Efficient synthesis method of ferrous picrate under anhydrous / low-water condition

Abstract

The invention discloses an efficient synthesis method of picric acid ferrous iron under anhydrous / low-water conditions, and relates to the technical field of preparation of fuel additives in the field of fine chemical engineering, and the efficient synthesis method comprises the following steps: stirring excessive high-surface-area iron powder and high-concentration aromatic hydrocarbon picrate or aromatic ether picrate in an anhydrous solvent system at 10-80 DEG C to react for 5-15 minutes; a picric acid ferrous solution is prepared; wherein the iron powder is subjected to acid activation treatment to remove an oxide layer, the anhydrous solvent system is aromatic hydrocarbon, fatty alcohol or a mixture of the aromatic hydrocarbon and the fatty alcohol, and the water content of aromatic hydrocarbon picrate or aromatic ether picrate is lower than 100 ppm; according to the invention, a water-free stable formula is prepared; high-concentration aromatic hydrocarbon picrate or high-concentration aromatic ether picrate and excessive high-surface-area iron powder are subjected to stirring reaction at normal temperature to medium high temperature, and high-concentration ferrous picrate can be obtained within five to fifteen minutes; the explosion risk is avoided, the shelf life of the product is remarkably prolonged, and the product is suitable for high-temperature storage and transportation environments.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of fuel additives in the field of fine chemicals, and specifically to an efficient synthesis method of ferrous picrate under anhydrous / low-water conditions. Background Art

[0002] Ferrous picrate / picrate-based fuel additives have been widely used in various fuel treatment fields such as alcohol-based fuels, gasoline, and diesel due to their significant benefits in improving fuel economy, reducing emissions, and reducing engine wear. Over the years, a large number of studies have been carried out on their manufacturing and application, including focusing on safety production, moisture control, stability, and shelf-life optimization. However, the existing technologies still face multiple key problems in practical applications:

[0003] I. Safety and Corrosion Risks:

[0004] 1. Inherent Defects of Excessive Picric Acid: To maintain an acidic environment to prevent the precipitation of ferrous ions (the increase in pH value is likely to cause the precipitation of iron), the existing formulations need to add excessive picric acid. In the existing technologies, the stable ratio of picric acid to ferrous picrate can reach 100:1, corresponding to a ratio of picric acid to iron as high as 917:1. Excessive picric acid makes the product highly corrosive and toxic, and the dry residue formed after the leakage or volatilization of the carrier solvent is easily ignited by sparks, posing an explosion risk. In addition, copper-containing alloys (such as brass and bronze) are easily eroded after contact, and may generate highly sensitive copper picrate, further exacerbating the safety hazards.

[0005] 2. Explosion Hazard of Dry Picric Acid: The sensitivity of dry picric acid exceeds that of TNT, and it belongs to a high explosive. Its reaction with iron in hydrocarbon solutions is extremely slow. Although low-water products can be finally obtained, the explosion risk caused by friction or impact during the production process is extremely high, seriously hindering industrial applications.

[0006] II. Stability and Shelf-Life Issues:

[0007] 1. Self-Catalytic Deterioration Induced by Moisture: Moisture is the main cause of product deterioration. The product containing 1345 ppm of water deteriorates within 3 days at 60°C, manifested as the fading of the emerald green color to yellow, turbidity, and the formation of dark brown to black precipitates (such as iron picrate hexahydrate), and the rapid loss of iron content (such as the initial 280 ppm of iron dropping to 71 ppm), resulting in the clogging of fuel filters and equipment shutdown. Even when the moisture is reduced to 800 - 1600 ppm, it will still deteriorate within 17 - 19 days under high-temperature storage and transportation environments (such as in Australia and the western United States, where the temperature often reaches 50 - 60°C). Its deterioration mechanism is related to the reduction of picric acid by ferrous ions under neutral to weakly acidic conditions to form insoluble products (such as iron picramate, molecular weight 650.19, insoluble in hydrocarbon-alcohol carriers). This reaction requires hydrogen ion catalysis or the formation of water, and once initiated, it exhibits self-catalytic characteristics.

