BTEX recovery from waste rubbers by catalytic pyrolysis over Zn loaded tire derived char

Chemical Recycling of Mixed Polyolefin Post-Consumer Plastic Waste Sorting Residues (MPO323)-Auto-Catalytic Reforming and Decontamination with Pyrolysis Char as an Active Material

Mixed plastic packaging waste sorting residue (MPO323) was treated by thermal pyrolysis to utilize pyrolysis oil and char. The pyrolysis oil was found to contain aromatic and aliphatic hydrocarbons. The chlorine and bromine contents were as high as 40,000 mg/kg and 200 mg/kg, respectively. Additionally, other elements like sulfur, phosphorous, iron, aluminum, and lead were detected, which can be interpreted as impurities relating to the utilization of oils for chemical recycling. The pyrolysis char showed high contents of potentially active species like silicon, calcium, aluminum, iron, and others. To enhance the content of aromatic hydrocarbons and to reduce the level of contaminants, pyrolysis oil was reformed with the corresponding pyrolysis char to act as an active material in a fixed bed. The temperature of the reactor and the flow rate of the pyrolysis oil feed were varied to gain insights on the cracking and reforming reactions, as well as on performance with regard to decontamination.

Desulfurization and upgrade of pyrolytic oil and gas during waste tires pyrolysis: The role of metal oxides

Pyrolysis can effectively convert waste tires into high-value products. However, the sulfur-containing compounds in pyrolysis oil and gas would significantly reduce the environmental and economic feasibility of this technology. Here, the desulfurization and upgrade of waste tire pyrolysis oil and gas were performed by adding different metal oxides (Fe2O3, CuO, and CaO). Results showed that Fe2O3 exhibited the highest removal efficiency of 87.7 % for the sulfur-containing gas at 600 °C with an outstanding removal efficiency of 99.5 % for H2S. CuO and CaO were slightly inferior to Fe2O3, with desulfurization efficiencies of 75.9 % and 45.2 % in the gas when added at 5 %. Fe2O3 also demonstrated a notable efficacy in eliminating benzothiophene, the most abundant sulfur compound in pyrolysis oil, with a removal efficiency of 78.1 %. Molecular dynamics simulations and experiments showed that the desulfurization mechanism of Fe2O3 involved the bonding of Fe-S, the breakage of C-S, dehydrogenation and oxygen migration process, which promoted the conversion of Fe2O3 to FeO, FeS and Fe2(SO4)3. Meanwhile, Fe2O3 enhanced the cyclization and dehydrogenation reaction, facilitating the upgrade of oil and gas (monocyclic aromatics to 57.4 % and H2 to 22.3 %). This study may be helpful for the clean and high-value conversion of waste tires.

A review on value-addition to plastic waste towards achieving a circular economy

Plastic and mixed plastic waste (PW) has received increased worldwide attention owing to its huge rate of production, high persistency in the environment, and unsustainable waste management practices. Therefore, sustainable PW management and upcycling approaches are imperative to achieve the objectives of the United Nations Sustainable Development Goals. Numerous recent studies have shown the application and feasibility of various PW conversion techniques to produce materials with better economic value. Within this framework, the current review provides an in-depth analysis of cutting-edge thermochemical technologies such as pyrolysis, gasification, carbonization, and photocatalysis that can be used to value plastic and mixed PW in order to produce energy and industrial chemicals. Additionally, a thorough examination of the environmental impacts of contemporary PW upcycling techniques and their commercial feasibility through life cycle assessment (LCA) and techno-economical assessment are provided in this review. Finally, this review emphasizes the opportunities and challenges accompanying with existing PW upcycling techniques and deliver recommendations for future research works.

