Chromia based fluorination catalyst

Abstract

A chromia-based fluorination catalyst comprising at least one additional metal selected from zinc, nickel, aluminum and magnesium in which from 0.1 to 8.0% by weight of the catalyst is in the form of one or more crystalline compounds of chromium and/or one or more crystalline compounds of the at least one additional metal. The catalyst can be used in processes for producing a fluorinated hydrocarbon.

Claims

1. A chromia-based fluorination catalyst comprising from 6% to 25% by weight of at least one additional metal selected Iron zinc, nickel, aluminium and magnesium in which from 0.5 to 2.5% by weight of the catalyst is in the form of one or more crystalline compounds of chromium.

2. A catalyst according to claim 1, wherein the additional metal is zinc.

3. A catalyst according to claim 1 having a surface area of at least 50 m.sup.2/g.

4. A catalyst according to claim 3 having a surface area of from 70 to 250 m.sup.2/g.

5. A canal according to claim 1 having a sulphate content of less 10% w/w.

6. A method for producing a catalyst as defined claim 1, which method comprises heat treating an amorphous catalyst precursor at a temperature of from about 300 to about 600° C. for a period of from about 1 to about 12 hours in an atmosphere of nitrogen or an atmosphere having an oxygen level of from about 0.1 to about 10% v/v in nitrogen.

7. A method for producing a catalyst as defined in claim 1, which method comprises heat treating an amorphous catalyst precursor at a temperature of from about 250 to about 500° C. for a period of from about 1 to about 16 hours at atmospheric or superatmospheric pressure in the presence of hydrogen fluoride.

8. A process for producing a fluorinated hydrocarbon, which process comprises reacting a halogenated hydrocarbon with hydrogen fluoride in the presence of a catalyst as defined in claim 1.

9. A process according to claim 8 that is carried out at elevated temperature in the vapour phase.

10. A process according to claim 9 for the production of 1,1,1,2-tetrafluoroethane or pentafluoroethane.

Description

EXAMPLE 1

(1) A mixture of zinc and chromium hydroxides made using the catalyst preparation method described above and containing 4% by weight zinc was further thermally processed by heating in nitrogen for 4 hours at 520° C. The resultant material contained 1.0% w/w crystalline chromium oxide.

(2) Using a 2 g charge of this catalyst, the methodology used in the base case study was repeated to give a data set for this partially crystalline catalyst. The results are presented in the summary Tables below and demonstrate that the partial crystallisation of the catalyst had induced a great increase in activity, allowing it to achieve a 30% perchloroethylene conversion at only 227° C. with only a 0.26% loss of selectivity to 133a, 134a, 114 and 115 by-products.

(3) As with the base case example, the partially crystallised catalyst was observed to activate on heating in HF to 480° C., reducing the operating temperature to 212° C., however little deactivation was observed after stressing the catalyst at 500° C. in HF. The by-product levels remained low after the catalyst had been stressed in HF.

EXAMPLE 2

(4) A mixture of zinc and chromium hydroxides made using the catalyst preparation method described above and containing 4% by weight zinc was further thermally process in nitrogen for 4 hours at 540° C. The resultant material contained 2.6% w/w crystalline chromium oxide.

(5) A 2 g charge of this catalyst was tested before and after HF stressing, following the methodology described above and the results of these studies are compared with those obtained for the base case and Example 1 catalyst in the following Tables.

(6) This 2.6% crystalline chromia content catalyst was found to have a lower peak activity than the 1.0% crystalline catalyst, having a minimum operating temperature of 217° C. rather than 212° C. The catalyst ageing rate and by-product levels were also found to be slightly higher that observed for the 1.0% crystalline catalysts, but still far superior to the amorphous base case Example.

EXAMPLE 3

(7) A mixture of zinc and chromium hydroxides made using the catalyst preparation method described above and containing 4% by weight zinc was further processed in nitrogen for 4 hours at 560° C. The processed catalyst contained 11.5% w/w crystalline chromium oxide. Using the methodology described above, this catalyst proved less active and less selective than the catalysts of Examples 1 and 2, but superior to the amorphous base case catalyst.

(8) The lowest reaction temperature required to deliver a 30% perchloroethylene conversion was 233° C., which was 21° C. above that required by the 1.0% crystalline catalyst and the by-product levels were approximately four times higher.

