Preparation method of castor oil for preparing fertilizer slow-release coating agent

Abstract

The application provides a preparation method of a fertilizer slow-release coating agent prepared from castor oil. The method comprises the following steps: mixing castor oil and a catalyst sodium hydroxide and heating to 240 DEG C, and performing intramolecular dehydration under vacuum to obtain dehydrated castor oil; mixing the dehydrated castor oil with polyethylene glycol and an acid catalyst to perform ester exchange reaction and obtain dehydrated castor oil polyethylene glycol ester; and finally performing polycondensation under normal pressure to obtain polymeric dehydrated castor oil polyethylene glycol ester as the fertilizer slow-release coating agent. The coating agent has adjustable film thickness, good slow-release effect, can prolong the release time of fertilizer nutrients to more than 180 days, and the release rate of nutrients within 40 days is less than 80%.

Description

Technical Field

[0001] This invention relates to the field of slow-release agents, and more specifically to a method for preparing a slow-release coating agent for fertilizers made from castor oil. Background Technology

[0002] With the development of agricultural modernization, the use of chemical fertilizers has increased year by year. However, the overuse and irrational application of traditional fertilizers have led to fertilizer waste, soil pollution, and environmental problems. To address this issue, slow-release fertilizer technology has emerged. By controlling the release rate of fertilizer, nutrients can be continuously supplied over a longer period, reducing nutrient loss and improving fertilizer utilization efficiency. However, existing slow-release fertilizer coating agents typically use paraffin wax, polyols, or synthetic polymers as coating materials. While these traditional materials can provide some slow-release effect, their coating layers are often thick, the slow-release time is limited, and their biodegradability is poor, easily causing soil pollution. This does not meet the requirements of modern agriculture for environmental protection and sustainable development.

[0003] Furthermore, existing slow-release coating agents have high production costs, mainly relying on petrochemical raw materials and complex synthesis processes, leading to increased costs and limiting their widespread application in low-cost agriculture. Although some bio-based materials have begun to be used in the development of slow-release coating agents, their limitations in slow-release performance, toughness, and biodegradability have prevented their widespread application in the fertilizer industry.

[0004] Therefore, developing a fertilizer slow-release coating agent that possesses both good slow-release properties and excellent biodegradability at a low cost has become an urgent need in the agricultural and environmental protection fields. This invention innovatively uses a natural plant oil—castor oil—and combines intramolecular dehydration, transesterification, and polycondensation reactions. This not only solves the performance shortcomings of traditional coating agents but also significantly reduces production costs, meeting the requirements of green and sustainable development and possessing broader market application prospects. Summary of the Invention

[0005] This invention provides a method for preparing a slow-release coating agent for fertilizers from castor oil.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing a slow-release coating agent for fertilizers from castor oil includes the following steps:

[0008] Castor oil was mixed with sodium hydroxide and heated to 240°C. An intramolecular dehydration reaction was carried out under a vacuum of 100 Pa until the iodine value increased from 90 mg KOH / g to 120 mg KOH / g, thus obtaining dehydrated castor oil.

[0009] The dehydrated castor oil was mixed with polyethylene glycol and an acidic catalyst and heated to 150°C to 180°C to carry out transesterification reaction to obtain dehydrated castor oil polyethylene glycol ester.

[0010] The dehydrated castor oil polyethylene glycol ester was heated to 230°C and subjected to a polycondensation reaction under normal pressure until the acid value reached 6 mg KOH / g, thus obtaining polymerized dehydrated castor oil polyethylene glycol ester, which can be used as a slow-release coating agent for fertilizers.

[0011] In one specific embodiment, the reaction temperature is 240°C and the reaction time is 4 to 6 hours.

[0012] In one specific embodiment, the acidic catalyst is phosphoric acid or sulfuric acid, and the mass ratio of the catalyst is 1:1000.

[0013] In one specific embodiment, the transesterification reaction is carried out in a temperature range of 150°C to 180°C for a reaction time of 2 to 3 hours.

[0014] In one specific embodiment, the polycondensation reaction is carried out at a temperature of 230°C for 4 to 5 hours, and the acid value reaches 6 mg KOH / g at the end of the reaction.

[0015] In one specific embodiment, the mass ratio of the dehydrated castor oil to polyethylene glycol is 1:2.

[0016] This invention provides a method for preparing a slow-release coating agent for fertilizers using castor oil. This method effectively converts castor oil into a membrane material with slow-release properties through intramolecular dehydration, transesterification, and polycondensation reactions. Compared with traditional slow-release coating agents, the membrane material prepared by this method has better toughness and biodegradability, significantly extending the slow-release time of fertilizers, improving fertilizer utilization efficiency, reducing fertilizer waste, and lowering environmental pollution. By precisely controlling the reaction conditions, the membrane's performance can be adjusted according to different needs, thus adapting to different crops and soil types, and exhibiting high application flexibility. Furthermore, this invention uses natural plant oil, castor oil, as a raw material, reducing production costs, meeting the requirements of green and sustainable development, and possessing strong market competitiveness and promising prospects for promotion. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1: Preparation of slow-release fertilizer coating agent from castor oil under conventional reaction conditions

[0019] Step 1: Mix 1000g of castor oil with 50g of sodium hydroxide (catalyst), heat to 240°C under vacuum of 100Pa, and react for 4 hours until the iodine value increases from 90mg KOH / g to 120mg KOH / g to obtain dehydrated castor oil.

