Microporous electrospun nonwovens combined with green solvents for the selective peel-off of thin coatings from painting surfaces

Over the last few decades, significant research efforts have been devoted to developing new cleaning systems aimed at preserving cultural heritage. One of the main objectives is to selectively remove aged or undesirable coatings from painted surfaces while preventing the cleaning solvent from permeating and engaging with the pictorial layers. In this work, we propose the use of electrospun polyamide 6,6 nonwovens in conjunction with a green solvent (dimethyl carbonate). By adjusting the electrospinning parameters, we produced three distinct nonwovens with varying average fiber diameters, ranging from 0.4 μm to 2 μm. These samples were characterized and tested for their efficacy in removing dammar varnish from painted surfaces. In particular, the cleaning process was monitored using macroscale PL (photoluminescence) imaging in real-time, while post-application examination of the mats was performed through scanning electron microscopy. The solvent evaporation rate from the different nonwovens was evaluated using gravimetric analysis and Proton Transfer Reaction- Time-of-Flight. It was observed that the application of the nonwovens with small or intermediate pore sizes for the removal of the terpenic varnish resulted in the swollen resin being absorbed into the mats, showcasing a peel-off effect. Thus, this protocol eliminates the need for further potentially detrimental removal procedures involving cotton swabs. The experimental data suggests that the peel-off effect relates to the microporosity of the mats, which enhances the capillary rise of the swollen varnish. Furthermore, the application of these systems to historical paintings underwent preliminary validation using a real painting from the 20th century.

Dimethyl Carbonate Synthesis from CO2 over CeO2 with Electron-Enriched Lattice Oxygen Species

Direct synthesis of dimethyl carbonate (DMC) from CO2 plays an important role in carbon neutrality, but its efficiency is still far from the practical application, due to the limited understanding of the reaction mechanism and rational design of efficient catalyst. Herein, abundant electron-enriched lattice oxygen species were introduced into CeO2 catalyst by constructing the point defects and crystal-terminated phases in the crystal reconstruction process. Benefitting from the acid-base properties modulated by the electron-enriched lattice oxygen, the optimized CeO2 catalyst exhibited a much higher DMC yield of 22.2 mmol g-1 than the reported metal-oxide-based catalysts at the similar conditions. Mechanistic investigations illustrated that the electron-enriched lattice oxygen can provide abundant sites for CO2 adsorption and activation, and was advantageous of the formation of the weakly adsorbed active methoxy species. These were facilitating to the coupling of methoxy and CO2 for the key *CH3OCOO intermediate formation. More importantly, the weakened adsorption of *CH3OCOO on the electron-enriched lattice oxygen can switch the rate-determining-step (RDS) of DMC synthesis from *CH3OCOO formation to *CH3OCOO dissociation, and lower the corresponding activation barriers, thus giving rise to a high performance. This work provides insights into the underlying reaction mechanism for DMC synthesis from CO2 and methanol and the design of highly efficient catalysts.

Part II: Purification of a therapeutic peptide

Preparative liquid chromatography in reversed phase conditions (RPLC) is the most common approach adopted in the downstream processing for the purification of therapeutic peptides at industrial level. Due to the strict requirements on the quality imposed by the Regulatory Agencies, routinary methods based on the use of aqueous buffers and acetonitrile (ACN) as organic modifier are commonly used, where ACN is practically the only available choice for the purification of peptide derivatives. However, ACN is known to suffers of many shortcomings, such as drastic shortage in the market, high costs and, most importantly, it shows unwanted toxicity for human health and environment, which led it among the less environmentally friendly ones. For this reason, the selection of a suitable alternative becomes crucial for the sustainable downstream processing of peptides and biopharmaceuticals in general. In this paper, a promising green solvent, namely dimethyl carbonate (DMC) has been used for the separation of a peptide not only in linear conditions but also for its purification through non-linear overloaded chromatography. The performance of the process has been compared to that achievable with the common method where ACN is used as organic modifier and to that obtained with two additional solvents (namely ethanol and isopropanol), already used as greener alternatives to ACN. This proof-of-concept study showed that, thanks to its higher elution strength, DMC can be considered a green alternative to ACN, since it allows to reduce method duration while reaching good purities and recoveries. Indeed, at a target purity fixed to 98.5 %, DMC led to the best productivity with respect to all the other solvents tested, confirming its suitability as a sustainable alternative to ACN for the purification of complex biopharmaceutical products.

