Sustainable hydrogen production via microalgae: Technological advancements, economic indicators, environmental aspects, challenges, and policy implications.

Hydrogen has emerged as an alternative energy source to meet the increasing global energy demand, depleting fossil fuels and environmental issues resulting from fossil fuel consumption. Microalgae-based biomass is gaining attention as a potential source of hydrogen production due to its green energy carrier properties, high energy content, and carbon-free combustion. This review examines the hydrogen production process from microalgae, including the microalgae cultivation technological process for biomass production, and the three main routes of biomass-to-hydrogen production: thermochemical conversion, photo biological conversion, and electrochemical conversion. The current progress of technological options in the three main routes is presented, with the various strains of microalgae and operating conditions of the processes. Furthermore, the economic and environmental perspectives of biomass-to-hydrogen from microalgae are evaluated, and critical operational parameters are used to assess the feasibility of scaling up biohydrogen production for commercial industrial-scale applications. The key finding is the thermochemical conversion process is the most feasible process for biohydrogen production, compared to the pyrolysis process. In the photobiological and electrochemical process, pure hydrogen can be achieved, but further process development is required to enhance the production yield. In addition, the high production cost is the main challenge in biohydrogen production. The cost of biohydrogen production for direct bio photolysis it cost around $7.24 kg-1; for indirect bio photolysis it costs around $7.54 kg-1 and for fermentation, it costs around $7.61 kg-1. Therefore, comprehensive studies and efforts are required to make biohydrogen production from microalgae applications more economical in the future.

Integrating life cycle assessment and characterisation techniques: A case study of biodiesel production utilising waste Prunus Armeniaca seeds (PAS) and a novel catalyst.

Prunus Armeniaca seed (PAS) oil was utilised as a waste biomass feedstock for biodiesel production via a novel catalytic system (SrO-La2O3) based on different stoichiometric ratios. The catalysts have been characterised and followed by a parametric analysis to optimise catalyst results. The catalyst with a stoichiometric ratio of Sr: La-8 (Sr-La-C) using parametric analysis showed an optimum yield of methyl esters is 97.28% at 65 °C, reaction time 75 min, catalyst loading 3 wt% and methanol to oil molar ratio of 9. The optimum catalyst was tested using various oil feedstocks such as waste cooking oil, sunflower oil, PAS oil, date seed oil and animal fat. The life cycle assessment was performed to evaluate the environmental impacts of biodiesel production utilising waste PAS, considering 1000 kg of biodiesel produced as 1 functional unit. The recorded results showed the cumulative abiotic depletion of fossil resources over the entire biodiesel production process as 22,920 MJ, global warming potential as 1150 kg CO2 equivalent, acidification potential as 4.89 kg SO2 equivalent and eutrophication potential as 0.2 kg PO43- equivalent for 1 tonne (1000 kg) of biodiesel produced. Furthermore, the energy ratio (measured as output energy divided by input energy) for the entire production process was 1.97. These results demonstrated that biodiesel obtained from the valorisation of waste PAS provides a suitable alternative to fossil fuels.

Utilisation of Non-Edible Source (Pongamia pinnata Seeds Shells) for Producing Methyl Esters as Cleaner Fuel in the Presence of a Novel Heterogeneous Catalyst Synthesized from Waste Eggshells.

Waste eggshells were considered for synthesising a precursor (CaO) for a heterogeneous catalyst, further impregnated by alkali caesium oxide (Cs2O). The following techniques were used to characterise the synthesised catalysts: X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and Temperature Programmed Desorption (CO2-TPD). The synthesised catalyst revealed its suitability for transesterification to produce biodiesel. The biodiesel production process was optimised, and it showed that the optimal biodiesel yield is 93.59%. The optimal set of process parameters is process temperature 80 °C, process time 90 min, methanol-to-oil molar ratio 8 and catalyst loading 3 wt.%. It has been found that the high basicity of the catalyst tends to give a high biodiesel yield at low methanol-to-oil ratio 8 when the reaction time is also less (90 min). The fuel properties of biodiesel also satisfied the standard limits defined by ASTM and the EN standards. Thus, the synthesised catalyst from waste eggshells is highly active, improved the biodiesel production conditions and PPSS oil is a potential nonedible source.

Microporous Carbon Nitride (C3 N5.4 ) with Tetrazine based Molecular Structure for Efficient Adsorption of CO2 and Water.

