Purification process

Abstract

A process for removing halogen compounds, particularly chlorine compounds, from a process fluid, includes the steps of (i) passing a process fluid containing hydrogen halide over a first sorbent to remove hydrogen halide and generate a hydrogen halide depleted process fluid and then, (ii) passing the hydrogen halide depleted process fluid over a second different sorbent to remove organic halide compounds therefrom. A purification system suitable for removing hydrogen halide and organic halide compounds from process fluids is also described.

Claims

1. A purification system for removing halogen compounds from process fluids, comprising: a feed source of a process fluid containing hydrogen halide, a first sorbent comprising an alkalized alumina or an alkalized zinc-alumina, wherein the first sorbent is in the form of pellets, granules, or extrudates; and a second sorbent comprising a mixed transition alumina and that is in the form of granulated or extruded shaped units comprising 1 wt %-10 wt % binder; wherein: the first sorbent is positioned between the feed source and the second sorbent, and the purification system is controlled to direct the flow of the feed gas through the purification system from the feed source to the first sorbent and then to the second sorbent, such that the second sorbent is positioned downstream from the first sorbent, relative to the directed flow of the process fluid.

2. The purification system according to claim 1, further comprising a third sorbent downstream of the second sorbent, wherein the third sorbent removes hydrogen halide from the process fluid.

3. The purification system according to claim 2, wherein the third sorbent is the same as the first sorbent.

4. The purification system according to claim 1, wherein the sorbents are placed in the same vessel.

5. The purification system according to claim 1, wherein the first sorbent is formed from a calcined intimate mixture of: a) an alumina component that is alumina and/or hydrated alumina, b) an optional zinc component that is a zinc oxide, zinc hydroxide, zinc carbonate, zinc bicarbonate and/or basic zinc carbonate, c) a basic metal component that is at least one compound of at least one alkali or alkaline earth metal, and d) 5 to 20% by weight of a binder.

6. The purification system according to claim 5, wherein the first sorbent comprises a zinc component with a basic metal to zinc atomic ratio in the range of from 0.5x to 2.5x and a basic metal to aluminum atomic ratio in the range of from 0.5x to 1.5x where x is the valency of the basic metal.

7. The purification system according to claim 5, wherein the first sorbent has a basic metal oxide content of at least 10%, by weight after ignition of a sample at 900 C.

8. The purification system according to claim 5, wherein the basic metal component is a compound of lithium, sodium, potassium, beryllium, magnesium, calcium, strontium, or barium.

9. The purification system according to claim 5, wherein the basic metal component is a compound of sodium or calcium.

10. The purification system according to claim 5, wherein the zinc component is zinc oxide, zinc carbonate, or basic zinc carbonate.

11. The purification system according to claim 5, wherein the binder comprises a hydraulic cement, or a clay.

12. The purification system according to claim 1, wherein the first sorbent comprises a calcined mixture of (i) hydrated alumina, (ii) sodium bicarbonate, (iii) zinc oxide or basic zinc carbonate, and (iv) a clay binder in which the alkali metal to zinc atomic ratio is above 0.8.

13. The purification system according to claim 12, wherein the alkali metal to zinc atomic ratio is in the range from about 0.8 to 2.2.

14. The purification system according to claim 1, wherein the first sorbent has a BET surface area of at least 10 m.sup.2/g.

15. The purification system according to claim 4, wherein the first sorbent has a BET surface area above 50 m.sup.2/g.

16. The purification system according to claim 1, wherein the first sorbent has a BET surface area above 90 m.sup.2/g.

17. The purification system according to claim 1, wherein the transition alumina is a gamma alumina, delta-alumina, theta-alumina, eta-alumina or chialumina, or a mixture thereof.

18. The purification system according to claim 1, wherein the transition alumina is formed by calcination of aluminum hydroxides and has a BET surface area in the range 50 to 400 m.sup.2/g.

19. The purification system according to claim 1, wherein the fast sorbent comprises acidic sites and forms one or more organic halide compound.

20. The purification system according to claim 1, wherein the first sorbent comprises an alkalized zinc-alumina.

21. A process for removing halogen compounds from a process fluid in a system of claim 1, comprising the steps of (i) passing the process fluid containing the hydrogen halide over the first sorbent to remove hydrogen halide and generate a hydrogen halide depleted process fluid, and (ii) passing the hydrogen halide depleted process fluid over the second sorbent to remove the organic halide compounds therefrom.

