Hydrothermal Medium Research Articles

Transformation of glucose into added value compounds in a hydrothermal reaction media

In this study, the chemical transformation of glucose into added value products (lactic acid and 5-hydroxymethylfurfural) was analyzed using a hydrothermal reaction medium. A continuous pilot plant that operates up to 400°C, 30MPa and residence times between 0.004s and 50s was used in order to study the process. The reactions of glucose in hot pressurized water were analyzed at 300°C, 350°C, 385°C and 400°C; the pressure was fixed at 23MPa and 27MPa for the experiments. No lactic acid was found at those conditions. High yield of glycolaldehyde (80%, w/w) was found operating at 400°C and 27MPa with reaction times of 20s. Two additives (H2O2 and NaOH) were added in different experiments to improve the lactic acid production. The maximum yield of lactic acid was 57% (w/w) carbon basis using NaOH (0.5M) as catalyst at 27MPa and 400°C with 20s of residence time. It was observed that the pH of the medium plays an important role in the selectivity of the process.

Synthesis, characterization and catalytic properties of SAPO-11 molecular sieve synthesized in hydrothermal media using di-isopropylamine as template

Abstract A microporous SAPO-11 Molecular sieve was successfully synthesized by the hydrothermal method, using a single agent, as an organic template: di-isopropylamine (DIPA). The obtained solid was calcined at 550◦C for three hours, after which the flow of nitrogen was exchanged for that of synthetic air and submitted for another ten hours of calcination, so as to remove the single agent: di-isopropylamine, which after the removal of the template could be observed by the high crystallization of the sample. Furthermore, the molecular sieve was characterized by XRD, SEM, TG-DTG and N2 adsorption desorption (BET analysis). The obtained catalyst proved to have a high potential catalytic activity and selectivity, through the obtained characterization results, exhibiting good hydrothermal stability. The catalytic performance of SAPO-11 was tested by the deactivation/regenerability of the coked sample, furthered by cracking of n-hexane reaction and high olefins selectivity was obtained.

Reaction engineering for process intensification of supercritical water biomass refining

Status reports from public and private organizations make a roadmap for achieving a bioeconomy for society. Biobased industries, based on renewable materials and energy, are still in development to supporting a decentralized production that can be an alternative to the well-supported centralized petrochemical production plants. The use of pressurized water has been proposed as an environmentally compatible process to integrate the depolymerization–reaction–separation of the biomass supported processes. Supercritical water is emerging as a solvent and reaction medium capable of providing selective processes while significantly reducing the reaction time, leading to the possibility of developing compact equipment for the use in biomass decentralized production plants. The main ways of biomass upgrading in a hydrothermal medium are reviewed in this work: hydrolysis, fractionation, gasification and reaction. In the last years, a significant progress was achieved in obtaining of added value products from biomass by hydrothermal technologies. However, some challenges must still be overcome before a sustainable and efficient decentralized production is achieved.

Emergence of biological organization through thermodynamic inversion

Biological organization arises under thermodynamic inversion in prebiotic systems that provide the prevalence of free energy and information contribution over the entropy contribution. The inversion might occur under specific far-from-equilibrium conditions in prebiotic systems oscillating around the bifurcation point. At the inversion moment, (physical) information characteristic of non-biological systems acquires the new features: functionality, purposefulness, and control over the life processes, which transform it into biological information. Random sequences of amino acids and nucleotides, spontaneously synthesized in the prebiotic microsystem, in the primary living unit (probiont) re-assemble into functional sequences, involved into bioinformation circulation through nucleoprotein interaction, resulted in the genetic code emergence. According to the proposed concept, oscillating three-dimensional prebiotic microsystems transformed into probionts in the changeable hydrothermal medium of the early Earth. The inversion concept states that spontaneous (accidental, random) transformations in prebiotic systems cannot produce life; it is only non-spontaneous (perspective, purposeful) transformations, which are the result of thermodynamic inversion, that lead to the negentropy conversion of prebiotic systems into initial living units.

