13th International Colloquium Fuels - September 2021 71 Novel purification routes for crude glycerol from biodiesel plants as a suitable feedstock for sustainable aviation fuel Taha Attarbachi University of Manchester, Manchester, UK taha.attarbachi@postgrad.manchester.ac.uk Martin Kingsley Argent Energy Ltd., Ellesmere Port, UK martin.kingsley@argentenergy.com Dr. Vincenzo Spallina University of Manchester, Manchester, UK vincenzo.spallina@manchester.ac.uk Summary GLAMOUR (Glycerol to Aviation and Marine prOducts with sUstainable recycling) is a H2020 research project looking to demonstrate the conversion of bio-waste feedstock such as glycerol into jetfuel and marine diesel oil by combining syngas generation with inherent CO2 removal using gas solid reactions. A special emphasis is put on the integration into existing biodiesel manufacturing facilities. For a reliable working process, the feedstock must be pre-treated and all inorganic material must be removed in order to avoid poisoning of the catalyst. This manuscript concentrates on the most efficient removal of ashes in the crude glycerol of Argent Energy. Therefore, a simple splitting step was utilized in order to encourage a phase separation of the highly viscous, dark crude glycerol. The influence of water on this splitting step is presented. A reduction of the initial ash content by 50 wt.% could be achieved in preliminary experiments. 1. Introduction Biofuels are pillars of a sustainable society and will play a significant relevant role in the coming decades and are superseding conventional fossil fuels increasingly. The EU set a target of 10 % for renewable energy use in transport for 2020 and increased this number to 14% for the year 2030 [1]. In particular, the aspect of increasing sustainability of biofuel production will play a more important role as the target increases. Advanced biofuels are considered the same product as first generation biofuels but utilizing waste-based, non-food feedstocks [2]. In the case of biodiesel this development has a significant impact due to the substitution of using waste-feedstocks such as tallow or used cooking oil instead of palm oil. However, in both cases a transesterification reaction is applied which yields by-product glycerol which is more impure when waste-based feedstocks are used. Hence, a big problem with an excess supply of highly impure glycerol arose during the last years which has been incinerated, used for cattle feed [3-4], biogas [5-6] generation or even disposed. Glycerol, also known as Propane-1,2,3-triol, is a relevant product in our daily lives. It is a major component in the personal care and pharmaceutical industry due to its antimicrobial and antiviral properties, used as a sweetener in the food industry and is in its crude form subject to research for technical applications such as gasification for the production of hydrogen and others [7]. Early in the 20th century glycerol was produced primarily as a by-product of the saponification of fats and was used as a raw material for the production of nitroglycerine. During the 1st world war glycerol became a strategic resource and therefore the demand exceeded the supply leading to the first synthetic plants for the production of glycerol by microbial sugar fermentation. Furthermore, the replacement of natural soaps with synthetical washing detergents has led to an increase in glycerol demand which accelerated the shift towards competitive petrochemical (synthetic) production routes. German, I.G. Farben used the high-temperature chlorination of propene to allyl chlore process to produce glycerol [8]. About 25% of the global glycerol demand was met by the petrochemical synthesis from propylene before the introduction of biodiesel into the market 72 13th International Colloquium Fuels - September 2021 Novel purification routes for crude glycerol from biodiesel plants as a suitable feedstock for sustainable aviation fuel in the early 2000s. The other 75% was obtained by the saponification of fats[9]. With the emergence of the biodiesel industry, the market changed significantly due to an excess supply of crude glycerol provided based on vegetable oils as well as waste feedstocks such as tallow, used cooking oil or even more impure feedstocks. During the transesterification reaction of triglycerides with methanol approximately 10 wt.