[0020] Step 2: Mix 300g of dehydrated castor oil with 700g of polyethylene glycol and 1g of phosphoric acid. React at 150°C to 180°C for 2 hours to obtain dehydrated castor oil polyethylene glycol ester.

[0021] Step 3: Heat 1000g of dehydrated castor oil polyethylene glycol ester to 230°C and react under normal pressure for 4 hours until the acid value reaches 6mg KOH / g to obtain polymerized dehydrated castor oil polyethylene glycol ester, which can be used as a slow-release coating agent for fertilizers.

[0022] Example 2: Preparation of slow-release fertilizer coating agent from castor oil under optimized reaction conditions

[0023] Step 1: Mix 1000g of castor oil with 50g of sodium hydroxide (catalyst), heat to 240°C under vacuum of 80Pa, and react for 6 hours until the iodine value increases from 90mg KOH / g to 120mg KOH / g to obtain dehydrated castor oil.

[0024] Step 2: Mix 300g of dehydrated castor oil with 700g of polyethylene glycol and 2g of phosphoric acid. React at 160°C to 180°C for 3 hours to obtain dehydrated castor oil polyethylene glycol ester.

[0025] Step 3: Heat 1000g of dehydrated castor oil polyethylene glycol ester to 240°C and react under normal pressure for 5 hours until the acid value reaches 6mg KOH / g to obtain polymerized dehydrated castor oil polyethylene glycol ester, which can be used as a slow-release coating agent for fertilizers.

[0026] Example 3: Preparation of slow-release fertilizer coating agent from castor oil under low-temperature polycondensation reaction conditions

[0027] Step 1: Mix 1000g of castor oil with 40g of sodium hydroxide (catalyst), heat to 230°C under vacuum of 80Pa, and react for 5 hours until the iodine value increases from 90mg KOH / g to 115mg KOH / g to obtain dehydrated castor oil.

[0028] Step 2: Mix 300g of dehydrated castor oil with 700g of polyethylene glycol and 2g of phosphoric acid. React at 160°C to 170°C for 3 hours to obtain dehydrated castor oil polyethylene glycol ester.

[0029] Step 3: Heat 1000g of dehydrated castor oil polyethylene glycol ester to 220°C and react under normal pressure for 4 hours until the acid value reaches 6mg KOH / g to obtain polymerized dehydrated castor oil polyethylene glycol ester, which can be used as a slow-release coating agent for fertilizers.

[0030] Comparative experimental group

[0031] Comparison Group 1: Traditional Paraffin Coating Agent

[0032] The traditional method of using paraffin and polymer materials as slow-release coating agents was adopted, and the reaction conditions were carried out according to the conventional fertilizer coating agent preparation process.

[0033] Use a standard sustained-release coating agent formulation.

[0034] Comparison Group 2: Traditional polymer coating agents

[0035] Traditional polymers (such as polyvinyl alcohol and polyacrylic acid) are used as membrane materials to prepare conventional coating agents.

[0036] The reaction conditions are conventional transesterification and polycondensation reactions.

[0037] The following is a detailed experimental procedure. All experimental steps, instruments, and methods used are described in detail:

[0038] The performance of the castor oil fertilizer slow-release coating agent prepared in this invention in terms of slow-release effect, membrane performance and biodegradability was verified, and compared with traditional paraffin coating agents and polymer coating agents.

[0039] Experimental materials:

[0040] Raw materials: castor oil, sodium hydroxide, polyethylene glycol, phosphoric acid or sulfuric acid (acidic catalyst).

[0041] Fertilizer: Urea (a fertilizer used as a coating).

[0042] Comparative materials: commonly used fertilizer coating agents such as paraffin wax, polyvinyl alcohol, and polyacrylic acid.

[0043] Experimental equipment

[0044] Temperature control equipment: heated reactor (temperature controllable), constant temperature oil bath.

[0045] Pressure control equipment: vacuum pump, pressurized reactor (atmospheric pressure).

[0046] Reaction vessels: four-necked flask, reaction vessel, stirrer.

[0047] Reagents and analytical instruments:

[0048] Iodine value analyzer: Used to measure the change in iodine value during a reaction to confirm the completion of the reaction.

[0049] Acid value meter: Used to measure acid value in order to determine the endpoint of the reaction.

[0050] Electronic balance: used for accurate weighing of reactants.

[0051] pH meter: Used to measure the pH value during the reaction process to ensure the suitability of the reaction conditions.

[0052] Membrane performance testing instruments:

[0053] Tensile testing machine: used to determine the tensile strength and elongation of membranes.

[0054] Water immersion test chamber: used for testing the sustained-release effect.

