METHOD FOR THE PRODUCE OF PHOSPHOROXYCHLORIDE FROM PHOSPHORUS-OXIDANT COMPOUND-CONTAINING MATERIAL

Description

[0001] The invention relates to a method for converting phosphorus-oxygen compound-containing material into phosphoryl chloride. This material can then be used for technical purposes.

[0002] The decomposition of phosphates, especially water-insoluble ones, with the aim of utilizing the contained phosphorus compound technically and economically or determining its quantity, plays a major role in analytical chemistry and engineering. In analytical chemistry, it serves to determine phosphorus in rocks or ores. Calcium phosphate sources are industrially reacted with sulfuric acid in enormous quantities to obtain water-soluble phosphoric acid, which is used primarily as a fertilizer or detergent additive, and secondarily as an acidulant, for example in the food industry.

[0003] Phosphate / phosphoric acid recovery is carried out industrially by lowering the pH value in an aqueous slurry of ground phosphate rock, preferably with mineral acids such as sulfuric acid or phosphoric acid, followed by filtration. A disadvantage of this process is that it requires very large quantities of acid and necessitates a technically difficult-to-control filtration step with corresponding byproducts. Furthermore, it generates large quantities of waste.

[0004] However, these reactions do not lead to the desired phosphorus-chlorine compounds.

[0005] The production of phosphorus-chlorine compounds on an industrial scale is carried out exclusively via the energy-intensive and cumbersome detour of synthesizing elemental phosphorus followed by reaction with elemental chlorine.

[0006] The production of phosphorus-chlorine compounds on an industrial scale generally involves the process of extracting elemental phosphorus from phosphate rock, coal, and additives in an electric arc furnace, followed by the combustion of the phosphorus with chlorine to form phosphorus-chlorine compounds. Disadvantages include the very high electricity consumption, the high temperatures, the handling of toxic white phosphorus, the presence of arsenic compounds, the handling of toxic chlorine, the immense quantities of slag that must be disposed of, and the very large CO₂ footprint.

[0007] However, only phosphorus chlorides such as PCl3 are accessible in this way. Phosphorus oxychloride (POCl3) is not obtainable via this route, but must first be produced from PCl3 in a further step by oxidation.

[0008] US1606319A describes a process for the production of phosphoryl chloride starting from phosgene and a calcium phosphate at about 500°C.

[0009] US patent 1730521A discloses the preparation of phosphorus-chlorine compounds (POCl 3 ; PCl 5 ) starting from calcium triphosphate, silica, carbon and chlorine gas.

[0010] US 3927179A discloses a continuous process for the preparation of phosphoryl chloride, comprising the steps of: a) providing liquid phosphorus trichloride in a first reaction zone; b) introducing phosphorus and air into the first reaction zone to form phosphorus pentoxide in the presence of the phosphorus trichloride; and c) transferring the phosphorus pentoxide and phosphorus trichloride mixture from the first reaction zone into a second reaction zone and reacting the mixture with chlorine introduced into the second reaction zone to form phosphorus oxychloride.

[0011] From Xiaojiang Wang et al. "Effect of pyrophosphate in the dichlorination of tetrachloroethene by Fenton reaction" in Environmental Toxicology and Chemistry, Peramon Press, US, Vol. 17, No. 9, November 2, 2009, pages 1689-1694, the ability of pyrophosphate to keep Fe in solution and thus improve the dechlorination of tetrachloroethene by Fenton (the Fenton reaction) is described.

[0012] One method for the direct recovery of phosphorus-chlorine compounds from phosphates as volatile compounds involves the use of carbon tetrachloride, sometimes in combination with chlorine and / or inert gases such as carbon dioxide. The sample is heated to 700°C to 900°C, and a gas stream is passed over it. The gas stream is then directed into a scrubber and analyzed for phosphate. Quantitative conversion has been reported, and the method has been tested on numerous metal phosphates (Jannasch, P., Jilke, W.; Journal für praktische Chemie, 21, 1908 and Jannasch P., Jilke, W.; Journal für praktische Chemie, 113, 1909).