[0008] 2. Solvent and environmental factors exacerbate degradation: Liquid formulations rely on flammable or combustible carrier solvents (such as butanol, toluene). The volatility of the solvent leads to low flash point problems, and the components are more prone to oxidation reactions after dissolution. In addition, high temperature, alkaline environment, and transition metal contamination (chromium, copper, etc.) will all accelerate degradation, while traditional antioxidants (such as hydroquinone) are ineffective or even may promote degradation.

[0009] III. Process efficiency and compatibility limitations:

[0010] 1. Harsh and inefficient reaction conditions: The direct iron -

[0011] picric acid reaction disclosed in foreign technologies requires moisture > 600 ppm to maintain a reasonable rate. Commercial picric acid contains 10 - 30% moisture and needs to be processed through multiple steps such as dissolution, stratification, and azeotropic distillation to reduce the water content (such as obtaining a picric acid hydrocarbon solution with 500 - 600 ppm water). The process is complex and time - consuming (such as the reaction taking several weeks). Although dry picric acid can avoid the influence of moisture, the reaction is extremely slow and the explosion risk is high, making it difficult to industrialize.

[0012] 2. Solvent compatibility and product form limitations: Existing liquid formulations are the only commercial form. Although large users prefer their characteristics of accurate metering and addition, liquid products have problems such as poor container compatibility, high sealing requirements, and easy stratification during long - term storage. For example, higher alcohols (such as butanol) have poor solubility for ferrous picrate, and 25% butanol needs to be added to produce a 1425 ppm iron solution. The final product still contains 1.9% free picric acid and 800 - 1600 ppm water, and it is impossible to avoid high - temperature degradation.

[0013] IV. Core contradictions of the existing technology:

[0014] The existing technology attempts to balance the reaction rate and stability by controlling the moisture (800 - 1600 ppm), but the actual effect is limited - insufficient moisture leads to too slow a reaction, and excessive moisture accelerates degradation. At the same time, the high danger of dry picric acid and the low reaction efficiency of wet picric acid form a technical bottleneck. There is an urgent need for an efficient synthesis method of ferrous picrate under anhydrous / low - water conditions to solve the above problems of stability, safety, and process efficiency. Summary of the Invention

[0015] The purpose of the present invention is to provide an efficient synthesis method of ferrous picrate under anhydrous / low - water conditions to solve the problems raised in the above - mentioned background technology.

[0016] To solve the above - mentioned technical problems, the efficient synthesis method of ferrous picrate under anhydrous / low - water conditions provided by the present invention includes the following steps:

[0017] An excess of high-surface-area iron powder is stirred and reacted with a high-concentration aromatic hydrocarbon picrate or aromatic ether picrate in an anhydrous solvent system at 10-80 °C for 5-15 minutes to obtain a ferrous picrate solution; wherein, the iron powder is acid-activated to remove the oxide layer, the anhydrous solvent system is an aromatic hydrocarbon, a fatty alcohol or a mixture thereof, and the water content of the aromatic hydrocarbon picrate or aromatic ether picrate is less than 100 ppm.

[0018] Further, the aromatic hydrocarbon picrate is selected from one or more of picric acid benzene, picric acid toluene, picric acid xylene, picric acid naphthalene, picric acid pyrene, and the aromatic ether picrate is selected from one or more of anisole picrate, diphenyl ether picrate, benzyl ether picrate.

[0019] Further, the anhydrous solvent system is a mixture of an aromatic hydrocarbon and a lower fatty alcohol, the aromatic hydrocarbon includes one or more of benzene, toluene, xylene, naphthalene, and the lower fatty alcohol includes one or more of methanol, ethanol, 2-

[0020] propanol, and the volume ratio of the lower fatty alcohol in the mixture is 10%-90%.

[0021] Further, the particle size of the iron powder is -200 mesh or finer, and the acid activation treatment is to treat with 12N hydrochloric acid for 30 seconds, and then wash with cold water and an alcohol solvent in sequence until neutral.

[0022] Further, the reaction temperature is 30-60 °C, and the stirring intensity maintains the uniform suspension of the iron powder to avoid local pH increase or product passivation.

[0023] Further, the concentration of the aromatic hydrocarbon picrate or aromatic ether picrate in the solvent is greater than 3%, the excess iron powder is 1.1-5 times the theoretical reaction amount, and the unreacted iron powder is removed by sedimentation filtration.

