Formation Of Carbonaceous Deposits Research Articles

On the reactivity and selectivity trends in the tandem Diels-Alder cycloaddition and dehydrative aromatization between dimethylfuran and ethene over solid acids

Tandem Diels-Alder (DA) cycloaddition and dehydration reactions between bio-derived furans and dienophiles offer a sustainable route potentially able to meet the growing demands of aromatic chemicals worldwide. In particular, efforts to maximize the production of p-xylene from dimethylfuran (DMF) and ethene have led to an expanding list of solid acids with, reportedly, outstanding catalytic performances. In this work, we have revisited the kinetic complexities of this reaction that are characterized by a distinct shift in the rate-limiting step depending sensitively on catalyst mass, and addressed the possible origins of reactivity and selectivity trends across a range of solid acids that hold promise for the target reaction, including aluminosilicates and a series of mesoporous metal phosphate catalysts (MOPOx; M = Sn, Ti, Zr, Hf, Nb and Ta), in both dehydration- and cycloaddition-limiting regimes. In contrast to initial p-xylene formation rates in the dehydration-limiting regime, which benefit from an increased acid strength of Brønsted acid sites, p-xylene formation rates within the cycloaddition-limiting regime are essentially unaffected by variations in acid site densities, Lewis and Brønsted acid strength, and pore confinement. Such weak dependences of DA reactivity on a multitude of acid properties provide strong hints that DA cycloaddition between DMF and ethene follows an inverse-electron-demand [4 + 2] route, most likely as a consequence of a more favorable adsorption of DMF than that of ethene on the acid sites enhancing so the electrophilicity of DMF, but not that of ethene as required by the normal-electron-demand cycloaddition. Product selectivities and carbon balances were tracked as functions of reaction time, conversion and reactant pressure or concentration to identify the side reactions and acid properties responsible for p-xylene selectivity losses and the ultimate formation of carbonaceous deposits. These findings deepen our understanding of the roles of Lewis acid sites and Brønsted acid sites for the chemical reactivities toward the DA cycloaddition, the consecutive cycloadduct dehydrative aromatization and undesired acid-catalyzed side reactions, and inform strategies to enhance DA reactivities and suppress deleterious side reactions from the standpoint of both materials and process design.

Pyrolysis of sawdust impregnated with bio-oil of the same origin: Influence of organics in bio-oil on property of biochar

Reactive organics in bio-oil might further react with biochar of the same origin during pyrolysis. This was investigated herein via conducting the pyrolysis of poplar sawdust impregnated with a heavy fraction of the bio-oil from the same biomass at 400 or 600 °C. The results showed that the organics in the bio-oil for impregnation involved in the pyrolysis by enhancing biochar production via cross-polymerization with the organics on biochar and/or the reactive products like aldehydes/furans and some heavy organics. This led to the formation of additional carbonaceous deposit of aliphatic nature on the surface of biochar. This, however, did not enhance the thermal stability of the biochar but lowered activation energy and ignition temperatures for combustion. In addition, the organics in the bio-oil impregnated could also enhance deoxygenation, producing the biochar with the O mass fraction lower than counterpart by 24.1% at 400 °C. Moreover, impregnation of bio-oil also facilitated the formation of mesopores (S > 2nm: 178.6 m2 g−1 versus 117.6 m2 g−1 of counterpart) and created a carbonyls-deficient surface of the biochar.

Periodicity of accumulation of carbonaceous formations in the Cryptozoic-Phanerozoic history of the Earth's development

The progressive development of the Precambrian organic world was superimposed by epochs of intense accumulation of organic matter in marine sediments and the formation of carbonaceous formations, which differentiated the Precambrian section into submegacycles at intervals of ~600, 400, 300, 100 Ma, reflecting the trend of biomass growth over time from Archaean to Vendian ( Ediacaran). In the Phanerozoic, 26 stratigraphic levels of the formation of the of bituminous combustible shales and black shales were identified, which are characterized by periodicity of 20, 30, 40 years, which make up harmonics of higher ranks - 60, 80, 100 and 200 Ma, which correlate with tectonic, volcanic, astrophysical cycles. The concept of continuous-discontinuous in time and space formation of carbonaceous deposits, the formation of which occurred under the influence of endogenous (tectono-geodynamic) and exogenous (astrophysical) processes, is substantiated.