Uncovering the role of yttrium in a cerium-based binary oxide in the catalytic conversion of carbon dioxide and methanol to dimethyl carbonate

Cerium(IV) oxide (CeO2)-based materials are effective catalysts for the synthesis of dimethyl carbonate (DMC) from carbon dioxide (CO2) and methanol (CH3OH). Herein, 5% Y-CeO2 was synthesized by the co-precipitation method. It forms a solid solution structure, which leads to the highest concentration of oxygen vacancies. The Y-VO-Ce active site created by Y3+ doping enhances the adsorption and activation of CO2 based on moderately passivating CH3OH adsorption. Consequently, 5% Y-CeO2 exhibited the highest CH3OH conversion rate of 0.8% and a DMC yield of 15 mmol⋅(g cat)-1, which is 1.4 times of pure CeO2 (reacting in a stainless-steel autoclave at 140 °C with a stirring speed of 1000 r⋅min-1 and an initial pressure of 3.0 MPa for 2 h). An adsorption test and in situ diffuse reflectance infrared Fourier transform spectroscopy showed that 5% Y-CeO2 could effectively inhibit the formation of triple-bonded methoxy species, and promote the formation of bidentate carbonate and bridged methoxy intermediates, which is conducive to the improvement of reaction activity.

Part I: Separation of small molecules

Nowadays, environmental problems are drawing the attention of governments and international organisations, which are therefore encouraging the transition to green industrial processes and approaches. In this context, chemists can help indicate a suitable direction. Beside the efforts focused on greening synthetic approaches, currently also analytical techniques and separations are under observation, especially those employing large volumes of organic solvents, such as reversed-phase liquid chromatography (RPLC). Acetonitrile has always been considered the best performing organic modifier for RPLC applications, due to its chemical features (complete miscibility in water, UV transparency, low viscosity etc); nevertheless, it suffers of severe shortcomings, and most importantly, it does not fully comply with Environmental, Health and Safety (EHS) requirements. For these reasons, alternative greener solvents are being investigated, especially easily available alcohols. In this work, chromatographic performance of the most common solvents used in reversed-phase chromatography, i.e., acetonitrile, ethanol and isopropanol, have been compared to a scarcely used solvent, dimethyl carbonate (DMC). The analytes of interest were two small molecules, caffeine and paracetamol, whose kinetics and retention behaviour obtained with the four solvents have been compared, and all contributions to band broadening have been assessed. Results about kinetic performance are very promising, indicating that a small amount (7 % v/v) of DMC is able to produce the same efficiency as a 2.5-times larger ACN volume (18 % v/v), and larger efficiency than alcohols. This paper reports, for the first time, fundamental studies concerning the mass transfer phenomena when DMC is used as an organic solvent in RPLC, and, together with the companion paper, represents the results of a research whose final aim was to discover whether DMC is suitable for chromatographic applications both in linear and preparative conditions.

A green formulation for superhydrophobic coatings based on Pickering emulsion templating for anti-biofilm applications

This study reports significant steps toward developing anti-biofilm surfaces based on superhydrophobic properties that meet the complex demands of today's food and medical regulations. It presents inverse Pickering emulsions of water in dimethyl carbonate (DMC) stabilized by hydrophobic silica (R202) as a possible food-grade coating formulation and describes its significant passive anti-biofilm properties. The final coatings are formed by applying the emulsions on the target surface, followed by evaporation to form a rough layer. Analysis shows that the final coatings exhibited a Contact Angle (CA) of up to 155° and a Roll-off Angle (RA) lower than 1° on the polypropylene (PP) surface, along with a relatively high light transition. Dissolving polycaprolactone (PCL) into the continuous phase enhanced the average CA and coating uniformity but hindered the anti-biofilm activity and light transmission. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed a uniform coating by a "Swiss-cheese" like structure with high nanoscale and microscale roughness. Biofilm experiments confirm the coating's anti-biofilm abilities that led to the reduction in survival rates of S.aureus and E.coli, by 90-95% respectively, compared to uncoated PP surfaces.

