# Improving Sorbents for Glycerol Capture in Biodiesel Refinement
## 4 Conclusions  
This study examined the potential for utilization of hierarchical organosilicate materials for the capture of glycerol as a representative biodiesel contaminant. Sulfonation of the sorbents promotes hydrogen bonding interactions and provides surface-target interactions similar to those of several commercially available sorbent materials, for example, Amberlite(tm) BD10 DRY. The varied chemical compositions used in organosilicate sorbent synthesis provide differing points within the frameworks for sulfonation as well as varied total site content. This study demonstrated the importance of access to the total surface area for optimal performance characteristics. Higher affinity could be achieved through a greater degree of sulfonation, but performance suffered due to a loss in access to the total surface of the sorbent associated with morphological collapse. D13-Ph2(5) provides a compromise between degree of sulfonation and the resulting damage to sorbent morphology. This material provides the best per mass binding of the sorbents evaluated here in both aqueous solution and in biodiesel. The open morphology of the sorbents, in addition to providing binding site access, provides reduced resistance to flow when the materials are used in a column format [20; 33]. This may prove useful for application relevant formats. Wood pulp-based materials like BD ZorbX offer extremely low backpressures but suffer from the resulting short contact times and low saturation capacities. Ongoing work with these sorbents is focused on their potential for binding other classes of contaminants from biodiesel such as fatty acids and surfactants. Binding of multiple targets is possible using the sorbents described here; some preliminary data on the binding of surfactants from biodiesel has been collected. This additional capability is similar to that of the commercial sorbents described in the introduction. Binding of targets other than glycerol could reduce binding of this target. However, surfactants would be expected to occur at significantly lower concentrations than that of glycerol and would likely have minimal impact. Designing an effective dry wash media based on these organosilicate sorbents would likely require a combination of sorbents providing glycerol capacity as well as capacity for catalysts and surfactants. Increase of production scale will also be necessary for any applications. The materials described here are synthesized on the single gram scale. We have scaled synthesis of the ethane-diethylbenzene sorbents (ED11) to produce tens of ggrams simply by increasing the capacity of vessel utilized. Ongoing work seeks to develop protocols for larger scale production and to identify considerations of import to commercial scale synthesis. The introduction mentions the potential for cost offset through recovery and repurposing of the glycerol byproduct. This effort did not focus on purification of glycerol. However, we have previously demonstrated the use of this type of sorbent in solid phase extraction for increasing the concentration of perchlorate and nitroenergetic targets [20; 25; 29; 33]. In these cases, the target is adsorbed from aqueous solution and eluted from the sorbent using a solvent or an acid containing solution. Elution of glycerol from a sorbent column would likely require the use of a salt containing aqueous solution or a mixture of solvents. This process would not necessarily produce purified glycerol: the eluent would be expected to contain the mixture of targets that were adsorbed by the materials. Research into this potential application as well as scale up and capture of additional targets is ongoing.