A low cost, green route to distillable spirosiloxanes via base catalyzed depolymerization of biogenic silica

Transcription

1 A low cost, green route to distillable spirosiloxanes via base catalyzed depolymerization of biogenic silica R. M. Laine, 1,2 V. Popova, 4 J. Furgal, 3 D. Pan, 2 P. Doan, 3 E. Yi, 1 1 Materials Sci. & Eng., 2 Macromolecular Sci. & Eng. 3 Chemistry University of Michigan 4 Mayaterials Inc., 1665 Highland Dr, Ann Arbor, MI talsdad@umich.edu Work at Mayaterials Funded by NSF, DOE, Wadham Energy, USDA 1

2 What s the problem? Surface area < 1 m 2 /g Photo courtesy of Rachail Laine

3 This is the problem Starts from SiO 2 goes to Si met and back to Si(OEt) 4 /SiO 2 3

4 Current Si pv floor price $22/kg, = full cost of best-practice systems Si pv = purity 4

5 Outline A Grand Challenge Dissolving silica Why rice hull ash? Pentacoordinated silicates Precipitated Silica (Sol-Gel) New Chemistries Si-C bonds Silicon 5

6 A Grand Challenge of Silicon Chemistry SiO 2 < 200 C Si(OR) 4 Problem Si-O bond 534 KJ/mole For tetrahedral Si If can t surmount by brute force, go around Si-O bonds in penta- and hexacoordinate Si compounds weaker. 6

7 Previous efforts Rosenheim et al. Znorg. Allg. Chem. 1931, 196, 160. Weiss et al Anorg. Allg. Chem. 1961, 311, 142, 151. Boer and Flynn J. Am. Chem. Soc., 1968, 90, 6973 Barnum et al Inorg. Chem, 1970, 9, 1942 Corriu et al Angew. Chem. 1986, 98, 473 Multiple Efforts Efforts to satisfy the grand challenge! 7

8 Laine et al, ( 90s) Previous efforts (fumed silica) Pentacoordinated Si Laine, Nature 1991, 353, 642 Hexacoordinated Si Hoppe et al, Angew. Chem. Int. 1993, 32, (). Kinrade et al ( 99) Science, 1999, 285, 1542 Penta and hexa coordinated Si in nearly neutral aqueous media from silica and sugars. 8

9 Kinetics (MOH) fumed silica/sand E a 15 kcal/mole Same E a as base dissolution of SiO 2 in H 2 O at 200 C/pressure Rxn runs best at 200 C First order in Surface Area Is there a natural source of silica that has a higher surface area? Are there stronger bases than alkali metal hydroxides? 9

10 What is rice hull ash (RHA) 1 M tons of rice produced in California alone/yr Milled in central facilities, RHs 25 wt % mass of rice wt % amorphous silica Burning 220k tons rice hulls generates electricity and 40k tons of rice hull ash (RHA)/year 90 + % high surface area (>20 m 2 /g) silica rest is 10 - % high surface area (>20 m 2 /g) carbon Plants do not transport heavy metals Perfect for our needs 10

11 Rice hull ash production, Wadham Energy Burning rice hulls produces 200 GigaW/yr

12 Rice Hull Ash % silica with 35-5 % carbon, 5 % minerals Surface Area m 2 /g 12

13 Rice Hull Ash--STEM picture Si Map C Map O Map 13

14 Silica Extraction---Scale-Up 14

15 Typical Precipitated Silica High Temperature: 1300 C Uses 2Na: 1SiO 2 Uses 1 H 2 SO 4 : 1 Na 2 SiO 3 Produces 1 CO 2 :1Na 2 SO 4 :1SiO 2 15

16 Next generation silica systems With RHA faster, easier 16

17 Next generation silica systems With RHA faster, easier Precipitates 17

18 Precipitated silica from Si(OCH 2 CH 2 OH) 4 No CO 2 produced. Catalytic base that can be recycled Water is recycled EGH 2 recycled SiO 2 will have some Na contamination 18

19 Successful depolymerization of SiO 2 to spirosiloxane

20 Successful depolymerization of SiO 2 to spirosiloxane % dissolved SiO 2 w/10 mol % NaOH. Distill 400 ml of diol

21 Next Grand Challenge Should be catalytic but this is first step Joe Furgal will talk about this

22 Nanopowders by Flame Spray Pyrolysis MCl x + H 2 /O 2 MO x + HCl +. MCl x must be volatile SiCl 4, TiCl 4, AlCl 3, Typical SiO 2 surface areas m 2 /g Fumed silica $8-9/kg Zhang Brinker et al Processing Pathway Dependence of Amorphous Silica Nanoparticle Toxicity: Colloidal vs Pyrolytic, J. Am. Chem. Soc ,

23 New route to fumed silica $4-5/kg

24 Why is RHA a great starting pt to produce ppt SiO 2 Rice plant takes up silica without heavy metal impurities RHA is produced coincident with 200 GW/yr of electricity RHA has high surface area ( 80 m 2 /g) and amorphous silica Silica can be extracted using catalytic base to form Si(OROH) 4 Filtered from RHA and acidified to ppt or Silica can be extracted using catalytic base to form Si(ORO) 2 Distilled at very high purity Combusted to make fumed silica Base and water recycled in both cases! 24

25 Why is RHA a great starting pt to produce Si pv Rice plant takes up silica without heavy metal impurities RHA is produced coincident with 200 GW/yr of electricity RHA has high surface area ( 20 m 2 /g) and amorphous silica Easy to purify by simple acid washing Easy to adjust Si:C ratios but simple silica extraction RHA has silica intimately mixed at nanometer length scale Thus EAF processing can be much faster than that used in commercial production of Si met Saves exceptional amounts of $$ ( ) in both equipment costs (CAPEX) and in operating costs (OPEX). 25