Mesoporous carbon nitrides with C3 N5 and C3 N6 stoichiometries created a new momentum in the field of organic metal-free semiconductors owing to their unique band structures and high basicity. Here, we report on the preparation of a novel graphitic microporous carbon nitride with a tetrazine based chemical structure and the composition of C3 N5.4 using ultra-stable Y zeolite as the template and aminoguanidine hydrochloride, a high nitrogen-containing molecule, as the CN precursor. Spectroscopic characterization and density functional theory calculations reveal that the prepared material exhibits a new molecular structure, which comprises two tetrazines and one triazine rings in the unit cell and is thermodynamically stable. The resultant carbon nitride shows an outstanding surface area of 130.4 m2 g-1 and demonstrates excellent CO2 adsorption per unit surface area of 47.54 µmol m-2 , which is due to the existence of abundant free NH2 groups, basic sites and microporosity. The material also exhibits highly selective sensing over water molecules (151.1 mmol g-1 ) and aliphatic hydrocarbons due to its unique microporous structure with a high amount of hydrophilic nitrogen moieties and recognizing ability towards small molecules.

Mixed Copper/Copper-Oxide Anchored Mesoporous Fullerene Nanohybrids as Superior Electrocatalysts toward Oxygen Reduction Reaction.

Developing a highly active, stable, and efficient non-noble metal-free functional electrocatalyst to supplant the benchmark Pt/C-based catalysts in practical fuel cell applications remains a stupendous challenge. A rational strategy is developed to directly anchor highly active and dispersed copper (Cu) nanospecies on mesoporous fullerenes (referred to as Cu-MFC60 ) toward enhancing oxygen reduction reaction (ORR) electrocatalysis. The preparation of Cu-MFC60 involves i) the synthesis of ordered MFC60 via the prevalent nanohard templating technique and ii) the postfunctionalization of MFC60 with finely distributed Cu nanospecies through incipient wet impregnation. The concurrence of Cu and cuprous oxide nanoparticles in the as-developed Cu-MFC60 samples through relevant material characterizations is affirmed. The optimized ORR catalyst, Cu(15%)-MFC60 , exhibits superior electrocatalytic ORR characteristics with an onset potential of 0.860 vs reversible hydrogen electrode, diffusion-limiting current density (-5.183 mA cm-2 ), improved stability, and tolerance to methanol crossover along with a high selectivity (four-electron transfer). This enhanced ORR performance can be attributed to the rapid mass transfer and abundant active sites owing to the synergistic coupling effects arising from the mixed copper nanospecies and the fullerene framework.

Visible photodegradation of ibuprofen and 2,4-D in simulated waste water using sustainable metal free-hybrids based on carbon nitride and biochar.

Rational designing of metal-free carbon nitride based photocatalysts can lead to an excellent optical response and a higher photocatalytic activity driven by visible and solar light. This combines green photocatalytic technology with greener materials prepared by facile approaches for environmental remediation. Herein we report utilization of star photocatalyst g-C3N4 (CN) to form highly efficient hetero-assemblies along with acidified g-C3N4 (ACN), polyaniline (PANI), reduced graphene oxide (RGO) and biochar. By use of these organic semiconductors we synthesize g-C3N4/ACN/RGO@Biochar (GARB), g-C3N4/PANI/RGO@Biochar (GPRB) and ACN/PANI/RGO@Biochar (APRB) nano-assemblies with different optical response and band edge positions for a better charge flow and reduced recombination of carriers. These synthesized catalysts were used for visible light powered degradation of 2,4-Dichlorophenoxy acetic acid (2,4-D) and ibuprofen (IBN). APRB performs the best and degrades 99.7% and 98.4% of 2,4-D and IBN (20 mg L-1) under Xe lamp exposure in 50 min and retention of high activity in natural sunlight. Optical analysis, photoelectrochemical response and radical quenching studies show both hydroxyl and superoxide radical anions as major reactive species and a Z-scheme photocatalytic mechanism. RGO acts as an electron mediator and protects higher positioned bands of PANI and ACN in APRB for a remarkable photocatalytic activity for a metal free material. The degradation pathway was analyzed by LC-MS analysis and 42% and 40% total organic carbon was removed in 2 h for 2,4-D and IBN degradation respectively. The toxicity of degraded products was analyzed by analyzing viability of human peripheral blood cells with retaining of 99.1% cells.

Dispersion and deposition estimation of fugitive iron particles from an iron industry on nearby communities via AERMOD.

