molecular sieve absorption. Several mercury cell chloralkali plants in Japan have been converted to diaphragm cells to eliminate the poisonous levels of methyl mercury found in fish. All of the bromine produced in the United States is extracted from naturally occurring brines using steam extraction.

The major air pollution concern is H2S from the stripper if H2S is present in the brine.

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The H2S can either be oxidized to SO2 in a flare or sent to a sulfur recovery plant. However, the petrochemical processes that use air-oxidation-type reactions normally vent large, continuous amounts of gaseous emissions to the atmosphere. Six major petrochemical processes employ reactions using air oxidation. They are the basic components of plastics and are also used for coatings on paper, particleboard, and other surfaces that require a decorative, protective, or special-purpose finish.

The common characteristic of resins is that heat is used in their manufacture and application, and gases are exhausted from these processes. Some of the gases that are economically recoverable may be condensed, but a large portion is lost to the atmosphere. Since most resins and their by-products have low-odor thresholds, disagreeable odor is the most common complaint against any operation using them.

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The same may be true of operations preparing paints, shellac, inks, and other protective or decorative coatings. The compounds emitted to the atmosphere are gases, some with extremely low-odor thresholds. The atmospheric emissions from varnish cooking appear to have little or no recovery value, whereas some of the solvents used in paint preparation are routinely condensed for recovery and returned to the process.

If a paint finish is baked to harden the surface by removal of organic solvents, the solvents must either be recovered, destroyed, or emitted to the atmosphere. The last course, emission to the atmosphere, is undesirable and may be prohibited by the air pollution control agency.