Hydrogen Donor Solvent Research Articles

A multi-component reaction kinetics model for the hydrothermal liquefaction of carbohydrates and co-liquefaction to produce 5-ethoxymethyl furfural

Hydrothermal liquefaction (HTL) as a waste management technology has been investigated to produce renewable bio-crude and other valuable products from wet biomass and bio-waste. However, carbohydrates as a vital component in biomass have shown to increase the complexity of the process. Undesirable solid yields produced by the carbonisation/re-condensation of reactive carbohydrate intermediates could limit the renewable crude yield and recovery. In the present study, the reaction mechanism and kinetic models for the HTL of monosaccharides and polysaccharides are investigated using gas chromatography–mass spectrometry (GC–MS) and high-performance liquid chromatography (HPLC) to characterise, validate and quantify the most abundant organic species in the aqueous phase. The experimental data and models presented provide an unbiased understanding of the carbohydrate decomposition during HTL conversion, while the analysis of solid products clarifies solid transformations and integrates both phases into a more comprehensive reaction mechanism approach, including a shrinking core model for cellulose. Finally, ethanol and acetic acid were added as co-solvents to elucidate the effects of a fully renewable hydrogen donor solvent system to generate 5-ethoxymethyl furfural and ethyl levulinate (validated with GC–MS), two renewable fuel additives and promising tunable monomers candidates. Experiments were conducted with glucose, fructose, and cellulose in a batch reactor with 20% by mass premixed feedstock at 250 °C and 300 °C.

Investigation of the improvement of Sivas-Kangal lignites liquefaction product yields

In recent years, converting and using coal into the most suitable product according to its properties has emerged as a modern approach. Among the main processes applied to coal are low and high-temperature carbonization, gasification and liquefaction. In coal liquefaction, coal is broken down into free radicals using hydrogen donor solvent and catalyst under high temperature and pressure conditions. Later, these radicals can be used in the production of both liquid fuel and chemical raw materials by being saturated with hydrogen. This study aims to improve the yields of Sivas-Kangal lignite liquefaction products (char, preasphaltene, asphaltene, oil-gas). For this purpose, firstly raw coal, then spiral enriched clean coal liquefaction experiments were carried out. The chemical characterizations of the obtained products were determined by proximate and ultimate analysis. The composition of the oil was identified by GC-MS. As a result of the enrichment, the char yield decreased by 16.5% whereas the oil+gas yield increased by 14.64%. Total conversion increased from 31.74% to 48.24%. It has been concluded that the enrichment process has a positive effect on the liquefaction yields.

Non-Catalytic Dissolution of Biochar Obtained by Hydrothermal Carbonization of Sawdust in Hydrogen Donor Solvent

The production of fuel hydrocarbons from CO2-neutral raw materials is a promising task at present. The thermal dissolution of biochar obtained by the method of hydrothermal carbonization of sawdust was studied. The dissolution of biochar in tetralin (hydrogen donor solvent) was studied at different temperatures (350–450 °C) and with two types of dilution of the mixture with tetralin: 1/3 and 1/4. The process proceeded without a catalyst. It was found that the samples subjected to thermal dissolution at temperatures of 425–450 °C had the highest conversion and yield of liquid products. The reaction temperature also had a significant effect on the composition of liquid products. It was found that an increase in the reaction temperature led to a significant increase in benzenes, both in the direct and in the hexane fraction. A benzene yield of more than 50% was observed for both fractions at a temperature of 450 °C. It was also suggested that the possible positive effect of abietates on the homogenization of the reaction mixture contributed to high conversion in the process. The biochar/tetralin ratio effects the yield and composition of the liquid products as well. An increase in the tetralin concentration in the mixture during thermal dissolution led to an increase in the conversion and yield of hydrocarbon fractions for fuel purposes. This is undoubtedly due to the large amount of elemental hydrogen involved in the hydrogenation of the reaction mixture.

