Organic Carbonate Production Utilizing Crude Glycerol Derived as By-Product of Biodiesel Production: A Review

A systematic review on utilization of biodiesel-derived crude glycerol in sustainable polymers preparation

With the rapid development of biodiesel, biodiesel-derived glycerol has become a promising renewable bioresource. The key to utilizing this bioresource lies in the value-added conversion of crude glycerol. While purifying crude glycerol into a pure form allows for diverse applications, the intricate nature of this process renders it costly and environmentally stressful. Consequently, technology facilitating the direct utilization of unpurified crude glycerol holds significant importance. It has been reported that crude glycerol can be bio-transformed or chemically converted into high-value polymers. These technologies provide cost-effective alternatives for polymer production while contributing to a more sustainable biodiesel industry. This review article describes the global production and quality characteristics of biodiesel-derived glycerol and investigates the influencing factors and treatment of the composition of crude glycerol including water, methanol, soap, matter organic non-glycerol, and ash. Additionally, this review also focused on the advantages and challenges of various technologies for converting crude glycerol into polymers, considering factors such as the compatibility of crude glycerol and the control of unfavorable factors. Lastly, the application prospect and value of crude glycerol conversion were discussed from the aspects of economy and environmental protection. The development of new technologies for the increased use of crude glycerol as a renewable feedstock for polymer production will be facilitated by the findings of this review, while promoting mass market applications.

Glycerol carbonate synthesis via transesterification of enriched glycerol and dimethyl carbonate using a Li-incorporated MCM-41 framework

Waste crude glycerol was successfully enriched and utilized as an inexpensive source for producing value-added chemicals, such as glycerol carbonate (GC) - a valuable compound with extensive industrial applications. The Li/MCM-41 heterogeneous catalyst was synthesized and used for the transesterification of enriched glycerol and dimethyl carbonate (DMC) to produce GC. The catalyst's physicochemical properties were characterized using thermogravimetric, Hammett indicator, inductively coupled plasma-optical emission spectroscopy, nitrogen adsorption-desorption, X-ray diffractometry, scanning electron microscopy, and Fourier-transform infrared spectroscopy analyses. Reaction conditions were optimized using response surface methodology and analysis of variance, yielding an accurate quadratic model to predict the GC yield under different transesterification variables. The results revealed that 5%Li/MCM-41 served as the optimal catalyst, achieving the highest TOF of 4.72 h-1. The DMC: enriched glycerol molar ratio had the greatest impact on the GC yield, with an R2 = 0.9743 and adjusted R2 = 0.9502. The optimal GC yield (58.77%) with a final purity of 78% was attained at a 5.15 wt% catalyst loading relative to the initial amount of enriched glycerol, DMC: enriched glycerol molar ratio of 4.24 : 1, and a reaction temperature of 86 °C for 165 min. The 5%Li/MCM-41 heterogeneous catalyst could be reused for four cycles with a decreased GC yield from 58.77% to 45.72%. Thus, the Li/MCM-41 catalyst demonstrated a remarkable efficiency and potential as a heterogeneous catalyst for synthesizing GC. This method not only contributes to environmental sustainability by making use of a byproduct from biodiesel production but also aligns with the principles of a circular economy.

Electrochemical Valorization of Glycerol via Electrocatalytic Reduction into Biofuels: A Review

Electrochemical conversion of underutilized biomass-based glycerol into high-value-added products provides a green approach for biomass and waste valorization. Plus, this approach offers an alternative to biofuel manufacturing procedure, under mild operating conditions, compared to the traditional thermochemical routes. Nevertheless, glycerol has been widely valorized via electrooxidation, with lower-value products generated at the cathode, ignoring the electroreduction. Here, a review of the efficient glycerol reduction into various products via the electrocatalytic reduction (ECR) process was presented. This review has been built upon the background of glycerol underutilization and theoretical knowledge about the state-of-the-art ECR. The experimental understanding of the processing parameter influences towards electrochemical efficiency, catalytic activity, and product selectivity are comprehensively reviewed, based on the recent glycerol ECR studies. We conclude by outlining present issues and highlighting potential future research avenues for enhanced ECR application.

