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Extraction of glycyrrhizic acid by aqueous two-phase system formed by PEG and two environmentally friendly organic acid salts - sodium citrate and sodium tartrate

  • Zhi Feng Zhang EMAIL logo , Rui Wang , Fei Ye , Haibin Wang and Wenxia Zhao
Published/Copyright: May 25, 2019
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Green Processing and Synthesis
From the journal Green Processing and Synthesis Volume 8 Issue 1

Abstract

Two aqueous two-phase systems (ATPS’s) formed by using PEG and sodium citrate/sodium tartrate are applied and compared for extraction of glycyrrhizic acid (GA) from its stock solution. Their binodal curves and tie-lines are studied firstly. Influence of usage amount of the salt and the PEG on the partition coefficient and extraction efficiency is investigated. The highest extraction efficiency and partition coefficient achieved is 73% and 6.5, when the sodium citrate and PEG concentration is 15% and 20% respectively. It is also found that the ATPS based on sodium citrate is better than sodium tartrate for GA extraction. The present study indicates that ATPS formed by biodegradable organic acid salts could be feasible and environment-friendly technique for GA and other bioactive compounds.

Keywords: glycyrrhizic acid; licorice; aqueous two-phase system; extraction

1 Introduction

Licorice, the root of Glycyrrhiza glabra, is one of the most important herbs in the traditional Chinese medicine (TCM) and appears in a large number of TCM prescriptions. Glycyrrhizic acid (GA) is one of the predominant bioactive components in licorice. In the past few decades, bio-effects of GA have been extensively studied and several beneficial effects are confirmed. It has been found that GA is anti-virus [1], anti-inflammatory [2,3], anti-allergic [4], anti-cancer [5] etc. In addition, recent studies reveal that GA also has markedly hepatoprotective effects [6,7]. Thus, facile and environment-friendly extraction of GA from licorice is practically needed.

Among various extraction and separation techniques, Soxhlet extraction of GA at ambient pressure is still the most widely used method due to its simplicity. Normally, water is used as the extraction solvent. To improve extraction ratio, selectivity and recovery, other solvents like methanol or ethanol are added [8]. To further enhance extraction, microwave-assisted extraction [9], microwave-assisted micellar extraction [10], ultrasound-assisted extraction [11,12], cloud point extraction [13], and multi-stage countercurrent extraction [14] etc are investigated and reported in literature. Another major extraction technique is supercritical fluid extraction. It has been used for separation because supercritical fluid has high dissolving power and low viscosity. Supercritical CO2 has been applied to extract GA and an extraction recovery of 54% is achieved. Superheated water is also utilized for GA extraction and it is found that the amount of extracted GA by superheated water is higher than Soxhlet method. Nevertheless, the process of supercritical fluid extraction is onerous and high-cost and thus its wide application is limited.

Liquid-liquid extraction based on aqueous two-phase system (ATPS) has quite a few advantages and hence is applied for extraction of active compounds from medical plants as well as bio-macromolecules including protein and DNA/RNA [15, 16, 17, 18, 19]. This extraction technology is facile and low-cost, and the used chemicals are not toxic. ATPS formed by EtOH-K2HPO4-H2O [20], PEG-(NH4)2SO4- H2O and PEG-K2HPO4-H2O [21] and nonionic surfactant with NaCl/Na2SO4/Na3PO4 [22] has been used to extract GA, demonstrating excellent extraction performance. Recently, biodegradable organic salts are explored to form ATPS’s to make this technology more environment-friendly, including citrate, tartrate, formate and succinate etc [23, 24, 25, 26]. There have been a large number of reports concerning ATPS’s formed by those organic salts with PEG and their according phase diagrams. Taking advantage of these clean ATPS’s, this paper utilizes ATPS formed by PEG-sodium citrate and PEG-sodium tartrate to extract GA from its stock solution, to investigate the feasibility of extracting GA by using these two ATPS’s. These two ATPS’s are selected because they are found having quite large heterogeneous region and thus good separation capability [27,28].

