PROCESS FOR PRODUCING PHOSPHORUS

Abstract

The subject of the invention is the development of a new process for producing phosphorus P4 from phosphoric acid. In this process, the phosphoric acid and a hydrophilic source of carbon and of hydrogen (biomass, kerogen, “STEP” purification plant sludge, organic polymer) are mixed, and the mixture is treated at a temperature of 80 to 150° C. in order to ensure grafting of the phosphates on the carbon backbone. The production of the phosphorus P4 is carried out by heat treatment of the precursor at a temperature at which phosphorus is produced. The temperature range is from 550° C. to 950° C. This process can be carried out at temperatures below those of conventional phosphorus production without the occurrence of the production of solid by-products normally formed in conventional phosphorus production. The process can be used to produce phosphoric acid for food or medical use.

Claims

1. Process for preparing elemental phosphorus from phosphoric acid, characterized in that the process is carried out in four steps described below: Step 1: making a mixture of phosphoric acid and a hydrophilic source of carbon and hydrogen Step 2: preparation of the precursor by heat treatment of the mixture obtained in step 1 at a temperature ranging from 80 to 150° C. Step 3: heat treatment of the precursor in an inert or partially inert atmosphere at a temperature ranging from 550° C. to 950° C. Step 4: Phosphorus recovery.

2. Method according to claim 1, characterized in that the carbon source is selected among plant biomass, fossil resources such as oil shale, fuel oil, heavy hydrocarbons or any residual organic matter such as spent activated carbon, ion exchange resins and WWTP sludge.

3. Method according to claim 1, characterized in that e heat treatment of the precursor produces phosphorus in the gaseous state from 550° C.

4. Method according to claim 3, characterized in that the gas formed rs recovered by condensation in the form of white phosphorus P4.

5. Method according to claim 3, characterized in that the gas formed is recovered by condensation in the form of red phosphorus.

6. Method according to claim 3, characterized in that the gas formed is dissolved either in a solvent or an organic oil or dissolved in a mineral oil.

Description

DESCRIPTION OF DRAWINGS

[0014] FIG. 1: Illustration of the grafting of phosphate ions onto the carbon skeleton via the formation of POC bridges after impregnation of the hydrophilic support With the phosphoric acid solution.

[0015] FIG. 2: Diagram of the pyrolizer.

[0016] FIG. 3: X-ray fluorescence analysis.

[0017] FIG. 4: Raman spectrum of white phosphorus P4.

[0018] FIG. 5: Illustration of the analysis of thermograms showing the dependence of the residue level on the amount of phosphoric acid impregnated in the biomass.

[0019] FIG. 6: Decrease in the residue rate as a function of temperature.

[0020] FIG. 7: Rate of conversion of phosphorus to the gaseous state.

[0021] FIG. 8: Evolution of the product of the percentage of phosphorous by the rate of the residue.

DESCRIPTION OF THE INVENTION

[0022] The object of the present invention is to implement a new process for the production of S phosphorus from phosphoric acid. To do this, the invention aims to develop an efficient process for obtaining elemental phosphorus by reduction of the phosphate ion in the presence of a hydrophilic source of carbon and hydrogen temperatures not exceeding 950° C.

[0023] The production phosphorus P4 is established in three stages:

1. Preparation of the mixture: phosphoric acid is mixed with a hydrophilic source of carbon and hydrogen, preferably cellulose biomass, kerogen, sludge from WWTPs, etc.).
2. Treatment of the fixture: the mixture is treated at a temperature ranging from 80 to 150° C., to ensure the grafting of the phosphates on the carbon skeleton.
3. Pyrolysis of the precursor: the precursor is heat treated, in a furnace with conventional fixed, rotary or fluidized bed heating, in a totally or partially inert medium at a temperature between 550 and 950° C.

EXAMPLE

[0024] The following example is presented to describe the manufacturing process for phosphorus P4. However, the example should not be interpreted as limiting the manufacturing process developed.

Preparation of the Precursor

[0025] Different sources of carbon, in particular of plant biomass (olive pomace, coffee grounds, pomegranate bark, sawdust, etc.) were tested for different mass ratios of the mixture of phosphoric acid/hydrophilic carbon source and hydrogen. The mixture was heat treated to ensure the grafting of the phosphates on the carbon skeleton. In fact, under the effect of temperature, water evaporates and thus allows the formation of organo-phosphate compounds. The grafting of the phosphate ions unto the carbon skeleton is ensured by the formation of POC bridges after impregnation of the hydrophilic support with the phosphoric acid solution (FIG. 1 below).

