Catalyst-free Process Research Articles

Microwave‐mediated noncatalytic synthesis of ethyl levulinate: A green process for fuel additive production

This study developed a new catalyst-free process for producing ethyl levulinate, a biofuel additive. Noncatalytic levulinic acid esterification with ethanol using microwave irradiation (MW) was compared with that using traditional heating (TH) under different reaction conditions. The results demonstrated that the esterification process using MW was more effective than that using TH. A reaction conversion of 90.38% was obtained for the esterification using MW at 473 K and reaction time of 3 hours. Moreover, this study established a model for depicting the kinetics of levulinic acid esterification using MW and TH. A good fit to the data (R2 of >.9999) was achieved, indicating the validity of the developed model. The rate constants and pre-exponential factor obtained for the esterification using MW were greater than those obtained using TH. Consequently, the microwave-assisted noncatalytic synthesis is a green and promising method for preparing ethyl levulinate.

A catalyst-free process for gas ozonation of reduced sulfur compounds

The feasibility of homogenous gas ozonation process was investigated in order to reduce the negative environmental impact caused by reduced sulfur compounds (RSCs). Emitted from a variety of industrial plants, this class of compounds are known by their odor properties. Selecting hydrogen sulfide (H2S), methyl ethyl sulfide (MES) and dimethyl disulfide (DMDS) as representative odorous RSCs, the influence of four gas ozonation process parameters (ozone concentration, humidity level, reactor temperature and residence time) on their removal efficiencies was evaluated using a Doehlert experimental design in an experimental domain compatible with industrial constraints. Ozone concentration was the only process parameter that has resulted in a positive – but limited – effect on the removal efficiency of the mix of RSCs. However, even if ozone was present in large excess (20 times the RSCs concentration), MES and DMDS were slightly consumed (around 30%). Only H2S has shown interesting removal efficiencies (up to 80%). In addition to the measurement of reagent concentrations, Selected Ion Flow Tube coupled with Mass Spectrometry (SIFT/MS) was applied to identify and quantify the potential products of RSCs-ozone reaction. Methyl ethyl sulfone (MESO2) was found to be the primary product of MES, whereas methyl methanethiosulfinate (DMSOS) and sulfur dioxide (SO2) for DMDS, suggesting that the organic monosulfide and disulfides would not follow the same reaction mechanism with ozone in gas phase. In addition, SO2 and H2O may not be the only end products for H2S ozonation, since additional peaks were detected in SIFT/MS spectra.

Tuning and fine morphology control of natural resource-derived vertical graphene

Tunability and fine control of structure and morphology in the patterns of vertically-oriented graphenes is of high importance for their efficient functionalization and application. In this work, we present an experimental and simulation insight into the formation of graphene structures. Detailed simulations by an ad hoc model based on a large number of interacting elemental processes were implemented to ensure a deeper insight into the processes which cannot be directly measured and assessed in the experiments, such as relative densities of adsorbed species and density of ion current at the nanostructures. The combination of the experimental and simulation approaches provided a new level of understanding of the processes that govern formation of the graphene network morphology. Moreover, the potential of novel analytical techniques such as Hough transformations, fractal dimension distributions and Minkovski connectivity, 2D FFT transforms, Hough transformation spectra and others for analysis of the graphene array morphology was successfully demonstrated. The evolution of surface morphology of graphene derived from cold-pressed Citrus sinensis oil, a by-product of orange juice production by centrifugation, synthesised via a catalyst‒free process, was investigated using experimental analyses, Raman spectroscopy, scanning electron microscopy and X‒ray photoelectron spectroscopy, and numerous advanced analytical techniques such as distributions of fractal dimensions.