Converting waste tires into p-cymene through hydropyrolysis and selective gas-phase hydrogenation/dehydrogenation

The resource utilization and valorization of waste tires (WT) are of significant importance in reducing environmental pollution. To produce high-value p-cymene from WT, we propose a catalytic cascade process combining hydropyrolysis and catalytic gas-phase hydrotreating in a two-stage fixed-bed reactor. The effect of catalysts prepared with three different acidic supports on the hydrogenation/dehydrogenation of limonene, a compound derived from the hydropyrolysis of WT, was investigated. The p-cymene formation could be controlled by optimizing process parameters, including hydropyrolysis temperature, hydrogenation temperature, and catalyst-to-feedstock ratio (C/F). Experimental results indicated that, in the absence of a catalyst, limonene was the main product of WT depolymerization. Under optimized conditions (hydropyrolysis temperature of 425 ℃, hydrotreating temperature of 400 ℃, C/F of 10:1, and reaction pressure of 0.15 MPa), the highest relative content of p-cymene (79.1%) was obtained over the Pd/SBA-15 catalyst. This demonstrates that our proposed catalytic cascade process of hydropyrolysis and selective gas-phase hydrogenation/dehydrogenation can convert WT into p-cymene with high added value.

Influences and mechanisms of pyrolytic conditions on recycling BTX products from passenger car waste tires

Pyrolysis is an effective method for waste tire disposal. However, it has rarely been used to recycle specific highly valuable components (such as benzene, toluene, and xylene (BTX)) from tire rubbers, owing to complicated pyrolytic reactions. This study investigated the pyrolysis process of passenger-car-waste-tires (PCWT) with the help of TG-DTG and Py-GC/MS. Based on response surface methodology (RSM), the effect of pyrolytic parameters on the yields of pyrolytic oil and BTX is evaluated. Furthermore, the BTX generation mechanisms are discussed from the perspective of aliphatic and aromatic hydrocarbon transformations. Additionally, pyrolytic conditions including temperature, rubber particle size, pressure, and gas flow rate were systemically investigated and the optimum pyrolytic condition for yield of BTX (26.5 g per 100 g tire rubber) was obtained [765 K, 0.7 mm, 0.52 MPa and 2.5 mL (g min)-1]. Therein, yield of benzene, toluene and xylene were 1.07, 5.03 and 20.40 g per 100 g tire rubber, respectively. During PCWT pyrolysis, BTX is primarily obtained via the Diels-Alder reactions of small-chain alkenes and transformations of limonene and aromatics. This study elucidates the BTX generation mechanisms during PCWT pyrolysis and clarifies the effects of varying pyrolytic conditions on BTX generation.

Valorisation of spent tire rubber as carbon adsorbents for Pb(II) and W(VI) in the framework of a Circular Economy

Spent tire rubber-derived chars and their corresponding H3PO4 and CO2-activated chars were used as adsorbents in the recovery of Pb(II) ion and (W(VI)) oxyanion from synthetic solutions. The developed chars (both raw and activated) were thoroughly characterized to have insight about their textural and surface chemistry properties. H3PO4-activated chars presented lower surface areas than the raw chars and an acidic surface chemistry which affected the performance of these samples as they showed the lowest removals of the metallic ions. On the other hand, CO2-activated chars presented increased surface areas and increased mineral content compared to the raw chars, having presented higher uptake capacities for both Pb(II) (103-116 mg/g) and W(VI) (27-31 mg/g) ions. Cation exchange with Ca, Mg and Zn ions was appointed as a mechanism for Pb removal, as well as surface precipitation in the form of hydrocerussite (Pb3(CO3)2(OH)2). W(VI) adsorption might have been ruled by strong electrostatic attractions between the negatively charged tungstate species and the highly positively charged carbons' surface.The results shown in this work allow concluding that the valorisation of spent tire rubber through pyrolysis and the subsequent activation of the obtained chars is an alternative and a feasible option to generate adsorbent materials with a high uptake capacity of critical metallic elements.

