1

REACTIVE CRYSTALLIZATION

PRESENTED BY- MADHURA N. CHINCHOLI

14CHE2032

30-04-2015

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.

30-04-2015

3

PREPARATION OF THE EXPLOSIVE TATB

30-04-2015

• 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.

30-04-2015

Nandi et al. (2014)

5

5 ELEMENTAL STEPS

30-04-2015

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.

30-04-2015

730-04-2015

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

30-04-2015

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

30-04-2015

1030-04-2015

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

30-04-2015

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)

30-04-2015Nandi et al. (2014)

13

REFERENCESNandi 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!30-04-2015