Hydrocarbon Pool Research Articles

The Paradoxical Influence of Hydrothermally Treated Zeolites on the Hydrocarbon Pool Mechanism.

Understanding the mechanistic intricacies of hydrothermally treated zeolite is crucial for valorizing any oxygen-containing renewable feedstocks (e.g., methanol, carbon dioxide, biomass). Additionally, the regeneration of deactivated zeolite catalysts under oxidative conditions, akin to hydrothermal treatment, is essential in industrial processes. While research in this area has predominantly focused on characterizing steaming-induced physicochemical changes in zeolite, their ultimate impact on the organic reaction mechanism governed by the hydrocarbon pool dual-cycle mechanism remains unclear. To bridge this knowledge gap, this study investigates the effect of steamed zeolite on the organic reaction mechanism during the industrially significant methanol-to-hydrocarbons process. We achieved this objective by strategically integrating catalytic and control experiments over the pristine and steamed zeolites and their advanced characterization, including under operando conditions, XRD structural refinement, and using "mobility-dependent" solid-state NMR spectroscopy. This multimodal characterization approach was instrumental in elucidating elusive mechanistic information in the dual-cycle mechanism, shedding light on phenomena such as the unchanged ethylene selectivity despite decreasing aromatics selectivity, while ethylene could solely be derived from arene-based reaction intermediates. This study could improve the process efficiency in zeolite catalysis by connecting steaming-induced changes in the organic reaction mechanisms with inorganic material aspects.

The Paradoxical Influence of Hydrothermally Treated Zeolites on the Hydrocarbon Pool Mechanism

Understanding the mechanistic intricacies of hydrothermally treated zeolite is crucial for valorizing any oxygen‐containing renewable feedstocks (e.g., methanol, carbon dioxide, biomass). Additionally, the regeneration of deactivated zeolite catalysts under oxidative conditions, akin to hydrothermal treatment, is essential in industrial processes. While research in this area has predominantly focused on characterizing steaming‐induced physicochemical changes in zeolite, their ultimate impact on the organic reaction mechanism governed by the hydrocarbon pool dual‐cycle mechanism remains unclear. To bridge this knowledge gap, this study investigates the effect of steamed zeolite on the organic reaction mechanism during the industrially significant methanol‐to‐hydrocarbons process. We achieved this objective by strategically integrating catalytic and control experiments over the pristine and steamed zeolites and their advanced characterization, including under operando conditions, XRD structural refinement, and using “mobility‐dependent” solid‐state NMR spectroscopy. This multimodal characterization approach was instrumental in elucidating elusive mechanistic information in the dual‐cycle mechanism, shedding light on phenomena such as the unchanged ethylene selectivity despite decreasing aromatics selectivity, while ethylene could solely be derived from arene‐based reaction intermediates. This study could improve the process efficiency in zeolite catalysis by connecting steaming‐induced changes in the organic reaction mechanisms with inorganic material aspects.

Unveiling the Brønsted acid mechanism for Meerwein–Ponndorf–Verley reduction in methanol conversion over ZSM-5

The conversion of methanol over zeolites offers a sustainable alternative for fuels and chemicals production. However, a complete understanding of the competing reaction pathways, particularly those leading to C-C bond formation, remains elusive. This work presents a novel mechanism for selective methanol conversion in ZSM-5 zeolites, involving a Brønsted acid site (BAS)-mediated Meerwein–Ponndorf–Verley (MPV) reduction pathway. Employing a multidimensional solid-state NMR spectroscopy combined with isotopic labeling and theoretical calculations, we identify this pathway for acetaldehyde reduction with methanol, directly contributing to ethene formation. This mechanism, involving carbenium ion intermediates like 1-hydroxyethane or 1-methoxyethane ions, contrasts with the well-established Lewis acid-catalyzed MPV process. Based on reactant adsorption modes, we propose two distinct reaction routes for BAS-MPV reduction, bridging the gap between direct and hydrocarbon pool mechanisms in methanol conversion. We further demonstrate the applicability of this pathway to acetone, highlighting its broader role in the early stages of the reaction.