22. The process according to claim 21, wherein the process fluid is a hydrogen gas stream comprising 50% vol hydrogen.

23. The process according to claim 21, wherein the process fluid is a gas stream comprising a hydrocarbon.

24. The process according to claim 21, wherein the process fluid is a liquid hydrocarbon stream.

25. The process according to claim 21, wherein the halogen compounds are bromine compounds or chlorine compounds.

26. The process according to claim 21, wherein the hydrogen halide content of the process fluid fed to the first sorbent is in the range 0.1-20 ppm.

27. The process according to claim 23, wherein the first sorbent comprises acidic sites that form one or more organic halide compounds.

28. The process according to claim 21, wherein the process fluid from which organic halide compounds has been removed is passed over a third sorbent to remove residual or formed hydrogen halide.

29. The process according to claim 28, wherein the third sorbent is the same as the first sorbent.

30. The process according to claim 21, operated at a temperature in the range 0-300 C.

31. The process according to claim 21, operated at a pressure in the range 1 to 100 bar abs.

Description

(1) The invention will now be further described by reference to the following examples.

EXAMPLE 1: PREPARATION OF SORBENTS

(2) a) Sorbents Used as Received.

(3) Sorbent (1) is PURASPEC2250, a hydrogen chloride sorbent material comprising alkalised zinc and alumina as described in WO 99/39819 A1. It is commercially available from Johnson Matthey Catalysts.

(4) Sorbent (2) is a mixed transitional phase alumina in the form of spheres (2.00-4.75 mm).

(5) Sorbent (3) is an activated carbon product, RX3 extra (26 mm extrudates), supplied by Norit.

(6) Sorbent (4) is a zeolite Y product, CBV500 (1.6 mm extrudates), supplied by Zeolyst.

(7) Sorbent (5) is a zeolite molecular sieve product, 13X (1.6 mm extrudates), supplied by BDH.

(8) B) Sorbents Prepared by Treatment.

(9) Sorbent (6). Sorbent (2) was charged to a basket and soaked in caustic soda solution (60 g NaOH/100 ml water) for a period of 45 minutes. The basket was drained, and the saturated material calcined under air for two hours at 350 C. The resultant material comprised ca.10 wt. % Na.sub.2O on alumina.

(10) Sorbent (7). 123.8 g Sorbent (2) was charged to a basket and soaked in an aqueous potassium hydroxide solution (2.1 g KOH/199.4 g water) for a period of 45 minutes. The basket was drained, and the saturated material calcined under air for two hours at 350 C.

(11) Sorbent (8) was prepared by impregnation of sorbent (2) with an aqueous iron nitrate solution. 60 ml of sorbent (2) was dried at 110 C. for 1 hr. This material was impregnated with a solution of 5.4 g of iron (Ill) nitrate nonahydrate dissolved in 20 ml of deionised water. The sample was then dried at 150 C. for 1 hr.

EXAMPLE 2: ORGANOCHLORIDE FORMATION OVER SORBENTS

(12) A series of tests was conducted to assess the level of organochloride produced as a by-product of hydrogen chloride removal in the presence of unsaturated hydrocarbons. Experiments were conducted using a stainless steel gas phase reactor and a sorbent volume of 500 cm.sup.3. A bed of 150 cm.sup.3 of alpha alumina chips was positioned below and above the bed of sorbent material for each test run. The identity of the sorbent was varied in different test runs (as given in Table 1) to assess the relative level of organochloride that was produced for each material. The reactor was operated at a pressure of 20 barg, temperature of 35 C. and gas contact time with the catalyst of 47.9 seconds. The feed gas consisted of hydrogen, with the addition of 50 ppm hydrogen chloride and 200 ppm isobutene. Hydrogen chloride concentration at the inlet and exit of the reactor was measured using hydrogen chloride gas detection tubes. Concentrations of organochloride (tertiary butyl chloride) at the reactor exit were determined by gas chromatography. The concentration of tertiary butyl chloride in the exit stream at the end of the test run for each of the sorbents is shown in Table 1.

(13) TABLE-US-00001 TABLE 1 Tertiary butyl chloride in exit Hydrogen chloride Time online stream at end in exit stream at Sorbent (days) of run (ppm) end of run (ppm) (1). alkalised zinc- 56 7 <2 alumina (6). Na.sub.2O/alumina 57 49 <2

(14) These results show that, while effective for hydrogen chloride removal, the alkalised alumina-containing sorbent released significant amounts of the organic chloride compound as a by-product of hydrogen chloride removal. The alkalised zinc-alumina sorbent produced significantly less organochloride.

