CO2-expanded Liquid Research Articles

Computational and experimental studies on the micellar morphology and emission mechanisms of AIE and H-bonding fluorescent composites.

In this work, we use density functional theory (DFT) calculated competitive hydrogen bonds and dissipative particle dynamics (DPD) simulated micellar structural information to uncover the CO2-expanded liquid (CXL)-aided self-assembled structure and emission mechanisms of the self-assembled fluorescent composites (SAFCs). Herein, the SAFCs are formed through the self assembly between diblock copolymer polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) blend and the dye molecule 4-(9-(2-(4-hydroxyphenyl)ethynyl)-7,10-diphenylfluoranthen-8-yl)phenol (4) in CO2-expanded toluene at 313.2 K and varied pressures. Firstly, from DPD simulation, we have demonstrated that the addition of CO2 to toluene favors both the expansion of the solvophobic P4VP phase and contraction of solvophilic PS chains, which facilitates the continuous morphological transitions of SAFCs from spherical micelles (3.0 MPa) through wormlike plus spherical micelles (4.0-4.8 MPa) to large vesicles (6.0-6.5 MPa) with pressure rise. Secondly, the DFT calculated bonding energies and IR spectra of the competitive hydrogen bonds help us to clarify the major type of hydrogen bonds determining the fluorescence (FL) performance of the SAFCs. Furthermore, we have revealed the SAFC emission mechanism via the pressure-tunable changes in the aggregation degrees and amount of hydrogen bonds involving 4 and P4VP chains. This work provides a good understanding for the morphology-property control of the self-assembled polymer composites in both microscopic and mesoscopic scales.

Native lignin extraction from soft- and hardwood by green and benign sub/supercritical fluid extraction methodologies.

Lignin constitutes an impressive resource of high-value low molecular weight compounds. However, robust methods for isolation of the extractable fraction from lignocellulose are yet to be established. In this study, supercritical fluid extraction (SFE) and CO2-expanded liquid extraction (CXLE) were employed to extract lignin from softwood and hardwood chips. Ethanol, acetone, and ethyl lactate were investigated as green organic co-solvents in the extractions. Additionally, the effects of temperature, CO2 percentage and the water content of the co-solvent were investigated using a design of experiment approach employing full factorial designs. Ethyl lactate and acetone provided the highest gravimetric yields. The water content in the extraction mixture had the main impact on the amount of extractable lignin monomers (LMs) and lignin oligomers (LOs) while the type of organic solvent was of minor importance. The most effective extraction was achieved by using a combination of liquid CO2/acetone/water (10/72/18, v/v/v) at 60 °C, 350 bar, 30 min and 2 mL min-1 flow rate. The optimized method provided detection of 13 LMs and 6 lignin dimers (LDs) from the hardwood chips. The results demonstrate the potential of supercritical fluids and green solvents in the field of mild and bening lignin extraction from wood.

Toward Sustainable Photo‐/Electrocatalytic Carboxylation of Organic Substrates with CO2

AbstractHistorically, carbon dioxide found many applications in organic chemistry from reaction medium e. g., super critical carbon dioxide (scCO2) or CO2‐expanded liquid (CXL) system; extraction (natural products), separation (supercritical fluid chromatography); chemo‐, regio‐, and stereoselective transformation via the formation of transient intermediates i. e., carbonate, carbamate etc. Recently, researchers have exploited CO2 as an inexpensive, renewable and non‐toxic C1 feedstock for carboxylation and carbonylation reactions. However, owing to its inherent kinetic and thermodynamic stability, most of the transformations require high temperatures, high pressure, and stoichiometric amounts of organometallic reductants that leads to accidental and environmental hazards. Inspired by the natural processes, photo‐ and electrocatalytic conversion of CO2 into value‐added products has emerged as a benign and practical approach in organic synthesis. Here in this review, we will discuss some recent photo‐ and electrocatalytic methods and their comparison toward sustainable development.