[0024] Further, the mixture of the aromatic hydrocarbon and the lower fatty alcohol is a mixed solvent of toluene and 2-

[0025] propanol, wherein the volume ratio of toluene is 10%-90%, and the volume ratio of 2-propanol is 10%-90%.

[0026] Further, the water content of the anhydrous solvent system is less than 100 ppm, and the reaction is carried out in a dry nitrogen inert environment.

[0027] Further, after the reaction, it is filtered through a 10-micron filter to obtain a ferrous picrate solution with a water content of less than 100 ppm and a free picric acid content of ≤0.4%.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] I. Breaking through water dependence and significantly improving product stability and shelf life:

[0030] 1. Achieving rapid reaction and long-term stability under anhydrous conditions:

[0031] Subverting traditional understanding: Breaking the limitation in existing technologies that "800 - 1600 ppm of water is required to maintain the reaction", it is proved that under an anhydrous environment (water content < 100 ppm), activated iron powder and picrate can still react rapidly (5 - 15 minutes), and the product shows no signs of deterioration at high temperatures (such as 50 - 80 °C). (In Example 15, the product remains emerald green after three years of storage, and the iron content is stable).

[0032] Eliminating the inducement of deterioration: Eliminating the autocatalytic reduction reaction caused by water (such as the formation of ferrous picrate precipitate), avoiding problems such as color fading, turbidity, and precipitation of liquid formulations due to water, and solving practical application problems such as fuel filter clogging and equipment shutdown.

[0033] 2. Adapting to harsh storage and transportation environments:

[0034] The low-water formulation (water content < 100 ppm) shows no precipitation at 60 °C. Compared with the rapid deterioration of the traditional system containing 1000 ppm of water, the storage and transportation adaptability in high-temperature regions such as Australia and the western United States is significantly improved.

[0035] II. Replacing with safe raw materials and reducing explosion risk and corrosiveness:

[0036] 1. Eliminating safety hazards with non-explosive raw materials:

[0037] Replacing dry picric acid with aromatic hydrocarbon / ether picrates (such as picric acid benzene and anisole picrate), these salts do not show detonation or deflagration after percussion and friction experiments (Example 5), solving the high-sensitivity explosion risk of dry picric acid and meeting the requirements of industrial safety production.

[0038] Reducing the use of excessive picric acid (the content of free picric acid is reduced to 0.4%, and the traditional process is 1.9%), reducing the corrosiveness, toxicity, and environmental hazards of the product, and avoiding the erosion of copper-containing alloys and the formation of highly sensitive copper picrate.

[0039] 2. Optimizing the safety of the solvent system:

[0040] Using a mixed solvent of aromatic hydrocarbon and lower alcohol (such as toluene / 2-propanol), balancing the solubility of picric acid and the stability of the product, reducing the low flash point problem caused by the volatilization of flammable solvents, and improving the container compatibility and sealing performance.

[0041] III. High-temperature and high-efficiency process, greatly improving synthesis efficiency and controllability:

[0042] 1. Improving reaction rate and reducing energy consumption:

[0043] High-temperature accelerated reaction: The anhydrous system allows operation at 10 - 80 °C (preferably 40 - 80 °C). The solubility of picric acid increases to 40 - 50% at high temperatures. In combination with highly active iron powder (below -200 mesh, activated with hydrochloric acid to remove the oxide layer), the reaction time is shortened from several weeks in the traditional process to 5 - 15 minutes (it can be shortened to 4 minutes with 300-mesh iron powder, Example 8), significantly improving the industrial production efficiency.

[0044] Process simplification: No complex water separation equipment is required. Anhydrous operation can be achieved through azeotropic distillation and sedimentation filtration, reducing equipment costs and energy consumption.

[0045] 2. Improvement of reaction controllability and product purity:

[0046] Excessive iron powder and stirring design: The iron powder exceeding the theoretical amount ensures complete reaction, and the unreacted iron powder is removed by sedimentation filtration; the backward-swept stirrer maintains the suspension of the iron powder, avoiding local pH increase or product passivation, and ensuring product uniformity (for example, the iron concentration is 400 ppm in Example 15 and is evenly distributed).

