Material efficiency

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 ... 

Batch processes can be synthesized by first synthesizing a continuous process and then converting it to batch operation. The process yield is an important measure of both raw materials efficiency and environmental impact. 

The economic tradeoffs now become more complex, and a new cost must be added to the tradeoffs. This is a raw material efficiency cost due to byproduct formation. If the PRODUCT formation is kept constant despite varying levels of BYPRODUCT formation, then the cost can be defined to be ... 

MPa (15—20 atm), 300—400 kg benzene per kg catalyst per h, and a benzene ethylene feed ratio of about 30. ZSM-5 inhibits formation of polyalkjlated benzenes produced with nonshape-selective catalysts. With both ethylene sources, raw material efficiency exceeds 99%, and heat recovery efficiency is high (see Xylenes and ethylbenzene). 

PPV and its alkoxy derivatives are /j-type conductors and, as a consequence, hole injection is more facile than electron injection in these materials. Efficient injection of both types of charge is a prerequisite for efficient LED operation. One approach to lowering the barrier for electron injection is the use of a low work function metal such as calcium. Encapsulation is necessary in this instance, however, as calcium is degraded by oxygen and moisture. An alternative approach is to match the LUMO of the polymer to the work function of the cathode. The use of copolymers may serve to redress this issue. 

Technology is called green if it uses raw materials efficiently, such that the use of toxic and hazardous reagents and solvents can be avoided while formation of waste or undesirable byproducts is minimized. Catalytic routes often satisfy these criteria. 

A foreseeable problem associated with improving material efficiency is the consequence of increased demand associated with the lowering of costs. Meeting such demand may fail to bring about any absolute reduction in waste, even though the waste produced per ton of product has been reduced. 

One can see that the forms of equations (4.4) and (4.5) are identical. It is clear that RME (AE) and Em (Emw) describe material efficiency from different points of view, the former with respect to the target product and the latter with respect to the waste products. Figure 4.1 shows the interconnections between the key material green metrics presented above. 

The required masses and raw material costs of any starting material or intermediate in a plan, including the final target product, may be determined by inspection. Overall kernel RME is shown to trump overall yield as the key metric to rank material efficiency of a synthesis plan. 

Table 4.6 Summary of reaction and overall material efficiency performances for the production of triclosan according to the tree diagram shown in Figure 4.14. of 1 mole...

It is important to realize that though the formulas for RME explicitly do not depend on reaction scale, x, since this variable cancels out in the computation, RME does in fact implicitly depend on reaction scale because reaction yields are scale dependent and RME in turn depends on reaction yield. Reaction yields are parameters whose magnitude cannot be predicted theoretically but must be verified experimentally. It does not always follow that a reported yield for a given reaction at a given scale will be the same at another scale. This requires experimental verification. Moreover, the direction of change as the scale is changed is also not predictable. AH of this means that when the same synthesis plan is run at a different scale, different reaction yields will be determined and hence different material efficiency performance values of RME, Em and mass of waste will be obtained. However, the... 

Table 4.19 summarizes the metrics parameters for 10 total synthesis plans to morphine. Figure 4.46 shows a synthesis map of various starting materials for some of the better performing plans to this target. The Rice plan remains the most material efficient plan... 

Tree diagrams for all five plans are shown in Figures 4.51-4.55. The tree analyses of the Kindler-Peschke-Pal and Dean methods highlight a useful material efficient synthetic... 

Figure 4.57 summarizes various starting materials to this target for some of the better performing plans. The classic Julian and recent Yu-Lu and Trost plans are shown in Schemes 4.17, 4.18 and 4.19 respectively. Figure 4.58 shows the synthesis tree for the most material efficient Yu-Lu plan. Remarkably, the Julian plan ranks second among the list yet it was the first reported synthesis for this compound that also proved its correct structure. The... 

Yu-Lu plan is a variant of the Julian one and its remarkable material efficiency is primarily due to a combined high atom economy and high reaction yields. The Trost plan has the best performing molecular weight first moment parameter. The Mukai plan has the highest degree of convergence. 

Andraos, J. (2007) Gauging Material Efficiency. Canadian Chemical News, 59(4), 14-17. 

As with the case of byproduct losses, another cost needs to be added to the trade-offs when there is a purge. This is a raw materials efficiency cost due to purge losses. If the PRODUCT formation is constant, this cost can be defined to be1213 ... 

The process yield is an important measure of both raw materials efficiency and environmental impact. 

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