DESC:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2005

COMPLETE SPECIFICATION
(See section 10, rule 13)

1. TITLE OF THE INVENTION:
METHOD OF MANUFACTURING OF DICYANDIAMIDE (DCDA)
2. APPLICANT:

(a) Name : Granules India Limited
(b) Nationality : Indian Company
(c) Address : 2nd Floor, 3rd Block, My Home Hub Madhapur,
Hyderabad, 500081, Telangana, India.

3. PREAMBLE OF THE DESCRIPTION:
PROVISIONAL
The following specification describes the invention. COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

METHOD OF MANUFACTURING OF DICYANDIAMIDE (DCDA)
Field of the invention:
The present invention generally relates to a method of manufacture of Dicyandiamide (popularly known in industry as DCDA), and in particular it relates to an energy efficient, two step, green method of manufacture of Dicyandiamide.
Background of the invention:
Commercially DCDA is manufactured through calcium carbide route followed by nitrogen fixation process to calcium cyanamide; which is subsequently converted to DCDA. Calcium carbide is a chemical compound with the chemical formula of CaC2. The calcium carbide is mainly used in the production of acetylene and calcium cyanamide. The pure calcium carbide is colorless, however pieces of technical-grade calcium carbide are grey or brown and consist of about 80–85% of CaC2 (the rest is CaO (calcium oxide), Ca3P2 (calcium phosphide), CaS (calcium sulfide), Ca3N2 (calcium nitride), SiC (silicon carbide), etc.). In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odour reminiscent of garlic.
The calcium carbide is mainly used in production of calcium cyanamide, manufacture of acetylene gas, generation of acetylene in carbide lamps, manufacture of chemicals for fertilizer; and in steelmaking
Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately 2200°C. This method has not changed since its invention in 1892. The following reaction shows the synthesis of calcium carbide at temperature of 2200°C.
CaO + 3 C ? CaC2 + CO (gas)
The high temperature required for this reaction is not practically achievable by traditional combustion, so the reaction is performed in an electric arc furnace with graphite electrodes. The calcium carbide product produced generally contains around 80% calcium carbide by weight. The carbide is crushed to produce small lumps that can range from a few mm up to 50 mm. The impurities are concentrated in the finer fractions. The CaC2 content of the product is assayed by measuring the amount of acetylene produced on hydrolysis. As an example, the British and German standards for the content of the coarser fractions are 295 L/kg and 300 L/kg respectively (at 101 kPa pressure and 20°C temperature). Impurities present in the carbide include phosphide, which produces phosphine when hydrolysed. This reaction is an important part of the industrial revolution in chemistry, and was made possible in the USA as a result of massive amounts of inexpensive hydroelectric power produced at Niagara Falls before the turn of the 20th century. The method for the production in an electric arc furnace was discovered in 1892 by T. L Wilson and independently by H. Moissan in the same year.
Calcium carbide reacts with nitrogen at high temperature (at around 1100°C to 1200°C) to form calcium cyanamide as follows
CaC2 + N2 ? CaCN2 + C
Calcium cyanamide is commercially known as nitrolime and is the inorganic compound with the formula CaCN2, it is the calcium salt of the cyanamide anion. Also, calcium cyanamide is used as fertilizer. Calcium cyanamide was first synthesized in 1898 by Adolph Frank and Nikodem Caro. Commercially it is available at 65% to 70% quality and it is analysed by total nitrogen content method.
Calcium cyanamide is hydrolysed with water in presence of carbon dioxide to hydrogen cyanamide, H2NCN and Calcium carbonate. This Hydrogen cyanamide further dimerizes in presence alkali to DCDA (Dicyandiamide).
CaCN2 + CO2 + H2O ? CaCO3 + H2NCN
H2NCN + H2NCN ? H2NCNH2NCN (DCDA)
Drawbacks of the existing process for manufacturing of DCDA are as below:
• Very high temperature is required to carry out the process. Calcium carbide is produced industrially in an electric arc furnace from a mixture of lime and coke at approximately 2200°C and Calcium carbide is further converted to Calcium cyanamide using Nitrogen gas at around 1100°C.
• In the Calcium carbide formation, the coal required is high calorific coal; generally, for that purpose anthracite coal is used. The reaction also emits toxic carbon monoxide gas and needs to be used / disposed properly.
• Both the processes viz. Calcium carbide formation and nitrogen fixation reactions are at very high temperature and energy intensive processes; requires higher electricity consumption.
• Both the products are dirty black colour, dusty appearance and having irritating properties.
Accordingly, there exists a need to provide an energy-efficient process for manufacture of DCDA that overcomes the above-mentioned drawbacks in the prior art.
Objects of the invention:
An object of present invention is to use provide an energy-efficient, green method for manufacture of DCDA, that requires at lower temperature in the range 500°C to 700°C
Another object of the present invention is to provide a process for manufacture of DCDA wherein the co-products can be recycled and reused.
Another object of the present invention is to provide a green process for manufacture of DCDA that does not harmful biproducts and effluents.
Still another object of the present invention is to manufacture dicyandiamide (DCDA) in good yield without formation of any unwanted products.

