Green Chemistry PAPER Cite this: Green Chem., 2013, 15, 1203 Received 14th February 2013, Accepted 2nd April 2013 DOI: 10.1039/c3gc40324f www.rsc.org/greenchem Alkali silicates and structured mesoporous silicas from biomass power station wastes: the emergence of bio-MCMs† J. R. Dodson,‡ a E. C. Cooper, a A. J. Hunt, a A. Matharu, a J. Cole, b A. Minihan, c J. H. Clark a and D. J. Macquarrie* a The waste ashes from a commercial biomass combustion facility are successfully converted into meso- porous structured silica utilising a biorefinery approach, with potential high value applications in catalysis, adsorption and separation processes. Potassium silicate solutions are formed via a simple hydrothermal extraction of miscanthus bottom ashes, rich in amorphous silica, with a reproducible extraction of 60–70%. The extension and validation of a rapid and facile infrared method for the quantification of the silicate solutions is demonstrated with important industrial applications for continuous online screening and tuning of the silicate solution ratio and concentration. The alkali solutions from thewaste ashes are used for the formation of a structured high surface area mesoporous silica, MCM-41 (1043 m 2 g -1 , 1.12 cm 3 g -1 ). The resulting mesoporous silica was analysed by XRD, N 2 adsorption porosimetry and TEM. 1. Introduction Over the past decade the large-scale combustion of agricultural residues such as straws and grasses has received significant research, commercial and governmental attention, with the aim of reducing greenhouse gas emissions through renewable power generation utilising indigenous biomass. 1,2 Drax Power Station, the largest in the UK, is currently converting to take half of its fuel from biomass whilst it is estimated that across Europe the primary production of heat and power from biomass could double to 2000 TWh by 2020. 3 It is predicted that 2/3 of this energy production increase will come from energy crops and agricultural residues, using around 130 million tonnes annually from biomass such as miscanthus and wheat straw. 3 Irrigation and fertiliser usage in the growth of these herbaceous plants leads to higher contents of in- organic species, compared to wood or coal, with ash contents of between 3–12 wt%. 4,5 The commercial combustion of this biomass will result in the production of significant quantities of new waste: biomass fly ash and bottom ash, which could be in the region of 4–15.6 million tonnes annually from energy crops and agricultural residues in Europe alone. The recovery and reuse of the inorganic species from these ashes would be a valuable addition to a biorefinery, both economically and in the context of elemental sustainability. 6,7 Despite bottom ashes being the largest contributor to the deposits in commercial combustion units, the vast majority of research on biomass ashes has studied the use of fly ashes as fertilisers or soil amendments. 5,8 The most frequently cited applications for combustion bottom ashes are in construction, by partly replacing cement or as an aggregate in road building. However, landfilling is currently the primary disposal method for biomass combustion residues. 9,10 Nevertheless, biomass ashes have been widely used in the past for soap production and glass making. 11 The main components of biomass ashes are silicates, car- bonates, chlorides, sulfates and phosphates. 5 Typically, there is a fractionation of the elements between the fly ash and the bottom ash during the combustion of herbaceous biomass, dependent on the volatility of the elements. Potassium, chlor- ine, sulfur, sodium and phosphorus are enriched in the fly ash, whilst the bottom ash is predominantly composed of silica. 12 This indicates that the bottom ashes could be used for forming silicate solutions by alkaline extraction with the use of these solutions to produce a higher value end-product. Research on rice hulls, rich in silica, has demonstrated the potential for producing silicate solutions by alkaline extraction of the hulls, pyrolysed, combusted or gasified below 800 °C. 13 † Electronic supplementary information (ESI) available. See DOI: 10.1039/c3gc40324f ‡ Present address: Institute of Chemistry, Federal University of Rio de Janeiro, Cidade Universitária, Rio de Janeiro, 21941-909, Brazil. a Green Chemistry Centre of Excellence, Department of Chemistry, The University of York, Heslington, York, Y010 5DD, UK. E-mail: duncan.macquarrie@york.ac.uk; Fax: +44 (0)1904 432705; Tel: +44 (0)1904 432559 b EPR Ely Limited, Elean Business Park, Cambridge, UK c PQ Corporation, PQ Silicas UK Limited, Bank Quay, PO Box 26, Warrington, WA5 1AB, UK This journal is © The Royal Society of Chemistry 2013 Green Chem., 2013, 15, 1203–1210 | 1203 Downloaded on 29/04/2013 19:18:45. Published on 03 April 2013 on http://pubs.rsc.org | doi:10.1039/C3GC40324F View Article Online View Journal | View Issue