Field of the invention:

The present invention relates to an improved process for the preparation of 2-ethyl hexyl chloroformate (EHCF) & Benzyl Chloroformate (BCF) individually by reacting gaseous phosgene with thin film of liquid 2-ethyl hexanol and benzyl alcohol in continuous thin film reactor (CTFR).

Background of the invention:

Various chloroformates are widely employed in a large number of applications such as agrochemical, pharmaceutical and other allied industries. As a general, chloroformates are produced by reacting various alcohols with phosgene in gas-liquid phase in conventional batch reactor.

2-Ethyl Hexyl Chloroformate:

In reaction, one mole of 2-Ethyl Hexanol reacts with one mole of phosgene instantaneously and release a mole of hydrochloric acid and a mole of 2-Ethyl Hexyl Chloroformate. Reaction is highly exothermic. Processes generally require about 60-65 % molar excess amount of phosgene, for completion of reaction.

2Et-Hex-OH + COCl2 = 2Et-Hex- H-O-CO-Cl + HCl

The process parameters are very critical in terms of molar ratios of (2-Ethyl Hexanol / Phosgene). For high ratio, product chloroformate further reacts with unreacted 2-Ethyl hexanol and produce carbonate derivative.

2-EH-O-CO-Cl + 2-EH-OH = EH-O-CO-O-EH + HCl

Benzyl Chloroformate (BCF):

In reaction, one mole of Benzyl Alcohol reacts with one mole of phosgene instantaneously and release a mole of hydrochloric acid and a mole of Benzyl Chloroformate. Reaction is highly exothermic. Processes generally require about 70 % molar excess amount of phosgene, for completion of reaction.

Ph CH2-OH + COCl2 = Ph-CH2-O-CO-Cl + HCl

The process parameters are very critical in terms of molar ratios of (BA/ Phosgene). For high ratio, product chloroformate further reacts with unreacted Benzyl Alcohol and produce carbonate derivative.

Ph-CH2-O-CO-Cl + Ph CH2-OH = Ph-CH2-O-CO-CH2 -Ph + HCl

Normal Industrial methods are usually carried out in mild steel glass-lined reactors provided with reflux condensers, chilling jackets and mixing stirrers.

The prior art of various industrial scale methods for the production of 2-Ethyl Hexyl Chloroformate have several disadvantages.

a. These include the fact that they are carried out necessarily in batch operation mode.
b. It requires installations of large batch volume and large chilling capacity for the condensing of phosgene and for maintaining of the reaction mass.
c. Furthermore, special costly construction materials (MSGL or Graphite or Hestalloy) are necessitated by the corrosive character of the end product and of the hydrogen chloride by-product.
d. The resulting crude product usually contains proportion of Chloride, Carbonate and colored impurities in chloroformate which requires vacuum distillation as purification step.
e. Another disadvantage of the prior art processes is that , in batch process at any given time the reaction vessel contains a large amount of highly toxic phosgene which represents high hazardous potential in case of any failure of equipment or unit operation.

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

Serendipitously, present inventors discovered that chloroformates of desirably high purity and high yield can be produced by treating gaseous phosgene with liquid 2-Ethyl Hexanol & Benzyl Alcohol in Continuous Thin Film Reactor (CTFR).

Object of the invention:

It is therefore an object of the present invention is to provide improved process for the preparation of chloroformates by using continuous thin film reactor which gives high yield and purity without use of any agitation power and carrier solvent.

Another object of the present invention is to provide improved process for the preparation of chloroformate which is operationally simple, easy to handle and applicable at an industrial scale.

Another object of the present invention is to provide improved process for the preparation of chloroformate by treating gaseous phosgene with respective liquid 2-Ethyl Hexanol & Benzyl Alcohol in Continuous Thin Film Reactor (CTFR).

Summary of the invention:

In one aspect, present invention provides improved process for the preparation of chloroformate treating gaseous phosgene with liquid 2-Ethyl Hexanol or Benzyl Alcohol in Continuous Thin Film Reactor (CTFR).

In another aspect, present invention provides improved process for the preparation of chloroformate, the improvement which comprises treating gaseous phosgene with liquid 2-Ethyl Hexanol or Benzyl Alcohol in Continuous Thin Film Reactor (CTFR).

