Feedstock options

The composition of the plastic feedstock for pyrolysis processes has a direct bearing on the quality of the resultant fuel products, especially flash point, cetane index, low-temperature properties and heteroatom content (e.g. sulphur, chlorine and nitrogen). 

While condensation polymers such as PET and polyamides can be broken down into their monomer nnits by thermal depolymerization processes, vinyl (addition) polymers snch as polyethylene and polypropylene are very difficnlt to decompose to monomers. This is becanse of random scission of the carbon-carbon bonds of the polymer chains during thermal degradation, which prodnces a broad prodnct range. 

There have been many reports on the thermal and catalytic degradation of high-density polyethylene (HDPE), as it is one of the main polymers in mnnicipal solid wastes [1]. 

Due to the high concentration of linear n-paraffin hydrocarbons in fnel derived from PE, it is desirable to isomerize them in order to lower the cloud point and the freezing point of the fuel. The branched isomers do not exhibit the same tendency to crystallize as linear paraffins, so that wax crystals do not form nntil lower temperatures are reached. 

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Obviously, there are more traditional treatment options for plastic waste than feedstock recycling. In the next chapter I will compare the feedstock option with more traditional options, here some data are given on the latter. In this section, I will discuss the following technologies ... 

The plant concept for co-production of hydrogen and electricity is applicable to a very broad range of fossil fuels and also biomass without paying tributes to climate change. At the same time energy supply security is improved, as a result of the diversification of (fossil) feedstock options. 

Although FT waxes are high in quality, their availability over the next decade is expected to be limited. Therefore, there is an effort to find other sources of feedstocks of equal quality to co-process along with FT waxes, both to meet the demand and decrease the cost of lubricant products. Waste plastic is a potentially significant new source for such waxy feed. We have performed combined pyrolysis-hydroisomerization experiments, looking at the following feedstock options ... 

Feedstock Options. Ethanol may be produced via fermentation (with yeast) of 6-carbon or 12-carbon sugars from a number of carbohydrate sources including sugar crops, starch crops, or lignocellulosic materials. 

Compounded WPC pellets are an expensive feedstock option. However, the high initial cost is offset by the fact that these can be molded with less expensive and less complex machines without the need for any additional processing and specialized handling equipment for wood flour. A number of companies have set up plants to produce compounded WPC pellets to sell on to plastics processors. In the compounding process, the filler (wood flour) and additives are dispersed in the molten polymers to produce a homt eneous blend. 

To produce bio-based plastics there is a broad spectrum of feedstock options. Today, bio-based plastics are mainly based on sugar, starch, vegetable oil and natural rubber, the so-called... 

Table 13.1 indicates the advantages and disadvantages for different feedstock options for bio-based plastics. It shows that there is no easy answer to the question of whether second-generation feedstock really is a better solution for the production of bio-based products. The answer depends on the criteria one is looking for. 

Gasification of coal can produce synthesis gas (syngas) not only from coals having a wide range of heat values but also from low-value carbon feedstocks such as petroleum coke, high-sulfur fuel oil, municipal wastes, and biomass. This flexibility increases the economic value of these resources and lowers costs by providing industry with a broader range of feedstock options. 

Due to the wide range of processing conditions (temperature and residence time) available and feedstock options (woody biomass, agricultural biomass, and diverse organic residues) that can be processed in slow pyrolysis units, the yield and properties of biochar can vary widely. This provides an opportunity to optimize the production to yield biochar with properties matching its application. In their research Ronsse et al. (2013) and Zhao et al. (2013) showed that certain biochar properties are primarily affected by processing conditions (eg, surface area, pH, carbon sequestration potential), while others are mainly feedstock-dependent (eg, content of total organic carbon. 

Eig. 1. The key steps for the Phillips PPS process are (/) production of aqueous sodium sulfide from aqueous sodium hydrogen sulfide (or hydrogen sulfide) and aqueous sodium hydroxide 2) dehydration of the aqueous sodium sulfide and NMP feedstocks 5) polymerization of the dehydrated sulfur source with -dichlorobenzene to yield a slurry of PPS and by-product sodium chloride in the solvent (4) polymer recovery (5) polymer washing for the removal of by-product salt and residual solvent (6) polymer drying (7) optional curing, depending on the appHcation and (< ) packaging. 