Reaction kinetics and phase behavior in the chemoselective hydrogenation of 3-nitrostyrene over Co-N-C single-atom catalyst in compressed CO2

Single-atom catalysts (SACs) have demonstrated excellent performances in chemoselective hydrogenation reactions. However, the employment of precious metals and/or organic solvents compromises their sustainability. Herein, we for the first time report the chemoselective hydrogenation of 3-nitrostyrene over noble-metal-free Co-N-C SAC in green solvent — compressed CO2. An interesting inverted V-curve relation is observed between the catalytic activity and CO2 pressure, where the conversion of 3-nitrostyrene reaches the maximum of 100% at 5.0 MPa CO2 (total pressure of 8.1 MPa). Meanwhile, the selectivities to 3-vinylaniline at all pressures remain high (> 99%). Phase behavior studies reveal that, in sharp contrast with the single phase which is formed at total pressure above 10.8 MPa, bi-phase composed of CO2/H2 gas-rich phase and CO2-expanded substrate liquid phase forms at total pressure of 8.1 MPa, which dramatically changes the reaction kinetics of the catalytic system. The reaction order with respect to H2 pressure decreases from ~0.5 to zero at total pressure of 8.1 MPa, suggesting the dissolved CO2 in 3-nitrostyrene greatly promotes the dissolution of H2 in the substrate, which is responsible for the high catalytic activity at the peak of the inverted V-curve.

Prediction of solvatochromic parameters of electronic transition energy for characterizing dipolarity/polarizability and hydrogen bonding donor interactions in binary solvent systems of liquid nonpolar-polar mixtures, CO2-expanded liquids and supercritical carbon dioxide with cosolvent

Solvatochromic parameter of electronic transition energy (ET) provides information on dipolarity/polarizability and hydrogen bonding donor interactions in the solvation shell. In this work, a predictive framework is proposed for estimating ET values of phenol blue indicator in three mixed-solvent systems as (i) liquid nonpolar-polar mixtures, (ii) CO2-expanded liquid solvent and (iii) supercritical carbon dioxide (scCO2)-polar cosolvent mixtures. The equations of the ET framework for binary mixtures of nonpolar solvent with polar hydrogen bond acceptor (HBA) solvent can be directly adopted from the previous framework for Kamlet-Taft dipolarity/polarizability (KT-π*) [Ind. Eng. Chem. Res. 2020, 59, 12319–12330] because of the linearity of the homomorphism line between ET and KT-π* for pure nonpolar solvents and pure polar HBA solvents. However, due to specific hydrogen bonding interactions of the phenol blue with polar hydrogen bond donor (HBD) solvents, the ET framework for binary mixtures of nonpolar solvent with polar HBD solvent was the modification by the addition of HBD contribution factor. The HBD contribution factor can be simply estimated by a deviation of an actual ET value of pure HBD solvents from the homomorphism line. To validate the framework, the ET values of seventeen liquid nonpolar-polar mixtures, (ii) three CO2-expanded solvent mixtures and (iii) five scCO2-polar cosolvent mixtures collected from the literature were used. The framework was found to give a reliable ET value with an overall deviation of 0.26% and was also applicable to ET values of Reichardt, Nile red and HxQMBu2 indicators with an overall deviation of 1.73%, 0.36% and 0.40%, respectively. Only four properties of pure components are required for predictions as: (i) gas-phase dipole moment of polar component, (ii) CO2 density, (iii) ET and KT-π* values and (iv) homomorphism relationship between ET and KT-π* values.

One-step sustainable preparation of superparamagnetic iron oxide nanoparticles supported on mesoporous SiO2

Superparamagnetic iron oxide nanoparticles (SPIONs) supported on high surface area mesoporous SiO2 are advanced materials of great interest in catalysis, adsorption and biomedicine. Here we present a new process to prepare SPION/SiO2 materials by the impregnation and insitu decomposition of Fe(NO3)3.9H2O on mesoporous SiO2 supports in a 25–50 % mol ethanol + CO2 mixture at 523 K and 25.0 MPa. γ-Fe2O3 nanoparticles (NPs) of average size between 6−9 nm were homogeneously distributed on the supports. NPs deposited into the SBA-15 mesopores but mostly on the external surface of MCM-41. Materials prepared with the highest ethanol content were very homogeneous. Magnetic measurements confirmed the superparamagnetic nature of the materials at room temperature. The process proposed is sustainable and scalable, avoids tedious preparations and the additional high temperature treatment under a controlled atmosphere, as the metal decomposition is performed insitu in the CO2-expanded liquid mixture.

