Environmental problem

We consider here all the objectionable alterations of nature that go beyond human health and safety. The problems are often divided into regional problems, which are limited to specific regions, and global problems, which affect the entire world. 

The release of man-made materials into the environment can have numerous harmful effects, as well as beneficial ones, but the cautious and conservative approach is to assume that any change in the environment could be potentially harmful unless proven otherwise. Actually, there is no way to prove that all the changes from the introduction of a product can be investigated within a given time period and are beneficial or neutral so, in effect, a strict application of this principle would mean a total ban on all product innovations and many existing products. 

There are numerous parameters to characterize the environmental effects of a chemical, once it is released either by accident and leakage or by disposal after the end of the usefulness of a product. We need to follow the journey of the chemicals released. 

There are many modes on how a chemical is transported in the environment. The most important mechanism is the natural flow of air, which is the most rapid method of dispersal and reaches all points on Earth. This is most important for gases and 

Many chemical and physical transformations can take place for a chemical in the environment, leading to products of transformation. Some of the most important physical and chemical transformations and their parameters are  

Although their economic importance is decreasing, progress with respect to environmental problems has also been made for the older processes which are still in use. 

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Since process design starts with the reactor, the first decisions are those which lead to the choice of reactor. These decisions are among the most important in the whole design. Good reactor performance is of paramount importance in determining the economic viability of the overall design and fundamentally important to the environmental impact of the process. In addition to the desired products, reactors produce unwanted byproducts. These unwanted byproducts create environmental problems. As we shall discuss later in Chap. 10, the best solution to environmental problems is not elaborate treatment methods but not to produce waste in the first place. 

Given that the objective is to manufacture a certain product, there are often a number of alternative reaction paths to that product. Reaction paths which use the cheapest raw materials and produce the smallest quantities of byproducts are to be preferred. Reaction paths which produce significant quantities of unwanted byproducts should especially be avoided, since they create significant environmental problems. 

In general, heterogeneous catalysts are preferred to homogeneous catalysts because the separation and recycling of homogeneous catalysts often can be very difficult. Loss of homogeneous catalyst not only creates a direct expense through loss of material but also creates an environmental problem. 

Raw materials efficiency. In choosing the reactor, the overriding consideration is usually raw materials efficiency (bearing in mind materials of construction, safety, etc.). Raw material costs are usually the most important costs in the whole process. Also, any inefficiency in raw materials use is likely to create waste streams that become an environmental problem. The reactor creates inefficiency in the use of raw materials in the following ways ... 

If an azeotropic mixture is to be separated by distillation, then use of pressure change to alter the azeotropic composition should be considered before use of an extraneous mass-separating agent. Avoiding the use of extraneous materials often can prevent environmental problems later in the design. 

Because we require a pure product, a separator is needed. The unreacted FEED is usually too valuable to be disposed of and is therefore recycled to the reactor inlet via a pump or compressor (see Fig. 4.16). In addition, disposal of unreacted FEED rather than recycling creates an environmental problem. 

Rather than send the vapor to one of the separation units described above, a purge can be used. This removes the need for a separator but incurs raw material losses. Not only can these material losses be expensive, but they also can create environmental problems. However, another option is to use a combination of a purge with a separator. 

Raw materials costs dominate the operating costs of most processes (see App. A). Also, if raw materials are not used efficiently, this creates waste, which then becomes an environmental problem. It is therefore important to have a measure of the efficiency of raw materials use. The process yield is defined as... 

Relief systems are expensive and introduce considerable environmental problems. Sometimes it is possibly to dispense with relief valves and all that comes after them by using stronger vessels, strong enough to withstand the highest pressures that can be reached. For example, if the vessel can withstand the pump delivery pressure, then a relief valve for overpressurization by the pump may not be needed. However, there may still be a need for a small relief device to guard against overpressurization in the event of a fire. It may be possible to avoid the need for a relief valve on a distillation column... 

Relief systems. Relief systems are expensive and may bring significant environmental problems with them. Strengthening vessels may be a cheaper option. 

As with safety, environmental considerations are usually left to a late stage in the design. However, like safety, early decisions often can lead to difficult environmental problems which later require complex solutions. Again, it is better to consider effluent problems as the design progresses in order to avoid complex waste treatment systems. 

Leaking fi om process flows may pose operational risks and cause environmental problems as well as economic losses. Two examples of tracer methods for testing, localising and quantifying leaks are given below. 

