Field of the invention:

The present invention relates to an improved process for the preparation of 3, 4, 4-trichlorocarbanalide by simultaneous reaction and drying operation of 4-chloro phenyl isocyanate and dichloroaniline (alternately, reaction between 3, 4-dichloro phenyl isocyanate and p-chloro aniline) under influence of high shear mixer followed by continuous reactive drying.

Background of the invention:

The present disclosure relates generally to the production of 3,4,4-trichlorocarbanalide from reaction of 4-Chlorophenyl Isocyanate and 3,4-dichlorocarbanalide, and more particularly to apparatus and methods for producing 3,4,4-trichlorocarbanalide via liquid phase condensation reaction between 4-Chlorophenyl isocyanate and 3,4-dichlorocarbanalide. More specifically, the disclosure relates to the reduction of mass transfer limitations in apparatus and further methods for converting 4-chlorophenyl isocyanate and 3, 4-dichlorocarbanalide into 3, 4, 4-trichlorocarbanalide by Continuous reactive drying (CRD).

The present disclosure relates to the production of 3, 4, 4-trichlorocarbanalide, also known as triclocarbon and TCC. 3, 4, 4-trichlorocarbanalide is a halogenated carbanalide and prepared by reaction of a halogenated aromatic amine with a halogenated aromatic isocyanate. The reaction takes place in an anhydrous and stable solvent. TCC is a high duty, wide-spectrum bacteriostatic agent. It is used in preparation of daily chemical products and medical antiseptics such as washing powder, medicated soap, antibacterial towel towel, cleaning facial tissue, wound paste and the like.

3, 4, 4-trichlorocarbanalide (TCC):
As per reaction below, one mole of aromatic amine reacts with one mole of isocyanate to yield one mole of trichlorocarbanalide. Reaction is highly exothermic.

R-NH2 + R’-N=C=O  R-NH-C=O-NH-R’.

Where, R = chlorinated aromatic ring and R’= dichlorinated aromatic ring.
Conventionally, the method for preparing TCC consists of addition of reactant in the reaction vessel in the form of a solution in halogenated solvent such as dichlorobenzene. The reactant are mixed and hence reacted. The product formed is solid which converts the system into heterogeneous system. Thus overall reaction becomes mass transferred controlled. Hence with conventional stirrer and very nature of heterogeneous system the reaction times for this conversion are substantially long, can be as much as 12 hours. Also followed by time consuming downstream process of filtration and drying.

Normal Industrial methods are usually carried out in SS reactors provided with reflux condensers, chilling jackets and mixing stirrers.

The prior art of various industrial scale methods for the production of 3, 4, 4’trichlorocarbanalide have following disadvantages
a. These include the fact that they are carried out necessarily in batch operation mode.
b. It requires installations of large batch volume.
c. The over all reaction becomes mass transferred controlled and hence it is time consuming operation.
d. Also the downstream processing of filtration operation is also time consuming operation

Therefore there is a need of a process which devoid drawbacks associated with prior art processes.

Object of the invention:

It is found that Higher the values of mixing dynamics results in lower resistance to mass transfer, which make this reaction instantaneous. In addition to this heat of reaction is utilized for in drying i.e carrier solvent evaporation, hence continuous reactive drying (CRD) is achieved.

It is therefore an object of the present invention is to provide improved process for the preparation of 3,4,4’ trichlorocarbanalide which reacts immediately by overcoming mass transfer limitation of reaction hence reaction completion takes place in few seconds.

Another object of the present invention is to provide improved process for the preparation of 3, 4, 4’ trichlorocarbanalide which eliminates time consuming down stream processing of filtration and handling additional filtration equipments

Another object of the present invention is to provide improved process for the preparation of 3, 4, 4’ trichlorocarbanalide where reaction completion and drying operations are simultaneously achieved by continuous reactive drying (CRD), thereby achieving dual objective of reaction completion and drying.

Another object of the present invention is to provide improved process for the preparation of 3,4,4’trichlorocarbanlide, the improvement which comprises high shear mixing followed by continuous reactive drying (CRD)

Summary of the invention:

In one aspect, present invention provides improved process for the preparation of 3,4,4’-trichlorocarbanalide by treating reactants 3,4-DCA and 4-CPI in CRD induced by high shear mixing thus gives complete dry product in few seconds.

In another aspect, present invention provides improved process for the preparation of 3,4,4’-trichlorocarbanalide by treating reactant 3,4-DCA and 4-CPI in continuous reactive drying (CRD), utilizing energy (heat) released from reaction (exothermic reaction) into drying by evaporation of solvent.

