TITLE
Extruded De-NOx catalyst honeycombs and the method of production thereof

FIELD OF INVENTION

The invention relates to production method for De-NOx catalyst in the form of extruded honeycomb for selective catalytic reduction of NOx from combustion flue gas with high dust such as thermal Power plants

BACKGROUND OF INVENTION

The reduction of NOx by selective catalytic reduction (SCR) is an important proven technology to reduce NOx from flue gas of combustion process and employed in automobile and thermal power plants. In a coal fired plant, the SCR catalyst can be used in three different places, most prominent being after the economizer and before the air preheater with flue gas temperature in the range of 300-350 deg C and with high dust concentration typically found in Indian thermal power plants. While the reductant ammonia concentration has to be optimized to curtail the ammonia slip, the active catalyst component vanadia also needs to be optimized to abate SO2 to SO3 formation; together resulting in forming another pollutant ammonium bisulphate (ABS) Therefore, the most important aspect of such catalyst preparation is the effective distribution of active catalyst component in a small quantity in the catalyst earner typically in a porous configuration In addition to this, other functional additives are required in appropriate quantities and the mixing of all such components forms an important role for achieving high catalytic efficiency. Another important parameter for SCR catalyst is the erosion resistance of SCR catalyst at high temperature operation in the presence of dust concentration.

While Titania in its anatase form is the basic catalyst support used by most of the inventors across the world, there are reports of alumina and diatomaceous earth either independently or mixed with titania are used Titania in its anatase form can be obtained by proper heat treatment during synthesis from its ore. Therefore instead of anatase titania as the main support material, many inventors have utilized hydrated titania, titanyl sulphate and metatitanic acid as the main ingredient to build the porous support so as to retain the high surface area which can support the active catalyst components on its base. The active catalyst component is vanadia along with promoters like molybdenum and tungsten in most cases. Though vanadium pentoxide is most widely used as active catalyst component, many inventors have also made catalyst using vanadium in its ammonium vanadate form Further, there are many other additives have been used in such compositions to improve the catalytic efficiency in a wide temperature range. Typically, the catalyst composition for DeNOx applications in thermal power plants mainly consists of the porous ceramic support which is mixed with many ceramic additives in smaller quantities. Homogenous mixing of such components play an important role in imparting the required catalytic properties with high NOx conversion efficiency and over a long period of time. One widely used method of making SCR catalyst is kneading the mixture of all the components together along with binding agents like silica and glass fibers and making in the form of honeycombs or plate configurations
US Patent 6054408 describes a method of kneading the compounds of titanium, molybdenum, vanadium with water and coating the supporting bodies with catalyst mass by extruding in the form of honeycombs following drying and calcination in the range of 500- 600 deg C.
In an invention reported in EP 2 719 454, the aqueous slurry of TiCV V powder was combined with bohemite or pseudo bohemite as an inorganic binder and coating the mixed solution to a cordierite substrate and drying with hot air stream to obtain the SCR catalyst

In another related invention applicable to plate type catalysts US 7 713 901, a silicone based polymer was dissolved in an organic solvent and added the glass fiber as a bonding agent and finally adding SCR catalyst powders to the resulting mixed solution The impregnation of a porous plate type glass fiber support into the mixed solution followed by suitably baking the same.
In another disclosure, US 6 419 889 B1, a commercially available titania powder was peptized in presence of hydrogen peroxide followed by compaction in a kneader and then extruded as trilobes The extrudates were then dried and calcined prior to testing for NOx conversion efficiency In this invention, vanadium was sourced as vanadium ammonium oxalate which was separately prepared by adding ammonia and oxalic acid to ammonium polyvanadate suspended in water, The catalyst obtained had a surface area in the range of 70-99 m2/g.
KR20130000891 assigned to Nano corp. describes method of manufacturing a honeycomb catalyst where in SCR catalyst is coated on extruded clay honeycombs
KR101042018- assigned to Nano corp discloses method for high density Titanium Dioxide Powder for using in extruded catalyst with higher green density,
CN105289580 discloses a preparation method honeycomb catalyst for low-temperature denization in which W03 and the active ingredient-V205 are soaked and adsorbed to the surface of a catalyst carrier after a material is molded
US6054408 assigned to Siemens discloses a method for producing the catalyst for reducing the nitrogen oxide concentration in a flowing medium by using less amount of molybdenum trioxide Mo03, is about 0.01 to 5% instead of molybdenum oxide proportion of about 10 to 12% by weight. A preparation method of a deNOx catalyst for selective catalytic reduction is provided in KR20020069621 to increase mechanical strength of deNOx catalysts by firing in nitrogen atmosphere for inhibiting crack formation during calcination.