An efficient, fast, and green procedure to quantify α- and β-acids and xanthohumol in hops and their derived products

The main precursors of bitter principles of beer are α-acids, followed by β-acids. Determination of their content in hop cones and their derivatives is an essential part of brewing. HPLC-UV is the preferred technique when a more precise quantification of some specific bitter acids are required. However, current methods do not allow the proper quantification of all the six major α- and β-acids; furthermore, these multi-step methods generate considerable volumes of chemical waste. In this work, a new UHPLC-UV protocol was developed and compared side-by-side with reference, considering traditional and sustainability parameters. Baseline separations were achieved for the six major bitter acids and xanthohumol, while a greener and faster sample preparation procedure was developed. The new validated procedure could be adopted for quality control of hops and their derivative products with enhanced sample throughput and with a potential gain in the safety of the analyst.

Ultrathin In-Plane Heterostructures for Efficient CO2 Chemical Fixation

Chemical fixation of carbon dioxide (CO₂ ) into value-added organics is regarded as a competitive and viable method in large scale industrial production, during which the catalysts with promoting CO₂ activation ability are needed. Herein, we proposed an in-plane heterostructure strategy to construct Lewis acid-base sites for efficient CO₂ activation. By taking ultrathin in-plane Cu₂ O/Cu heterostructures as a prototype, we show that Lewis acid-base sites on heterointerface can facilitate a mixed C and O dual coordination on surface, which not only strengthen CO₂ adsorption, but also effectively activate the inert molecules. As revealed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and quasi in situ X-ray photoelectron spectroscopy (XPS), Lewis acid-base sites could readily activate CO₂ to ^. CO₂ ^- species, which is the key intermediate radical for CO₂ fixation. As a result, abundant Lewis acid-base sites endow Cu₂ O/Cu nanosheets with excellent performances for dimethyl carbonate generation, a high conversion yield of 28 % with nearly 100 % selectivity under mild conditions. This study provides a model structure for CO₂ fixation reactions.

Toxicity assessment of dimethyl carbonate following 28 days repeated inhalation exposure

Dimethyl carbonate (DMC) has been used as a reagent in methylation reactions, can be used as paints, coatings, and adhesives, and is a chemical that is being used increasing, which poses a health hazard to workers who handle it. So, the toxic reactions of F344 rats with inhalation exposure to 600, 1600, and 5000 ppm concentrations for 6 hours, 5 days a week, 4 weeks was evaluated. During the exposure period, general signs were observed, body weight and food consumption were measured, and hematologic and blood biochemical tests, organ weight measurements, necropsy, and histopathological examination were performed after the end of exposure. During the exposure period, dimethyl carbonate was exposed to an average of 599.26±31.40, 1614.64±80.79 and 5106.83±297.13 ppm in the chambers of the T1, T2 and T3 test groups, respectively. During the test period, general signs, weight change, food consumption, organ weight measurement, necropsy, and histopathological examination did not show any effects related to exposure to the test substance. However, as a result of blood and blood biochemical tests, an increase in AST, ALP, APTT, and PT levels was observed. From these results, it is judged that liver is the target organ when repeated inhalation exposure of dimethyl carbonate, the test substance, for 4 weeks, and the exposure-related effects of the test substance were observed at PT and ALP levels up to 600 ppm exposure concentration, but NOEC (No Observed Effect Concentration) was determined to be less than 600 ppm because it was not judged as an adverse effect.

Engine performance and emission characteristics of palm biodiesel blends with graphene oxide nanoplatelets and dimethyl carbonate additives

This study investigated the engine performance and emission characteristics of biodiesel blends with combined Graphene oxide nanoplatelets (GNPs) and 10% v/v dimethyl carbonate (DMC) as fuel additives as well as analysed the tribological characteristics of those blends. 10% by volume DMC was mixed with 30% palm oil biodiesel blends with diesel. Three different concentrations (40, 80 and 120 ppm) of GNPs were added to these blends via the ultrasonication process to prepare the nanofuels. Sodium dodecyl sulphate (SDS) surfactant was added to improve the stability of these blends. GNPs were characterised using Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FTIR), while the viscosity of nanofuels was investigated by rheometer. UV-spectrometry was used to determine the stability of these nanoplatelets. A ratio of 1:4 GNP: SDS was found to produce maximum stability in biodiesel. Performance and emissions characteristics of these nanofuels have been investigated in a four-stroke compression ignition engine. The maximum reduction in BSFC of 5.05% and the maximum BTE of 22.80% was for B30GNP40DMC10 compared to all other tested blends. A reduction in HC (25%) and CO (4.41%) were observed for B30DMC10, while a reduction in NO_x of 3.65% was observed for B30GNP40DMC10. The diesel-biodiesel fuel blends with the addition of GNP exhibited a promising reduction in the average coefficient of friction 15.05%, 8.68% and 3.61% for 120, 80 and 40 ppm concentrations compared to B30. Thus, combined GNP and DMC showed excellent potential for utilisation in diesel engine operation.