To solve some of the environmental problems of mixed-acid nitration, we were able to replaee sulfuric acid with solid superacid catalysts. This allowed us to develop a novel, clean, azeotropic nitration of aromatics with nitric acid over solid perfluorinated sulfonic acid catalysts (Nafion-H). The water formed is continuously azeotroped off by an excess of aromatics, thus preventing dilution of acid. Because the disposal of spent acids of nitration represents a serious environmental problem, the use of solid aeid eatalysts is a significant improvement. 

Prilling. The manufacture of ptiUs is rapidly decreasiag owiag to both environmental problems and product quaUty as compared to granules. 

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. 

Nitric Phosphate. About 15% of worldwide phosphate fertilizer production is by processes that are based on solubilization of phosphate rock with nitric acid iastead of sulfuric or phosphoric acids (64). These processes, known collectively as nitric phosphate or nitrophosphate processes are important, mainly because of the iadependence from sulfur as a raw material and because of the freedom from the environmental problem of gypsum disposal that accompanies phosphoric acid-based processes. These two characteristics are expected to promote eventual iacrease ia the use of nitric phosphate processes, as sulfur resources diminish and/or environmental restrictions are tightened. 

Amino and Phenolic Resins. The largest use of formaldehyde is in the manufacture of urea—formaldehyde, phenol—formaldehyde, and melamine—formaldehyde resins, accounting for over one-half (51%) of the total demand (115). These resins find use as adhesives for binding wood products that comprise particle board, fiber board, and plywood. Plywood is the largest market for phenol—formaldehyde resins particle board is the largest for urea—formaldehyde resins. Under certain conditions, urea—formaldehyde resins may release formaldehyde that has been alleged to create health or environmental problems (see Amino RESINS AND PLASTICS). 

Factors which may affect the cost of coal upgrading are environmental considerations such as toxicity, hazardous waste disposal, and carcinogenic properties (131). These and other environmental problems from process streams, untreated wastewaters, and raw products would figure significantly into the cost of commercialization. 

Electrolysis. GalHum can be extracted by direct electrolysis of the aluminate solution at a strongly agitated mercury cathode. The recovery from a sodium gallate solution resulting from the carbonation process is another possibiHty. This process is probably no longer operative because of the environmental problems associated with the mercury. 

Environmental Issues. Hydrothermal energy, recognized as one of the clean power sources for the twenty-first century, is not entirely free of environmental problems. 

Although 4-hydroxybenzaldehyde can be made by the saligenin route, it has been made historically by the Reimer-Tiemann process, which also produces sahcylaldehyde (64). Treatment of phenol with chloroform and aqueous sodium hydroxide results in the formation of benzal chlorides, which are rapidly hydrolyzed by the alkaline medium into aldehydes. Acidification of the phenoxides results in the formation of the final products, sahcylaldehyde and 4-hydroxybenzaldehyde. The ratio of ortho and para isomers is flexible and can be controlled within certain limits. The overall reaction scheme is shown in Figure 1. Product separation is accomphshed by distillation, but this process leads to environmental problems because of the quantities of sodium chloride produced. 

Several antimicrobials have been banned or severely restricted by the EPA based on documented or suspected toxicity or environmental problems. Others have been discontinued in the face of testing costs required by the EPA reregistration program mandated by the Pederal Insecticide, Pungicide, and Rodenticide Act (PIPRA) of 1988 (10). Some of the significant products that have become obsolete are 2,4,5-trichlorophenol/P3 -5 3 -47, sodium... 

DDT is highly toxic to fish (LC q for trout and blue gill, 0.002—0.008 ppm), and it is only moderately toxic to birds (oral LD q mallard 1300 and pheasant >2240 mg/kg). However, widespread bird kills have resulted from bioconcentration of DDT through food chains, ie, from fish or earthworms. A significant environmental problem has resulted from the specific effects of DDE on eggshell formation in raptorial birds where accumulation has caused decreases in shell thickness of 10—15%, resulting in widespread breakage. 

Alternative Methods of Curing. The presence of salt in hides and skins has been a problem for taimers. Moreover, the quantity of salt, usually 10—20% by weight in cured hides, is an environmental problem. In the discharge of the water from the rewet and washing, the soluble soHds are normally greater than 20, 000 mg/L. This amounted to 2000 4000 mg/L in the combined waste stream of the taimery. 

Due to possible environmental problems with acetone, new technologies are being developed for the production of deoiled lecithins involving treatment of Hpid mixtures with supercritical gases or supercritical gas mixtures (10—12). In this process highly viscous cmde lecithin is fed into a separation column at several levels. The supercritical extraction solvent flows through the column upward at a pressure of 8 MPa (80 bar) and temperature between 40 and 55°C. The soy oil dissolves together with a small amount of lecithin. 

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