Zeolite agglomerates with a halloysite clay binder

Abstract

A molecular sieve blend containing a zeolite, particularly a zeolite X or A, blended with a halloysite clay binder, wherein the binder contains at least 90% by weight halloysite clay, with a particle length less than about 1 m and processes for the production and use of this blend, particularly for adsorption of water from a feedstream and for the production of oxygen.

Claims

1. A molecular sieve blend used for adsorption comprising a zeolite; and a halloysite clay binder; wherein the halloysite clay binder present in the molecular sieve blend comprises from about 0.5% to about 20% of the blend, by weight, and wherein the average particle length of particles of the halloysite clay binder is less than 1 m.

2. The molecular sieve blend of claim 1 wherein the zeolite comprises zeolite A or zeolite X.

3. The molecular sieve blend of claim 1, wherein it has a median pore diameter of at least 0.25 m and less than about 1.5 m.

4. The molecular sieve blend of claim 1, wherein the aspect ratio of the halloysite particles is less than 9.

5. The molecular sieve blend of claim 1 wherein the halloysite clay binder comprises at least about 90% halloysite clay.

6. The molecular sieve blend of claim 1 wherein the halloysite clay binder comprises at least about 95% halloysite clay.

7. The molecular sieve blend of claim 1 wherein the halloysite clay binder comprises from about 0.5 to about 10%, by weight, of the molecular sieve blend.

8. A molecular sieve blend used for production of oxygen for medical, industrial or commercial purposes comprising a zeolite; and a halloysite clay binder; wherein the halloysite clay binder present in the molecular sieve blend comprises from about 0.5% to about 20% of the blend by weight, and wherein the average particle length of particles of the halloysite clay binder is less than 1 m.

9. The molecular sieve blend of claim 8 wherein the zeolite comprises zeolite A or zeolite X.

10. The molecular sieve blend of claim 8, wherein it has a median pore diameter of at least 0.25 m and less than about 1.5 m.

11. The molecular sieve blend of claim 8, wherein the aspect ratio of the halloysite particles is less than 9.

12. The molecular sieve blend of claim 8 wherein the halloysite clay binder blend comprises at least about 90% halloysite clay.

13. The molecular sieve blend of claim 8 wherein the halloysite clay binder comprises at least 95% halloysite clay.

14. The molecular sieve blend of claim 8 wherein the halloysite clay binder comprises from about 0.5 to about 10%, by weight, of the molecular sieve blend.

15. A molecular sieve blend used for dehydration of a gaseous or liquid hydrocarbon feed stream comprising a zeolite A; and a halloysite clay binder; wherein the amount of halloysite clay binder blend present in the molecular sieve blend comprises from about 0.5% to about 20%, by weight; wherein the halloysite clay binder comprises at least about 90% halloysite clay; and wherein the average particle length of particles of halloysite clay binder is less than 1 m.

16. The molecular sieve blend of claim 15, wherein it has a median pore diameter of at least 0.25 m and less than about 1.5 m.

17. The molecular sieve blend of claim 15, wherein the aspect ratio of the halloysite particles is less than 9.

18. The molecular sieve blend of claim 15 wherein the halloysite clay binder comprises from about 0.5 to about 10%, by weight, of the molecular sieve blend.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 compares physical characteristics of various molecular sieve blend examples. Inventive Examples contain as a binder, halloysite clay, and either zeolite 3A (Inventive Example 2) or zeolite 4A (Inventive Example 4). Comparative Examples contain a conventional attapulgite binder and zeolite 3A or 4A. (Comparative Examples 1 and 3).

(2) FIG. 2 compares the mercury porosity and pore distribution between Comparative Example 1 and Inventive Example 2.

(3) FIG. 3 compares the dynamic water adsorption performance of Comparative Examples 1 and 3 with Inventive Examples 2 and 4.

(4) FIG. 4 compares the water adsorption performance of Comparative Example 3 with Inventive Example 4 over various adsorption times.

(5) FIG. 5 compares water performance adsorption curves for Comparative Example 1 with Inventive Example 2 over various adsorption times.