A sustainable approach for the extraction of cholesterol-lowering compounds from an olive by-product based on CO2-expanded ethyl acetate

Olive (Olea europaea) processing results in large amounts of by-products that contain valuable molecules such as phenolic compounds and phytosterols. These molecules have demonstrated to reduce blood cholesterol levels. This work proposes the development of a method to obtain simultaneously phenolic compounds and phytosterols from the olive stone using CO2-expanded liquid extraction. Hansen solubility parameters were employed for the theoretical prediction of the most suitable bio-based solvent to extract target compounds. The Box–Behnken experimental design was employed to select the optimal conditions of pressure (8–25 MPa), the molar fraction of CO2 in ethyl acetate (0.15–0.55), and the temperature (40–80 °C). Extracts showing the highest and the lowest reductions of micellar cholesterol solubility capacity were analyzed by gas chromatography coupled to mass spectrometry to find out the compounds responsible for this activity. Different phenolic compounds, free fatty acids, and phytosterols were identified in the extracts. β-Sitosterol and, especially, tyrosol and hydroxytyrosol were the compounds that primarily contributed to the reduction of micellar cholesterol solubility capacity.

Synergy of in-situ formation of carbonic acid and supercritical CO2-expanded liquids: Application to extraction of andrographolide from Andrographis paniculata

The environmental impact of excessive solvent usage in the pharmaceutical industry has generated research interests in the area of green and sustainable extraction processes. In this study, solvent minimization was done by exploiting the synergistic effect of pH lowering (via in-situ H2CO3 formation) and solvent’s volume expansion (via CO2-expanded solvent) in the extraction of andrographolide from Andrographis paniculata. Conventional solid-liquid extraction (CSLE) and CO2-expanded liquid extraction (CXLE) were conducted using different solvents at a pressure range of 0.1–10 MPa and 40 °C in a batch-type extraction vessel to verify both the independent and combined effect of pH and the solvent’s volume expansion coefficient (V/V0) in the extraction recovery. Also, fresh and spent biomass were analyzed using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) in order to assess the physical impact of the extraction scheme. The highest andrographolide recovery of 65% was obtained using CXLE with ethanol and water at pH = 3.02 and V/V0 = 4.8, owing to the synergistic effects of the two variables. Furthermore, an increase in extraction recovery with decreasing pH and increasing V/V0 was observed. Moreover, a significant morphological difference between the fresh and spent samples was observed from the results of characterizations, indicating a disruption in the cell wall associated to the expansion of the solvent as it penetrated the plant matrix. The proposed novel extraction strategy allowed a high extraction recovery of andrographolide while complying with sustainable and green practices.

From supercritical carbon dioxide to gas expanded liquids in extraction and chromatography of lipids

Analytical-scale extraction and chromatography of oils, fats and other liposoluble compounds can be achieved by using supercritical carbon dioxide as a solvent. Since the 90's when supercritical fluid chromatography (SFC) was a hot topic, this technology has developed into a robust, modern analytical technique that uses any proportions of compressed CO2 mixed with an organic solvent. Supercritical fluid extraction (SFE) on the other hand is only recently starting to reform in a similar way, towards the use of more robust extraction system and enabling mixing of compressed CO2 with larger proportions of organic solvents. In this Feature article, the development of SFC and SFE into what options we have today is described, including the latest trend of using CO2-expanded liquid (CXL) as extraction solvent for lipids.

Preparation of liposomes using a modified supercritical process via depressurization of liquid phase

Liposomes were prepared utilizing a modified supercritical process. In this method, phospholipid suspension in water was equilibrated with high pressure CO2 and the CO2-expanded liquid phase was depressurized via two protocols. In protocol (I), depressurization rate was kept constant while in protocol (II), both the depressurization rate and the pressure inside the vessel were constant. Pressure, depressurization rate and temperature were the processing parameters evaluated in terms of their effect on the properties of the liposomes obtained. Particle size of liposomes prepared by the modified supercritical method was as small as 265±4nm and 214±3nm for protocols (I) and (II), respectively. Elevated pressure contributed to a smaller size while higher depressurization rates resulted in enhanced uniformity. Amount of unhydrated CO2 dissolved in the phospholipid bilayer seems to be important for a small particle size while release rate from between the bilayers may affect size distribution. Liposomes prepared by the modified supercritical method were stable for up to 8 and 6 weeks for protocols (I) and (II), respectively, with a high zeta potential. Protocol (II) yielded smaller and more uniform particles while protocol (I) gave higher storage stability. The modified supercritical method is more effective in liposome preparation than conventional thin film hydration method for a reduced size and enhanced stability.