2 Materials and methods

2.1 Materials

PEG with molecular weight of 10000 g/mol, sodium citrate dihydrate (ACS, ≥99%), and glycyrrhizic acid (≥98%) are purchased from Sinopharm Chemical Reagent and used without further purification. Deionized water with an electrical conductivity of 5 μS/cm was purified from tap water and used. Licorice (cultivated in Guyuan, Ningxia, China) in slices was purchased from a local TCM store.

2.2 Determination of binodal curves and tie-lines

Binodal curves of the PEG 10000 + sodium citrate + H2O and PEG 10000 + sodium tartrate + H2O were measured by using the cloud point method. Ten water solutions of PEG ranging from 2 wt% to 45 wt%, and a sodium citrate or sodium tartrate solution of 35 wt% were prepared in assay tubes and kept in a water bath maintained at 25 ± 0.1°C (SYC-15B, Nanjing Sangli Electronic Instrument Co). Mass of all assay tubes with solutions was precisely measured on a precision electronic balance (FA1004N, Shanghai Precision Scientific Instrument Co) with an uncertainty of ±0.0002 g. Assay tubes were kept in the bath for 1 h to reach temperature equilibrium. Then salt solution was dipped into each PEG solutions until the PEG solutions became cloudy. Tubes with PEG solutions were all weighed again to determine the mass of added salt solution, so that mass fraction of the salt and the PEG in the solution was calculated. Tie-lines were measured by adding excess salt solution to PEG solutions, vigorously shaken and kept in the water bath for 48 h to reach phase equilibrium. Mass fraction of the salt and the PEG was determined by measuring refractive index and electrical conductivity of the top and the bottom phases. Two correlation functions were obtained by measuring refractive index and electrical conductivity of solutions with known fraction of PEG and sodium citrate/sodium tartrate. The used Abbe refractometer (WYA-2S, Shanghai Precision Scientific Instrument Co.) has a precision of 0.0002 and the measurement was carried out at 25 ± 0.1°C, maintained by circulating water from the water bath. The electrical conductivity meter (DDS-II A, Shanghai Leici) has a measurement error of 2%. It should be noted that all experiments were conducted under the local ambient pressure of 84 ± 1 kPa.

2.3 Extraction of GA

Soxhlet extraction technique was applied for the preliminary extraction of GA from licorice for its convenience and relatively high extraction efficiency. Licorice slices were dried at 60°C for 8 h in an oven, then milled and filtered by a 60 mesh screen to obtain powder sample. An amount of 10 g powder sample was precisely weighed on the electronic balance, wrapped up by a clean filter paper and inserted into a Soxhlet assembly filled with 100 mL deionized water as extraction solvent. Each Soxhlet extraction continued for 24 h, and the extracted solution was stocked for ATPS extraction in the following step.

ATPS extraction was conducted by dripping 2 g of stock solution into an ATPS with known PEG and salt mass fraction in a centrifuge tube. The tube was vigorously shaken, centrifuged at 2000 rotations/min for 30 min and submerged in a water bath of 25°C for at least 24 h to reach phase equilibrium. Finally, the top and the bottom phases were separated by using a syringe and weighed. GA concentration in each phase was determined by diluting solution of each phase and measuring absorbance at 252 nm. Mass fraction of PEG and salt was determined by the aforementioned method. To study the influence of PEG fraction and also salt fraction on the performance of ATPS extraction, one of them was fixed while the other was changed to measure partition coefficient and extraction efficiency.

2.4 Measurement of GA concentration

Concentration of GA in the top and the bottom phases after equilibrium was determined by using a UV spectrometer, since GA absorbs UV light close to 250 nm in ethanol/water solution. The calibration curve was obtained by measuring absorbance of GA solution with known concentration at 252 nm. After reaching phase equilibrium, a small amount of solution from the top and the bottom phases was drawn by a syringe and diluted, and its absorbance was measured to calculate GA mass fraction. The standard uncertainty for GA concentration is experimentally determined as 10-3 wt/wt.

2.5 Extraction parameters

The partition coefficient K is defined as the ratio of GA mass fraction of the top phase (PEG-rich) over the bottom phase (salt-rich):

(1)K=w(salt)TPw(salt)BP

Where w(salt)TP and w(salt)BP is the mass fraction of GA in the top and the bottom phase, respectively.

