Synthesis Of Butyl Glycerol Ethers On Sulfonated Graphene

Glycerol is a renewable resource, which is available from the saponification and the biodiesel-production of animal fat and vegetable oil or from the cellulolytic fermentation process. With the increasing glycerol production, great interest has been addressed to the catalytic etherification of glycerol with isobutene or tert-butanol to form butyl glycerol ethers,among which DTBGs(2,3-di-tert-butoxy-1-propanol and 1,3-di-tert-butoxy-2-propanol) and TTBG(1,2,3-tri-tert-butoxy propane), the so-called “multi-butyl glycerol ethers”, can be used as additives for diesel and biodiesel reformulation. In this study, sulfonated graphene catalyst was synthesized and tested for the etherification of glycerol with isobutene or tert-butanol.Characterizations with various tools such as TEM, SEM, AFM, XRD, TGA etc. were carried out aiming to correlate the catalyst’s physical and chemical properties with its catalytic performance. Special attention was paid to develop a simple but efficient method for product isolation as well as catalyst recycle.The TEM and SEM images as well as AFM image of the sulfonated graphene(SG)showed two-dimensional feature of the catalyst with clear layer. The same weight loss behaviors of the fresh and spent SG catalysts demonstrated the good thermal stability of the catalyst during the reaction. With its ultra thin two-dimensional open substrate, stable sulfonic acid sites, amphiphilic property and light texture, SG exhibited excellent catalytic performance in the etherification of glycerol with isobutene. At 60~70o C with 4 wt% catalyst loading and a molar ratio of isobutene/glycerol 4, nearly a complete conversion of glycerol in7 h and a selectivity of more than 90 mol% to desired multi-butyl glycerol ethers were achieved. Moreover, undesired oligomerization of isobutene was successfully suppressed. The mixture after reaction was successfully layered to two phases with fresh glycerol addition.The top phase was a transparent product consisted of no less than 96 wt% di- and tri-butyl glycerol ethers, and the bottom phase was a black mixture containing glycerol, MTBGs and SG, which was ready to start a new run with fresh isobutene addition. The catalyst presented robust performance in six consecutive reaction-extraction cycles. Etherification of glycerol with tert-butanol didn’t yield the conversion and selectivity to multi-butyl glycerol ethers as high as that with isobutene did, but it showed a better performance compared to those reported in the literature using tert-butanol as the tert-butylation reagent. The great catalytic performance and the highly viable recycle process were largely attributed to the special properties of the SG catalyst, such as ultra thin two-dimensional open substrate, selective andstable sulfonated acid sites, amphiphilic property and light texture. It is believed that this process using SG as catalyst has high potential for practical practice.