Deposition of zwitterionic polymer brushes in a dense gas medium

Poly(sulfobetaine methacrylate) (PSBMA) films known for their resistance to nonspecific protein adsorption, cell/bacterial adhesion and biofilm formation were produced by surface initiated polymerization on a silicon surface via a batch reaction system in CO2 expanded liquid (CO2-EL) medium. Atom transfer radical polymerization (ATRP) was carried out using 2,2′-bipyridyl as ligand and CuBr as a catalyst in water/methanol mixture with trichloro[4-(chloromethyl)phenyl]silane (CMPS) used as the initiating species. The films were grown in the CO2-EL environment at a range of conditions and thickness up to 10nm. In contrast to films produced by conventional solvent systems at atmospheric pressure, the polymer films grown by the CO2-EL process showed uniform thickness and pin-hole free topography. Most importantly, the CO2-EL processed PSBMA films showed no trace of copper (used as the catalyst), thus obviating the need for post-deposition processing and avoiding adverse effects of the metal leaching during service. Finally, PSBMA films from both the conventional and CO2-EL processes were exposed to Human mesenchymal stem cells (hMSCs) and the results showed that, while in both the cases the cell proliferation rate was inhibited by the charged polymeric brush surface, the CO2-EL-processed brush exhibited inhibition to a larger extent due to the reduced occurrence of pinholes. The process can be easily exploited effectively when carrying out surface initiated polymerization on non-flat topographies, such as in trenches and nanostructured features with high aspect ratios.

Development of a Greener Hydroformylation Process Guided by Quantitative Sustainability Assessments

Environmental impacts and economics associated with a potentially greener, Rh-catalyzed, 1-octene hydroformylation process in CO2-expanded liquid (CXL) medium are quantitatively assessed against a conventional Co-catalyzed process. The economic analysis shows a more than 30% lower capital investment for the CXL process compared to the conventional Co-catalyzed process of similar capacity. This is due to the higher reaction and catalyst recovery efficiencies at milder reaction temperature and pressures (compared to the conventional process) used in the CXL process. The total production cost (TPC) associated with the CXL process is lower than the conventional process when the Rh makeup rate is lower than 0.94% (of the total amount of Rh in the reactor) per hour at the current Rh price ($20,800/lb). This translates to an economic viability criterion of ($makeup Rh/$TPC) being 0.042 or less. Life cycle analysis (LCA) was performed using GaBi software and an EIO-LCA method based on plant scale simulation of both the conventional and continuous CXL processes to produce 150 kton/year of nonanal. Gate-to-gate LCA projections show that the CXL process is environmentally friendlier than the conventional process in most impact categories such as ecotoxicity, greenhouse gas emissions, and smog formation. Predicted emissions for the conventional process are of the same order of magnitude as those reported from an actual plant of similar capacity. Cradle-to-gate environmental impacts are 1 to 2 orders of magnitude greater than the gate-to-gate impacts with energy usage for the production of raw materials being the major source of adverse environmental impacts. The EIO-LCA results agree with the GaBi analysis. Our results show that the environmental performance of the CXL process can be further improved with lower solvent usage, thus also providing valuable guidance for process optimization.

Kinetics and polarity effects in the synthesis of the ionic liquid, 1-hexyl-3-methyl-imidazolium bromide, using compressed CO2

Compressed carbon dioxide, as a solvent medium, offers unique benefits for the synthesis of ionic liquids (ILs) especially for the ability to combine reaction and separation. The second-order reaction rate constants were determined for the synthesis of 1-hexyl-3-methylimidazolium bromide ([HMIm][Br]) at 313.15K and 333.15K and 30–150bar from the reactants, 1-methylimidazole and 1-bromohexane. Two different scenarios were encountered based upon the pressure: a one-phase supercritical mixture of the reactants becoming a vapor-liquid IL/CO2 system at complete conversion; or a two-phase CO2-expanded liquid (CXL) that yielded a three-phase vapor-liquid-liquid equilibrium (VLLE) at intermediate conversions. Despite multiphase phenomena, the vast majority of the reaction occurs in the reactant-rich liquid phase. The kinetic rate constants were comparable with traditional organic solvents. The reaction rates were higher in the CXL mode than in the initially supercritical mixtures. The changes in the kinetic rate constant with pressure (CO2 composition) could be explained and quantified using Kamlet–Taft (KT) polarity parameters that were measured in the mixtures using solvatochromic probes.