Feedstock for Chemical Synthesis. It is estimated that <0.5% of the sucrose produced each year is used for nonfood purposes (41). An alternative appHcation, namely the production of chemicals, is an attractive option as the feedstock is plentiful, renewable, and of consistently high purity. Moreover, the biodegradabiUty of many sucrochemicals makes them environmentally friendly. 

Oxidation and reduction reactions can be carried out usiag reformer hydrogen and oxygen from the air. To decide when electroorganic synthesis is likely to be a viable option for a desired product, some opportunity factors are use of cheaper feedstock elimination of process step(s) or a difficult reaction avoidance of waste disposal, toxic materials, and/or abiUty to recycle reagent and abiUty to obtain products from anode and cathode. 

As discussed in Chapter 2, nickel, vanadium, and sodium are the metal compounds usually present in the FCC feedstock. These metals deposit on the catalyst, thus poisoning the catalyst active sites. Some of the options available to refiners for reducing the effect of metals on catalyst activity are as follows ... 

Processing residue or purchased feedstocks. Sometimes, the option of processing supplemental feed or other components, such as atmospheric residue, vacuum residue, and lube oil extract, is a means of increasing the yields of higher-value products and reducing the costs of raw material by purchasing less expensive feedstocks. 

Since plastics are generally made from hydrocarbon feedstocks they should be recycled to conserve energy. The most effectives energy conservation is to refabricate plastic items, though this is not always technically feasible. Under circumstances where recycling is not a feasible option the use of plastics in waste-derived fuels may be an acceptable conservation measure. 

Section 3 discusses options for feedstock recycling of mixed plastic waste ... 

By cooling the gas is condensed and then available as hydrocarbon feedstock for other processes (some 85% of the MPW input). The light hydrocarbon gas (15% of the MPW input) that remains after cooling is compressed, reheated and returned to the reactor as fluidising gas. It can also be used as a fuel for the cracking process, though other recovery options are being studied as well. 

A LCA on treatment options of MPW was performed by the Dutch Centrum voor Energiebesparing en Schone Technologie (CE, Delft) in 1994. This LCA used the VEBA process as an example for feedstock recycling (a.ll). Another LCA was performed by Heyde and Kremer (a.6). Particularly the CE studies suggested that the VEBA process was a bit less advantageous than the Texaco process, mainly due to the fact that the Texaco process does not need agglomeration of MPW as pre-treatment, whereas the VEBA process apparently does. 

Finally, other relevant treatment options for plastics waste include landfill and mechanical recycling. Since these options (unlike Vinyloop and cement kiln incineration) are not even similar to feedstock recycling we discuss them here only very briefly. Mechanical recycling of plastics (be it PVC or other plastics), needs dedicated collection of the plastic waste in question. This is only possible for selected plastic flows (high volumes, recognisable products, products consisting mainly of one plastic). Landfill can accept plastic waste in any waste context (pure plastic type, MPW, mixed materials). I will only address the costs of these alternative technologies. 

Brighton, 20th-22nd April 1999, p. 123-31 OPTIONS FOR PVC FEEDSTOCK RECYCLING RESULTS OF THE ECVM R D PROJECT ON PVC FEEDSTOCK RECYCLING PROCESSES Buehl R... 

This paper diseusses in detail the option of fluidised-bed reaetors to eraek mixed plastics waste into valuable raw materials, under the headings thermal cracking for feedstocks, pyrolysis of polyolefins, and other options. 7 refs. 

This paper explores the use of plastics in cars to make them more environmentally friendly. It lists major environmental issues. It then discusses in detail the positive role of plastics during the lifetime of a car (more plastics means less fuel consumption), the fact that automotive plastic parts are user-friendly and safe, the current and future uses of plastics in cars, recovery options for plastics in end-of-life vehicles, mechanical recycling (which is the best recovery option for many large automotive parts), energy recovery (the solution for small plastic parts), and feedstock (or chemical) recycling. Lastly, the way forward is considered. 

This article examines the recovery of automobile shredder residue (ASR), and considers three recovery options ASR as a landfill day cover, ASR in the production of composite materials, and the pyrolysis of ASR to recover chemical feedstock. All are discussed in detail. 

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