Pyrolysis behaviour and synergistic effect in co-pyrolysis of wheat straw and polyethylene terephthalate: A study on product distribution and oil characterization

Renewable lignocellulosic biomass is a favorable energy resource since its co-pyrolysis with hydrogen-rich plastics can produce high-yield and high-quality biofuel. In contrast to earlier co-pyrolysis research that concentrated on increasing product yield, this study comprehends the synergistic effects of two distinct feedstocks that were not considered earlier. This work focuses on co-pyrolyzing wheat straw (WS) with non-reusable polyethylene terephthalate (PET) for the production of pyrolysis oil. WS and PET were blended in different ratios (100/0, 80/20, 60/40, 40/60, 20/80, and 0/100), and pyrolysis experiments were conducted in a fixed-bed reactor under different temperatures to assess their synergistic effect on oil yield. Synergy rates of up to 7.78 % were achieved on yield for the blends of plastic and biomass at a temperature of 500 °C. In comparison to individual biomass or plastics, co-pyrolyzing PET-biomass blends demonstrated good process interaction and promoted the yields of value-added products. The heating value of the pyrolysis oils was in the range of 16.45–28.64 MJ/kg, which depends on the amount of plastic present in the feedstock. The physical analysis of the oils shows that they can be used for heat production by direct combustion in boilers or furnaces. The correlation between WS and PET was validated with the aid of Fourier transform infrared spectroscopy (FT-IR) and gas chromatography-mass spectrometry (GC-MS) analysis. The GC-MS result demonstrated the presence of different compounds such as O-H compounds, esters, carbonyl group elements, acids, hydrocarbons, aromatics, and nitrogenated compounds in the pyrolysis oil, which differed based on the proportions of PET in the feedstock. The increased hydrocarbon and reduced oxygen percentages in the pyrolysis oil were implicitly caused by enhanced hydrocarbon pool mechanisms, in which the breakdown of PET may be supplied as a hydrogen donor. Overall, waste lignocellulosic biomass and plastics can be used to produce biofuels, which helps reduce the amount of solid waste that ends up in landfills. This study also revealed that future research should be focused on the reaction mechanisms of WS and PET co-pyrolysis in order to examine the synergistic interactions.

Presence of oxygen in catalytic pyrolysis of lignin impacts evolution of both coke and aromatic hydrocarbons

Coking is a major issue in catalytic pyrolysis of biomass over zeolite catalysts. Using oxidative gas might mitigate formation of carbonaceous deposits. This was verified herein by catalytic pyrolysis of lignin with different oxygen concentrations (0 %, 3 %, 6 %, 9 % and 12 %) in carrier gas using ZSM-5 as the catalyst at 600 °C. The results indicated that the O2 introduced oxidized both volatiles and biochar, reducing bio-oil yield from 29.2 to 20.7 % and biochar yield from 56.8 to 53.7 % with increasing O2 concentration from 0 to 12 %. Oxidation of intermediates in “hydrocarbon pool” on surface of catalyst decreased the yield of BTX from 11.5 % in inert gas to 6.1–8.0 % and also other aromatics with 1 or 2 benzene rings. The aromatics with rigid polycyclic aromatic structures were more resistant towards oxidation. However, toluene, xylene, and other aromatic hydrocarbons or phenolics with side chains were more prone to be oxidized, abundance of which decreased more significantly at high O2 concentrations. Such results were also observed in catalytic pyrolysis of guaiacol or vanillin. The benefit of using O2 was diminished formation of coke and/or precursors of coke over ZSM-5. Characterization of reaction intermediates in catalytic pyrolysis of lignin with in-situ IR showed that O2 presence remarkably decreased the abundance of aliphatic intermediates containing –OH, -C-H and C=O through oxidation reactions and also interrupted aromatization organics in both coke and biochar.

