Век химии (Английский язык для студентов химического профиля). Учебное пособие
.pdfbound to the catalyst; and as the chemical binding to the catalyst is also a chemical reaction, it may affect the kinetics.
The behavior of the catalyst is also a consideration. Particularly in high-temperature petrochemical processes, catalysts are deactivated by sintering, coking, and similar processes.
A common example of a catalytic reactor is the catalytic converter following a motor.
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MEMBRANE FILTERS
Membrane filters are widely used for filtering both drinking water and sewage (for reuse). For drinking water, membrane filters can remove virtually all particles larger than 0.2 um--including Giardia and cryptosporidium. Membrane filters are an effective form of tertiary treatment when it is desired to reuse the water for industry, for limited domestic purposes, or before discharging the water into a river that is used by towns further downstream. They are widely used in industry, particularly for beverage preparation (including bottled water). However no filtration can remove substances that are actually dissolved in the water such as phosphorus, nitrates and heavy metal ions.
Slow sand filters
Slow sand filters may be used where there is sufficient land and space as the water must be passed very slowly through the filters. These filters rely on biological treatment processes for their action rather than physical filtration. The filters are carefully constructed using graded layers of sand with the coarsest sand, along with some gravel, at the bottom and finest sand at the top. Drains at the base convey treated water away for disinfection. Filtration depends on the development of a thin biological layer, called the zoogleal layer or Schmutzdecke, on the surface of the filter. An effective slow sand filter may remain in service for many weeks or even months if the pretreatment is well designed and produces water with a very low available nutrient level which physical methods of treatment rarely achieve. Very low nutrient levels allow water to be safely sent through
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distribution system with very low disinfectant levels thereby reducing consumer irritation over offensive levels of chlorine and chlorine byproducts. Slow sand filters are not backwashed; they are maintained by having the top layer of sand scraped off when flow is eventually obstructed by biological growth.
A specific 'large-scale' form of slow sand filter is the process of bank filtration, in which natural sediments in a riverbank are used to provide a first stage of contaminant filtration. While typically not sufficiently clean enough to be used directly for drinking water, the water gained from the associated extraction wells is much less problematic than river water taken directly from the major streams where bank filtration is often used.
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LAVA FILTERS
Lava filters are similar to sand filters and may also only be used where there is sufficient land and space. Like sand filters, the filters rely on biological treatment processes for their action rather than physical filtration. Unlike slow sand filters however, they are constructed out of 2 layers of lava pebbles and a top layer of nutrientfree soil (only at the plant roots). On top, water-purifying plants (as Iris pseudacorus and Sparganium erectum) are placed. Usually, around 1/4 of the dimension of lavastone is required to purify the water and just like slow sand filters, a series of herringbone drains are placed (with lava filters these are placed at the bottom layer). Removal of ions and other dissolved substances.
Ultrafiltration membranes use polymer membranes with chemically formed microscopic pores that can be used to filter out dissolved substances avoiding the use of coagulants. The type of membrane media determines how much pressure is needed to drive the water through and what sizes of micro-organisms can be filtered out.
Ion exchange: Ion exchange systems use ion exchange resinor zeolite-packed columns to replace unwanted ions. The most common
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case is water softening consisting of removal of Ca2+ and Mg2+ ions replacing them with benign (soap friendly) Na+ or K+ ions. Ion exchange resins also used to remove toxic ions such as nitrate, nitrite, lead, mercury, arsenic and many others.
Electrodeionization. Water is passed between a positive electrode and a negative electrode. Ion exchange membranes allow only positive ions to migrate from the treated water toward the negative electrode and only negative ions toward the positive electrode. High purity deionized water is produced with a little worse degree of purification in comparison with ion exchange treatment. Complete removal of ions from water is regarded as electrodialysis. The water is often pre-treated with a reverse osmosis unit to remove non-ionic organic contaminants.
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WATER PURIFICATION
Water purification is the process of removing undesirable chemical and biological contaminants from raw water. The goal is to produce water fit for a specific purpose. Most water is purified for human consumption (drinking water) but water purification may also be designed for a variety of other purposes, including to meet the requirements of medical, pharmacology, chemical and industrial applications. In general the methods used include physical process such as filtration and sedimentation, biological processes such as slow sand filters or activated sludge, chemical process such as flocculation and chlorination and the use of electromagnetic radiation such as ultraviolet light. The purification process of water may reduce the concentration of particulate matter including suspended particles, parasites, bacteria, algae, viruses, fungi; and a range of dissolved and particulate material derived from the minerals that water may have made contacted after falling as rain. The standards for drinking water quality are typically set by Governments or by international standards. These standards will typically set minimum and maximum concentrations of contaminants for the use that is to be made of the water.
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It is not possible to tell whether water is of an appropriate quality by visual examination. Simple procedures such as boiling or the use of a household activated carbon filter are not sufficient for treating all the possible contaminants that may be present in water from an unknown source. Even natural spring water - considered safe for all practical purposes in the 1800s - must now be tested before determining what kind of treatment, if any, is needed. Chemical analysis, while expensive, is the only way to obtain the information necessary for deciding on the appropriate method of purification.