Sequential pyrolysis for understanding specific influence of cellulose- and lignin-derived volatiles on properties of counterpart char

Interactions of cellulose- and lignin-derived intermediates have been well documented during pyrolysis of lignocellulosic biomass. The reaction network for the interactions is rather complex, as cellulose-derived volatiles could interact/react with not only lignin-derived volatiles but also lignin-derived char and vice versa. To probe specifically the impacts of cellulose-derived volatiles on the lignin-derived char or the opposite, herein the sequential pyrolysis was performed by arranging cellulose in the upper bed with lignin in the lower bed or lignin above with cellulose below at 350 and 650 °C, respectively. The results indicated that the sequential pyrolysis of cellulose→lignin or lignin→cellulose at 350 °C induced increased char yield from formation of carbonaceous deposits via volatiles-char interactions. Compared with the lignin-derived volatiles, the cellulose-derived volatiles, especially aldehyde fractions, were more reactive towards the lignin-derived char at 350 °C, forming oxygen-rich lignin-derived char with a higher yield, an abundance of aliphatic structures and consequently lower thermal stability. In sequential pyrolysis of lignin→cellulose, more aromatics-rich species were deposited on cellulose-derived char, but the lignin-derived volatiles were less reactive for enhancing the char yield. At 650 °C, instead of polymerisation of the volatiles on the char, either the cellulose- or lignin-derived char catalyzed the cracking of the counterpart volatiles to remove the aliphatic functionalities, which made the char more aromatic and thermally more stable.

Sinter‐Resistant Nickel Catalyst for Lignin Hydrogenolysis Achieved by Liquid Phase Atomic Layer Deposition of Alumina

AbstractLignin hydrogenolysis is a key step in the sustainable production of renewable bio‐based chemicals and fuels. Heterogeneous metal catalysts have led to high yields but they rapidly deactivate, notably due to nanoparticle sintering and carbonaceous deposit formation. While these deposits can be removed by regeneration, sintering is irreversible and a significant barrier to commercialization. Here, simple liquid phase atomic layer deposition is used to deposit an alumina layer to protect nickel particles from sintering. In the gas phase, it is proved that alumina can prevent sintering during reduction up to 600 °C. This catalyst for hydrogenolysis of extracted lignin in batch and continuous operation is used. In batch, the overcoated catalyst maintains high monomer yields with little sintering over four cycles of reuse while the yield obtained with the catalyst without an overcoat reduces to half and severe sintering occurs. In a continuous flow reactor, deactivation rates are three times lower for the catalyst with the alumina overcoat. Microscopy images confirm that the alumina overcoat largely preserves nickel particle sizes after ten days of operation. The results demonstrate that catalyst overcoating with metal oxides substantially slows irreversible deactivation during lignin hydrogenolysis, which could facilitate the development of continuous lignin upgrading.

Разработка методики расчета температуры внутренней стенки мультитопливной форсунки с учетом плотности теплового потока

The article presents results of development of a new method for temperature calculation of the multi-fuel nozzle inner wall based on data on heat flux. A patent search and an analysis of scientific and technical information on the multi-fuel nozzles were carried out. It was established that one of the most effective ways to prevent appearance and rapid formation of carbonaceous deposits in liquid hydrocarbon fuels was to reduce temperature of the metal wall. New formulae were obtained to calculate the inner surface temperature depending on the amount of heat-transfer agents and their thermophysical properties, geometric characteristics of the supply channels and the injector “dry” mass. A comparative theoretical calculation of the temperature decrease inside a single-fuel and a dual-fuel nozzles was carried out at different mass flow rates of kerosene. The results obtained indicate higher cooling efficiency of multi-fuel nozzles compared to the single-fuel ones.