Anomalous diffusion of hydrocarbon vapor through an aqueous foam bubble structure

Hydrocarbons are known as “anti-foamers” because they cause bubble rupture, coalescence, and reduce foaming. We show that the dynamics of bubble structure allows hydrocarbon vapors permeate rapidly when an aqueous foam is placed on a hydrocarbon pool. Two distinct foam layers are formed. Vapor accumulates in an expanding bottom layer at the foam-pool interface where bubbles grow rapidly, rupture, and coalesce. Simultaneously, vapor diffuses through a top layer having small bubble structure, which changes slowly due to Ostwald-ripening. Very little vapor accumulates in the top layer, which has a constant thickness equal to the initial foam thickness. Surprisingly, both accumulation in the bottom layer and diffusion through top layer occur at constant rates, which are independent of time and initial foam thickness. The vapor diffusion rate in the top layer should have decreased, inversely proportional to the initial foam thickness, based on classical diffusion theory; only the fluorosurfactant containing foam (RefAFFF) placed on gasoline follows the classical theory where the bottom foam layer is absent. Therefore, we propose a theory to show a linear increase in diffusion time with initial foam thickness using an effective diffusion-coefficient. Experiments show that this variation could be because of increased liquid drainage, drying, and bubble coarsening, which are not considered explicitly in the theory. We also describe a theory for the expanding bottom layer to show that most vapor formed at the pool surface accumulates for very volatile hydrocarbons. The vapor diffusion controls foam ignition. We show that the measured foam ignition time also increases linearly with initial foam thickness, qualitatively consistent with the predicted diffusion time. By employing different hydrocarbons, we show that the measured foam ignition times decrease inversely proportion to square root of hydrocarbon vapor concentration for a given surfactant. This could be because a surfactant exhibits different degrees of oleophobicity towards different hydrocarbons that can reduce vapor adsorption, solubility, and diffusion at a bubble surface. Different surfactants also exhibit different degrees of oleophobicity towards a given hydrocarbon (n-pentane) and increase ignition times by a factor of six: RefAFFF having the longest ignition time, followed by siloxane-polyoxyethylene formulation, and its individual surfactant components.

Recent Progress on the Involvement of Formaldehyde in the Methanol-to-Hydrocarbons Reaction.

The conversion of methanol-to-hydrocarbons (MTH) over zeolite catalysts has been the subject of intense research since its discovery. Great effort has been devoted to the investigation of four key topics: the initiation of C-C bonds, the establishment of hydrocarbon pool (HCP), the adjustment of product selectivity, and the deactivation process of catalysts. Despite 50 years of study, some mechanisms remain controversial. However, an intermediate species, formaldehyde (HCHO), has recently garnered considerable attention for its influence on the entire MTH process. The discovery of HCHO and its significant role in the MTH process has been facilitated by the application of in situ analytical techniques, such as synchrotron radiation photoionization mass spectrometry (SR-PIMS) and photoelectron photoion coincidence spectroscopy (PEPICO). It is now revealed that HCHO is involved in the initiation, propagation, and termination process of MTH reaction. Such mechanistic understanding of HCHO's involvement has provided valuable insights for optimizing the MTH process.

Mechanistic investigation of methanol-to-olefins conversion catalyzed by H-ZSM-5 zeolite: a DFT study.

The mechanisms for the formation of the first C - C bond and lower olefins on methanol to olefins (MTO) conversion on H-ZSM-5 had been focused in dispute. In this paper, density functional theory has been used to study the reaction mechanisms of methanol to olefins on ZSM-5. The configurations of reactants, intermediates, products and transition state of the numerous reactions involved in such a process have been optimized, as well as the elementary reactions related to these configurations were determined by the calculation of corresponding activation energy barriers and reaction heats. Here, two different kinds of the mechanisms were proposed for the formation of dimethylether (DME), one involving an associative interaction of two methanol molecules with the zeolite Brønsted acid sites and the other occurring via a surface methoxy species and a methanol molecule. A critical intermediate of the methoxy methyl cation was theoretically verified by the reaction of the methoxy species and dimethylether. Besides, it was found that the first intermediates containing a C - C bond were 1,2-dimethoxyethane and 2-methoxy-ethanolare, in which the former was formed from methoxy species with dimethyl ether and the latter was formed from methanol by onium ions((CH3)2O+CH2CH2OCH3), respectively. For the whole reaction mechanism, the results in this paper indicated that the ethene formation is more favorable than propylene formation due to the low activation energy barrier for ethene formation (123.49 vs. 162.09kJ.mol-1). From these calculations, it would be concluded that ethene is the first alkene product that induces the occurrence of the hydrocarbon pool mechanism. All the periodic density function theory (DFT) calculations were performed by the Vienna Ab Initio Simulation package (VASP). The interaction between nucleus and valence electron was described using the pseudopotentials found in the projector augmented wave (PAW) method. PBE-D3 was used in the whole DFT calculations and CI-NEB was used to locate transition state.