The study of hydrargillite and γ-alumina conversion process in boehmite in different hydrothermal media

The transition of hydrargillite and γ-alumina in boehmite was investigated under hydrothermal conditions at a temperature of 200°C. The methods of X-ray fluorescnce (XRF) analysis, infrared spectroscopy (IR spectroscopy) DTA, TGA, DSC, scanning electron microscopy (SEM), and thermal desorption were used to study the samples subjected to autoclave treatment in different media. It was shown that, at the hydrothermal treatment of hydrargillite and γ-alumina at the initial stages of treatment, regardless of the conditions of the process and the reaction medium, the formed boehmite is characterized by a high specific surface and low value of the heat effect of the formation and decomposition, which is determined by the weak ordering of its structure.

26 Inversion approach to the origin of life: theoretical notions and experimental data

The essence of the inversion concept of the origin of life can be narrowed down to the following theses: (1) thermodynamic inversion is the key transformation of prebiotic microsystems leading to their transition into primary forms of life; (2) this transformation might occur only in the microsystems oscillating around the bifurcation point under far-from-equilibrium conditions. The transformation consists in the inversion of the balance “free energy contribution entropy contribution” (as well as “information contribution informational entropy contribution”), from negative to positive values. At the inversion moment, the microsystem radically reorganizes in accordance with the new negentropy (i.e. biological) way of organization. According to this concept, the origin-of-life process on the early Earth took place in oscillating hydrothermal medium. The process was taking two successive stages: (1) spontaneous self-assembly of initial three-dimensional prebiotic microsystems composed mainly of hydrocarbons, lipids, and simple amino acids, or their precursors, within the temperature interval of 100–300 °C (prebiotic stage); (2) nonspontaneous synthesis of sugars, ATP, and nucleic acids started at the inversion moment under the temperature 70–100 °C (biotic stage). Macro and microfluctuations of thermodynamic and physicochemical parameters able to sustain this way of chemical conversion have been detected in several contemporary hydrothermal systems (Kompanichenko, 2012). Conditions in potential hydrothermal medium for the origin of life were explored on the examples of several hydrothermal systems in Kamchatka peninsula. Temperature of water in hot springs ranges from < 60 to 98 °C, in the bore holes water-steam temperature varies from < 100 to 239 °C, and pressure from < 1 to 35 bars at the wellheads; pH is within the interval 2.5–9.0. Pressure monitoring at the depth 950 meters in the borehole No. 30 (Mutnovsky field) has revealed high-amplitude (up to 1–2 bars) irregular macrofluctuations and low-amplitude quite regular microoscillations of pressure (amplitudes 0.1–0.3 bars). Hydrocarbons, lipid precursors, and simple amino acids are available in the fluid. The lifeless condensate of water-steam mixture (temperature 108–175 °C) contains aromatic hydrocarbons, n-alkanes, ketons, alcohols, and aldehydes. In addition to those, cycloalkanes, alkenes, dietoxyalkanes, naphtenes, fatty acids, ethyl ethers of fatty acids, and monoglycerides have been detected in hot solutions inhabited by thermophiles and hyperthermophiles (temperature 70–98 °C). According to Mukhin et al. (1979), glycine of probably abiotic origination was detected in lifeless condensate.

Catalytic Oxidation and Reduction of Polycyclic Aromatic Hydrocarbons (PAHs) Present as Mixtures in Hydrothermal Media

The reactivity of fluorene, anthracene, and fluoranthene under oxidation and reduction conditions were investigated in this study. This project looks at catalytic and green approaches of converting PAHs to less toxic and/or less stable derivatives that are amenable to further degradation. Hydrothermal reactions have been performed at 300°C with pure H2O and Nafion-SiO2 catalyst for oxidation, and pure H2O, HCOOH, Pd-C, and Nafion-SiO2 catalysts for reductive hydrogenation. Time series has been performed for both the oxidation and hydrogenation systems. The products of the reaction were identified and quantified by the use of Gas Chromatography-Mass Spectrometry and the NIST Library. The reaction products include oxidized products of anthracene and fluorene; and hydrogenated derivatives of anthracene and fluoranthene. Fluoranthene did not undergo oxidation, and fluorene did not undergo hydrogenation under the conditions of this research.