Sustainable Thermosetting Polyurea Vitrimers Based on a Catalyst-Free Process with Reprocessability, Permanent Shape Reconfiguration and Self-Healing Performance

Traditional thermosetting polyureas (TPUs) with eminently comprehensive performance have been used in a variety of industrial applications. However, they suffer from a certain intractable difficulty in achieving multiple functions such as reprocessability, shape reconfiguration, or self-healing performance due to the extremely stable covalent cross-linking. Herein, we employ hindered urea bonds (HUBs) as a reversible dynamic covalent cross-linkage to design catalyst-free hindered thermosetting polyureas (HTPUs). By incorporating HUBs into TPUs, the synthesized HTPUs can be reprocessed by using hot press or microinjection technique without any catalyst. In addition, those obtained materials have achieved great abilities of permanent shape reconfiguration and self-healing. Especially, the combination of the conventional elastic shape memory with the solid-state plastic shape reconfiguration in these HTPUs will broaden the geometrically complex shapes for shape memory polymer. Importantly, introducing longer and more bulky substituents into HTPUs can simultaneously endow the materials with excellent mechanical properties and the aforementioned multiple functions. Despite what is mentioned in this article, more potential HTPUs with excellent mechanical properties and multiple functions could be further designed by introducing longer and more bulky substituents into the formal polymers.

Sono-Polymerization of Poly(ethylene glycol)-Based Nanoparticles for Targeted Drug Delivery.

Engineering functional nanoparticles (NPs) with low nonspecific interactions and a high specific targeting property is highly desired for improved drug delivery. Herein, we report a targeted poly(ethylene glycol) (PEG)-based chemotherapy system synthesized via a catalyst-free sono-polymerization process for drug delivery. The polymerization process was fast (20 min), and different monomers were able to be polymerized to form NPs in a one-pot process. Glutathione (GSH)-responsive platinum prodrugs and fluorescent dyes could be encapsulated in NPs by amidation formation. Cyclic peptides containing Arg-Gly-Asp (RGD)-modified PEG-based NPs possessed a much higher cell targeting (∼90%) than the unmodified PEG-based NPs (∼10%) after a 12 h incubation with U87 MG cells, which could improve drug delivery efficacy. The IC50 (50% inhibitory concentration) could also be reduced more than 50% compared to the nontargeted PEG-based NPs. Importantly, these PEG-based NPs can be freeze-dried into a powder form and redispersed in an aqueous solution without aggregation, which may facilitate the storage and transportation of nanomedicine. This study establishes a green and efficient method to engineer targeted drug carriers for drug delivery.

Production of high-quality biofuel via ethanol liquefaction of pretreated natural microalgae

The conversion of algal lipids to fatty acid alkyl esters is a promising way for the production of high-grade biofuel, due to the lower oxygen content of lipids than that of saccharides and proteins. Herein, a catalyst-free conversion process of natural microalgae cyanobacteria was developed for biodiesel production. The conversion involved two steps: (1) pretreatment of raw microalgae by Soxhlet extraction of lipids or hydrothermal treatment for extraction of saccharides and part of proteins at 200 °C; (2) liquefaction of raw and pretreated samples in sub/supercritical ethanol. In the first step, a maximum lipid yield of 6.5 wt% was extracted by Soxhlet extraction, while the hydrothermal treatment dissolved saccharides and a part of proteins. The composition of biocrude obtained from raw algae was complex, containing hydrocarbons, N-containing compounds, esters, fatty acids and other oxy-compounds. The biocrude from lipid extracted algae had a poor quality, from which the degradation of proteins was facilitated. Better yet, the extraction of saccharides and part of proteins by hydrothermal pretreatment simplified the composition (mainly fatty acid ethyl esters), reduced the nitrogen content (<4%) and improved the higher heating value (∼41 MJ kg−1) for biocrude.

Catalyst-free growth of ZnO nanowires: structural, optical, vibrational and field emission properties

High density of ZnO nanowires is grown over zinc foil by a catalyst-free thermal evaporation process. Electron microscopy studies confirmed that the as-grown nanowires are hexagonal wurtzite structure. The nanowires diameter was ~ 50 nm with typical length of the order of μm. Photoluminescence (PL) spectrum of the wires consist of a strong blue emission peak at 2.54 eV accompanied by other peaks of relatively lower intensities. The Raman spectra of the ZnO nanowires exhibit compressive stress due to the local heating effects during the synthesis. The field emission measurement indicated that ZnO nanowires have a turn-on field of 13.5 V/μm at current density of 0.001 μA/cm2.