Energy Densification of Biomass-Derived Furfurals to Furanic Biofuels by Catalytic Hydrogenation and Hydrodeoxygenation Reactions

The concomitant hydrolysis and dehydration of biomass-derived cellulose and hemicellulose to furfural (FUR) and 5-(hydroxymethyl)furfural (HMF) under acid catalysis allows a dramatic reduction in the oxygen content of the parent sugar molecules with a 100% carbon economy. However, most applications of FUR or HMF necessitate synthetic modifications. Catalytic hydrogenation and hydrogenolysis have been recognized as efficient strategies for the selective deoxygenation and energy densification of biomass-derived furfurals generating water as the sole byproduct. Efficient and eco-friendly catalysts have been developed for the selective hydrogenation of furfurals affording renewable furanic compounds such as 2-methylfuran, 2,5-dimethylfuran and 2-methyltetrahydrofuran with potential applications as biofuel, solvent and chemical feedstock. Hydrogen gas or hydrogen donor molecules, required for the above processes, can also be renewably obtained from biomass using catalytic processes, enabling a circular economy. In this review, the recent developments in the energy densification of furfurals to furanic compounds of commercial significance are elaborated, emphasizing the role of catalyst and the reaction parameters employed. Critical discussion on sourcing hydrogen gas required for the processes, using hydrogen donor solvents, catalyst design and the potential markets of furanic intermediates have been made. Critical evaluations of the accomplishments and challenges in this field are also provided.

Mechanochemical Synthesis of Nickel-Modified Metal–Organic Frameworks for Reduction Reactions

In this work, we report the incorporation of nickel oxide nanoparticles into a metal–organic framework (MOF) structure by a solvent-free mechanochemical strategy. In particular, the zirconium-based MOF UiO-66 was modified with different Ni loadings and characterized using complementary techniques including X-ray diffraction (XRD), N2 porosimetry and X-ray photoelectron spectroscopy (XPS). The catalytic potential of the as-prepared Ni/UiO-66 materials in the hydrogenation reaction of methyl levulinate using 2-propanol as hydrogen donor solvent has been investigated under flow conditions. Under optimized conditions, the 5%Ni/UiO-66 led to the best catalytic performance (70% yield, 100% selectivity to gamma-valerolactone), which could be attributed to the higher content of the Ni species within the MOF structure. The obtained results are promising and contribute to highlighting the great potential of MOFs in biomass upgrading processes, opening the path to the sustainable development of the chemical industry.

γ-Valerolactone as a promising solvent and basic chemical product. Catalytic synthesis from components of vegetable biomass

γ-Valerolactone (GVL), which is a valuable chemical compound and a platform molecule, is considered as an intermediate product for the synthesis of chemical compounds with high added value, components of motor fuels and biopolymers. GVL is successfully used as an environmentally friendly solvent, fuel additive, fragrance and food additive. This review summarizes recent advances in the development of catalytic methods for the production of GVL from levulinic acid (LA), alkyl levulinates (AL), carbohydrates and vegetable polymers. Particular attention is paid to heterogeneous catalysts based on metals and metal oxides, which are more promising for practical application. The proposed mechanisms of processes are considered in detail, and prospects of using hydrogen-donor solvents in the production of GVL are discussed. Catalysts with the best catalytic performance were compared in terms of their productivity, which is an important parameter for industrial catalysis.

In Situ Hydrodeoxygenation of Phenol as a Model Compound for Pyrolysis Oil Using Raney Ni and Molecular Sieve Catalysts

In order to reduce the consumption of a large amount of externally supplied hydrogen, methanol was used as the hydrogen donor solvent. Phenol, a model compound of coconut clothes pyrolysis oil, was...

Progress in thermochemical conversion of duckweed and upgrading of the bio-oil: A critical review

The processing of duckweed has been included in the list of promising pathways for biofuels production. This property is attributed to its simple manual harvesting method and its ability for high protein or starch content, depending on its species and growing environment. The biofuels production from duckweed, is not only a solution to energy and environmental problems, but also a reliable way to realize the utilization of duckweed. This critical review focuses on the bio-oil production from duckweed via pyrolysis and hydrothermal liquefaction processes. First, characteristics and eco-environmental benefits of duckweed are reviewed. Next, the impacts of different parameters on the properties and distribution of bio-oil from pyrolysis and hydrothermal liquefaction are discussed in detail. Subsequently, the effect of hydrogen donor solvents (as reaction media for upgrading) and catalysts on the upgrading of duckweed bio-oil are extensively discussed. This paper ends with the prospects for further development in thermochemical valorization of duckweed.

