Patent Analysis of the Process Technology for Producing Monocyanamide from Urea
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I. Background Introduction Cyanamide, also known as amino cyanide (H₂N-CN), is an important chemical intermediate that possesses both highly reactive cyano and amino groups. It finds wide applications in fields such as pesticides, pharmaceuticals, resin processing, flame retardants, feed additives, and plant growth regulators. Traditional industrial production of cyanamide relies mainly on the calcium cyanamide method, which has issues such as high energy consumption, high pollution, complex process flows, large equipment investment, and residues of free calcium carbide in the product. Using urea, which is widely available and inexpensive, as a raw material to produce cyanamide through a catalytic dehydration reaction aligns with the principles of atom economy. It offers significant advantages such as low energy consumption, minimal pollution, low costs, and a green manufacturing process, making it an ideal alternative to the traditional calcium cyanamide method. It has thus become a focus of research and industrial development in the chemical industry in recent years.
II. Raw material situation: As the main type of nitrogen fertilizer, urea enjoys sufficient global production capacity. Its low and stable price provides a solid cost foundation for using it as a raw material in the production of high-value-added chemicals. Ammonia, used as a reaction atmosphere gas or carrier gas, is also a basic chemical product that is readily available. The raw materials involved in the catalyst, such as zinc salts, cadmium salts, pseudoboehmite, molecular sieves, and ammonium iron sulfate, are all conventional chemical materials with a well-established market supply. The raw material side of this process route possesses significant potential for scale-up and cost efficiency. III. Catalytic process route for the preparation of cyanamide via urea dehydration The key to preparing cyanamide from urea dehydration lies in the development of an efficient and highly selective catalytic system. Currently, patented technologies primarily focus on the design and optimization of catalysts: 1. Molecular sieve-based catalyst approach: Using molecular sieves such as H-ZSM-5 as carriers, metal active components (such as Zn, Cd, Mn, Ce, etc.) are loaded onto them via ion exchange and similar methods. The regular pore structure and tunable acidic sites of these molecular sieves help to enhance reaction selectivity and catalyst longevity. 2. Metal oxide catalyst route: Using metal oxides formed by high-temperature roasting of materials such as pseudoboehmite as carriers, various acids (sulfuric acid, phosphoric acid, etc.) are impregnated onto them to serve as active centers, thereby creating catalysts with numerous acid sites in order to improve conversion rates and selectivity. 3. Solid superacid catalyst route: Solid superacids formed by the high-temperature calcination and decomposition of substances such as ammonium iron sulfate are used as catalysts to facilitate reactions within a dispersed system of alcoholic solvents. This approach aims to address the issue of excessive by-products generated by traditional catalysts. 4. Nanoscale structured catalyst approach: By synthesizing nanosized ZSM-5 (Nano-ZSM-5) or using special templates and composite processes, the specific surface area of the catalyst is increased, more active sites are made available, and mass transfer as well as reaction efficiency are improved.