In JPH01258741 assigned to MITSUBISHI HEAVY IND LTD, a honeycomb denox catalyst Is prepared using gypsum as a component of the catalyst by adding glycerol and/or a nonionic surface active agent to extruded body obtained by kneading II type anhydrous gypsum.
EP0826409 discloses a honeycomb catalyst having a front surface of more than 50%. The channels have a hydraulic diameter of more than 2 mm. The catalyst has a main component of Ti02 and a hydraulic diameter of 6.8-7 8 mm
US2014157763 assigned to JOHNSON MATTHEY discloses an extruded honeycomb catalyst for nitrogen oxide reduction according to the selective catalytic reduction (SCR) method in exhaust gases from motor vehicles includes an extruded active carrier in honeycomb form having a first SCR catalytically active component in the form of honeycombs and a washcoat coating having a second SCR catalytically active component being applied to the extruded body.
In WO2009080155A, a process for the gentle and efficient drying of a ceramic honeycomb body is specified. The process is suitable for achieving, with uniform drying of the honeycomb body, a short drying time and low shrinkage of the honeycomb body. For this, the honeycomb body which is in a moist prefabrication state is frozen and the moisture is removed from the frozen honeycomb body under vacuum.
CN105126818 discloses a wear-resistant anti- poisoning honeycomb SCR denization catalyst and a preparation by adding montmorillonite clay for replacing part of titanium tungsten powder.
WO2016012490 assigned to Yara Int, discloses a honeycomb monolith with polygon structure
CN103736482 discloses a preparation method of continuous extrusion SCR honeycomb catalyst.

Integrally-extruded honeycomb catalyst for selective catalytic reduction (SCR) smoke denitration and preparation process of catalyst is disclosed in CN102886266. Here FeS04 and Ti-V-W active ingredients is used. Because a La element is added, structural phase transition from an anatase to a rutile is greatly restrained, a phase transition temperature is obviously increased, and the catalyst can be calcined at a temperature of 800 DEG C,
The above prior art indicates, though there are many methods suggested for production of extruded SCR catalyst in a vacuum screw extruder for continuous production, the amount of binders required, both organic and inorganic binders to make clay type extrudable dough is very high up to 30% due to fine particle and high surface area of catalyst material which reduces the catalytic activity. Maintaining high catalytic activity and high mechanical strength using conventional binders is difficult, Moreover catalyst material being costly chemical are getting wasted as green and fired rejections or end cut parts. In order to overcome these technical problems for a continuous extrusion process using a vacuum screw extruder, innovative processing method in each process step is required
OBJECTS OF THE INVENTION:
An object of the present invention is to propose a method for De-NOx catalyst in the form of extruded honeycomb for selective catalytic reduction of NOx from combustion flue gas
Another object of the present invention is to propose a method of preparing SCR catalyst by using combined method of dry mixing, wet mixing and paste mixing to produce homogenous SCR catalyst composition with both inorganic and organic binders embedded in it

