Efficiency of Raw Materials

Measures can be used to characterize a chemical process in term of environmental efficiency of raw materials, as described below [2]. Consider the reaction  

A is the reference reactant, B the coreactant, P the product, R the byproduct (valuable) and S the waste product. 

Stoichiometric yield RY is defined as the ratio of the actual product to the theoretical amount that may be obtained from the reference reactant  

This measure is useful, but gives only a partial image of productivity, since it ignores the contribution of other reactants and auxiliary materials, as well as the formation of secondary valuable products. 

The next measures are more adequate for analyzing the efficiency of a process by material-flow analysis (MFA). Two types of materials can be distinguished  

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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... 

Phenone is produced by the acetylation of benzyl chloride with o-xylene via a Friedel-Crafts reaction. Table 1.1 presents the elements of the material balance. Calculate the efficiency of raw materials. 

By a systems approach, a process is designed as a complex system of interconnected components so as to satisfy agreed-upon measures of performance, such as high economic efficiency of raw materials and energy, down to zero waste and emissions, together with flexibility and controllability faced with variable production rate. 

A reactive distillation (RD) process would bring evident technological and ecological advantages. An important feature is that the reactants can be fed in the stoichiometric ratio ensuring in this way the maximum efficiency of raw materials. Unlike a batch process, where the excess of alcohol is recovered by costly distillation, higher reaction rate can be achieved by internal alcohol recycle. However, the presence of water as a byproduct makes this wish much more difficult than it appears. 

Economics This process uses a proprietary resin catalyst system it has consistently achieved greater than 98% efficiency of raw-material utilization. The process is simple and requires few processing steps resulting in a low equipment count and capital cost. 

Quality of glass depends on the efficiency of raw material mixing... 

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 ... 

Single-reaction-step processes have been studied. However, higher selectivity is possible by optimizing catalyst composition and reaction conditions for each of these two steps (40,41). This more efficient utilization of raw material has led to two separate oxidation stages in all commercial faciUties. A two-step continuous process without isolation of the intermediate acrolein was first described by the Toyo Soda Company (42). A mixture of propylene, air, and steam is converted to acrolein in the first reactor. The effluent from the first reactor is then passed directiy to the second reactor where the acrolein is oxidized to acryUc acid. The products are absorbed in water to give about 30—60% aqueous acryUc acid in about 80—85% yield based on propylene. 

Prices of spandex fibers are highly dependent on thread size selling price generally increases as fiber tex decreases. Factors that contribute to the relatively high cost of spandex fibers include (/) the relatively high cost of raw materials, (2) the small size of the spandex market compared to that of hard fibers which limits scale and thus efficiency of production units, and (J) the technical problems associated with stretch fibers that limit productivity rates and conversion efficiencies. 

Methane. As our most abundant hydrocarbon, methane offers an attractive source of raw material for organic chemicals (see Hydrocarbons). Successful commercial processes of the 1990s are all based on the intermediate conversion to synthesis gas. An alternative one-step oxidation is potentially very attractive on the basis of simplicity and greater energy efficiency. However, such processes are not yet commercially viable (100). 

Cerium(IV) oxidizes ferrous ion to ferric and the cerium ions are stable under the conditions of a molten silicate—glass bath. Furthermore, cerium itself has no absorption ia the visible region. Economical additions of cerium, as cerium concentrate, enable the efficient use of raw materials containing trace quantities of iron (26). 

The trends dcinoiistratc the capability of industiy to improve energy efficiency when it has the incentive to do so. Energy requirements can be cut by new process development. In addition, the amount of raw materials demanded by a society tends to decline as countries reach certain stages of industrial development, which leads to a decrease in industrial energy use. The accounting of trends in structural shift, material intensity, and technical energy efficiency... 

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