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The oil obtained by LDPE thermal cracking, which is formed by linear olefins and paraffins with a broad carbon atom range, has been upgraded by hydroprocessing over Pd/ZSM-5 catalysts. As a consequence of this treatment, gasoline and diesel range hydrocarbons are produced with an enhanced content of isoparaffins and aromatics, while the presence of olefins is strongly reduced. The use of hierarchical zeolitic supports with a secondary porosity has a positive effect on the catalytic activity in the main reactions taking place (hydrogenation, hydroisomerization, cracking, oligomerization and aromatization), which is assigned to the higher reactant accessibility achieved with the hierarchical ZSM-5 compared to a nanocrystalline ZSM-5 sample used as reference. On the other hand, the acidic features of the zeolite have been controlled by variation of the Si/Al ratio in the 30–300 range, which has allowed adjusting the extension of the metal and acid sites catalyzed reactions. In overall, the use of Pd/h-ZSM-5 catalysts allows the hydroprocessing of the LDPE thermal cracking oil to be conducted in an effective way improving significantly the feed properties regarding its potential use in the formulation of transportation fuels. Thus, adjusting the catalyst properties and the operating conditions it is possible to achieve a high selectivity towards liquid fuels (over 95%), avoiding excessive cracking, and to control their composition leading to high isoparaffins and aromatics content with a low share of olefinic compounds. Finally, a reaction scheme has been proposed taking into account the main transformations occurring during the hydroprocessing treatment. [ABSTRACT FROM AUTHOR]

The effect of Ru on co-impregnated NiRu-supported hierarchical Beta zeolite (NiRu/h-Beta) and Ru/h-Beta as catalysts in the hydroreforming of the oil obtained by LDPE thermal cracking has been investigated, determining the thermal stability of the metal particles after two reaction-regeneration cycles. The formation of Ni–Ru particles on the fresh catalysts has been evidenced by XRD, H 2 -TPR and EDS analyses. Bimetallic Ni–Ru catalysts enhanced the light diesel share. Regeneration treatment by calcination in air and reduction under hydrogen of the spent catalysts largely recovered the original activity of fresh Ni5% + Ru1%/h-Beta while a stabilizing effect of ruthenium on nickel particles against sintering was observed. On the contrary, regeneration treatments on Ru1%/h-Beta clearly modified the feature of the metallic phase forming larger Ru nanoparticles. Thus, the regenerated Ru/h-Beta gave rise to more oligomerization activity in the second reaction cycle, leading to almost 24% of heavy diesel. [ABSTRACT FROM AUTHOR]

Abstract: The hydroreforming of the liquid product resulting from LDPE thermal cracking at 400°C (C5–C40) has been studied using Ni supported hierarchical zeolites (Ni/h-ZSM-5, Ni/h-Beta) and mesostructured materials (Ni/Al-MCM-41 and Ni/Al-SBA-15) as catalysts. Hydroreforming experiments were carried out at 310°C under 20bar of hydrogen. All the catalysts were synthesized with a Si/Al atomic ratio of 30 and a Ni content of 7wt%. According to XRD, TPR and TEM data, the activated catalysts displayed Ni particles both over the external surface and inside the catalyst pores in different percentages depending on their porous structure and nature. Complete hydrogenation of the olefins was observed over both mesostructured catalysts (Ni/Al-SBA-15 and Ni/Al-MCM-41) and hierarchical Ni/h-Beta. In contrast, over Ni/h-ZSM-5, there is always left about 30% of olefins, due to an imbalance in the acid and metal function. Ni/h-ZSM-5 led towards significant amounts of gases (∼18%) while gasoline range hydrocarbons were the main products (55%) over Ni/h-Beta, at the expense of diesel fractions. In contrast, the hydrocracking extent was far lower over Ni/Al-MCM-41 and Ni/Al-SBA-15, the latter showing additionally the appearance of a slight degree of oligomerization, which led towards an increase in the heavy diesel fraction (C19–C40). Hydroisomerization reactions also occur, mostly in the case of Ni supported hierarchical zeolites. Likewise, aromatics were formed over these catalysts in a large extent. The RON number of the gasolines obtained at 310°C was within 81–89 depending on the chosen catalysts while the cetane index (CCI) of the diesel fraction was around 70–80. On the other hand, Ni leaching was not detected. [Copyright &y& Elsevier]