Upgrading Major Waste Streams Derived from the Biodiesel Industry and Olive Mills via Microbial Bioprocessing with Non-Conventional Yarrowia lipolytica Strains

This study reports the development of a bioprocess involving the valorization of biodiesel-derived glycerol as the main carbon source for cell proliferation of Yarrowia lipolytica strains and production of metabolic compounds, i.e., citric acid (Cit), polyols, and other bio-metabolites, the substitution of process tap water with olive mill wastewater (OMW) in batch fermentations, and partial detoxification of OMW (up to 31.1% decolorization). Increasing initial phenolics (Phen) of OMW-glycerol blends led to substantial Cit secretion. Maximum Cit values, varying between 64.1–65.1 g/L, combined with high yield (YCit/S = 0.682–0.690 g Cit/g carbon sources) and productivity (0.335–0.344 g/L/h) were achieved in the presence of Phen = 3 g/L. The notable accumulation of endopolysaccharides (EPs) on the produced biomass was determined when Y. lipolytica LMBF Y-46 (51.9%) and ACA-YC 5033 (61.5%) were cultivated on glycerol-based media. Blending with various amounts of OMW negatively affected EPs and polyols biosynthesis. The ratio of mannitol:arabitol:erythritol was significantly affected (p < 0.05) by the fermentation media. Erythritol was the major polyol in the absence of OMW (53.5–62.32%), while blends of OMW-glycerol (with Phen = 1–3 g/L) promoted mannitol production (54.5–76.6%). Nitrogen-limited conditions did not favor the production of cellular lipids (up to 16.6%). This study addressed sustainable management and resource efficiency enabling the bioconversion of high-organic-load and toxic waste streams into valuable products within a circular bioeconomy approach.

Transformation of CO2 with Glycerol to Glycerol Carbonate over ETS-10 Zeolite-Based Catalyst

Catalytic conversion of CO₂ with the surplus glycerol (GL) produced from biodiesel manufacturing has attracted much academic and industrial attention, which proves the urgent requirement for developing high-performance catalysts to afford significant environmental benefits. Herein, titanosilicate ETS-10 zeolite-based catalysts with active metal species introduced by impregnation were employed for coupling CO₂ with GL to efficiently synthesize glycerol carbonate (GC). The catalytic GL conversion at 170 °C miraculously reached 35.0% and a 12.7% yield of GC was obtained on Co/ETS-10 with CH₃CN as a dehydrating agent. For comparison, Zn/ETS- Cu/ETS-10, Ni/ETS-10, Zr/ETS-10, Ce/ETS-10, and Fe/ETS-10 were also prepared, which showed inferior coordination between GL conversion and GC selectivity. Comprehensive analysis revealed that the presence of moderate basic sites for CO₂ adsorption-activation played a crucial role in regulating catalytic activity. Moreover, the appropriate interaction between cobalt species and ETS-10 zeolite was also of great significance for improving the glycerol activation capacity. A plausible mechanism was proposed for the synthesis of GC from GL and CO₂ in the presence of CH₃CN solvent over Co/ETS-10 catalyst. Moreover, the recyclability of Co/ETS-10 was also measured and it proved to be recycled at least eight times with less than 3% decline in GL conversion and GC yield after a simple regeneration process through calcination at 450 °C for 5 h in air.