Catalytic transfer hydrogenation of cellulose to hydrocarbons using straight-chain aliphatic hydrocarbon as a solvent

Catalytic transfer hydrogenation is effective for converting cellulose to liquid fuel. This method typically uses an alcohol or a cyclic compound as a liquid hydrogen resource. However, alcohol causes side reactions, and oxygen-containing compounds remain in liquid fuel. Cyclic compounds such as tetralin suppress side reactions, but negatively affect liquid fuel properties because of difficult cyclic compound-liquid fuel separation. Therefore, catalytic transfer hydrogenation of lignocellulose requires a hydrogen donor solvent that is easily separated or does not need to be separated from liquid fuel. Thus, we focused on the use of straight-chain aliphatic hydrocarbon as a solvent. When used with lignocellulose-based liquid fuel, straight-chain aliphatic hydrocarbon can remain in transportation fuel. In addition, a palladium catalyst added to this solvent is expected to behave as a hydrogen donor, because this catalyst dehydrogenates alkane while serving as a hydrogen resource. This expectation was investigated by using cellulose, a main component of lignocellulose, and hexadecane, as a straight-chain aliphatic hydrocarbon. Using this solvent for catalytic transfer hydrogenation resulted in suppressed formation of the solid residue and increased liquefied oil production. Because of this reaction, hexadecane dehydrogenation and the hydrogenation of ɤ-valerolactone and furfural from cellulose were promoted. The hydrocarbon (C10–44) yield in liquefied oil reached over 35 wt% of cellulose, and the liquefied oil was collected while still being mixed with hexadecane. Hexadecane served to extract the hydrocarbon derived from cellulose and acted as a hydrogen resource.

New Approach to Synthesis of Tetralin via Naphthalene Hydrogenation in Supercritical Conditions Using Polymer-Stabilized Pt Nanoparticles

Supercritical (SC) fluid technologies are well-established methods in modern green chemical synthesis. Using SC fluids as solvents instead of traditional liquids gives benefits of higher diffusivity and lower viscosity, which allows mass transfer intensification and, thus, an increased production rate of chemical transformations. Therefore, a conjugation of heterogeneous catalysis with SC media is a large step toward a green chemistry. Tetralin (TL) is an important hydrogen donor solvent used for biomass liquefaction. In industry, TL is obtained via catalytic hydrogenation of naphthalene (NL). Herein, for the first time we have demonstrated the NL hydrogenation with close to 100% selectivity to TL at almost full conversion in the SC hexane. The observed transformation rates in SC hexane were much higher allowing process intensification. The downstream processes can be also facilitated since hexane after depressurisation can be easily separated from the reaction products via simple rectification. The TL synthesis was studied in a batch reactor at variation of reaction temperature and overall pressure. For the first time for this process, low Pt-loaded (1 wt.%) nanoparticles stabilized within hyper-cross-linked aromatic polymer (HAP) were applied. The Pt/HAP catalyst was stable under reaction conditions (250 °C, 6 MPa) allowing its recovery and reuse.

Further discussion on the mechanism of hydrogen transfer in direct coal liquefaction

The hydrogen-donor solvent (H-donor) used in direct coal liquefaction (DCL) plays a critical role in both the oil yield and distribution of the products. However, the mechanism of the reaction between H-donor and coal in the DCL is unclear. In this study, the reaction of H-donor and coal in the DCL was investigated using the model compounds tetralin (H-donor) and diphenylmethane (DPM, coal). Density functional theory calculations were employed to examine both pyrolytic radical and solvent-mediated hydrogenolysis mechanisms. Based on the computed results, a modified solvent-mediated hydrogenolysis mechanism was proposed, namely the synergistic double-hydrogen-transfer mechanism, in which the β- and α-hydrogen atoms simultaneously transfer from tetralin to the ipso- and meta-carbon atoms of DPM. The calculated energy barriers of hydrogen transfer were lower than most of the bond dissociation enthalpies for coal. The energy barriers range of the synergistic double-hydrogen-transfer reaction did not correlate with the dissociation enthalpies of Caryl−Calkyl bond, although they were consistent with the order of the hydrogen-donating abilities of different solvents. This study may provide a theoretical guidance to improve the efficiency of H-donor in the DCL.