Pyrolysis-catalysis of waste tire to enhance the aromatics selectivity via metal-modified ZSM-5 catalysts

Excessive untreated waste tires (WT) have posed threats to the environment and human health. Pyrolysis-catalysis, as a promising treatment technology, could convert WT into high-valued products such as pyrolysis oil. Moreover, BTX compounds (Benzene, toluene, and xylene) were important raw materials in the chemical industry. In order to sharply increase the BTX selectivity in the pyrolytic oil, transition metals (Ni and Fe) were impregnated on the ZSM-5 catalyst. Furthermore, this paper also explored the effect of catalysis modes, catalysts-to-feedstock mass ratios, and catalysis temperatures on the distribution of the aromatics in the WT pyrolysis-catalysis oil. The results suggested that the optimal operating parameters for BTX compound production with a selectivity of 39.87% were in-situ mode, catalysis temperature=600 °C, and catalyst-to-feedstock mass ratio=1:1 by applying Ni/ZSM-5. According to the GC-MS identification results, it proposed that the Diels-Alder reaction of isoprene and cracking and recombination of limonene in the aliphatic hydrocarbon pool were the main paths to generate the aromatics, while the addition of ethylene radicals in the monocyclic aromatic hydrocarbon (MAH) and polycyclic aromatic hydrocarbon (PAH) pools was dominant in the growth of the aromatics. The study provided a viable approach for upgrading WT to produce high-value aromatic products.

Boosted regeneration of coked SAPO-34 catalyst in MTO fluidized bed reactor by diluted air at elevated temperatures

SAPO-34 zeolite as an excellent catalyst for methanol-to-olefins (MTO) reaction suffers rapid deactivation by prevalent coking. Herein, regeneration of coked-SAPO-34 in a fluidized-bed reactor was successfully intensified by altering temperature (550–650 °C) and oxygen content (7–21 vol.%). Fresh, used, and regenerated catalysts were characterized by different methods to understand the correlation between regeneration conditions, coke content, and catalyst performance. The minor residual coke over the regenerated catalyst comprised active hydrocarbon pool intermediates (like naphthalene, benzaldehyde, phenol, and derivatives), which increased by decreasing regeneration temperature and promoted the selectivity to light olefins at earlier reaction times. The restored microporosity and lifetime of regenerated catalyst were superior by increasing temperature. However, higher attrition at 650 °C, as confirmed by SEM images, caused a partial weight loss of the catalyst and a slight decline in relative crystallinity, hence 600 °C was preferred with additional advantage of less energy consumption. Meanwhile, introducing lower oxygen not only moderated the coke oxidation rate but also enhanced the recovery of beneficial catalytic features for the MTO conversion. Consequently, considering an excellent regeneration as well as lower emission of CO2 detected in the flue gas, diluted air containing 14 vol.% O2 at 600 °C was suggested as the most promising method.

Influence of acid strength on olefin selectivity of chabazite (CHA) framework zeolite/zeotype during tandem CO2 hydrogenation

The role of Brønsted acid sites (BAS) strength of chabazite (CHA) framework on olefin selectivity during methanol-to-olefin (MTO) and tandem CO2 hydrogenation was investigated over an aluminosilicate, SSZ-13 and a silicoaluminophospate, SAPO-34 and their bifunctional admixtures with In2O3. During MTO, SSZ-13 and SAPO-34 yielded primarily olefins (cumulative selectivity of ∼60 % and ∼90 %, respectively at cumulative turnover number, TON over 500 molC/molH+). Interestingly, an interpellet admixture of In2O3/SSZ-13 (distance between redox sites and BAS of 260–900 µm) predominantly yielded paraffins (cumulative selectivity of ∼93 % at cumulative TON over 40) via the secondary hydrogenation of olefins as seen from the cumulative paraffin-to-olefin (P/O) ratio of ∼21 during CO2 hydrogenation. In comparison, an interpellet In2O3/SAPO-34 admixture yielded majority olefins (cumulative selectivity of ∼67 % at cumulative TON over 60) due to a lesser degree of secondary hydrogenation (cumulative P/O ratio of ∼0.2) on the BAS in SAPO-34, which has a lower acid strength as compared to SSZ-13. Interestingly, both interpellet admixtures of In2O3/SSZ-13 and In2O3/SAPO-34 remained stable during tandem CO2 hydrogenation by favoring the olefin cycle and suppressing the formation of deactivation-inducing-aromatics as probed via occluded hydrocarbon analysis, unlike MTO, where SSZ-13 and SAPO-34 showed fast deactivation. However, in intrapellet admixtures (distance between redox sites and BAS of 270–1500 nm) of In2O3/SSZ-13 and In2O3/SAPO-34, ion exchange of BAS (H+) with Inδ+ (from In2O3) inhibited C–C coupling and predominantly formed CH4. Overall, our study related the product selectivity and deactivation in MTO and tandem CO2 hydrogenation over CHA framework zeolite/zeotype to the aromatic and olefin cycle propagation in the hydrocarbon pool mechanism. These underpinnings will help with rational catalyst design for tandem CO2 hydrogenation.