Efficient Propylene Carbonate Synthesis from Urea and Propylene Glycol over Calcium Oxide-Magnesium Oxide Catalysts

A series of calcium oxide-magnesium oxide (CaO-MgO) catalysts were prepared under the effects of different precipitating agents and using varied Mg/Ca ratios. The physiochemical characteristics of the prepared catalysts were analyzed using XRD, FE-SEM, BET, FTIR, and TG/DTA techniques. Quantification of basic active sites present on the surface of the CaO-MgO catalysts was carried out using the Hammett indicator method. The as-prepared mixed oxide samples were tested for propylene carbonate (PC) synthesis through the alcoholysis of urea with propylene glycol (PG). The effects of the catalyst composition, catalyst dose, reaction temperature, and contact time on the PC yield and selectivity were investigated. The maximum PC yield of 96%, with high PC selectivity of 99% and a urea conversion rate of 96%, was attained at 160 °C using CaO-MgO catalysts prepared using a Mg/Ca ratio of 1 and Na₂CO₃ as a precipitating agent. The best-performing catalysts also exhibited good reusability without any significant loss in PC selectivity. It is expected that the present study will provide useful information on the suitability of different precipitating agents with respect to the catalytic properties of the oxides of Ca and Mg and their application in the synthesis of organic carbonates.

Fabrication of novel buckypaper metal oxide nano-catalysis glycerol carbonate/MWCNTs membrane for efficient removal of heavy metals

This study describes the fabrication of novel buckypaper membranes through the dispersion of multi-walled carbon nanotubes (MWCNTs) in the presence of surfactants metal oxide nano-catalysis Zinc oxide and magnesium oxide (ZnO and MgO) glycerol carbonate separately. Following vacuum filtration of the scattered solutions, self-supporting membranes known as buckypapers (BPs) were produced. The suggested membranes were employed for the efficient removal of heavy metals. The obtained data indicated that the incorporation of both glycerol carbonates prepared by two different nano metal oxides enhanced the permeability of MWCNTs membranes rejection efficiency. The characterization of the synthesized metal oxide nanoparticles, as well as the physicochemical and morphological properties of the membranes, were investigated. The rejection capabilities of membranes for the heavy metal ions were examined. Moreover, the suggested MWCNTs/ZnO nano-catalyst glycerol carbonate BP membrane displayed high rejection efficiency for heavy metals (Cd²⁺, Cu²⁺, Co²⁺, Ni²⁺, and Pb²⁺) than that prepared from the MgO nano-catalyst one.

Upgrading of Biobased Glycerol to Glycerol Carbonate as a Tool to Reduce the CO2 Emissions of the Biodiesel Fuel Life Cycle

With regards to oil-based diesel fuel, the adoption of bio-derived diesel fuel was estimated to reduce CO₂ emissions by approximately 75%, considering the whole life cycle. In this paper, we present a novel continuous-flow process able to transfer an equimolar amount of CO₂ (through urea) to glycerol, producing glycerol carbonate. This represents a convenient tool, able to both improve the efficiency of the biodiesel production through the conversion of waste streams into added-value chemicals and to beneficially contribute to the whole carbon cycle. By means of a Design of Experiments approach, the influence of key operating variables on the product yield was studied and statistically modeled.

Enantioseparation of syn- and anti-3,5-Disubstituted Hydantoins by HPLC and SFC on Immobilized Polysaccharides-Based Chiral Stationary Phases

The enantioseparation of syn- and anti-3,5-disubstituted hydantoins 5a–i was investigated on three immobilized polysaccharide-based columns (CHIRAL ART Amylose-SA, CHIRAL ART Cellulose-SB, CHIRAL ART Cellulose-SC) by high performance liquid chromatography (HPLC) using n-hexane/2-PrOH (90/10, v/v) or 100% dimethyl carbonate (DMC) as mobile phases, respectively, and by supercritical fluid chromatography (SFC) using CO2/alcohol (MeOH, EtOH, 2-PrOH; 80/20, v/v) as a mobile phase. The chromatographic parameters, such as separation and resolution factors, have indicated that Amylose-SA is more suitable for enantioseparation of the most analyzed syn- and anti-3,5-disubstituted hydantoins than Celullose-SB and Cellulose-SC in both HPLC and SFC modalities. All three tested columns showed better enantiorecognition ability toward anti-hydantoins compared to syn-hydantoins, both in HPLC and SFC modes. We have demonstrated that environmentally friendly solvent DMC can be efficiently used as the mobile phase in HPLC mode for enantioseparation of hydantoins on the immobilized polysaccharide-based chiral stationary phases.