Brief description of Figures:

Figure-1 is schematic sketch representation which discloses a process of the present Invention, where the high shear mixing and reaction followed by continuous reactive drying takes place

Part -1 of fig. 1 indicates reaction vessel were the reactant 3,4-DCA and 4-CPI (alternately PCA and 3,4-DCPI) are premixed.

Part – 2 of fig. 1 indicates high shear mixer with toothed rotor-stator set rotating at high RPM (in order of 7500 rev per minute and above). This device is capable of providing high shear micro mixing, and discharging the mixer out of mixing chamber in micro seconds while keeping the mixing in fluid state.

Part – 3 of fig. 1 indicates typical rotary dryer with vacuum system. Here the continuous reactive drying takes place which achieves dual target, that is 1st complete completion of reaction and second drying.

Detail description of the invention:

TCC is formed by reacting 3,4-Dichloro aniline (DCA) and 4-chloro phenyl isocyanate (4CPI). Alternatively it is formed by reacting Parachloro aniline (PCA) and 3,4-dichlorophenyl isocyanate (3,4-DCPI). The reactant are dissolved in aromatic solvent preferably mono chlorobenzene (MCB) and then reacted. The reaction is exothermic.

It was found that reaction is instantaneous, but still it used to take 8 to 10 hours for reaction completion. The explanation for this time consumption is that 4-CPI and 3,4-DCA in solution of MCB are homogeneous but moment they react it produces TCC which is not soluble in MCB. As the TCC builds up it makes solution heterogeneous and thus reaction becomes mass transfer controlled in later stage.

Hence it was envisaged to introduce homogenizer or high shear mixing technology to over come mass transfer limitation. Thus it was planned to mix 4-CPI and 3,4-DCA immediately in a homogenizer thus drastically reduce time of reaction.

Also it was found that immediately after passing through high shear mixer the heat liberated by reaction (exothermic reaction) can be utilized for solvent evaporation, thus reducing energy load and achieving dual target of reaction and drying simultaneously.

The advantages of CRD induced by high shear mixer are,
1. It is semi continuous
2. It makes reaction instantaneous.
3. It eliminates cumbersome down stream processing like filtration
4. Reactor size can be reduced to minimal size for pre mixing purpose, filtration equipment no required, hence saving on fixed cost.
5. Energy input during drying is minimized.
6. Solvent handled in minimized drastically compared to used in conventional agitated reactor, hence minimum handling so minimum loss.
7. Solvent used is directly recovered during drying, hence no need of sending solvent for recovery as would be required to recover solvent from filtration mother liquor. Hence no loss of solvent during recovery.

While the present invention has been described in terms of its specific embodiments, certain modifications and equivalents will be apparent to those skilled in the art and are intended to be included within the scope of the present invention.

The process of the present invention is described by the following examples, which are illustrative only and should not be construed so as to limit the scope of the invention in any manner.

EXAMPLE – 1

Preparation of 3, 4, 4’-trichlorocarbanalide in high shear mixer device followed by continuous reactive drying

10 kg of 3, 4-DCA dissolved in 3.4 volume of Monochloro benzene and 9.5 Kg 4-CPI is mixed with 10 lit of Monochlorobenzene and premixed in 100 liter reactor. The reaction mixer is then passed to high shear mixer device also called homogenizer which is jacketed at ambient temperature (30 to 40°C). The mixer discharge from the homogenizer is continuously pumped into RVD. The mixer is agitated in RVD under vacuum and heated upto 70°C. The product discharge from RVD is pure 3, 4, 4’-trichlorocarbanalide.

A following data shows yield and purity of final product obtained according to process of present invention. This data is the best mode to illustrate utility of the invention.

Data for 3,4,4’-trichlorocarbanalide (TCC)

TYPICAL VALUES:

Premixing time: : Maximum 2 minutes
Temperature of reaction : Ambient (35 to 40°C)
Tip speed of rotor-stator mixer : 28 m/s
Temperature of rotor-stator mixer zone : Max 70°C.
Vacuum during continuous reactive drying : 550 to 600 mm Hg
Temperature during continuous reactive drying : 70°C
Heat of Reaction : - 92.75 kcal/Kg DCA
Product obtained : 19 Kg
% Molar Yield (based on 100 % Purity) : 98 to 100 %

OBTAINED QUALITY DATA:

Parameters TCC DCC T4CC TAB CA LOD

Typical limit NLT 99% NMT 0.50% NMT 0.30% NMT 0.20% NMT 450 NMT 0.15%

Achieved quality 99.49 0.34 0.02 0.06 292 0.13