% of glycerol is produced as a by-product. Hence, the biodiesel industry became the main supplier of glycerol for the world market leading to a lack of interdependence between supply and demand of glycerol. Since most of the crude glycerol cannot be utilized due to major impurities, it is highly relevant to review conventional and most importantly recent and novel purification methods to prevent further excess supply of impure crude glycerol to the market. This manuscript presents a simple method to reduce the amount of ashes significantly 2. Materials 2.1 Chemicals The feedstocks used for the experiments are provided by Argent Energy Ltd. Depending on the location where the crude glycerol is drawn off at the plant, it has an almost black colour (Fig. 1a), is highly viscous or is yellowish and less viscous. In both cases, the crude glycerol contains about 35-75 wt.% glycerol. In table 1 the crude glycerol composition which was used in these experiments can be found. Table 1: Crude glycerol composititon. Glycerol [% w/ w] 57.8% Water [% w/ w] 11.5% Ash [% w/ w] 12.7% MONG [% w/ w] 18.0% pH [-] 5.7 85% Phosphoric acid from Emsure was used as an acidification agent while for the neutralization reaction 12.5 M potassium hydroxide from Sigma Aldrich was used. As a solvent 2-Propanol from Sigma Aldrich was used due to its high availability and high polarity. Activated carbon WP220-90 from Pulsorb was used for the finishing step and VWR 303 filter paper. 2.2 Analysis The analysis of the probes were conducted according to the British standards. Glycerol content was analysed according to BS 5711-3-1979. Water content was measured according to BS 5711-8-1979. Ash content was measured according to BS 5711-6-1979. 3. Experimental The first attempts to purify the glycerol were based on procedures in the literature, mainly based on Manosak et al. [10]derived from a waste used-oil utilizing biodiesel (methyl ester and Kongjao et al. [11]. These procedures did not work due to the highly viscous, dark organic content which was mixed with the glycerol, resulting in an emulsion. Acidification, neutralization and subsequent addition of alcohol did not show the expected results. Hence, in a first step the emulsion was stirred at 200-500 rpm for 30 min and poured into a separatory funnel to encourage phase splitting. This was also done with the addition of some water. 3.1 Addition of Water To understand the effect of water, a serial experiment was set up. 100 g of crude glycerol was mixed with 200-5 g of water under stirring at 200-500 rpm for 30 min. The mixture was subsequently poured into a separatory funnel for overnight separation. 3.2 Acidification After the phase separation, the mixture was acidified. During the acidification step, the pH was reduced to 2.5 at 200-500 rpm for 60 minutes at ambient temperature. After the acidification, the mixture was poured into a separatory funnel. 3.3 Neutralization For the neutralization potassium hydroxide was used. The neutralization reaction was conducted at ambient temperature a stirring speed of 200-500 rpm and a time of 60 min. After the neutralization the mixture was poured into a separatory funnel to let the salts precipitate. 3.4 Solvent extraction For the solvent extraction, a ratio of 2: 1 (v/ v) of 2-propanol was poured into the mixture and stirred for 20 min at 200-500 rpm. Due to the turbulence in the beaker, the mixture was again poured into a separatory funnel to encourage further precipitation of salts and overnight phase separation. 13th International Colloquium Fuels - September 2021 73 Novel purification routes for crude glycerol from biodiesel plants as a suitable feedstock for sustainable aviation fuel 3.5 Evaporation The evaporation of the solvent was conducted at 85°C for 20 min at a stirring rate of 200-500 rpm. Prior to the evaporation, the mixture was separated by vacuum filtration to remove any precipitated salts. 3.6 Adsorption In the last step, activated carbon (PULSORB WPS230- 90) was used to remove any colour and residual organic contact with a smaller molecular size. Therefore, about 100g/ L were added to a beaker with the evaporated solvent in it and stirred for two hours at 200-500 rpm. 3.7 Vacuum filtration The blackish mixture was subsequently vacuum filtrated with 303 filtrate paper. 4. Results At this stage only for the first splitting step quantitative results are available. 4.1 Splitting step The first, simple splitting step had a significant effect on the crude glycerol (Fig. 1a). After a settling time of 24 h in a separatory funnel, the emulsion separated into two phases: a top organic layer which was entirely black and a bottom aqueous layer consisting most likely of glycerol, water and some short-chain organics which are soluble in the aqueous layer (Fig.1c). The layers were decanted with an average ratio of 80 wt.% aqueous and 20 wt.