Perspectives for the Upgrading of Bio-Based Vicinal Diols within the Developing European Bioeconomy

The previous decade has witnessed a drastic increase of European incentives aimed at pushing forward the transition from an exclusively petro-based economy toward a strong and homogeneous bio-based economy. Since 2012, numerous programs have been developed to stimulate and promote research and innovation relying on sustainable and renewable resources. Terrestrial biomass is a virtually infinite reservoir of biomacromolecules, the biorefining of which provides platform molecules of low complexity yet with tremendous industrial potential. Among such bio-based platform molecules, polyols and, more specifically, molecules featuring vicinal diols have gained tremendous interest and have stimulated an increasing research effort from the chemistry and chemical engineering communities. This Review revolves around the most promising process conditions and technologies reported since 2012 that specifically target bio-based vicinal diols and promote their transformation into value-added molecules of wide industrial interest, such as olefins, epoxides, cyclic carbonates, and ketals.

An Overview of the Latest Advances in the Catalytic Synthesis of Glycerol Carbonate

In recent years, the development of renewable energy alternatives to traditional fossil fuels has become one of the major challenges all over the world, due to the decline of fossil fuel reserves and their effect on global warming. Biodiesel has become a popular alternative energy source to reduce gas emissions compared to traditional fossil fuels. According to statistics, a nine-fold increase in global biofuel production between 2000 and 2020 was observed. However, its production generates a large amount of glycerol as a by-product, posing an environmental problem when disposed directly in landfills or by incineration. Therefore, low-value glycerol should be converted into high value-added derivatives. As glycerol carbonate is one of the most important derivatives of glycerol, this review aims to discuss the studies over the last ten years about glycerol carbonate synthetic methods, including the typical routes such as phosgene, esterification reaction, urea, oxidative and direct carbonylation as well as several rare synthetic procedures. At the same time, it summarizes the different catalytic reaction systems of each route comparing the advantages and disadvantages of various catalysts and evaluating their catalytic activity. Finally, the future development of glycerol carbonate synthesis is prospected from the point of view of development, technology research and industrialization.

Process and Energy Intensification of Glycerol Carbonate Production from Glycerol and Dimethyl Carbonate in the Presence of Eggshell-Derived CaO Heterogeneous Catalyst

The process and energy intensifications for the synthesis of glycerol carbonate (GC) from glycerol and dimethyl carbonate (DMC) using an eggshell-derived CaO heterogeneous catalyst were investigated. The transesterification reaction between glycerol and DMC was typically limited by mass transfer because of the immiscible nature of the reactants. By varying the stirring speed, it was observed that the mass transfer limitation could be neglected at 800 rpm. The presence of the CaO solid catalyst made the mass transport-limited reaction process more prominent. Mass transfer intensification using a simple kitchen countertop blender as an alternative to overcome the external mass transfer limitation of a typical magnetic stirrer was demonstrated. A lower amount of the catalyst and a shorter reaction time were required to achieve 93% glycerol conversion or 91% GC yield, and the turnover frequency (TOF) increased almost 5 times from 1.5 to 7.2 min−1 when using a conventional magnetic stirrer and countertop blender, respectively. In addition, using a simple kitchen countertop blender with 7200 rpm, the reaction temperature of 60 °C could be reached within approximately 3 min without the need of a heating unit. This was the result of the self-frictional heat generated by the high-shear blender. This was considered to be heat transfer intensification, as heat was generated locally (in situ), offering a higher homogeneity distribution. Meanwhile, the trend toward energy intensification was promising as the yield efficiency increased from 0.064 to 2.391 g/kJ. A comparison among other process intensification techniques, e.g., microwave reactor, ultrasonic reactor, and reactive distillation was also rationalized.

