Geopolymer Cement

43 downloads 0 Views 1MB Size Report
Accelrys Material Studio 5.5. VAMP module: Simulation of reactions and properties of molecule in gas phase or solvent phase. Run AM1, PM3 and PM6 ...
Semi-empirical AM1, PM3 and PM6 Calculations on the Metakaolin Molecular Structure: Practical Application in Geopolymer Cement Production Ojas A. Chaudhari1, Joseph J. Biernacki1 and Scott Northrup2 (1) Department of Chemical Engineering (2) Department of Chemistry Tennessee Technological University Cookeville, Tennessee, USA

AIChE Annual Meeting- October 2012

Need of geopolymer cement concrete • 80% less CO2 emission • Uses waste materials • Reduces pollution • High strength and durability • fire Resistant • Acid, base & salt resistant

Portland Cement Concrete Plant

World’s 3rd Largest CO2 Production

Source: http://media.treehugger.com/assets/images/2012/01/cement_plant.png.492x0_q85_cropsmart.jpg

Total CO2 production from OPC plant: 825kg CO2/ton PC In 2011, United States produced 68400 TMT and China 200,000TMT.

http://minerals.usgs.gov/minerals/pubs/commodity/cement/cemenmcs06.pdf

Geopolymer Cement  Joseph Davidovits (1978) “geopolymeric cements” are inorganic polymers with a

3D framework structure having good mechanical and physical properties.



Metakaolin: • dehydroxylated form of clay mineral kaolinite • Highly reactive pozzolan and high rate of dissolution in

the alkali solution •

Higher % of alumino silicate material compare to fly ash

Caijun Shi, T., Jiménez A and Angel Palomo, "New cements for the 21st century: The pursuit of an alternative to Portland cement," Cement and Concrete Research, 41, 2011, pp 750-763.

Geopolymerization reaction  Dissolution of

metakaolin = type and amount of geopolymer product  It is difficult to get experimental data for each step individually 

Semi empirical calculations of dissolution process

Descriptive model of geopolymerization reaction

Pozzolanic reaction under alkaline condition results in 3-D polymeric chain and ring structure with Si-O-Al-O bonds. Mn [-(SiO2) z-AlO2] n .wH2O Where: M= the alkaline element –sodium, potassium or calcium, N= degree of polymerization •

Caijun Shi, T., Jiménez A and Angel Palomo, "New cements for the 21st century: The pursuit of an alternative to Portland cement," Cement and Concrete Research, 41, 2011, pp 750-763.

Metakaolin (MK) Structure 

Dehydroxylation of Kaolinite clay



X-ray amorphous structure Sheet molecular structure alumino-silicate material Various assumptions for small molecular units

    

Two sheet structure: SiO4 tetrahedral layer and distorted AlO4 layer Five-membered alumino-silicate single ring cluster (Xu and Devanter, 2000) Six membered alumino-silicate single ring (Yunsheng and Wei, 2007)

To built a structure representing metakaolin





Size of molecular cluster



Single 6-membered ring SiO4 and AlO4 tetrahedron structure terminated OH bonds. 6-membered SiO4 and AlO4tetrahedron ring cluster

•Xu, H. and J. S. J. Deventer, "Ab initio calculations on five- membered alumino-silicate frameworks rings model: implications for dissolution in alkaline solutions," Computers and Chemistry, 24, 2000, pp 391-404. •Yunsheng, Z. and S. Wei, "Semi-empirical AM1 calculations on 6- membered alumino-silicate rings model: implications for dissolution process of metakaolin in alkaline solutions " Journal Of Material Science, 42, 2007, pp 3015-3023.

Quantity

PM6

ΔHf

Simulation Outline

Bond Lengths Angles

PM3

AM1

Units

8.01

18.2

22.86 Kcal/mol

0.091

0.104

0.13 Angstroms

7.86

8.5

8.77 Degrees

Average Unsigned Errors in PM6 Predictions

 Accelrys Material Studio 5.5  VAMP module: Simulation of reactions and

properties of molecule in gas phase or solvent phase

AM1

 Run AM1, PM3 and PM6 methods  Dissolution in water

 NaOH and KOH alkaline environment

dissolution

PM3

Si(OH)4 and NaOH geometry optimized structure

AM1 104°

PM3 107°

http://cccbdb.nist.gov/exp2.asp?casno=1310732 http://openmopac.net/manual/index_accuracy.html

PM6 109°

PM6

Si(OH)4 and NaOH geometry optimized structures

Geometry optimization of SiO4 and AlO4 Software and Method

Bond Length (nm)

SiO4

Bond Angle

Si-Onbr

Si-Obr

Obr-Si-Obr

Obr-Si-Onbr

Onbr-Si-Onbr

Si-Obr-Si

DMOL3

0.167

0.164

107.470

110.100

109.141

139.713

MS AM1

0.156

0.161

110.223

109.295

109.59

171.441

MS PM3

0.169

0.165

113.255

108.241

107.16

137.553

MS PM6

0.156

0.162

109.960

109.332

109.689

175.372

Software and Method

Bond Length(nm)

