Shape-selectivity in Biomass Conversion: Zeotype-catalyzed Formation of C4 Sugars

Søren Tolborg,a,b Irantzu Sádaba,b Saravanamurugan Shunmugavel,a Sebastian Meier,a Peter Fristrup,a and Esben Taarning.b,* a Technical University of Denmark, Department of Chemistry, Kgs. Lyngby, 2800, Denmark b Haldor Topsøe A/S, New Business R&D, Kgs. Lyngby, 2800, Denmark * Corresponding author: [email protected] selective formation of tetrose sugars from 1. Introduction glycolaldehyde using a range of different catalysts. Glycolaldehyde (GA), a ‘two carbon’ sugar, could become a valuable biomass-derived platform chemical. 2. Experimental Part It is currently obtained in high yields in supercritical Several zeolite and amorphous silicate catalysts were water or as a byproduct in bio-oil, but other processes prepared for this study including Sn-Beta and Sn-MFI are currently being developed to efficiently prepared following procedures described in [6] and [7], transforming sugars to GA in high yields.1, 2 respectively. A variety of both homogeneous and Current catalytic valorization of glycolaldehyde heterogeneous catalysts were tested for the conversion include; a) hydrogenation to ethylene glycol, b) of glycolaldehyde to tetrose sugars in water. In a amination to ethylene diamine,3 and c) aldol typical experiment; 0.125 g of glycolaldehyde (5 wt%) condensation using tin-containing catalysts to yield C3 and 0.075 g of catalyst was added to a glass pressure and C4 α-hydroxy acids (AHAs) such as lactic and tube (ACE) and heated to 80 °C for 0.25 - 24 h. The vinyl glycolic acids or esters.4, 5 reaction mixture was then analyzed using an Aminex

HPX-87H (BioRad) column (0.004 M H2SO4, 0.6 O C6 sugars OH mL/min, 65 °C) and a Carbohydrate (Zorbax) column Glycolaldehyde (60 wt% acetonitrile/water, 0.5 mL/min, 30 °C) on Agilent 1200 series HPLCs. Aldol condensation 3. Results and discussion OH OH OH HO HO HO We found that very high selectivities towards tetrose O O OH OH OH O sugars (~85 %, Figure 2) could be obtained using tin- Threose Erythrose Erythrulose containing MFI at moderate temperatures (80 °C) in

water, leading to C4 yields of up to 70 %. TS-1 was Aldol condensation found to also catalyze the aldol condensation but at lower selectivities (≤70 %) than with tin as the active C6+ sugars site. Selectivities obtained using the different catalysts Figure 1. Schematic representation of the selectively formed C4 sugars from the C2 sugar glycolaldehyde. were all dependent on the level of conversion of glycolaldehyde (Figure 2). At high conversion (>60 %),

The C4 sugars (threose, erythrose and erythrulose) are other byproducts were observed and the selectivity rare and expensive sugars, and especially erythrose is towards C4 dropped to below 60 % as a consequence. interesting due to the production of erythritol and its These other products are likely formed by additional use as a food additive. Formation of these sugars can dehydration reactions to yield AHAs or larger C6+ be achieved by a single aldol condensation step, sugars formed from additional aldol condensation however subsequent steps must be avoided to maintain steps between tetrose and GA. A similar dependence a high selectivity (Figure 1).5 In this study we show the on conversion was also observed at 60 and 100 °C. Catalysts known to catalyze aldol condensation with Acknowledgments large or no pore structure (e.g. basic resins, tin salts, The work of ST is funded by the Bio-Value platform (http://biovalue.dk) under the SPIR initiative by The Danish etc.) all resulted in higher amounts of C6+ sugars. We Council for Strategic Research and The Danish Council for speculate that the 10 membered rings making up the Technology and Innovation, case number 0603-00522B. pore system of Sn-MFI hinders this formation. References 1) M. Sasaki, K. Goto, K. Tajima, T. Adschiri, K. Arai, Green Chem. 2002, 4, 285-287 2) R. Vinu, L. J. Broadbelt, Energy Environ. Sci. 2012, 5, 9808- 9826 3) W. Mägerlein, J. P. Melder, J. Pastre, J. Eberhardt, T. Krug, M. Kreitschmann, US4321414, 1982 4) M. Dusselier, P. Van Wouwe, S. De Smet, R. De Clercq, L. Verbelen, P. Van Puyvelde, F. E. Du Prez, B. F. Sels, ACS Catal. 2013, 3, 1786-1800 5) M. S. Holm, Y. J. Pagán-Torres, S. Saravanamurugan, A. Riisager, J. A. Dumesic, E. Taarning, Green Chem. 2012, 14, 702- 706 6) S. Tolborg, A. Katerinopoulou, D. D. Falcone, I. Sádaba, C. M. Osmundsen, R. J. Davis, E. Taarning, P. Fristrup, M. S. Holm, J. Mater. Chem. A 2014, 2, 20252-20262. 7) C. M. Osmundsen, M. S. Holm, S. Dahl, E. Taarning, Proc. R. Soc. A 2012, 468, 2000-2016.

Figure 2. Selectivity towards C4 sugars as a function of conversion of glycolaldehyde using the tin-containing silicates; Sn-Beta (Si/Sn = 150) and Sn-MFI (open: Si/Sn = 100, closed: Si/Sn = 400). Reaction conditions: 0.125 g glycolaldehyde, 0.075 g catalyst, 2.5 g water, 80 °C, 0.25 - 24h.

4. Conclusions A very selective condensation of glycolaldehyde to the rare tetrose sugars was achieved with tin-containing zeotype catalyst Sn-MFI. The tin sites in the medium 10-membered ring pores in this catalyst appears to effectively catalyze the aldol condensation leading to the C4 sugars, while being hindered in additional condensation to form larger sugars. This allowed combined yields of tetrose sugars to reach ~70 % with selectivities reaching ~85 %. When Sn-Beta (12- membered pores) was used, much lower yields (~23 %) and selectivities (~53 %) were observed, presumably due to the formation of larger sugars as well as the further conversion of the formed sugars to α-hydroxy acids.