Glycerol waste to value added products and its potential applications

The rapid industrial and economic development runs on fossil fuel and other energy sources. Limited oil reserves, environmental issues, and high transportation costs lead towards carbon unbiased renewable and sustainable fuel. Compared to other carbon-based fuels, biodiesel is attracted worldwide as a biofuel for the reduction of global dependence on fossil fuels and the greenhouse effect. During biodiesel production, approximately 10% of glycerol is formed in the transesterification process in a biodiesel plant. The ditching of crude glycerol is important as it contains salt, free fatty acids, and methanol that cause contamination of soil and creates environmental challenges for researchers. However, the excessive cost of crude glycerol refining and market capacity encourage the biodiesel industries for developing a new idea for utilising and produced extra sources of income and treat biodiesel waste. This review focuses on the significance of crude glycerol in the value-added utilisation and conversion to bioethanol by a fermentation process and describes the opportunities of glycerol in various applications.

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Kinetic Studies of the Glycerolysis of Urea to Glycerol Carbonate in the Presence of Amberlyst-15 as Catalyst

Amberlyst-15, a strong acidic ion-exchange resin, has showed as a potential and an effective catalyst for the glycerolysis process of urea to glycerol carbonate. In this work, the kinetic model of the urea glycerolysis over Amberlyst-15 catalyst was investigated. The kinetic model was developed by considering simultaneous steps of urea dissolution in glycerol, mass transfer of urea and glycerol from the bulk of the liquid into the outer part of the catalyst, diffusion of urea and glycerol into the inner part of the particle through the catalyst pores, and irreversible second order reaction of urea and glycerol on the active sites. The irreversibility of second order reaction of urea glycerolysis was validated and proven. The proposed kinetic model was simulated and validated with the experimental data. The kinetic studies show that mechanism proposed works well. Furthermore, the activation energy was found to be 145.58 kJ.mol−1 and the collision factor was in 8.00×1010 (m3)2.kg−1.mol−1.s−1. The simulation result shows that the predicted liquid temperatures were close to the experimental temperature data. It also gave glycerol concentration profile inside the catalyst particle as a function of glycerolysis time and position. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Optimizing Docosahexaenoic Acid (DHA) Production by Schizochytrium sp. Grown on Waste Glycerol

The aim of this study was to optimize biomass and docosahexaenoic acid (DHA) production by Schizochytrium sp. grown on waste glycerol as an organic carbon source. Parameters having a significant effect on biomass and DHA yields were screened using the fractional Plackett–Burman design and the response surface methodology (RSM). Schizochytrium sp. growth was most significantly influenced by crude glycerin concentration in the growth medium (150 g/dm3), process temperature (27 °C), oxygen in the bioreactor (49.99% v/v), and the concentration of peptone as a source of nitrogen (9.99 g/dm3). The process parameter values identified as optimal for producing high DHA concentrations in the biomass were as follows: glycerin concentration 149.99 g/dm3, temperature 26 °C, oxygen concentration 30% (v/v), and peptone concentration 2.21 g/dm3. The dry cell weight (DCW) obtained under actual laboratory conditions was 66.69 ± 0.66 g/dm3, i.e., 1.27% lower than the predicted value. The DHA concentration obtained in the actual culture was at 17.25 ± 0.33 g/dm3, which was 3.03% lower than the predicted value. The results obtained suggest that a two-step culture system should be employed, with the first phase focused on high production of Schizochytrium sp. biomass, and the second focused on increasing DHA concentration in the cells.

New Glycerol Upgrading Processes

Energy policies in the US and in the EU during the last decades have been focused on enhanced oil and gas recovery, including the so-called tertiary extraction or enhanced oil recovery (EOR), on one hand, and the development and implementation of renewable energy vectors, on the other, including biofuels as bioethanol (mainly in US and Brazil) and biodiesel (mainly in the EU) [...]