[0047] IV. Key process collaborative optimization to expand application scenarios:

[0048] 1. Solvent compatibility and formulation flexibility:

[0049] The mixed solvent (such as toluene / 2-

[0050] propanol) can dissolve both picric acid and ferrous picrate simultaneously, adapting to various fuel systems such as alcohol-based, gasoline, and diesel, meeting the component requirements of large users for accurate metering addition and liquid additive packages.

[0051] 2. Raw material utilization rate and environmental protection advantages:

[0052] The acid-activated iron powder (washed after hydrochloric acid treatment) improves the reaction activity and reduces raw material waste; the anhydrous system avoids the discharge of water-containing waste liquid, conforming to the concept of green chemistry.

[0053] Through the technical breakthroughs of anhydrous reaction + safe raw materials + high-temperature efficiency, the present invention systematically solves the core problems in the traditional process, such as deterioration caused by water dependence, dangerous raw materials, and low reaction efficiency, realizing the safe production, long-term stable storage, and efficient synthesis of ferrous picrate fuel additives, and providing an effective solution for the field of fuel additives. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a schematic diagram of the high-efficiency synthesis method of ferrous picrate under anhydrous / low-water conditions of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0055] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0056] Please refer to Figure 1 , the present invention provides a technical solution:

[0057] Refer to Figure 1 As shown, an example of a method for the efficient synthesis of ferrous picrate under anhydrous / low-water conditions:

[0058] Example 1:

[0059] An initial ferric picrate fuel additive formulation containing 280 ppm of iron, 56 ppm of free picric acid, and 1085 ppm of water (the solvent is 85% toluene and 15% isopropanol). After deterioration, the iron content was detected to have decreased to 71 ppm, the free picric acid was 45 ppm, and the water content had increased to 1200 ppm (the solvent composition remained unchanged). The initially prepared product was a clear and bright emerald green solution without precipitation. The deteriorated product was a light yellow-green solution, and obvious dark brown to black precipitates were visible at the bottom of a 55-gallon drum. The clear liquid was separated from the dark solid through a Buchner funnel and a suction flask under reduced pressure. The recovered solid was washed with fresh cold solvent (85% toluene, 15% isopropanol) and dried to a constant weight in an 80 °C oven. Infrared spectroscopy showed:

[0060] —— A strong and broad peak appeared at 3450 cm -1 (characteristic peak of hydrated picrate);

[0061] —— A sharp and strong peak appeared at 1604 cm -1 (characteristic peak of aromatic amine salt);

[0062] —— Another sharp and strong peak appeared at 1329 cm -1 (symmetric N-O stretching vibration of aromatic nitro functional group).

[0063] This spectrum was consistent with that of iron picrate hexahydrate. The dark solid was insoluble in acid but soluble in 1N sodium hydroxide solution, forming a blood-red solution. After acidification, the solution turned light blue-green and finally precipitated (characteristic reaction of picric acid). Elemental analysis measured the iron content to be 7.36%, which was highly consistent with the theoretical value of 7.37% for iron picrate hexahydrate. It was speculated that the deteriorated product was iron picrate hydrate or other similar picric acid reduction products, with ferrous ion as the reducing agent and ferric ion as a by-product.

[0064] Example 2:

[0065] Dissolve 5.6 g of commercial picric acid (4.6 g dry basis) in 10 ml of boiling benzene, remove water by azeotropic distillation, and obtain about 6.2 g of picrate of benzene dissolved in 4 ml of hot benzene. After cooling, the solution solidifies to obtain 4.6 g of pale yellow crude needle-shaped picrate of benzene, with a melting point of 83 - 84 °C.

[0066] Example 3:

[0067] Dissolve 2.8 g of naphthalene in the minimum amount of boiling methanol, and dissolve 5.6 g of commercial picric acid (4.7 g dry basis) in the minimum amount of boiling methanol. Pour the hot picric acid solution into the hot naphthalene solution. When the mixture cools, bright yellow needle-shaped picrate of naphthalene precipitates, and finally forms a yellow needle-shaped solid. After filtration, separation and drying, 6.7 g of yellow needles are obtained, with a melting point of 148 - 149 °C.

