|Title of Invention||
A PROCESS FOR THE MANUFACTURE OF SUPPORTED ZEOLITE FILMS
|Abstract||This invention relates to a process for the manufacture of supported zeolite film employing two distinct heating characterised by 1st step of microwave heating at a temperature range of 40 to 100°C of substrate such as herein described which are treated with zeolite precursor solution such as herein described for zeolite nucleation wherein said precursor solution contains a silica source and an alumina source and 2nd step is hydrothermal heating at a temperature at 130 to 200°C of these substrates while dipped in the precursor solution for zeolite crystal growth, followed by cleaning and calcining at 500 to 600°C for 1 to 4 hrs, the zeolite containing substrates to obtain the zeolite films and membranes on the substrates.|
|Full Text||TITLE : A proces of the manufactur of supported Zeolite films .
FIELD OF INVENTION
This invention relates to a process for the manufacture of supported zeolite films & membranes
This invention relates to a process for the manufacture of supported zeolite films & membranes for gas separation, sensors , HC adsorber & DeNOx catalyst, etc.
BACKGROUND OF INVENTION
Zeolite films and membranes have been prepared on various supports for applications as
gas separation membranes, sensors , HC adsorber & DeNOx catalyst etc. Much work has
be done on MF1 type zeolites such as ZSM-5 because of its wide spread application
ranging from selective gas separation to deNOx catalytic converters. Most of the
applications need supports in the form of multi-channeled honeycomb monoliths for high
surface area and low pressure drop. There are mainly 3 methods of forming zeolite
containing honeycombs known in the art such as by
1 . Wash coating of zeolite slurry on the surface of support. (JP 4224109, US 5,260,242)
2. In situ forming zeolite on honeycomb by hydrothermal treatment : Forming zeolite on
cordierite honeycomb by dipping it in silica containing synthesizing mixture and
hydrothermal ly converting (US 4,800,187) to zeolite and method of forming mixed
zeolite on cordierite honeycombs by hydrothermal synthesis in a solution containing
seed of different zeolites( US 5,248,643).
3. Extruding zeolite containing materials using fiber as reinforcement (US 5,348,987,
US 5,518,678) or Extruding zeolite forming materials and converting them to zeolite
in Hydrothermal conditions. In this type mainly there are methods for converting clay
honeycombs to zeolite (GB 2017520, US 4,157,375 , JP 1 1 171668 )
In the first method, the zeolite adhesion is poor and support is mostly intact. But in the last two methods, the adhesion is very good since it is formed in situ but, honeycombs
substrates undergoes sever hydrothermal treatment in alkali conditions resulting in lose of substrate strength. So a method to solve the disadvantages of above methods is needed.
US patents 5,019,263, 5,100,596, 5,266,542, 5,362,522, 5,871,650 disclose methods of forming zeolite film or membranes on supports other than honeycombs. All these methods involve the wet hydrothermal synthesis while substrate is dipped in the synthesis mixture for a prolonged time ranging from 24 to 48 hr
Forming zeolite in dry state by using mildi hydrothermal condition is finding attention now, because of above mentioned advantages JP 08319112 & US 5,258,339 disclose a method using dry gel and steam. Another method ( EP 0808655) describes coating by either washcoating a zeolite colloidal solution or in situ crystallization by hydrothermal treatment after dipping supports in colloidal precursor. It was also suggested to take care to avoid undue weakening of the supports due to prolonged exposure to high temperature and alkali indicating the disadvantages of this wet method. Further, the above 3 methods do not disclose forming zeolite film on honeycomb supports or forming honeycomb containing zeolite in dry state. A method (JP 2002154822 ) disclosed by present authors solves some of the above problems. In this method, the zeolite film is formed on the surface of porous honeycomb supports by gelling the zeolite precursor sol on the surface of support followed by in-situ crystallization of zeolite ZSM-5 in solid state. In this, the synthesis time is about 24 hr and the zeolite coverage is not sufficient to use as membranes. Thus method to improve this process is needed.