Perfluoromethacrylate-styrene statistical copolymers synthesized in CO2-expanded monomers

Statisticalcopolymersofperfluoroalkylethylmeth- acrylate(Zonyl-TM)andstyrene(S)weresynthesizedinCO2- expanded monomer medium at a low initial pressure of 25 MPa. Different Zonyl-TM/S feed ratios were used during copolymerizations, and it was determined that the increase in the Zonyl-TM content and decrease of the CO2 amount in the comonomer feed resulted in a decrease of the molecular weights of copolymers due to earlier precipitation of copoly- mers giving shorter chains. The cloudy CO2-expanded liquid monomer phase was found to be the main loci of copolymer- ization. In addition, the increase in the Zonyl-TM feed ratio resulted in an increase in the critical degree of the polymeri- zation time (Jcrit) as the time when the copolymer chains start to precipitate. The higher the Zonyl-TM content used in the feed, the higher the Jcrit time and the lower the weight-average molecular weight (Mw )o f the copolymer obtained. Thermalanalysisresultsofthecopolymerindicated that the copolymers are stable up to 387-403 °C.

Near-infrared spectroscopic measurements of volume expansion and composition of CO2-expanded ethyl acetate, acetone, tetrahydrofuran, acetonitrile, methanol-OD, and dimethyl sulfoxide

CO2-expanded liquid (CXL) is a mixture of organic solvent with high-pressure CO2 whose volume is increased by CO2 dissolved in it. CXLs have attracted attention as tunable solvents, because the solvent properties can be widely controlled by the pressure. The volume expansion and the solubility of CO2 were measured by near-infrared spectroscopy for 6 CXLs at various pressures up to 55bar and 40°C. The molarity of organic solvent was determined from the absorbance of the 3ν and 2ν+δ bands, and that of CO2 was obtained from the area of the 3ν3 band, whose peak shifted to higher frequency with increasing pressure due to a decrease in the molecular interaction around CO2. The expansion coefficient was shown to be an increasing function of the pressure with larger slope at higher pressure, and the mole fraction of CO2 in the liquid phase was an almost linearly increasing function of the pressure. The results were in quantitative agreement with the literature data measured by conventional sampling method, indicating the validity of the spectroscopic method.

Formation of nanoscale networks: selectively swelling amphiphilic block copolymers with CO2-expanded liquids

Polymeric films with nanoscale networks were prepared by selectively swelling an amphiphilic diblock copolymer, polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP), with the CO(2)-expanded liquid (CXL), CO(2)-methanol. The phase behavior of the CO(2)-methanol system was investigated by both theoretical calculation and experiments, revealing that methanol can be expanded by CO(2), forming homogeneous CXL under the experimental conditions. When treated with the CO(2)-methanol system, the spin cast compact PS-b-P4VP film was transformed into a network with interconnected pores, in a pressure range of 12-20 MPa and a temperature range of 45-60 °C. The formation mechanism of the network, involving plasticization of PS and selective swelling of P4VP, was proposed. Because the diblock copolymer diffusion process is controlled by the activated hopping of individual block copolymer chains with the thermodynamic barrier for moving PVP segments from one to another, the formation of the network structures is achieved in a short time scale and shows "thermodynamically restricted" character. Furthermore, the resulting polymer networks were employed as templates, for the preparation of polypyrrole networks, by an electrochemical polymerization process. The prepared porous polypyrrole film was used to fabricate a chemoresistor-type gas sensor which showed high sensitivity towards ammonia.