Co-transesterification of waste cooking oil, algal oil and dimethyl carbonate over sustainable nanoparticle catalysts

Key challenges for the application of biodiesel include their high acid value, high viscosity, and low ester content. It is essential to develop later-generation biodiesel from unexploited non-food resources for a more sustainable future. Reuse of biowaste is critically important to address these issues of food safety and sustainability. Thus, the co-transesterification of waste cooking oil (WCO), algal oil (AO) and dimethyl carbonate (DMC) for the synthesis of fatty acid methyl esters (FAMEs) was investigated over a series of nanoparticle catalysts containing calcium, magnesium, potassium or nickel under mild reaction conditions. Nanoparticle catalyst samples were prepared from biowaste sources of chicken manure (CM), water hyacinth (WH) and algal bloom (AB), and characterized using XRD, Raman and FESEM techniques for the heterogeneous production of biodiesel. The catalyst was initially prepared by calcination at 850 °C for 4 h in a major presence of Ca_xMg_yCO₃, KCl and K₂CO₃. The WCO and AO co-conversion of 98% and FAMEs co-selectivity of 95% were obtained over CM nanoparticle catalyst under the reaction conditions of 80 °C, 20 mins and DMC to oil molar ratio of 6:1 with 3% catalyst loading and 3% methanol addition. Under the optimum condition, the density, viscosity, and cetane number of the biodiesel were in the range of diesel standards. Nanoparticle catalysts have been proven as a promising sustainable material in the catalytic transesterification of WCO and AO with the major presence of calcium, magnesium and potassium. This study highlights a sustainable approach via biowaste utilization for the enhancement of biodiesel quality with high ester content, low acid value, high cetane number, and low viscosity.

Novel insights in dimethyl carbonate-based extraction of polyhydroxybutyrate (PHB)

BACKGROUND

Plastic plays a crucial role in everyday life of human living, nevertheless it represents an undeniable source of land and water pollution. Polyhydroxybutyrate (PHB) is a bio-based and biodegradable polyester, which can be naturally produced by microorganisms capable of converting and accumulating carbon as intracellular granules. Hence, PHB-producing strains stand out as an alternative source to fossil-derived counterparts. However, the extraction strategy affects the recovery efficiency and the quality of PHB. In this study, PHB was produced by a genetically modified Escherichia coli strain and successively extracted using dimethyl carbonate (DMC) and ethanol as alternative solvent and polishing agent to chloroform and hexane. Eventually, a Life Cycle Assessment (LCA) study was performed for evaluating the environmental and health impact of using DMC.

RESULTS

Extraction yield and purity of PHB obtained via DMC, were quantified, and compared with those obtained via chloroform-based extraction. PHB yield values from DMC-based extraction were similar to or higher than those achieved by using chloroform (≥ 67%). To optimize the performance of extraction via DMC, different experimental conditions were tested, varying the biomass state (dry or wet) and the mixing time, in presence or in absence of a paper filter. Among 60, 90, 120 min, the mid-value allowed to achieve high extraction yield, both for dry and wet biomass. Physical and molecular dependence on the biomass state and solvent/antisolvent choice was established. The comparative LCA analysis promoted the application of DMC/ethanol rather than chloroform/hexane, as the best choice in terms of health prevention. However, an elevated impact score was achieved by DMC in the environmental-like categories in contrast with a minor contribution by its counterpart.

CONCLUSION

The multifaceted exploration of DMC-based PHB extraction herein reported extends the knowledge of the variables affecting PHB purification process. This work offers novel and valuable insights into PHB extraction process, including environmental aspects not discussed so far. The findings of our research question the DMC as a green solvent, though also the choice of the antisolvent can influence the impact on the examined categories.