The extraction efficiency (EE) is defined as the mass of GA in the PEG-rich phase over the total mass in both phases:

(2)EE=m(GA)TPm(GA)TP+m(GA)BP×100%

Where m(GA)TP and m(GA)BP is the mass of GA in the top phase and the bottom phase, respectively.

3 Results and discussion

3.1 Phase diagram

Binodal curves and tie-lines of PEG 10000 + sodium citrate + H2O and PEG 10000 + sodium tartrate + H2O are shown in Figures 1 and 2, and the according data of tie-lines as well as tie-line length (TLL) and slope of tie-line (STL) are listed in Tables 1 and 2, respectively. For comparison, binodal curves of PEG 8000 + sodium citrate + H2O reported in Ref and PEG 4000 + sodium tartrate + H2O reported in Ref are plotted in two figures for comparison [25,29]. For both systems, PEG of higher molecular weight produces larger heterogeneous region. This is already confirmed by many previous studies [27,28,30]. It is evident that ATPS formed by sodium tartrate has larger STL than sodium citrate. To further check validity of the data, binodal curves are fitted by using the empirical equation proposed by Merchuk et al. [31]:

Figure 1 Binodal curve (■) and tie-line (▲) of PEG 10000 + sodium citrate + H2O at T = 298.15 K and P = 84 kPa. Dash line is the cloud point data in [15] (PEG 8000 + sodium citrate + H2O, 298.15 K) for comparison.
Figure 1

Binodal curve (■) and tie-line (▲) of PEG 10000 + sodium citrate + H2O at T = 298.15 K and P = 84 kPa. Dash line is the cloud point data in [15] (PEG 8000 + sodium citrate + H2O, 298.15 K) for comparison.

Figure 2 Binodal curve (■) and tie-line (▲) of PEG 10000 + sodium tartrate + H2O at T = 298.15 K and P = 84 kPa. Dash line is the cloud point data in [29] (PEG 4000 + sodium tartrate + H2O, 298.15 K) for comparison.
Figure 2

Binodal curve (■) and tie-line (▲) of PEG 10000 + sodium tartrate + H2O at T = 298.15 K and P = 84 kPa. Dash line is the cloud point data in [29] (PEG 4000 + sodium tartrate + H2O, 298.15 K) for comparison.

Table 1

Mass fraction of feed, top and bottom phases for PEG 10000 + Sodium Citrate + H2O at 298.15 K and 84 kPa, and the calculated TLL and STL.a

FeedTop PhaseBottom Phase
w(Salt)w(PEG)w(Salt)w(PEG)w(Salt)w(PEG)TLLSTL
0.1120.1170.0420.2570.1640.0150.27–1.98
0.1230.1270.0390.2770.1850.0110.30–1.82
0.1280.1520.0290.3200.2110.0120.36–1.69
0.1370.1710.0240.3600.2410.0080.41–1.62
0.1510.2010.0220.3890.2790.0050.46–1.49

  1. a Standard uncertainties u are u(w) = 0.001, u(T) = 0.1 K, u(P) = 1 kPa.

Table 2

Mass fraction of feed, top and bottom phases for PEG 10000 + Sodium tartrate + H2O at 298.15 K and 84 kPa, and the calculated TLL and STL.a

FeedTop PhaseBottom Phase
w(Salt)w(PEG)w(Salt)w(PEG)w(Salt)w(PEG)TLLSTL
0.0850.1360.0290.2600.1350.0150.27–2.31
0.0950.1450.0250.2920.1550.0110.31–2.16
0.1050.1600.0230.3220.1810.0090.35–1.98
0.1160.1770.0180.3630.2130.0080.41–1.82
0.1290.1920.0150.3860.2410.0050.44–1.68

  1. a Standard uncertainties u are u(w) = 0.001, u(T) = 0.1 K, u(P) = 1 kPa.

(3)y=a⋅eb⋅x0.5−c⋅x3

Where x and y are mass fraction of the salt and PEG respectively, and a, b and c are fitting parameters. The fitted values for them and the coefficient of determination R2 are presented in Table 3. The R2 for both systems are very close to unity, indicating high measurement accuracy.