Synthesis of zeolites A,X, ZSM-5 by Microwave heating (MW) was reported first in a US patent 4,778,666 (1988)and in many patents (JP2095435, JPJP2002058973) and papers. The advantageous over conventional heating (CH) are faster crystallization, smaller crystal size for high surface area and activity, avoiding formation of undesirable phases by reducedjyjne. The MW preparation of ZSM-5 film require special fixtures to have high pressure autoclave in the microwave cavity and a sophisticated thermocouple and temperature controller to maintain the temperature. US 5908604 discloses the special arrangements needed to make zeolite film of MFI type in special MW oven. It is
very difficult to prepare ZSM-5 in Domestic type MW oven because difficulty in obtaining and maintaining high temperature ( 150-175 °C). Any over heating will causes template ions to degrade
Thus a method is needed to overcome the above mentioned difficulties and use advantage of MW for faster synthesis of zeolite films
OBJECTS OF THE INVENTION
An object of the present invention is to propose a process for the manufacture of supported zeolite films using simple kitchen microwave oven and a Two - step heating approach.
A further object of the present invention is to propose a process for the manufacture of supported zeolite films whereby the zeolite film is fully covered on the substrates so as to use as membranes.
Another object of the present invention is to propose a process for the manufacture of supported zeolite films using MW for forming zeolite seeds over which zeolite crystals grows during subsequent treatment.
Still another object of the present invention is to propose a process for the manufacture of supported zeolite films on wall flow honeycomb filters and manufacture of zeolite membrane filter by selectively forming the zeolite film on one surface of honeycomb wall
Further objects and advantages of this invention will be more apparent from the ensuing description.
BRIEF DESCRIPTION OF THE INVENTION:
This invention relates to a process for the manufacture of supported Zeolite films
comprising of preparing a precursor solution, treating substrates in the precursor solution
followed by microwave heating to obtain Zeolite seeds formed on the substrate, nirtner
heating the substrates thus obtained, in a second precursor solution to obtain the substrate
with Zeolite crystals, cleaning and calcining the substrate to obtain the supported Zeolite films.
The precursor solution contains a silica source and alumina source such as whose mixture forms Zeolite of crystals structure such as LTA, FAU, MFI, etc. under hydrothermal conditions. The Zeolite forming precursor sol also comprises of water and templates like Tetra prophyl ammonium hydroxide, Tetra prophyl ammonium bromide, Tetra methyl ammonium hydroxide, Tetra methyl ammonium chloride to crystallize various MFI family and may also contain sodium containing compound like NaOH and or nitrogen containing compound like NH3F or NH3OH, etc. The reaction mixture further may also comprise of Zeolite seeds which will partially or fully replace templates to crystallize various ZSM-5 iamily and the Zeolite crystallized may be anyone of the types, Silicalite-1, ZSM-5, ZMS-4, ZMS-11, etc. depending on templates and/or seeds used. The substrate is preferably a ceramic having anyone of the mixed phases of cordierite , mullite, alumina, magnesia, zirconia, spinel, silicon carbide, clays, metakaolin or combination of these. The honeycomb substrate is a monolith having various cell density and wall thickness depending on back pressure and geometric surface area requirement. The cell density is preferably 40 to 600 cpsi. However, the monolithic substrate is not restricted to honeycomb shapes. It can be any other shape such as plates, discs, tubes, pipes, corrugates cross-section made by extrusion or by any other known method to get good geometric surface area and strength. The honeycomb monoliths have porosity preferably in the range of 20 to 70%, but not restricted to porous honeycomb only. Non-porous substrates such as metals, glass can also be used for application other them membranes. The substrates containing aluminosilicates may be optionally treated with acid or by any known method to get thin surface of micro porous silica.
Preparation step consists of mixing the solution of silica, alumina and other ingredients for about 1 to 4 hrs to obtain a precursor sol of silica, alumina and templates or other optionally added components. The dry substrate is dipped in the sol till the pores are saturated with the sol for a period ranging from 10 mins to 24 hrs, preferably 30 min to 2 hrs depending on the requirement of the extent of filling. The dipping can be done at atmospheric pressure or at reduced pressure for better filling of pores with sols. After removing from the sol, extra sols can be removed carefully. The coated honeycomb is heated in an enclosed vessel in a domestic microwave oven at a temperature in the range of 40 to 100 °C and for 1 to 60 min more preferably 5 to 30 min. This is sufficient to get the sols absorbed and form the seed crystals. The domestic microwave oven works at a frequency of 2.45 GHZ and power from 800 to 2000KW. Power may be controlled from 25 to 100% of full power. The substrates containing Zeolite seeds are then heated in a closed, air tight vessel, preferably in a Teflon lined autoclave for 3-24hrs, at a temperature in the range or 130-200 °C, preferably 150 to 180 °C for the crystallization of Zeolite. The container is filled with 50 to 70% volume precursor solution. The substrates containing Zeolite crystals are then cleaned in deionised water optionally using ultrasonic to remove any loosely adhered crystals mainly at the corners followed by drying. This is followed by calcining the substrates having Zeolite film for l-4hrs at 500-600 °C to remove the template ions, if any. The steps may be repeated 2-3 times for recoating the substrate to get more thickness and more continuous film of Zeolite.