Greener approach for synthesis of N,N,N-trimethyl chitosan (TMC) using ternary deep eutectic solvents (TDESs)

N,N,N-trimethyl chitosan (TMC), quaternized hydrophilic derivative of chitosan, has been projected to have wide applications in the pharmaceutical industry owing to its improved solubility at physiological conditions. However, the conventional synthesis of TMC involves toxic organic agents, which complicates its use for biological applications. Moreover, these reactions result into unwanted O-methylation and scission of the parent polymer. In the present study we have addressed these limitations by employing a green approach to synthesize TMC, by using lipase as the biocatalyst and dimethyl carbonate (DMC) as the green methylating agent, in a reaction medium comprising of ternary deep eutectic solvents (TDESs). Synthesis of TMC was carried out by using two different lipases from Burkholderia cepacia and Candida rugosa. The resulting TMC was characterized by using FTIR, ¹H NMR, DSC, XRD. Methylation was confirmed by FTIR analysis (-CH at 1666 cm^-1) and ¹H NMR (?? = 3.3 ppm). DSC study revealed a lower thermal stability of TMC as compared to chitosan. These results indicated the possibility of using DMC as a green methylating agent, along with TDESs as green and sustainable solvents, for lipase catalyzed reactions. TMC was successfully synthesized and exhibited a degree of quaternization of about 12.5%, 15.69%, when synthesized used lipases from Burkholderia cepacia and Candida rugosa, respectively.

Ultrasound assisted methanolysis of polycarbonate at room temperature

The present work demonstrates an attempt to depolymerize Polycarbonate (PC) at room temperature, which otherwise requires extreme temperature and pressure conditions. It was achieved by the use of ultrasound to intensify the methanolysis reaction of PC. Use of ultrasound showed a significant enhancement in the rate of methanolysis which leads to a reduction in the reaction time from 45 min to 15 min to depolymerize 5 g PC at 30 °C by using 0.1 g NaOH and THF to methanol ratio equaling 3 (w/w). Bubble dynamic study also leads to a conclusion that the highest cavitational enhancement can be achieved at THF to methanol ratio equaling 3 (w/w) which might be due to the fact that this solvent mixture exhibits the least viscosity at this composition. The effect of various parameters such as temperature, NaOH concentration, ultrasonic input power and solvent composition were investigated. The products obtained were bisphenol-A(BPA) and dimethyl carbonate (DMC) which were characterized by Fourier Transform Infrared Spectroscopy (FT-IR) and gas chromatography (GC) respectively.

Explosion characteristics for Li-ion battery electrolytes at elevated temperatures

Li-ion batteries are used in electronic devices and electric cars, yet they create safety concerns due to the possibility of the release of combustible materials. The electrolyte, one of the main components in a Li-ion cell, consists of organic carbonates. Venting and thermal runaway release organic carbonates and when mixed with air, it can result in fires and explosions. A 20-liter explosion sphere was used to determine the explosion characteristics for three typical carbonates used in electrolytes, at 373 K, and 100 kPa absolute pressure. The explosion pressure and the maximum rate of explosion pressure rise are presented for the carbonates and for hydrogen, methane, and propane, and the explosive limits for the carbonates are also identified at the same conditions. This allowed a comparison of the explosion characteristics for the carbonates with those for hydrogen, methane, and propane. Theoretical calculations gave a higher explosion pressure than that from the experimental results most likely due to losses in the hydrocarbon experiments. The carbonates analyzed have very similar explosion pressures and rate of explosion pressure rise as propane. The explosion characteristics found for the three carbonates can be used in future consequence and risk assessments for Li-ion battery installations.

Synthesis and characterization of TiO2-V2O5-MCM-41 for catalyzing transesterification of dimethyl carbonate with phenol

A series of TiO₂-V₂O₅-MCM-41 molecular sieve catalysts were prepared by the impregnation method. The prepared catalysts were characterized by different techniques including X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and N₂ adsorption–desorption. These catalysts were applied in the catalytic synthesis of diphenyl carbonate (DPC) by the transesterification of dimethyl carbonate (DMC) with phenol. The synthesis results indicated that the catalysts possessed the high specific surface area and large pore volume and included titanium with four ligands. Due to the vanadium introduction into Ti-MCM-41, the catalytic activity was promoted, by-products were reduced, and the catalytic activity and stability of the catalyst were significantly improved. With 10%V-20%Ti-MCM-41 catalyst, the optimal synthesis results including the conversion rate of DMC of 33.88%, the selectivity of DPC of 35.84%, and the yield of DPC of 12.14% were obtained.

