Synthesis of nano γ- AlOOH from aluminate solutions for catalytic applications

Prof. Panias DimitriosProf. Panias DimitriosKrestou Athina, MSc Krestou Athina, MSc

22/04/23SLM 2008, Belgrade National Technical University of

Athens

22/04/23 SLM 2008, Belgrade National Technical University

of Athens

BauxitBauxitee

AluminaAlumina


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BAYER PROCESSBAYER PROCESS to lower the SiOto lower the SiO22 concentration and concentration and control the level of control the level of phosphates phosphates

may contain may contain Al(OH)Al(OH)33 or or AlOOHAlOOH

for the extraction for the extraction of all of the Alof all of the Al22OO3 3 in bauxite in bauxite

Al(OH)3 Calcination above 1380KCalcination above 1380K

2Al(OH)2Al(OH)33 α-α-AlAl22OO33 +3H+3H22OO


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(energy saving,(energy saving, topotactictopotactic

transformation into transformation into γ-γ-AlAl22OO33))


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PropertiesProperties ApplicationsApplications

MicrostructureMicrostructure


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ApplicationsApplications

(catalysis, (catalysis, adsorption)adsorption)

MicrostructureMicrostructure (homogeneous, defect-free)(homogeneous, defect-free)

PropertiesProperties(high surface area, mesoporosity,(high surface area, mesoporosity,

proper crystallite size) proper crystallite size)


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Applications of Applications of γγ- Al- Al22OO33• catalyst or catalyst support in heterogeneous catalysiscatalyst or catalyst support in heterogeneous catalysis• adsorbent in purification and bleaching processesadsorbent in purification and bleaching processes• composite reinforcementcomposite reinforcement• membrane in separation processes of industrial waste streams membrane in separation processes of industrial waste streams and foodand food• in biomedical and chemical processes in biomedical and chemical processes

absence of defectsabsence of defectsEnhanced performance: homogeneous Enhanced performance: homogeneous microstructure microstructure uniform size uniform size distributiondistributionNANO-METER or SUB-MICROMETERNANO-METER or SUB-MICROMETER sized sized particlesparticles

Previous research in the Laboratory of Metallurgy (NTUA)Previous research in the Laboratory of Metallurgy (NTUA) Synthetic Bayer liquor (SSA)Synthetic Bayer liquor (SSA) Boehmite seedsBoehmite seeds T<100T<100ooCC precipitation of coarse precipitation of coarse γ-γ-AlOOH particles by decreasing the AlOOH particles by decreasing the free NaOHfree NaOH

More information:More information:D. Panias, A. Asimidis, I. Paspaliaris, Hydrometallurgy D. Panias, A. Asimidis, I. Paspaliaris, Hydrometallurgy 15-2915-29 (2001) 59. (2001) 59.C.Skoufadis, D.Panias, I Papsaliaris, Hydrometallurgy C.Skoufadis, D.Panias, I Papsaliaris, Hydrometallurgy 5757 (2003) 68. (2003) 68.D. Panias, Hydrometallurgy D. Panias, Hydrometallurgy 203203 (2004) 74. (2004) 74.D. Panias, A. Krestou, Powder Technology D. Panias, A. Krestou, Powder Technology 163-173163-173 (2007) 175. (2007) 175.


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This study: This study: Precipitation of pure nano-Precipitation of pure nano-boehmite by the destabilization of SSA boehmite by the destabilization of SSA through neutralization at atmospheric through neutralization at atmospheric conditions conditions

without without γ-γ-AlOOH seed additionAlOOH seed addition


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SSA SSA (solution A)(solution A)

Acid Acid (solution B)(solution B)

ReagentReagentss

HNO3, HCl, H2SO4, HNO3, HCl, H2SO4, H3PO4, CH3COOHH3PO4, CH3COOH

BABA

ABAB

Mode Mode of of

mixingmixing 30<T<10030<T<100ooCC

5<pH<13,5<pH<13,66

ParameterParameters Studieds Studied

0<t0<tagag<2weeks<2weeks

addition rateaddition rate

calcination Tcalcination T

Characterization Characterization of precipitatesof precipitates

XRDXRD

TGTG

ssa, ps, pv, psdssa, ps, pv, psdby Nby N22 adsorption adsorption

/desorption/desorption

SEM, TEMSEM, TEM


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Precipitates: well crystallised gibbsite Precipitates: well crystallised gibbsite gibbsite/bayerite mixturesgibbsite/bayerite mixtures gibbsite/bayerite/boehmite gibbsite/bayerite/boehmite mixturesmixtures

NO PURE γ-AlOOH with the BA experiments


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PURE nano-crystallite PURE nano-crystallite γ-γ-AlOOH AlOOH

with the AB experimentswith the AB experiments


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Effect of Temperature and Effect of Temperature and pHpH


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Effect of ageing timeEffect of ageing timeT60-pH7

0

20

40

60

80

100

120

140

160

180

200

5 10 15 20 25 30 35 40 45 50 55 60

2θ

cps

020120

140

131

051200

220 151

t=0t=2

t=24

t=48

t=144t=168


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Effect of different acidsEffect of different acidsT60°C- pH7- t24h

050

100150200250300350400450500550600650

5 10 15 20 25 30 35 40 45 50 55 60

2θ

cps

HNO3

HCl

H2SO4

CH3COOH

020120

140 200

020 120 140,031 051,020HNO3 3,10 3,97 4,33 7,03HCl 3,00 4,39 3,50 5,84H2SO4 - 3,30 3,40 5,27CH3COOH - 2,89 2,68 3,52

crystallite size (nm)