[0068] Example 4:

[0069] Dissolve 2.0 g of pyrene and 2.7 g of commercial picric acid (2.2 g dry basis) in 25 ml of boiling toluene (about 15 ml after azeotropic dehydration of water). After cooling, dark red fine needle-shaped picrate of pyrene precipitates from the reaction solution. Filter and separate the red solid and dry it to obtain 4.1 g of product, with a melting point of 221 - 222 °C.

[0070] Example 5:

[0071] Perform infrared spectroscopic analysis on the above picrates and compare with the infrared spectrum of dry picric acid. The melting point of dry picric acid is 122 - 123 °C. The infrared spectra of each picrate show that:

[0072] ——The peak of phenolic hydroxyl group (OH) is located at 3415 - 3440 cm -1 ;

[0073] ——The peak of aromatic C-H is located at 3100 - 3106 cm -1 ;

[0074] ——The vibration peak of the aromatic ring is located at 1632 - 1622 cm -1 and 1603 - 1610 cm -1 ;

[0075] ——The strong symmetric aromatic nitro stretching peak is located at about 1330 cm -1 .

[0076] Place each picrate sample alone or mixed with 10% quartz sand, 10% quartz sand + 10% copper powder on a steel plate, and strike it violently with a sledgehammer, or rub it vigorously with garnet sandpaper. Repeat the experiment five times under each condition, and no detonation or deflagration phenomenon is observed.

[0077] Example 6:

[0078] Add 2.0 g of dried picric acid, 0.50 g of unactivated dry iron powder and 100 ml of anhydrous solvent to four sealed 250 ml conical flasks respectively:

[0079] ——Bottle A: toluene;

[0080] - Bottle B: toluene / isopropanol (50:50);

[0081] ——Bottle C: isopropyl alcohol;

[0082] ——Bottle D: methanol.

[0083] The reaction was monitored by observing the release of gas, the disappearance of iron powder, and the appearance of emerald green color (characteristic of iron picrate). After 14 days, there was no significant change in the amount of iron powder in the four reactions. Bottles C and D initially released gas, which stopped after about 1 hour. Free picric acid precipitated in bottle C (solubility in isopropanol <2%), and the solution was light yellow-green at the end of the experiment (partial reaction). Bottle D turned yellow-green after about 6 days and maintained this color at the end of the experiment.

[0084] Repeat the above experiment, but the iron powder is activated with 12N hydrochloric acid for 30 seconds → quenched with cold water → washed with cold water three times → washed with dry isopropanol three times → washed with reaction solvent twice (bottle D is only washed with methanol). When the activated iron powder is mixed with picric acid solution, all four groups of reactions quickly turn green. After 24 hours:

[0085] ——Bottle A: obvious yellow-green;

[0086] ——Bottle B: deep emerald green (opaque);

[0087] ——Bottle C: deep emerald green (translucent);

[0088] ——Bottle D: Slight yellow-green.

[0089] The experiment shows that activation treatment in an anhydrous system significantly accelerates the reaction, and the reaction solvent must be able to dissolve the generated iron picrate.

[0090] Embodiment 7:

[0091] Three groups of reactions were carried out using anhydrous methanol as solvent. Steps for iron powder activation:

[0092] ——Treat with 10 parts of 12N hydrochloric acid for 30 seconds → quench with 200 parts of cold water → wash with 200 parts of cold water twice → wash with 200 parts of anhydrous methanol three times.

[0093] After activation, iron powder reacts with picric acid in methanol:

[0094] 1. Reaction 1: 0.100 g of activated iron powder + 1.00 g of dry picric acid + 10 g of methanol → gently shake for 10 minutes. The weight of the unreacted iron powder after drying is 0.080 g, and the iron concentration in the solution is 2000 ppm (before dilution). The actual iron concentration measured by ICP is 1520 ppm.

[0095] 2. Reaction 2: 1.00 g of activated iron powder → the weight of the unreacted iron powder is 0.930 g, and the iron concentration in the solution is 7000 ppm (calculated value). The iron concentration before dilution measured by ICP is 9470 ppm.