Brief description of figure:

Figure-1 is schematic sketch of continuous thin film reactor (CTFR), which discloses a process of the present Invention, where the gas-liquid reaction of EHCF or BCF was conducted in CTFR.

Figure-2 is schematic sketch of process description which discloses a process of the present Invention, where the gas-liquid reaction of EHCF or BCF was conducted in CTFR.

Detail description of the invention:

The gas-liquid process is a reactive diffusion of phosgene gas in the thin film of 2-ethyl hexanol or Benzyl Alcohol which results in high level of exotherm in Continuous Thin Film Reactor (CTFR).

Higher the values of gas-liquid diffusivity results in lower resistance to mass transfer which allows the reaction to take place in the Gas-liquid interface film only. Thus, it is possible to carry out such instantaneous reaction in Continuous Thin Film Reactor (CTFR).

A Schematic Sketch shown in Figure-1 is a CTFR - “Continuous Thin Film Reactor”. Industrially it is also known as Falling Film Calandria or Wetted Wall Column, used for unit operations. Conventional use of falling film phenomena is for unit operations like absorption, degassing, evaporation etc. In present invention, same phenomena is used for unit process i.e. to carry out gas-liquid reaction in thin film by increasing surface to volume ratio and optimizing residence time i.e. film thickness.

CTFR was fabricated from glass and the main component of it consisting of a spiral coil, jacketed assembly for utility supply and bottom Teflon flange to hold the column structure. CTFR contains a spiral glass tube coil (A), it is about 1000 mm long and having a 8 mm tube diameter with 40 Nos. of coils arrange at 25 mm. pitch. An adjustable teflon notch (Liquid distributor–B) as shown in (Figure-1) at top which distributes the liquid reactant on the outer surface of column C2. CTFR is having three tubes C1, C2, and C3 in increase order of diameter within one another. C3 is the outer tube & known as shell. Annulus between C3 and C2 is defined as passage (P) for gas in counter current direction. However outer surface (i.e. exposing towards gas) of C2 is wetted with thin film of reaction liquid distributed from the top adjustable liquid distributor (B). C1 is the vertical utility pass partition and inner most tube which is open from top. Cold utility (temperature -5 to 0°C) enters from nozzle (E) & moves upward in spiral coil is the most inner element having diameter less then C1. Annulus between C1 and spiral coil, which act as 1st pass of utility. Utility overflows from open end of tube C1 and move downward through annulus between C1 and C2, which acts as 2nd pass of utility. Utility returns back from nozzle (F) at bottom. Reactant liquid passes upward through spiral coil (i.e. 1st pass across utility) & distributed from the top on outer surface of C2. Liquid reactant material is charged from nozzle (G) by using a peristaltic pump , which was pre-calibrated for ( Flow Vs. RPM). It flows upward in spiral coil and getting pre-cooled by outgoing utility. Liquid flow ends in cup (D) and overflows in a telfon notch (B) (Liquid distributor) which is fitted in tapered position on the tube (C2). Position of a teflon notch (B) can be change up and down on a central shaft (N) and fit tightly or loss depending upon it’s position on column (C2). This position can be changed by rotating notch in circular motion using handle (K). Desired film thickness can be maintained depending up on the nature of reaction and physical properties of the liquid material being handled.

Reaction mass overflows from Nozzle (H) and can be can be drained from bottom most nozzle (N) and can be used for further process. The assembly is covered from bottom by using a teflon flange which can facilitate the entry and exit of utility and entry of reactant liquid, and it covered from top by using a cap (L) and flange arrangement.

As both the raw materials (2-ethyl hexanol or Benzyl Alcohol and phosgene gas) react in the thin film, product produced by the method is having very high degree of GC purity and high degree of molar yield , which completely eliminates further purification step (i.e. distillation of crude BCF or EHCF). Present invention of process does not require any carrier solvent or agitation power for mixing.