Table 3

Fitted parameters of the Merchuk equation for the two studied ATPS’s and coefficient of determination R2.

SystemabcR2
PEG + Sodium citrate + H2O0.927–6.256570.998
PEG + Sodium tartrate + H2O0.850–6.868530.999

3.2 Effect of PEG concentration

The influence of overall PEG concentration on the partition coefficient K and extraction efficiency EE is illustrated in Figure 3, while the slat concentration is

Figure 3 Dependence of Partition coefficient K and extraction efficiency EE on total mass fraction of PEG in ATPS of (a) PEG 10000 + sodium citrate + H2O and (b) PEG 10000 + sodium tartrate + H2O. The mass fraction of sodium citrate and sodium tartrate are 12%.
Figure 3

Dependence of Partition coefficient K and extraction efficiency EE on total mass fraction of PEG in ATPS of (a) PEG 10000 + sodium citrate + H2O and (b) PEG 10000 + sodium tartrate + H2O. The mass fraction of sodium citrate and sodium tartrate are 12%.

fixed at 12 wt%. Within the studied concentration range, more PEG produces better extraction, that is, higher K and EE. However, the increase of EE becomes small as the fraction of PEG approaches 20%. The reason is that the mass of PEG phase reduces compared to the bottom phase although the fraction of GA in the PEG phase rises. Practically, raising PEG concentration is limited by its solubility in water, especially for PEG with molecular weight higher than 10000. Besides, the PEG phase would become too viscous and phase separation will be too slow if PEG concentration exceeds suitable value. Considering all results, it is evident that the ATPS formed by sodium citrate is better than sodium tartrate for extracting GA.

3.3 Effect of salt concentration

Figure 4 shows influence of salt concentration on the partition coefficient K and extraction efficiency EE, while the fraction of PEG is maintained at 20%. K ranges from 4 to 7 and increases as mass fraction of salt is raised. High salt concentration also leads to high extraction efficiency below 20%. No further increase is observed for sodium citrate more than 14%, while EE decreases slightly for sodium tartrate based ATPS. The highest partition coefficient occurs when the mass fraction of sodium citrate and PEG are 15% and 20%, respectively. In terms of K and EE, PEG-sodium citrate is better than PEG-sodium tartrate for extraction of GA from its stock solution. It has to admit that the highest extraction efficiency achieved by the present study is lower than that by other in previous studies. For example, the highest EE of GA by other ATPSs is well above 90%, such as EtOH-K2HPO4-H2O [20], PEG-(NH4)2SO4-H2O and PEG-K2HPO4-H2O [21]. Nevertheless, the EE of GA for PEG + sodium citrate + H2O can be improved by further optimizing the extraction conditions like salt and PEG concentration, temperature, pH, etc.

Figure 4 Dependence of Partition coefficient K and extraction efficiency EE on total mass fraction of salt in ATPS of (a) PEG 10000 + sodium citrate + H2O and (b) PEG 10000 + sodium tartrate + H2O. The mass fraction of PEG is 20% for the both systems.
Figure 4

Dependence of Partition coefficient K and extraction efficiency EE on total mass fraction of salt in ATPS of (a) PEG 10000 + sodium citrate + H2O and (b) PEG 10000 + sodium tartrate + H2O. The mass fraction of PEG is 20% for the both systems.

4 Conclusions

Extraction of GA from its stock solution by using ATPS formed by PEG 10000 and two organic acid salts, namely, sodium citrate and sodium tartrate, are studied. Binodal curves and tie-lines of two ATPS’s are experimentally measured. The influence of concentration of PEG and salts on two extraction parameters is investigated, including partition coefficient and extraction efficiency. Results indicate that both ATPS’s are effective in extraction of GA from the stock solution, while the ATPS of sodium citrate is slightly better than sodium tartrate. Among all experiments, the highest extraction efficiency is 73% by PEG 10000 + sodium citrate + H2O while the mass fraction of sodium citrate and PEG are 15 wt% and 20 wt%, respectively. The overall extraction efficiency could be dramatically improved by using ultrasound-assisted or microwave-assisted extraction since the present study just used the most basic Soxhlet extraction. Nevertheless, this study shows ATPS formed by bio-degradable organic acid salts could be a feasible and environment-friendly technique for extraction of GA from licorice.