Inversion concept of the origin of life.

The essence of the inversion concept of the origin of life can be narrowed down to the following theses: 1) thermodynamic inversion is the key transformation of prebiotic microsystems leading to their transition into primary forms of life; 2) this transformation might occur only in the microsystems oscillating around the bifurcation point under far-from-equilibrium conditions. The transformation consists in the inversion of the balance "free energy contribution / entropy contribution", from negative to positive values. At the inversion moment the microsystem radically reorganizes in accordance with the new negentropy (i.e. biological) way of organization. According to this approach, the origin-of-life process on the early Earth took place in the fluctuating hydrothermal medium. The process occurred in two successive stages: a) spontaneous self-assembly of initial three-dimensional prebiotic microsystems composed mainly of hydrocarbons, lipids and simple amino acids, or their precursors, within the temperature interval of 100-300°C (prebiotic stage); b) non-spontaneous synthesis of sugars, ATP and nucleic acids started at the inversion moment under the temperature 70-100°C (biotic stage). Macro- and microfluctuations of thermodynamic and physico-chemical parameters able to sustain this way of chemical conversion have been detected in several contemporary hydrothermal systems. A minimal self-sufficient unit of life on the early Earth was a community of simplest microorganisms (not a separate microorganism).

Non-catalytic and catalytic hydrothermal liquefaction of biomass

Both the non-catalytic and catalytic hydrothermal liquefaction of biomass have been the objective of extensive research in recent years. An impressive amount of scientific studies related to non-catalytic and catalytic hydrothermal liquefaction of biomass has been reported in the literature. The experimental conditions such as temperature, residence time, pressure, the types of biomass, and the types of catalysts have an important effect on the product distributions. The details about the experimental conditions as well as the compositions of bio-oils are important for a better understanding of the biomass liquefaction pathways in hydrothermal media. This review is intended to summarize and discuss a survey of relevant research.

Catalytic hydrothermal hydrodenitrogenation of pyridine

We herein report on the hydrothermal catalytic conversion of pyridine to hydrocarbons. The catalytic activity of several supported noble metal (5wt%) catalysts (Pt/C, Pd/C, Ru/C and Rh/C, sulfided Pt/C, and Pt/γ-Al2O3), a traditional hydrodenitrogenation (HDN) catalyst (sulfided CoMo/γ-Al2O3), a transition metal carbide (Mo2C) and sulfide (MoS2), and a noble metal oxide (PtO2) toward the HDN of pyridine in a hydrothermal reaction medium between 250 and 400°C was determined. The Pt/γ-Al2O3 catalyst proved to be the most active for hydrothermal HDN of pyridine, and we report the effects of batch holding time, reaction temperature, catalyst loading, initial hydrogen pressure, and water density on the Pt/γ-Al2O3-catalyzed HDN of pyridine in supercritical water. The latter two process variables had the greatest influence on the product yields and distribution. Conditions were identified that lead to essentially 100% conversion of pyridine to N-free hydrocarbons. The catalyst shows some modest loss in activity upon being reused. An HDN reaction network for pyridine under hydrothermal conditions was proposed. The main HDN products are n-butane and n-pentane. Nitrogen was removed as ammonia.