[0013] A disadvantage of this process is the long reaction time described. Above all, however, the use of carbon tetrachloride in industrial processes has now been banned because the compound damages the ozone layer, making this reaction technically impossible. Task

[0014] The object of the present invention was therefore to find a process for the production of phosphorus oxychloride that no longer exhibits the described disadvantages of the prior art. Surprisingly, a process for the production of phosphorus oxychloride was found that is characterized by the fact that one i. reacts a phosphorus-oxygen compound-containing material from the group of calcium phosphates in the presence of tetrachloroethene at a temperature of 500 to 1000°C, preferably 600 to 900°C, particularly 700 to 850°C, and ii. discharges and isolates the phosphorus oxychloride formed in the exhaust gas stream. Phosphorus-oxygen compounds

[0015] Preferably, the phosphorus-oxygen compound-containing material from the group of calcium phosphates contains the corresponding orthophosphates, metaphosphates, polyphosphates, or mixtures thereof. It particularly preferably contains calcium phosphate, most preferably calcium orthophosphate or calcium hydroxylapatite.

[0016] The phosphorus-oxygen compound-containing material from the group of calcium phosphates preferably contains a content, calculated as elemental phosphorus, of 1 to 44 wt.%, preferably of 1 to 30 wt.%, in particular of 5 to 28 wt.%, based on the phosphorus-oxygen compound-containing material.

[0017] The phosphorus-oxygen compound used, from the group of calcium phosphates, preferably has an average particle size of 0.1 µm to 50 mm, more preferably of 0.5 to 10 mm. Depending on the dimensions, the particle size can be easily determined by sieving, or, for smaller particles, by laser diffraction or laser scattering. The most suitable method is known to those skilled in the art.

[0018] The water content of the phosphorus-oxygen compound used from the group of calcium phosphates is preferably less than 5 wt.%, in particular less than 1 wt.%. Proceedings

[0019] The reaction of the phosphorus-oxygen compound-containing material from the calcium phosphate group takes place in the presence of tetrachloroethene. This can be used as such, or in the form of its precursor chloroform, which releases HCl at temperatures above 500°C and converts to tetrachloroethene, or in the form of a mixture containing tetrachloroethene and chloroform.

[0020] Since the thermal conversion of chloroform to tetrachloroethene is accompanied by the formation of HCl, which is useless for further reaction with phosphorus-oxygen compounds, tetrachloroethene is preferably used as a starting material, provided it is available.

[0021] The reaction can optionally be carried out in the presence of an inert gas. Suitable inert gases include nitrogen, carbon dioxide, and / or argon. Preferably, the tetrachloroethene, which may be used together with chloroform and optionally a carrier gas, contains less than 0.1% oxygen by volume, and in particular less than 0.05% by volume, based on the sum of the gas stream containing these components. The preferably used inert gas is nitrogen, carbon dioxide, or argon.

[0022] Preferably, a weight ratio of the sum of tetrachloroethene and / or chloroform to inert gas of 1:0 to 1:6 is used, preferably between 1:0 and 1:4.

[0023] The conversion of the phosphorus-oxygen compound-containing material from the calcium phosphate group is preferably carried out in a fluidized bed, packed bed, or fluidized bed reactor, in a shaft furnace, or in a furnace, which can be most easily designed as an indirectly heated tube furnace or rotary kiln. The respective reactors are preferably gas-tight. Optionally, the material can be shaped before being introduced into a furnace, for example, by briquetting, extrusion, or pelletizing. For this purpose, auxiliary materials such as layered silicates, especially bentonites, as well as lignosulfonate, methylcellulose, water glass, starch, or others can be used.

[0024] The phosphorus-oxygen compound-containing material from the group of calcium phosphates used in the process according to the invention is preferably placed in a reactor, which is preferably provided with a layer resistant under the reaction conditions to be set. Preferred reactor materials are nickel- or graphite-coated reactors. Reactors that allow movement of the material during the reaction are particularly preferred in order to allow the most effective possible contact of the reactants and heat distribution. Fluidized bed devices, rotary kiln reactors, or a reaction in an extruder with screw feed are preferred in this regard.

