Claims:We claim;
1. An improved and cost effective process for preparation of malic acid from maleic anhydride with co-production of Fumaric Acid in a titanium tubular reactor, wherein the improvement comprises reduced process time to about 90 mins during heating of maleic anhydride dissolved in water in tubular reactor at 180-190?C to obtain stoichiometric yield of malic acid and fumaric acid.

2. The improved process according to claim 1, wherein the process is carried in absence of external catalyst.

3. The improved process according to claim 1, wherein the process is a batch, semi-continuous or continuous process.

4. The batch process for preparation of malic acid from maleic anhydride with co-production of Fumaric Acid according to claim 3, comprising;

i. heating maleic anhydride dissolved in water in the titanium reactor tube assembly to a temperature in the range of 180-190?C for about 90 mins;
ii. draining the entire solution of step (i) into the flash tank, cooling, separating fumaric acid from malic acid followed by purifying, concentrating the malic acid.

5. The semi-continuous process for preparation of malic acid from maleic anhydride with co-production of Fumaric Acid according to claim 3, comprising;

i. heating maleic anhydride dissolved in water in the titanium reactor tube assembly to a temperature in the range of 180-190?C for about 90 mins;
ii. draining part of the solution of step (i) into the flash tank and simultaneously adding equal quantity of feed Maleic acid solution in the titanium reactor tube assembly and heating the mixture at same temperature range for about 10-20 mins;
iii. draining part of the solution of step (ii) recirculating the feed and performing the process repeatedly until stoichiometric yields of malic acid and fumaric acids are obtained.

6. The continuous process for preparation of malic acid from maleic anhydride with co-production of Fumaric Acid according to claim 3, comprising;

i. heating maleic anhydride in the titanium reactor tube assembly to a temperature in the range of 180-190?C for about 90 mins;
ii. draining the solution of step (i) in to the flash tank at a constant rate and simultaneously adding equal quantity of feed Maleic acid solution in the titanium reactor tube assembly and repeating the process steps until stoichiometric yields of malic acid and fumaric acids are obtained.
, Description:Field of Invention:

The present invention relates to an improved and cost effective process for commercial production of Malic Acid from maleic anhydride with co-production of Fumaric Acid in a Titanium Tubular Reactor with reduced processing hours. The present invention further relates to the process which is carried out in a Titanium Tubular Reactor as a Batch Tubular process or Semi-continuous tubular process or a Continuous Tubular Process.

Background and Prior art:

Process for synthesis of malic acid from maleic acid at high temperature involving metal catalysts was described in US3379756. Monsanto’s Patent US5210295 discloses a process for hydration of an acid selected from maleic acid, fumaric acid and others, where the high temperature reaction is done in presence of sodium ions in specified molar ratios. Other related process patents are, CN1560016, CN102452931, CN103121936, GB1368596, JP2003104934, US3117991, US3379756, US3379757, US4035419, USRE31139. Processes involving micro-organisms and microbiological agents are also described in Patents CN102352382, CN102492734, TW200914620 and US5270190. Processes described in these Patents are batch processes with high temperature involving long reaction times. The traditional batch stirred vessel reactors involve very large volumes as well as very high/long processing times and extremely high operating costs.

Summary of Invention:

The present invention offers substantial improvement in economy of scale of operations, reduced volumes, reduced processing hours and is highly energy saving. The production of malic acid is carried out in a specially designed tubular reactor/reactors of suitable material such as Titanium, without involving a catalyst. The present invention provides substantial improvements in costs, reduced time-lines (reaction hours) and consequent savings in energy, time leading to enhanced productivity. The process leads to production of malic acid and/or fumaric acid alone or as coproducts. The Tubular process involving materials such as Titanium can be used for Batch processes, semi-continuous process or continuous process. The Titanium tubular process effectively becomes a self-catalysed process without use of any additional catalyst. The process of this invention leads to the following critically important commercial and operating advantages.

a) Reduced Time consumption and high production capacity for the Production Reactors.
b) Very low Energy Use.
c) Improved Productivity and thus reduced plant size and manpower.
d) Lower investment.
e) Lower in process inventories of expensive inputs, and intermediates.
f) Easier and better process control than in traditional batch processes so far existing.
g) Lower Operating costs and production costs.

Description of Drawings:

Drawing in Fig. 1 represents traditional batch stirred vessel process. Figures 2 to 4 represents the embodiments of the process in the present invention. The Tubular Reactors are 50 meters in length and diameter of 1.25inches (3.15 centimetres). The reactor consists of 10 such tubes, affixed parallely. The shell side materials are made of SS316 and Tube side material is preferably Titanium.

Detailed Description of Invention:

Development of processes with economy in scale up operations, cost saving, energy saving and time saving have become the need of the hour. A process which is time and energy saving and which results in high yields and purity is described herein.

The present process is carried out in Tubular reactor of suitable design to prevent plugging and promote high speed conversion, made with specific anticorrosive material like Titanium, with a high pressure circulating pump. The feed end of the titanium tubular Reactor is connected to this pump, the other end back to the suction of the pump for continuous circulation at pressure, with a bypass valve; alternatively there is a bypass in the piping after Tubular reactor, for removal of all or some material into a flash/ drain tank. This latter Flash /Drain tank is also connected back to the circulating pump suction. By circulation of the feed mixture or solution at high temperatures for a certain number of batches, then draining or partial draining and removal of a Stream, Semi- Continuous or Continuous or Batch processes for the production of Malic acid and Fumaric either in flexible ratios, as desired is achieved.