Study of the stability of Pt/SiO2–Al2O3 catalysts in aqueous medium: Application for sorbitol transformation

Sorbitol transformation in aqueous medium can be used to produce alkanes from lignocellulosic sugars over a bifunctional catalyst, usually Pt/SiO2–Al2O3. However, the catalyst is modified by the hydrothermal medium. In this study, the separated effects of water and medium generated during sorbitol transformation reaction on a Pt/SiO2–Al2O3 catalyst have been investigated. Reaction products, in particular acidic ones, also alter catalyst properties. Catalyst pre-treatment by steaming appears to be an interesting way to obtain a catalyst which is less sensitive to liquid water in terms of platinum dispersion and textural properties. Steaming pre-treatment has no impact on selectivity. These investigations provide an incentive for the development of new sorbitol transformation catalysts more suitable under hydrothermal conditions.

Enhancement of Biochar Gasification in Alkali Hydrothermal Medium by Passivation of Inorganic Components Using Ca(OH)2

The challenges with thermal gasification of biomass to produce syngas include high transportation and drying costs of biomass and the need for high-temperature (700–1000 °C) gasifiers and conditioning of the produced gases. Some of these challenges can be addressed by first converting biomass into high-energy-density biochar before transportation and then hydrothermal gasification of biochar at the site of the Fischer–Tropsch plant for liquid fuel synthesis. In this work, a high-energy-density (>27 MJ/kg) biochar is first produced via hydrothermal carbonization of switchgrass at 300 °C, and then the biochar is gasified in hydrothermal medium at 400–650 °C. The carbon gasification efficiency in hydrothermal medium is much better than that in the thermal medium. For example, at 550 °C, only 5.9% carbon gasification was achieved in the thermal medium, as compared to 23.8% in hydrothermal medium. The addition of 25 wt % K2CO3 catalyst enhances the hydrothermal gasification to 43.8%. The gasification can be fu...

Synthesis of precious and non-ferrous metals in hydrothermal medium

This paper contains an overview of our results on platinum group metals disperse particles synthesis in water solutions in hydrothermal conditions. Metal phases (metal sols, powders and coatings) are formed in halogen and halogenammin complexes solutions in autoclave conditions at 110–230°C. The received materials are promising for the practical applications (catalysts, sensor controls, fuel elements, photonics and etc.).

Halogen Exchange in Near-Critical Water

Bromoaromatics are ubiquitous in chemistry, and their manufacture is often wasteful. Halogen exchange under hydrothermal conditions constitutes a viable alternative for their synthesis in some cases. The prepara-tion of 1,2-dibromobenzene and 1-bromo-2-chlorobenzene from 1,2-dichlorobenzene, by treatment with hy-drobromic acid in hydrothermal media at temperatures ranging from 240?C to 320?C was investigated as a viable alternative to de novo synthesis. The effects of temperature, exchange duration and the presence of Fe3+ salts on product yields are discussed. Yields for both targeted haloarenes of up to 37% and 48%, respec-tively, were achieved, with very limited formation of 1,3- and 1,4-dihalobenzene isomers. A mechanism for halogen exchange was proposed.

Insight into the crystal lattice formation of brookite in aqueous ammonia media: the electrolyte effect

A feasible approach to synthesize pure brookite was achieved in an aqueous ammonia system via a hydrothermal process. By hydrothermal treatment of the titanate that directly hydrolyzed from tetrabutyl titanate (TBOT), a phase transition from titanate to TiO2 was observed with XRD. Anatase TiO2 was produced with an unobstructed closure of titanate layers. The phase transition process can be controlled by adding an electrolyte such as NaCl into the hydrothermal media. Na+ ions locally stop the direct closure of titanate layers at their adjacent position, which induce the formation of a brookite-like structure. The optimal hydrothermal reaction parameters for the crystal lattice formation of brookite in aqueous ammonia media were found to be 180 °C, 0.5 M NaCl and ≥72 h. The phase transition process of titanate precursor to TiO2 depends heavily on the electrolyte. Metal cations play a crucial role in conducting the transition procedure from layered titanate into brookite or anatase. Na+ is preferred to conduct the phase transition from titanate to brookite rather than K+ and Li+. Although anions do not determine the phase transition rule during the hydrothermal process, they are influential in the phase transition process, as they can promote the phase transition by interacting with the TiO6 octahedra.