Chain length effects of phenylene sulfide modifiers on selective acetylene partial hydrogenation over Pd catalysts

We recently reported that polymer chains with phenylene sulfide moieties can efficiently modify the Pd catalyst surface, enabling selective partial hydrogenation of acetylene under ethylene-rich conditions. In the present study, we synthesized oligomeric and polymeric phenylene sulfides with tailored molecular sizes to systematically investigate the catalytic effect of chain length of organic modifiers. The results showed that the increased chain length of the modifiers is beneficial for improving the acetylene partial hydrogenation selectivity by inhibiting adsorption and full hydrogenation of ethylene. This was attributed to the fact that modifiers with a greater number of sulfide groups per molecule can bind more efficiently to the Pd surface for entropic reasons (chelate effect) and thus better inhibit ethylene adsorption. In contrast, the adsorption of acetylene to Pd was nearly unaffected by the presence and size of the modifiers owing to its stronger binding ability and small kinetic diameter. Modifiers with larger chain lengths were also advantageous in improving long-term catalyst stability because of their higher thermochemical stability and greater ability to inhibit the formation of carbonaceous deposits. The present results showed that polymers can act as more efficient and long-lasting selectivity modifiers than commonly used small organic molecules.

Methanol to gasoline (MTG): Parametric study and validation of the process in a two-zone fluidized bed reactor (TZFBR)

Methanol to Gasoline (MTG) process transforms methanol to hydrocarbons within the boiling point range of gasoline. The result is a wide spectrum of products (olefins, paraffins, aromatics and naphthenics, among others), with the total conversion of methanol to hydrocarbons and water. Catalyst deactivation by coke is a main problem in this process. This work aims to determine the feasibility of carrying out the production of gasoline from methanol in a two-zone fluidized bed reactor (TZFBR). The hypothesis is that the formation of carbonaceous deposits (coke) on the catalyst particles can be counteracted by its combustion in the regeneration zone that this novel reactor presents, thus achieving stable and continuous operation. In this way, both processes (reaction and regeneration) would be being carried out simultaneously in the same reactor (process intensification). The comparison of results between a conventional fluidized bed reactor and a TZFBR shows that the second one actually provides a better stability over time.

Structure and Assessment of the Oil Potential of Carbonaceous Carbonate-Siliceous Domanik Deposits in the Volga–Ural Oil and Gas Province

Abstract —The paper considers the regularities in the structure and conditions of formation of Domanik carbonaceous carbonate-siliceous productive deposits. They are shown to occur in the stratigraphic interval from middle Frasnian to upper Famennian. The highly persistent structure of their sections for many kilometers within specific sedimentation zones and the drastic changes in the structure at the boundaries of the zones are justified. Lithological classification of rocks is considered. Methods and results of combined paleontological, lithological, geochemical, and petrophysical core studies are presented, as well as interpretation of well logging data and seismic-survey materials used in the assessment of oil resources and identification of oil- and gas-promising zones and areas. The conducted studies have proved significant oil resources in the Domanik productive sequence; their extraction might compensate for the decline in oil production from conventional pools.

Selective hydrogenation of ethyne with highly-dispersed sub-2 nm Pd nanoparticles in a hemicellulosic gel-based microreaction chamber

Ethyne is often an unwanted impurity in ethene streams used in plastics industry. Supported Pd catalysts offer high ethyne conversion, but poor ethene selectivity due to over-hydrogenation which leads to the formation of carbonaceous deposits. In this paper, acrylamide was grafted by free radical polymerization onto bagasse pith hemicellulose (to form HEMI-g-AAMs), which was then used as a porous bio-based carrier of Pd nanoparticles. The obtained Pd/HEMI-g-AAMs catalyst showed an ethyne conversion and ethene selectivity of 100% and 94.70%, respectively, at 100 °C and a space velocity of 70,000 h−1. The nitrogen-rich bio-based support regulated the physicochemical properties and catalytic activity of the supported Pd nanoparticles. Results guide the development of new and improved Pd-based catalysts for the partial catalytic hydrogenation of ethyne to ethene.