[0096] 3. Reaction 3: 0.100 g of activated iron powder + 1.00 g of picric acid + 50 g of methanol → the weight of the unreacted iron powder is 0.097 g, and the iron concentration in the solution is 300 ppm (calculated value). The iron concentration before dilution measured by ICP is 600 ppm.

[0097] Experiments show that excessive iron and high picric acid concentration can significantly increase the reaction rate and iron concentration.

[0098] Example 8:

[0099] React 5.00 g of 80 - mesh activated iron powder with 16.1 g of tolyl picrate in 50 ml of toluene and 50 ml of isopropanol at 50 °C for 10 minutes. Steps for iron powder activation:

[0100] ——Treat with 25 ml of 12N hydrochloric acid for 30 seconds → quench with 100 ml of cold water → wash twice with 50 ml of cold water → wash three times with 20 ml of dry isopropanol.

[0101] The reaction solution quickly turns dark emerald green. After 10 minutes, the unreacted iron powder is separated. Assuming picric acid is the rate - limiting reagent, the calculated iron concentration is 12,452 ppm, and the actually measured iron concentration is 6,850 ppm (including the washing solution). When using 300 - mesh iron powder, the reaction is completed within 4 minutes.

[0102] Examples 9 - 12:

[0103] React with activated iron powder in butanol / xylene (Example 9), 2 - ethylhexanol / mixed xylene (Example 10), isopropanol / toluene (Examples 11, 12) using o - xylene picrate (Example 9), m - xylene picrate (Example 10), naphthalene picrate (Example 11), anisole picrate (Example 12) as raw materials respectively. The reaction time is 10 - 15 minutes. The final solution is dark emerald green, and the iron concentration reaches 6,000 - 10,000 ppm. When phenetole picrate is replaced with anisole picrate in Example 12, the results are the same, proving that aromatic ether picrates can be used as an anhydrous picric acid source.

[0104] Example 13:

[0105] By mixing equimolar amounts of hydrocarbons with picric acid in a hot saturated solution in methanol, ethanol, or 2-

[0106] propanol (using chloroform as the solvent for picrates of anthracene and hot saturated hydrocarbon solutions of picric acid for liquid hydrocarbons), the following picrates of aromatic hydrocarbons were prepared, and their colors and melting points are as follows:

[0107] Aromatic hydrocarbon Color Melting point (℃) Benzene Light yellow 84 Tolene Light yellow 88 Ethylbenzene Light yellow 96.6 1,4 - Dimethylbenzene Light yellow 90 1,3 - Dimethylbenzene Light yellow 91 1,2 - Dimethylbenzene Light yellow 88 n - Propylbenzene Light yellow 103 Mesitylene Yellow 97 Indene Yellow 98 Tolane Yellow 111 Naphthalene Yellow 149 Acenaphthylene Yellow 201-202 Acenaphthene Orange - red 162 Phenanthrene Yellow 144 Fluorene Yellow 87 Trans - stilbene Light yellow 94-95 Anthracene Yellow 138 Pyrene Red 222

[0108] Example 14:

[0109] By dissolving equimolar amounts of picric acid and aromatic ethers in hot methanol, ethanol, or 2-

[0110] propanol and mixing the hot saturated solutions (chloroform or dichloromethane are sometimes preferred; picrates of aromatic ethers can also precipitate after cooling the hot saturated ether solution of picric acid), the following picrates of aromatic ethers were prepared, and their colors and melting points are as follows:

[0111]

[0112]

[0113] Example 15:

[0114] In an 8000-liter glass-lined reactor equipped with a pitched-blade agitator and H-type baffles, 50 kg of commercial picric acid containing 21% water was dissolved in 4250 kg of toluene. After the picric acid was completely dissolved, stirring was stopped, and the water layer was drained from the bottom of the reactor. Subsequently, the toluene was heated to boiling, and the residual water was removed by azeotropic distillation. An equal amount of dry toluene to compensate for the loss during azeotropic distillation was added and 750 kg of dry 2-

[0115] propanol was pumped in, and then 2.5 kg of iron powder was added. The reactor was inerted with dry nitrogen and stirred at room temperature for three and a half weeks until most of the iron had reacted. The final product was drained from the bottom of the reactor, filtered through a 10-μm filter, and filled into a 195-liter (55-gallon) steel drum with a phenolic epoxy coating. The finished product had a water content of less than 100 ppm, contained 85% toluene, 15% 2-

[0116] propanol, 400 ppm of iron, and 0.4% free picric acid, was clear and bright emerald green, and was characterized by density, refractive index, infrared spectroscopy, ultraviolet-visible spectroscopy, and gas chromatography. After three and a half years of storage, the sample remained emerald green, and the analysis results were consistent with the original product.