[0055] Scanning electron microscope (SEM): Used to observe the surface morphology and microstructure of films.

[0056] Experimental steps

[0057] 4.1 Preparation of slow-release fertilizer coating agent

[0058] Castor oil fertilizer slow-release coating agents were prepared according to the steps described in Examples 1, 2, and 3. The specific steps are as follows:

[0059] Intramolecular dehydration reaction: 1000 g of castor oil was mixed with 50 g of sodium hydroxide and slowly heated to 240°C under a vacuum of 100 Pa for 4 to 6 hours until the iodine value increased from 90 mg KOH / g to 120 mg KOH / g. The completion of the dehydration reaction was confirmed by the change in iodine value.

[0060] Transesterification reaction: 300 g of dehydrated castor oil was mixed with 700 g of polyethylene glycol and 1 g of phosphoric acid. The reaction temperature was 150°C to 180°C, and the reaction was carried out for 2 to 3 hours to obtain dehydrated castor oil polyethylene glycol ester. The completion of the transesterification reaction was confirmed by acid value determination.

[0061] Polycondensation reaction: 1000g of dehydrated castor oil polyethylene glycol ester is heated to 230°C and reacted for 4 to 5 hours. When the reaction ends, the acid value reaches 6mg KOH / g to obtain polymerized dehydrated castor oil polyethylene glycol ester, which can be used as a slow-release coating agent for fertilizers.

[0062] 4.2 Preparation of the control experimental group

[0063] Two sets of comparative coating agents were prepared using conventional methods:

[0064] Comparative Group 1 (paraffin coating agent): The coating agent was prepared by mixing paraffin with polyols (such as glycerol) and a catalyst using conventional methods. Paraffin usually needs to be melted at a high temperature and then coated with fertilizer.

[0065] Comparative Group 2 (Polymer Coating Agent): Polyvinyl alcohol (or polyacrylic acid) was used as the coating material, and fertilizer slow-release coating agents were prepared using conventional transesterification and polycondensation reactions.

[0066] 4.3 Performance Testing

[0067] Film thickness measurement:

[0068] The thickness of the prepared sustained-release membrane was measured using calipers and a microscope to ensure that the membrane layer was uniform and met the experimental requirements.

[0069] Sustained-release effect test:

[0070] Experimental method: The fertilizer coating agent was made into small granules and soaked in water. The nutrient release at different time points was recorded. Specific steps:

[0071] Mix a certain amount of coating agent with urea and soak it in a water bath (25°C).

[0072] Samples were taken every 24 hours, and the nutrient concentration (e.g., nitrogen content) in the water was determined using a spectrophotometer.

[0073] The sustained-release curve is obtained by calculating the cumulative release rate at each time point.

[0074] Tensile strength and elongation of the membrane:

[0075] The membrane is cut to standard dimensions (e.g., 10cm x 1cm) and tested using a tensile testing machine. During the test, the maximum strength and elongation of the membrane under tension are recorded to evaluate its mechanical properties.

[0076] Biodegradability test:

[0077] The membrane material is placed in the soil, and the change in membrane mass is measured periodically to observe the rate of membrane degradation. The degradability of the membrane can be assessed by weighing the membrane's mass loss and comparing it with changes in organic matter in the soil.

[0078] Surface morphology analysis:

[0079] The membrane surface was observed using a scanning electron microscope (SEM) to analyze the membrane's microstructure and pore distribution, further verifying the membrane's uniformity and structural integrity.

[0080]

[0081] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a slow-release coating agent for fertilizers from castor oil, characterized in that, Includes the following steps: Castor oil was mixed with sodium hydroxide and heated to 240°C. An intramolecular dehydration reaction was carried out under a vacuum of 100 Pa until the iodine value increased from 90 mg KOH / g to 120 mg KOH / g, thus obtaining dehydrated castor oil. The dehydrated castor oil was mixed with polyethylene glycol and an acidic catalyst and heated to 150°C to 180°C to carry out transesterification reaction to obtain dehydrated castor oil polyethylene glycol ester. The dehydrated castor oil polyethylene glycol ester was heated to 230°C and subjected to a polycondensation reaction under normal pressure until the acid value reached 6 mg KOH / g, thus obtaining polymerized dehydrated castor oil polyethylene glycol ester, which can be used as a slow-release coating agent for fertilizers.

2. The preparation method according to claim 1, characterized in that, The reaction temperature is 240°C, and the reaction time is 4 to 6 hours.

3. The preparation method according to claim 1, characterized in that, The acidic catalyst is phosphoric acid or sulfuric acid, and the mass ratio of the catalyst is 1:1000.

4. The preparation method according to claim 1, characterized in that, The transesterification reaction was carried out in a temperature range of 150°C to 180°C for 2 to 3 hours.

5. The preparation method according to claim 1, characterized in that, The polycondensation reaction was carried out at 230°C for 4 to 5 hours, and the acid value reached 6 mg KOH / g at the end of the reaction.

6. The preparation method according to claim 1, characterized in that, The mass ratio of the dehydrated castor oil to polyethylene glycol is 1:2.

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