Kinetic study of carbonaceous deposit formation and catalyst deactivation in hydrotreating of fast pyrolysis bio-oil

Fast pyrolysis of biomass followed by hydrotreating of bio-oil is considered to be a promising thermochemical conversion process of biomass to liquid fuel. Catalytic hydrotreating converts the crude bio-oil from biomass pyrolysis into liquid intermediates with reduced oxygen content, and low viscosity and acidity. However, effective lifetime of catalyst can be significantly reduced by coking which has been recognized as the main cause of catalyst deactivation during the hydrotreating process. In this study, similar phenomenon has been observed but the catalyst deposit was different from the reported coke and thus a new term of carbonaceous deposit is introduced. Kinetics of the carbonaceous deposit formation and its characteristics have been investigated for hydrotreating of bio-oil derived from fast pyrolysis of rice husk using commercial HTB-45 Ni-based catalyst. A mathematical model for the hydrotreating process, which is based on key chemical reactions and consists of ordinary differential equations (ODEs), has been developed and solved with the kinetic parameters being obtained from the experiments. Results of this study are helpful for better understanding and optimization of the catalytic upgrading of fast pyrolysis bio-oil.

Oxidative Condensation of Furfural with Ethanol Using Pd-Based Catalysts: Influence of the Support

PdO nanoparticles were deposited on several supports (β-zeolite, Al2O3, Fe2O3, MgO, and SiO2), which displayed different crystallinity, textural properties, and amount of acid and basic sites. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption–desorption isotherms at −196 °C, NH3 and CO2 thermoprogrammed desorption analyses (NH3- and CO2-TPD, and X-ray photoelectron spectroscopy (XPS). Pd-based catalysts were tested in the oxidative condensation of furfural with ethanol to obtain value-added chemicals. The catalytic results revealed high conversion values, although the presence of a high proportion of carbonaceous deposits, mainly in the case of the PdO supported on β-zeolite and Al2O3, is also noteworthy. The presence of basic sites led to a beneficial effect on the catalytic behavior, since the formation of carbonaceous deposits was minimized. Thus, the 2Pd-MgO (2 wt.% Pd) catalyst reached the highest yield of furan-2-acrolein (70%) after 3 h of reaction at 170 °C. This better catalytic performance can be explained by the high basicity of MgO, used as support, together with the large amount of available PdO, as inferred from XPS.

Minimizing carbon deposition in plasma-induced methane coupling with structured hydrogenation catalysts

The effect of temperature and hydrogen addition on undesired carbonaceous deposit formation during methane coupling was studied in DBD-plasma catalytic-wall reactors with Pd/Al2O3, using electrical power to drive the reaction. Experiments with thin catalyst layers allowed comparison of the performance of empty reactors and catalytic wall reactors without significantly influencing the plasma properties. The product distribution varies strongly in the temperature window between 25 and 200 °C. Minimal formation of deposits is found at an optimal temperature around 75 °C in the catalytic-wall reactors. The selectivity to deposits was c.a. 10% with only 9 mg of catalyst loading instead of 45% in the blank reactor, while decreasing methane conversion only mildly. Co-feeding H2 to an empty reactor causes a similar decrease in selectivity to deposits, but in this case methane conversion also decreased significantly. Suppression of deposits formation in the catalytic-wall reactor at 75 °C is due to catalytic hydrogenation of mainly acetylene to ethylene. In the empty reactor, H2 co-feed decreases conversion but does not change the product distribution. The catalytic-wall reactors can be regenerated with H2-plasma at room temperature, which produces more added-value hydrocarbons.

Producing gasoline-like hydrocarbons by cracking crude soybean oil: tuning the NaZSM-5 zeolite’s acidity for increasing the catalyst lifetime

