Pyrolysis of mixed plastic waste: Predicting the product yields.

The predictability of pyrolysis yields and product composition of mixed plastics has been studied. To do so, pyrolysis of virgin polymers (HDPE, LDPE, PP, PS and PET) and eight individual sorting categories from a real waste DKR-350 stream (PE rigid/film, PP rigid/film, PET, PS, multilayer flexibles, and clogged materials) was performed in a batch reactor at 500 °C at laboratory scale. The obtained oil/wax, gas, and solid yields and the composition of oil/wax of those individual feedstocks were used as input of a superposition model to predict the corresponding pyrolysis yields and oil/wax composition of mixed feeds, which were later compared with the experimentally measured product yields from the pyrolysis of those mixed streams. This linear model predicts the oil/wax yield of the mixed streams to a reasonable extent, with a maximum yield deviation (overestimation) of 8 percentage points. However, the presence of significant amounts of PET (above 33 wt%) in the mixed plastic streams negatively impacts the production of the condensable product and promotes the formation of solid products beyond the expected predicted values. Quantification of the type of carbon (aliphatic, aromatic and carbonyl) present in all the oil/wax products was done using 13C NMR spectroscopy. A linear model could also predict the aliphatic carbon yield in the condensable product from plastic waste streams with high accuracy (maximum yield difference of 6 percentage points). However, the aromatic carbon yield could not be predicted, probably due to the observed behavior of PET, which interacts with other polymers to promote solid product formation.

Novel Route to Produce Hydrocarbons from Woody Biomass Using Molten Salts.

The thermochemical decomposition of woody biomass has been widely identified as a promising route to produce renewable biofuels. More recently, the use of molten salts in combination with pyrolysis has gathered increased interest. The molten salts may act as a solvent, a heat transfer medium, and possibly also a catalyst. In this study, we report experimental studies on a process to convert woody biomass to a liquid hydrocarbon product with a very low oxygen content using molten salt pyrolysis (350-450 °C and atmospheric pressure) followed by subsequent catalytic conversions of the liquids obtained by pyrolysis. Pyrolysis of woody biomass in molten salt (ZnCl2/NaCl/KCl with a molar composition of 60:20:20) resulted in a liquid yield of 46 wt % at a temperature of 450 °C and a molten salt/biomass ratio of 10:1 (mass). The liquids are highly enriched in furfural (13 wt %) and acetic acid (14 wt %). To reduce complexity and experimental issues related to the production of sufficient amounts of pyrolysis oils for further catalytic upgrading, model studies were performed to convert both compounds to hydrocarbons using a three-step catalytic approach, viz., (i) ketonization of acetic acid to acetone, (ii) cross-aldol condensation between acetone and furfural to C8-C13 products, followed by (iii) a two-stage catalytic hydrotreatment of the latter to liquid hydrocarbons. Ketonization of acetic acid to acetone was studied in a continuous setup over a ceria-zirconia-based catalyst at 250 °C. The catalyst showed no signs of deactivation over a period of 230 h while also achieving high selectivity toward acetone. Furfural was shown to have a negative effect on the catalyst performance, and as such, a separation step is required after pyrolysis to obtain an acetic-acid-enriched fraction. The cross-aldol condensation reaction between acetone and furfural was studied in a batch using a commercial Mg/Al hydrotalcite as the catalyst. Furfural was quantitatively converted with over 90% molar selectivity toward condensed products with a carbon number between C8 and C13. The two-stage hydrotreatment of the condensed product consisted of a stabilization step using a Ni-based Picula catalyst and a further deep hydrotreatment over a NiMo catalyst, in both batch setups. The final product with a residual 1.5 wt % O is rich in (cyclo)alkanes and aromatic hydrocarbons. The overall carbon yield for the four-step approach, from pinewood biomass to middle distillates, is 21%, assuming that separation of furfural and acetic acid after the pyrolysis step can be performed without losses.

Iron Tetrasulfonatophthalocyanine-Catalyzed Starch Oxidation Using H2O2: Interplay between Catalyst Activity, Selectivity, and Stability.

Oxidized starch can be efficiently prepared using H2O2 as an oxidant and iron(III) tetrasulfophthalocyanine (FePcS) as a catalyst, with properties in the same range as those for commercial oxidized starches prepared using NaOCl. Herein, we performed an in-depth study on the oxidation of potato starch focusing on the mode of operation of this green catalytic system and its fate as the reaction progresses. At optimum batch reaction conditions (H2O2/FePcS molar ratio of 6000, 50 °C, and pH 10), a high product yield (91 wt %) was obtained with substantial degrees of substitution (DSCOOH of 1.4 and DSCO of 4.1 per 100 AGU) and significantly reduced viscosity (197 mPa·s) by dosing H2O2. Model compound studies showed limited activity of the catalyst for C6 oxidation, indicating that carboxylic acid incorporation likely results from C-C bond cleavage events. The influence of the process conditions on the stability of the FePcS catalyst was studied using UV-vis and Raman spectroscopic techniques, revealing that both increased H2O2 concentration and temperature promote the irreversible degradation of the FePcS catalyst at high pH. The rate and extent of FePcS degradation were found to strongly depend on the initial H2O2 concentration where also the rapid decomposition of H2O2 by FePcS occurs. These results explain why the slow addition of H2O2 in combination with low FePcS catalyst concentration is beneficial for the efficient application in starch oxidation.