(9) TABLE-US-00001 TABLE 1 4% Zinc promoted Chromium oxide Catalyst Measurement of Catalyst Perchloroethylene Fluorination Activity (Temperature Required to Convert 30% of the Perchloroethylene Fed) Calcination % Cryst High Temperature HF Treatment Temperature Cr.sub.2O.sub.3 Temperature Deg. C. Catalyst Deg. C. Content 380 480 500 Basecase 1 300 0.0 348 313 337 Ex. 1 520 1.0 227 212 228 Ex. 2 540 2.6 220 217 235 Ex. 3 560 11.5 246 233 291

(10) TABLE-US-00002 TABLE 2 4% Zinc promoted Chromium oxide Catalyst Measurement of unwanted By-product Levels (% Loss of Selectivity to Byproducts at 30% Per Conversion) Calcination % Cryst High Temperature Treatment Temperature Cr.sub.2O.sub.3 Temperature Deg. C. Catalyst Deg. C. Content 380 480 500 Basecase 1 300 0.0 6.54 3.37 4.83 Ex. 1 520 1.0 0.26 0.13 0.23 Ex. 2 540 2.6 0.14 0.24 0.41 Ex. 3 560 11.5 1.01 0.55 1.12

EXAMPLE 4

(11) The methodology described above and used in Examples 1 to 3 was repeated using a mixture of zinc and chromium hydroxides made using the catalyst preparation method described above and containing 6% by weight zinc and thermally processed by heating in nitrogen for 4 hours at 520, 540, 560, 580 and 600° C.

(12) TABLE-US-00003 TABLE 3 6% Zinc promoted Chromium oxide Catalyst Measurement of Catalyst Perchloroethylene Fluorination Activity (Temperature Required to Convert 30% of the Perchloroethylene Fed) Calcination % Cryst High Temperature HF Treatment Temperature Cr.sub.2O.sub.3 Temperature Deg. C. Catalyst Deg. C. Content 380 480 500 Basecase 1 300 0.0 256 272 325 1 520 0.7 226 220 235 2 540 1.0 223 218 232 3 560 2.6 219 218 238 4 580 5.2 224 235 285 5 600 >10 234 299 —

(13) TABLE-US-00004 TABLE 4 6% Zinc promoted Chromium oxide Catalyst Measurement of unwanted By-product Levels (% Loss of Selectivity to Byproducts at 30% Per Conversion) Calcination % Cryst High Temperature Treatment Temperature Cr.sub.2O.sub.3 Temperature Deg. C. Catalyst Deg. C. Content 380 480 500 Basecase 1 300 0.0 0.578 0.645 2.191 1 520 0.7 0.254 0.236 0.378 2 540 1.0 0.231 0.216 0.283 3 560 2.6 0.267 0.236 0.343 4 580 5.2 0.284 0.333 1.015 5 600 >10 0.336 1.146 —

EXAMPLE 5

(14) The methodology described above and used in Examples 1 to 3 was repeated using a mixture of zinc and chromium hydroxides made using the catalyst preparation method described above and containing 8% by weight zinc and thermally processed by heating in nitrogen for 4 hours at 540, 560, 580, 600 and 620° C.

(15) TABLE-US-00005 TABLE 5 8% Zinc promoted Chromium oxide Catalyst Measurement of Catalyst Perchloroethylene Fluorination Activity (Temperature Required to Convert 30% of the Perchloroethylene Fed) Calcination % Cryst High Temperature HF Treatment Temperature Cr.sub.2O.sub.3 Temperature Deg. C. Catalyst Deg. C. Content 380 480 500 Basecase 1 300 0.0 325 — — 1 540 1.0 229 237 265 2 560 3.0 237 237 257 3 580 4.0 227 240 263 4 600 6.0 232 242 276 5 620 10 236 259 345

(16) TABLE-US-00006 TABLE 6 8% Zinc promoted Chromium oxide Catalyst Measurement of unwanted By-product Levels (% Loss of Selectivity to Byproducts at 30% Per Conversion) Calcination % Cryst High Temperature Treatment Temperature Cr.sub.2O.sub.3 Temperature Deg. C. Catalyst Deg. C. Content 380 480 500 Basecase 1 300 0.0 3.57 — — 1 540 1.0 1.151 0.447 0.829 2 560 3.0 0.528 0.381 0.628 3 580 4.0 0.298 0.422 0.650 4 600 6.0 0.353 0.472 0.819 5 620 10 0.393 0.570 3.466

EXAMPLE 6

(17) The methodology described above and used in Examples 1 to 3 was repeated using a mixture of zinc and chromium hydroxides made using the catalyst preparation method described above and containing 10% by weight zinc and thermally processed by heating in nitrogen for 4 hours at 600° C.

