Process chemical

Neutralization is applied to many processes in water technology. In water treatment it concerns particularly removal of aggressive CO2 from water which consists in addition of alkaline agents to water (e.g. Ca(OH)2, NaOH, Na2C03) or in filtration through various materials removing carbon dioxide (marble, dolomite, fermago, etc.). 

Precipitation is a process in which dissolved compounds are separated from the reaction medium in the form of low soluble compounds in their solid states, which can then be separated by sedimentation, filtration, centrifugation, flotation, etc. Precipitation is carried out either by a chemical change of dissolved substance, or by a change of the reaction medium. As precipitants, mostly acid, base or salt solutions are used. 

If the substances removed enter the crystalline lattice of the precipitating solid phase, one refers to primary effect precipitation reactions. During the precipitation reactions with a secondary effect, pollutants enter the particles of the precipitate via sorption or mutual coagulation. 

The transition category between these two groups of reactions is represented by the process of alkaline clarification, during which suspended coUoid substances are removed by coagulation, and calcium, magnesium, iron and manganese by precipitation. 

Precipitation reactions are used in water treatment for the removal of Ch, and Mg by decarbonization (addition of lime), employing the low solubility of CaCOg and Mg(OH)2. 

The gas fluidized bed is a good medium in which to carry out a chemical reaction involving a gas and a solid. Advantages of the fluidized bed for chemical reaction include  

The excellent solids circulation within the bed promotes good heat transfer between bed particles and the fluidizing gas and between the bed and heat transfer surfaces immersed in the bed. 

Homogeneous gas-phase reactions Heterogeneous non-catalytic reactions Heterogeneous catalytic reactions 

Rapid heating of entering gas. Uniform controllable temperature 

Ease of solids handling. Temperature uniformity. Good heat transfer 

Whether the end product is a pharmaceutical or a plastic bag, each industry is part of a value chain. The pharmaceutical company that markets the drug depends on fine chemicals or speciality producers to make the active pharmaceutical or its precursors. In turn, the commodity chemical companies supply the building blocks for the basic fine chemicals, whilst the refiners produce the feedstock for the commodity chemical companies. 

Commodity chemicals share the same benefits of economies of scale. Typical process units are 1-2 orders of magnitude smaller than refinery units, although large methanol synthesis plants can produce up to several Mt/a (Section 4.7.1). Since a chemically pure material is being produced, often in a stoichiometric reaction, the catalyst system now becomes more specialized, the reactor may require special metallurgy, and product purification starts to be an issue. 

The products are not necessarily single compounds. Polymers for example are a range of compounds of varying molecular weights but which are chemically identical. For commodity chemicals the expense of feed purification, a more exotic catalyst, the corrosion resistant metallurgy and the need for a product purification train, start to add cost. But like refinery processes these are dedicated to one product, run 24 hours a day and are part of an integrated complex benefiting from heat and waste recovery. As the cost to build these refinery and petrochemical complexes is many billions of dollars, time is needed to pay back the investment. Once built, both commodity chemical and refinery 

The fine and speciality chemicals industries span a wide range from the manufacture of well defined, characterizable chemical compounds such as are used in pharmaceuticals, to making compounds which have a critical performance in a defined end-use application for a specific customer, such as inks for ink-jet printers where the design of the printer is closely matched to the performance of the ink. Indeed the manufacture of a catalyst is an example of a speciality chemical in itself. 

The scale of production of a fine chemical can range from a few t/a up to tens of kt/a. Two of the final intermediates in the synthesis of the world s top selling drug, the anticholesterol Lipitor , or atorvastin, are only produced on a scale of 500 t/a each. The consequence of the smaller scale and more specialist nature of these industries, is that the processes are far more likely to be batch or discontinuous. Thus process units will be flexible to produce more than one product and the product s lifetime in the market may be comparatively short, either for economic or performance reasons. However, product added value is high. 