According to a 2007 World Health Organization report, 1.1 billion people lack access to an improved drinking water supply, 88 % of the 4 billion annual cases of diarrheal disease are attributed to unsafe water and inadequate sanitation and hygiene, and 1.8 million people die from diarrheal diseases each year. The WHO estimates that 94 % of these diarrheal cases are preventable through modifications to the environment, including access to safe water.[1] Simple techniques for treating water at home, such as chlorination, filters, and solar disinfection, and storing it in safe containers could save a huge number of lives each year.
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ENVIRONMENTAL ENGINEERING SCIENCE
Environmental Engineering Science (EES) is a multidisciplinary field of engineering that combines the biological, chemical and physical sciences with the field of engineering. This major traditionally requires the student to take many basic engineering classes in fields such as thermodynamics, advanced math, computer modeling and simulation as well as technical classes in subjects such as statics, mechanics, hydrology, and fluid dynamics. As the student progresses, the upper division elective classes define a specific field of study for the student with a choice in a wide range of science, technology and engineering related classes[1]:
In chemical engineering and related fields, a unit operation is a basic step in a process. For example in milk processing, homogenization, pasteurization, chilling, and packaging are each unit
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operations which are connected to create the overall process. A process may have many unit operations to obtain the desired product.
Historically, the different chemical industries were regarded as different industrial processes and with different principles. Chemical engineering unit operations consist of five classes:
Fluid flow processes, including fluids transportation, filtration, solids fluidization. Heat transfer processes, including evaporation, condensation
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RUBBER
The Part Played by Rubber in Modern Life. – Rubber is indispensable to modern civilization. Its importance in every form of transport for tyres and tubes is self-evident. In its other applications it plays equally important roles. About 80 per cent of all rubber is used in the motor industry, a large proportion of the remainder going into such articles as belting, packings, hose, and innumerable other types of products. Most of these articles are absolutely vital to the operation of the industry in general. A large quantity of rubber is made into rubber footwear and rubberised fabrics. Rubber has been in use for well over a century. But its really important and large-scale application runs parallel with the development of the motor-car.
Historical. – Rubber trees are native to many parts of Africa and the Far East, but there is no record of rubber or the trees that produce it prior to the discovery of America.
By the end of the eighteenth century the general properties of rubber were known to scientists throughout Europe. In the 19th century Charles Macintosh discovered that naphtha, one of the byproducts from gas manufacture, was an excellent solvent for rubber.
In 1823 Macintosh patented his discovery. The original process was for the manufacture of what came later to be known as doubletexture fabric. A “sandwich” was made with cotton or other fabric on the outside and a ‘‘filling” of rubber which had been deposited from solution. This method, still in use, has the advantage that the cloth protects the rubber.
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Vocabulary List indispensable – необходимый;
rubberized fabrics – прорезиненные изделия; naphtha – лигроин, сырая нефть, керосин; by-product – побочный продукт;
solvent – растворитель;
double-texture fabric – ткань, имеющая двойную структуру, ткань с наполнителем;
solution – раствор.
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SYNTHETIC RUBBER
Historical. – When it became clear that rubber could be broken down to isoprene it was natural that the reverse process should be attempted. As early as 1887 it was observed that, exposed to light in a sealed tube for a long time, isoprene underwent a change; on adding alcohol a tough rubbery mass was obtained. In 1902 the spontaneous polymerization of isoprene into rubber was recorded.
This spontaneous polymerization is an extremely slow process. After four years’ storage a sample of isoprene had become thick but had not yet yielded a solid polymer. In addition to isoprene, its isomers received attention and in 1900-1901 Kondakov prepared what was probably the first commercial production of synthetic rubber.
As well as isoprene, butadiene itself received attention. But it was not until 1910 that Lebedev reported it to yield a rubberlike polymer on heating. Butadiene is now the most important diene for the preparation of synthetic rubbers; it polymerizes far more readily than substituted dienes.
Synthetic Rubber Manufacture. – Synthetic rubber manufacture may be divided into two main steps – production of the monomers, and their polymerization. Manufacturing of monomers involves a series of steps, starting with the selected raw material. Both the selected raw material and the route followed may differ, still yielding the same end product. Butadiene, for example, the most important monomer so far utilized, may be synthesized from acetylene and also from alcohol.
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Two direct methods are in current use for conversion of alcohol to butadiene. Both are due to the discoveries of Russian chemists. The acetaldehyde route from alcohol was first tried in Russia, a pilot plant being erected in Moscow, but the process was abandoned in 1922. In 1928, S. V. Lebedev and his collaborators were awarded a prize for a new method of producing synthetic rubber. The Lebedev process consists essentially in the direct conversion of ethyl alcohol to butadiene by a special mixed catalyst which removes both water and hydrogen.
Vocabulary List break down – распадаться;
reverse process – обратный процесс; sealed tube – запечатанный сосуд; rubberlike – каучукоподобный;
spontaneous polymerization – самопроизвольная полимеризация;
yield – превращаться; sample – образец;
route – метод/способ получения; utilize – использовать; conversion – превращение;
acetaldehyde – ацетальдегид, уксусный альдегид; ethyl alcohol – винный спирт;
catalyst – катализатор; remove – удалять.