The preferred embodiment of the invention will now be described with reference to the accompanying drawing in which
Figure 1 shows the process flow chart of the invented method
Figure 2: Comparison of BET specific surface area (SSA) of the zeolite coated
substrate obtained after hydrothermal treatment for samples with and without
Figure 3: Microstructure of zeolite film over cordierite substrate obtained after 10 min
Microwave and 6 hr hydrothermal treatment showing the full coverage of substarte
surface by zeolite filmr indicating the fester and better formation of zeolite by the invented method.
Figure 4: BET specific surface area of samples prepared by varied dipping time.
Figure 5: Sketch of zeolite membrane module made using honeycomb filter as per the present invention. The membrane module consists of porous ceramic honeycomb (1) whose alternate channels are blocked using ceramic plugs (2) to make a wall flow filter, zeolite film (3) is formed inside surface of the channels by the method described in this invention. The provision of inlet gas (4), permeated gas (5) and retentate gas (6) is provided using metallic canning (7).
The new process invented is disclosed in Figure 1. The preparation of zeolite film is made in 2 steps. The first step involves treating supports in precursor solution in domestic MW oven to get nanosized seed formed on support. The 2nd step involves heating this substrates in the 2nd precursor solution for further growth of zeolite for 3 to 24 hr. 2nd precursor solution may be similar to 1 st precursor solution or different such that it will be used for grow the zeolite of required crystal structure such as LTA, FAU, MFI etc on the seeded supports.
The formation of zeolite of MFI structure was confirmed by powder X-ray diffraction (XRD; Geigerflex, Rigaku, Japan) as early as 4 hr. The specific surface area (SSA) and pore volume measured by N2 gas adsorption and desorption isotherms is shown in table 1. The comparison of surface area with and without microwave heating is shown in Fig 2. which shows that high surface area obtained at low processing time using this invented method. The microstructure of the zeolite film on the honeycomb substrate was observed using a scanning electron microscope and is shown in Fig. 3 which shows full coverage of substrate surface by zeolite crystals.
The present invention is well understood from the following examples.
Precursor solution was mixed in appropriate amount by stirring for 3 h at room temperature to produce a composition with a molar ratio of SiO2: TPAOH: H2O =100:10:1500. The solution is prepared using colloidal silica as SiO2 source, Tetra prophyl ammonium hydroxide (TPAOH) and distilled water. The solution was aged for 24 h. The substrate samples were dipped in the precursor solution for about 2 h. The samples were then removed from the solution and the excess solution on the surface was removed by careful air blowing.
These samples were then heated in an sealed Teflon vessel in a domestic microwave oven ( Frequency 2.45 Hz and power 800W) for 2 to 15 minutes. 100 % power was used in most of the experiments and few trials with 25, 50 % power also carried out. The samples then vertically kept in a Teflon lined autoclave and filled with precursor solution just covering the substrates and about 50 % volume of the container. Teflon lined autoclave was then heated in a conventional oven at 150 °C for 3 to 24h. After autoclaving, the samples were washed with distilled water in an ultrasonic bath for 30 min to remove any loosely adhering coating especially in the corners of the honeycomb. After drying at 110 °C for 1 day, the samples were calcined at 600 °C for 2 h to remove the template ions. The calcined samples are once again washed with distilled water in an ultrasonic bath for 10 min to remove any detached thick coating during calcination. The BET specific surface area (SSA) obtained indicated the amount of zeolite formation as shown in table 1. Fig. 4 shows the BET surface area obtained by the same method but varying time of dipping the substrates in the precursor solution prior to Microwave heating to control the degree of filling and in turn thickness of the film
In this case, the precursor solution used was same as in example 1, but substrates used is Alumina disk of 18 mm diameter and 2 mm thick. The porosity of these substrates was varied from 0 to 50 %. Microwave heating time was 0 and 15 min, Autoclave time was 6 ,12 and 24 hrs. All other process conditions were as in example 1. The amount of zeolite film formation is shown as weight gained after the hydrothermal treatment in Table 2. The permeability of these samples for Hydrogen gas was tested at room temperature. The
permeability of hydrogen through the membrane made in experiment No. 29 is 8.56 Xltt 6 mol / (m2.sec.Pa)
In this case, the substrate is changed to silicon carbide with porosity of 40 % All other process conditions were as in example 2. The amount of zeolite film formation is shown as weight gained after the hydro thermal treatment in Table 3. Increase in zeolite formation and BET surface area increased with increasing Microwave heating time and without increasing autoclave time using the invented method.