Yet another object of the present invention is to propose the steps of mixing one each of fresh catalyst, calcined catalysts and mixing of both,
Further, object of the present invention is to propose addition of binders at each step of mixing to get extrudable dough,
Still further object of the present invention is to propose process steps of production of SCR catalyst honeycombs with minimum process loss by re-using calcined catalyst materials.
BRIEF DESCRIPTION:
This discloses a method of manufacturing of De-NOx catalyst in the form of extruded honeycomb for selective catalytic reduction of NOx from combustion flue gas where two step mixing process for preparing extrudable dough, continuous extrusion of honeycombs, two step drying process and reuse of calcined honeycombs
DESCRIPTION OF THE INVENTION:
The embodiment of the present invention is based on an approach for producing stable, defect free catalyst honeycombs which has got good mechanical properties as well as high catalytic behavior for NOx reduction in high dust laden power plants exhaust. Another approach is to minimize process loss of catalyst material by re-using with proper processing The inventive process is consists of following steps:
1. Preparation of catalyst powder, This process involves cone blending the intermediate titania material along with transition metal oxide additives like vanadium pentoxide, Molybdenum oxide, tungstic acid and manganese oxide in different proportions, and metal oxide like tin dioxide all in commercial punty, The blending process mixes the powders of different constituents and in very small to large quantities uniformly, The blended powder is then added with appropriate amount of ammonia solution along with part of the inorganic colloidal

silica binder in its nano-form for effective binding and wet milled for further homogenous mixing of the constituents. The water based slurry is then dried in a gas fired/ electrical fired oven and the mixed composition is calcined at a temperature range of 400-500 deg C to convert ammonium tungstate to tungsten oxide with uniform mixing at molecular level After sieving the catalyst powder is obtained
2L Preparation of catalyst paste- Parti: The catalyst powder prepared in Step 1 is mixed in a high shear mixer such as sigma mixer with water, organic binder like methyl cellulose, inorganic binder like colloidal silica and reinforcing agent like chopped e -glass fiber strands, lubricating agent like low molecular weight polyethylene glycol etc. Homogenous SCR catalyst paste are kept in a cold room at a temperature of 4 deg C for 24 h
3 Preparation of catalyst paste- Part2; Another batch of catalyst powder preferably calcined powder obtained by grinding of fired rejects of end cut catalyst wastes is mixed with resins preferably water soluble or silicon resins along with oganic solvent Quantity of resins can vary 10 to 40 % of catalyst powder to get paste with gel consistency Mixing is preferably done in a planetary mixer or any known method of mixing suitable to make paste
4. Preparation of extrusion dough: Catalyst paste prepared by step 2 and step 3
are mixed to get a homogeneous extrudable dough with good plasticity and cake
hardness. Quantity of part 2 is preferably 10 to 50 % of total mix. Total moisture
content maintained in the range of 25 to 30% The mixing is done in a high shear
mixer such as sigma blade mixer Thus prepared extrudable catalyst dough is
stored in temperature around 20 Deg C
5, Preparation of extruded honeycombs: Dough prepared in step 4 is fed to a de-
airing screw extruder of suitable capacity to produce the product size. For
producing Honeycombs of typical size 150mmX150mm cross section, the
extruder with auger diameter of about 300mm is preferred Extrusion speed to be
maintained to get good flow of continuous monolithic structure of honeycombsN
Honeycomb cells can very depending on requirement such as 12 to 18 cells for
150X150 mm cross sections. The extruded honeycombs are cut to required
length by a thin wire.