[0025] In the case of a tubular reactor, the reactor length is preferably 0.2 to 40 m. The residence time in the reactor during the reaction generally depends on the temperature and the potential for contact between the reactants. The process according to the invention can be operated as a batch or continuously.

[0026] A gas stream of tetrachloroethene and / or chloroform, optionally diluted by an inert carrier gas stream, is preferably passed through the reactor and over the phosphorus-oxygen compounds from the calcium phosphate group, while the reaction temperature is simultaneously maintained at 500 to 1000°C, preferably at 600 to 900°C, and particularly at 700 to 850°C. The reaction time can range from a few minutes to 10 hours, preferably between 20 minutes and 5 hours.

[0027] Preferably, 0.75 to 4 mol of tetrachloroethene or 1 to 4.5 mol of chloroform is used per mol of phosphorus in the phosphorus-oxygen compound-containing material.

[0028] The products formed during the reaction, which may be volatile at the reaction temperature, in these examples primarily phosphoryl chloride, iron chloride, but also aluminum chloride and possibly other heavy metal chlorides such as zinc chloride or rare earth chlorides, are preferably resublimed from the exhaust gas stream at points of different temperatures and collected separately.

[0029] Preferred deposition temperatures are less than 701°C for FeCl 2, in particular less than 700°C to 307°C, less than or equal to 307°C for FeCl 3, in particular 150°C to 300°C and less than or equal to 150°C for AlCl 3, in particular 110°C to 149°C.

[0030] Phosphoryl chloride is preferably collected in a condenser at preferably less than 110°C.

[0031] Both the sublimate and the residue are essentially water-soluble and can preferably be further separated and isolated from their aqueous solutions, for example, after determining their possible existence, by separating and isolating them from each other in the form of their sulfides, chlorides, phosphates, fluorides or other precipitate compounds according to the classical H₂S separation process. Examples Analytics

[0032] The analysis was performed, after dissolving the calcium phosphate sample in suitable acids, in an ICP-OES, after calibration for the respective element by calibrated standard solutions of the respective elements. Example 1

[0033] 10 g of technical-grade calcium phosphate (obtained from sewage sludge ash processing) containing (in wt.%): Ca: 35%, PO₄: 52%, Fe: 0.14%, Al: 0.48%, each determined by ICP-OES, are placed in a quartz reactor (120 mm diameter) which is immersed in a tube furnace. The reactor is heated to 150°C.

[0034] 0.2 ml / min of tetrachloroethene is evaporated in a total evaporator and mixed with a nitrogen stream of 1 l / min at 150°C. The tetrachloroethene-nitrogen mixture enters the quartz reactor, which is heated to 150°C to prevent condensation of the reactant, and passes over the calcium phosphate. The gaseous reaction products exit the reactor as an exhaust stream, which is cooled to 100°C and passed through a gas cell with optical windows, through which an infrared spectrum of the gas phase is recorded. The heating in this phase of the reaction serves solely to prevent condensation of reactants and products.

[0035] The solid is heated to 780°C within 2 hours in the reactor and gas stream, while the exiting exhaust gas stream is continuously monitored by recording IR spectra.

[0036] It is also possible to heat the sample to 780°C before adding tetrachloroethene.

[0037] Above a temperature of 750°C, the conversion to POCl3 begins to accelerate rapidly, as evidenced by the bands in the IR (observed: 592cm⁻¹ (P-Cl), 1322cm⁻¹ (P=O), literature: 590cm⁻¹ and 1322cm⁻¹ (±6cm⁻¹), Shimanouchi, T., Tables of Molecular Vibrational Frequencies Consolidated Volume II, J. Phys. Chem. Ref. Data, 1972, 6, 3, 993-1102).