Hydrogen donating capacity of water in catalytic and non-catalytic aquathermolysis of extra-heavy oil: Deuterium tracing study

The goal of this work is to try to figure out the role of water in catalytic and non-catalytic aquathermolysis by using isotope tracing techniques. For this purpose, heavy water (deuterium oxide, D2O) was used to replace the ordinary water (H2O) for catalytic and non-catalytic aquathermolysis processes of extra-heavy oil with high sulfur content in autoclave. The donating and upgrading performance of D2O were deeply investigated by analyzing the upgraded (deuterated) oil and their SARA (saturates, aromatics, resins and asphaltenes) fractions using different tracing techniques (FTIR, isotope and elemental analysis), evolved gases by GC, and change in physical-chemical properties of upgraded (deuterated) oils by viscosity measurement, SARA analysis, elemental analysis and GC, etc. The results proved the chemical role of water as a green and environmental hydrogen-donor solvent during aquathermolysis process, verified by considerable deuterium substitution (deuteration) obtained from isotope analysis both in upgraded oil and SARA fractions. The results are further supported by significant deuterium exchanges (deuteration) of aliphatic and aromatics parts in the initial and deuterated oil samples and their individual SARA fractions in FTIR spectra. Simultaneously, introducing Ni-tallate as an oil-soluble catalyst promoted the donating capacity of water, thus significantly improving the upgrading performance. The important finding about the role of water in catalytic and non-catalytic aquathermolysis not only enriches the theoretical basis in this area, but also provides a strong support for the use of catalysts in aquathermolysis for improving in-situ heavy oil upgrading performance.

Kinetic Study of Noncatalytic Dissolution of Cellulose Biochar in Hydrogen Donor Solvent

Biochar was produced from cellulose by hydrothermal carbonization at 220 and 300 °C. The produced biochars were subjected to dissolution in hydrogen donor solvent (tetralin) at 400 °C for 1 h. To understand the kinetics of biochar dissolution, various experiments were carried out at various temperatures of the heating stage and at different times during the isothermal stage (at 400 °C). It was observed that most of the conversion of biochar occurred during the heating stage of the dissolution reaction (200–400 °C), and there was no significant change in conversion during the isothermal stage (400 °C). It was concluded that the dissolution of biochar prepared at 220 °C consisted of two different steps in the heating stage based on its conversion to products where first the unconverted cellulose (present in the biochar) decomposed at a lower temperature (200–325 °C) to form products followed by the decomposition of biochar (325–400 °C). However, for the dissolution of biochar prepared at 300 °C, only one step (biochar decomposition) in the heating stage was observed above 300 °C (300–400 °C) to form products due to the absence of unconverted cellulose and its higher C/O ratio. A temperature-dependent two-step kinetic model was proposed where the pre-exponential factor and activation energies were determined by nonlinear regression of the experimental data.

Insights into catalytic valorization of different lignin feedstocks into liquid fuels with microwave heating in hydrogen-donor solvents

Microwave-assisted valorization of alkaline lignin, dealkaline lignin, and lignosulfonate over CuNiAl-based catalysts was investigated in hydrogen-donor solvents. The effect of lignin structures, solvents, and catalysts was investigated concerning the bio-oil yields and properties. A common phenomenon was observed that the highest bio-oil yields were all obtained in methanol over CuNiAl-based oxides under mild conditions. The synergistic and promotional effect of catalyst and solvent was discussed in detail, considering the elemental composition, HHV, and molecular weights of bio-oil. The bio-oil yields improved, and the molecular weights decreased with the increased Cu content in the catalysts, indicating the promotional effect of Cu during the lignin depolymerization. CuNiAl-based catalysts exhibited to be effective to convert lignin to bio-oil with higher HHV and decreased molecular weights, confirming the hydrogenation/hydrodeoxygenation during microwave-assisted hydrogenolysis.