Process can be carried out in a column in which liquid flows down in the form of thin film on outside tube surface and gas diffuses into the film in counter current mode. Cooling utility (i.e Brine 0°C to -5°C) is provided inside the tubes maintains reaction temperature close to mean metal temperature and helps in condensing phosgene gas as well to remove heat of reactions. Liquid product EHCF or BCF in form of thin film is collected in jacketed receiver provided at bottom of column. Product vapor of HCl along with excess phosgene leave from top of column to caustic scrubbing system.

The liquid reactant is perfectly metered and distributed through the annular slot forming a continuous and uniform thin film at one end which allows good productivity. At the top, the liquid reactant meets the gaseous reactant immediately starting the exothermic and heterogeneous chemical reaction. The heat of reaction is continuously transferred and removed by the circulating chilled water. The finished product i.e. chloroformate is continuously recovered at the other end. Being a continuous process, the production of this product claims low overhead requirements and raw material wastage.

The advantages of CTFR are,

1. It is continuous
2. It conducts instantaneous reaction because high surface to volume ratio.
3. It doesn’t require agitation power or any solvent for reaction.
4. Reaction vessel or complete set up is very small size and low cost.
5. It can be used with glass or compatible material
6. Hazardous potential: At any given time, relatively small amount of material in form of thin film is present in the reactor. Moreover phosgene gas passage provided is very narrow hence it immediately reacts with the alcohol film in the reaction zone. Only excess to stoichiometric amount of gas will remain in the free state. Therefore, if any malfunction of apparatus or accident occurs, the amount of phosgene which can escape is only very small. Material inventory requirement will be minimum compared to conventional batch process reactor.

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 2-Ethyl Hexyl Chloroformate (EHCF) in CTFR
Liquid 2-Ethyl Hexanol (20-25°C) is perfectly distributed through the annular slot at a rate of 0.5-0.75 kg/hr forming a continuous and uniform thin film at top of the column, where it reacts in continuous counter current flow of phosgene gas (20-25°C) at a rate of 0.6-0.9 kg/hr in gas phase. Reaction temperature ranges from 0 to -5°C under cold condition. Product EHCF produced at a rate of about 1.0 kg/hr is continuously recovered and kept at 0to -5°C to allow dissolved phosgene to react with unreacted 2-Ethyl Hexanol if present in product pot. Product EHCF liquid has GC purity value of 99.02 % and product have molar yield value of 98.7 % based on 2-Ethyl Hexanol. About 60-65 % excess phosgene gas was utilized for the completion of reaction and avoidance of any impurities due to side reactions. However, a typical industrial process mixes both the reactants in liquid state to produce EHCF, But the present invention uses liquid 2-Ethyl hexanol to react with phosgene gas. This claims large amount of agitation power to waive from process in production of EHCF.

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 BCF (2-Ethyl Hexyl Chloroformate):

TYPICAL VALUES:

Liquid Rate of 2-Ethyl Hexanol : 0.5-0.75 kg/hr
Temperature of Reaction : 0-5 ° C
Phosgene Gas rate : 0.6-0.9 kg/hr
Temperature of Phosgene gas entering to Reaction : 20-25°C
Pressure of Phosgene gas entering to Reaction : 0.1 – 0.15 kg/cm2 gauge
% Excess Phosgene used over stoichiometry : 60-65%
Temperature of Reaction zone : 0 to -5°C
Heat of Reaction : -6.965 kcal / kg of 2-Ethyl Hexanol
Product rate of BCF liquid : 0.6-1.0 kg/hr
% Molar Yield : 97.0 - 98.5 %
% GC Purity : 98.0 – 99.0 %
Film Thickness : 0.15 mm
Residence time (Gas-Liquid Exposure) : 92 Seconds

YIELD AND QUALITY DATA ( EHCF):