In this case, the substrate used is cordierite honeycomb filter of 30 mm diameter and 25 mm long. Cell density is 200 cpsi , wall thickness is 0.35 mm. Porosity of the wall is 45%. The alternative channels are blocked by ceramic plugs. Only one surface of the channels are coated with zeolite by pouring the precursor solution inside the channels. The opposite end and outside surface of the filter is covered with Teflon tapes. The precursor is prepared as in example 1. After soaking the one side surface of the channels by the precursor for 2 hr, the honeycomb filter is heated in microwave for 15 min. Then the filter is kept in the autoclave for 24 h and heated to 170 °C. The filter then washed. Cleaned and calcined at 600 °C for 5 hrs. The filter is canned in a stainless steel casing with the provision of gas inlet and out let at the both ends and a retentate outlet on the periphery. Thus fabricated membrane module is tested for gas separation using Hydrogen and methane at room temperature. The permeability of hydrogen through the membrane module is 13.99 X10"5 mol / (m2.sec.Pa). This is about 3 times higher than that of zeolite membrane formed on flat membrane as in example 2. This is mainly because of multi-channeled honeycomb design and forming zeolite only one surface of the honeycomb wall using this invented method. The permeability of methane through the membrane module is 5.11 X10"5 mol / (m2.sec.Pa) which is much lower than that of Hydrogen.
1. A process for the manufacture of supported zeolite film employing two
distinct heating characterised by 1st step of microwave heating at a
temperature range of 40 to 100°C of substrate such as herein
described which are treated with zeolite precursor solution such as
herein described for zeolite nucleation wherein said precursor solution
contains a silica source and an alumina source and 2nd step is
hydrothermal heating at a temperature at 130 to 200°C of these
substrates while dipped in the precursor solution for zeolite crystal
growth, followed by cleaning and calcining at 500 to 600°C for 1 to 4
hrs, the zeolite containing substrates to obtain the zeolite films and
membranes on the substrates.
2. The process as claimed in claim 1, wherein said step of microwave
heating is carried out in a domestic microwave oven for 1 to 60 min
preferably for 5 to 30 min.
3. The process as claimed in claim 1, wherein said step of hydrothermal
heating is carried out in a closed vessel using a oven or any other
heating device suitable for hydrothermal heating for 3 to 24 hrs
preferably at 150 to 180°C.
4. The process as claimed in claim 1, wherein said substrate used is a
non ceramic or ceramic substrate, preferably a ceramic substrate
such as cordierite, mullite, magnesia, zirconia, spinel, silicon carbide,
clay, metakaolln and combinations thereof.
5. The process as claimed in claim 1, wherein said precursor further
contains water, templates, optionally sodium containing compound,
nitrogen containing compound and zeolite seeds.
6. The process as claimed in claim 5, wherein said templates are
compounds such as tetrapropyl ammonium hydroxide (TPAOH),
tetrapropyl ammonium bromide (TPABR), tetramethyl, ammonium
hydroxide (TMAOH), tetramethyl ammonium chloride (TMACL).
7. The process as claimed in claim 1, wherein said substrate is in the
form of multi-channeled honeycomb or any other shape such as plate,
discs, tubes, pipes, corrugated cross-section.
8. The process as claimed in claim 1, wherein treating the substrate in
the precursor solution comprises dipping the substrate in the solution
for a period ranging from 10 mins to 24 hrs, preferably for 30 mins to
9. The process as claimed in claim 1, wherein the zeolite film and
membrane comprises of zeolite crystals of any one of the types:
Silicalite 1, ZSM-5, ZMS-4, ZMS-11, depending on the precursor
|Indian Patent Application Number||268/DEL/2003|
|PG Journal Number||14/2010|
|Date of Filing||11-Mar-2003|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LIMITED|
|Applicant Address||BHEEL HOUSE, SIRI PORT NEW DELHI 110049, INDIA|
|PCT International Classification Number||B01D 71/02|
|PCT International Application Number||N/A|
|PCT International Filing date|