Acknowledgement

Zhi Feng Zhang acknowledges the financial support of this research by funding from Ningxia Normal University under grant No. NXSFZDA1808, and its College of Chemistry and Chemical Engineering under grant No. HGZD18-03. Haibin Wang acknowledges the financial support by Ningxia Education Department under grant No. NGY2016197 and National Natural Science Foundation of China under grant No. 31860518. Wenxia Zhao acknowledges the financial support by National Natural Science Foundation of China under grant No. 21561027.

  1. The authors declare no competing financial interest.

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Received: 2018-11-08
Accepted: 2019-03-27
Published Online: 2019-05-25
Published in Print: 2019-01-28

© 2019 Zhang et al., published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 Public License.

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  46. Green and eco-friendly synthesis of Co3O4 and Ag-Co3O4: Characterization and photo-catalytic activity
  47. Adsorption optimized of the coal-based material and application for cyanide wastewater treatment
  48. Aloe vera leaf extract mediated green synthesis of selenium nanoparticles and assessment of their In vitro antimicrobial activity against spoilage fungi and pathogenic bacteria strains
  49. Waste phenolic resin derived activated carbon by microwave-assisted KOH activation and application to dye wastewater treatment
  50. Direct ethanol production from cellulose by consortium of Trichoderma reesei and Candida molischiana
  51. Agricultural waste biomass-assisted nanostructures: Synthesis and application
  52. Biodiesel production from rubber seed oil using calcium oxide derived from eggshell as catalyst – optimization and modeling studies
  53. Study of fabrication of fully aqueous solution processed SnS quantum dot-sensitized solar cell
  54. Assessment of aqueous extract of Gypsophila aretioides for inhibitory effects on calcium carbonate formation
  55. An environmentally friendly acylation reaction of 2-methylnaphthalene in solvent-free condition in a micro-channel reactor
  56. Aegle marmelos phytochemical stabilized synthesis and characterization of ZnO nanoparticles and their role against agriculture and food pathogen
  57. A reactive coupling process for co-production of solketal and biodiesel
  58. Optimization of the asymmetric synthesis of (S)-1-phenylethanol using Ispir bean as whole-cell biocatalyst
  59. Synthesis of pyrazolopyridine and pyrazoloquinoline derivatives by one-pot, three-component reactions of arylglyoxals, 3-methyl-1-aryl-1H-pyrazol-5-amines and cyclic 1,3-dicarbonyl compounds in the presence of tetrapropylammonium bromide
  60. Preconcentration of morphine in urine sample using a green and solvent-free microextraction method
  61. Extraction of glycyrrhizic acid by aqueous two-phase system formed by PEG and two environmentally friendly organic acid salts - sodium citrate and sodium tartrate
  62. Green synthesis of copper oxide nanoparticles using Juglans regia leaf extract and assessment of their physico-chemical and biological properties
  63. Deep eutectic solvents (DESs) as powerful and recyclable catalysts and solvents for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones
  64. Biosynthesis, characterization and anti-microbial activity of silver nanoparticle based gel hand wash
  65. Efficient and selective microwave-assisted O-methylation of phenolic compounds using tetramethylammonium hydroxide (TMAH)
  66. Anticoagulant, thrombolytic and antibacterial activities of Euphorbia acruensis latex-mediated bioengineered silver nanoparticles
  67. Volcanic ash as reusable catalyst in the green synthesis of 3H-1,5-benzodiazepines
  68. Green synthesis, anionic polymerization of 1,4-bis(methacryloyl)piperazine using Algerian clay as catalyst
  69. Selenium supplementation during fermentation with sugar beet molasses and Saccharomyces cerevisiae to increase bioethanol production
  70. Biosynthetic potential assessment of four food pathogenic bacteria in hydrothermally silver nanoparticles fabrication
  71. Investigating the effectiveness of classical and eco-friendly approaches for synthesis of dialdehydes from organic dihalides
  72. Pyrolysis of palm oil using zeolite catalyst and characterization of the boil-oil
  73. Azadirachta indica leaves extract assisted green synthesis of Ag-TiO2 for degradation of Methylene blue and Rhodamine B dyes in aqueous medium