DETAILED DESCRIPTION OF ONE EMBODIMENT

(6) One embodiment includes molecular sieve blends formed from a zeolite blended with a halloysite clay binder, uses of those blends, and processes for the production of these blends.

(7) These embodiments are based on the surprising discovery that the adsorption rate and selectivity of molecular sieve blends are dependent not only upon the choice of the zeolite, but also the type and characteristics of the binder blended with the zeolite to form the molecular sieve blends.

(8) It has been surprisingly discovered that the same type of zeolite, when blended with different types of binders, produces molecular sieve blends which exhibit surprisingly improved performance characteristics. (For purposes of this disclosure, the phrases adsorption rate or absorption rate or sorption rate or mass transfer rate mean the rate at which the adsorbate loading in a feed stream changes over a given period of time for a given adsorption process.)

(9) It has been surprisingly discovered that the type of binder that is used in the molecular sieve blends may enhance particular characteristics of the molecular sieve blends, such as adsorption rate, tapped bulk density, LUB, and breakthrough of the zeolite blend.

(10) The zeolites, as used for preparing the molecular sieve blends according to the embodiments, can be in many form. Preferably, the zeolites are in the form of crystals, crystal aggregates, or mixtures thereof. It is also possible to use a mixture of different types of zeolites for preparing the molecular sieve blends. Within the context of the present invention, the term molecular sieve blend refers to a blend of zeolites, binders and additional materials that can be formed into a shaped material suitable for the desired absorption processes.

(11) The molecular sieve blends are preferably formed by preparing a mixture comprising one or more types of zeolite, and one or more types of binder material.

(12) In one preferred embodiment, the molecular sieve blends are prepared by using a mixture comprising one or more types of zeolites, and one or more types of halloysite clay binders.

(13) Different types of zeolites that can be used include, for example, zeolite A, zeolite X, zeolite Y, zeolite ZSM-5, zeolite Beta, synthetic mordenite and blends thereof, with zeolite A and zeolite X preferred. The ion-exchange of these zeolites can vary, but generally utilizes alkali and/or alkaline earth metals. The zeolites, as used for preparing the molecular sieve blends, have a crystal size, preferably in a range from 0.1 to 30 m.

(14) Particularly effective zeolites that are useful for oxygen production for medical, commercial or industrial uses, removal of water from an ethanol:water mixture, and for the drying of cracked hydrocarbons are zeolite 3A or 4A. Zeolite 3A is particularly effective for the adsorption of water because of the size of the pore openings in this zeolite. It permits the passage of water molecules but restricts the passage of larger hydrocarbon molecules, such as ethanol. While zeolite 3A is an especially useful zeolite for this process and related processes, other zeolites may also be used for other processes, such as the use of zeolite 5A for iso/normal paraffin separation.

(15) In one embodiment, the zeolite chosen is a low silica zeolite with a ratio of SiO.sub.2:Al.sub.2O.sub.3 less than 50, alternatively less than 20, alternatively less than 10, alternatively less than 5, and as low as 1. It is thus useful to reduce the SiO.sub.2:Al.sub.2O.sub.3 ratio of these zeolites. Processes for the production of low silica zeolites are well known. Low silica zeolites are more effective as adsorbents of water from hydrocarbon/water mixtures than are high silica zeolites, which are commonly used, for example, for catalytic reactions. (Zeolite blends useful for catalytic reactions are not embodiments that are included in the disclosures herein. Further, the molecular sieve blends of this disclosure are not conventionally utilized for these catalytic reactions.)

(16) Binder materials are necessary for use with these zeolites to bind the individual zeolite crystals together to form shaped products to reduce the pressure drop during the adsorption process. However, in the past, the binder materials have not enhanced the adsorption capability and selectivity of the zeolite. Binder materials which have been utilized with zeolites in the past generally include conventional clay types, such as kaolin, palygorskite-type minerals, particularly attapulgite, and smectite-type clay minerals, such as montmorillonite or bentonite. These clay binders have been used singly or in mixtures of two or more different types of clay binders.

