**6. Economic considerations**

The most important economic issues that influence the viability of primary and secondary (mechanical) plastic recycling are the price of the recycled polymer compared with virgin polymer and the cost of recycling compared with alternative forms of acceptable disposal (Hopewell et al., 2009).

More individuals, organizations, business, and government agencies are collecting materials for recycling than ever before. The number of curbside recycling programs has grown during the last decade and new economic opportunities allow the birth of new markets. Recycling also creates new businesses that haul, process, and broker recovered materials, as well as companies that manufacture and distribute products made with recycled content. By recycling 1 ton of plastic, you can help save the same amount of energy that two people use in one year, or almost 2,000 pounds of oil (USEPA, 2009).

According to the American Chemistry Council, about 1,800 US business handle or reclaim post-consumer plastics. Plastics from MSW are usually collected from curbside recycling

Materials and Methods for the Chemical Catalytic Cracking of Plastic Waste 171

and fuel oil, corresponding to fuel fractions obtained in industrial petroleum refinery plants. The selectivity towards particular products depends mainly on the choice of catalyst and reaction conditions. The study of the catalytic cracking of plastic waste has led to relevant

The large-scale application of these processes has been limited by economical and profitability reasons. Previous stages involve plastic separation from municipal waste and, since different mixtures of products are obtained, end stages involve product separation processes. Up to now, it is hard to compete with the still cheap option of producing fuels from natural gas and crude oil and to produce plastics from new raw materials. However, worldwide growing concerns about preserving our environment give plenty of room for

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bins or drop-off sites. Then, they go to a material recovery facility, where the materials are sorted into broad categories (plastics, paper, glass, etc.). The resulting mixed plastics are sorted by plastic type, baled, and sent to a reclaiming facility. A Mexican study reported than the average cost of one ton of trash is around 350 US Dollars (USD), but if plastics are reduced, the cost would be around 4 USD less (Cortinas, 2009). The investment for recycling of 150 ton could be 300,000 USD producing a monthly utility of 30,000 USD.

The price of virgin plastic is influenced by the price of oil, which is the principle feedstock for plastic production. As the quality of recovered plastic is typically lower than that of virgin plastics, the price of virgin plastic sets the ceiling for prices of recovered plastic. The net heat generation from the use of crude oil in plastic making is roughly 0.4x1014 kWh from 1939 to 2000. It corresponds to 1.3% of the missing heat and contributes to 0.5% of the global warming (Gervet, 2007).

The profitability of feedstock, chemical recycling methods depends on three key factors: the degree of separation required in the raw wastes, the capital investment involved in the processing facilities and the value of the products obtained (Clark, 1999). For most of feedstock recycling methods, some pretreatment or separation operations are unavoidable. Feedstock recycling methods can be ordered according to the separation steps required (Clark, 1999):

Gasification < thermal cracking < hydrogenation < catalytic cracking < chemical depolymerization

Whereas the value of the products obtained by the feedstock recycling methods follows the opposite order:

Thermal oils < synthesis gas < hydrogenation oils < catalytic olefins and paraffins < monomers

Important benefits of the catalytic cracking of polymer waste with respect to other chemical feedstock recycling methods is the possibility of controlling the selectivity towards desired products and the possibility of reducing energy consumption. The use of cheap catalysts is central under the actual circumstances and some of the current best options are natural materials and waste catalysts from other industries. To use existing industrial facilities is a way for much cost reduction. Since the catalysts and the reaction mechanism of the polymer catalytic cracking are about the same as for the hydrocarbon fluid catalytic cracking (FCC), it is possible to incorporate plastic waste into the FCC refinery feed, with the added benefit that plastic waste has almost no sulfur content and no heavy metals content.