[0117] Summary:

[0118] Traditional liquid picric acid / ferrous picrate fuel additives have multiple defects: First, high moisture causes deterioration and stability problems. The commercial process relies on 800 - 1600 ppm of moisture to maintain the reaction rate, but when the moisture exceeds 1600 ppm, it will accelerate the deterioration, generating insoluble precipitates such as ferrous picramate, resulting in the loss of iron content and clogging of the fuel filter. For example, a product containing 1345 ppm of water deteriorates within 3 days at 60 °C. Even when the moisture is reduced to 800 ppm, it will still deteriorate within 17 - 19 days in a high-temperature storage and transportation environment. Second, the safety risks are prominent. Dry picric acid is a high explosive with a sensitivity exceeding that of TNT, and excessive picric acid (the ratio to iron reaches 917:1) leads to strong corrosiveness and toxicity of the product. The dry residue after the leakage of the carrier solvent is prone to explosion and may also generate highly sensitive copper picrate. Third, the reaction efficiency and process limitations are obvious. When using dry picric acid in the traditional anhydrous reaction, the reaction is extremely slow and the explosion risk is high. After wet picric acid is dissolved, the water content is difficult to control, the reaction time is long (such as several weeks), the solvent compatibility is poor, and the liquid formulation faces the problem of low flash point due to the volatility of the solvent. The finished product is prone to react with copper alloys.

[0119] In response to the above problems, the present invention has achieved three major breakthroughs: First, it is proved that water is not necessary. Under anhydrous conditions, high-surface-area iron powder (such as below -200 mesh, with the oxide layer removed by hydrochloric acid) treated by acid activation and non-explosive aromatic hydrocarbon / ether picrates (replacing dry picric acid to avoid friction or impact sensitivity, such as phenyl picrate, anisole picrate) in a mixed solvent (such as toluene / 2-

[0120] propanol, which balances the solubility of picric acid and the stability of the product), are stirred and reacted at a high temperature of 10 - 80 °C (preferably 40 - 80 °C), and the reaction time can be shortened to 5 - 15 minutes, solving the dependence on moisture and the slow reaction problem of the traditional process. Second, safe raw materials are used. Anhydrous aromatic hydrocarbon / ether picrates are prepared by methods such as alcohol co-solubility, azeotropic dehydration, and mixed solvent method. Experiments have proved that such raw materials have no explosion risk (such as no detonation in Example 5 when struck and rubbed). Third, the process parameters are optimized. Excessive iron powder is used to ensure complete reaction, and the unreacted iron powder is removed by sedimentation and filtration. Strong stirring is used to maintain the suspension of the iron powder to prevent local pH increase or product passivation, improving the reaction efficiency and safety.

[0121] Example 6 shows that unactivated iron powder has no obvious reaction in an anhydrous solvent for 14 days, and it turns green rapidly within 24 hours after activation, proving the key role of iron powder activation in the anhydrous reaction. In Example 8, when using 300-mesh activated iron powder to react with toluene picrate at 50 °C, the iron concentration reaches 6850 ppm within 10 minutes, and the reaction can be completed in 4 minutes, demonstrating the high efficiency of high temperature and highly active iron powder. In Example 15, through toluene / 2-

[0122] The product with a water content of <100 ppm, an iron concentration of 400 ppm, and a free picric acid content of 0.4% was prepared by reacting with a propanol solvent, azeotropically dehydrating, and activated iron powder. It remained a stable emerald green after three years, directly demonstrating the long-term stability of the anhydrous formulation. Examples 2-5 and 13-14 proved the feasibility of safe raw materials by preparing various aromatic hydrocarbon / ether picrates and verifying their safety and melting points.