[0038] The POCl 3 is collected in a capacitor.

[0039] After the reaction is complete, 13.2 g of a solid, colored black by adhering traces of soot, are obtained. This solid consists mainly of CaCl₂ and is partially molten. This solid reaction product can be dissolved in water and used for other purposes, such as phosphate precipitation in wastewater treatment plants. Example 2

[0040] 50g of technical-grade calcium phosphate (obtained from sewage sludge ash processing) containing (in wt%) Ca: 35%, PO₄: 52%, Fe: 0.14%, Al: 0.48%, each determined by ICP-OES, are placed in a quartz reactor (120mm diameter) which is immersed in a tube furnace. The reactor is heated to 150°C.

[0041] 0.2 ml / min of chloroform is evaporated in a total evaporator and mixed with a nitrogen stream of 1 l / min at 100°C. The chloroform-nitrogen mixture enters the quartz reactor, which is heated to 150°C to prevent condensation of the reactants, and passes over the calcium phosphate. The gaseous reaction products leave the reactor, are cooled to 100°C, and are passed through a gas cell with optical windows, through which an infrared spectrum of the gas phase is recorded. The heating in this phase of the reaction serves solely to prevent condensation of reactants and products.

[0042] The solid is heated to 780°C within 2 hours in the reactor and gas stream, while the exiting exhaust gas stream is continuously monitored by recording IR spectra.

[0043] It is also possible to heat the sample to 780°C before adding chloroform.

[0044] At temperatures above 500°C, chloroform decomposes into HCl and tetrachloroethene.

[0045] Above 600°C, the tetrachloroethene formed reacts increasingly rapidly with the calcium phosphate to form calcium chloride and phosphoryl chloride. The POCl₃ is collected in a condenser. The latter can be identified by characteristic bands in the infrared spectrum. Above 750°C, the reaction reaches a rate at which significant conversion rates are achieved. The reaction is stopped 20 minutes after reaching the target temperature of 780°C.

Claims

1. Process for preparing phosphorus oxychloride, characterized in that i. a phosphorus-oxygen compound-containing material from the group of calcium phosphates is reacted in the presence of tetrachloroethene at a temperature of 500°C to 1000°C and ii. the formed phosphorus oxychloride is led off in the offgas stream and isolated.

2. Process for preparing phosphorus oxychloride according to Claim 1, characterized in that the reaction is performed at a temperature of 600°C to 900°C, in particular at 700°C to 850°C.

3. Process for preparing phosphorus oxychloride according to at least one of Claims 1 to 2, characterized in that the phosphorus-oxygen compound-containing material contains at least one orthophosphate or metaphosphate or polyphosphate or mixtures thereof.

4. Process for preparing phosphorus oxychloride according to at least one of Claims 1 to 3, characterized in that the phosphorus-oxygen compound-containing material from the group of calcium phosphates contains calcium orthophosphate and / or calcium hydroxylapatite.

5. Process for preparing phosphorus oxychloride according to at least one of Claims 1 to 4, characterized in that the phosphorus-oxygen compound-containing material from the group of calcium phosphates contains at least a content, calculated as elemental phosphorus, of 1% to 44% by weight, preferably of 1% to 30% by weight, in particular of 5% to 28% by weight, based on the phosphorus-oxygen compound-containing material.

6. Process for preparing phosphorus oxychloride according to at least one of Claims 1 to 5, characterized in that the phosphorus-oxygen compound-containing material from the group of calcium phosphates has an average particle size of 0.1 µm to 50 mm, preferably of 0.5 to 10 mm.

7. Process for preparing phosphorus oxychloride according to at least one of Claims 1 to 6, characterized in that tetrachloroethene and / or chloroform optionally with an inert gas is / are used for the reaction of the phosphorus-oxygen compound-containing material from the group of calcium phosphates.

8. Process for preparing phosphoryl chloride according to at least one of Claims 1 to 7, characterized in that phosphoryl chloride is led off from the offgas stream and separated out by condensation, preferably at less than 110°C.