Byproduct

Byproducts that are not used for commercial purposes do not need to be listed on the Inventory and consequently are not subject to premanufacture notification requirements, although they are chemical substances and are subject to other TSCA provisions. Byproduct is defined in the Inventory rules as  

A chemical substance produced without separate commercial intent during the manufacture or processing of another chemical substance(s) or mixture(s).  

TSCA Questions and Answers from the October, 1990 EPA-Industry Living with TSCA Workshop, question 5 (Oct. 1992) [hereinafter Living with TSCA Q A], 

See Draft PMN Q A, 2-1, question 201-2. The Draft PMN Q A has been in draft form since at least 1995, and has not been issued as formal guidance. 

Living With TSCA Q A, question 3. See Chapter 3, The Inventory. 

It is important to note that the differentiation between ozone and its byproducts in such tests is often not possible. 

Most of the possible toxic effects from ozone in gas can also occur when using liquid ozone, due to the potential risk of it gassing-out. Consequently, liquid ozone has a strong odor and should always be used in closed piping and vessels. 

In order to evaluate the toxicity of ozonation byproducts, the health effects of specific, unidentified substances (byproducts) need to be determined for each target organism (human, animals, fish, etc). The often observed lack of substantial information on toxicity can in part be attributed to the lack of appropriate testing methods. Since identifying all the substances which compose the TOC of a ground-, drinking- or waste water can rarely be 

A good overview of the different methods of measuring human toxicological effects can be found in Langlais et al. (1991). They summarize results from many human toxicity studies on ozone and ozonation byproducts. Some results on human toxicity are also presented below. 

Standardized ecotoxicity tests (bioassays) have been developed and optimized over the last few years and encompass the effects on bacteria, daphnia and fish (DIN 38 412, parts 30, 31 and 34). These tests are designed to assess the toxicity on aquatic organisms. They are quick to perform, easy to handle and comparatively inexpensive, with the goal of allowing the toxicity of a complex water matrix to be estimated. However, they use pre-concentration steps so that it is possible that not all byproducts are recovered (which itself is hard to prove). 

3 Stoichiometry Must Be Known. The stoichiometry for the path must be known in detail. This means that all main reaction products must be considered at each reaction step. The fact that 2 moles of NaCl or other simple reaction products are produced during a reaction can have a major impact on the reaction s economics. 

The fraction of the limiting reagent which is transformed into the desired target molecule must be known. 

Byproducts. The amount and type of byproduct produced are necessary pieces of information. The main reaction byproducts and side reaction byproducts are needed for both the yield calculation and the determination of separation difficulty, corrosiveness, safety, etc. 

ACS Symposium Series American Chemical Society Washington, DC, 1977. 

OTHER REACTIONS THAT OCCUR AT THE SAME CONDITIONS 

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Consider the process illustrated in Fig. 1.2. The process requires a reactor to transform the FEED into PRODUCT (Fig. 1.2a). Unfortunately, not all the FEED reacts. Also, part of the FEED reacts to form BYPRODUCT instead of the desired PRODUCT. A... 

Since process design starts with the reactor, the first decisions are those which lead to the choice of reactor. These decisions are among the most important in the whole design. Good reactor performance is of paramount importance in determining the economic viability of the overall design and fundamentally important to the environmental impact of the process. In addition to the desired products, reactors produce unwanted byproducts. These unwanted byproducts create environmental problems. As we shall discuss later in Chap. 10, the best solution to environmental problems is not elaborate treatment methods but not to produce waste in the first place. 

Given that the objective is to manufacture a certain product, there are often a number of alternative reaction paths to that product. Reaction paths which use the cheapest raw materials and produce the smallest quantities of byproducts are to be preferred. Reaction paths which produce significant quantities of unwanted byproducts should especially be avoided, since they create significant environmental problems. 

Paths 1 and 3 are clearly not viable. Only path 2 shows a positive economic potential when the byproduct HCl can be sold. In practice, this might be quite difficult, since the market for HCl tends to be limited. 

The preference is for a process based on ethylene rather than the more expensive acetylene and chlorine rather than the more expensive hydrogen chloride. Electrolytic cells are a much more convenient and cheaper source of chlorine than hydrogen chloride. In addition, we prefer to produce no byproducts. 

Example 2.2 Devise a process from the three reaction paths in Example 2.1 which uses ethylene and chlorine as raw materials and produces no byproducts other than water. Does the process look attractive economically ... 

An example of this t3T)e of reaction which does not produce a byproduct is the production of allyl alcohol from propylene oxide ... 

Multiple reactions in parallel producing byproducts. Rather than a single reaction, a system may involve secondary reactions producing (additional) byproducts in parallel with the primary reaction. Multiple reactions in parallel are of the tj ie... 

Multiple reactions in series producing byproducts. Rather than... 

Mixed parallel and series reactions producing byproducts. In more complex reaction systems, both parallel and series reactions can occur together. Mixed parallel and series reactions are of the type... 

Some of the benzene formed undergoes a secondary reaction in series to an unwanted byproduct, diphenyl, according to the reaction... 

Unwanted byproducts usually cannot be converted back to useful products or raw materials. The reaction to unwanted byproducts creates both raw materials costs due to the raw materials which are wasted in their formation and environmental costs for their disposal. Thus maximum selectivity is wanted for the chosen reactor conversion. The objectives at this stage can be summarized as follows ... 

Multiple reactions in series producing byproducts. Consider the system of series reactions from Eq. (2.7) ... 

Multiple reactions also can occur with impurities that enter with the feed and undergo reaction. Again, such reactions should be minimized, but the most efiective means of dealing with byproduct reactions caused by feed impurities is not to alter reactor conditions but to introduce feed purification. 

Multiple reactions in parallel producing byproducts. Consider again the system of parallel reactions from Eqs. (2.16) and (2.17). A batch or plug-flow reactor maintains higher average concentrations of feed (Cfeed) than a continuous well-mixed reactor, in which the incoming feed is instantly diluted by the PRODUCT and... 

In general terms, if the reaction to the desired product has a higher order than the byproduct reaction, use a batch or plug-flow reactor. If the reaction to the desired product has a lower order than the byproduct reaction, use a continuous well-mixed reactor. 

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