Pyrolysis of the Precursor

[0026] This step consists of a heat treatment of the precursor, in a furnace with conventional fixed heating, rotary or fluidized bed, in a tubular pyrolizer (FIG. 2).

[0027] The gaseous phosphorus formed is transported to the cold zone and condenses on the walls of the reactor. The non-condensed phosphorus is bubbled through methanol (or ethanol) and dissolves in the latter. Only the carbon dioxide is evacuated to an extractor and can be recovered and stored for possible use.

[0028] At the end of the reaction, the solid phosphorus produced can be recovered in solid form (taking the necessary precautions) or dissolved in an organic solvent, preferably an oil or an alcohol.

[0029] Organic solutions containing phosphorus can be used as a raw material for the synthesis of phosphorus compounds. White or red phosphorus has various applications in the synthesis of phosphorus-based materials. Another application is in the production of high purity phosphoric acid.

[0030] The process is characterized by an almost total recovery of the raw material used and generates a limited quantity of by-products.

[0031] Fluorescence analysis (FIG. 3) clearly showed that the material contains more than 97% phosphorus. To determine the nature of the phosphorus obtained, a study by Raman spectroscopy was carried out.

[0032] The Raman spectrum of the material (FIG. 4) shows 3 fine modes which correspond exactly to white phosphorus P4. Indeed, a comparison was made with the Raman spectrum of P4 carried out in the 1930s [5, 6]. The most intense, polarized mode corresponds to the breathing mode of the P4 tetrahedron.

[0033] The thermogravimetric analysis of the various samples in an inert medium shows that all the samples have the same appearance on the thermograms, regardless of the precursors used (FIG. 5). However, the residue levels depend greatly on the quantities of phosphoric acids introduced during the preparation of the precursors (FIG. 6).

[0034] By comparing the thermograms (FIG. 5) with the observations made during the pyrolysis of the precursor, it can be noted that around a temperature of 550° C., a mist of vapors appears; a gas which begins to form in the tube at the exit of the furnace (at the level of the condenser). The flow rate of these vapors increases with the increase in pyrolysis temperature as well as with the rate of heating of the furnace. The gas cools and condenses in a tubular exchanger, placed just at the outlet of the pyrolvzer. A trapping system makes it possible to recover the product of the reaction P4 in its solid form, deposited on the walls of the tubes.

[0035] Analysis of the thermograms (FIG. 6) shows that the residue level depends on the amount of phosphoric acid impregnated in the biomass. At around 750° C., the amount of P4 generated with ratio 3 is greater than that generated with ratio 2. FIG. 6 shows that the residue level decreases with increasing temperature. It reaches a value of 8% at 950° C.

[0036] Knowing that the amount of calcium in the precursor remains co stain during the heat treatment, monitoring the change in the ratio of the percentage of phosphorus to the, percentage of calcium will give a precise idea of the amount of phosphorus transformed. FIG. 7 shows that the ratio of the percentages of compositions goes from 22 (T=600° C.) to 2.4 (950+ C.). which shows that practically all of the phosphorus passes to the gaseous state.

[0037] The evolution of the product of the percentage of phosphorus by the rate of residue, P*TR (FIG. 8) confirms the previous findings and clearly shows that the amount of residual phosphorus at 950° C. is very low.

INDUSTRIAL APPLICATION

[0038] The reaction can be carried out at a much lower temperature than that by the conventional method, thus producing a great saving of energy. As an application we can consider the production of pure phosphoric acid for food or medical use.

BIBLIOGRAPHICAL REFERENCES

[0039] 1—Phosphorus recovery from hydrothermal treatment of biomass; US008624070B2
2—Process for recovering phosphorus from organic sludge; US006022514A.
3—Processes and equipment for production of elemental phosphorus and thermal phosphoric acid; US004919906
4—Method of preparing phosphorus; US006207024B1
5—S. Bhagantam, Ind. Phys. day 5 73 (1910)
6—C. s. Venkateswaran, proc. Ind. Acad sci. 2260 (1935).