[0123] Through the above measures, the present invention has significantly improved the defects of the prior art: in terms of stability and shelf life, the anhydrous formulation completely eliminates the deterioration caused by moisture, has no precipitation and unchanged color after three years of storage at room temperature, and its lifespan in high-temperature storage and transportation environments far exceeds that of traditional formulations (traditional formulations deteriorate in 2-19 days, while the present invention has no deterioration); in terms of safety, the use of dry picric acid is avoided and the excess picric acid is reduced, reducing the explosion risk during production and transportation, and significantly reducing corrosion and toxicity; in terms of process efficiency, the reaction time is shortened from several weeks to the minute level, complex equipment is not required, and energy consumption and costs are reduced; in terms of solvent compatibility, the mixed solvent system improves the solubility of the product, avoids flash point problems, is applicable to various fuels and reduces the corrosion of copper alloys, providing a safe, efficient and stable solution for the field of fuel additives.

Claims

1. A method for efficiently synthesizing ferrous picrate under anhydrous / low water conditions, characterized in that, It includes the following steps: Stir and react excessive high-surface-area iron powder with high-concentration aromatic hydrocarbon picrates or aromatic ether picrates in an anhydrous solvent system at 10 - 80 °C for 5 - 15 minutes to obtain a ferrous picrate solution; wherein, the iron powder is acid-activated to remove the oxide layer, the anhydrous solvent system is an aromatic hydrocarbon, a fatty alcohol or a mixture thereof, and the water content of the aromatic hydrocarbon picrate or aromatic ether picrate is less than 100 ppm.

2. The high-efficiency synthesis method of ferrous picrate under anhydrous / low-water conditions according to claim 1, characterized in that: The aromatic hydrocarbon picrates are selected from one or more of picric acid benzene, picric acid toluene, picric acid xylene, picric acid naphthalene, picric acid pyrene, and the aromatic ether picrates are selected from one or more of anisole picrate, diphenyl ether picrate, benzyl ether picrate.

3. The high-efficiency synthesis method of ferrous picrate under anhydrous / low-water conditions as claimed in claim 1, characterized in that: The anhydrous solvent system is a mixture of an aromatic hydrocarbon and a lower fatty alcohol. The aromatic hydrocarbon includes one or more of benzene, toluene, xylene, naphthalene, and the lower fatty alcohol includes one or more of methanol, ethanol, 2 - Propanol, and the volume ratio of the lower fatty alcohol in the mixture is 10% - 90%.

4. The high-efficiency synthesis method of ferrous picrate under anhydrous / low-water conditions according to claim 1, wherein: The particle size of the iron powder is - 200 mesh or finer. The acid activation treatment is to treat with 12N hydrochloric acid for 30 seconds, and then wash with cold water and an alcohol solvent in sequence until neutral.

5. The efficient synthesis method of ferrous picrate under anhydrous / low water conditions according to claim 1, wherein: The reaction temperature is 30 - 60 °C, and the stirring intensity maintains the uniform suspension of the iron powder to avoid local pH increase or product passivation.

6. The high-efficiency synthesis method of ferrous picrate under anhydrous / low-water conditions according to claim 1, characterized in that: The concentration of the aromatic hydrocarbon picrate or aromatic ether picrate in the solvent is greater than 3%, the excessive iron powder is 1.1 - 5 times the theoretical reaction amount, and the unreacted iron powder is removed by sedimentation filtration.

7. The high-efficiency synthesis method of ferrous picrate under anhydrous / low-water conditions as described in claim 3, wherein: The mixture of the aromatic hydrocarbon and the lower fatty alcohol is a mixed solvent of toluene and 2 - Propanol, wherein the volume ratio of toluene is 10% - 90%, and the volume ratio of 2 - propanol is 10% - 90%.

8. The efficient synthesis method of ferrous picrate under anhydrous / low water conditions according to claim 1, wherein: The water content of the anhydrous solvent system is less than 100 ppm, and the reaction is carried out in a dry nitrogen inert environment.

9. As claimed in claims 1 - The method for efficiently synthesizing ferrous picrate under anhydrous / low-water conditions as described in 8, characterized in that: After the reaction, filter through a 10-micron filter to obtain a ferrous picrate solution with a water content of less than 100 ppm and a free picric acid content ≤ 0.4%.

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