Silicon Nano Wires Anodes for High-Performance Lithium Ion Batteries

We report on the scalable synthesis and characterization of novel architecture three-dimensional high-capacity amorphous Silicon Nanowires (SiNWs)-based anodes, with a quarter of the thickness of common graphite anode. The SiNWs were grown in a novel, catalyst free process, on a thin stainless steel (SS) net. With the use of two and three electrodes coin cells we focus on studying their electrochemical performance and degradation mechanisms. By using our novel, low cost and high mass loading chemical vapor deposition (CVD) procedure we synthesized anodes that have shown stable cycle life for over 600 cycles and provided capacities of up to 6mAh/cm2, very low (<10%) irreversible capacity and good compatibility with commercial cathodes. Notably, it was found that the growth of the solid electrolyte interphase (SEI) thickness and its concomitant increase in resistivity, represents the major reason for the observed capacity loss of the SiNWs-based anodes. Our anodes have been coupled with commercial cathodes (LFP and NCA), and have the potential to increase the energy density of LIBs by over 40%. In order to prove the scalability of our anodes, they have been successfully incorporated in industrial hardware cylindrical cells, proving they are a viable candidate for anodes of the next generation lithium ion batteries for portable applications and electric vehicles. Most recently, these anodes have successfully been cycled in all solid state cells consisting of solid polymer electrolytes, paving the way for safer, more durable LIBs.

Sustainable Microwave-Assisted Aerobic Oxidation of Tomato Plant Waste into Bioaromatics and Organic Acids

Lignin is the second most abundant polymer in lignocellulosic biomass. A biorefinery approach to lignin valorisation, as an alternative to the use of heating, can produce bioaromatics, and this idea is attracting ever more interest. However, the isolation of lignin for further processing is really quite challenging, making the valorisation of native lignin (i.e., lignin in raw biomass) crucially important. An analysis of vanillin yields in relation to total reaction feedstock weight shows that the economic viability of the process depends on the valorisation of all biomass components. This paper reports a microwave-assisted, catalyst-free aerobic oxidation process for biomass. The protocol yields bioaromatics (mainly vanillin and syringaldehyde, with traces of p-hydroxybenzaldehyde and acetovanillone) and organic acids (38.4 wt % maximum total yield) in only 30 min. Vanillin is the most valuable of the aromatic compounds to be produced by lignin oxidation, accounting for 8.7 wt % of the initial lignin. The use of biomass as the starting material means that no pretreatment is needed for component separation. Furthermore, the use of air as the oxidant and the catalyst-free nature of the protocol render the process environmentally sustainable and scalable, as the energy consumption is counterbalanced by the clean production of high market value products.

Thermo-Promoted Reactions of Anthranils with Carboxylic Acids, Amines, Phenols, and Malononitrile under Catalyst-Free Conditions.

A convenient and atom-economical procedure for the thermo-promoted reactions of anthranil with different substrates was developed. The catalyst-free process affords various useful building blocks with good to moderate yields. This chemistry enables several step- and cost-effective approaches for biologically interesting molecules and provides an efficient platform for the investigation of untapped reactions at high temperature.

Synthesis and Characterization of Multi-Angular Branched ZnO Microstructures and Peculiar Nanopushpins Obtained by Thermal Treatment from Compacted ZnS Powder

Multi-angular branched ZnO microstructures with rods-shaped tips and nanopushpins with hexagonal cap on top have been synthesized by a simple thermal treatment process of compacted ZnS powder used as starting material and substrate. The structures have been grown at different temperatures (800, 900 and 1000 °C) for 60 min, in a constant nitrogen environment at atmospheric pressure via a catalyst-free process. XRD results of the as-grown products from ZnS powder show a significant reduction in the cubic zincblende phase to the hexagonal wurtzite phase with the increase of treatment temperature, as compared to the bulk value. Post-anneal analyses indicated that the transformation of morphologies of the as-grown structures also depends strongly on the treatment temperature. The proposed method represents an easy and economical way to grow complex structures of ZnO, with a relatively short time, furthermore, without the neediness of use an external substrate to grow. These new and interesting nanostructures have potential in applications such as optoelectronics.

Scalable electrochemical oxidant-and metal-free dehydrogenative coupling of S-H/N-H.

