SYSTEMS AND METHODS FOR SYNTHESIS OF ZSM-22 ZEOLITE

Abstract

Systems and methods for production of consistently-sized ZSM-22 zeolite catalyst crystals, a method including preparing an aluminate solution; preparing a silica solution; mixing the aluminate solution and the silica solution to form a zeolite-forming solution; heating the zeolite solution with microwave irradiation in a first, a second, a third, and a fourth distinct isothermal stage to produce the consistently-sized ZSM-22 zeolite catalyst crystals within a pre-selected crystal size range using a non-ionic surfactant.

Claims

1. A system for producing consistently-sized ZSM-22 zeolite catalyst crystals, the system comprising: an aluminate solution mixing chamber; a silica solution mixing chamber; and a microwave-application mixing unit, the microwave-application mixing unit in fluid communication with both the aluminate solution mixing chamber and the silica solution mixing chamber, wherein the microwave-application mixing unit mixes and heats a zeolite-forming solution from the aluminate solution mixing chamber and the silica solution mixing chamber with microwave irradiation in a first, a second, a third, and a fourth distinct isothermal stage to produce the consistently-sized ZSM-22 zeolite catalyst crystals within a pre-selected nano-scale crystal size range using a non-ionic surfactant.

2. The system according to claim 1, wherein the aluminate solution mixing chamber prepares an aluminate solution for the zeolite-forming solution and the silica solution mixing chamber prepares a silica solution for the zeolite-forming solution.

3. The system according to claim 1, where the system comprises controllable stirring means in the aluminate solution mixing chamber, the silica solution mixing chamber, and the microwave-application mixing unit.

4. The system according to claim 1, where a majority of the consistently-sized ZSM-22 zeolite catalyst crystals within the pre-selected nano-scale crystal size range exhibit lengths varying from about 50 nm to about 600 nm, and widths ranging from about 55 nm to about 75 nm.

5. The system according to claim 2, where the system is operable to control a ratio of silicon to aluminum to produce the consistently-sized ZSM-22 zeolite catalyst crystals within the pre-selected crystal size range.

6. The system according to claim 1, where in the first isothermal stage microwave irradiation is applied to heat the zeolite-forming solution to between about 35° C. and about 65° C. for between about 3 minutes and about 7 minutes, with stirring applied at a speed between about 200 rpm and about 300 rpm.

7. The system according to claim 6, where in the second isothermal stage microwave irradiation is applied to heat the zeolite-forming solution to between about 90° C. and about 120° C. for between about 5 and about 15 minutes, with stirring applied at a speed between about 200 rpm and about 300 rpm.

8. The system according to claim 7, where the non-ionic surfactant is added after the second isothermal stage.

9. The system according to claim 8, where in the third isothermal stage microwave irradiation is applied to heat the zeolite-forming solution to between about 35° C. and about 65° C. for between about 60 and about 80 hours, with stirring applied at a speed between about 350 rpm and about 450 rpm.

10. The system according to claim 9, where in the fourth isothermal stage microwave irradiation is applied to heat the zeolite-forming solution to between about 155° C. and about 205° C. for between about 8 and about 16 hours.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] These and other features, aspects, and advantages of the present disclosure will become better understood with regard to the following descriptions, claims, and accompanying drawings. It is to be noted, however, that the drawings illustrate only several embodiments of the disclosure and are therefore not to be considered limiting of the disclosure's scope as it can admit to other equally effective embodiments.

[0021] FIG. 1 is a schematic diagram for a system and process to produce consistently-sized ZSM-22 catalyst crystals without agglomeration or impurities using microwave heating and non-ionic surfactant.

[0022] FIG. 2 shows a scanning electron microscope (SEM) image for crystals of nano-sized ZSM-22 zeolite produced at a surfactant to aluminum oxide molar ratio of 2.5.

[0023] FIG. 3 shows a SEM image for crystals of nano-sized ZSM-22 zeolite produced at a surfactant to aluminum oxide molar ratio of 5.0.

[0024] FIG. 4 shows a SEM image for crystals of nano-sized ZSM-22 zeolite produced at a surfactant to aluminum oxide molar ratio of 7.5.

[0025] FIG. 5 shows X-ray diffraction (XRD) patterns confirming ZSM-22 structured zeolite was produced.