(17) These clay binders, particularly attapulgites, often have a high metal content. Such metals can cause carbon polymerization to occur at the acid sites on the clay binders during utilization in some of the processes disclosed herein. This often results in the production of coke and green oil, resulting in a shortened life span for the molecular sieve blend. Such prior art zeolite/clay binder agglomerate materials, when used for adsorption or separation processes often exhibit a high incidence of coking in the presence of unsaturated hydrocarbons. One advantage of the molecular sieve blend disclosed herein is a reduction in the polymerization of hydrocarbons and a reduction in the production of coke and green oil and thus, an increase in the life expectancy of the molecular sieve blends.

(18) It has been surprisingly discovered that improved performance from the molecular sieve blends can be achieved when the binder material that is used comprises a halloysite clay. In one embodiment, the molecular sieve blend comprises a low silica zeolite with a ratio of SiO.sub.2:Al.sub.2O.sub.3, as defined herein, and a binder comprising halloysite clay.

(19) It has been surprisingly discovered that molecular sieve blends produced using halloysite clay as a binder produce better performing adsorbents than traditional adsorbents, wherein the zeolite is bound using a conventional clay binder, such as an attapulgite.

(20) It has also been surprisingly discovered that molecular sieve blends using halloysite clay as binders have better performance as shown by various adsorption characteristics, such as tapped bulk density, breakthrough time, length of unused bed (LUB), and pore distribution coefficient. Comparisons of the performance of molecular sieve blends utilizing a halloysite clay binder with molecular sieve blends utilizing conventional attapulgite binders are shown in various Figures within this specification.

(21) Halloysite clay is a member of the kaolin clay group. While the chemical formula for all members of the kaolin clay group is similar, the structure of halloysite clay, in the form of hollow tubes, nanotubes or split tubes in the form of ribbons or laths, differentiate it from other members of the kaolin clay group. The halloysite clay may be in hydrated form, which normally exhibits a shape of a hollow tube or nanotube or a non-hydrated halloysite clay which may be in the form of a broken or split tube, laths or ribbons. It has been surprisingly discovered that all forms of halloysite clay show improved performance as a binder with zeolite clays and improve various adsorption characteristics of the blend over conventional molecular sieve blends. While hydrated forms of the halloysite clay group are preferred for use as the binder, all forms of the halloysite clay included within the definition of halloysite herein are useful as a binder.

(22) The performance of molecular sieve blends produced using halloysite clay as a binder and a zeolite was surprising because halloysite clay is high in bulk density. Given its porosity profile, especially its lower total porosity with a higher amount of relatively small pores, it was anticipated that a molecular sieve blend containing halloysite clay as a binder would have an earlier water breakthrough time, as well as much lower LUB. In fact, it was surprisingly discovered that the LUB was substantially reduced by as much as about 70%, which, in conjunction with the higher volumetric loading potential of the material, led to an increased breakthrough time of at least 20% and often as much as 30 to 50%. These values are especially important for specific applications of the molecular sieve blends disclosed herein. See, for example, FIGS. 1 and 3.

(23) It has also been discovered that in applications of the disclosed composition where smaller quantities of the halloysite clay are used, i.e. from about 0.5 to about 10%, it is useful that the halloysite clay be dispersed using dispersion processes disclosed, for example, by U.S. Pat. Nos. 6,918,948 and 6,130,179. When such dispersion occurs, the median particle size of the dispersed halloysite clay particles has a range from about 0.5 to about 1.5 microns, d.sup.50, with a ratio of d.sup.90/d.sup.10 approaching 1.

(24) It has also been surprisingly discovered that when higher quantities of the halloysite clay are used as the binder, i.e. in ranges above about 10 to 20% or greater, it may not be necessary to disperse the halloysite clay to the same extent as when lower percentages are used.

(25) It has also been surprisingly discovered that particle size and shape of the halloysite clay particles have an impact on the performance of the halloysite binder utilized in the disclosed molecular sieve blends. The length of halloysite binder particles is generally from about 0.5 m to 2.0 m with a diameter of 50 nm to 100 nm or so. It has been surprisingly discovered that improved performance for molecular sieve blends utilizing halloysite clay as the binder occurs when the average particle length is less than 1 micron, alternatively less than 0.9 micron and further alternatively less than 0.8 micron. Further, molecular sieve blends utilizing a halloysite binder wherein the halloysite particles have an aspect ratio (ratio of length to diameter) less than 10, alternatively less than 9, have shown improved performance over molecular sieve blends using the same quantity of halloysite binder wherein the aspect ratio is greater than 10 and/or the average particle length is greater than 1 m.