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Effect of different acids (T90-Effect of different acids (T90-pH7-t24h)pH7-t24h)

Region Ι

Region ΙΙ Region ΙΙΙ

Crystallites<50nm

Transformation to γ-AlOOH of higher crystallinity

Transformation of γ-AlOOH to γ-Al2O3

Transformations

SLM 2008, Belgrade National Technical University of Athens

acids Calcination Temperature, (°C) 390 450 650 900 1100

HNO3 Precip. phase

γ-AlOOH

η-Al2O3

η-Al2O3

η-Al2O3

η/α/θ-Al2O3

ssa (m2/g) 98,44 220,59 186,78 102,78 38,08 pore size (Å) 56,26 54,07 71,92 116,66 216,5 ads. isotherm Type II Type II Type II Type II Type II

HCl Precip. phase

γ-AlOOH

η/ γ- Al2O3

η/ γ- Al2O3

η/ γ- Al2O3

α/δ-Al2O3

ssa (m2/g) 170,56 219,27 - - 60,18 pore size (Å) 53,80 59,26 - - 191,56 ads. isotherm Type II Type II - - Type II

H2SO4 Precip. phase

γ-AlOOH

η-Al2O3

η-Al2O3

Al4(OH)10SO4*5H2O

η-Al2O3

Al4(OH)10SO4*5H2O

α/η-Al2O3

Al4(OH)10SO4*5H2O ssa (m2/g) 74,14 59,11 - - 9,02

pore size (Å) 65,07 47,11 - - 105,32 ads. isotherm Type II Type II - - Type II CH3COOH

Precip. phase

γ-AlOOH

η-Al2O3

η-Al2O3

η-Al2O3

α/η-Al2O3 ssa (m2/g) 302,99 329,30 - - 68,93

pore size (Å) 25,20 43,92 - - 157,01 ads. isotherm Type I Type II - - Type III

Effect of different acids (T90-Effect of different acids (T90-pH7-t24h)pH7-t24h)

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Effect of addition rate(T90-ph7-Effect of addition rate(T90-ph7-t0)t0)

390 400 650 900 11001ml/minphase precipitated γ-AlOOH - - - - -ssa (m2/g) 85,25 - - - - -pore size (Å) 50,68 - - - - -ads. Isotherm type Type II - - - - -

3ml/minphase precipitated γ-AlOOH η/γ-Al2O3 η/γ-Al2O3 γ-Al2O3 α/δ-Al2O3

ssa (m2/g) 148,10 241,20 191,39 125,92 47,14pore size (Å) 47,55 54,56 73,02 113,22 191,19ads. Isotherm Type II Type II Type II Type II Type II

5ml/minphase precipitated γ-AlOOH γ-Al2O3 γ-Al2O3 γ-Al2O3 α-Al2O3

ssa (m2/g) 170,87 284,35 173,62 114,13 5,84pore size (Å) 33,47 45,01 66,16 77,91 -ads. Isotherm Type II Type IV Type IV Type IV Type III

7ml/minphase precipitated γ-AlOOH η/γ-Al2O3 η/γ-Al2O3 γ/δ-Al2O3 α/δ-Al2O3

ssa (m2/g) 144,52 - - - -pore size (Å) 41,18 - - - -ads. Isotherm Type II - - - -

10ml/minphase precipitated γ-AlOOH η/γ-Al2O3 η/γ-Al2O3 γ/δ-Al2O3 α/δ-Al2O3

ssa (m2/g) 118,31 - - - -pore size (Å) 44,45 - - - -ads. Isotherm Type II - - - -

abruptphase precipitated γ-AlOOH η/γ-Al2O3 γ/δ-Al2O3 γ/δ-Al2O3 α/δ/θ-Al2O3

ssa (m2/g) 104,25 206,43 157,27 110,08 11,99pore size (Å) 33,33 42,18 58,9 84,75 -ads. Isotherm type Type II Type IV Type IV Type IV Type III

Calcination Temperature (oC)Addition rate 90oC, pH7

rate (ml/min) d (020) d(100) d(001)1ml/min 2,764 4,519 5,833ml/min 2,769 4,476 5,4175ml/min 3,029 4,579 7,0587ml/min 2,970 4,984 6,49010ml/min 2,750 4,284 6,004abrupt 4,3801 4,9615

Ab. add.Ab. add.

10ml/10ml/minmin7ml/min7ml/min5ml/min5ml/min3ml/min3ml/min1ml/mi1ml/minn

Only the AB experiments resulted in Only the AB experiments resulted in γ-γ-AlOOH AlOOH precipitation : effect of Al-species precipitation : effect of Al-species


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0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 2 4 6 8 10 12 14

pH

%A

l

Al +3

Al(OH) +2

Al(OH)2 +1

Al(OH)3

AL(OH)4 -1

AL2(OH)2 +4

AL3(0H)4 +5

Al3(OH)4 5+ Al3+

Al2(OH)2 4+

Al(OH)3

Al(OH)4-

Al(OH)2+

Al(OH)2+

HCl : higher specific surface HCl : higher specific surface areaarea addition rate 5ml/min: most promising for the addition rate 5ml/min: most promising for the precipitation of nanocrystallite precipitation of nanocrystallite γ-γ-AlOOH and calcined AlOOH and calcined products for catalytic applicationsproducts for catalytic applications

T & pH: better crystallinity in less tT & pH: better crystallinity in less tageing ageing

22/04/23 SLM 2008, Belgrade

Synthesis of nano γ- AlOOH from aluminate solutions for catalytic applications

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