Modelling and simulation of waste tire pyrolysis process for recovery of energy and production of valuable chemicals (BTEX)

The pyrolysis oil fraction is highly attractive for pyrolysis products. A simulated flowsheet model of a waste tire pyrolysis process is presented in this paper. A kinetic rate-based reaction model and equilibrium separation model are created in the Aspen Plus simulation package. The simulation model is effectively proven against experimental data of literature at temperatures of 400, 450, 500, 600 and 700 °C. Also, the developed model was employed to investigate the impact of temperature on the pyrolysis procedure and demonstrated that there is an optimum temperature for chain fractions. The optimum temperature to have the highest amount of limonene (as a precious chemical product of waste tire pyrolysis process) was found 500 °C. The findings indicated that the pyrolysis process is ecologically benign, although there is still space for development. In addition, a sensitivity analysis was carried out to see how altering the heating fuel in the process would affect the non-condensable gases produced in the process. Reactors and distillation columns in the Aspen Plus^® simulation model was developed to assess the technical functioning of the process (e.g., upgrading the waste tires into limonene). Furthermore, this work focuses on the optimization of the operating and structure parameters of the distillation columns in the product separation unit. The PR-BM, as well as NRTL property models, were applied in the simulation model. The calculation of non-conventional components in the model was determined using HCOALGEN and DCOALIGT property models.

On Fractioning the Tire Pyrolysis Oil in a Pilot-Scale Distillation Plant under Industrially Relevant Conditions

Tire pyrolysis oil (TPO) is one of the most interesting products derived from the pyrolysis of end-of-life tires. Among others, it contains valuable chemicals, such as benzene, toluene, ethylbenzene, and xylene (BTEX), as well as limonene. In order to recover these chemicals, a pilot-scale distillation plant has been designed, erected, and operated using TPO derived from an industrial-scale pyrolysis plant. The distillation facility consists of a packed column (20 kg/h) and is within the fifth technological readiness level. This work describes for the first time the fractioning of the TPO in a continuous operational mode under industrially relevant conditions. For this purpose, different reboiler temperatures (250-290 °C) and reflux ratios (up to 2.4) were preliminarily assessed on the yields and properties of the resulting products: light fraction (LF) and heavy fraction (HF). Thus, the distillation plant is capable of producing 27.0-36.7 and 63.3-73.0 wt % of LF and HF, respectively. The highest BTEX concentration in the LF (55.2 wt %) was found using a reboiler temperature of 250 °C and a reflux ratio of 2.4. Contrarily, the highest limonene concentration (4.9 wt %) in the LF was obtained at 290 °C in the reboiler without reflux. In this sense, the lower the reboiler temperature, the higher the BTEX, and the lower the limonene concentration in the LF. The main results herein obtained serve to gain key insights to operate packed distillation columns using complex and promising hydrocarbons as TPO in order to recover valuable products. In addition, this work provides significant information for optimizing the recovery efficiencies of both BTEX and limonene, as well as their potential applications including that for the resulting HF.

Formation Mechanism of Monocyclic Aromatic Hydrocarbons during Pyrolysis of Styrene Butadiene Rubber in Waste Passenger Car Tires

The production of aromatic hydrocarbons from the waste tire pyrolysis attracts more and more attention because of its tremendous potential. Based on styrene-butadiene rubber (SBR), which is the main rubber in the waste passenger car tires, this work studies the temperature influence on primary pyrolysis product distribution by experimental techniques (Py-GC/MS, TG-MS), and then, the formation mechanism of monocyclic aromatic hydrocarbons (MAHs) observed in the experiment was analyzed by first-principles calculations. The experimental results show that the MAHs during the pyrolysis mainly include styrene, toluene, and xylene, and subsequent calculations showed that these compounds were formed through a series of primary and secondary reactions. The formation pathways of these typical MAHs were studied via the reaction energy barrier analysis, respectively. It shows that the MAHs were not only derived from the benzene ring in the SBR chain but also generated from short-chain alkenes through the Diels-Alder reaction. The obtained pyrolysis reaction mechanism provides theoretical guidance for the regulation of the pyrolysis product distribution of MAHs.