CuY zeolite catalysts prepared by ultrasonication-assisted ion-exchange for oxidative carbonylation of methanol to dimethyl carbonate

The influence of ultrasonication treatment on the catalytic performance of CuY zeolite catalysts was investigated for the liquid-phase oxidative carbonylation of methanol to dimethyl carbonate (DMC). The deammoniation method of NH₄Y into HY zeolites was optimized and characterized by elemental analyzer, derivative thermogravimetry, Brunauer-Emmett-Teller (BET) analyzer, and powder X-ray diffractometry, revealing that the HY zeolite deammoniated at 400 °C presented the highest surface area, complete ammonium/proton ion exchange, and no structure collapse, rendering it the best support from all the prepared zeolites. CuY zeolites were prepared via aqueous phase ion exchange with the aid of ultrasonication. Upon ultrasonication, the Cu⁺ active centers were uniformly dispersed in the Y zeolites, penetrating the core of the zeolite particles in a very short time. In addition to enhancing the Cu dispersity, the ultrasonication treatment influenced the BET surface area, acid amount, Cu⁺/Cu²⁺ ratio, and also had a relatively small impact on the Cu loading. Consequently, adequate exposure to ultrasonication was able to increase the conversion rate of methanol into dimethyl carbonate up to 11.4% with a comparable DMC selectivity of 23.7%. This methanol conversion is 2.65 times higher than that obtained without the ultrasonication treatment.

Calcium oxide-modified mesoporous silica loaded onto ferriferrous oxide core: Magnetically responsive mesoporous solid strong base

The design of new type of solid strong base with ideal activity, stability, and reusability is strongly urged by the growing demand of green chemistry and sustainable development. In this study, a new type of mesoporous solid strong base, denoted as CaO/mSiO₂/Fe₃O₄, is successfully fabricated by successively coating SiO₂ onto Fe₃O₄ magnetic nanoparticles and loading CaO into the mesoporous SiO₂. Compared with a series of other typical solid bases, the CaO/mSiO₂/Fe₃O₄ exhibits higher activity towards the synthesis of dimethyl carbonate by the transesterification of ethylene carbonate and methanol. The activity of the CaO/mSiO₂/Fe₃O₄ is not observed to decrease obviously even after sextic catalyst recirculation, and in particular, the recovery of the catalyst without quality loss is very convenient due to the good magnetic responsiveness of the Fe₃O₄ cores.

Fabrication of Yolk-Shell Cu@C Nanocomposites as High-Performance Catalysts in Oxidative Carbonylation of Methanol to Dimethyl Carbonate

A facile way was developed to fabricate yolk-shell composites with tunable Cu cores encapsulated within hollow carbon spheres (Cu@C) with an average diameter about 210 nm and cavity size about 80 nm. During pyrolysis, the confined nanospace of hollow cavity ensures that the nucleation-and-growth process of Cu nanocrystals take place exclusively inside the cavities. The size of Cu cores can be easily tuned from 30 to 55 nm by varying the copper salt concentration. By deliberately creating shell porosity through KOH chemical activation, at an optimized KOH/HCS mass ratio of 1/4, the catalytic performance for the oxidative carbonylation of methanol to dimethyl carbonate (DMC) of the activated sample is enhanced remarkably with TOF up to 8.6 h^-1 at methanol conversion of 17.1%. The activated yolk-shell catalyst shows promising catalytic properties involving the reusability with slight loss of catalytic activity and negligible leaching of activated components even after seven recycles, which is beneficial to the implementation of clean production for the eco-friendly chemical DMC thoroughly.

