Reactive crystallization basics explained with the case study of production of high explosive TATB (1,3,5-Triamino-2,4,6-trinitrobenzene). Includes the kinetics, mass transfer and crystallization rates.

1. PRESENTED BY-
MADHURA N. CHINCHOLI
14CHE2032
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2. REACTIVE CRYTALLIZATION
 It involves reaction between reactants to form a solute which
crystallizes into a solid product.
 Eg. Production of (NH4)2SO4 from liquid or gaseous NH3 and conc.
H2SO4
 A complex phenomenon comprising simultaneous reaction, mass
transfer, rapid nucleation and growth, as well as possible secondary
processes of aging, ripening, agglomeration and breakage.
 The driving force responsible for the crystallization: Generation of
supersaturation by the chemical reaction.
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3. PREPARATION OF THE EXPLOSIVE TATB
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• 1,3,5-Triamino-2,4,6-trinitrobenzene(TATB)
• Insensitivity, thermal stability (>350 ºC) and respectable performance
• Virtually insoluble in most common solvents
• Aromatic nucleophilic substitution mechanism
• Aim: large particle size(>50 µm) and low chloride impurity(<1 %)

4. •It is an isothermal, single-feed, semi-batch, gas-liquid heterogeneous,
reaction crystallization process.
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Nandi et al. (2014)

5. 5 ELEMENTAL STEPS
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6. MASS TRANSFER AND CHEMICAL
REACTION KINETICS
 An equation for the NH3 flux consumed in the amination reaction (A)
and the neutralization reaction (B) based on Two-Film Mass-Transfer
(TFMT) theory
 ASSUMPTIONS
(i) Steady-state model, i.e. the conc. profiles inside the films are
established instantaneously
(ii) Steady-state transport of NH3 and TCTNB through the stagnant gas
and liquid film respectively, i.e. essentially driven by molecular
diffusion and hence, characterized by the molecular diffusivity 𝔇NH3
and 𝔇TCTNB, respectively.
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Figure 2. The conceptual model for the amination reaction based on TFMT theory.
Nandi et al. (2014)

8.  The mass transfer of NH3 from gas to liquid can be defined by two
separate rate expressions
 Similarly for TCTNB,
 At the interface,
 The consumption rate of NH3 and TCTNB are stoichiometrically
related as
 Thus, we have a rate expression (𝑟NH3(A)) for the reaction between NH3
and TCTNB as shown in Scheme A
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9.  The relation between the liquid-phase diffusivities and the mass-
transfer coefficients is defined as,
 Solving the previous equations,
 NH3 sparingly soluble in toluene, gas side mtc greater than that of the
liquid side
 Above equation therefore reduces to
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 HCl neutralization by NH3 gas (Scheme B) is essentially an
instantaneous inorganic reaction
 As kNHl3 << KTATB <<< KNH4Cl, we can make the valid
assumption from the reaction stoichiometry:
 Reaction (B) NH3 is consumed at the mol ratio of 1:1,
 The net consumption of NH3 by the two reactions
NNH3 = NNH3(A) + NNH3(B)
 Therefore, we have,

11. CRYSTALLIZATION KINETICS
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 Two important steps, nucleation(tiny crystals) and crystal growth.
 Secondary nucleation insignificant
 The supersaturation level (ΔC) for the precipitation process is very high.
 The primary nucleation rates for TATB and NH4Cl which relate the
primary nucleation rate (j) to the supersaturation (ΔC), the primary
nucleation rate constant ( ), and the order of the nucleation process (n)
 Similarly, the crystal growth rates,

12. RESULTS
 Temperature(125 °C) (Optimized values)
 Water (5 %)
 NH3 flux (0.03 )
 Mixing (200 rpm)
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Nandi et al. (2014)

13. REFERENCES
 Nandi A. K., Kshirsagar A. S. & Thanigaivelan U.,
“Process Optimization for the Gas-Liquid Heterogeneous
Reactive Crystallization Process Involved in the
Preparation of the Insensitive High Explosive TATB”,
Central European Journal of Energetic Materials, 11, 31–
57 (2014).
 Kelkar V.V. & Ng K.M., “Design of Reactive Crystallization
Systems Incorporating Kinetics and Mass-Transfer
Effects” AIChE Journal, 45, No. 1 ,69-81 (1999)
THANK YOU!
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