Selecting Processing

The nature of the process may have a profound influence on a product s mechanical strength. 

Excessive heat during processing can consume sacrificial heat stabilizers for certain plastics, rendering stabilization levels insufficient to ensure long life at elevated temperatures. Thermal degradation usually results in embrittlement (tests can be conducted to determine the remaining levels, as in Chapter 9). 

The slow cooling of crystalline polymers, such as HDPE and PP, can allow large crystal formations to develop. Such crystals embrittle the resin and make it prone to stress cracking. 

The rapid cooling of certain plastic parts can result in frozen in stresses and strains (particularly with injection molding). The stresses may decay with time, in a viscoelastic manner. However, they will act like any other sustained stress to aggravate cracking or crazing in the presence of aggressive media and hostile environments like UV radiation. 

In RPs, insufficient compaction and consolidation of a composite before resin cure will result in air pockets, incomplete wet-out and encapsulation of the fibers, and/or insufficient fiber or uniform fiber content. These deficiencies lead to loss of strength and stiffness and susceptibility to deterioration by water and aggressive agents. 

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Figure B3.4.6. Reaction probabilities for the initial-state-selected process H2(v = 0,J = 0)+OH(v,y = 0) — H2O+H, for zero total angular momentum. Taken from [75] with pennission.

The ability of living organisms to differentiate between the chemically similar sodium and potassium ions must depend upon some difference between these two ions in aqueous solution. Essentially, this difference is one of size of the hydrated ions, which in turn means a difference in the force of electrostatic (coulombic) attraction between the hydrated cation and a negatively-charged site in the cell membrane thus a site may be able to accept the smaller ion Na (aq) and reject the larger K (aq). This same mechanism of selectivity operates in other ion-selection processes, notably in ion-exchange resins. 

The descriptor set can then be reduced by eliminating candidates that show such bad characteristics. Optimization techniques such as genetic algorithms (see Section 9.7) are powerful means of automating this selection process. 

For purely alicyclic compounds, the selection process proceeds successively until a decision is reached (a) the maximum number of substituents corresponding to the characteristic group cited earliest in Table 1.7, (b) the maximum number of double and triple bonds considered together, (c) the maximum length of the chain, and (d) the maximum number of double bonds. Additional criteria, if needed for complicated compounds, are given in the lUPAC nomenclature rules. 

The original German process used either carbonyl iron or electrolytic iron as hydrogenation catalyst (113). The fixed-bed reactor was maintained at 50—100°C and 20.26 MPa (200 atm) of hydrogen pressure, giving a product containing substantial amounts of both butynediol and butanediol. Newer, more selective processes use more active catalysts at lower pressures. In particular, supported palladium, alone (49) or with promoters (114,115), has been found useful. 

Table 9. Selected Processes for Leaf Protein Concentrate Production, 1993...

Once the need for a LIMS has been justified, specifications have been written, and available vendors surveyed, the LIMS selection process begins. Each vendor s product must be evaluated for conformance to the specification and flexibiUty for future modifications. If an adequate solution is not available commercially, consideration must be given to constmcting a custom LIMS solution. This could be done in-house or by contractors. If the custom option is preferred, resources needed for future modifications and maintenance should be factored into the cost. 

Defining the requirements for a pilot-plant control system is often difficult because process plant experience for comparison and evaluation is commonly lacking and the design is frequentiy performed by personnel inexperienced in either instmmentation systems or pilot-plant operations. The isolated and often intermittent nature of pilot-plant operations also inhibits evolution and promotes individual unique installations. This compHcates the selection process. 

Any program developed in-house must be easy to use, or user-friendly. If the program has various options for input, analysis, computation, and output, then it must provide the user with a fast way to select them. To meet this need, the system is likely to be menu-driven. The peripheral interactive devices such as mice, joysticks, light pens, graphic tablets, and templates are helpful and often used to expedite the selection process. 

