FIELD OF THE INVENTION

The present invention is generally directed to improved processes for the preparation of various phosphorus oxides and phosphoric acid. Phosphorus oxides prepared in accordance with the present invention include phosphorus (III) oxides (e.g., tetraphosphorus hexaoxide (P4O6)). Phosphorus (III) oxides such as P4O6are useful products and are also useful as precursors in preparation of other products, including phosphorous acid (H3PO3) and other phosphorus-containing chemicals. Certain aspects of this invention are also directed to using various byproducts formed during P4O6production as precursors for the formation of phosphoric acid (H3PO4) and P2O5. In particular, the present invention is directed to improved processes for the preparation of phosphorus (III) oxides (e.g., P4O6) suitable for use in the preparation of phospho-herbicides such N-(phosphonomethyl)glycine (glyphosate) and precursors thereof (e.g., N-(phosphonomethyl)iminodiacetic acid (PMIDA)). The present invention is thus further directed to preparation of these compounds.

BACKGROUND OF THE INVENTION

Methods for producing phosphorus (III) oxides such as P4O6are known in the art. The term “P4O6” as used herein is intended to include all formulae conventionally used to define phosphorus (III) oxides, including P2O3. As used herein, the terms phosphorus (III) oxide and P4O6are used interchangeably.

P4O6is useful as a product itself and as a precursor for production of various other products. Methods to prepare P4O6are known in the art and have proven to some extent to be effective, but there exists room for improvement in terms of yield, purity, and process efficiencies. For example, prior methods for producing P4O6typically encounter limitations or issues during scale-up to commercial scale operations.

Both as a product itself and precursor for preparation of other compounds, P4O6is often considered in comparison to phosphorus trichloride (PCl3), which is conventionally used in various processes as a source of phosphorus. As a product itself, P4O6if produced effectively on a commercial scale would provide an advantage over PCl3since it would contain a higher weight percent of phosphorus as compared to PCl3(over 50 weight % as compared to 22 weight %). P4O6as a product itself would therefore provide a more concentrated phosphorus product and would avoid the issues and risks associated with the dangerous chemical chlorine required for production of PCl3and released as a byproduct of its production. These same advantages are provided when P4O6is used as an alternative to PCl3as a precursor for preparing other compounds where, in one form or another (e.g., as hydrochloric acid) large amounts of chlorine are generated as undesired byproducts that must dealt with or disposed. In addition, intermediates and end products to be made from PCl3usually do not contain chloride. An alternative to PCl3as a starting material is phosphorous acid. However, phosphorous acid is generally prepared from PCl3and therefore does not completely avoid the undesired byproduct issue, but simply shifts it to another point in the process.

A need exists, therefore, for improved processes to prepare P4O6as a phosphorus-containing product itself and as alternative to PCl3as a source of phosphorus for use in preparation of various phosphorus-containing compounds.

BRIEF SUMMARY OF THE INVENTION

Briefly, therefore, the present invention is directed to processes for the manufacture of phosphorus (III) oxide.

In various embodiments, the process comprises, in a reactor unit, reacting phosphorus with oxygen, thereby forming an intermediate reaction product stream comprising P2O3and one or more byproducts; in a quenching unit, quenching the intermediate reaction product stream by contacting with a quenching liquid, thereby forming a reaction product slurry comprising P4O6and one or more byproducts; recovering the one or more byproducts from the reaction product slurry; and in a vaporizer unit, vaporizing the one or more byproducts to form a vaporized recycle stream.

In other embodiments, the process comprises, in a reactor unit, reacting phosphorus with oxygen, thereby forming an intermediate reaction product stream comprising P2O3and one or more byproducts; in a quenching unit, quenching the intermediate reaction product stream by contacting with a quenching liquid, thereby forming a reaction product slurry comprising liquid P4O6and one or more byproducts; separating solid components of the reaction product slurry therefrom, thereby forming a slurry byproduct stream comprising the one or more solid byproducts and a crude product stream comprising liquid P4O6; and introducing at least a portion of the slurry byproduct stream into a vaporizer unit.

In still further embodiments of processes for the manufacture of phosphorus (III) oxide, the process comprises, in a reactor unit, reacting phosphorus with oxygen, thereby forming an intermediate reaction product stream comprising P2O3and one or more byproducts; in a quenching unit, quenching the intermediate reaction product stream by contacting with a quenching liquid, thereby forming a reaction product slurry comprising liquid P4O6and one or more solid byproducts; recovering the one or more solid byproducts from the reaction product slurry; and introducing the one or more solid byproducts into the reactor unit for direct cooling of the contents of the reactor unit, and wherein the temperature within the reactor unit is controlled by external cooling of the reactor unit.

The present invention is also directed to processes for the manufacture of phosphoric acid (H3PO4).

In certain such embodiments the process comprises reacting phosphorus with oxygen in a reactor unit, thereby forming an intermediate reaction product comprising P2O3and one or more byproducts; in a quenching unit, quenching the intermediate reaction product by contacting with a quenching liquid, thereby forming a reaction product slurry comprising liquid P4O6and one or more byproducts; separating the reaction product slurry into a crude liquid P4O6stream and a thickened product slurry; introducing the crude liquid P4O6stream into the quenching unit; separating liquid P4O6from the thickened product slurry, thereby forming a crude product stream comprising liquid P4O6and a byproduct stream comprising phosphorus (III), phosphorus (V) and/or phosphorus (III and V) oxides; introducing the byproduct stream and oxygen into a vaporizer unit, thereby oxidizing phosphorus oxides present in the byproduct stream to produce a vapor product stream comprising P2O5and/or P4O10; and contacting the vapor product stream with water, thereby forming a liquid product stream comprising H3PO4.

The present invention is also directed to processes for the manufacture of phosphorus pentoxide (P2O5).

In certain such embodiments, the process comprises reacting phosphorus with oxygen in a reactor unit, thereby forming an intermediate reaction product comprising P2O3and one or more byproducts; in a quenching unit, quenching the intermediate reaction product by contacting with a quenching liquid, thereby forming a reaction product slurry comprising liquid P4O6and one or more byproducts; separating liquid P4O6from the reaction product slurry, thereby forming a crude product stream comprising liquid P4O6and a byproduct stream comprising phosphorus (III), phosphorus (V) and phosphorus (III and V) oxides; introducing the byproduct stream and oxygen into a vaporizer unit, thereby oxidizing phosphorus oxides present in the byproduct stream to produce a vapor product stream comprising P4O10; and condensing the vapor product stream, thereby forming a liquid product stream comprising P2O5.

The present invention is further directed to processes combining the embodiments listed above. For example, any of the embodiments describing processes for the preparation of phosphorus (III) oxide may be combined with the processes for the manufacture of phosphoric acid (H3PO4) and/or phosphorus pentoxide (P2O5) described above and/or elsewhere herein.

Other objects and features will be in part apparent and in part pointed out hereinafter.