Prediction of multicomponent phase behavior of CO2-expanded liquids using CEoS/GE models and comparison with experimental data

Models utilizing cubic equation of state and excess Gibbs free energy-based mixing rules (CEoS/GE) were used for predicting the multicomponent VLE phase behavior involving CO2-expanded liquids. Four such models were selected out of 36 models (four CEoS in conjunction with nine mixing rules each) and evaluated with regard to their predictive capability using 14 systems, including 12 sub-systems (eight ternary systems, three quaternary systems and one quinary system) of 1-octene hydroformylation in CO2-expanded acetone (with the components H2, CO, CO2, 1-octene, n-nonanal, and acetone), a CO2-expanded toluene ternary system and a CO2-expanded acetonitrile ternary system. Model discrimination was based on their relative abilities to predict experimental VLE data generated within this work (ternary, quaternary or quinary systems with various combinations of H2, CO, CO2, 1-octene or n-nonanal) and from the literature. The results indicate that the CEoS/GE modeling approach is successful in predicting the phase behavior of the 14 investigated CO2-expanded liquid systems. The selected models are expected to be useful in the rational selection of CO2-expanded liquids and operating conditions (p & T) for optimal performance of reaction and/or separation units.

Aromatic hydrogenation of benzyl alcohol and its derivatives using compressed CO2/water as the solvent

A green approach to the aromatic hydrogenation of benzyl alcohol and its derivatives to produce cyclohexanemethanol was demonstrated in this report. In this work, the hydrogenation reactions were carried using neat, CO2-expanded liquid (CXL), water and compressed CO2/water, as the solvents. It was found out that using water as the solvent achieved the highest yield of the hydrogenation product (>96%). On the other hand, using the compressed CO2/water system as the solvent significantly enhanced the reaction rate (only 1/5 of the reaction time needed for total conversion when compared to reactions in water) while still maintained high product yield (>90%). It is believed that CO2 molecules dissolved in water could form carbonic acid simultaneously and the acid was proved to act as a promoter throughout the reaction.

The influence of hydrogen pressure on the heterogeneous hydrogenation of β-myrcene in a CO 2-expanded liquid

This paper presents the second part of work on the effect of hydrogen partial pressure on the hydrogenation of a terpene in a CO 2-expanded liquid. The effect of hydrogen partial pressure on the hydrogenation of β-myrcene possessing three C C bonds catalysed by alumina-supported ruthenium and rhodium was studied. Experiments were performed at various hydrogen pressures in the range from 2.0 up to 4.5 MPa at a fixed total pressure of 12.5 MPa. In all the conditions the reaction proceeded in two phases (liquid + gas), that is, the total pressure was below the critical pressure of the CO 2 + β-myrcene + H 2 system. The liquid phase volume is expanded in relation to the initial volume of β-myrcene in a fashion that is strongly dependent on the hydrogen and carbon dioxide pressures. An increase of H 2 pressure concomitantly diminishes carbon dioxide pressure, which leads to the enhancement of the liquid phase in hydrogen and a terpene. It does not direct to straightforward higher reaction rate, but surprisingly the effect of higher concentrations either hydrogen or β-myrcene is opposite. It is attributed to the fact that the hydrogenation of β-myrcene rate-controlling factor turns out to be the hydrogen to β-myrcene ratio which decreases as the hydrogen pressure increases. These unexpected appealing results present that lower pressures of hydrogen guide to higher hydrogen/β-myrcene ratios in the liquid phase, but on the other hand they also amplify the initial reaction rate constant. The obtained results are opposite to the results achieved for effect of hydrogen pressure on the Pd-catalysed hydrogenation of limonene consisting of two C C double bonds.

Chemical and phase equilibria calculation of α-pinene hydration in CO 2-expanded liquid

Modeling of chemical and phase equilibria of α-pinene hydration in subcritical CO 2 was carried out by calculation. A simplified scheme of the conversion includes 6 reaction routes. Thermochemical and physicochemical parameters of individual compounds ( T cr, P cr, T b, Δ H f ° (298.15 K), Δ S f ° (298.15 K), C p ( T), ω) were preliminary estimated. Phase diagrams of the model reaction mixtures were calculated, coordinates of the critical point were found, and the region of subcritical parameters T and P, where the initial mixture divides into the gas phase and CO 2-expanded liquid, was located. Dependence of the products distribution and yield of CO 2-expanded liquid on the reaction temperature and pressure was studied. The reaction equilibrium as a function of temperature and pressure was determined, and heat effects of all reactions under consideration were calculated. The drift of critical parameters versus reaction mixture composition was examined. It was shown that during the hydration and alcohols accumulation the critical pressure of reaction mixture increases continuously, the critical temperature at first elevates and then begins to decrease, and the phase diagrams starts to degenerate. If amount of alcohols becomes more than 80 mol%, the mixture has no critical point and cannot pass to a supercritical state.