% organic layer. The addition of water (Fig. 1b) led to reduced settling time, a brighter aqueous layer, less viscous aqueous and organic layer and a sharper interphase between both phases which improved the decanting. The more water added, the brighter the aqueous phase which can also be seen in figure 2. The analysis of the water splitting step yielded the results in table 2. By reducing the amount of water, the amount of ashes are reduced as well. Table 2 Similar results are achieved by using no water for the splitting step. The ash content could be reduced to 7.68 wt.% reducing it by approximately 40%. After the solvent extraction, two phases were yielded (Fig. 1d). A top alcohol-glycerol phase and a bottom salt phase which was separated by vacuum filtration. After the addition of activated carbon, the mixture was vacuum filtrated again and a transparent mixture was yielded (Fig. 1e). 5. Conclusion and Outlook The splitting step is a quick, simple and cheap way to separate crude glycerol in the first step and prepare it for subsequent steps. Adding some deionized water to this step will lead even to brighter colour of the aqueous phase and less viscosity, making the handling of the material easier. Furthermore, with the splitting a reduction of ash content by approximately 40% was reached. In the future further experiments with deep refining technologies are expected to be conducted, namely ion-exchange chromatography, electrodialysis and adsorption with waste based materials. Furthermore, additional efforts will be made to utilize the residual organic top layer in the future to avoid further waste and close the entire value chain. [1] B. Flach, S. Lieberz, and S. Bolla, “GAIN Report - EU Biofuels Annual 2019,” Glob. Agric. Inf. Netw., p. 52, 2019, [Online]. Available: https: / / apps.fas. usda.gov/ newgainapi/ api/ report/ downloadreportbyfilename? filename=Biofuels Annual_The Hague_EU-28_7-15-2019.pdf. [2] M. M. K. Bhuiya, M. G. Rasul, M. M. K. Khan, N. Ashwath, and A. K. Azad, “Prospects of 2nd generation biodiesel as a sustainable fuel - Part: 1 selection of feedstocks, oil extraction techniques and conversion technologies,” Renew. Sustain. Energy Rev., vol. 55, pp. 1109-1128, 2016, doi: 10.1016/ j. rser.2015.04.163. [3] V. R. Fávaro et al., “Glicerina na alimentaç-o de bovinos de corte: Consumo, digestibilidade, parâmetros ruminais e sanguíneos,” Semin. Agrar., vol. 36, no. 3, pp. 1495-1505, 2015, doi: 10.5433/ 1679-0359.2015v36n3p1495. [4] L. E et al., “Crude Glycerol: By-Product of Biodiesel Industries As an Alternative Energy Source for Livestock Feeding,” J. Exp. Biol. Agric. Sci., vol. 5, no. 6, pp. 755-766, 2017, doi: 10.18006/ 2017.5(6).755.766. [5] J. Á. Siles López, M. de los Á. Martín Santos, A. F. Chica Pérez, and A. Martín Martín, “Anaerobic digestion of glycerol derived from biodiesel manufacturing,” Bioresour. Technol., vol. 100, no. 23, pp. 5609-5615, 2009, doi: 10.1016/ j.biortech.2009.06.017. [6] Q. (Sophia) He, J. McNutt, and J. Yang, “Utilization of the residual glycerol from biodiesel production for renewable energy generation,” Renew. Sustain. Energy Rev., vol. 71, no. January, pp. 63-76, 2017, doi: 10.1016/ j.rser.2016.12.110. 74 13th International Colloquium Fuels - September 2021 Novel purification routes for crude glycerol from biodiesel plants as a suitable feedstock for sustainable aviation fuel [7] H. W. Tan, A. R. A. Aziz, and M. K. Aroua, “Glycerol production and its applications as a raw material: A review,” 2013, doi: 10.1016/ j.rser.2013.06.035. [8] T. Seidensticker and A. Behr, Einführung in die Chemie nachwachsender Rohstoffe, vol. 4, no. 1. 2016. [9] R. Ciriminna, C. Della Pina, M. Rossi, and M. Pagliaro, “Special Feature Understanding the glycerol market,” pp. 1432-1439, 2014, doi: 10.1002/ ejlt.201400229. [10] R. Manosak, S. Limpattayanate, and M. Hunsom, “Sequential-refining of crude glycerol derived from waste used-oil methyl ester plant via a combined process of chemical and adsorption,” Fuel Process. Technol., vol. 92, no. 1, pp. 92-99, 2011, doi: 10.1016/ j.fuproc.2010.09.002. [11] S. Kongjao and S. Damronglerd, “Purification of crude glycerol derived from waste used-oil methyl ester plant,” vol. 27, no. 3, pp. 944-949, 2010, doi: 10.1007/ s11814-010-0148-0. Figure 1: Different glycerol purification steps. (a) crude glycerol (b) glycerol after addition of 5g DI-water (c) glycerol after splitting step without water (d) glycerol after solvent addition and overnight separation (e) purified glycerol after adsorption Figure 2: Water splitting step with increasing mass of water from left to right by constant crude glycerol mass.