Sr. Flow Rates (gm/min) Rxn Temp (°C) % GC Purity
Phos 2-Et-OH Ratio %Ex. Phos. BCF 2-EtH-OH 2-Et
-Cl Di-2-Hexyl
Carbonate Other
Imp % Molar
Yield
1 12.00 9.16 1.31 70.00 0 to -4 97.49
0.83 0.01 1.23 0.44 97.77
2 12.00 9.16 1.31 70.00 0 to -4 97.77 0.25 0.14 0.32 1.52 97.33
3 10.70 8.33 1.28 69.24 0 to -5 98.73 0.03 ND 0.01 1.23 98.50
4 9.48 8.33 1.14 49.94 0 to -5 92.55 5.34 ND 0.65 1.46 98.20
5 9.51 8.33 1.14 50.00 0 to -5 89.18 9.95 ND 0.34 0.53 97.39
6 10.14 8.33 1.22 60.00 0 to -5 98.83 0.48 ND 0.01 0.68 97.01
7 15.20 12.49 1.22 60.00 0 to -5 99.11 0.31 ND 0.18 0.40 97.29
8 15.20 12.49 1.22 60.00 0 to -5 99.17 0.12 ND 0.31 0.40 97.40
9 14.00 11.20 1.25 60.00 0 to -5 96.65 2.32 ND 0.60 0.43 97.25
10 13.00 10.33 1.26 65.00 0 to -5 98.20 0.08 ND 0.78 0.94 98.90
11 13.40 11.00 1.22 60.00 0 to -5 99.02 0.01 ND 0.47 0.50 98.70
12 14.60 12.00 1.22 60.00 0 to -5 98.59 0.13 ND 0.29 0.99 98.00

EXAMPLE–2

Preparation of Benzyl Chloroformate (BCF) in CTFR
Liquid Benzyl Alcohol (BA) (0 to -5 °C) is perfectly distributed through the annular slot at a rate of 0.5 kg/hr forming a continuous and uniform thin film at top of the column where it reacts in continuous counter current flow of phosgene gas (20-25°C) at a rate of 0.79 kg/hr in gas phase. Reaction temperature ranges from 0 to -5°C under cold condition. Product BCF produced at a rate of about 0.75 kg/hr is continuously recovered and kept at 0-5°C to allow dissolved phosgene to react with un reacted BA present in product pot. Product BCF liquid has GC purity value around 95 % and product have molar yield value of 97 % based on BA. About 70 % excess phosgene gas was utilized for the completion of reaction and avoidance of any impurities due to side reactions. However, a typical industrial process mixes both the reactants in liquid state to produce BCF. But the present invention uses liquid BA to react with phosgene gas. This claims large amount of agitation power to waive from process in production of BCF.
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 BCF (Benzyl Chloroformate):

TYPICAL VALUES:

Liquid Rate of BA : 0.5 kg/hr
Temperature of Reaction : 0 to -5 ° C
Phosgene Gas rate : 0.79 kg/hr
Temperature of Phosgene gas entering to Reaction : 20-25°C
Pressure of Phosgene gas entering to Reaction : 0.35 – 0.55 kg/cm2 gauge
% Excess Phosgene used over stoichiometry : 70%
Temperature of Reaction zone : 0 to -5°C
Heat of Reaction : -13.0 kcal/kg of BA
Product rate of BCF liquid : 0.75 kg/hr
% Molar Yield : 97-98 %
% GC Purity : 95 %
Film Thickness : 97 Seconds

YIELD AND QUALITY DATA ( BCF):

Ex. Sr.
No. Flow Rate (gm/min) Reaction Temp.
° C % GC Purity % Molar Yield
(BCF/BA)
Phos BA Ratio % Ex. BCF BA BCl Other Imp
GAS-LIQUID REACTION (FALLING-FILM COLUMN)
Lab Development & Fesibility Trials
1 12.0 8.30 1.45 57.48 (-5) 0 0 0 0 96.83
2 12.0 8.32 1.44 57.48 (-5) 12.2 25.1 0 62.71 96.16
3 13.0 8.32 1.56 70.60 (-5) 0.00 0.00 0.00 0.00 94.54
4 13.0 8.32 1.56 70.60 (-4) 90.7 0.05 4.04 5.20 94.03
5 13.0 8.32 1.56 70.60 (-4) 94.4 0.29 1.67 3.61 96.35
6 13.2 8.40 1.57 73.23 (-5) 95.3 0.27 1.25 3.18 97.21
7 13.0 8.00 1.63 70.60 (-3) 95.6 1.23 1.58 1.58 97.51
8 13.2 8.40 1.57 73.23 (-4) 96.6 0.29 0.9 2.21 98.20
9 13.2 8.3 1.59 73.23 (-4) 95.8 0.09 0.8 3.35 98.39