(18) TABLE-US-00007 TABLE 7 10% Zinc promoted Chromium oxide Catalyst Measurement of Catalyst Perchloroethylene Fluorination Activity (Temperature Required to Convert 30% of the Perchloroethylene Fed) Calcination % Cryst High Temperature HF Treatment Temperature Cr.sub.2O.sub.3 Temperature Deg. C. Catalyst Deg. C. Content 380 480 500 Basecase 1 300 0.0 352 — — 1 600 1.0 239 258 297

(19) TABLE-US-00008 TABLE 8 10% Zinc promoted Chromium oxide Catalyst Measurement of unwanted By-product Levels (% Loss of Selectivity to Byproducts at 30% Per Conversion) Calcination % Cryst High Temperature Treatment Temperature Cr.sub.2O.sub.3 Temperature Deg. C. Catalyst Deg. C. Content 380 480 500 Basecase 1 300 0.0 4.365 — — 1 600 1.0 0.567 0.580 0.969

(20) The procedure described above for testing the properties of the catalysts in the fluorination of perchloroethylene was repeated except that perchloroethylene was replaced by R123 and the target was 50% conversion of the R123 fed.

(21) TABLE-US-00009 TABLE 9 10% Zinc promoted Chromium oxide Catalyst Measurement of Catalyst R123 Fluorination Activity (Temperature Required to Convert 50% of the R123 Fed) Calcination % Cryst High Temperature HF Treatment Temperature Cr.sub.2O.sub.3 Temperature Deg. C. Catalyst Deg. C. Content 380 480 500 Basecase 1 300 0.0 329 — — 1 600 1.0 288 307 336

(22) In all of the above Tables “−” indicates that it was not possible to obtain the target.

EXAMPLE 7

(23) An amorphous catalyst comprising 6% Zn and a catalyst having a degree of crystallinity of 1% and containing 6% Zn (obtained as described in Example 4) were used in a process for the production of HFC-134a from trichloroethylene and hydrogen fluoride at a fixed residence time of about 1.3 seconds.

(24) TABLE-US-00010 % Cryst Cr.sub.2O.sub.3 Catalyst ageing temperature (° C.) Content 460 500 519 527 0 293.9 300.3 311.1 354.6 1 287.4 288.7 293.8 324.7

(25) The catalyst comprising 1% crystalline chromia was both more active and more stable than amorphous material as evidenced by lower temperatures required for 10% yield at all ageing conditions.

EXAMPLE 8

(26) The interaction between calcination temperature, time and atmosphere and their effect on the crystallization of a 6% Zn/chromia catalyst was studied and statistical modeling methods were used to illustrate how the calcinations conditions can be used to induce varying levels of crystallinity as required.

(27) A series of experiments were performed in which 8 g samples of a 6% Zn/chromia catalyst were subjected to calcination across a range of conditions and the level of crystallinity induced determined by X-Ray diffraction:

(28) TABLE-US-00011 Calcination Atmosphere % Cryst Calcination Time Temperature (T, nitrogen:air (D, Cr.sub.2O.sub.3 (t, hrs) ° C.) v/v) Content 4 400.0 15 1 4 400.0 15 1 2 450.0 20 9 6 350.0 20 0 2 450.0 10 18 2 350.0 10 0 6 450.0 20 20 6 350.0 10 0 6 450.0 10 30 4 400.0 15 1 2 350.0 20 0

(29) Statistical modeling methods were used to generate a polynomial function that could be used to predict the crystallinity level induced in the catalyst given t,T and D. It was found that crystallinity could be predicted using the following polynomial:
Xst (%)=−71.75−11.37*Time+0.2050*Temperature+0.975*Dilution+0.03250*Time*Temperature+0.087501*Time*Dilution-0.008500*Temperature*Dilution-0.0002500*Time*Temperature*Dilution

(30) The following list illustrates how this polynomial can be used to identify possible solutions of this equation in which the predicted level of chromia crystallinity induced would <4% i.e. in the optimum range:

(31) TABLE-US-00012 Dilution Temperature (air:nitrogen Number Time (hrs) (° C.) v/v) 1 4.000 436.5 13.86 2 4.000 446.9 19.98 3 4.000 440.4 10.45 4 4.000 356.1 17.72 5 4.000 391.8 16.42 6 4.000 382.1 14.32 7 4.000 444.9 12.35 8 4.000 380.1 10.22 9 4.000 444.6 19.20 10 4.000 426.6 10.67