Alternative Process

On the other hand, if the hazard is toxicity, process alternatives can be compared by assessing the mass of toxic material that would enter the vapor phase on release from containment, weighting the components according to their lethal concentration. 

If the material in two process alternatives is both flammable and highly toxic, then they can be compared on both bases separately. If the assessments of the relative flammability and toxicity are in conflict, then we can only resort to a safety index. 

A drawback of this approach is that it typically generates enormous and imwieldy synthesis trees which contain a large number of dead-end branches which are not worth further consideration. Furthermore, the chemist is forced to follow a rigid scheme during the planning process, alternating between the application of transforms, the derivation of new precursors, and again the application of further transforms to these precursors. 

The alcoholysis reaction may be carried out either batchwise or continuously by treating the triglyceride with an excess of methanol for 30—60 min in a well-agitated reactor. The reactants are then allowed to settle and the glycerol [56-81-5] is recovered in methanol solution in the lower layer. The sodium methoxide and excess methanol are removed from the methyl ester, which then maybe fed directiy to the hydrogenolysis process. Alternatively, the ester may be distilled to remove unreacted material and other impurities, or fractionated into different cuts. Practionation of either the methyl ester or of the product following hydrogenolysis provides alcohols that have narrow carbon-chain distributions. 

Reductive amination of cyclohexanone using primary and secondary aHphatic amines provides A/-alkylated cyclohexylamines. Dehydration to imine for the primary amines, to endocycHc enamine for the secondary amines is usually performed in situ prior to hydrogenation in batch processing. Alternatively, reduction of the /V-a1ky1ani1ines may be performed, as for /V,/V-dimethy1 cyclohexyl amine from /V, /V- di m e th y1 a n i1 i n e [121 -69-7] (12,13). One-step routes from phenol and the alkylamine (14) have also been practiced. 

During process development, a model can be developed as soon as a conceptual flow sheet has been formulated. This model can be updated as more information about the process is obtained. Even at an early stage in the project, the model can be used to assess the preliminary economics of the process and the effect of technological changes on these economics. The model can aid in interpreting pilot-plant data and allows the study of many process alternatives. 

Ethanol-water Minimum-hoiling azeotrope Ethylene glycol, acetate salts for salt process Alternative to azeotropic distillation, pressure swing distillation... 

Properties are similar to those of PTFE, and PFA fluoropolymers are generally considered to be the best melt-processable alternative to PTFE yet available. They are, however, more expensive than PTFE. Compared with the TFE-FEP copolymers such as Teflon I P the PFA fluoropolymers ... 

Using Non-Cryogenic Absorption to Reject Nitrogen From Subquality Namral Gases - The Mehra Process Alternative, Gas Separation International Conference, Austin, TX, Apr. 22 - 24, 1991. 

In considering the economics of process alternatives, it is important to think about the total life cycle costs. There is an increasing interest in this concept in the environmental area, with a recognition of the need to incorporate waste treatment, waste disposal, regulatory compliance, potential liability for environmental damage, and other long term environmental costs into project economic evaluation. Similarly, we must consider life cycle safety costs. Some examples of factors which should be considered include ... 

Note that we refer to a process as inherently safer, when compared to some other alternative, but not as "inherently safe. All materials and processes have hazards, and it is not realistic or practical to propose that we can eliminate all of them. In many cases we can identify material and process alternatives which clearly reduce hazards, and we can consider those alternatives to be inherently safer. 

Unfortunately, many times it is not clear which of several process alternatives is inherently safer. Because nearly all chemical processes have a number of hazards associated with them, an alternative which reduces one hazard may increase a different hazard. For example, process A uses flammable materials of low toxicity process B uses noncombustible materials, which are volatile and moderately toxic, and process C uses noncombustible and nontoxic materials but operates at high pressure. Which process is inherently safer The answer to this question will depend on the specific details of the... 

Often an organization will strive for the elimination of a specific toxic material from a given process. Alternatives will also have other hazards and risks that require an informed choice. The industrial hygienist, chemist, and safety engineer play an important role in developing the information for making the selection between alternatives. 

The initial aim of the procedure is to generate a reasonable base case design that can be used for preliminary economic evaluation of the process. This can subsequently be optimized and/or compared with any process alternatives that are identified. The complete process is always considered at each decision level, but additional fine detail is added to the structure of the flowsheet at any stage. Established heuristics and equipment selection procedures are used together with new process synthesis insights to guide each flowsheet decision. 

An analysis of this type is appropriate during the preliminary design stage when process alternatives may have to be screened economically, or when it is necessary to determine a feasible design as the basis for equipment trials and/or final designs. 

Optimize design to reduce cost or satisfy functional and performance requirements General configuration Configuration proportions such as rib depths, shell radii, fillet radii, etc. Material thickness Material alternatives—consider additives to tailor properties Process alternatives... 

Groh P. Bolesta, Cast High Explosives Fill Plant NAD McAlester. Equipment and Process Alternatives for A-Plant. NAD McAlester ,... 

A and E refer to the desorption, dissociation, decomposition or other surface reactions by which the reactant or reactants represented by M are converted into products. If [M] is constant within the temperature interval studied, then the values of A and E measured refer to this process. Alternatively, if the effective magnitude of [M] varies with temperature, the apparent Arrhenius parameters do not specifically refer to the product evolution step. This is demonstrated quantitatively by the following example [36]. When E = 100 kJmole-1 andA [M] = 3.2 X 1030 molecules sec-1, then rate coefficients at 400 and 500 K are 2.4 X 1017 and 1.0 X 1020 molecules sec-1, respectively. If, however, E is again 100 kJ mole-1 and A [M] varies between 3.2 X 1030 molecules sec-1 at 500 K and z X 3.2 X 1030 molecules sec-1 at 400 K, the measured values of A and E vary significantly, as shown in Fig. 7, when z ranges from 10-3 to 103. Thus, the measured value of E is not necessarily identifiable with the rate-limiting step if a concentration of a participant is temperature-dependent. This... 

This chloride ion may come from PClg, (which is also present in solid PCI5). There follows a two-step SnI process. Alternatively, 17 can be converted to the product without going through the chlorocarbocation, by an SNi process. 

A combined use of mass balancing and LCA may however be the most promising option. Mass balancing may then be used to screen possibly large numbers of alternative synthesis routes. LCA would be valuable for a more detailed evaluation of process alternatives in later stages of scale up, where more data are available. 

In-house process control. This comprises the achievement of optimum efficiency in relation to production and processing methods including the introduction, where feasible, of cleaner processes (alternative technology) or processing methods (substitute materials and/or reformulations, process modifications, and equipment redesign). 

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