Emission of fugitive iron particles from anthropogenic sources can have significant effects on the human health and the environment. In this study, a regulatory air pollutant dispersion model (AERMOD) was implemented to predict the dispersion and deposition of fugitive iron particles towards a mid-sized residential area in Sultanate of Oman. The performance of the model was validated using air, soil, and dust fall samples. PM10 was found as the most abundant iron particles in the soil samples. The results showed that the maximum daily concentration level of fugitive iron particles simulated through AERMOD was 7.19 µg/m3. Statistical analysis, including fractional bias (FB), normalized mean square error (NMSE), and predicted/observed ratio (Pred./Obs.), showed a reliable agreement in accuracy and precision between the datasets (for air samples FB = 0.024, NMSE = 0.001, Pred./Obs. = 0.976; for dust fall samples FB = -0.004, NMSE = 0.000, Pred./Obs. = 1.004). However, uncertainties and differences were from the external sources, such as other industries in the region. The results presented that the concentration levels were below the national and international guidelines proposed by the US Environmental Protection Agency (USEPA) and Omani Ambient Air Quality Standards (OAAQS). The methodology followed and the developed dispersion model can be generalized to other industries from which the dispersion of fugitive metal particles need to be evaluated as a potential route for human exposure. Graphical abstract ᅟ.

Characterization of adsorption of aqueous arsenite and arsenate onto charred dolomite in microcolumn systems.

In this work, the removal of arsenite, As(III), and arsenate, As(V), from aqueous solutions onto thermally processed dolomite (charred dolomite) via microcolumn was evaluated. The effects of mass of adsorbent (0.5-2 g), initial arsenic concentration (50-2000 ppb) and particle size (<0.355-2 mm) on the adsorption capacity of charred dolomite in a microcolumn were investigated. It was found that the adsorption of As(V) and As(III) onto charred dolomite exhibited a characteristic 'S' shape. The adsorption capacity increased as the initial arsenic concentration increased. A slow decrease in the column adsorption capacity was noted as the particle size increased from>0.335 to 0.710-2.00 mm. For the binary system, the experimental data show that the adsorption of As(V) and As(III) was independent of both ions in solution. The experimental data obtained from the adsorption process were successfully correlated with the Thomas Model and Bed Depth Service Time Model.

Removal of Carbamazepine from Water by a Novel TiO2-Coconut Shell Powder/UV Process: Composite Preparation and Photocatalytic Activity.

A novel TiO2-coconut shell powder (TCNSP) composite, prepared by the controlled sol-gel method with a subsequent heat treatment, was investigated as an innovative photocatalytic absorbent for the removal of carbamazepine (CBZ). CBZ is used worldwide as an antiepileptic drug, which has recently been recognized as an important organic pollutant increasingly found in wastewaters from urban areas and other aquatic environments. The granulation process was performed by using a semiautomated mass production line to produce sufficient quantities of TCNSP composites, possessing sufficient crush strength for commercialization. Physical properties of the TCNSP composite such as crystallinity, morphology, crush strength, and the Brunauer-Emmett-Teller (BET)-specific surface area were controlled by the mass ratio of titanium dioxide sol and coconut shell powder (CNSP). Calcination at 700°C produced anatase phase TiO2 in the TCNSP composites with a BET high surface area of 454 m2/g. Anatase crystallite size of the TCNSP composite increased from 2.37 to 15.11 nm with increasing calcination temperature from 500°C to 800°C. Calcinated TCNSP composites had higher CBZ removal efficiency (98%) than pure TiO2 (23%) and CNSP (34%) within a 40-min reaction time. Optimization of this innovative adsorption/photocatalytic process was obtained by a response surface methodology and a central composite design model, which indicated that this novel and sustainable technology was successful in removing CBZ from a solution.

Fermentable sugars recovery from lignocellulosic waste-newspaper by catalytic hydrolysis.