Nanocones rolling in hydro-thermal medium and flows in conical domains

In many applications of tubular nanostructures it is necessary to describe fluid flows through these systems, which have many specific features. Moreover, these flows play an important role in the processes of nanotubes formation. Our report is devoted to the description of these processes in conical nanostructures. Hydro-thermal method of nanotube formation is very effective. But it is often leads to formation of nanostructures of different morphology, particularly, nanocones. Process of nanocone formation due to rolling from plane structure in hydro-thermal medium is considered. The system comes to equilibrium if there is lattices correspondence between neighbor layers. Due to this reason the conical angle depends on the lattice parameters. This dependence is analyzed. Movement of the conical surface during the formation process leads to the appearance of flow in conical domain which has an influence on the formation process.

Novel method to control the size of well-crystalline ceria particles by hydrothermal method

Well-crystalline ceria particles were synthesized by heating peptized ceria sol as precursor under hydrothermal conditions. The morphology and the crystallites size of hydrothermal ceria particles were controlled by varying the dielectric property of solvent used in preparation of the ceria precursor. The synthesized particles exhibit cubic fluorite structure with size ranged from 20 to 400 nm without the formation of hard aggregates. In this work, the relationships between dielectric property of the solvent and particle size were investigated in terms of the supersaturation of solute. In addition, the influences of precipitation participating anions (OH −) and acidic hydrothermal medium on crystallites size of ceria particles were studied.

Catalytic hydrothermal deoxygenation of palmitic acid

We herein report a new approach to convert fatty acids to hydrocarbons in near- or supercritical water. We tested several different metal salts, bases, and high-surface-area supported metal catalysts for activity toward deoxygenation of palmitic acid in a hydrothermal reaction medium. Two heterogeneous catalysts, 5% platinum on activated carbon (Pt/C) and 5% palladium on activated carbon (Pd/C), proved to be very effective for hydrothermal deoxygenation of palmitic acid. The reactions were done in water with no added H2. The catalysts can be reused without significant activity loss, and the selectivity was more than 90% toward pentadecane, the deoxygenation product. We examined the effect of the catalyst loading, reactant loading, batch holding time, and reaction temperature on the Pt/C-catalyzed deoxygenation rate. The results show that the reaction is first-order in palmitic acid, and the rate constants displayed Arrhenius behavior with an activation energy of 79 kJ mol−1.

Hydrodynamics of nanorolling

An initial stage of nanoroll formation in a hydrothermal medium is investigated - the stage of rolling of a double layer under the action of internal stresses. A critical role in the rolling process is attributed to the viscous liquid surrounding the roll. A method is proposed to calculate the liquid flow around the forming nanoroll. A calculation of the rolling process is also performed. Finally, disturbance of the liquid by the rolling nanotube is studied.

Influence of microwave and ultrasonic treatment on the formation of CoFe2O4 under hydrothermal conditions

The formation of CoFe2O4 nanocrystals under hydrothermal conditions at a temperature of 130°C is investigated. The average size of CoFe2O4 particles varies from 6 to 11 nm depending on the synthesis time. The hydrothermal medium is heated by two different methods, i.e., the microwave (with a synthesis time from 1 min to 2 h) and conventional (with a synthesis time from 30 min to 45 h) methods. It is demonstrated that the use of microwave heating considerably accelerates the formation of CoFe2O4 particles. Preliminary ultrasonic treatment for 3 min increases the phase formation rate in the case of microwave heating and hardly affects the occurrence of the process upon conventional heating. It is revealed that the exposure of the initial mixture (preliminarily treated with ultrasound) to room temperature for 2 h or longer almost completely reduces the efficiency of the action of ultrasonic treatment on the phase formation process under hydrothermal conditions.