Alternative catalytic processes for the valorization of plastic wastes to fuels .

Abstract

The first chapter analyses the state of the art on plastic production and mainsectors of application, and on generation of plastic wastes, focused on theenvironmental problem generated by uncontrolled dumping and the differentalternatives and processes, at the research or industrial stage, proposed for themanagement and valorization of plastic wastes.Pyrolysis has been found to be one of the most common strategies to produceliquid hydrocarbons from plastic wastes. However, the oil product obtained requiresupgrading through hydrotreatment to be used as a fuel. Catalytic hydrocracking isproposed as an alternative treatment to pyrolysis and hydrotreatment, in a singlestage. In a previous work, the conditions of catalytic hydrocracking of PS forworking under kinetic control were established, and the kinetic model wasproposed.Hydrocracking of plastics has been carried out in a three-phase stirred reactorunder kinetic control with bifunctional catalysts in slurry and hydrogen pressure.Bifunctional Pt/zeolite catalysts have been prepared and characterized, in order toestablish a relationship between properties and performance. Several virginplastics and plastic wastes have been characterized and tested, so that theirbehavior in reaction can be related to their composition. The required experimentalequipments and procedures used all over the work for reaction, preparation andcharacterization are described in detail in Chapter 2.Chapters 3 and 4 have been devoted to optimization of the bifunctional catalyst forhydrocracking of plastics, using virgin PS as the base polymer for comparison. InChapter 3, the effect of the acid properties of the zeolitic supports on activity andselectivity has been studied; the acid properties of the supports have beenmodified by either dealumination or desilication.On the other hand, optimization of the metallic function has been studied inChapter 4, where the effect of platinum content and preparation procedure onactivity and selectivity has been analyzed. Platinum contents in the range 0.1¿1.0 wt.% and prepared by either ionic exchange or impregnation on HBeta zeolitehave been studied.Plastic wastes are composed by a mixture of different polymeric materials. Hence,once catalyst was optimized for PS, its performance in hydrocracking with otherpolymeric materials was studied. In Chapter 5, common polymers with only carbonand hydrogen atoms in their composition, such as PB and HIPS, were chosen.HIPS, besides, is composed by a mixture of PS and PB. Thus, the effect of mixturehas been also analyzed. Thermal hydrocracking experiments were also carried outfor comparison.Hydrocracking of more complex polymers has been studied in Chapter 6. Polymersin plastic wastes are not only composed of carbon and hydrogen. Thus, ABS, withalso nitrogen, has been first studied. ABS, besides, is composed of PS, PB andPAN, and the effect of mixture can be also analyzed. Additionally, halogens arecommonly found in plastic wastes, either in the polymer molecules or in additivessuch as flame retardants. Thus, a residual ABS, with additives and fillers, has beenalso studied in Chapter 6. The effect of pressure, temperature and concentration ofpolymer has been analyzed, mainly focused on the yield to gasoline and itscomposition.Actual, more complex, plastic wastes have been also studied in Chapter 6. Plasticwastes from cellular phones (CP) have been chosen because of their content ofABS and complexity, focused also in the yield to gasoline and its composition.Plastic wastes with a high content of inorganic components, such as many of thewastes from electrical and electronic equipment, are not suitable for catalytichydrocracking. Thus, steam gasification to produce hydrogen has been proposedand studied as an alternative valorization process in Chapter 7, applied to phenolicboards, the main plastic component in printed circuits.Electronic wastes usually include a significant amount of metals in theircomposition. These metals could act as catalysts in steam reforming of theplastics. This catalytic effect has been also studied, with nickel or tantalumcapacitors (TC). The catalytic effect of the presence of molten carbonates in avessel together with the wastes was the object of a previous study. In this work, thecombined effect of nickel and molten carbonates has been also analyzed.Finally, Chapters 9 and 10 summarize the nomenclature and the literature used allover the work, respectively.