Abstract: Hierarchical ZSM-5 zeolite has been synthesized by means of a method involving a precrystallization stage to form the protozeolitic units, the addition and subsequent grafting of both silanization and alkoxylation agents, and a final hydrothermal crystallization. The influence of the alkoxylation with different alcohols (methanol, ethanol, 2-propanol and n-butanol) on the properties of the final hierarchical ZSM-5 samples has been investigated. In every case, the alcohol addition increased the incorporation of the seed silanization agent as it decreases the gel viscosity. In addition, the presence of alcohols deeply affects the physicochemical properties of the final materials. The samples prepared with 2-propanol and methanol were highly crystalline and presented improved textural properties with regard to the reference h-ZSM-5 and n-ZSM-5. In contrast, the samples obtained with ethanol and n-butanol were partially and totally X-ray amorphous, respectively. 1H and 13C-CP solid state MAS NMR spectra proved the alkoxylation of the external surface of the protozeolitic units. Catalytic cracking of LDPE pointed out the higher TOF values obtained over the hierarchical samples prepared with methanol and 2-propanol due to a right combination of accessibility and crystallinity in these materials. The differences observed among the samples prepared with alcohols were ascribed to the strong interaction produced between the silanization agent and the linear alcohols on the surface of the protozeolitic nanounits, which form a very stable protective layer, hindering their aggregation and subsequent crystallization. [Copyright &y& Elsevier]

Abstract: Two series of hierarchical nanocrystalline ZSM-5 zeolites prepared by different synthesis strategies (at low temperature and from silanized seeds) and with external surface areas ranging from 150 to 250m2 g−1 were tested in the cracking of pure LDPE and HDPE at 340°C and of waste polyethylene at 360°C. Hierarchical zeolites showed quite higher activity, with values even six times higher than a standard nanocrystalline sample used as reference (n-HZSM-5). The activity values decreased from LDPE to HDPE due to the occurrence of some degree of branching in the former polymer, which act as preferential cracking sites. The major products were C1–C4 hydrocarbons (in the range 30–70%, mostly C3–C4 olefins) and C5–C12 hydrocarbons (20–60%), whose share depends on both the polyolefin and the catalyst. The amount of C13–C40 hydrocarbons was practically negligible (<1%) due to the high acid strength of the zeolites which promotes end-chain cracking reactions. Likewise, hierarchical nanocrystalline HZSM-5 zeolites prepared from silanized protozeolitic units showed higher activities than the hierarchical nanocrystalline HZSM-5 samples synthesized at low temperature and atmospheric pressure. The differences were especially remarkable in the case of waste polyethylene cracking. These results were ascribed to the stronger acidity of the hierarchical zeolite samples prepared from silanized seeds. [ABSTRACT FROM AUTHOR]

Abstract: Catalytic cracking of low density polyethylene (LDPE) has been investigated using different samples of mordenite zeolite as catalyst. In order to obtain materials with different textural properties, a new synthesis method based on the functionalization of the zeolite seeds with an organosilane was employed. Mordenite samples with BET and external surface areas in the range 385–485 and 9–57m2/g, respectively, were prepared. LDPE catalytic cracking reactions were performed at 420°C for 2h in a batch reactor provided with a screw stirrer under a continuous nitrogen flow. Thermal cracking of LDPE leads to plastic conversion lower than 30%, while values of 40% are reached when traditional mordenite is used as catalyst. In contrast, when mordenite samples with enhanced textural properties were employed, a plastic conversion of 60% is attained, both gas (C1–C5) and gasoline (C6–C12) fractions being obtained as main products. On the contrary, gasoline fraction is not observed and a heavier hydrocarbon fraction in the range C13–C35 is detected when thermal cracking or even catalytic cracking over traditional mordenite samples are carried out. The formation of lighter hydrocarbon products (C6–C12) over mordenite samples with enhanced textural properties is assigned to the higher activity and accessibility of their acid sites, which promotes both end-chain and random scission cracking reactions of the polymer molecules. [Copyright &y& Elsevier]