EXAMPLE 3: ORGANOCHLORIDE REMOVAL FROM A GAS STREAM

(15) A series of tests was conducted to see the effectiveness of different sorbents for the removal of organochloride from a gas stream. In this case tertiary butyl chloride was used as the organochloride.

(16) Work was conducted in a glass reactor using a sorbent volume of 60 cm.sup.3. The feed gas for the reactor was 100 ppm tertiary butyl chloride in a hydrogen carrier. The feed gas was passed over the sorbent at a flow rate of 45 l hr.sup.1 at ambient temperature (about 20 C.) and atmospheric pressure. Samples were taken by syringe from the inlet and exit of the reactor, and levels of tertiary butyl chloride measured by gas chromatography. Each individual test was terminated when the exit tertiary butyl chloride level exceeded 5 ppm by volume. The time taken to achieve this breakthrough of 5 ppm tertiary butyl chloride is given for each sorbent in Table 2.

(17) TABLE-US-00002 TABLE 2 Time for 5 ppm tertiary butyl chloride to breakthrough sorbent bed Sorbent (minutes) (2) alumina 24485 (3) carbon 11530 (4) zeolite Y 32055 (5) zeolite 13X 58105

(18) In comparison, Sorbent (1) had a breakthrough time of 8695 minutes. Thus alumina sorbent (2) and Zeolite sorbents (4) and (5) are particularly effective as organochloride sorbents under these conditions.

EXAMPLE 4: ORGANOCHLORIDE REMOVAL FROM A LIQUID STREAM

(19) A series of tests was performed to demonstrate the effectiveness of the sorbents in removing chlorine compounds at very high levels from liquid. A glass reactor was charged with a 60 cm.sup.3 bed of the sorbent. The feed (500 ppmv tertiary butyl chloride in n-heptane) was passed at ambient temperature (about 20 C.) through the reactor at 4.8 cm.sup.3/min in an upflow configuration. The test was terminated when the exit concentration of tertiary butyl chloride had reached 5 ppmv, as measured by gas chromatography. The results are given in Table 3.

(20) TABLE-US-00003 TABLE 3 Sorbent Breakthrough time (mins) (5) zeolite 13X 2285 (8) iron oxide/alumina 890

(21) The results demonstrate that the treated alumina or zeolite sorbents are effective in the liquid phase.

EXAMPLE 5: REMOVAL OF HYDROGEN CHLORIDE AND BY-PRODUCT ORGANOCHLORIDE USING A COMBINATION OF MATERIALS IN DIFFERENT BEDS

(22) A series of tests was conducted to combine the effects demonstrated in Example 2 and Example 3, whereby a range of different sorbents were placed downstream of a hydrogen chloride sorbent to demonstrate the effectiveness of the second sorbent bed for the removal of by-product organochloride. The experiments were carried out using the same reactor system as described in Example 3. A hydrogen feed gas containing 1% v hydrogen chloride and 1% v propene was used. The vessel was loaded with 60 cm.sup.3 each of the first and second sorbents. The first sorbent in each case was the alkalised zinc-alumina, sorbent (1), for hydrogen chloride removal. The second sorbents are set out below in Table 4. The feed gas was fed to the vessel such that it passed through the first sorbent bed and then the second sorbent bed. The feed gas was passed over the sorbents at a rate of 45 lhr.sup.1. The reactor was operated at ambient temperature (about 20 C.) and atmospheric pressure. Gas samples were taken by syringe from the midpoint of the reactor between the first and second sorbents and the exit of the bottom bed and analysed for organochloride (by gas chromatography) and hydrogen chloride (using gas detection tubes). Breakthrough times for hydrogen chloride and organochloride were recorded. The experiment was terminated when hydrogen chloride exiting the first bed exceeded 10 ppmv, or the organochloride exciting the second bed exceeded 0.5 ppmv, whichever occurred first. The results are given in Table 4.

(23) TABLE-US-00004 TABLE 4 Time for Time for hydrogen organochloride chloride at exit of first chloride exiting sorbent (sorbent A) second sorbent to Second Sorbent to exceed 10 ppmv exceed 0.5 ppmv (2) alumina 165 mins (3) carbon 990 mins (7) K.sub.2O/alumina 300 mins (5) zeolite 13X 1055 mins

(24) In comparison, using sorbent (1) as the second sorbent as well gave an organochloride breakthrough time of 60 mins. The choice of material in the second bed influences the ability of the purification system to prevent the passage of by-product organochloride.