The urgent need for alternative renewable energies to supplement petroleum-based fuels and the reduction of landfill sites for disposal of solid wastes makes it increasingly attractive to produce inexpensive biofuels from the organic fraction of the municipal solid waste. Therefore, municipal waste in the form of newspaper was investigated as a potential feedstock for fermentable sugars production. Hydrolysis of newspaper by dilute phosphoric acid was carried out in autoclave Parr reactor, where reactor temperature and acid concentration were examined. Xylose concentration reached a maximum value of 14 g/100 g dry mass corresponding to a yield of 94% at the best identified conditions of 2.5 wt% H3PO4, 135 degrees C, 120 min reaction time, and at 2.5 wt% H3PO4, 150 degrees C, and 60 min reaction time. For glucose, an average yield of 26% was obtained at 2.5 wt% H3PO4, 200 degrees C, and 30 min. Furfural and 5-hydroxymethylfurfural (HMF) formation was clearly affected by reaction temperature, where the higher the temperature the higher the formation rate. The maximum furfural formed was an average of 3 g/100 g dry mass, corresponding to a yield of 28%. The kinetic study of the acid hydrolysis was also carried out using the Saeman and the two-fraction models. It was found for both models that the kinetic constants (K) depend on the acid concentration and temperature. The degradation of HMF to levulinic acid is faster than the degradation of furfural to formic acid. Also, the degradation rate is higher than the formation rate for both inhibitors when degradation is observed.

Methanol production and purification via membrane-based technology: Recent advancements, challenges and the way forward.

Industrial revolution on the back of fossil fuels has costed humanity higher temperatures on the planet due to ever-growing concentration of carbon dioxide emissions in Earth's atmosphere. To tackle global warming demand for renewable energy sources continues to increase. Along renewables, there has been a growing interest in converting carbon dioxide to methanol, which can be used as a fuel or a feedstock for producing chemicals. The current review study provides a comprehensive overview of the recent advancements, challenges and future prospects of methanol production and purification via membrane-based technology. Traditional downstream processes for methanol production such as distillation and absorption have several drawbacks, including high energy consumption and environmental concerns. In comparison to conventional technologies, membrane-based separation techniques have emerged as a promising alternative for producing and purifying methanol. The review highlights recent developments in membrane-based methanol production and purification technology, including using novel membrane materials such as ceramic, polymeric and mixed matrix membranes. Integrating photocatalytic processes with membrane separation has been investigated to improve the conversion of carbon dioxide to methanol. Despite the potential benefits of membrane-based systems, several challenges need to be addressed. Membrane fouling and scaling are significant issues that can reduce the efficiency and lifespan of the membranes. The cost-effectiveness of membrane-based systems compared to traditional methods is a critical consideration that must be evaluated. In conclusion, the review provides insights into the current state of membrane-based technology for methanol production and purification and identifies areas for future research. The development of high-performance membranes and the optimization of membrane-based processes are crucial for improving the efficiency and cost-effectiveness of this technology and for advancing the goal of sustainable energy production.

A critical review on the role of abiotic factors on the transformation, environmental identity and toxicity of engineered nanomaterials in aquatic environment.

Engineered nanomaterials (ENMs) are at the forefront of many technological breakthroughs in science and engineering. The extensive use of ENMs in several consumer products has resulted in their release to the aquatic environment. ENMs entering the aquatic ecosystem undergo a dynamic transformation as they interact with organic and inorganic constituents present in aquatic environment, specifically abiotic factors such as NOM and clay minerals, and attain an environmental identity. Thus, a greater understanding of ENM-abiotic factors interactions is required for an improved risk assessment and sustainable management of ENMs contamination in the aquatic environment. This review integrates fundamental aspects of ENMs transformation in aquatic environment as impacted by abiotic factors, and delineates the recent advances in bioavailability and ecotoxicity of ENMs in relation to risk assessment for ENMs-contaminated aquatic ecosystem. It specifically discusses the mechanism of transformation of different ENMs (metals, metal oxides and carbon based nanomaterials) following their interaction with the two most common abiotic factors NOM and clay minerals present within the aquatic ecosystem. The review critically discusses the impact of these mechanisms on the altered ecotoxicity of ENMs including the impact of such transformation at the genomic level. Finally, it identifies the gaps in our current understanding of the role of abiotic factors on the transformation of ENMs and paves the way for the future research areas.

Facile Synthesis and Life Cycle Assessment of Highly Active Magnetic Sorbent Composite Derived from Mixed Plastic and Biomass Waste for Water Remediation.

