Plant waxes degradation

There are several natural non-combustion sources of PAHs. A study in 1980 by Wakeham [43] concluded that phenanthrene could be created by the dehydrogenation of steroids, retene could be produced by the diagenesis of abietic acid, and alkyl chrysenes could form from the degradation of the pentacyclic triterpenes alpha- and beta-amyrin, which are components of higher plant waxes. In this section we will look at the natural non-combustion sources of retene and perylene and how these sources might impact the Great Lakes. 

Tulloch (1976) has described taxonomic and physical aspects of plant waxes while Kolattukudy et aL (1976) and Kolattukudy (1980) have detailed their biosynthesis and degradation. 

Traditionally, dried or powdered plant material is used and extracts can be obtained by mixing the material with food-grade solvents like dichloromethane or acetone followed by washing, concentration, and solvent removal. The result is an oily product that may contain variable amounts of pheophytins and other chlorophyll degradation compounds usually accompanied by lipid-soluble substances like carotenoids (mainly lutein), carotenes, fats, waxes, and phospholipids, depending on the raw material and extraction techniques employed. This product is usually marketed as pheophytin after standardization with vegetable oils. 

Waxes are biosynthesized by plants (e.g., leaf cuticular coatings) and insects (e.g., beeswax). Their chemical constituents vary with plant or animal type, but are mainly esters made from long-chain alcohols (C22-C34) and fatty acids with even carbon numbers dominant (Fig. 7.11). They may also contain alkanes, secondary alcohols, and ketones. The majority of wax components are fully saturated. The ester in waxes is more resistant to hydrolysis than the ester in triacylglycerols, which makes waxes less vulnerable to degradation, and therefore more likely to survive archaeologically. 

Naturally occurring fats contain small amounts of soluble minor consituents pigments (carotenoids, chlorophyll, etc.), sterols (phytosterols in plant fats, cholesterol in animal fats), vitamin A (from carotenes), vitamin D (calciferol), waxes (esters of long-chain alcohols and fatty acids), ethers, and degradation products of fatty acids, proteins, and carbohydrates. Most of these minor compounds are removed in processing, and some are valuable by-products. 

Extraction from vegetation may produce complicated sample extracts, because organic plant material (fats, waxes, resins, etc.) will be dissolved as well. Before GC/MS analysis of these samples, a cleanup step is usually performed to remove compounds originating from the matrix. Injection of resins, typically organic acids, could degrade the GC performance dramatically. 

In particular, as far as the plastic catalytic degradation is concerned, there are various possible scenarios. In large urban areas the best approach probably is to build a plastic waste pyrolysis plant in an acceptable near area at not to great distance, in order to minimize transport cost of the plastic waste. In that case, safety and environmental concerns of such a new plant should first be denied with satisfactorily before the new plant can get the go-ahead. Near refineries however, the best approach might be to co-feed plastic waste with oil fractions into refinery crackers, or even have a unit of pure thermal pyrolysis first with the produced wax-type fraction to be upstaged in another reactive refinery process. In the first case of co-feeding, a lot of research has to be carried out, addressing aspects of defluidization mainly, before an alteration of a process of the scale of FCC units can go ahead. 

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