In one embodiment of the invention, the process employs a tubular reaction system of limited Process ‘residence time’, with closed circulation for a sufficient number of cycles, leads to near full conversion to the Final equilibrium, until it is stopped and drained to undergo further separation and purification processes. This may be called the Batch Tubular process.

In another embodiment of the invention, the system consists of a number of such tubular reactor sub-systems, each system with a pump, a drain/ flash tanks and recirculation piping, and then each sub-system connected in series, leads to stepwise increase in conversion of each sub-system, and eventually once we ensure enough residence- conversion time overall, to final equilibrium conversion, whereupon the resultant final outflow from the overall system is drained to undergo further separation and purification processes. This is termed as a Semi-Continuous Tubular process.

In yet another embodiment herein, as a further improvement, the single Tubular reactor is designed (unlike in earlier embodiments) with large enough Residence time ‘once through’ so that there is no recirculation required, but within a single step of passing through the reactor at high speeds and short time, the final equilibrium conversion is achieved. This final solution- slurry is then drained and sent for further separation processes. This embodies the Continuous Tubular Process.

In a typical embodiment of the process, the feed maleic acid solution (obtained on dissolving maleic anhydride in DM water) is taken in a dissolver tank and it is circulated through the circulation pump & discharged into the titanium reactor tube assembly with high velocity. The solution is continuously circulated through the titanium tubes. Heating is given to increase the temperature of the solution in the range of 180-190°C at a pressure of about 15 barg. This setup is maintained for about 90mins.

Step 1:
In the batch process, after the above operations, the solution is drained into a flash tank & taken for further processing.

Step 2:
In the continuous process, after the above operations, a very small quantity of the solution is drained into a flash tank continuously & simultaneously the same quantity of feed maleic acid solution is fed into the titanium tubes.

Step 3:
In the semi continuous process, after the above operations, a part of the solution is drained after about 90mins and equal quantity of feed maleic acid solution is fed into titanium tube recirculated and again after a fixed period of time another fixed quantity is drained and the process is repeated again.

Example 1: (Batch Process):
5.7 Kgs of Maleic Anhydride is dissolved in 10 litres of demineralised water in a separate vessel. This solution is then pumped into the reactor tube assembly and circulation started. Parallely, the temperature of the solution in the tube is increased to 180-190°C. The circulation and the temperature are maintained for 90 mins. After 90 mins the heating is cut off by closing the steam valve. After about 30 mins the temperature of the solution in the tube comes down to about 140 – 150°C. The entire solution is then drained into the flash tank. The solution is cooled. Fumaric Acid is separated and the ML is taken for further purification, concentration and crystallization etc. The exact quantities of Malic Acid, Fumaric Acid obtained are arrived from the quantities obtained and the yield is calculated.

TABLE 1:
Experimental conditions for above example are as given below:
EXAMPLE NO QTY OF MALEIC ANHYDRIDE (Kg) QTY OF DM WATER (LITR) TEMPERATURE RANGE IN DEG C TOTAL VOLUME OF REACTOR(LITR) DURATION IN MINS
1 5.7 10 185-190 13.4 90

The stoichiometric yields obtained are nearly as same as that in any batch process.

NAME OF THE COMPOUND PERCENT YIELD
Malic Acid 57-58 %
Fumaric Acid 37-38%
Maleic Acid 1.2-1.5 %
Loss/Unaccounted (CO, CO2 etc.,) 2-3 %

EXAMPLE 2: (Continuous process):
5.7 Kgs of Maleic Anhydride is dissolved in 10 litres of demineralised water in a separate vessel. This solution is pumped into the reactor tube assembly and circulation started. Parallely the temperature of the solution in the tube is increased to 180-190 deg C. The circulation and the temperature are maintained for 90 mins.

After 90 mins duration the solution in the reactor is drained into the flash tank at the rate of 20 ml/min; simultaneously equal quantity of feed Maleic acid solution is fed into the titanium tube .This process is continued for several hours. The solution in the flash tank shows the following analytical parameters.

Constituent Percentage
1. Malic Acid 58 -62 %
2. Fumaric Acid 38-42 %
3. Maleic Acid 1-2 %

EXAMPLE 3 (Semi Continuous process):
5.7 Kgs of Maleic Anhydride is dissolved in 10 litres of demineralised water in a separate vessel. This solution is pumped into the reactor tube assembly and circulation is started. Parallely the temperature of the solution in the tube is increased to 180-190 deg C. The circulation and the temperature are maintained for 90 mins.

After 90 mins reaction, 500 ml of the solution is drained into the flash tank, the reactor pressure reduces to around 12-13 bar, the same quantity of feed Maleic acid solution is fed into the titanium tube assembly ,and the reaction is carried out for another 20 mins and then the 500 ml solution is drained into the flash tank. This process is continued for several hours to be termed as a semi continuous process.

The solution in the flash tank shows the following analytical parameters.

Constituent Percentage
1. Malic Acid 58 -62 %
2. Fumaric Acid 38-42 %
3. Maleic Acid 1-2 %

The examples and figures described herein are by way of illustration and therefore, should not be construed to limit the scope of the invention.