Bond Angle

AlO4

Al-Onbr

Al-Obr

Obr-Al-Obr

Obr-Al-Onbr

Onbr-Al-Onbr

Al-Obr-Al

DMOl3

0.189

0.176

124.098

102.762

105.016

166.508

MS AM1

0.1802

0.1735

131.955

94.36

102.71

151.902

MS PM3

0.1858

0.1787

125.257

104.365

98.825

174.823

MS PM6

0.1851

0.1761

122.075

91.706

102.866

132.643

AM1

PM3

PM6

AM1

PM3

PM6

Dissolution in water  (Si(OH2)O)6 + 2H2O → (OH)3Si-(Si(OH)2O)3-Si(OH)3

+ HO-Si-(OH)3 E1 (1)  (Al(OH2)O)6 + 2H2O → (OH)3Al-(Al(OH)2O)3-Al(OH)3 + HO-Al-(OH)3 E2 (2)  The reaction energy of AlO4 broken ring is -1477 KJ/mol (PM6) which is highly exothermic as compare to SiO4 broken ring (-19 KJ/mol, PM6).

Dissolution in alkaline solution  Ion pairing reaction:

(Si(OH2)O)6 + 3NaOH → (OH)3Si-(Si(OH)2O)3-Si(OH)3 + HO-Si-(ONa)3 + H2O E3  Ion pairing and interaction with broken cluster:

(Si(OH2)O)6 + 4NaOH → (OH)3Si-(Si(OH)2O)3-Si(OH)2-ONa + HO-Si-(ONa)3 + 2H2O E5

Heat of reaction comparison  Reaction in alkaline medium is highly exothermic [E1(-19

KJ/mol) > E3 (-230.44 KJ/mol)]  The ion pairing reaction between HO-Si-O3- and Na+ gives energy |E3| (230.44 KJ/mol). Similarly |E4| (215 KJ/mol) is obtained with K+ ion pairing.  More heat of reaction generated when silicate species reacted with smaller size alkali cation in ion paring reaction (Sawddle et al., 1994)  Reaction of dissolution of MK in the NaOH is more favorable than reaction of MK in the KOH, which is consistent with published literature. PM6 Reaction heat (KJ/mol) E3 (Si1-Na)

-230.44

E4 (Si1-K) E5 (Si2-Na) E6 (Si2-K) E7 (Al1-Na) E8 (Al1-K) E9 (Al2-Na) E10 (Al2-K)

-215.99

-522.18

-442.25

-1388.50

-1380.84

-1453.59

-1477.92

•Sawddle, T., Salereno J and P. Tregloan, "Aqueous aluminates, silicates, and aluminosilicates," Chemical society review, 23, 1994, pp 319.

Bond lengths and angles after dissolution 200 180

Bond Angle (deg)

120

NaOH dissolution

100 80 60 40 20

0.19

Al-Obr-Al

Onbr-Al-Onbr

Obr-Al-Onbr

Obr-Al-Obr

Si-Obr-Si

Onbr-Si-Onbr

Obr-Si-Onbr

0

Obr-Si-Obr

bonds on the ring Si/Al-Obr are both stretched after dissolution in the highly alkaline solution.  The angles on ring (Obr-Si-Obr, Obr-Al-Obr) and angles on bridge (Si-Obr-Si, Al-Obr-Al) are reduced after dissolution.  Yunsheng and Wei (2007) reported that single 6-membered AlO4 tetrahedron ring model shows contraction after dissolution in the highly alkaline solution.

KOH dissolution

140

Local Dissolution KOH dissolution NaOH Dissolution

0.185 0.18

Bond Length (A⁰)

 Bonds on corner Si/Al-Onbr and

160

Local Dissolution

0.175 0.17 0.165 0.16 0.155

0.15 0.145 0.14 Si-Onbr

Si-Obr

Al-Onbr

Al-Obr

Conclusion  In order to know dissolution of metakaolin in alkaline solution process, semi-

  

 

empirical PM6, PM3 and AM1 calculations have been conducted on optimized geometry of 6- membered SiO4 and AlO4 single ring clusters. The geometry optimization shows that PM6 semi-empirical method gives better idea about SiO4 and AlO4 ring clusters in the metakaolin. PM6 method achieved much more realistic geometry optimization for NaOH and Si(OH)4 molecule. SiO4 and AlO4 ring clusters demonstrates contraction after dissolution in the highly alkaline solution, which indicates that structure of metakaolin will distort after dissolution. In the highly alkaline environment, AlO4 ring cluster is more reactive and easily dissoluble as compared to SiO4 ring cluster. Also small size Na+ cation shows easy ring breakage and ion pairing interaction than K+ cation. Therefore metakaolin dissolution in the NaOH is more favorable than KOH solution

Acknowledgement  Dr. Biernacki1 and Dr. Northrup2, (1) Department of

Chemical Engineering (2) Department of Chemistry Tennessee Technological University, Tennessee  Center of Energy Systems Research (CESR) for their financial assistance.  Joel Seber and Michael Renfro  All my friends and work colleagues.

Thank you.