A practical and scalable electrochemical oxidation of S-H and N-H was developed. This oxidant- and catalyst-free electrochemical process enables S-N bond formation with inexpensive nickel electrodes in an undivided cell. This procedure exhibits broad substrate scopes and good functional-group compatibility. A 50 g scale oxidative coupling augurs well for industrial applications.

Nanosecond laser ablation for enhanced adhesion of CuO nanowires on copper substrate and its application for oil-water separation

Nanotextured materials have been used extensively for water treatment and purification to minimize wastewater pollution from factories and oil spill accidents from damaging our ecosystem. With constant erosion from the environment, the adhesion of nanomaterials to surfaces has thus been a long-standing challenge for practical deployment in industrial settings. Thermally-induced oxidative growth of copper oxide (CuO) nanowires (NWs) on Cu foil is a readily accessible and scalable technique of mass producing nanostructures. However, the NWs readily exfoliate from the substrate, limiting its utilization. The use of a pulsed 1064 nm laser texturing approach to greatly improve adhesion and sturdiness of CuO NWs array on Cu foil with laser fabricated microholes is presented. This is a catalyst-free and controllable process to create functional surfaces with microholes lined with hierarchical CuO NWs array. The resultant superhydrophilic nano-textured surface demonstrated the ability as an efficient filter for potential applications in separation of oil-water emulsions. It achieves enhanced speed of separation withstanding higher intrusion pressure and higher efficiency. This work has a great potential for scalable applications in high-efficiency oily wastewater treatment, underwater oil manipulation, self-cleaning and bioadhesion control.

A Rapid Method to Aromatic Aminoalkyl Esters via the Catalyst-Free Difunctionalization of C–N Bonds

A novel multicomponent reaction involving a direct C–N esterification/arylation has been developed. This catalyst-free process was conducted with cyclic tertiary amines via a facile C–N cleavage to provide the alkyl group and nitrogen source. The operationally simple method to rapidly combine cyclic tertiary amines, haloazaarenes and carboxylic acids (or anhydrides) affords an efficient access to aromatic aminoalkyl esters, potential drug-like products, in good to excellent yields.

Characterization and Modeling of Catalyst-free Carbon-Assisted Synthesis of ZnO Nanowires

ZnO nanowires have been widely studied due to their unique material properties and many potential applications in electronic and optoelectronic devices. Many growth processes have been developed to synthesize ZnO nanowires. It is critically important to develop predictive process models so as to maximize the output of the nanowire synthesis. Here we report a method to characterize, quantify, and model a catalyst-free carbon-assisted ZnO nanowire growth process. Two key factors were identified for the synthesis conditions, which are reaction temperature and flow rate. Based on a factorial design method, we conducted experiments with different combinations of the two factors to study their effects on the process output (i.e. density of the nanowires), which was evaluated by a scanning electron microscope (SEM). The experimental results were analyzed using ANOVA test, and then a semi-empirical model was built to correlate the ZnO nanowire output with synthesis conditions. This model was able to describe the ZnO nanowire density with respect to synthesis conditions, which can provide guideline for synthesis parameters selection and process optimization.

Nitrogen-doped graphene approach to enhance the performance of a membraneless enzymatic biofuel cell

Heteroatom-doping of pristine graphene is an effective route for tailoring new characteristics in terms of catalytic performance which opens up potentials for new applications in energy conversion and storage devices. Nitrogen-doped graphene (N-graphene), for instance, has shown excellent performance in many electrochemical systems involving oxygen reduction reaction (ORR), and more recently glucose oxidation. Owing to the excellent H2O2 sensitivity of N-graphene, the development of highly sensitive and fast-response enzymatic biosensors is made possible. However, a question that needs to be addressed is whether or not improving the anodic response to glucose detection leads to a higher overall performance of enzymatic biofuel cell (eBFC). Thus, here we first synthesized N-graphene via a catalyst-free single-step thermal process, and made use of it as the biocatalyst support in a membraneless eBFC to identify its role in altering the performance characteristics. Our findings demonstrate that the electron accepting nitrogen sites in the graphene structure enhances the electron transfer efficiency between the mediator (redox polymer), redox active site of the enzymes, and electrode surface. Moreover, the best performance in terms of power output and current density of eBFCs was observed when the bioanode was modified with highly doped N-graphene.