Influence of Sulfuric Acid on the Performance of Ruthenium-based Catalysts in the Liquid-Phase Hydrogenation of Levulinic Acid to γ-Valerolactone.

The presence of biogenic or process-derived impurities poses a major problem on the efficient catalytic hydrogenation of biomass-derived levulinic acid to γ-valerolactone; hence, studies on their influence on catalyst stability are now required. Herein, the influence of sulfuric acid as feed impurity on the performance of Ru-based heterogeneous catalysts, including Ru/ZrO2 and mono- and bimetallic Ru-on-carbon catalysts in dioxane as solvent, was investigated. The carbon-supported Ru catalysts proved to be very sensitive to minor amounts of sulfuric acid. In stark contrast, Ru/ZrO2 showed a remarkable stability in the presence of the same impurity, which is attributed to the sulfate-ion adsorption capacity of the support. Preferential sulfate adsorption onto the surface of ZrO2 effectively protects the Ru active phase from deactivation by sulfur poisoning. A simple catalyst regeneration strategy was effective in removing adsorbed impurities, allowing efficient catalyst recycling.

Selectivity Control in the Tandem Aromatization of Bio-Based Furanics Catalyzed by Solid Acids and Palladium.

Bio-based furanics can be aromatized efficiently by sequential Diels-Alder (DA) addition and hydrogenation steps followed by tandem catalytic aromatization. With a combination of zeolite H-Y and Pd/C, the hydrogenated DA adduct of 2-methylfuran and maleic anhydride can thus be aromatized in the liquid phase and, to a certain extent, decarboxylated to give high yields of the aromatic products 3-methylphthalic anhydride and o- and m-toluic acid. Here, it is shown that a variation in the acidity and textural properties of the solid acid as well as bifunctionality offers a handle on selectivity toward aromatic products. The zeolite component was found to dominate selectivity. Indeed, a linear correlation is found between 3-methylphthalic anhydride yield and the product of (strong acid/total acidity) and mesopore volume of H-Y, highlighting the need for balanced catalyst acidity and porosity. The efficient coupling of the dehydration and dehydrogenation steps by varying the zeolite-to-Pd/C ratio allowed the competitive decarboxylation reaction to be effectively suppressed, which led to an improved 3-methylphthalic anhydride/total aromatics selectivity ratio of 80 % (89 % total aromatics yield). The incorporation of Pd nanoparticles in close proximity to the acid sites in bifunctional Pd/H-Y catalysts also afforded a flexible means to control aromatic products selectivity, as further demonstrated in the aromatization of hydrogenated DA adducts from other diene/dienophile combinations.

A Facile Solid-Phase Route to Renewable Aromatic Chemicals from Biobased Furanics.

Renewable aromatics can be conveniently synthesized from furanics by introducing an intermediate hydrogenation step in the Diels-Alder (DA) aromatization route, to effectively block retro-DA activity. Aromatization of the hydrogenated DA adducts requires tandem catalysis, using a metal-based dehydrogenation catalyst and solid acid dehydration catalyst in toluene. Herein it is demonstrated that the hydrogenated DA adducts can instead be conveniently converted into renewable aromatics with up to 80% selectivity in a solid-phase reaction with shorter reaction times using only an acidic zeolite, that is, without solvent or dehydrogenation catalyst. Hydrogenated adducts from diene/dienophile combinations of (methylated) furans with maleic anhydride are efficiently converted into renewable aromatics with this new route. The zeolite H-Y was found to perform the best and can be easily reused after calcination.

Substituted Phthalic Anhydrides from Biobased Furanics: A New Approach to Renewable Aromatics.

A novel route for the production of renewable aromatic chemicals, particularly substituted phthalic acid anhydrides, is presented. The classical two-step approach to furanics-derived aromatics via Diels-Alder (DA) aromatization has been modified into a three-step procedure to address the general issue of the reversible nature of the intermediate DA addition step. The new sequence involves DA addition, followed by a mild hydrogenation step to obtain a stable oxanorbornane intermediate in high yield and purity. Subsequent one-pot, liquid-phase dehydration and dehydrogenation of the hydrogenated adduct using a physical mixture of acidic zeolites or resins in combination with metal on a carbon support then allows aromatization with yields as high as 84 % of total aromatics under relatively mild conditions. The mechanism of the final aromatization reaction step unexpectedly involves a lactone as primary intermediate.

