Glycerol Oligomers Synthesized from Etherification of Glycerol with Zeolite-Supported Catalysts

Glycerol oligomers synthesized from etherification of glycerol with zeolite-supported catalysts

 

Chin-Kai Chen, Bing-Hung Chen*

Department of Chemical Engineering, National Cheng Kung University,

1 University Road, Tainan 70101, Taiwan

e-mail: bkchen@mail.ncku.edu.tw (BHC)

Abstract

In this work, zeolite-supported Ca/Mg/Sr catalysts were synthesized to produce glycerol oligomers from the catalyzed etherification of glycerin which is the abundant byproduct from transesterification of oils and fats for biofuel, using. Both zeolite ZSM-5 and zeolite LTA were chosen as supports impregnated with Ca, Mg, or Sr, to catalyze the etherification reaction of glycerol to glycerol oligomers, mainly the diglycerol and triglycerol, in the Dean-Stark apparatus as a semi-batch reactor. The properties of these zeolite bases catalysts were characterized with XRD, FT-IR, SEM, BET, TGA and TPD. In addition to the heterogeneous zeolite based catalysts, homogeneous catalysts, both acid (sulfuric acid) and base (NaOH), were tested to provide the benchmark. The chemical structure of the product from etherification of glycerin were analyzed with GC-MS, GC-FID and ¹³C-NMR.It It indicated that diglycerol and triglycerol, either in linear or cyclic form, were dominant products. Moreover, the yield of polyglycerols (diglycerol + triglycerol) could exceed 85% after 6 h of reaction at 260¢XC using Ca-impregnated zeolite ZSM-5. The activation energy of 107.71 kJ/mol of the pseudo-first order reaction confirmed a high energy barrier in glycerin etherification.

Keywords: Glycerin, Diglycerol, etherification, Zeolite ZSM-5, impregnation.

Figure 1: The XRD patterns of Zeolite ZSM-5 impregnated with Ca(NO₃)₂ solutions

Figure 2: Etherification of glycerin catalyzed by zeolite ZSM-5 impregnated with alkaline earth metals. (Reaction conditions: (1) catalyst loading = 2 wt% of glycerin, (2) reaction time = 8h, (3) reaction temperature = 260¢XC, (4) N₂ flow = 50 sccm).