Modeling of Catalyst-free Growth Process of ZnO Nanowires

ZnO nanowires have been widely studied due to their unique material properties and many potential applications in electronic and optoelectronic devices. Many growth processes have been developed to synthesize ZnO nanowires. It is critically important to develop predictive process models so as to maximize the output of the nanowire synthesis. Here we report a method to characterize, quantify, and model a catalyst-free carbon-assisted ZnO nanowire growth process. Two key factors were identified for the synthesis conditions, which are reaction temperature and flow rate. Based on a factorial design method, we conducted experiments with different combinations of the two factors to study their effects on the process output (i.e. density of the nanowires), which was evaluated by a scanning electron microscope (SEM). The experimental results were analyzed using ANOVA test, and then a semi-empirical model was built to correlate the ZnO nanowire output with synthesis conditions. This model was able to describe the ZnO nanowire density with respect to synthesis conditions, which can provide a guideline for synthesis parameters selection and process optimization.

Biodegradable and High-Performance Poly(butylene adipate-co-terephthalate)–Lignin UV-Blocking Films

Renewable and biodegradable UV-blocking films are in high demand for the increasing need of sustainable environment. Lignin can offer significant UV absorption, but it deteriorates the mechanical properties of films at a high content. In this effort, biobased 10-undecenoic and oleic acids were successfully grafted on soda lignin via solvent- and catalyst-free processes, as confirmed by 31P and 1H NMR and Fourier transform infrared (FTIR). The resulting lignin ester derivatives and neat lignin were then melt-blended with a biodegradable poly(butylene adipate-co-terephthalate) (PBAT) to prepare UV-protective films. The incorporation of the modified lignins into the PBAT matrix exhibited good dispersion of lignin particles with almost unaffected tensile properties as well as good thermal stability for up to 20 wt % loading of lignin derivatives. The resulting films showed excellent UV-barrier property with 10 wt % lignin loading, having full protection in the whole UV-irradiation range (280–400 nm). The UV p...

Arrayed Arrangement of 13 C Isotopes During the Growth of Inner Single‐Walled Carbon Nanotubes

The growth of single wall carbon nanotubes (SWCNT) inside host SWCNTs remains a compelling alternative to the conventional catalyst induced growth processes. It not only provides a catalyst free process but the ability to control the constituents of the inner tube if appropriate starting molecules are used. We report herein the growth of inner SWCNTs from $^{13}$C labeled toluene and natural carbon C$_{60}$. The latter molecule is essentially a stopper which acts to retain the smaller toluene. The Raman spectrum of the inner nanotubes is anomalous as it contains a highly isotope shifted "tail", which cannot be explained by assuming a homogeneous distribution of the isotopes. {\color{black}Semi-empirical} calculations of the Raman modes indicate that this unsual effect is explicable if small clusters of $^{13}$C are assumed. This indicates the absence of carbon diffusion during the inner tube growth. When combined with appropriate molecular recognition, this may enable a molecular engineering of the atomic and isotope composition of the inner tubes.

Assessment of process variables on the use of macauba pulp oil as feedstock for the continuous production of ethyl esters under pressurized conditions

ABSTRACT This study evaluated the potential of macauba pulp oil (MPO) as a feedstock for continuous ester production using ethanol under pressurized conditions. Experiments were performed in order to obtain data for the effect of process variables on ethyl ester (FAEE) and free fatty acid (FFA) conversion in a catalyst-free process. From the results, it appears that the MPO to ethanol mass ratio and the pressure were the variables with more favorable effect on the evaluated response variables. The addition of n-hexane caused an increase in the production of esters; however, this had a negative effect on FFA conversion. The addition of water was unfavorable for oil processing with high acidity. In this process, esterification and transesterification occur simultaneously, and the high FFA content in MPO provides high yields (85 wt% of esters; 93% FFA conversion) at low temperature, since the esterification reaction rate is higher than the transesterification. The decomposition of fatty acids was evaluated and levels <5% were observed under the evaluated experimental conditions.