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DIRECT USES OF LATEX
Latex is compounded by introducing the ingredients in the form of very fine aqueous dispersion, colloidal where possible. Compounding is carried out in pebble mills, and also in special pieces of equipment known as colloidal mills. Generally speaking, the same ingredients are added to latex as to rubber; it should be noted that reinforcing fillers do not affect latex. It has been found desirable to
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add a certain number of special ingredients, the principal ones being as follows:
a)Dispersing agents, which prevent agglomeration of the colloidally - dispersed particles.
b)Stabilisers, to prevent coagulation during processing of the
latex.
c)Thickeners, for increasing the viscosity of the mix as
required.
d)Wetting agents, to reduce the surface tension of the latex thus enabling it to penetrate more easi1y into materials to be impregnated with it.
Various processes exist for the working up of latex mixes. In
the dipping process a former (usually of porcelian, aluminium or glass) is dipped into the mix, and then withdrawn, the thin layer of latex adhering to it being then dried. An article of the desired thickness is obtained by repeated dripping. Electrodeposition is the process by which rubber is deposited from the latex when an electric current is passed through the bath, the particles of rubber being deposited on an anode in the form of the object to be reproduced. Latex may be used for impregnation and rubberising, not only of textiles but of many other materials, e.g. paper, leather fibres, and horsehair. Goods may also be made by moulding with latex. The field in which latex finds widest application is that of cellular goods mattresses, pillows – made of latex foam, usually obtained by beating the mix, then gellifying as in the case of moulding, followed by drying.
Vocabulary List dispersion – дисперсия; compounding – смешивание; pebble mills – галечные мельницы;
dispersing agents – диспергатор, диспергирующий агент; agglomeration – скопление;
colloidally-dispersed particles – коллоидные дисперсные частицы;
coagulation – коагуляция;
thickener – сгуститель, агент сгущения; viscosity – вязкость;
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impregnate – пропитывать; impregnation – пропитка; dipping – окунание, макание;
electrodeposition – электроотложение; rubberising – прорезинивание;
moulding – формование, формирование; cellular – ячеистый, клеточный;
foam – пена;
gelify – затвердевать.
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APPLICATION OF POLYURETHANE ELASTOMERS
TODAY AND IN THE FUTURE
The high performance properties make polyurethane elastomers the material of choice for an endless assortment of mechanical and manufacturing goods, including gaskets, casters, hammerheads, elastomer-lined pipe, oil pipeline pigs, cable jacketing and cone dischargers used in taconite mining. They are also used in electrical potting, farming equipment, recreational goods including golf carts and snowmobiles, golf ball covers, swim fins, bicycle tires, football helmet liners, bowling balls and pins, and pour-in-place running tracks. Medical equipment uses include antishock trousers and artificial heart chambers.
Now let us look at some examples.
Conduit to life. The disposable tubing used in heart/lung machines in the well over 100,000 open heart and coronary bypass operations performed yearly used to be made entirely of PVC. Now, a PVC tube lined with polyurethane elastomer provides improved compatibility with blood and better resistance to the abrasion caused by the continuous rolling of peristaltic pumps. Because polyurethane elastomers can be fabricated without plasticizers, there is no danger of these toxic compounds migrating into the blood.
TPUs get the boot. Polyurethane elastomers provide strength, stiffness and flex properties demanded of a ski boot at subzero temperatures. Light weight and superior comfort, acceptable cycle
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times, consistent color and a long-lasting, hard, high gloss finish are other advantages TPUs bring to this application.
Chopper protector. The Army wanted a one-piece helicopter cover to keep copters weather-safe and action-ready. The covers had to be flexible, yet tough, as well as abrasion, weather and fuel resistant and repairable in the field. They also wanted covers in different colours to distinguish various models of aircraft. Polyurethane elastomers filled the bill.
Tags iron out herd management. Manufacturers of the millions of ear tags made yearly for domestic use and export need a material that resists degradation by moisture, oxidation, tearing and abrasion; that remains flexible even at low temperatures; and is lightweight It also helps if the material can be pigmented and even impregnated with insecticide. Polyurethane elastomers fit these criteria, offering cattle owners an excellent aid to herd management
And what about future applications of elastomers?
Tomorrow may see additional applications for polyurethane elastomers in space. Chances are good that the high performance characteristics of these materials will also be used to expand the horizons of telecommunications, electronics and other burgeoning technologies.
Whatever chapters the next decade or so adds to the history of elastomers, one thing is certain: new opportunities to exploit the inherent and unduplicated versatility and performance of these materials will continue to arise in the marketplace - and polyurethane producers will continue to respond.
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ERA OF ELASTOMERS
Imagine a material that combines the toughness and loadbearing capacity of metal, the abrasion resistance of ceramics and the resilience of rubber. Add several processing and performance options for economy and efficiency and you've got polyurethane elastomers, extremely versatile materials which can be subdivided into five groups:
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