Continuous catalytic oxidation process for phosphorus removal from yellow phosphorus off-gases

Thread Content

Phosphorus yellow industry is optimistic about the process of producing ethylene glycol from syngas; the successful model of producing ethylene glycol from calcium carbide exhaust gases offers valuable insights for these companies. However, the issue of purifying phosphorus yellow exhaust gases prevents these two approaches from being combined. The utilization of yellow phosphorus exhaust gas requires the removal of impurities such as fluorine, arsenic, phosphorus, and sulfur. Among them, there are relatively mature processes for the removal of fluorine, arsenic, and sulfur; therefore, the technical challenge in purifying yellow phosphorus exhaust gas lies in the removal of phosphorus. Currently, the three common methods used by enterprises to purify yellow phosphorus exhaust gases are water washing combined with alkali washing, temperature-dependent adsorption, and discontinuous catalytic oxidation. However, all three methods present different problems during industrial operation: in the water washing plus alkali washing method, elemental phosphorus reacts with the alkali during the alkali washing process to form phosphine, thus failing to achieve effective removal of phosphorus; at the same time, large amounts of waste alkaline solution are generated ； The temperature-variable adsorption process is relatively complex, and improper treatment of impurities such as phosphorus released during desorption may lead to secondary pollution ； The discontinuous catalytic oxidation method for phosphorus removal is a batch process that requires switching between multiple towers; the catalysts that have become saturated with adsorbates need to be regenerated, and their catalytic efficiency declines significantly as a result of this regeneration. Given the problems associated with the aforementioned methods, Beijing Peking Pioneer Technology Co., Ltd. set out to address the challenge of phosphorus removal from yellow phosphorus exhaust gases. If this research achieves industrial success, it is likely to push the high-value utilization of yellow phosphorus exhaust gases to a new level. The continuous catalytic oxidation dephosphorization process developed by Peking University Pioneer operates on the principle of catalytically oxidizing phosphorus pentoxide exhaust gas that has been filtered and pressurized; the resulting phosphorus oxides desorb from the surface of the catalyst and are carried away from the reactor bed in gaseous form. Since the catalyst does not need to be regenerated, the purification of phosphorus pentoxide exhaust gas can proceed continuously. This process features few operating units and a simple design, which reduces the complexity of equipment and operations; as a result, it significantly lowers investment costs and energy consumption, helping phosphorus yellow production enterprises save on the long-term operational costs associated with their equipment. The key to enabling continuous catalytic oxidation in this process lies in the three prominent innovative advantages of the catalyst developed by Beida Pioneer. First, conventional dephosphorization catalysts need to be regenerated repeatedly, and after a period of time they become ineffective; new catalysts must be installed in order for the system to continue operating. The new catalyst developed by Peking University Pioneer does not require regeneration during continuous phosphorus removal reactions, effectively addressing the many issues associated with existing discontinuous phosphorus removal technologies. Second, unlike any previous purification processes for yellow phosphorus exhaust gases, the new catalyst developed by Peking University Pioneer exhibits excellent sulfur resistance; the total sulfur content in the yellow phosphorus exhaust gases remains unchanged before and after the removal of phosphorus impurities, and this does not affect the catalyst’s ability to remove phosphorus continuously. This means that Peking University Pioneer’s continuous phosphorus removal process can first remove total phosphorus, after which phosphorus yellow industry companies can choose the desulfurization method and degree of desulfurization based on how they intend to utilize the phosphorus yellow exhaust gas. For example, when generating electricity using yellow phosphorus exhaust gas, coal is required as a supplementary fuel. Both the total sulfur in yellow phosphorus exhaust gas and the sulfur in coal produce sulfur dioxide upon combustion. For boilers, there is no need to remove hydrogen sulfide in advance; therefore, the sulfur in the exhaust gas can be removed simultaneously with that in the coal, thereby simplifying a processing step. Third, the new catalyst features stable performance, ensuring the long-term operation of the equipment; it can be used continuously for 3 to 5 years as a conservative estimate, which greatly enables yellow phosphorus manufacturers to supply purified exhaust gas to downstream processes in a stable manner over the long term. In October 2014, a pilot test of this process was carried out at a phosphorus-electricity company in Yunnan. The device has been in continuous operation for 1.5 years, purifying a total of 1.2 million cubic meters of exhaust gas. The total phosphorus content in the purified exhaust gas dropped from 1200–1500 mg/m³ before purification to below 1 mg/m³ (approximately 0.7 ppm), thus achieving the goal of keeping total phosphorus at less than 1 ppm. This meets the requirements for raw gas used in power generation and chemical synthesis, and no other forms of waste are generated throughout the process. Based on the operational data from the pilot plant, assuming an exhaust gas flow rate of 20,000 cubic meters per hour for yellow phosphorus waste gas, the initial investment for the continuous catalytic oxidation phosphorus removal process is approximately 20 million yuan. The operating cost per cubic meter of exhaust gas is around 0.08 yuan (including depreciation). Both the investment and operating costs associated with this process are lower than those of the discontinuous oxidation adsorption phosphorus removal method and the temperature-controlled adsorption phosphorus removal method. Currently, phosphorus yellow manufacturers are paying great attention to this purification process, and Beida Pioneer plans to start construction of the first industrial-scale facility in the near future.