This work investigates the effect of NaZSM-5 zeolite’s acid properties on the catalytic cracking of crude soybean to produce gasoline-like hydrocarbons. We modified both the acid concentration and the acid strength of the NaZSM-5(60) zeolite (where 60 denotes the SiO2/Al2O3 molar ratio) either by varying the SiO2/Al2O3 ratio (i.e., 30, and 90) or by exchanging the compensation cation (i.e., from Na+ to H+). Given the ammonia temperature-programmed desorption and temperature-programmed oxidation tests, we observed that the acid strength of the catalyst is associated not only with the distribution of the cracking products, but also with the nature of the carbonaceous deposits formed during the reaction. Weak, medium, and strong acidity were associated with the formation of heavy hydrocarbon species, soft, and hard coke, respectively. The NaZSM-5 zeolites exhibited weak and medium acidity, while the HZSM-5(60) zeolite exhibited weak and strong acidity. Although both NaZSM-5(30) and HZSM-5(60) zeolites delivered higher gasoline yield than the NaZSM-5(60) zeolite due to its higher acid concentration, the HZSM-5(60) zeolite formed carbonaceous deposits with lower reactivity (i.e., hard coke). Therefore, low values of SiO2/Al2O3 ratio in the NaZSM-5 zeolite drive the reaction products towards gasoline-like hydrocarbons and favor the catalyst reactivation through the formation of more reactive carbonaceous deposits.

Enhanced H2 production in the aqueous-phase reforming of maltose by feedstock pre-hydrogenation

Coupled hydrogenation and aqueous-phase reforming (APR) was studied as an approach to enhance H2 production from brewery wastewater, where maltose is the main component. Hydrogenation of maltose-bearing wastewater produced essentially maltitol. APR stage was performed over PtPd/C catalysts. Faster catalyst deactivation was observed in the APR of maltose than in the APR of maltitol, especially at high feedstock concentration. Higher H2 selectivity and yield were achieved in the APR of maltitol. The increase of temperature from 175 to 225 °C changed the reaction pathways, favouring the production of C1-C2 alkanes for both feedstocks. Higher selectivity to liquid-phase products was obtained in the APR of maltose, evidencing also reaction routes favouring the formation of solid carbonaceous deposits that lead to higher catalyst deactivation. The coupled process can be considered as efficient since H2 production compensated for H2 consumption in the hydrogenation stage and catalyst durability was increased.

Understanding “Fouling” in Extremely Complex Petroleum Mixtures

“Fouling”, the unwanted deposition of solids, causes significant operational difficulties in petroleum producing and processing industries and is considered a billion dollar problem. There are two routes of petroleum fouling: physical fouling, where material of low-solubility precipitates, and chemical fouling, where a chemical reaction produces insoluble material, often on the surface of heat exchangers. By implementing laboratory-scale experimental simulations of the industrial process using a petroleum derived light crude oil fraction, it is shown that chemical fouling proceeds via multistep pathways involving dehydrogenation and radical formation reactions on PAHs, resulting in the formation of carbonaceous deposits.

Substrate-specific mineralization and deactivation behaviors of TiO2 as an air-cleaning photocatalyst

Volatile organic compounds (VOCs) having the same number of carbon atoms with different functional groups were selected to investigate the substrate-specific mineralization and deactivation behaviors of TiO2. The mineralization rate of VOCs decreased in the order of n-propylaldehyde > n-propanol >> n-propylamine > n-propanethiol > n-chloropropane, which indicates that the presence of heteroatoms significantly retards the mineralization rate. The mineralization of tested VOCs is closely related to the efficient production of aldehydes as intermediates. During the PCD, the formation of carbonaceous deposits on the TiO2 surface was observed, which was the most significant with n-propylamine, much less with other VOCs, and negligible with n-chloropropane. The repeated PCD cycles of n-propylamine and n-propanethiol caused the significant deactivation of TiO2, while those of other VOCs little reduced their PCD activity. The photocatalyst deactivation is associated with the deposition of non-volatile products on the TiO2 surface such as carbonaceous residues, ammoniums, and sulfates.

