Blending operations

The manufacture of useful, stable blends involves two major steps (I) The eom-ponents are mixed to a degree of dispersion that is appropriate for the particular purpose for which the blend is intended (2) additional procedures arc followed, if necessary, to ensure that the dispersion produced in step I will not demix during its use period. 

Note that it is useful to consider step 2 as a problem involving retardation of a kinetic process (demixing). Tlie viewpoint that focuses on blending as a problem in thermodynamic stability is included here as a special case but should not exclude other routes to stabilization which may be practical under some circumstances. 

To illustrate this point consider the production of lacquers for PVC films and sheeting. Such lacquers contain a PVC homopolymer or low-acetate vinyl chloride-vinyl acetate copolymer, poly(methyl methacrylate), a plasticizer and perhaps some stabilizers, dulling agents (such as silica), pigments, and so on. Methyl ethyl ketone (MEK) is the solvent of choice because it gives the best balance of low toxicity, volatility, and low cost. Any other solvent is effectively 

Although the scientific principles behind this simple example of practical technology are easily understood, it illustrates the benefits that can be realized by considering the blending process as a dispersion operalion that may be followed, if necessary, by an operation to retard the rate at which the ingredients of the blend demix. In special cases, of course, the latter operalion may be rendered unnecessary by the selection of blend ingredients that are miscible in the first instance. 

It is also well known in compounding technology that the quality of a dispersion may be sensitive to the condition of the blend that is fed to the mixing machine and in some cases also to the order in which the ingredients are added to the mixer. 

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Fig. 17. Tumble blend operation using portable BINSERT containers where A represents the blend stage B, transport and C, discharge.

The particle size distribution of Rhovanil Extra Pure vanillin shows a less narrow profile than other standard mesh grades available on the market. The product shows an improved mixabiUty in blending operations, allowing shorter blending time of compounds or food mixes, and better homogeneity of vanillin content, especially in low content vanillin blends. 

Flammable liquids are considered particularly static-prone if their elec trical conductivity is within the range of 0.1 to 10 pS/m. If no particulates or immiscible liquid are present, these prodlic ts are considered safe when their conductivity has been raised to 50 pS/m or higher. Blending operations or other two-phase mixing may cause such a high rate of charging that a conductivity of at least 1000 pS/m is needed for safe charge dissipation (British Standard 5958, part 1, Control of Undesirable Static Electricity, para. 8, 1991). 

Applications for mixers in blending operations vary from small laboratory mixers to large petroleum tanks of several million gallons. Three common mixing operations are ... 

For side entering horizontal mixers not limited to blending operations, there are some differences in recommendations concerning the physical location of the impeller ... 

Propellers are frequently of the three-bladed marine type and are used for in-tank blending operations with low viscosity liquids, and may be arranged as angled side-entry units, as shown in Figure 7.22. Reavell 1 has shown that the fitting of a cruciform baffle at the bottom of the vessel enables much better dispersion to be obtained, as shown in... 

We all share a national security interest in working with Russia to assure that material removed from nuclear warheads is removed from weapons applications. Of course, there is no simple blending operation that will convert weapons plutonium into material that cannot be used for weapons without major effort... 

Under certain conditions, dry mixtures of lead chromate pigments with the azo-dyes l-(2. 4 -dimtrobenzcncazo)-2-hydroxynaphthalene (dinitroaniline orange) or l-(4 -chloro-2 -nitrobenzcncazo)-2-hydroxynaphthalene (chlorinated para-red) may lead to violent explosions dining mixing/blending operations. 

Question 2 ("Is there any mixing or combining of different substances ") would be answered YES, since the blending operation involves mixing of the ingredients. Assuming no indication of heat generation is reported for the intended operation, Question 6 would be answered NO. 

On April 21, 1995, an explosion and fire at Napp Technologies in Lodi, New Jersey, killed five employees and destroyed the facility (Figure l).19 The plant was conducting a toll blending operation to produce a commercial gold precipitation agent. The chemicals involved were water reactive (i.e., aluminum powder, a combustible metal in the form of finely divided particles and sodium hydrosulfite, a combustible solid). 

In the catalyst preparation area where the fire occurred, aluminum alkyl and isopentane are mixed in a batch blending operation in three 8000-gallon kettles. The flow rates of components are regulated by an operator at the control room. Temperature, pressure, and liquid level within the kettles are monitored by the control room operator. The formulated catalyst is stored in four 12,000-gallon vertical storage tanks within this process unit. Aluminum alkyl is a pyrophoric material and isopentane is extremely flammable. Each vessel was insulated and equipped with a relief valve sized for external fire. 

The emulsion polymerization process has several distinct advantages. The physical state of the emulsion (colloidal) system makes it easy to control the process. Thermal and viscosity problems are much less significant than in bulk polymerization. The product of an emulsion polymerization, referred to as a latex, can in many instances be used directly without further separations. (However, there may be the need for appropriate blending operations,... 

Water and sediment usually result from poor fuel handling and storage practices. Water and sediment can enter from atmospheric air, through fuel transportation systems, and from blending operations. Corrosion, filter blocking, injection system wear, and deposit formation can result. A listing of some classes of compounds which can be found in middle distillate fuel is provided in TABLE 3-15. 

Di(2-ethylhexyl) adipate may be released into the environment during its manufacture and distribution, during PVC blending operations and cutting of PVC film, and from consumer use and disposal of finished products (lARC, 1982 Environmental Protection Agency, 1998). 

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