Plastic and biomass waste pose a serious environmental risk; thus, herein, we mixed biomass waste with plastic bottle waste (PET) to produce char composite materials for producing a magnetic char composite for better separation when used in water treatment applications. This study also calculated the life cycle environmental impacts of the preparation of adsorbent material for 11 different indicator categories. For 1 functional unit (1 kg of pomace leaves as feedstock), abiotic depletion of fossil fuels and global warming potential were quantified as 7.17 MJ and 0.63 kg CO2 equiv for production of magnetic char composite materials. The magnetic char composite material (MPBC) was then used to remove crystal violet dye from its aqueous solution under various operational parameters. The kinetics and isotherm statistical theories showed that the sorption of CV dye onto MPBC was governed by pseudo-second-order, and Langmuir models, respectively. The quantitative assessment of sorption capacity clarifies that the produced MPBC exhibited an admirable ability of 256.41 mg g-1. Meanwhile, the recyclability of 92.4% of MPBC was demonstrated after 5 adsorption/desorption cycles. Findings from this study will inspire more sustainable and cost-effective production of magnetic sorbents, including those derived from combined plastic and biomass waste streams.

Membrane based reactors for sustainable treatment of Coronopus didymus L. by developing Iodine doped potassium oxide Catalyst under Dynamic conditions.

Green nano-technology together with the availability of eco-friendly and alternative sources are the promising candidates to combat environment deteriorations and energy clutches globally. The current work focuses on the synthesis and application of newly synthesized nano catalyst of Iodine doped Potassium oxide I (K2O) for producing sustainable biodiesel from novel non-edible seed oils of Coronopus didymus L. using membrane based contactor to avoid emulsification and phase separation issues. Highest biodiesel yield (97.03%) was obtained under optimum conditions of 12:1 methanol to oil ratio, reaction temperature of 65 °C for 150 min with the 1.0 wt% catalyst concentration. The lately synthesized, environment friendly and recyclable Iodine doped Potassium oxide K (IO)2 catalyst was synthesized via chemical method followed by characterization via advanced techniques including EDX, XRD, FTIR and SEM analysis. The catalyst was proved to be stable and efficient with the reusability of five times in transesterification reaction. These analysis have reported the sustainability, stability and good quality of biodiesel from seed oil of Coronopus didymus L. using efficient Iodine doped potassium oxide catalyst. Thus, non-edible, environment friendly and novel Coronopus didymus L. seeds and their extracted oil along with Iodine doped potassium oxide catalyst seems to be highly affective, sustainable and better alternative source to the future biodiesel industry. Also, by altering the reaction equilibrium and lowering the purification phases of the process, these studies show the potential of coupling transesterification and a membrane contactor.

Ordered Mesoporous Boron Carbon Nitrides with Tunable Mesopore Nanoarchitectonics for Energy Storage and CO2 Adsorption Properties.

Porous boron carbon nitride (BCN) is one of the exciting systems with unique electrochemical and adsorption properties. However, the synthesis of low-cost and porous BCN with tunable porosity is challenging, limiting its full potential in a variety of applications. Herein, the preparation of well-defined mesoporous boron carbon nitride (MBCN) with high specific surface area, tunable pores, and nitrogen contents is demonstrated through a simple integration of chemical polymerization of readily available sucrose and borane ammonia complex (BAC) through the nano-hard-templating approach. The bimodal pores are introduced in MBCN by controlling the self-organization of BAC and sucrose molecules within the nanochannels of the template. It is found that the optimized sample shows a high specific capacitance (296 F g-1 at 0.5 A g-1 ), large specific capacity for sodium-ion battery (349 mAg h-1 at 50 mAh g-1 ), and excellent CO2 adsorption capacity (27.14 mmol g-1 at 30 bar). Density functional theory calculations demonstrate that different adsorption sites (BC, BN, CN, and CC) and the large specific surface area strongly support the high adsorption capacity. This finding offers an innovative breakthrough in the design and development of MBCN nanostructures for energy storage and carbon capture applications.

Theoretical study on the unimolecular decomposition of thiophenol.

The potential energy surface for the unimolecular decomposition of thiophenol (C(6)H(5)SH) is mapped out at two theoretical levels; BB1K/GTlarge and QCISD(T)/6-311+G(2d,p)//MP2/6-31G(d,p). Calculated reaction rate constants at the high pressure limit indicate that the major initial channel is the formation of C(6)H(6)S at all temperatures. Above 1000 K, the contribution from direct fission of the S-H bond becomes important. Other decomposition channels, including expulsion of H(2) and H(2)S are of negligible importance. The formation of C(6)H(6)S is predicted to be strong-pressure dependent above 900 K. Further decomposition of C(6)H(6)S produces CS and C(5)H(6). Overall, despite the significant difference in bond dissociation, i.e., 8-9 kcal/mol between the S-H bond in thiophenol and the O-H bond in phenol, H migration at the ortho position in the two molecules represents the most accessible initial channel.

