Sanjib Kumar Karmee

1. India generates approximately 657 million tonnes of agro-residues every year, of which approximately 230 million tonnes are surplus. This substantial biomass resource represents a significant po...

Growing environmental concerns associated with fossil‐based materials, coupled with their limited reserves, have intensified the global pursuit of renewable alternatives. Among these, natural pigments derived from plants and algae are emerging as promising sustainable resources with diverse industrial applications. This review highlights major categories of natural pigments including chlorophylls, carotenoids, xanthophylls, and phenolics, focusing on their extraction methodologies and significance in food, textile, pharmaceutical, and life sciences industries. Particular emphasis is placed on supercritical carbon dioxide (scCO ₂ ) extraction, an eco‐friendly approach that ensures high selectivity and improves pigment yields under optimized operational conditions. The effect of critical parameters, such as, pressure, temperature, co‐solvent, and extraction time on pigment recovery and quality are evaluated comprehensively. Furthermore, the review addresses current limitations related to scale‐up of scCO ₂ based extraction systems and explores future directions, which includes integration of machine learning tools to enhance process efficiency and pigment recovery.

Glycerol is the main byproduct produced in the oleochemical and biodiesel industries. Surplus crude glycerol devalues commercially available refined glycerol and is perceived as waste. Currently, crude glycerol is mainly used as a low-value, low-energy fuel as well as a feed additive for ruminants. The valorisation of crude glycerol through novel, sustainable processes that generate valuable chemicals is crucial, as this approach creates new revenue streams from this industrial byproduct for both the biodiesel and oleochemical industries. Along this line, glycerol can be converted into diglycerol, which can subsequently be employed to prepare diglycerol dicarbonate. Diglycerol dicarbonate is a potential monomer for the synthesis of biobased Non- Isocyanate Polyurethanes (bio-NIPUs), biomaterials, and surfactants. In this contribution, for the first time, diglycerol dicarbonate was synthesised under microwave irradiation in the absence of a catalyst or solvent. Initially, the reaction was carried out under conventional heating conditions, yielding 56% of the product in 36 hours. Around 88% yield of diglycerol dicarbonate was achieved in 35 minutes when the transesterification of diglycerol with dimethyl carbonate was performed under microwave irradiation. Furthermore, fifteen readily available green catalysts were tested for the carbonyl transfer reaction. The results revealed that the use of catalysts reduced reaction time from 35 to 20 minutes, with 82-95% product yield. The resulting diglycerol dicarbonate product was characterized using 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopy, Infrared (IR) spectroscopy, and melting point measurements. The method described here is environmentally benign as it is performed at a reduced reaction time using green catalysts, resulting in a more sustainable process.

Glycerol is a biogenic waste that is generated in both the biodiesel and oleo-chemical industries. The value addition of surplus glycerol is of utmost importance for making these industries economically profitable. In line with this, glycerol is converted into glycerol carbonate, a potential candidate for the industrial production of polymers and biobased non-isocyanate polyurethanes. In addition, glycerol can also be converted into solketal, which is the protected form of glycerol with a primary hydroxyl functional group. In this contribution, we developed a microwave-assisted solvent and catalyst-free method for converting solketal into solketal carbonate. Under conventional heating conditions, the reaction of solketal with dimethyl carbonate resulted in 70% solketal carbonate in 48 h. However, under microwave heating, 90% solketal carbonate was obtained in just 30 min. From the perspective of sustainability and green chemistry, biomass-derived heterogeneous catalysts are gaining importance. Therefore, in this project, several green catalysts, such as molecular sieves (MS, 4Å), Hβ-Zeolite, Montmorillonite K-10 clay, activated carbon from groundnut shell (Arachis hypogaea), biochar prepared from the pyrolysis of sawdust, and silica gel, were successfully used for the carbonyl transfer reaction. The obtained solketal carbonate was thoroughly characterized by ¹H NMR, ¹³C NMR, IR, and MS. The method presented here is facile, clean, and environmentally benign, as it eliminates the use of complicated procedures, toxic solvents, and toxic catalysts.

Biodiesel and oleo-chemical industries have been producing huge quantities of glycerol as a by-product. Value-added products can be synthesized from glycerol through different chemical and enzymatic reactions, such as oxidation, carbonylation, reforming, acetalyzation, etherification, dehydration, hydrogenolysis, hydrolysis, esterification, and transesterification. Glycerol is a low-cost polyol that can be converted into glycerol carbonate, which has potential applications in polymer and biobased non-isocyanate polyurethanes industries (Bio-NIPUs). The present contribution is the first of its kind to report on the synthesis of glycerol carbonate via catalyst and solvent-free transesterification of glycerol with dimethyl carbonate under conventional as well as microwave heating. Additionally, a comparative study of conventional and microwave-assisted transesterification was performed. Under conventional heating, 78% glycerol carbonate is obtained at 120 o C in 36 hours, whereas, using microwaves, 92% of glycerol carbonate can be achieved in 30 minutes. Presently, biomass-based heterogeneous materials are used in catalysis due to their importance within the context of sustainability. In line with this, in this work, a series of green catalysts, namely, molecular sieves (MS, 4Å), HβZeolite, Montmorillonite K-10 clay, activated carbon prepared from the shell of groundnut (Arachis hypogaea), and biochar from sawdust pyrolysis were successfully employed. Glycerol carbonate was thoroughly characterized by 1 H and 13C NMR, FT-IR and MS. The method described here is facile and green since the utilization of bioresource (glycerol) for the production of glycerol carbonate is performed under microwave.

Biomass-derived furanics play a pivotal role in chemical industries, with 2-methyltetrahydrofuran (2-MTHF), a hydrogenated product of levulinic acid (LA), being particularly significant. 2-MTHF finds valuable applications in the fuel, polymer, and chemical sectors, serving as a key component in P-series biofuel and acknowledged as a renewable solvent for various chemical processes. Numerous research groups have explored catalytic systems to efficiently and selectively convert LA to 2-MTHF, using diverse metal-supported catalysts in different solvents under batch or continuous process conditions. This comprehensive review delves into the impact of metal-supported catalysts, encompassing co-metals and co-catalysts, on the synthesis of 2-MTHF from LA. The article also elucidates the influence of different reaction parameters, such as temperature, type and quantity of hydrogen source, and time. Furthermore, the review provides insights into reaction mechanisms for all documented catalytic systems.