Preparation of N, N, N-trimethyl chitosan via a novel approach using dimethyl carbonate

N,N,N-trimehtyl chitosan (TMC) is a water-soluble derivate of chitosan, which has been widely used as a biomedical material due to its excellent biocompatibility, biodegradability and bacterial properties. To date, TMC can only be prepared by the quaternization of chitosan using alkyl halide or dimethyl sulfate. However, alkyl halide and dimethyl sulfate are highly toxic, cancerigenic for humans, and harmful to the environment. This paper puts forward a novel approach to preparing TMC using dimethyl carbonate as a methylation reagent in an ionic liquid. The as-synthesized O-methyl-free TMC was characterized using NMR, FTIR, XRD and TG analyses. The results showed that TMC with a degree of quaternization of 9.11% was successfully obtained and the crystallinity of chitosan decreased with the increasing degree of N-methylation, the thermal stability of TMC was lower than that of chitosan. Furthermore, the effects of the dose of ionic liquid and dimethyl carbonate were disscussed.

Estimating total lipid content of Camelina sativa via pyrolysis assisted in-situ transesterification with dimethyl carbonate

Direct derivatization of C. sativa seed into FAMEs without lipid extraction was conducted for the quantification of lipid analysis via in-situ thermal methylation with dimethyl carbonate as an acyl acceptor on silica (SiO₂). The introduced method had an extraordinarily high tolerance against impurities such as pyrolytic products and moisture. To ensure the technical completeness of in-situ methylation, thermal cracking of FAMEs transformed from C. sativa seed was also explored. Thermal cracking of unsaturated FAMEs such as C_18:1, C_18:2, C_18:3 and C_20:1 occurred at temperatures higher than 365°C due to their thermal instability. Thus, experimental findings in this study suggests not only that qualitative analysis of fatty acid profile in C. sativa seed via in-situ methylation using SiO₂ could be achieve, but also that the total lipid content (42.65wt.%) in C. sativa seed could be accurately estimated.

Synthesis and characterization of cellulose carbonate using greenchemistry: Surface modification of Avicel

The development of new derivatives based on renewable natural resources using green chemistry is a concept gaining recognition in several industries. This work focused on the preparation and characterization of cellulose carbonate using dimethyl carbonate as the green reagent in ethanoic KOH solution. The effect of several reaction parameters were evaluated, i.e., temperature (25°C, 50°C, 90°C, 120°C, 150°C, and 180°C), time (6, 24, 48, and 72h), KOH concentration (15% and 30%), and the use of a catalyst (DBU). The degree of substitution (DS) of the resulting materials was evaluated by ¹³C CP/MAS NMR. The spectra of the prepared cellulose carbonate exhibited the main peaks associated with cellulose macromolecules (C1-C6) and those corresponding to carbonate functions at approximately 162ppm. Moreover, XPS was performed and confirmed the reaction modifications. Nevertheless, it is worth noting that ¹³C NMR and XPS spectra showed a significant difference in DS value, due to the difference between both techniques. However, our results from NMR and XPS experiments confirm that the major modifications during all the reactions occurred mainly at the surface. This green process opens the way for the easy production of a new class of cellulose derivatives.

In-situ pyrogenic production of biodiesel from swine fat

In-situ production of fatty acid methyl esters from swine fat via thermally induced pseudo-catalytic transesterification on silica was investigated in this study. Instead of methanol, dimethyl carbonate (DMC) was used as acyl acceptor to achieve environmental benefits and economic viability. Thermo-gravimetric analysis of swine fat reveals that swine fat contains 19.57wt.% of water and impurities. Moreover, the fatty acid profiles obtained under various conditions (extracted swine oil+methanol+NaOH, extracted swine oil+DMC+pseudo-catalytic, and swine fat+DMC+pseudo-catalytic) were compared. These profiles were identical, showing that the introduced in-situ transesterification is technically feasible. This also suggests that in-situ pseudo-catalytic transesterification has a high tolerance against impurities. This study also shows that FAME yield via in-situ pseudo-catalytic transesterification of swine fat reached up to 97.2% at 380°C. Therefore, in-situ pseudo-catalytic transesterification can be applicable to biodiesel production of other oil-bearing biomass feedstocks.