Highly stable Pt/CoAl2O4 catalysts in Aqueous-Phase Reforming of glycerol

Pt/CoAl2O4 catalysts with small amounts of Pt (0.3 and 1 wt.%) were prepared by wet impregnation of platinum on cobalt aluminate (mole ratio Co/Al = 0.625). These catalysts were compared with monometallic Pt/alumina and cobalt aluminate counterparts. The physicochemical characteristics of the obtained materials were thoroughly analysed. The catalytic performance of the prepared assays was investigated in the Aqueous-Phase Reforming (APR) of glycerol for up to 100 h TOS, and in liquid phase Water-Gas Shift (WGS). It was concluded that the addition of Pt to cobalt aluminate resulted in a synergistic effect that promoted the reduction of both Pt and Co species, as well as cobalt dispersion, what increased the amount of exposed metallic sites. These effects were, however, sensitive to the amount of Pt loaded. The glycerol APR activity of bimetallic catalysts was very stable over 100 h TOS with conversion values above 99 %. Conversion to gas was also above 95 % during the whole operation. Contrarily, the counterpart monometallic catalysts suffered noticeable deactivation at above 70 h TOS. Also, WGS activity of bimetallic assays was higher than the monometallic counterparts. Addition of Pt to cobalt aluminate lowered selectivity to hydrogen, due to a higher CO hydrogenation activity. Examination of the spent catalysts showed better textural stability of the bimetallic samples, as well as much lesser formation of carbonaceous surface deposits. Nevertheless, oxidation and leaching of cobalt remains as the main drawback of bimetallic catalysts to be used in APR.

The role of NO2 and NO in the mechanism of hydrocarbon degradation leading to carbonaceous deposits in engines

A hypothetical mechanism of degradation of the fuel droplet leaking out from the injector nozzle in a direct injection combustion engine has been proposed recently. This involves as a key step a radical chain oxidation initiated by NO2 and branched by nitric oxide, NO, both produced by the combustion. The degradation causes the formation of injector nozzle carbonaceous deposits. The present work gives an experimental validation of some of the assumptions behind this model. An autoclave is used to oxidize isooctane under conditions relevant to the cylinder wall near the nozzle (~150 °C, 10 bar, 5% O2, 100 ppm of NO2 by mole and 500 ppm NO in the gas phase), and the degradation products are monitored via gas chromatography-mass spectrometry (GC–MS). The results show no observable fuel degradation in the absence of NOx. NOappears to be able to initiate a radical chain by producing NO2. Nitric oxide also alters the radical chain by transforming the alkyl peroxy radicals (ROO⋅) to more reactive alkoxy radicals (RO⋅), resulting in a range of different products. In addition, NO tends to terminate the radical chain by neutralizing a fraction of the alkyl peroxy radicals, producing alkyl nitrates as termination products. The existence of a radical chain is supported by demonstrating the antioxidative action of a radical scavenger. The chemical reaction mechanism is investigated, based on the detected products, and the key species involved in the degradation process are identified.

Electrochemical Behavior of (Fe,Ni)Ox-Based Anodes for Solid-Oxide Fuel Cells in Methane-Containing Atmospheres

The work is devoted to investigation of the electrochemical behavior of (Fe,Ni)Ox-based composite anodes in the hydrogen- and methane-containing fuel. Among the studied composites, the optimum electrochemical characteristics were observed for anodes with Fe : Ni ratio approaching 2. In particular, for the electrodes with initial composition 50 vol % Fe0.67Ni0.33Oх–50 vol % Zr0.85Y0.15O1.93 the anode overpotential equals 20–30 mV at a current density of 50–80 mA/cm2 in 10% Н2–Ar–H2O at relatively low temperatures (873–923 K). Increasing current leads to further activation, presumably due to a partial oxidation of metallic particles located at the anode surface. However, the microstructure degradation of the anode layers still represents a significant problem for their utilization. Testing of the electrocatalytic activity of the anodes fabricated from Ni, Zr0.83Sc0.17O1.92 (ScSZ) and Ce0.9Gd0.1 O2 – δ (GDC) revealed a high activity toward catalytic partial methane oxidation with the subsequent electrochemical oxidation of the conversion products, as well as formation of carbonaceous deposits at the nickel surface. The methane conversion degree on Ni-anode comes to 60–90% and decreases with time and on cooling. The doping of nickel oxide with iron lowers the conversion degree and promotes the carbon poisoning, supposedly, because of the lowering of the anodic current density resulting from the worsening of the electrochemical activity.