Microwave-assisted ionic liquid-mediated rapid catalytic conversion of non-edible lignocellulosic Sunn hemp fibres to biofuels

Coupled microwave hydrothermal dechlorination and geopolymer preparation for the solidification/stabilization of heavy metals and chlorine in municipal solid waste incineration fly ash

To improve the degradation efficiency of persistent organic pollutants (POPs) in municipal solid waste incineration fly ash (MSWIFA), as well as to overcome the difficulties of subsequent hydrothermal liquid and hydrothermal slag treatment, a two-step treatment strategy of microwave hydrothermal degradation coupled with geopolymer immobilization was proposed. Results showed that the optimal process parameters for microwave hydrothermal dechlorination were a temperature of 220 °C, a time of 1 h, and NaOH addition of 10 wt%. Microwaves accelerated the OH^- mediated hydrolysis reactions and promoted the breaking of CCl bonds, leading to dechlorination. The compressive strength of the 20 % MSWIFA-based geopolymers reached 75.79 MPa, and the immobilization rate of the heavy metals (HMs) and Cl^- surpassed 90 %. Alkaline environment provided by microwave hydrothermal promoted the formation of Ca(OH)₂, which subsequently formed Friedel's salt (3CaO•Al₂O₃•CaCl₂•10H₂O) with Cl^- in the geopolymer. The charge density difference and density of states (DOS) of Friedel's salt were analyzed by first-principles calculations, confirming that the existence of strong interactions between Ca-s, Al-p, O-p, and Cl-p states was the chemical mechanism of Cl^- immobilization. The Friedel's salt and HMs were encapsulated by geopolymers with dense silica-alumina tetrahedral frameworks, achieving the solidification/stabilization (S/S) of HMs and Cl^-. This work provided a new approach for the environmentally sound and resourceful treatment of MSWIFA.

Novel Challenges on the Catalytic Synthesis of 5-Hydroxymethylfurfural (HMF) from Real Feedstocks

The depletion of fossil resources makes the transition towards renewable ones more urgent. For this purpose, the synthesis of strategic platform-chemicals, such as 5-hydroxymethylfurfural (HMF), represents a fundamental challenge for the development of a feasible bio-refinery. HMF perfectly deals with this necessity, because it can be obtained from the hexose fraction of biomass. Thanks to its high reactivity, it can be exploited for the synthesis of renewable monomers, solvents, and bio-fuels. Sustainable HMF synthesis requires the use of waste biomasses, rather than model compounds such as monosaccharides or polysaccharides, making its production more economically advantageous from an industrial perspective. However, the production of HMF from real feedstocks generally suffers from scarce selectivity, due to their complex chemical composition and HMF instability. On this basis, different strategies have been adopted to maximize the HMF yield. Under this perspective, the properties of the catalytic system, as well as the choice of a suitable solvent and the addition of an eventual pretreatment of the biomass, represent key aspects of the optimization of HMF synthesis. On this basis, the present review summarizes and critically discusses the most recent and attractive strategies for HMF production from real feedstocks, focusing on the smartest catalytic systems and the overall sustainability of the adopted reaction conditions.

Effect of lignin-blocking agent on enzyme hydrolysis of acid pretreated hemp waste

Hemp wastes (stems and branches), fractionated after hemp flower extraction for the production of cannabidiol oil, were utilized as a potentially renewable resource for the sugar flatform process. Hydrolysis of cellulose from the acid pretreated hemp biomass using a commercial enzyme was tested and evaluated for its chemical composition, morphological change, and sugar recovery. Acid pretreated hemp stems and branches, containing 1% glucan (w/v) solids, were hydrolyzed for 72 h using 25 mg enzyme protein per g glucan. A 54% glucose conversion was achieved from the treated branches versus a 71% yield from the treated stems. Raw branches and stems yielded 35% and 38% glucose, respectively. Further tests with a lignin-blocking additive (e.g. bovine serum albumin) resulted in a 72% glucose yield increase for stem hydrolysis using 10 mg enzyme protein per g glucan. While pretreatment promotes amorphous hemicellulose decrease and cellulose decomposition, it causes enzyme inhibition/deactivation due to potential inhibitors (phenols and lignin-derived compounds). This study confirms the addition of non-catalytic proteins enhances the cellulose conversion by avoiding non-productive binding of enzymes to the lignin and lignin-derived molecules, with lignin content determining the degree of inhibition and conversion efficiency.

Chemo-enzymatic approaches for consolidated bioconversion of Saccharum spontaneum biomass to ethanol-biofuel

A novel strategy involving sodium dodecylsulfate (SDS) (SDS assisted tris (2-hydroxyethyl) methyl- ammonium methyl sulphate ([TMA][MeSO₄], ionic liquid) pretreatment of Saccharum spontaneum biomass (SSB) following its enzymatic saccharification, and conversion into ethanol-biofuel in a consolidated bioprocess (CBP) was developed. Ionic liquid stable enzyme preparation developed from Bacillus subtilis G₂ was used for saccharification. Optimized pretreatment and saccharification variables enhanced the sugar yield (2.35-fold), which was fermented to ethanol content of 104.42 mg/g biomass with an efficiency of 35.73%. The pretreated biomass was examined for textural/ultrastructural alterations by scanning electron microscopy (SEM), ¹H/¹³C nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), surface area measurements, water retention value, and cellulase adsorption isotherms. The combined [TMA][MeSO₄] and SDS pretreatment disrupted the lignocellulosic microfibrils, and increased the porosity and surface area. The study provides new mechanistic insights on combined IL and surfactant pretreatment of biomass for its efficient conversion to biofuel.

Conversion of liquid hot water, acid and alkali pretreated industrial hemp biomasses to bioethanol

In this work, four varieties of hemp biomasses (Helena, SS Beta, Tygra, and Elleta Campana) pretreated with liquid hot water (LHW), H₂SO₄, and NaOH were investigated for ethanol production. Physicochemical and morphological properties of the pretreated hemp biomass were characterized. LHW achieved high glucan (85-98%) and xylan (67-71%) recoveries. H₂SO₄ induced significant glucan decomposition (5.9-10.6 g/L) and inhibitor formation (4.5-7.4 g/L of HMF and 2.8-4.5 g/L of furfural) in resulting slurries. Both LHW and H₂SO₄ pretreatments resulted in low glucose and ethanol yields due to recondensed lignin units. NaOH pretreatment achieved high glucose and ethanol yields due to efficient lignin removal (58.6-75.3%). There was no significant variation in ethanol yield among the four hemp varieties pretreated by NaOH. H₂SO₄ and NaOH pretreated biomasses showed apparent terraced-field structures and microporous protuberances. Changes in crystallinity indexes and intensities of FTIR peaks were consistent with enhanced cellulose and decreased amorphous hemicellulose.