Spontaneous Imbibition and an Interface-Electrostatics-Based Model of the Transition Zone Thickness of Hydrocarbon Reservoirs and Their Theoretical Interpretations

The transition zone (TZ) of hydrocarbon reservoirs is an integral part of the hydrocarbon pool which contains a substantial fraction of the deposit, particularly in carbonate petroleum systems. Consequently, knowledge of its thickness and petrophysical properties, viz. its pore size distribution and wettability characteristic, is critical to optimizing hydrocarbon production in this zone. Using classical formation evaluation techniques, the thickness of the transition zone has been estimated, using well logging methods including resistivity and Nuclear Magnetic Resonance, among others. While hydrocarbon fluids’ accumulation in petroleum reservoirs occurs due to the migration and displacement of originally water-filled potential structural and stratigraphic traps, the development of their TZ integrates petrophysical processes that combine spontaneous capillary imbibition and wettability phenomena. In the literature, wettability phenomena have been shown to also be governed by electrostatic phenomena. Therefore, given that reservoir rocks are aggregates of minerals with ionizable surface groups that facilitate the development of an electric double layer, a definite theoretical relationship between the TZ and electrostatic theory must be feasible. Accordingly, a theoretical approach to estimating the TZ thickness, using the electrostatic theory and based on the electric double layer theory, is attractive, but this is lacking in the literature. Herein, we fill the knowledge gap by using the interfacial electrostatic theory based on the fundamental tenets of the solution to the Poisson–Boltzmann mean field theory. Accordingly, we have used an existing model of capillary rise based on free energy concepts to derive a capillary rise equation that can be used to theoretically predict observations based on the TZ thickness of different reservoir rocks, using well-established formation evaluation methods. The novelty of our work stems from the ability of the model to theoretically and accurately predict the TZ thickness of the different lithostratigraphic units of hydrocarbon reservoirs, because of the experimental accessibility of its model parameters.

Mechanistic insights into Ga-modified hollow ZSM-5 catalyzed fast pyrolysis of cassava residue

The preparation of valuable chemicals by catalytic fast pyrolysis (CFP) is a promising and environmentally-friendly approach for the selective upgrading of waste cassava residue (CR). This work systematically investigated the conversion mechanism and kinetic characteristics of CR pyrolysis over Ga-modified hollow ZSM-5, for the purpose of enhancing aromatics production. The hollow configuration significantly regulated the structural characteristics of ZSM-5, thus facilitating the diffusion, deoxygenation, and aromatization of pyrolysis intermediates. The incorporation of Ga species and generated Brønsted acid sites remarkably accelerated the reaction rate and suppressed the carbonization at high temperatures, through enhancing the end scission of starch and cellulose components. With the aid of 5Ga/ZSM-H, the relative content of aromatics achieved 95.4% at 700 °C, and still maintained over 92.5% even after 5 cycles. The ring-opening and retro-aldol degradation were identified as crucial steps for the production of ketones and aldehydes separately, which were further transformed into hydrocarbon pools by deoxygenation and subsequently converted into aromatics via Diels-Alder reaction. Kinetic analysis demonstrated that the use of 5Ga/ZSM-H lowered the average activation energy of CR pyrolysis by 14.8%, particularly for the initial pyrolysis stage. Moreover, the plausible mechanism for aromatics formation from Ga-modified hollow ZSM-5 catalyzed CR pyrolysis was proposed.