6. First stage of drying: The extruded honeycombs after cutting, the both end are brushed with a catalyst paste to close the opening generated by wire cutting and also to avoid fast drying The paste used is taken from catalyst paste prepared in step 3. After this process, the extruded honeycombs are covered to avoid any drying by means of carton boxes or wrapping in polythene sheets. These protected honeycombs are stored for 7 to 10 days in a humidity chamber. Drying is done to reduce moisture below 10 % preferably 8%. Accordingly humidity is reduced from 80 to 30 RH and temperature is increased from 35 to 70 degree C
7. 2nd stage of drying: After first stage of drying as per step 6, honeycombs are removed from wrapped covers or from cartoons This stage of drying preferably carried out in microwave dryer having good exhaust for removal of water vapors. Drying time is 1 to 4 hrs, Power required is 2 to 4 KW per kgs of catalyst honeycombs dried
8 Firing is done at temperature range of 500 - 700 deg C for 10 to 24 hr cycle time
in a gas fired furnace. 9. End cutting to get exact size required for the applications End cut catalyst parts
are recycled by powdering it a ball mill and using as per step 3
The SCR catalyst honeycombs produced as per this inventive step has erosion loss of 0.01 to 0.04 g/min at impact angle of 15 to 90 degree when tested as per ASTM G76, A -axis crushing strength of 4MPa, BET surface area of 50m2/g, Catalytic activity when tested as NOx to N2 conversion efficiency of > 85 % in the temperature range of 300 to 375 deg C hence suitable De-NOx application in high dust laden power plant flue gas.

We Claim:

1. Method for manufacturing of De-NOx catalyst in the form of extruded honeycomb
for selective catalytic reduction of NOx from combustion flue gas which consists
of
a. Preparation of catalyst powder by blending the intermediate titania
material along with transition metal oxide additives like vanadium
pentoxide, Molybdenum oxide, tungstic acid and manganese oxide in
different proportions ammonia solution along with part of the inorganic
colloidal silica binder, calcining and powdering.
b. Preparation of catalyst paste in two Parts
c. The catalyst powder is mixed in a high shear sigma mixer with water,
organic binder, inorganic binder, reinforcing agent and lubricating agent,
d. Another batch of catalyst powder preferably calcined powder mixed with
resins.
e. Preparation of extrudable dough by mixing Catalyst paste prepared by
above two parts
f. Extrusion of honeycombs and cutting into required length
g. Drying of honeycombs in two steps: first step in humidity chamber and
2nd drying in a microwave dryer
h. Firing of the dried honeycombs at temp 500-700C
i. End cutting to desired length and using end cut rejects for reuse
2. A method as claimed in claiml, where in preparation of paste part 1 consists of mixing of catalyst powder in a high shear mixer such as sigma mixer with water, organic binder preferably methyl cellulose, inorganic binder preferably colloidal silica , reinforcing agent preferably e -glass fiber strands and lubricating agent preferably low molecular weight polyethylene glycol.
3. A method as claimed in claiml, where in preparation of paste part 2 consists of mixing of calcined powder obtained by grinding of fired rejects of end cut catalyst wastes is mixed with resins to get paste with gel consistency
4. A method as claimed in claim3, where in resins preferably water soluble or silicon resins along with oganic solvent. Quantity of resins can vary 10 to 40 % of catalyst powder to get paste with gel consistency.

5. A method as claimed in claim!, where in extrudable dough is prepared by mixing catalyst paste 1 and catalyst paste 2 where quantity of part 2 is preferably 10 to 50% of total mix.
6. A method as claimed in claiml, where in extrusion of honeycombs are done in a de-airing screw type extruder and honeycomb sizes of size upto150X150mm is done on continuous extrusion process,
7. A method as claimed in claiml, where in drying of honeycombs are done in a two stages humidity drying followed by microwave drying
8. A method as claimed in claim7,where in humidity drying is done by wrapping the honeycombs in polythene or in carton boxes for 7 to 10 days to reduce moisture below 10 % preferably 8%
9. A method as claimed in claim7, where microwave drying is done in a microwave dryer having good exhaust for removal of water vapors. Drying time is 1 to 4 hrs, Power required is 2 to 4 KW per kgs of catalyst honeycombs dried to reduce moisture below 1 % preferably below 0.5%
10. A method as claimed in claiml, where firing is done temperature range of 500 -700 deg C for 10 to 24 hr cycle time in a gas fired furnace
11. A method as claimed in Claim 1, where in after firing the end cut catalyst parts are recycled by powdering it a ball mill and reused as per claim 3.