Esterification of glycerol from biodiesel production to glycerol carbonate in non-catalytic supercritical dimethyl carbonate

Conversion of glycerol from biodiesel production to glycerol carbonate was studied by esterification with dimethyl carbonate in a non-catalytic supercritical condition. It was found that in a non-catalytic supercritical condition, glycerol at higher purity gave higher yield of glycerol carbonate at 98 wt% after reaction at 300 °C/20–40 MPa/15 min. The yield of glycerol carbonate was observed to increase with molar ratio, temperature, pressure and time until a certain equilibrium limit. The existence of impurities such as water and remnants of alkaline catalyst in crude glycerol will direct the reaction to produce glycidol. Although impurities might not be desirable, the non-catalytic supercritical dimethyl carbonate could be an alternative method for conversion of glycerol from biodiesel production to value-added glycerol carbonate.Graphical abstract

Extraction of polyhydroxyalkanoates from mixed microbial cultures: Impact on polymer quality and recovery

Polyhydroxyalkanoates (PHAs) can be extracted from mixed microbial cultures (MMCs) by means of dimethyl carbonate (DMC) or combination of DMC and sodium hypochlorite (NaClO). The protocol based on DMC, a green solvent never used before for the extraction of PHAs from MMC, allows an overall polymer recovery of 63%; also the purity and the molecular weight of the recovered polymers are good (98% and 1.2 MDa, respectively). The use of NaClO pretreatment before DMC extraction increases the overall PHA recovery (82%) but lowers the mean molecular weight to 0.6-0.2 MDa. A double extraction with DMC results to be the method of choice for the recovery of high quality PHAs from attractive but challenging MMCs.

Production of biodiesel fuel from canola oil with dimethyl carbonate using an active sodium methoxide catalyst prepared by crystallization

In this study, a novel method for the production of biodiesel under mild conditions using fine particles of sodium methoxide formed in dimethyl carbonate (DMC) is proposed. Biodiesel is generally produced from vegetable oils by the transesterification of triglycerides with methanol. However, this reaction produces glycerol as a byproduct, and raw materials are not effectively utilized. Transesterification with DMC has recently been studied because glycerol is not formed in the process. Although solid-state sodium methoxide has been reported to be inactive for this reaction, the catalytic activity dramatically increased with the preparation of fine catalyst powders by crystallization. The transesterification of canola oil with DMC was studied using this catalyst for the preparation of biodiesel. A conversion greater than 96% was obtained at 65°C for 2h with a 3:1M ratio of DMC and oil and 2.0 wt% catalyst.

KR-1 biomass

Fatty acid methyl esters (FAMEs) and glycerol carbonate were simultaneously prepared from Chlorella sp. KR-1 containing 40.9% (w/w) lipid using a reactive extraction method with dimethyl carbonate (DMC). DMC was used as lipid extraction agent, acyl acceptor for transesterification of the extracted triglycerides, substrate for glycerol carbonate synthesis from glycerol, and reaction medium for the solvent-free reaction system. For 1g of biomass, 367.31 mg of FAMEs and 16.73 mg of glycerol carbonate were obtained under the optimized conditions: DMC to biomass ratio of 10:1 (v/w), water content of 0.5% (v/v), and Novozyme 435 to biomass ratio of 20% (w/w) at 70°C for 24h. The amount of residual glycerol was only in the range of 1-2.5mg. Compared to conventional method, the cost of FAME production with the proposed technique could be reduced by combining lipid extraction with transesterification and omitting the extraction solvent recovery process.

Highly efficient extraction and lipase-catalyzed transesterification of triglycerides from Chlorella sp. KR-1 for production of biodiesel

We developed a method for the highly efficient lipid extraction and lipase-catalyzed transesterification of triglyceride from Chlorella sp. KR-1 using dimethyl carbonate (DMC). Almost all of the total lipids, approximately 38.9% (w/w) of microalgae dry weight, were extracted from the dried microalgae biomass using a DMC and methanol mixture (7:3 (v/v)). The extracted triglycerides were transesterified into fatty acid methyl esters (FAMEs) using Novozyme 435 as the biocatalyst in DMC. Herein, DMC was used as the reaction medium and acyl acceptor. The reaction conditions were optimized and the FAMEs yield was 293.82 mg FAMEs/g biomass in 6 h of reaction time at 60 °C in the presence of 0.2% (v/v) water. Novozyme 435 was reused more than ten times while maintaining relative FAMEs conversion that was greater than 90% of the initial FAMEs conversion.