Detailed description of the invention:
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with the prior art techniques and approaches are overcome by the present invention as described below in the preferred embodiment.
The present invention provides a two-step process for manufacture of dicyandiamide (DCDA). In the prior art process, the conversion of lime into calcium carbide requires very high temperature (2200°C), higher energy and generates toxic gases. Further, calcium carbide is converted to calcium cyanamide by reacting calcium carbide with nitrogen at 1100°C and calcium cyanamide is further converted to dicyandiamide using carbon dioxide at almost 60°C to 80°C.
When compared to the existing process for manufacture of DCDA, the two-step process of the present invention is far more energy efficient and economical. The process of present invention consumes very less power and the co-products viz. ammonia and carbon dioxide generated in this process are recycled in the process or useful in producing other valuable products; whereas is any solid waste like partially rejected waste lime is converted into construction bricks so that the whole process does not generate any wastes and is a green process. In the present invention, high yield of calcium cyanamide is first obtained by pyrolysis of urea in presence of lime in a continuous or batch reactor in a most optimal mode, which is then converted to dicyandiamide in the next step without generating any effluents.
The method for manufacturing of dicyandiamide (DCDA) comprises the steps as below:
In first step, urea is first heated with an alkaline earth metal oxide selected from CaO, MgO, BaO, BeO at a temperature ranging from 150°C to 350°C. On heating of urea, Isocyanic acid is formed and ammonia gas is emitted. The isocyanic acid on reaction with alkaline earth metal oxide produces alkaline earth metal isocyanate. The salt, alkaline earth metal isocyanate on further heating to temperature ranging from 500°C to 700°C decomposes into alkaline earth metal cyanamide and carbon dioxide.
The reaction stages (1), (2) and (3) of the first step of the green method for manufacturing of dicyandiamide (DCDA) happen in a single reactor with sequential manner. In an embodiment, the reaction is carried out either in a batch mode or in a continuous mode.
In a second step, alkaline earth metal cyanamide is hydrolyzed in the presence of carbon dioxide to give hydrogen cyanamide (H2NCN). Hydrogen cyanamide further dimerizes in presence alkali to give DCDA (Dicyandiamide). The byproduct obtained in this reaction is alkaline earth metal carbonate.
In a preferred embodiment, the alkaline earth oxide is calcium oxide (CaO).
The reaction sequence of the first step of the green method for manufacturing of dicyandiamide (DCDA) is given below:
First Step:
(NH2)2CO ? HCNO + NH3? (1)
Urea Isocyanic acid Ammonia gas
2HCNO + CaO ? Ca(OCN)2 + H2O (2)
Isocyanic acid Lime Calcium isocyanate
Ca(OCN)2 ? CaCN2 + CO2? (3)
Calcium isocyanate Calcium cyanamide Carbon di-oxide gas
Second Step:
CaCN2 + CO2 + H2O ? H2NCN + CaCO3
Calcium cyanamide Hydrogen cyanamide

H2NCN + H2NCN ? H2NCNH2NCN
Hydrogen cyanamide (DCDA)
The two-step green method for manufacturing of dicyandiamide (DCDA) has the advantages as below:
i) The method of the present invention is economical and has significant advantages in terms of CAPEX and OPEX.
ii) The method of the present invention can be carried out as batch process or continuous process.
iii) The method of the present invention is easy to operate and it is convenient to recover co-products like ammonia and carbon di-oxide. These co-products viz. carbon di-oxide and ammonia are used partly in self-consumption for converting calcium cyanamide to DCDA.
iv) This continuous process setup of the method of the present invention makes it easy for automation resulting in good process safety and process control with equipment such as hot-melt extruder, Screw feeder reactor, pin mill, RVPD, bucket conveyor furnace, graphite crucible furnace, continuous rotary furnace etc..
v) The method of the present invention is easy to scale-up and requires very less of electrical energy, with leaving no effluent thus is a green process.
The foregoing objects of the invention are accomplished and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiment. Detailed descriptions of the preferred embodiment are provided herein; however, it is to be understood that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure, or matter. The embodiments of the invention as described above and the methods disclosed herein will suggest further modification and alterations to those skilled in the art. Such further modifications and alterations may be made without departing from the scope of the invention.

Dated this 16th day of May, 2024.

Ashwini Kelkar
(Agent for Applicant)
(IN/PA-2461)
,CLAIMS:We claim:
1. A method for manufacturing of dicyandiamide comprises the steps:
1) heating and decomposing: heating urea with an alkaline earth metal oxide at 150°C to 350°C to provide alkaline earth metal isocyanate, and further heating to 500°C to 700°C to provide alkaline earth metal cyanamide;
2) hydrolyzing and dimerizing the obtained alkaline earth metal cyanamide to provide dicyandiamide.

2. The process as claimed in claim 1, wherein the alkaline earth metal oxide is selected from CaO, MgO, BaO and BeO.

3. The process as claimed in claim 1, wherein the reaction can be carried out in a single reactor with sequential manner.

4. The process as claimed in claim 1, the reaction can be carried out either in a batch mode or in a continuous mode.

5. The process as claimed in claim 1, while heating urea, Isocyanic acid is formed and ammonia gas is emitted.

6. The process as claimed in claim 1, wherein ammonia and carbon dioxide generated in the first reaction step are recycled.

Dated this 16th day of May, 2024.

Ashwini Kelkar
(Agent for Applicant)
(IN/PA-2461)