The tube-to-tubesheet joint, how is it made Many use O rings to add another material to the selection process. Preference should be given to a fusing technique of similar material. 

Precoat Procedure Precoat filtration tests are run in exactly the same manner as bottom-feed tests except that the leaf must first be precoated with a bed of diatomaceous earth, perhte, or other shave-able inert sohds. Some trial and error is involved in selecting a grade of precoat material which will retain the filtered solids to be removed on the surface of the bed without any significant penetration. During this selection process, relatively thin precoat beds of I to 2 cm are satisfactory. After a grade has been selected, bench-scale tests should be... 

Assistance in problem definition and in developing a test program should be sought from persons experienced in the field. If your organization has a consultant in separations of this land, by all means m e use of the expertise available. If not, it may be wise to employ an outside consultant, whose special knowledge and guidance can save time, money, and headaches. It is important to do this early after the separation equipment has been installed, there is httle a consultant can do to remedy the sometimes disastrous effects of a poor selection. Often it is best to work with established equipment manufacturers throughout the selection process, unless the problem is unusually sensitive or confidential. Their experience with problems similar to yours may be most helpful and avoid many false starts. 

Approximate ranges of space velocities in rotaiy Idlns, metric tons/(m d), of selected processes are as follows ... 

Introduction Theprevious sections dealt with techniques for the identification of hazards and methods for calculating the effects of accidental releases of hazardous materials. This section addresses the methodologies available to analyze and estimate risk, which is a function of both the consequences of an incident and its frequency. The apphcation of these methodologies in most instances is not trivial. A significant allocation of resources is necessary. Therefore, a selection process or risk prioritization process is advised before considering a risk analysis study. 

Carefully and deliberately select process chemicals and synthesis route... 

Investigations of incidents associated with tolling projects have identified that appropriate selection of a toller based upon proper equipment and expertise is important in reducing the likelihood of future process safety related incidents and environmental releases. It is likewise important to review toller safety, health, and environmental practices (current and past) in the selection process. This review can identify those practices that would need to be modified to be acceptable. Eliminating less qualified candidate firms at an early stage is a best practice. 

The technology package for the toll should be at least partially established prior to starting the active search for a toller. This will assist you in defining the level and areas of expertise needed for the project. Some companies that frequently let toll contracts have internal service groups that assist in the toller selection process. An example of an internal questionnaire used at such a company is shown in Example 2-1. It is an excellent way to identify the expertise required for a specific tolling project. 

However, just asking the purchasing department for a list of companies previously used for tolling is not enough. Prior successful use of a given firm is not adequate qualification for future tolls, especially if the new toll involves a different product. At this point in the selection process the five facets mentioned in the previous chapter come into play ... 

In this phase of the toller selection process, we assume the long list became a short list and now one or more candidate tollers from the short list will be given an opportunity to prepare a commercial bid. This by no means indicates the short listed tollers are perfect. There may be deficiencies that need to be corrected in concert with the client. With proper effort, one will be successful and be engaged for the toll. Sometimes it is appropriate to decide on a backup toller, as complications can develop that prevent the primary candidate from executing the project as originally planned, due to an incident in their plant, departure of key personnel, or unexpected production demands on the toller. 

A confidentiality agreement is frequently required prior to the final selection process. Depending on the process technology, a confidentiality agreement may be required during initial discussions with the toller. Alternately, it may be included in the request for bid or when the final contract is executed. 

Some companies that let toll contracts do not visit a site until this last phase in the toller selection process and would need a signed agreement to make the visit and discuss proprietary aspects of the project. 

It is incumbent upon the toller to develop and follow internal management systems as appropriate to support business needs, production needs, process safety, environmental responsibility, and worker health. The selection process should have considered whether or not satisfactory systems are in place. Nevertheless, the contract or auxiliary documents may be the vehicle used to help ensure that the system reviewed is the system actually used for completing the toll in question. Within the process safety management system, the management of change and training elements are essential subsystems. 

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