Patent Application
20080035525
For the production of the ZSM-12 zeolite, a synthesis gel composition was prepared which had the following composition:
8.5952 H2O:SiO2:0.0099 Al2O3:0.0201 Na2O:0.1500 TEAOH
271.2 g of sodium aluminate and 99.1 g of NaOH were dissolved with stirring in 9498.3 g of an aqueous solution of tetraethylammonium hydroxide (35% by weight) and 15905.3 g of water. The solution was initially charged in a pressure vessel of capacity 40 l which was equipped with a stirrer. With vigorous stirring, 10 226.1 g of precipitated silica having a specific surface area of 170 m2/g were added in small portions. A highly viscous gel was obtained which had a pH of 13.7 at 24.0° C. The pressure vessel was closed and the contents were heated to 163° C. over 12 h and then kept at this temperature for a total reaction time of 155 h. In the pressure vessel, a pressure of 13 bar was established.
After 155 h had passed, the pressure vessel was cooled to room temperature. The solid product was removed from the mother liquor by filtration and subsequently washed with demineralized water until the conductivity of the washing water was below 100 μS/cm. The filtercake was dried at 120° C. with ingress of air over 16 h and subsequently calcined with ingress of air. For the calcination, the dried solid was heated initially to 120° C. at a heating rate of 1 K/min and kept at this temperature for 3 h. Subsequently, the solid was heated to 550° C. at a heating rate of 1 K/min and this temperature was maintained for 5 h.
The analysis by x-ray diffraction showed that ZSM-12 had formed. The scanning electron microscopy analysis showed agglomerates having a diameter of about 0.8 μm which had formed from small primary crystals, and the agglomerates exhibited a broccoli-like structure.
920 g of the zeolite ZSM-12 obtained in Example 1 were suspended in a solution of 349.60 g of NH4NO3 in 4250.40 g of demineralized water and stirred for 2 h. The solid was removed by filtration and the filtercake washed four times with 500 ml each time of demineralized water. Subsequently, the washed filtercake was slurried again in a fresh solution of 349.60 g of NH4NO3 in 4250.40 g of demineralized water and stirred for 2 h. The solid was again removed by filtration and washed with demineralized water until the conductivity of the washing water had fallen below 100 μS/cm. The filtercake was subsequently dried under air at 120° C. over 14 h and then calcined under air. To this end, the washed and dried filtercake was heated to 480° C. at a heating rate of 1° C./min and then kept at this temperature for 8 h.
Yield: 916.7 g.
The chemical and physical analysis gave the data reported in Table 1:
a)based on the ZSM-12 ignited at 1000° C.
b)BET surface area to DIN 66131
330 g of the ZSM-12 zeolite obtained in the acidic form in Example 2 were mixed over 15 min in a kneader with 156.3 g of commercial pseudoboehmite as a binder with addition of 294 g of demineralized water, and processed to a plastic mass. The mass was kneaded for a further 10 min and then 21.0 g of mold release oil (steatite oil) were added. The mass was subsequently extruded to moldings (d= 1/16″). The moldings were dried under air at 120° C. over 16 h and subsequently calcined under air. To this end, the moldings were initially heated to 120° C. at a heating rate of 1° C./min and kept at this temperature for 2 h. Subsequently, the temperature was increased to 550° C. at a heating rate of 1° C./min and the moldings were kept at this temperature for 5 h. The moldings were cooled to room temperature and then comminuted to a mean size of 3 mm. The catalyst had the chemical and physical properties reported in Table 2:
a)after ignition at 1000° C.
b)BET surface area to DIN 66131
300 g of the ZSM-12 zeolite in the H+ form obtained in Example 2 were mixed in a kneader with 473.7 g of colloidal silica having a weight fraction of 25% silica and dried with cold air until a plastic mass formed. The plastic mass was kneaded for a further 10 min and then 6.0 g of methylcellulose were added. Subsequently, the mass was extruded (d= 1/16″). The extrudates were dried under air at 60° C. over 16 h and then calcined with ingress of air. To this end, the dried extrudates were heated initially at a heating rate of 1 K/min to 600° C. and kept at this temperature for 5 h. The extrudates were subsequently comminuted to a granule having a mean length of 3 mm.