DETAILED DESCRIPTION

[0026] So that the manner in which the features and advantages of the embodiments of systems and methods that apply microwave heating to a zeolite solution comprising non-ionic surfactant for producing consistently-sized ZSM-22 zeolite catalyst crystals, as well as others, which will become apparent, may be understood in more detail, a more particular description of the embodiments of the present disclosure briefly summarized previously may be had by reference to the embodiments thereof, which are illustrated in the appended drawings, and which form a part of this specification. It is to be noted, however, that the drawings illustrate only various embodiments of the disclosure and are therefore not to be considered limiting of the present disclosure's scope, as it may include other effective embodiments as well.

[0027] Referring first to FIG. 1, a schematic diagram is shown for a system and process to produce consistently-sized nano-scale ZSM-22 catalyst crystals without agglomeration or impurities using microwave heating and non-ionic surfactant. FIG. 1 is described with respect to an example process for production of ZSM-22 zeolite crystals. Surfactant-microwave application system 100 includes an aluminate solution mixer unit 200 and a separate silicate solution mixer unit 300. System 100 also includes surfactant-microwave mixing unit 400, which is fluidly coupled to both aluminate solution mixer unit 200 and silicate solution mixer unit 300. Surfactant-microwave mixing unit 400 carries out controlled hydrothermal treatment for nucleation growth and crystallization of ZMS-22 nano-crystals.

[0028] In one example embodiment, a process operates as follows. In aluminate solution mixer unit 200, 88.4 kg of deionized water and 3.8 kg of potassium hydroxide (KOH) (purity: 99%) are introduced via line 210 and stirred at about between 270 rpm and about 330 rpm, preferably about 300 rpm, via stirring rod 220 at a temperature between about 15° C. and about 35° C. for between about 25 minutes and about 35 minutes, preferably about 30 minutes. Other suitable hydroxide-containing alkali and alkaline earth compounds can be used alternatively to or in addition to KOH, including, but not limited to, NaOH, CsOH, LiOH, or Ca(OH).sub.2.

[0029] Next, 1.8 kg of aluminum sulfate octadecahydrate (formula: Al.sub.2(SO.sub.4).sub.3.18H.sub.2O) is introduced via line 210 to aluminate solution mixer unit 200 and mixed with the solution for between about 25 minutes and about 35 minutes, preferably about 30 minutes, with stirring via stirring rod 220 at between about 270 rpm and about 330 rpm, preferably about 300 rpm, at a temperature between about 15° C. and about 35° C. Other aluminum-containing compounds can be used in addition to or alternative to aluminum sulfate octadecahydrate including, but not limited to, aluminum oxide (Al.sub.2O.sub.3), aluminum hydroxide (Al(OH).sub.3), and aluminum metal (Al).

[0030] Next, 8.2 kg of 1,6-diaminohexane (DAH) (purity: 99.5%) is added to aluminate solution mixer unit 200 as an organic template via line 210 and stirred by stirring rod 220 at between about 270 rpm and about 330 rpm, preferably about 300 rpm, for between about 25 minutes and about 35 minutes, preferably about 30 minutes. In some embodiments, heating is not applied in aluminate solution mixer unit 200, and temperature is in the range of about 15° C. to about 35° C. Finally, the solution in aluminate solution mixer unit 200 is evacuated via outlet 230 to be introduced to surfactant-microwave mixing unit 400 via inlet 405. Other suitable organic templates can be used in addition to or alternative to DAH, including, but not limited to, N-ethylpyridine, 1,4-diaminohexane, or diethylamine.

[0031] Separately in silicate solution mixer unit 300, 36 kg of silica colloidal solution (40 wt. % in water) and 62 kg of water are introduced to the compartment via line 310. Stirring is applied via stirring rod 320 for between about 25 minutes and about 35 minutes, preferably about 30 minutes at a speed of between 270 rpm and about 330 rpm, preferably about 300 rpm. In some embodiments, heating is not applied in silicate solution mixer unit 300, and temperature is in the range of about 18° C. to about 35° C. The solution is evacuated via outlet 330 and sent to surfactant-microwave mixing unit 400 via inlet 410.

[0032] Surfactant-microwave mixing unit 400 operates after the separate solutions of aluminate and silica are introduced to the unit via inlets 405 and 410. In one embodiment, four separate stages of isothermal heating are carried out with electrical heater 440 producing microwave irradiation 450 to synthesize the nano-sized ZSM-22. In a first isothermal stage, electrical heater 440 operates to heat the solution mixture in surfactant-microwave mixing unit 400 to between about 35° C. and about 65° C., or to between about 45° C. and about 55° C., for between about 3 minutes and about 7 minutes, preferably about 5 minutes. Mixing via stirring rod 420 is applied when microwave application begins via electrical heater 440 at a speed between about 200 rpm and about 300 rpm, preferably about 250 rpm.