A num ber of different techniques have been used to study the surface preparation techniques used prior to anodic oxidation. For device fabrication, mechanical polishing Is usually necessary to insure a relatively flat surface. Some chemical treatment is necessary to remove the mechanical damage induced by grit polishing. Often etching or chem-mechanical polishing is used to remove this damaged layer. However, it has been shown that chemical treatments do not leave a stoichiometric surface (27-30)(63). A kinetic study of the reaction of 0.1N Br in methanol with (Hg,Cd)Te under etch conditions found the relative rates of reaction of the individual constituents to be  

A closely related experiment attempted to determine the effect of hydroxide ion concentration on the rate of anodic processes in the absence of polarization (78). This was done with a series of Tafel plots (79) (l-V relationship near the region where the OCP) in varying hydroxide ion concentrations. The results indicated that the anodic current representative of dissolution rate in the absence of overpotential is independent of hydroxide concentration. 

For a simple system in which this relationship is only affected by the diffusion coefficient of the species being reduced, a straight line should be observed. This is the case for o.l N KOH. However, as the KOH concentration is dropped, non-iinear behavior is observed which should be indicative of a change of species being reduced at the ring, resuiting from an increased half-life of whatever species is reacting with the hydroxide ion. 

Another interesting component of the impedance that came to light 

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The most frequent application of phase-equilibrium calculations in chemical process design and analysis is probably in treatment of equilibrium separations. In these operations, often called flash processes, a feed stream (or several feed streams) enters a separation stage where it is split into two streams of different composition that are in equilibrium with each other. 

This text will attempt to develop an understanding of the concepts required at each stage during the creation of a chemical process design. 

Thus the complexity of chemical process synthesis is twofold. First, can we identify all possible structures Second, can we optimize each structure for a valid comparison When optimizing the structure, there may be many ways in which each individual task can be performed and many ways in which the individual tasks can be interconnected. This means that we must simulate and optimize... 

In broad terms, there are two approaches to chemical process design ... 

Catalytic gas-phase reactions play an important role in many bulk chemical processes, such as in the production of methanol, ammonia, sulfuric acid, and nitric acid. In most processes, the effective area of the catalyst is critically important. Since these reactions take place at surfaces through processes of adsorption and desorption, any alteration of surface area naturally causes a change in the rate of reaction. Industrial catalysts are usually supported on porous materials, since this results in a much larger active area per unit of reactor volume. 

Douglas, J. M., Conceptual Design of Chemical Processes, McGraw-Hill, New York, 1988. 

Walas, S. M., Chemical Process Equipment Selection and Design, Butterworth, Reading, Mass., 1988. 

The recycling of material is an essential feature of most chemical processes. Therefore, it is necessary to consider the main factors which dictate the recycle structure of a process. We shall start by considering the function of process recycles and restrict consideration to continuous processes. Later the scope will be extended to include batch processes. 

Growl, D. A., and Louvar, J. F., Chemical Process Safety Fundamentals with Applications, Prentice-Hall, Englewood Cliffs, N.J., 1990. 

Two classes of waste from chemical processes can be identified ... 

The purpose of chemical processes is not to make chemicals The purpose is to make money. However, the profit must he made as part of a sustainable industrial activity which retains the capacity of ecosystems to support industrial activity and life. This means that process waste must be taken to its practical and economic minimum. Relying on methods of waste treatment is usually not adequate, since waste treatment processes tend not so much to solve the waste problem but simply to move it from one place to another. Sustainable industrial activity also means that energy consumption must be taken to its practical and economic minimum. Chemical processes also must not present significant short-term or long-term hazards, either to the operating personnel or to the community. 

In addition to battery limits investment, off-site investment is required. This includes all structures, equipment, and services that do not enter directly into the chemical process. Within this broad category there are two major classifications, namely, utilities and service facilities. 

Costs of utilities are considered from their sources within the site to the limits of the chemical process served. 

DILLON Materials Selection for the Chemical Process Industries freeman Hazardous Waste Minimization... 

Chemical processes will in the future need to be designed as part of a sustainable industrial development which retains the capacity of ecosystems to support industrial activity and life. This book therefore places a high emphasis on waste minimization and energy efficiency in the context of good economic performance and good health and safety practices. 

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