Disposal problems

The use of excess reactants, diluents, or heat carriers in the reactor design has a significant effect on the flowsheet recycle structure. Sometimes the recycling of unwanted byproduct to the reactor can inhibit its formation at the source. If this can be achieved, it improves the overall use of raw materials and eliminates effluent disposal problems. Of course, the recycling does in itself reuse some of the other costs. The general tradeoffs are discussed in Chap. 8. 

Desulfurize the flue gas. A whole range of processes have been developed to remove SO, from flue gases, such as injection of limestone into the furnace, absorption into wet limestone after the furnace, absorption into aqueous potassium sulfite after the furnace, and many others.However, the byproducts from many of these desulfurization processes cause major disposal problems. 

Other compounds which may be found in crude oil are metals such as vanadium, nickel, copper, zinc and iron, but these are usually of little consequence. Vanadium, if present, is often distilled from the feed stock of catalytic cracking processes, since it may spoil catalysis. The treatment of emulsion sludges by bio-treatment may lead to the concentration of metals and radioactive material, causing subsequent disposal problems. 

By introduction of Real-Time X-Ray the consumable costs and the waste disposal problems are reduced. The capacity of the system allowed an increase of production volume without the need for a investment for an additional film X-Ray unit which would have been needed otherwise. 

The terms green chemistry and environmentally benign synthesis have been coined to refer to procedures explicitly designed to minimize the for mation of byproducts that present disposal problems Both the National Science Foundation and the Envi ronmental Protection Agency have allocated a por tion of their grant budgets to encourage efforts m this vein... 

Environmental Considerations. Environmental problems in Ziegler chemistry alcohol processes are not severe. A small quantity of aluminum alkyl wastes is usually produced and represents the most significant disposal problem. It can be handled by controlled hydrolysis and separate disposal of the aqueous and organic streams. Organic by-products produced in chain growth and hydrolysis can be cleanly burned. Wastewater streams must be monitored for dissolved carbon, such as short-chain alcohols, and treated conventionally when necessary. 

Throughout the history of the development of fats and oils, many wet chemical methods have been developed to assess the quaUty of the raw materials and products. As sophisticated instmmentation develops, many of the wet methods are being replaced. Particular attention is being given to methods that eliminate the use of solvents which cause an environmental disposal problem. Many in-line sensors are also being developed to allow corrections of critical parameters to be made more quickly in the process. 

Phosphoric acid [7664-38-2] is rarely used because of cost and disposal problems. Nitric acid [7697-37-2] is to be avoided because it is known to cause catastrophic damage to resin, equipment, and personnel if appropriate controls and monitoring systems are not installed. 

However, rotary furnaces tend to produce more exhaust gas and fumes, require more skill fill manipulation, and are more labor intensive. Also, the slags produced in the rotary furnaces, soda or fayaUte [13918-37-1] slags, normally do not pass the toxic characteristic leach procedure (TCLP) test and pose a disposal problem. 

Mercury from these accumulated wastes is generally best recovered by total degradation in stills, where metallic mercury is condensed and collected. The recovery costs are amply compensated by the value of the metal recovered. Moreover, disposal problems are either eliminated or severely diminished. 

Nonregenerative caustic treatment is generally economically appHed when the contaminating materials are low in concentration and waste disposal is not a problem. However, the use of nonregenerative systems is on the decline because of the frequentiy occurring waste disposal problems that arise from environmental considerations and because of the availabiHty of numerous other processes that can effect more complete removal of contaminating materials. 

Additional phosphonic acid is derived from by-product streams. In the manufacture of acid chlorides from carboxyUc acids and PCl, phosphonic acid or pyrophosphonic acid is produced, frequentiy with copious quantities of yellow polymeric LOOP. Such mixtures slowly evolve phosphine, particularly on heating, and formerly were a disposal problem. However, purification of this cmde mixture affords commercial phosphonic acid. By-product acid is also derived from the precipitate of calcium salts in the manufacture of phosphinic acid. As a consequence of the treatments of the salt with sulfuric acid, carbonate is Hberated as CO2 and phosphonic acid goes into solution. 

This PAG contains 1—2% sulfate as soluble calcium sulfate. Sulfate has been found to make PAG products unstable precipitate forms in less than one week at 50°G. Sulfate, however, has also been seen to increase PAG activity in water clarification and is thus intentionally added in one preparation (24). Precipitated calcium sulfate creates a sludge disposal problem. Typical Al content as AI2O2 of PAG products made from alum is 6 —8%. 

Commercially, a small amount of the 4,4 -MDA is isolated by distillation from PMDA. Depending on the process employed, the removal of MDA can be partial (as is done with the isocyanates) or total. Partial removal of MDA gives some processiag latitude but yields of 4,4 -MDA are reduced. Distillation residues from PMDA manufacture that contain less than 1% MDA pose a disposal problem. Processes for the regeneration of MDA by heating these residues ia the presence of aniline and an acid catalyst have been patented (33—35). Waste disposal of PMDA is expensive and reclamation processes could become commercially viable. The versatility of the isocyanate process, however, can be used to avoid the formation of low MDA content distillation residues. 

Further Modifications. There have been attempts to improve the pulp strength and decrease the energy requirement of the groundwood process by the addition of chemicals, eg, sodium carbonate or sodium sulfite. Although some benefits can be obtained, the additional costs and chemical disposal problems have not been justified. Presteaming of wood is practiced in Europe to add moisture and to soften the lignin, which is especially advantageous for certain hardwoods. 

Dialkyldimethyl and alkyltrknethyl quaternaries can be prepared direcdy from secondary and primary amines as shown ia equations 7 and 8, respectively. This process, known as exhaustive alkylation, is usually not the method of choice on a commercial scale. This technique requires the continuous addition of basic material over the course of the reaction to prevent the formation of amine salts (223,224). Furthermore, products such as inorganic salt and water must be removed from the quaternary. The salt represents a significant disposal problem. 

Half of all sodium sulfate made is actually a waste by-product and may even present a disposal problem. For this reason, manufacturers sell it at a low price to ensure quick sale. This in turn sets the price for all naturally produced sodium sulfate and tends to keep values low. Figure 3 shows price fluctuations from 1970 to 1995. 

Absorption Processes. Most flue gas desulfurization (FGD) systems are based on absorption of the sulfur dioxide into a n on regen erabi e alkali-salt solvent. Sulfur absorbed using n on regen erabi e solvents is not recovered and the alkali sulfite—sulfate produced presents a disposal problem. 

One problem resulting from the hot-water process is disposal and control of the tailings. Each ton of oil sand in place has a volume of ca 0.45 m, which generates ca 0.6 m of tailings and gives a substantial volume gain. If the mine produces 200,000 t/d of oil sand, volume expansion represents a considerable soflds disposal problem. 

Recycling. Beryllium is typicaUy recycled, thus it is not a waste disposal problem in fact, it is rarely a waste product at aU. Because of the high cost of producing beryUium, beryUium producers repurchase clean scrap from customers for recycling and reuse. 

The polymer-supported catalysts are thus important conceptually in linking catalysis in solutions and catalysis on supports. The acid—base chemistry is fundamentally the same whether the catalytic groups are present in a solution or anchored to the support. The polymer-supported catalysts have replaced acid solutions in numerous processes because they minimise the corrosion, separation, and disposal problems posed by mineral acids. 

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