Alkali Lignin Catalytic Hydrogenolysis with Biofuel Production

AbstractIn this paper synthesized palladium (Pd)-containing catalysts were used in the hydrogenolysis of lignin in the presence of a hydrogen donor solvent, i-propanol, to obtain liquid fuel components. A study of the influence of the catalyst support nature, catalyst preparation method and supercritical solvent nature on the lignin depolymerization was completed. It was found that the use of Pd-containing catalysts results in the formation of aromatic compounds (mainly benzene and toluene) for both supercritical solvents used (i-propanol and CO2). The maximum conversion of lignin (50 %) was achieved when the supercritical i-propanol was used and maximum selectivity to aromatics (over 70 %) was observed in the presence of the Pd-containing catalyst synthesized by hydrothermal deposition on the polymeric matrix of hyper-crosslinked polystyrene.

Hydroconversion of asphaltene in a hydrogen donor solvent: Stability analysis of the asphaltene-solvent colloidal system

Asphaltene aggregation and precipitation out of the reaction mixture limits the extent of its hydroconversion. In this work, the colloidal stability of asphaltenes undergoing hydroconversion in tetralin solvent was monitored with time. The separability number was measured and the Gibbs energy of mixing together with the onset of asphaltene precipitation were calculated. The results show that the hydrogen transfer from tetralin to asphaltene radicals effectively quench the radicals. The colloidal stability of the system, nevertheless, decreased with reaction time and vanished for reaction times >3 h. In line with this observation, the onset of asphaltene precipitation decreased and, while the Gibbs energy of mixing was negative, it increased with time. The colloidal stability of the reaction system was chiefly influenced by the increased aromaticity of the asphaltene, which in turn decreased its solubility parameter. Within the stable colloidal domain, approximately 44% of the asphaltenes were converted with <1 wt% coke generation. This work is the first attempt in the literature to analytically and mathematically characterize the colloidal stability of asphaltenes undergoing reactions in a hydrogen donor solvent.

Coal and waste direct liquefaction, using glycerol, polyethylene waste and waste tyres pyrolysis oil. Optimisation of liquids yield by response surface methodology

Coal and waste direct liquefaction was carried out to decrease the hydrocarbons production negative bearing to environment. The wastes studied were glycerol, polyethylene waste and waste tyres pyrolysis oil. Glycerol and waste tyres pyrolysis oil were blended with tetralin and used as solvent for coal direct liquefaction (T = 350–450 °C; N2; waste:tetralin at different weight ratios). Glycerol may be considered as a waste from the production of fatty acid methyl esters (FAME). Waste tyres pyrolysis oil showed to be a good hydrogen donor solvent. Solid polyethylene wastes were mixed with coal and used in coal co-liquefaction tests, which showed to be a good option to produce liquid hydrocarbons for fuels or raw materials for chemical industry. Although liquids yield using waste tyres pyrolysis oil or glycerol were high, respectively 62% wt. and 51% wt., the use of polyethylene allowed increasing them to 80% wt. Different experimental conditions were studied, namely: experimental temperature, run time, solvent type and composition and hydrogen initial pressure. The effect of commercial catalysts on co-liquefaction was also studied and the results obtained were compared with those obtained with coal impregnated with Fe or Mo (1% wt./coal). Response surface methodology (RSM) was used to predict the influence of the main experimental conditions studied on product yields. This methodology resulted to be a good one to predict coal liquefaction and co-liquefaction products yields, as predicted values were similar to experimental data. In addition, RSM approach led to the selection of tetralin as solvent and to the use of coal impregnated with 1% of Mo, as liquids yield increased up to 96% wt.