  74. Synthesis of vitamin E succinate catalyzed by nano-SiO2 immobilized DMAP derivative in mixed solvent system
  75. Extraction of phytosterols from melon (Cucumis melo) seeds by supercritical CO2 as a clean technology
  76. Production of uronic acids by hydrothermolysis of pectin as a model substance for plant biomass waste
  77. Biofabrication of highly pure copper oxide nanoparticles using wheat seed extract and their catalytic activity: A mechanistic approach
  78. Intelligent modeling and optimization of emulsion aggregation method for producing green printing ink
  79. Improved removal of methylene blue on modified hierarchical zeolite Y: Achieved by a “destructive-constructive” method
  80. Two different facile and efficient approaches for the synthesis of various N-arylacetamides via N-acetylation of arylamines and straightforward one-pot reductive acetylation of nitroarenes promoted by recyclable CuFe2O4 nanoparticles in water
  81. Optimization of acid catalyzed esterification and mixed metal oxide catalyzed transesterification for biodiesel production from Moringa oleifera oil
  82. Kinetics and the fluidity of the stearic acid esters with different carbon backbones
  83. Aiming for a standardized protocol for preparing a process green synthesis report and for ranking multiple synthesis plans to a common target product
  84. Microstructure and luminescence of VO2 (B) nanoparticle synthesis by hydrothermal method
  85. Optimization of uranium removal from uranium plant wastewater by response surface methodology (RSM)
  86. Microwave drying of nickel-containing residue: dielectric properties, kinetics, and energy aspects
  87. Simple and convenient two step synthesis of 5-bromo-2,3-dimethoxy-6-methyl-1,4-benzoquinone
  88. Biodiesel production from waste cooking oil
  89. The effect of activation temperature on structure and properties of blue coke-based activated carbon by CO2 activation
  90. Optimization of reaction parameters for the green synthesis of zero valent iron nanoparticles using pine tree needles
  91. Microwave-assisted protocol for squalene isolation and conversion from oil-deodoriser distillates
  92. Denitrification performance of rare earth tailings-based catalysts
  93. Facile synthesis of silver nanoparticles using Averrhoa bilimbi L and Plum extracts and investigation on the synergistic bioactivity using in vitro models
  94. Green production of AgNPs and their phytostimulatory impact
  95. Photocatalytic activity of Ag/Ni bi-metallic nanoparticles on textile dye removal
  96. Topical Issue: Green Process Engineering / Guest Editors: Martine Poux, Patrick Cognet
  97. Modelling and optimisation of oxidative desulphurisation of tyre-derived oil via central composite design approach
  98. CO2 sequestration by carbonation of olivine: a new process for optimal separation of the solids produced
  99. Organic carbonates synthesis improved by pervaporation for CO2 utilisation
  100. Production of starch nanoparticles through solvent-antisolvent precipitation in a spinning disc reactor
  101. A kinetic study of Zn halide/TBAB-catalysed fixation of CO2 with styrene oxide in propylene carbonate
  102. Topical on Green Process Engineering
https://doi.org/10.1515/gps-2019-0024
Keywords for this article
glycyrrhizic acid; licorice; aqueous two-phase system; extraction
Creative Commons
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  2. Studies on the preparation and properties of biodegradable polyester from soybean oil
  3. Flow-mode biodiesel production from palm oil using a pressurized microwave reactor
  4. Reduction of free fatty acids in waste oil for biodiesel production by glycerolysis: investigation and optimization of process parameters
  5. Saccharin: a cheap and mild acidic agent for the synthesis of azo dyes via telescoped dediazotization
  6. Optimization of lipase-catalyzed synthesis of polyethylene glycol stearate in a solvent-free system
  7. Green synthesis of iron oxide nanoparticles using Platanus orientalis leaf extract for antifungal activity
  8. Ultrasound assisted chemical activation of peanut husk for copper removal
  9. Room temperature silanization of Fe3O4 for the preparation of phenyl functionalized magnetic adsorbent for dispersive solid phase extraction for the extraction of phthalates in water
  10. Evaluation of the saponin green extraction from Ziziphus spina-christi leaves using hydrothermal, microwave and Bain-Marie water bath heating methods