IV. Patent Analysis (1) Patent No. 1 (CN117800361A): “A Method for Preparing Monocyanamide by Dehydration of Urea”. Addressing the issues associated with existing urea dehydration methods for producing monocyanamide, such as low conversion rates, poor selectivity, and numerous by-products, this patent proposes the use of H-ZSM-5 molecular sieve catalysts modified with elements from Group IIB (Zn, Cd, Hg) as an innovative solution. Its core technology lies in introducing Group IIB metals into the molecular sieve framework through ion exchange, thereby modifying the acidity and surface properties of the molecular sieve; this helps to suppress side reactions during the catalytic dehydration of urea and improves the selectivity for monocyanamide. The experimental results show that under conditions of 550–570°C, atmospheric pressure, and an ammonia atmosphere, this process can achieve a urea conversion rate of 92%–97% and a monocyanamide selectivity of 39%–47%, which represents a significant improvement compared to the unmodified H-ZSM-5 catalyst (with a selectivity of 22%). Claim analysis: This patent comprises 9 claims, establishing an integrated protection system that covers both the catalyst preparation method and the application process. Independent Claim 1 defines the core six-step process for catalyst preparation, covering the entire process from salt solution preparation to ion exchange, separation, drying, and calcination. Independent Claim 9 covers the process conditions for the urea dehydration reaction using this catalyst, including key parameters such as reaction temperature (450–700°C), pressure (atmospheric pressure to 1.0 MPa), and residence time (0.2–3 s). Dependent claims 2-8 provide more detailed specifications for the core process: Claim 2 specifies that the Group IIB metals are Zn, Cd, and Hg ； Right 3 lists a wide range of anion types (halide ions, oxyanions, organic acid radicals, etc.) ； Ranges 4–8 specify the mass ratio of the salt solution to the molecular sieve (2:1–15:1), the concentration of the salt solution (0.05–1 mol/L), the temperature and time for ion exchange, as well as the conditions for drying and calcination. The overall layout originates from the core preparation method; through successive specifications regarding specific components and process parameters, it forms a rigorous protective framework for the Group IIB metal-modified HZSM-5 catalyst and its application in the urea dehydration process.
(2) Patent 2 (CN115282952A): “A catalyst for catalyzing the decomposition of urea to produce cyanamide”. This patent aims to provide a catalyst that uses readily available raw materials, is simple to prepare, and can achieve both high conversion rates and high selectivity. The technical core lies in using alumina obtained through the high-temperature roasting of pseudoboehmite as a carrier, and loading inorganic or organic acids (such as sulfuric acid, phosphoric acid, citric acid, etc.) via impregnation as active centers. The examples show that under optimized conditions (550°C, molten urea feed), the urea conversion rate can reach up to 97.65%, and the monocyanamide selectivity can reach up to 56.77%; it is also stated that the catalyst exhibits good stability. Claim analysis: This patent comprises 9 claims, establishing a multi-dimensional protection framework that covers “catalyst preparation – catalyst products – application processes – testing methods”. Independent Claim 1 defines a four-step method for preparing the catalyst: carrier calcination, acid solution mixing, acid loading, and precursor calcination. Independent Claim 4 protects the fixed-bed reaction process using this catalyst. It is worth noting that Claims 8 and 9 respectively define the characteristics of the “solid, liquid, and gas” phases in the process and testing (“solid” refers to the catalyst, “liquid” to molten urea, and “gas” to ammonia), aiming to establish a protective barrier based on the characteristics of the reaction system. Dependent claims 2-3, 5-7 further specify the acid loading (0.1-10 wt%), the type of acid, the form of urea feed (solid or molten), the feed rate, and the residence time, among other things. The scope of protection for this patent covers the key stages from catalyst synthesis to industrial application simulation.
(3) Patent 3 (CN110304638A): “A Method for Preparing Monocyanamide Using Urea”. This patent focuses on addressing the issues of by-product control and operational safety during the reaction process. Its innovation lies in the use of alcohols (methanol/ethanol) as dispersants and solvents for urea, along with a solid superacid produced by high-temperature calcination of ammonium ferric sulfate dodecahydrate as a catalyst. The alcohol solvent system facilitates the uniform feeding of urea and prevents clogging; the quenching operation after the reaction aims to prevent the further polymerization of the product dicyandiamide from cyanamide. According to the patented embodiment, this method enables 100% conversion of urea, a selectivity of 45%-55% for monocyanamide, and a content of the by-product melamine below 1%. Claim analysis: This patent comprises a total of 5 claims, establishing a protection chain of “process method – catalyst preparation”. Independent Claim 1 protects the complete process of using an alcohol as a dispersant, reacting in an ammonia atmosphere, then rapidly cooling, and subsequently concentrating and crystallizing to obtain solid cyanamide. Independent Claim 2 protects the core catalyst – namely, the method for preparing a solid superacid obtained by calcining and grinding ammonium ferric sulfate dodecahydrate under specific conditions (calcination at 550°C for 3.5–4.5 hours). Dependent claims 3-5 specify in detail the grade of the catalyst’s raw materials, the type of solvent (methanol/ethanol), and the negative pressure conditions during the concentration step (above -0.095 MPa). The focus of this patent protection is clear, centering on the combined process of solvation reaction and rapid cooling crystallization, as well as its dedicated catalyst.