One-step hydrothermal synthesis of manganese-containing MFI-type zeolite, Mn-ZSM-5, characterization, and catalytic oxidation of hydrocarbons.

Manganese-containing MFI-type Mn-ZSM-5 zeolite was synthesized by a facile one-step hydrothermal method using tetrapropylammonium hydroxide (TPAOH) and manganese(III)-acetylacetonate as organic template and manganese salts, respectively. A highly crystalline MFI zeolite structure was formed under pH = 11 in 2 days, without the need for additional alkali metal cations. Direct evidence of the incorporation of Mn in the zeolite framework sites was observed by performing structure parameter refinements, supported by data collected from other characterization techniques such as IR, Raman, UV-vis, TGA, N2-adsorption, SEM, TEM, EDAX, and XPS. UV-vis spectra from the unique optical properties of Mn-ZSM-5 show two absorption peaks at 250 and 500 nm. The absorption varies in different atmospheres accompanied by a color change of the materials due to oxygen evolution. Raman spectra show a significant and gradual red shift from 383 cm(-1) to 372 cm(-1) when the doping amount of Mn is increased from 0 to 2 wt %. This suggests a weakened zeolite structural unit induced by the Mn substitution. The catalytic activity was studied in both gas-phase benzyl alcohol oxidation and toluene oxidation reactions with remarkable oxidative activity presented for the first time. These reactions result in a 55% yield of benzaldehyde, and 65% total conversion of toluene to carbon dioxide for the 2% Mn-ZSM-5. Temperature programmed reduction (TPR) using CO in He demonstrates two reduction peaks: one between 300 and 500 °C and the other between 500 and 800 °C. The first reduction peak, due to manganese-activated oxidation sites shifted from higher temperature to lower temperature, and the peak intensity of CO2 rises when the dopant amount increases. For the first time, calculated photophysical properties of a model Mn(O-SiH3)4(-) compound, an Mn-embedded zeolite cluster, and model Mn oxides help to explain and interpret the diffuse reflectance spectroscopy of Mn-ZSM-5 zeolites.

Effects of visible and UV light on the characteristics and properties of crude oil-in-water (O/W) emulsions.

The effects of visible and UV light on the characteristics and properties of Prudhoe Bay (PB) and South Louisiana (SL) emulsions were investigated to better understand the role of sunlight on the fate of spilled crude oils that form emulsions with a dispersant in the aquatic environment. Before irradiation, crude oil emulsions showed the presence of dispersed crude oil micelles in a continuous water phase and crude oil components floating on the surface. The crude oil micelles decreased in size with irradiation, but emulsions retained their high degree of polydispersity. UV irradiation reduced the stability of emulsions more effectively than visible light. The reduction of micelles size caused the viscosity of emulsions to increase and melting point to decrease. Further, irradiation increased acid concentrations and induced ion formation which lowered the pH and increased the conductivity of emulsions, respectively. Ni and Fe in PB emulsions were extracted from crude oil with UV irradiation, which may provide an efficient process for metal removal. The emulsions were stable toward freeze/thaw cycles and their melting temperatures generally decreased with irradiation. Evidence of ˙OH production existed when emulsions were exposed to UV but not to visible light. The presence of H(2)O(2) enhanced the photodegradation of crude oil. Overall, the changes in emulsion properties were attributed to direct photodegradation and photooxidation of crude oil components.

Occurrence and sources of bromate in chlorinated tap drinking water in Metropolitan Manila, Philippines.

Significant levels of potentially carcinogenic bromate were measured in chlorinated tap drinking water in Metropolitan Manila, Philippines, using an optimized ion-chromatographic method. This method can quantify bromate in water down to 4.5 µg l⁻¹ by employing a postcolumn reaction with acidic fuchsin and subsequent spectrophotometric detection. The concentration of bromate in tap drinking water samples collected from 21 locations in cities and municipalities within the 9-month study period ranged from 7 to 138 µg l⁻¹. The average bromate concentration of all tap drinking water samples was 66 µg l⁻¹ (n = 567), almost seven times greater than the current regulatory limit in the country. The levels of bromate in other water types were also determined to identify the sources of bromate found in the distribution lines and to further uncover contaminated sites. The concentration of bromate in water sourced from two rivers and two water treatment plants ranged from 15 to 80 and 12 to 101 µg l⁻¹, respectively. Rainwater did not contribute bromate in rivers but decreased bromate level by dilution. Groundwater and wastewater samples showed bromate concentrations as high as 246 and 342 µg l⁻¹, respectively. Bromate presence in tap drinking water can be linked to pollution in natural water bodies and the practice of using hypochlorite chemicals in addition to gaseous chlorine for water disinfection. This study established the levels, occurrence, and possible sources of bromate in local drinking water supplies.