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  13. Synergistic effect between CO2 and H2O2 on ethylbenzene oxidation catalyzed by carbon supported heteropolyanion catalysts
  14. Hydrocyanation of 2-arylmethyleneindan-1,3-diones using potassium hexacyanoferrate(II) as a nontoxic cyanating agent
  15. Green synthesis of hydratropic aldehyde from α-methylstyrene catalyzed by Al2O3-supported metal phthalocyanines
  16. Environmentally benign chemical recycling of polycarbonate wastes: comparison of micro- and nano-TiO2 solid support efficiencies
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  18. Production of value-added chemicals from esterification of waste glycerol over MCM-41 supported catalysts
  19. Green synthesis of zerovalent copper nanoparticles for efficient reduction of toxic azo dyes congo red and methyl orange
  20. Optimization of the biological synthesis of silver nanoparticles using Penicillium oxalicum GRS-1 and their antimicrobial effects against common food-borne pathogens
  21. Optimization of submerged fermentation conditions to overproduce bioethanol using two industrial and traditional Saccharomyces cerevisiae strains
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  24. Green cyclic acetals production by glycerol etherification reaction with benzaldehyde using cationic acidic resin
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  30. Green synthesis and structural characterization of novel N1-substituted 3,4-dihydropyrimidin-2(1H)-ones
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  42. A comparative sorption study of Cr3+ and Cr6+ using mango peels: kinetic, equilibrium and thermodynamic
  43. Effects of acid hydrolysis waste liquid recycle on preparation of microcrystalline cellulose
  44. Use of deep eutectic solvents as catalyst: A mini-review
  45. Microwave-assisted synthesis of pyrrolidinone derivatives using 1,1’-butylenebis(3-sulfo-3H-imidazol-1-ium) chloride in ethylene glycol
  46. Green and eco-friendly synthesis of Co3O4 and Ag-Co3O4: Characterization and photo-catalytic activity
  47. Adsorption optimized of the coal-based material and application for cyanide wastewater treatment
  48. Aloe vera leaf extract mediated green synthesis of selenium nanoparticles and assessment of their In vitro antimicrobial activity against spoilage fungi and pathogenic bacteria strains
  49. Waste phenolic resin derived activated carbon by microwave-assisted KOH activation and application to dye wastewater treatment
  50. Direct ethanol production from cellulose by consortium of Trichoderma reesei and Candida molischiana
  51. Agricultural waste biomass-assisted nanostructures: Synthesis and application
  52. Biodiesel production from rubber seed oil using calcium oxide derived from eggshell as catalyst – optimization and modeling studies
  53. Study of fabrication of fully aqueous solution processed SnS quantum dot-sensitized solar cell
  54. Assessment of aqueous extract of Gypsophila aretioides for inhibitory effects on calcium carbonate formation
  55. An environmentally friendly acylation reaction of 2-methylnaphthalene in solvent-free condition in a micro-channel reactor
  56. Aegle marmelos phytochemical stabilized synthesis and characterization of ZnO nanoparticles and their role against agriculture and food pathogen
  57. A reactive coupling process for co-production of solketal and biodiesel
  58. Optimization of the asymmetric synthesis of (S)-1-phenylethanol using Ispir bean as whole-cell biocatalyst
  59. Synthesis of pyrazolopyridine and pyrazoloquinoline derivatives by one-pot, three-component reactions of arylglyoxals, 3-methyl-1-aryl-1H-pyrazol-5-amines and cyclic 1,3-dicarbonyl compounds in the presence of tetrapropylammonium bromide
  60. Preconcentration of morphine in urine sample using a green and solvent-free microextraction method
  61. Extraction of glycyrrhizic acid by aqueous two-phase system formed by PEG and two environmentally friendly organic acid salts - sodium citrate and sodium tartrate
  62. Green synthesis of copper oxide nanoparticles using Juglans regia leaf extract and assessment of their physico-chemical and biological properties
  63. Deep eutectic solvents (DESs) as powerful and recyclable catalysts and solvents for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones
