Is sulfuric acid needed in the production of nitrophosphorus compound fertilizers?

You might want to take a look at Tianji’s production methods for nitro compound fertilizers. The process involves the synthesis of ammonia, which is then oxidized to produce nitric acid; this nitric acid is used to react with phosphate rock, allowing calcium nitrate to be separated. Ammonia is used for neutralization and granulation to produce nitro compound fertilizers. That’s the simple process. The production process does not use sulfuric acid. This post was last edited by 921027abcd on 2008-3-1 18:38]

In the production process of phosphoric acid fertilizers, various manufacturing methods have emerged due to different approaches to calcium removal or fixation. To date, the technically mature and industrialized methods include: freezing method, nitric acid-sulfuric acid method, nitric acid-sulfate (such as potassium sulfate, ammonium sulfate) method, nitric acid-phosphoric acid method, carbonization method, liquid-liquid extraction method, etc. 1. Production of phosphoric acid fertilizer by freezing: The excess CaO is precipitated from the acidolysis solution in the form of Ca(NO3)2•4H2O crystals by cooling the acidolysis solution. Depending on the amount of calcium removed, products with different water solubilities of P2O5 can be obtained. The frozen-process phosphoric acid nitrate fertilizer, also known as the Odda method, involves the following basic steps: the decomposition of phosphate rock using nitric acid, the separation of acid-insoluble substances from the acidulated solution, the freezing and crystallization of the acidulated solution, the separation and washing of Ca(NO3)2•4H2O crystals, the neutralization of the mother liquor with ammonia, the concentration of the neutralized slurry, granulation and drying, cooling and screening, coating, packaging of the final product, processing of the by-product calcium nitrate, as well as the treatment of waste gases and wastewater. The freezing method for producing phosphoric acid nitrogen fertilizers is the earliest and most widely used method in the world, with the largest production capacity. A typical example of this method is Norway’s Norsk Hydro process; more than a dozen large-scale plants using this technology have been built around the world, with a total production capacity of over 10 million tons. In addition, other frozen-process phosphatic nitrogen fertilizer processes such as the Stamicarbon process, Hoechst-Uhde process, Kamka-Nitro process, BASF process, etc., also achieve certain production volumes. Representative product specifications include 20‑20‑0, 28‑14‑0 (26‑13‑0), etc. By adding potassium salts during the production process, a ternary compound fertilizer can be produced. 2. Production of nitric acid phosphate fertilizer via the nitric acid-sulfuric acid method: This method utilizes hydrogen ions from nitric acid and sulfuric acid to decompose phosphate rock; the sulfate ions (SO42-) then react with calcium to form insoluble calcium sulfate (CaSO4•H2O) crystals, which retain the calcium in the acidulated solution. As a result, the molar ratio of CaO to P2O5 in the solution is less than or equal to 2.0, thereby producing nitric acid phosphate fertilizer that contains both water-soluble and sulfate-soluble P2O5. The basic reaction equations for the decomposition of phosphate rock using nitric acid and sulfuric acid are as follows: Ca5F(PO4)3 + 10HNO3 = 5Ca(NO3)2 + 3H3PO4 + HF; Ca5F(PO4)3 + 5H2SO4 = 5CaSO4•2H2O + 3H3PO4 + HF. The amount of sulfuric acid required is determined by the water solubility of P2O5 in the product, while the amount of nitric acid needed is determined by the weight ratio of N to P2O5 in the product and the water solubility of P2O5. The greater the sulfuric acid consumption, the more calcium is fixed, and the higher the water solubility of the product. When producing a fertilizer with a 50% water solubility, the reaction equation is as follows: 2Ca5F(PO4)3 + 8HNO3 + 6H2SO4 = 4Ca(NO3)2 + 6CaSO4•2H2O + 6H3PO4 + 2HF. Further, 6CaSO4•2H2O + 4Ca(NO3)2 + 6H3PO4 + 2HF + 11NH3 = 6CaSO4•2H2O + 3CaHPO4 + 3NH4H2PO4 + 8NH4NO3 + CaF2. The key to the nitric acid-sulfuric acid method lies in obtaining large calcium sulfate crystals that are easy to filter. Adding potassium salts during granulation can result in the production of ternary compound fertilizers. 3. Production of phosphatic nitrate fertilizers by the sulfate method (including the ammonium sulfate cycle method): During the decomposition of phosphate rock with nitric acid, soluble sulfates (such as potassium sulfate, ammonium sulfate, etc.) are added. The sulfate ions (SO42-) react with calcium to form insoluble calcium sulfate crystals, which help to remove excess calcium from the solution. This results in a molar ratio of CaO to P2O5 in the solution that is less than or equal to 2.0, thereby yielding phosphatic nitrate fertilizers containing both water-soluble and insoluble P2O5. The basic reaction is a double-displacement reaction of salts: Ca(NO3)2 + (NH4)2SO4 = CaSO4•2H2O + 2NH4(NO3)2; Ca(NO3)2 + K2SO4 = CaSO4•2H2O + 2KNO3. The amount of sulfate used depends on the required solubility of P2O5 in the product, and it is equivalent to the amount of sulfate used in the nitric acid-sulfuric acid method. The amount of nitric acid, on the other hand, is determined based on theoretical calculations and the N:P2O5 ratio of the product. Like the nitric acid-sulfuric acid method, the key to the sulfate method lies in obtaining large, easily filterable gypsum crystals. During ammonia neutralization, the pH value must be strictly controlled to prevent the degradation of phosphates. During the acidolysis process, HF, SiO2, and potassium nitrate (KNO3) undergo the following reaction: 6HF + SiO2 + 2KNO3 = K2SiF6↓ + 2HNO3 + 2H2O. A potassium fluorosilicate precipitate is formed, which is separated from calcium sulfate; an alkaline solution is used for washing in order to recover potassium and reduce its loss. 4. Nitric acid-phosphoric acid method: Phosphoric acid is added to the acid digestion solution used to decompose phosphate rock, causing the excess calcium to precipitate as CaHPO4•2H2O, thereby meeting the requirements for calcium removal and simultaneously adjusting the N/P2O5 ratio in the solution. The chemical reaction equation for this method is as follows: 2Ca5F(PO4)3 + 20HNO3 + 4H3PO4 = 10Ca(NO3)2 + 10H3PO4 + 2HF. 10Ca(NO3)2 + 10H3PO4 + 2HF + 21NH3 = 20NH4NO3 + 9CaHPO4 + NH4H2PO4 + CaF2. The amount of phosphoric acid can be used to adjust the N:P2O5 ratio of the product and to change its water solubility in P2O5 terms.

Currently, Xinghua, United Chemical, Tianji, Heihua, and Chuanhua are all producing nitro compound fertilizers or upstream products. Some of them are listed companies. Whoever can develop a process that eliminates the need for sulfuric acid is truly amazing – such a person would be a great investment opportunity. Have you ever thought about using your expertise to make money in the stock market? Xinghua Shares have picked up; everyone should pay attention to them. I study finance and am good at trading stocks, but unfortunately I know nothing about the chemical industry. Thank you to 921027abcd and zhangchaosen for their replies! This post was last edited by fdzzs on 2008-3-2 at 15:42.]