b) Ion Exchange
349.5 g of the granulated extrudate obtained under a) were introduced into a sieve and the sieve was immersed into a solution of 158.32 g of NH4NO3 in 2103.44 g of demineralized water. The granule was left in the solution at room temperature over 1.5 h, in the course of which the sieve was regularly removed briefly from the solution in order to improve the ion exchange. The granule was removed from the NH4NO3 solution and washed with demineralized water until the conductivity of the washing water had fallen to below 50 μS/cm. The granule laden with ammonium ions was dried under air at 120° C. over 16 h and subsequently calcined. For the calcination, the dried granule was heated initially at a heating rate of 1 K/min to 600° C. and kept at this temperature for 5 h.
The properties of the catalyst are summarized in Table 3:
a)1000° C./3 h
b)uncalcined
c)Hg method to DIN 66133
d)BET surface area to DIN 66131; multipoint method (p/po = 0.004 − 0.14)/conditioning: 350° C./3 h; under reduced pressure
Example 1 was repeated, except that colloidal silica was used instead of precipitated silica. The synthesis gel composition was selected as follows:
8.5952 H2O:SiO2:0.0099 Al2O3:0.0201 Na2O:0.1500 TEAOH
A solid was obtained which, in addition to ZSM-12 zeolite, contained ZSM-5 zeolite in a content of 30%. The solid was analyzed by scanning electron microscopy. From the scanning electron micrographs, the average diameter of the ZSM-12 primary crystals was determined to be 50-70 nm. The primary crystals formed by combination of tightly packed, continuous agglomerates. The proportion of the continuous agglomerates in the total number of agglomerates was more than 20%.
A ZSM-12 zeolite, as described by S. Ernst, P. A. Jacobs, J. A. Martens, J. Weitkamp; Zeolites, 1987, Vol. 7, 458-62, was produced. The zeolite was produced using methyltriethylammonium bromide (MTEABr). The zeolite powder had an SiO2/Al2O3 ratio of 108. Scanning electron micrographs under 1980- to 20 000-fold magnification showed rice grain-shaped crystals having an average length of from 0.5 to 13 μm.
As described in Example 2, the zeolite powder was converted to the acidic H+ form by ion exchange with NH4NO3 and subsequent calcination.
The zeolites in the H form obtained in Examples 2 and 6 were each pressed to tablets without further additives with the aid of a Carver laboratory press at a pressure of 18 tonnes. These tablets were crushed and the granules of sieve fraction 0.5-1.0 mm were removed. These granules were covered with 0.5% by weight of platinum by impregnating with 30% H2PtCl6 solution. The granule was subsequently dried at 120° C. for 16 h and then calcined at 450° C. for 5 h. The properties of the granules are compiled in Table 4.
a)BET surface area to DIN 66131; multipoint method (p/po = 0.004-0.14)/conditioning: 350° C./3 h; under reduced pressure
c)HG method to DIN 66133
The platinum catalysts obtained according to Example 7 were tested in a microreactor with pure n-heptane. The test conditions were as follows:
The reactor was started up as follows: First, air was introduced at atmospheric pressure at a rate of 33.33 ml/min, and then the reactor was heated from room temperature to 400° C. This temperature was maintained for 1 h and then the temperature was lowered from 400° C. to 250° C. The air stream was then interrupted and replaced by a nitrogen stream (33.33 ml/min) for 30 min. The nitrogen stream was finally replaced by a hydrogen stream (33.33 ml/min) for 30 min. The pressure was then increased to 20 bar of H2, and then pure n-heptane was introduced and the product stream was analyzed by gas chromatography. The peak areas of all C1 to C7 components were measured every 30 min. The peak areas of all i(so)-heptanes (e.g. methylhexanes, dimethylpentanes, etc.) were combined and denoted as i(so)-heptane areas. The parameters are defined as follows:
Conversion (%)=(1−area(n-heptane)/total area)×100
Selectivity (%)=(area(i-heptane)/total area−area(n-heptane))×100
Yield (%)=(area(i-heptane)/total area)×100
The inventive catalyst exhibited steady state conversion and yield of 40% at virtually 100% selectivity. Cracking of the n-heptane to smaller molecules only took place in small fractions. The comparative catalyst exhibits no significant conversion of n-heptane at 250° C. The inventive catalyst exhibits a higher activity and converts n-heptane with very high selectivity even at low temperatures.