Rate constants for hydrogen abstraction reactions by the hydroperoxyl radical from methanol, ethenol, acetaldehyde, toluene, and phenol.

An important step in the initial oxidation of hydrocarbons at low to intermediate temperatures is the abstraction of H by hydroperoxyl radical (HO(2)). In this study, we calculate energy profiles for the sequence: reactant + HO(2) → [complex of reactants] → transition state → [complex of products] → product + H(2)O(2) for methanol, ethenol (i.e., C(2)H(3)OH), acetaldehyde, toluene, and phenol. Rate constants are provided in the simple Arrhenius form. Reasonable agreement was obtained with the limited literature data available for acetaldehyde and toluene. Addition of HO(2) to the various distinct sites in phenol is investigated. Direct abstraction of the hydroxyl H was found to dominate over HO(2) addition to the ring. The results presented herein should be useful in modeling the lower temperature oxidation of the five compounds considered, especially at low temperature where the HO(2) is expected to exist at reactive levels.

Theoretical investigation into competing unimolecular reactions encountered in the pyrolysis of acetamide.

Motivated by the necessity to understand the pyrolysis of alkylated amines, unimolecular decomposition of acetamide is investigated herein as a model compound. Standard heats of formation, entropies, and heat capacities, are calculated for all products and transition structures using several accurate theoretical levels. The potential energy surface is mapped out for all possible channels encountered in the pyrolysis of acetamide. The formation of acetamedic acid and 1-aminoethenol and their subsequent decomposition pathways are found to afford the two most energetically favored pathways. However, RRKM analysis shows that the fate of acetamedic acid and 1-aminoethenol at all temperatures and pressures is to reisomerize to the parent acetamide. 1-Aminoethenol, in particular, is predicted to be a long-lived species enabling its participation in bimolecular reactions that lead to the formation of the major experimental products. Results presented herein reflect the importance of bimolecular reactions involving acetamide and 1-aminoethenol in building a robust model for the pyrolysis of N-alkylated amides.

Fabrication of Mesoporous C60/Carbon Hybrids with 3D Porous Structure for Energy Storage Applications.

We report on the synthesis of 3D mesoporous fullerene/carbon hybrid materials with ordered porous structure and high surface area by mixing the solution of fullerene and sucrose molecules in the nanochannels of 3D mesoporous silica, KIT-6 via nanotemplating approach. The addition of sucrose molecules in the synthesis offers a thin layer of carbon between the fullerene molecules which enhances not only the specific surface area and the specific pore volume but also the conductivity of the hybrid materials. The prepared hybrids exhibit 3D mesoporous structure and show a much higher specific surface area than that of the pure mesoporous fullerene. The hybrids materials are used as the electrodes for supercapacitor and Li-ion battery applications. The optimised hybrid sample shows an excellent rate capability and a high specific capacitance of 254 F/g at the current density of 0.5 A/g, which is much higher than that of the pure mesoporous fullerene, mesoporous carbon, activated carbon and multiwalled carbon nanotubes. When used as the electrode for Li-ion battery, the sample delivers the largest specific capacity of 1067 mAh/g upon 50 cycles at the current density of 0.1 A/g with stability. These results reveal that the addition of carbon in the mesoporous fullerene with 3D structure makes a significant impact on the electrochemical properties of the hybrid samples, demonstrating their potential for applications in Li-ion battery and supercapacitor devices.

Theoretical study on the thermodynamic properties and self-decomposition of methylbenzenediol isomers.

Alkylated hydroxylated aromatics are major constituents of various types of fuels, including biomass and low-rank coal. In this study, thermochemical parameters are obtained for the various isomeric forms of methylbenzenediol isomers in terms of their enthalpies of formation, entropies, and heat capacities. Isodesmic work reactions are used in quantum chemical computations of the reaction enthalpies for O-H and H2C-H bond fissions and the formation of phenoxy- and benzyl-type radicals. A reaction potential energy on the singlet-state surface surface is mapped out for the unimolecular decomposition of the 3-methylbenzene-1,2-diol isomer. According to the calculated high pressure-limit reaction rate constants, concerted hydrogen molecule elimination from the methyl group and the hydroxyl group, in addition to intermolecular H migration from the hydroxyl group, dominates the unimolecular decomposition at low to intermediate temperatures (T ≤ 1200 K). At higher temperatures, O-H bond fission and concerted water elimination are expected to become the sole decomposition pathways.