Raw materials variations

Chemical process systems are subject to uncertainties due to many random events such as raw material variations, demand fluctuations, equipment failures, and so on. In this chapter we will utilize stochastic programming (SP) methods to deal with these uncertainties that are typically employed in computational finance applications. These methods have been very useful in screening alternatives on the basis of the expected value of economic criteria as well as the economic and operational risks involved. Several approaches have been reported in the literature addressing the problem of production planning under uncertainty. Extensive reviews surveying various issues in this area can be found in Applequist et al. (1997), Shah (1998), Cheng, Subrahmanian, and Westerberg (2005) and Mendez et al. (2006). 

Successful scale-up of the tableting process also requires control of the raw materials used in compaction. Typically, pharmaceutical excipients vary in their physicochemical properties, which result in batch-to-batch variations. The tableting process, especially direct compression processes where there is limited raw material alteration before compaction, is susceptible to raw material variation, which may be magnified upon scale-up. Compaction science affords the ability to fingerprint raw materials, including the drug substance, to determine if the same compaction properties will be observed from batch to batch. This also allows for a rational approach for determining alternate vendor sources of the same materials. 

Your preparation should also include following a realistic simulation of a process through a complete phase of eight to ten cycles. Realistic simulation implies that measurements of the response to be optimized (e.g., yield, profit, etc.) include some error, or noise, t)-pical of that caused by such factors as raw-material variations, equipment fluctuations and instrument deviations. Because of the conservative nature of EVOP, the response changes and the noise may occasionally have comparable values however, as the number of cycles increases, the simulation will show that even though the best run may vary from cycle to cycle, the effects of the noise will eventually average out so that the true responses and variable effects can be determined. At the completion of a phase, the worksheet calculations... 

The particle size of an emulsion is an important factor in its application and it is also a useful indicator of stability. A robust recipe will produce latices with a small spread of particle size. There will always be variations in weighing or metering reactants, in reaction temperatures and times as well as raw material variations. If these variations do not cause particle instability, good consistency of particle size will result. The first sign of instability is particle agglomeration, which will give an increase in particle size if moderate and emulsion breakdown if highly unstable. 

There are numerous variations of the wet process, but all involve an initial step in which the ore is solubilized in sulfuric acid, or, in a few special instances, in some other acid. Because of this requirement for sulfuric acid, it is obvious that sulfur is a raw material of considerable importance to the fertilizer industry. The acid—rock reaction results in formation of phosphoric acid and the precipitation of calcium sulfate. The second principal step in the wet processes is filtration to separate the phosphoric acid from the precipitated calcium sulfate. Wet-process phosphoric acid (WPA) is much less pure than electric furnace acid, but for most fertilizer production the impurities, such as iron, aluminum, and magnesium, are not objectionable and actually contribute to improved physical condition of the finished fertilizer (35). Impurities also furnish some micronutrient fertilizer elements. 

Polyethylene. Polyethylene remains the largest volume film and sheet raw material. It is available in a wide range of types, with variations in copolymers, homopolymers, molecular weight, and other factors contributing to a long Hst of resins. Resins are designed specifically for end use, and in addition blends of the various types may be used by processors to optimize properties, processibiUty, and economics. Almost two-thirds of the volume of all polyethylene resins are used in film or sheet appHcations (see Olefin polymers). 

Portiand cement clinker structures (18,19) vary considerably with composition, particle size of raw materials, and burning conditions, resulting in variations of clinker porosity, crystallite sizes and forms, and aggregations of crystallites. Alite sizes range up to about 80 p.m or even larger, most being 15—40 )J.m. 

Another aspect of process improvement is color improvement. Eor example, use of phosphoric acid and formaldehyde on the dimer product is said to improve color (68). Other treatments, both on the raw materials and on the finished product, have also been used. Most of these are variations of standard fatty material color reduction techniques. 

Ejfect of Raw-Materials Prices Raw materials for the chemical-process industries are subject to relatively wide variations in price. These effects on profits will now be considered. 

Since the possible variations in binder alone are limitless, it is possible to produce an infinite number of paints. As the range of raw materials available to the formulator becomes wider, their chemical purity is continually being improved. Mathematical models of binders can be constructed using computers and it is usually possible to predict fairly accurately the properties of a particular formulation before it is made. Nevertheless, the formulation of paints for specific purposes is still considered to be very much a technological art. 

The success of any continuous extrusion process depends not only upon uniform quality and conditioning of the raw materials but also upon the speed and continuity of the feed of additives or regrind along with virgin plastic upstream of the extruders hopper. Variations in the bulk density of materials can exist in the hopper, requiring controllers such as weight feeders, etc. 

There is wide variation in the activity, specificity, compatibility, and mode of action of the many individual raw material organics used in product formulations. The quality of some raw materials, and ultimately supplier formulations, may be suspect. Not all competitive polymers or formulated products provide equal performance for an equivalent price. 

Due to the chemical structure, fimctionality and composition of their constituents, ordinary variations of the processing conditions as well as the quality of the raw materials have been observed to lead to changes of the fine structure which are often responsible of lower ageing resistence of the polymer. The data reported here correlate the morphology of some widely utilized epoxy matrices to the informations that can be obtained from the study of the sorption behaviours. 

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