Effect of decomposition of oxygen-containing structures on the conversion of lignite in the presence of hydrogen donor solvent

In this paper, pyrolysis behaviors of oxygen-containing structures of Xilinhaote (XLHT) lignite in hydrogen donor solvent (HDS) were investigated to reveal the effect of HDS on the pyrolysis sequence characteristics of XLHT and the difference of the pyrolysis behaviors of oxygen-containing structures in the presence or absence of HDS. Results showed that coal conversion was closely associated to the decomposition of oxygen-containing structures of lignite, and HDS could promote the cleavage of oxygen-containing groups and inhibit the resolidification of decomposed products, while its effect on the pyrolysis sequence of different structures of lignite was tiny. Thermal cleavage of weak aryl-alkyl ether bonds and carbonyl groups of lignite at relatively low temperatures of 280−380 °C contributed to the depolymerization of XLHT lignite to form preashphaltene (PA) with coal conversion and PA yield increasing from 12.85 % and 1.98 % to 64.58 % and 13.08 %, respectively. As the temperature rose to 430 °C, coal conversion was up to 84.13 %, and HDS could promote the cleavage of relatively stable oxygen-containing groups, aryl-aryl ethers, and methylene structures, which was the major contributor to increase coal conversion at relatively high temperatures during liquefaction. Besides, C–O and CO moieties retained on the surface of LR at 430 °C, which netted 12.54 % and 3.52 % of carbon single bond forms, respectively.

Transformation Characteristics of Hydrogen-Donor Solvent Tetralin in the Process of Direct Coal Liquefaction.

The aim of this study is to investigate the transformation of hydrogen-donor solvent tetralin in the direct liquefaction process of coal. Pure tetralin liquid as well as mixture of tetralin and Wucaiwan coal (WCW) were separately reacted under a liquefaction condition, and constituents of liquid product were analyzed by GC-MS. The results show that after the tetralin liquid reacts with high-pressure hydrogen, 90% of the reaction product is in liquid state, the gaseous products mainly include alkane gas and COx gas. When the reaction temperatures were set at 380 and 420°C, respectively, the corresponding transformation rates of tetralin can be 34.72 and 52.74%. At 380°C, the tetralin mainly plays a role of passing active hydrogen, while at 420°C, it mainly occurs dehydrogenation transformation to provide active hydrogen, as well as generate naphthalene, methyl indan, and substituted benzene, etc. Taking tetralin as the hydrogen-donor solvent, the WCW was performed liquefaction reaction, and the obtained results show that the transformation rates of tetralin are 69.76 and 83.86% at liquefaction temperatures of 380 and 420°C, respectively. Tetralin mainly occur to dehydrogenation transformation to generate naphthalene, followed by methyl indan, where contents order of main constituents of the liquefaction products were: naphthalene> tetralin > methyl indan.

Effect of Waste Type on Liquid Products Yields and Quality Obtained by Co-Liquefaction of Coal and Waste

The need to find alternative liquid fuels more environmental friendly and with a more secure supply, has led to the idea of studying the conversion of carbonaceous wastes, like plastics, used tyres and biomass into liquid products to be used as fuels or as raw materials for several industries. As coal liquefaction is a well-known process to produce liquid products, coal blended with used tyres and plastic wastes was co-liquefied. Coal impregnated with 1 % wt. of molybdenum was used in co-liquefaction tests blended with 50 % wt. of used tyres or with the main plastics present in municipal solid wastes: PE (polyethylene), PP (polypropylene), PS (polystyrene) and a mixture of these plastics. The results obtained showed that all wastes promoted coal liquefaction. However, liquids yield and quality improved with the presence of plastics, while more solids were obtained when used tyres were used. Coal blends with PS wastes led to the highest liquid yield (74 % wt.) and conversion (88 % wt.) The presence of PE favoured the formation of linear alkanes, while PS promoted the formation of more aromatic compounds, which is in agreement with these plastics initial molecular structure. Some co-liquefaction tests were done in presence of tetralin, a hydrogen donor solvent that promoted the formation of liquids. Tetralin allowed increasing liquids yields obtained with plastics to values higher than 90 % wt., while in co-liquefaction of coal with used tyres led to liquids yields around 77 % wt.