Combined Strategies Enable Highly Selective Light Olefins and para-Xylene Production on Single Catalyst Bed.

Achieving multiple high-value-added chemical production through novel reaction processes and shape-selective catalytic strategy is the key to realizing efficient low-carbon catalytic processes. In this work, a methanol-toluene coreaction system was developed, and combined control strategies of reaction pathway guidance and shape-selective catalysis were applied for the successful production of light olefins and para-xylene on single HZSM-5 catalyst bed. Cofeeding toluene additionally provides reactive and flowing aromatic hydrocarbon pool species that change the dominant reaction pathway in the complex network of the methanol reaction on HZSM-5 and promote the formation of ethylene. For the first time, the key reaction intermediates methylmethylenecyclodiene are directly captured and identified by experimental and theoretical techniques. This helps to propose the catalytic cycle for the dominant generation of ethylene and, more importantly, enriches the methanol-to-hydrocarbons (MTH) chemistry and hydrocarbon pool mechanism. Furthermore, 0.4HZSM-5@S-1-CLD, an optimized HZSM-5 catalyst modified by the silicalite-1 epitaxial growth followed by silanization approach, realizes highly selective production of light olefins (especially ethylene) and para-xylene, while excellent reactant activity is maintained. This highly efficient coreaction route gives an important leading significance in synthesizing the raw materials for the polyolefin and polyester industries. The establishment of the combined control strategies provides a model for the joint production of multiple target chemicals in complex catalytic processes.

Controlling product selectivity and catalyst lifetime by altering acid strength, cavity size of SAPO, and diffusion rate of methanol in the MTO reaction: DFT and MD calculations.

The initiation mechanisms of the MTO process over silicoaluminophosphate (SAPO) catalysts with zeolite-like structures using first-principles calculations have been investigated. The supramolecular system of silicoaluminophosphates consisting of inorganic cages with Brønsted acid sites and trapped organic compounds was used as a catalyst in the MTO reaction. To study the structure-property relationship in more detail, the effect of acidity and cage size of different types of SAPOs (SAPO-18, SAPO-34, and SAPO-17 with CHA, AEI, and ERI structures, respectively) in the aromatic cycle of hydrocarbon pool mechanism was investigated. The differences in reaction barriers can be explained by the cage size, pore topology, and environment of framework protons of materials. Product selectivity was controlled by using cavity-type zeolite, the steric constraint of the cavity for the formation of critical intermediates, and acidic strength. The results show that ethylene selectivity increases as the cavity size decreases, and the elliptical pore size of the structures decreases, thereby decreasing the acidity of the zeolite structure, leading to an increase in propylene selectivity. SAPO-18 exhibits the longest reaction lifetime and has the highest amount of carbonaceous material after reaction completion. SAPO-17 with small pore and cavity size is selective to ethylene, although it shows a rapid catalyst deactivation rate.

Selectivity descriptors of the catalytic n-hexane cracking process over 10-membered ring zeolites.

Zeolite-mediated catalytic cracking of alkanes is pivotal in the petrochemical and refining industry, breaking down heavier hydrocarbon feedstocks into fuels and chemicals. Its relevance also extends to emerging technologies such as biomass and plastic valorization. Zeolite catalysts, with shape selectivity and selective adsorption capabilities, enhance efficiency and sustainability due to their well-defined network of pores, dimensionality, cages/cavities, and channels. This study focuses on the alkane cracking over 10-membered ring (10-MR) zeolites under industrially relevant conditions. Through a series of characterizations, including operando UV-vis spectroscopy and solid-state NMR spectroscopy, we intend to address mechanistic debates about the alkane cracking mechanism, aiming to understand the dependence of product selectivity on zeolite topologies. The findings highlight topology-dependent mechanisms, particularly the role of intersectional void spaces in zeolite ZSM-5, influencing aromatic-based product selectivity. This work provides a unique understanding of zeolite-catalyzed hydrocarbon conversion, linking alkane activation steps to the traditional hydrocarbon pool mechanism, contributing to the fundamental knowledge of this crucial industrial process.