H-ZSM-5 and H-Beta zeolites ion-exchanged with alkali (Na+ and K+) and alkaline-earth (Mg2+) metals have been explored for the catalytic fast pyrolysis of lignin. Incorporating these metals led to a significant change in the acidic properties of the parent zeolites turning into mostly Lewis-type acidity. Catalytic fast pyrolysis experiments of lignin were performed in a fixed bed reactor with ex-situ configuration operating at 550 °C (thermal zone) and 450 °C (catalytic zone), atmospheric pressure and under a nitrogen flow. Moreover, two catalysts to lignin mass ratios (C/L = 0.2 and 0.4) were studied. Compared with non-catalytic tests, the use of parent zeolites caused a decrease in the bio-oil* (water-free basis) yield due to enhanced production of gases, water, and the coke deposition on the catalyst. In addition, the quality of bio-oil* was improved since it presents a lower oxygen content regarding the thermal test. H-Beta zeolite showed a higher deoxygenation degree than H-ZSM-5, but the latter exhibited a higher share of light components in the bio-oil* that can be detected by GC-MS analyses. Both catalysts promoted the production of light oxygenates, aromatics, and oxygenated aromatics. Regarding the effect of the incorporation of metals, oxygenated aromatic compounds were the predominant family in the bio-oil* obtained with all ion-exchanged zeolites. Likewise, significant differences were observed among the catalysts regarding the main components of this family (alkylphenols, guaiacols, syringols, catechols, and methoxybenzenes), achieving guaiacols concentrations in bio-oil* near to 24 wt.% for NaH-ZSM-5 and KH-ZSM-5 catalysts, and alkylphenols concentrations close to 16 wt.% for MgH-Beta and KH-Beta zeolites. [Display omitted] • Compared to thermal test, bio-oil* quality is improved by using H-Beta and H-ZSM-5. • CFP increases the concentration of GC-MS detected bio-oil* compounds. • The main family in bio-oil* is oxygenated aromatics for all the ion-exchanged zeolites. • NaH-ZSM-5 and KH-ZSM-5 catalysts favoured the formation of guaiacols. • MgH-Beta and KH-Beta zeolites promote guaiacols and alkylphenols production. [ABSTRACT FROM AUTHOR]

Abstract: Six acid solids of varying acid and textural characteristics has been investigated for their catalytic activity in the degradation of plastic polymers using thermogravimetric and differential thermal analysis. The polymers included pure low-density polyethylene, pure high-density polyethylene and two samples of recycled polyethylene of urban and agricultural origins. The catalysts were three zeolitic materials (standard ZSM-5, nanocrystalline n-ZSM-5 and Beta) and three mesostructured solids (sol–gel Al-MCM-41 (sg), hydrothermal Al-MCM-41 (hy) and Al-SBA-15). The catalytic activity of each acid solid has been related to its capacity to shift the degradation reaction to lower temperatures. Despite showing strong acid properties, standard ZSM-5 zeolite exhibited a very low catalytic activity on most plastics, which was attributed to diffusional impediments that affected the access of the bulky polymer molecules to its internal active sites. These impediments were partly overcome in the case of Beta zeolite and even more markedly with nanocrystalline n-ZSM-5, which exhibited the strongest catalytic activity due to a combination of strong acid properties and large external surface area. Owing to their non-crystalline nature, mesostructured solids showed weaker acid properties than their zeolitic counterparts. However, this disadvantage was partly compensated by the presence of larger pores that reduced diffusional hindrances. Thus, Al-MCM-41 (hy) exhibited one of the highest catalytic activities, largely surpassing the performance of crystalline solids with stronger acid properties. The catalytic activity of all the acid solids tested in this work was significantly reduced when they were used on waste plastics. This deactivating effect was more notable in mesostructured solids. [Copyright &y& Elsevier]