  64. Biosynthesis, characterization and anti-microbial activity of silver nanoparticle based gel hand wash
  65. Efficient and selective microwave-assisted O-methylation of phenolic compounds using tetramethylammonium hydroxide (TMAH)
  66. Anticoagulant, thrombolytic and antibacterial activities of Euphorbia acruensis latex-mediated bioengineered silver nanoparticles
  67. Volcanic ash as reusable catalyst in the green synthesis of 3H-1,5-benzodiazepines
  68. Green synthesis, anionic polymerization of 1,4-bis(methacryloyl)piperazine using Algerian clay as catalyst
  69. Selenium supplementation during fermentation with sugar beet molasses and Saccharomyces cerevisiae to increase bioethanol production
  70. Biosynthetic potential assessment of four food pathogenic bacteria in hydrothermally silver nanoparticles fabrication
  71. Investigating the effectiveness of classical and eco-friendly approaches for synthesis of dialdehydes from organic dihalides
  72. Pyrolysis of palm oil using zeolite catalyst and characterization of the boil-oil
  73. Azadirachta indica leaves extract assisted green synthesis of Ag-TiO2 for degradation of Methylene blue and Rhodamine B dyes in aqueous medium
  74. Synthesis of vitamin E succinate catalyzed by nano-SiO2 immobilized DMAP derivative in mixed solvent system
  75. Extraction of phytosterols from melon (Cucumis melo) seeds by supercritical CO2 as a clean technology
  76. Production of uronic acids by hydrothermolysis of pectin as a model substance for plant biomass waste
  77. Biofabrication of highly pure copper oxide nanoparticles using wheat seed extract and their catalytic activity: A mechanistic approach
  78. Intelligent modeling and optimization of emulsion aggregation method for producing green printing ink
  79. Improved removal of methylene blue on modified hierarchical zeolite Y: Achieved by a “destructive-constructive” method
  80. Two different facile and efficient approaches for the synthesis of various N-arylacetamides via N-acetylation of arylamines and straightforward one-pot reductive acetylation of nitroarenes promoted by recyclable CuFe2O4 nanoparticles in water
  81. Optimization of acid catalyzed esterification and mixed metal oxide catalyzed transesterification for biodiesel production from Moringa oleifera oil
  82. Kinetics and the fluidity of the stearic acid esters with different carbon backbones
  83. Aiming for a standardized protocol for preparing a process green synthesis report and for ranking multiple synthesis plans to a common target product
  84. Microstructure and luminescence of VO2 (B) nanoparticle synthesis by hydrothermal method
  85. Optimization of uranium removal from uranium plant wastewater by response surface methodology (RSM)
  86. Microwave drying of nickel-containing residue: dielectric properties, kinetics, and energy aspects
  87. Simple and convenient two step synthesis of 5-bromo-2,3-dimethoxy-6-methyl-1,4-benzoquinone
  88. Biodiesel production from waste cooking oil
  89. The effect of activation temperature on structure and properties of blue coke-based activated carbon by CO2 activation
  90. Optimization of reaction parameters for the green synthesis of zero valent iron nanoparticles using pine tree needles
  91. Microwave-assisted protocol for squalene isolation and conversion from oil-deodoriser distillates
  92. Denitrification performance of rare earth tailings-based catalysts
  93. Facile synthesis of silver nanoparticles using Averrhoa bilimbi L and Plum extracts and investigation on the synergistic bioactivity using in vitro models
  94. Green production of AgNPs and their phytostimulatory impact
  95. Photocatalytic activity of Ag/Ni bi-metallic nanoparticles on textile dye removal
  96. Topical Issue: Green Process Engineering / Guest Editors: Martine Poux, Patrick Cognet
  97. Modelling and optimisation of oxidative desulphurisation of tyre-derived oil via central composite design approach
  98. CO2 sequestration by carbonation of olivine: a new process for optimal separation of the solids produced
  99. Organic carbonates synthesis improved by pervaporation for CO2 utilisation
  100. Production of starch nanoparticles through solvent-antisolvent precipitation in a spinning disc reactor
  101. A kinetic study of Zn halide/TBAB-catalysed fixation of CO2 with styrene oxide in propylene carbonate
  102. Topical on Green Process Engineering
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