[0033] In a second isothermal stage, a selected quantity of non-ionic surfactant is added via line 430. First, electrical heater 440 is set at a temperature of between about 90° C. and about 120° C., or between about 100° C. and about 110° C., and stirring is applied via stirring rod 420 at between about 200 rpm and about 300 rpm, preferably about 250 rpm, for between about 5 and about 15 minutes. Then, the selected weight of nonionic surfactant, for example a nonionic surfactant including poly-oxyethylene groups, is added to surfactant-microwave mixing unit 400 via line 430. In one embodiment, if polyoxyethylene(10)oleyl ether (molecular weight 709 g/mole) is used as surfactant, suitable surfactant to aluminium oxide molar ratios are from about 0.1:1 to 10:1, or from about 1:1 to about 7.5:1, or about 2.5:1, 5:1, or 7.5:1, for example.

[0034] Optional nonionic surfactants based on polyoxyethylene surfactants include, but are not limited to, any one of or any combination of: polyoxyethylene (2) stearly ether, polyoxyethylene (2) olleyl ether, polyoxyethylene (2) cetyl ether, sorbitan monopalmirate, sorbitan monolaurate, polyoxyethylene sorbitan monostearate, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monooleate, polyoxyethylene (4,5) p-tert-octylphenol, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbitan tristearate, polyoxyethylene (6) tridecyl ether, polyoxyethylene (10) stearyl ether, polyoxyethylene (10) oleyl ether, polyoxyethylene (7-8) p-tert-octylphenol, polyoxyethylene (10) cetyl ether, polyoxyethylene alkyl aryl ether, polyoxyethylene (9) p-tert-octylphenol, polyoxyethylene sorbitan monolaurate, polyoxyethylene (9-10) nonyl ohenol, polyoxyethylene (9-10) p-tert-octyl phenol, polyoxyethylene esters of mixed fatty acids, polyoxyethylene (12) tridecyl ether, polyoxyethylene (12-13) p-tert-octylphenol, polyoxyethylene sorbitan monostearate, polyoxyethylene (17) cetyl-stearyl alcohl, polyoxyethylene (20) stearyl ether, polyoxyethylene (20) oleyl ether, polyoxyethylene (15) tridecyl ether, polyoxyethylene sorbitan monopalmitate, polyoxyethylene (20) cetyl ether, polyoxyethylene (16) p-tert-octylphenol, polyoxyethylene sorbitan monolaurate, and polyoxyethylenelauryl ether.

[0035] The use of nonionic surfactants has several advantages versus long chain alcohols as there are no electronic charge groups or limited charge in the nonionic molecules. The utilization of surfactant helps control the sizes of nano-scale crystals of ZSM-22 without negatively affecting the zeolite framework and crystallinity. Systems and processes adapt the use of one or more nonionic surfactant to ZSM-22 zeolite crystal production under controlled microwave irradiation in order to meet the crystallinity of the ZSM-22 framework and synthesize different size scales of nano-sized of ZSM-22.

[0036] The weight of nonionic surfactant is adjusted, in part, according to the weight of aluminum oxide applied in the process. The molar ratio of the nonionic surfactant to aluminum oxide can vary from about 0.05:1 to 30:1.

[0037] For nano-scale ZSM-22 crystal size of length of about 80-95 nm by a width of about 55-65 nm, the surfactant to aluminum oxide molar ratio is between about 2.4 and about 2.6, preferably about 2.5 (See FIG. 2). For ZSM-22 crystal size of length of about 125-140 nm by a width of about 55-65 nm, the surfactant to aluminum oxide molar ratio is between about 4.9 and about 5.1, preferably about 5 (See FIG. 3). For nano-scale ZSM-22 crystal size of length of about 280-300 nm by a width of about 65-75 nm, the surfactant to aluminum oxide molar ratio is between about 7.4 and about 7.6, preferably about 7.5 (See FIG. 4).

[0038] In a third isothermal stage, zeolite aging is applied and electrical heater 440 is set such that the temperature of surfactant-microwave mixing unit 400 is between about 35° C. and about 65° C., or is between about 45° C. and about 55° C., and stirring is applied via stirring rod 420 at a speed of between about 350 rpm and about 450 rpm, preferably 400 rpm, for about 60 to about 80 hours, preferably about 72 hours.