(26) Regardless of the extent of dispersion or particle size and aspect ratio, an important requirement of the content of the binder is that it contains predominately halloysite clay in quantities greater than 90%, alternatively greater than 95%, and also alternatively greater than 98% halloysite clay. Halloysite clay when mined often is present in blends, particularly with kaolinite clay. However, it has been surprisingly discovered that the quantity of kaolinite, or other non-halloysite clay, with the halloysite, should be reduced to less than 10%, alternatively less than 5%, alternatively less than 2%, as larger quantities of kaolinite (or other clay materials), when blended with the halloysite clay, may bind the particles of halloysite clay together producing a less efficient molecular sieve blend.

(27) Once the appropriate zeolite material is chosen for a given application, such as a low silica zeolite A or zeolite X, alternatively a zeolite 3A or 4A, it is mixed with a halloysite clay binder in the presence of water. The zeolite powder and the halloysite clay binder are then blended together using conventional mixing procedures.

(28) Certain pore forming agents, such as saw dust fibers, such as rayon, sisal, nylon, flax and the like and organic polymer, such as corn starch, cellulose derivatives and the like may also be added to the blend, but are not required elements of the disclosed molecular sieve blends. If used, the amount added is generally form about 2 to 15 percent, by weight.

(29) Once the formed products are produced in the appropriate shape, they are hydrothermally treated (or calcined) at conventional temperatures to reduce the pore openings to a size that excludes the desired material, such as ethanol, but retains the capacity to adsorb water from a feed stream.

(30) The molecular sieve blends exhibit a preferred pore structure. An analysis of this pore structure can be determined using mercury porismetry. Using data from analysis by mercury porismetry, the total particle porosity, medium pore diameter, volume of pores between 0.1 and 1.0 m, and pore distribution coefficient can be determined. Examples of the improvements disclosed herein are shown by the following examples:

EXAMPLES

(31) Samples of molecular sieve adsorbent, agglomerate blends were prepared and compared for performance. The inventive examples (Inventive Examples 2 and 4) contained 20% of a halloysite clay blended with approximately 80% of a conventional 3A zeolite (Inventive Example 2) or a 4A zeolite (Inventive Example 4). The comparative examples (Comparative Examples 1 and 3) contained 20% of an attapulgite clay blended with approximately 80% of a conventional 3A zeolite (Comparative Example 1) or a 4A zeolite (Comparative Example 3). The attapulgite clay was obtained from ITC Floridin. The halloysite and zeolites were obtained from conventional sources. The halloysite was essentially pure halloysite. Four samples of about 10 grams of the molecular sieve blends were prepared using conventional procedures.

(32) FIG. 1.

(33) FIG. 1 compared physical characteristics of the four examples. Note that the Inventive Examples show better performance for tapped bulk density while maintaining the H.sub.2O capacity and crush strength.

(34) FIG. 2.

(35) The mercury porosity and pore distribution of the examples are shown in FIG. 2. Note the median pore diameter and total porosity of Inventive Example 2 in comparison with that of Comparative Example 1.

(36) FIG. 3.

(37) The water adsorption performance of Inventive Examples 2 and 4 was compared with that of Comparative Examples 1 and 3. Note the superior performance for the Inventive Examples for packed density dynamic, breakthrough time, and length of unused bed (LUB), while maintaining similar water capacity dynamic.

(38) FIG. 4.

(39) FIG. 4 compared the performance of Comparative Example 1 with Inventive Example 2 for water adsorption. Note the superior performance of Inventive Example 2 with regard to water adsorption.

(40) FIG. 5.

(41) FIG. 5 compares the performance of Comparative Example 3 with Inventive Example 4 for water adsorption over time. Note the superior performance of Inventive Example 4 over time.

(42) Although the invention has been described in detail, it is clearly understood that the disclosure is not to be taken as any limitation on the invention.