New trends on crude glycerol purification: A review

Getting high purity glycerol at a low cost from biodiesel (methylricinoleate) production is of great economic interest. Therefore, exist several strategies for raw glycerol purification. Some involve liquid-liquid extraction steps using ether, toluene, n-butanol, cyclohexanol, aniline, or solvent mixtures to remove organic impurities from glycerol. However, the phase's equilibrium data is not available for the convenient process design in some cases. This work purified raw glycerol obtained from the alkaline methanolysis of castor oil by neutralization, filtration, distillation, wash with acetone, adsorption with activated charcoal, and drying with sodium sulfate. Furthermore, liquid-liquid equilibrium (LLE) of the ternary system glycerol-acetone-biodiesel was monitored by 1H NMR spectroscopy at 281.15, 290.15, and 299.15 K and correlated by the NRTL model. Finally, we evaluated the COSMO-RS implicit solvation model predictive methodology due to the lack of LLE data for glycerol purification systems in the literature. The experimental results indicate that the process produces glycerol at 96.42% purity wt., and the LLE evaluated consists of two pairs of partially miscible liquids, glycerol-biodiesel, and glycerol-acetone. Therefore, the glycerol purification with acetone proposed here allows less process dangerous conditions, a less toxic product for food applications, eliminates 100% of organic impurities with low volumetric ratios, and helps to precipitate the persistent ash content. The theoretical results indicate COSMO-RS model overestimated the solubility glycerol-acetone, predicting only the pair of partially miscible liquids glycerol-biodiesel, this limiting the accuracy of COSMO-RS to predict LLE data for glycerol purification systems with acetone. 

A theoretical and experimental study of liquid-liquid equilibrium to refine raw glycerol obtained as a byproduct on the biodiesel production

The aim of this work is to synthesise glycerol carbonate from carbon dioxide (CO2) and
glycerol. Two key challenges that were investigated in this work including:
(1) thermodynamic limitation of this work and (2) desirability of using crude glycerol as
a feedstock. In this work, carboxylation of glycerol is carried out over La2O3 (commercial)
and La2O2CO3 catalysts prepared via co-precipitation, sol-gel and hydrothermal methods.
These catalysts are characterised using BET, ATR-FTIR, SEM, XRD, TPD-CO2 and
TPD-NH3.
The carboxylation reaction is thermodynamically limited, therefore a range of dehydrating
agents were introduced to improve the glycerol conversion by shifting the reaction
equilibrium to the product side. The impact of dehydrating agents on glycerol conversion
and glycerol carbonate formation were therefore studied. Reaction conditions were as
follows: 6 wt.% La2O3, relative to glycerol, glycerol to dehydrating agent ratio of
22.5:50 mmol, 160 °C and reaction pressure, 45 bar CO2 and reaction time, 18 hours. High
selectivity to glycerol carbonate is observed upon the introduction of adiponitrile (17%),
followed by benzonitrile (5%), acetonitrile (4%), and no glycerol carbonate was detected
upon the introduction of acetic anhydride.
Additionally this work demonstrated for the first time the efficacy of lanthanum-based
catalysts to synthesise glycerol carbonate via the direct carboxylation of crude glycerol.
Crude glycerol employed herein comprises 74% glycerol, 20% of fatty acid methyl esters,
5 wt.% water, 1% methanol, and 7 g/L of sodium methoxide. It was analysed by GG-MS,
ICP-MS and Karl Fisher titration technique. The impact of single and multiple impurities
are the aspects investigated in this work. The addition of 10 wt.% water inhibited the
formation of glycerol carbonate while blending of glycerol and methanol (80:20 mol%)
increased the selectivity to glycerol carbonate to 22%. Only 4% selectivity to glycerol
carbonate over La2O3-C was observed in the presence of multiple impurities including
methanol, fatty acid methyl ester and sodium methoxide. As a result, modification of
La2O3-C catalyst is crucial. Introduction of ZrO2/La2O2CO3/Ga2O3 greatly improved the
selectivity to glycerol carbonate (21%); while a selectivity of 5% to glycerol carbonate
observed for the direct carboxylation of crude glycerol

The synthesis of glycerol carbonate fromglycerol and carbon dioxide overheterogeneous catalysts

Abstract A combination of different physio‐chemical treatment steps was applied to purify industrially derived crude glycerol at laboratory scale. The full process included acid–base treatments, phase separation, and adsorption, and the glycerol purity and recovery were optimized by varying the pH during saponification and acidification, the solvent‐to‐glycerol ratio, and type of base used in the process to enhance both. The testing campaign resulted in a final purity of up to 87% wt starting from a very low‐quality ‘end‐of‐life’ waste glycerol sampled from different refineries. The net glycerol recovery at laboratory scale reached 42% of the initial glycerol in the feedstock and the maximum ash removal exceeded 90% given the low quality of the feedstock and high content of impurities and the attempt to achieve high glycerol recovery. The experiment showed that mild operations such as saponification with KOH (pH of 8), acidification with H 3 PO 4 (pH of 6), an ideal 2‐propanol to glycerol volume ratio equal to 3 and potassium hydroxide as a base for the neutralisation step were the optimum conditions despite the differences between samples. The sequence of the processes proposed was therefore considered a viable option to treat any kind of crude glycerol to make it profitable for fuel and chemical applications. 

Waste‐derived low‐grade glycerol purification and recovery from biorefineries: an experimental investigation

The effect of concentration and acid types on the acidification process for improving the glycerol concentration and its application as a bio additive

Biodiesel production generates crude glycerol with low purity as a byproduct. It must be purified to increase the economic value of glycerol. Purification can be performed using adsorbent from tea waste. This study aimed to examine the optimum condition of adsorption process, characterize the biosorbent from tea waste and determine the quality of purified glycerol. Crude glycerol was produced by transesterification reaction of used cooking oil with methanol using KOH as a catalyst. The reaction temperature was 60°C which was maintained for 60 minutes.Crude glycerol was separated from biodiesel and added with H3PO4 85% untilthe pH reached ±2.5. Glycerol level after acidification was 77%. After that, adsorption was performed using tea waste which was previously activated by 0.05 M NaOH. Adsorption process was conducted by varying contact time (30, 60, 75, 90 and 120 minutes), adsorption temperature (30, 45, 60 and 75°C), biosorbent concentration (6, 9, 12, 15 and 18 %) andbiosorbent particle size (180, 250 and 630 μm). The highest glycerol level (95.9544%) was achieved by setting the contact time for 90 minutes, adsorption temperature at 60°C, biosorbent concentrationat 12% andparticle sizeat 180 μm. The glycerol obtained from this process meets the quality requirements set bySNI06-1564-1995with water content3%,ash content0.3% andMONG level 0.7%. In addition, the purifiedglycerol had density 1.26 g/mL, potassium metal content 107 ppm andhad no sugar.There were alterations in functional group and surface morphology of tea waste after the adsorption took place.

https://iopscience.iop.org/article/10.1088/1755-1315/175/1/012010/pdf

Purification of Crude Glycerol from Acidification Using Tea Waste

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Purification of Crude Glycerol from Acidification Using Tea Waste