[0039] In a fourth isothermal stage, zeolite crystallization is carried out, and microwave irradiation is applied to surfactant-microwave mixing unit 400 for heating, and the temperature increases to between about 155° C. and about 205° C., or between about 165° C. and about 195° C., or between about 170° C. and about 190° C., and stirring is applied via stirring rod 420 at a speed of between about 350 rpm and about 450 rpm, preferably 400 rpm, for between about 8 and about 16 hours, or between about 10 hours and about 14 hours.

[0040] At the end of crystallization of nano-sized ZSM-22, the fourth isothermal stage, surfactant-microwave mixing unit 400 is cooled down to between about 18° C. and about 40° C. Zeolite solution is evacuated via line 460 for further treatment in a separate container (not pictured). In the separate container, the acidity of the solution is adjusted to between about pH 6.5 and about pH 7.5, preferably about pH 7 (neutralized), by addition of HCl in water solution (concentration of about 0.1 mol/L), with the volume to be added from about 5 mL to about 200 mL, depending on the scale of the system and process.

[0041] After pH neutralization, a centrifuge is applied to collect the powder comprising nano-sized ZSM-22 zeolite crystals. The centrifuge is run at a speed between about 2000 rpm and about 4000 rpm and a temperature between about 18° C. and about 40° C. Next, distilled water washing is carried out 2-3 times to wash the zeolite powder, and the washed zeolite powder is retrieved via filtration. Drying is applied to nano-sized ZSM-22 zeolite powder at a temperature of between about 90° C. and about 100° C. for between about 12 and about 24 hours. Calcination of dried nano-sized ZSM-22 zeolite is carried out under static atmospheric air and at a temperature of between about 500° C. and about 550° C., preferably 525° C. for between about 6 and about 12 hours. The oven ramping rate can be set at between about 1 and about 3° C./min.

[0042] In some embodiments, the resulting zeolite has a framework crystal of nano-size ZSM-22 zeolite, and this is shown in FIG. 5. FIG. 5 shows X-ray diffraction (XRD) patterns of ZSM-22 zeolite. ZSM-22 is characterized via the 2-theta angle peaks at 20.4°, 24.4°, 24.6°, and 25.8°.

[0043] Thus, the surfactant-microwave system and process of FIG. 1 synthesizes nano-sized ZSM-22 zeolite with pre-selected recipes and process steps, which control sizes of nano-scale crystals produced in order to use ZSM-22 as catalyst. The ZSM-22 zeolite crystals produced can be used as material for catalyst support, and can be used for gas adsorption and catalyst applications in chemical and hydrocarbon conversion reactions, including those involving steam cracking.

[0044] FIG. 2 shows a scanning electron microscope (SEM) image for crystals of nano-sized ZSM-22 zeolite produced at a surfactant to aluminum oxide molar ratio of 2.5. The ratio of surfactant to aluminum oxide can vary for example between about 2.4 and about 2.6. In FIG. 2, the length of the zeolite crystals is between about 80 nm and about 95 nm, and the width is between about 55 nm and about 65 nm. In various embodiments a wide molar ratio range of Si:Al can be used, varying between about 10 and about 200.

[0045] FIG. 3 shows a SEM image for crystals of nano-sized ZSM-22 zeolite produced at a surfactant to aluminum oxide molar ratio of 5.0. The ratio of surfactant to aluminum oxide can vary for example between about 4.9 and about 5.1. In FIG. 3, the length of the zeolite crystals is between about 125 nm and about 140 nm, and the width is between about 55 nm and about 65 nm.

[0046] FIG. 4 shows a SEM image for crystals of nano-sized ZSM-22 zeolite produced at a surfactant to alumina oxide molar ratio of 7.5. The ratio of surfactant to aluminum oxide can vary for example between about 7.4 and about 7.6. In FIG. 4, the length of the zeolite crystals is between about 280 nm and about 320 nm, and the width is between about 65 nm and about 75 nm.

[0047] The term “about” when used with respect to a value or range refers to values including plus and minus 5% of the given value or range.

[0048] The singular forms “a,” “an,” and “the” include plural referents, unless the context clearly dictates otherwise.

[0049] In the drawings and specification, there have been disclosed embodiments of systems and methods which apply microwave heating to a zeolite solution comprising non-ionic surfactant for producing consistently-sized ZSM-22 zeolite catalyst crystals, and although specific terms are employed, the terms are used in a descriptive sense only and not for purposes of limitation. The embodiments of the present disclosure have been described in considerable detail with specific reference to these illustrated embodiments. It will be apparent, however, that various modifications and changes can be made within the spirit and scope of the disclosure as described in the foregoing specification, and such modifications and changes are to be considered equivalents and part of this disclosure.