(4) Patent No. 4 (CN114751844A): “A process method for catalyzing the dehydration of urea to produce cyanamide.” This patent proposes the use of nanoscale ZSM-5 (Nano-ZSM-5) catalysts in order to improve the intrinsic activity and selectivity of the catalyst. The core idea is to use special silane reagents as templates to synthesize nano-ZSM-5 with a larger specific surface area, more pore sizes, and more acidic sites, thereby improving catalytic efficiency. Examples show that at 550°C and extremely short residence times (0.4–0.5 s), the conversion rate of urea can exceed 90%, while the selectivity for dicyandiamide is greater than 30%. Claim analysis: This patent comprises 6 claims, with its structure organized around “catalyst characteristics – preparation process – application process”. Independent Claim 1 defines the use of a Nano-ZSM-5 catalyst and includes the process steps of preheating and melting urea, as well as reacting it in an ammonia atmosphere. Claims 2 and 3 protect, respectively, the specific silane reagent template and precursor material used in the preparation of this catalyst. Claim 4 protects a specific type of fixed-bed reactor (solid-liquid-gas three-phase bed) as well as the operating parameters (temperature of 550°C, feed rate of 0.32 g/min, residence time of 0.4–0.5 s). Claim 5 reiterates the “solid-liquid-gas” three-phase characteristic of its process (similar to CN115282952A, but with a different definition). Claim 6, on the other hand, sets requirements regarding the purity of the raw material urea. This patent focuses on protecting the nanostructured catalyst itself and its use in specific reactions with ultra-short residence times. The patent system analyzed in this study reveals the competitive landscape in catalyst innovation and process optimization for the urea dehydration method used in monocyanamide production. In catalyst design, there are various technical approaches, ranging from molecular sieve modification and the loading of acids on metal oxides to solid superacids and nanostructured materials; all of these aim to increase the quantity and quality of active sites while suppressing side reactions ； In terms of process optimization, various strategies such as melt feeding, solvent dispersion, extremely short residence times, and rapid cooling after reaction have been developed to address engineering challenges related to mass transfer, heat control, and product stability. In the future, this technology will continue to evolve toward higher selectivity for cyanamide (>60%), lower formation of by-products, longer catalyst life, and further reduction in energy consumption across the entire process. Precise design of catalytic materials combined with integrated optimization of reaction engineering will be key to achieving these advancements.
V. Conclusion: As a green alternative route, the technological progress and industrialization prospects of the process for preparing cyanamide via urea dehydration directly benefit from the impetus of environmental protection policies and the window period for phasing out traditional processes. From a patent perspective, current technological innovation is highly concentrated on the development of catalyst systems, with four main approaches emerging: those based on molecular sieves, oxides, solid acids, and nanomaterials. Among them, the IIB-group metal-modified HZSM-5 approach shows robust performance in terms of improved selectivity; the acid-modified pseudoboehmite route is reported in the literature to achieve the highest combination of conversion rate and selectivity. The solid superacid combined with solvent method focuses on safety and control of by-products, while the Nano-ZSM-5 approach represents the cutting-edge strategy for enhancing intrinsic activity through material nanomorphology. Each patent focuses on establishing a comprehensive network of claim protections that covers everything from catalyst preparation, to key process parameters, and even the characteristics of the reaction system. There are already industrial applications of the urea method, and future patent analyses will continue to monitor the progress of this technology.
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