Microkinetic simulations of ketene conversion to olefins in H-SAPO-34 zeolite for bifunctional catalysis

Distribution and evolution preference of the olefinic hydrocarbon pool in H-SAPO-34 for ketene conversion were addressed from microkinetic simulations. The similarities and differences between ketene and methanol conversions were compared.

Thermal and catalytic fast hydropyrolysis of lignin: Optimization for selective production of aromatics using high-pressure tandem μ-reactor – gas chromatography/mass spectrometry

Hydropyrolysis is a promising route for converting biomass into valuable chemicals. A high-pressure tandem μ-reactor – gas chromatography/mass spectrometry was used to study the pyrolysis of lignin and probe the effects of reaction atmosphere (H2 vs He), temperature, catalyst (HZSM-5) presence/absence, and pressure on product yields and distributions. Hydropyrolysis favored the demethoxylation and demethylation of guaiacyl-derived intermediates, generating catechol- and phenol-type compounds. The yields of guaiacyl- and catechol-type compounds decreased with increasing temperature and H2 pressure. The products formed at the highest examined temperature (700 °C) and H2 pressure (3.0 MPa) were dominated by phenol-type compounds, monoaromatic hydrocarbons (MAHs), and polycyclic aromatic hydrocarbons (PAHs). The substantial decrease in char yield with increasing H2 pressure at 700 °C indicated that active hydrogen radicals enhanced the cracking of lignin macromolecules and suppressed the condensation reactions to form char at high temperatures. HZSM-5 exhibited considerable hydrocracking activity for converting lignin pyrolysis vapor into aromatics, with an increase in H2 pressure further improving the formation of benzene, toluene, and xylenes (BTX) at the expense of phenolics. However, high catalytic upgrading temperatures favored the coupling reactions in the hydrocarbon pool, promoting the formation of PAHs. Evolved gas analysis showed that lignin hydropyrolysis involved two stages (at 250–500 and 500–800 °C), suggesting that the labile fraction of the nascent char underwent further hydrocracking at high pressure and temperature. The high production of BTX and naphthalenes through catalytic hydropyrolysis of lignin provides a promising route for the valorization of lignin-rich resources.

Effect of flame thickness on the temperature measurement error for bare-bead thermocouple in open pool fires with different fuels

Accurately obtaining the temperature distribution of the flame is crucial for a comprehensive understanding of the combustion behavior of the pool fire. The correction method is needed to compensate the measurement error when the temperature is measured by bare-bead thermocouple in the open pool experiment, but the effect of flame thickness is rarely considered in the current method. Thus, this work develops a coupled heat transfer model of bare-bead thermocouples in open pool fires and modifies the flame radiation characteristics based on the fuel type and flame thickness. The control mechanism of measurement error in the model is identified, and then the effects of main parameters such as flame thickness and flame temperature on measurement error are analyzed. The results show that the flame emissivity decreases exponentially with the decrease of flame thickness, the minimum emissivity of gasoline flame is 0.26 when flame thickness is 0.1 m. The decrease of flame thickness leads to a sharp increase of temperature measurement error. The maximum increment of error can reach 227.3 K. On this basis, the flame thickness limit value, considering the correction of temperature measurement error in different hydrocarbon pool fire experiments is proposed.

Green hydroxyapatite-zeolite catalyst derived from steel waste as an effective catalyst for the hydrocarbon production via co-catalytic pyrolysis of sugarcane bagasse and high-density polyethylene

Hydroxyapatite-zeolite (HAP-ZE) catalyst prepared from steel waste was utilised in co-catalytic pyrolysis of sugarcane bagasse (SB) and high-density polyethylene (HDPE) for bio-oil production. The highest bio-oil yield (71.19 wt%) was obtained at HAP-ZE to SB/HDPE ratio of 1:6, and mass ratio of SB to HDPE of 40:60. HAP-ZE favoured the production of hydrocarbon and alcohol and inhibited the production of acid. The acid sites promoted the hydrogenation and deoxygenation via hydrocarbon pool while the basic sites promoted the deoxygenation reactions via decarboxylation and decarbonylation. HAP-ZE large pores facilitates access of bulky pyrolyzates to active sites, promoting deoxygenation and hydrocarbons formation.