Example 1 was repeated, except that the composition of the synthesis gel was adjusted to the following ratio:
7.8918 H2O:SiO2:0.0091 Al2O3:0.0185 Na2O:0.1377 TEAOH
The crystallization time was increased to 175 hours. Otherwise, the process procedure corresponded to the sequence described in Example 1. A crystalline solid was obtained which was composed of ZSM-12. The solid was analyzed by scanning electron microscopy. The scanning electron micrograph reveals agglomerates which have a broccoli-like structure (open agglomerates). The proportion of closed agglomerates in the total number of agglomerates is less than 10%, while the open agglomerates correspond to a proportion of more than 90%.
The platinum catalysts obtained according to Example 7 were tested in a microreactor with pure n-octane. The test conditions were as follows:
The reactor was started up as follows: First, air was introduced at atmospheric pressure at a rate of 33.33 ml/min, and then the reactor was heated from room temperature to 400° C. This temperature was maintained for 1 h and then the temperature was lowered from 400° C. to 250° C. The air stream was then interrupted and replaced by a nitrogen stream (33.33 ml/min) for 30 min. The nitrogen stream was subsequently replaced by a hydrogen stream (33.33 ml/min) for 30 min. The pressure was then increased to 20 bar of H2, and then pure n-octane was introduced and the product stream was analyzed by gas chromatography.
In this test, the peak areas of all C1 to C8 components were determined every 30 min. The peak areas of all iso-octanes (e.g. methylheptanes, dimethylhexanes . . . ) were combined and denoted as isooctane areas. The parameters are defined as follows:
Conversion (%)=(1−area (n-octane)/total area)×100
Selectivity (%)=(area(isooctane)/total area−area(n-octane))×100
Yield=(area(isooctane)/total area)×100
The catalyst was tested in the microreactor for 110 hours, in the course of which the activity and the selectivity were determined at 245 and 250° C.
The inventive catalyst (Example 7 in conjunction with Example 2) showed an extremely high conversion rate of more than 85% and a selectivity after 10 hours of 80% at 250° C. At 245° C., the conversion was 70% and the selectivity 85%.
In contrast, the comparative catalyst (Example 7 in conjunction with Example 6) exhibited a considerably lower selectivity and conversion rate. A comparative catalyst produced according to Smirniotis, J. of Catalysis 182, 400-416 (1999) had a very low conversion rate on the corresponding conditions. Only at higher temperatures of about 290° C. was an acceptable conversion rate and selectivity observed.
The solids obtained in Examples 1, 5 and 9 were analyzed for their specific volume by mercury porosimetry to DIN 66133. The experimental conditions were as follows:
The values found for the samples are listed in Table 5.
The loose structure and thus the high fraction of cavities between the primary crystals is shown in the mercury porosimetry in the range of pore radii of from 1.9 to 100 nm. The calcined inventive zeolite from Examples 1 and 9 exhibits a specific volume of from about 110 to 125 mm3/g in mercury porosimetry in the range from 4 to 10 nm. The calcined comparative example (ZSM-12 zeolite, produced using colloidal silica, Example 5) has a specific volume of 2.5 mm3/g in the range from 4 to 10 nm. In the range from 10 to 100 nm, the inventive zeolites of Examples 1 and 9 have a specific volume of from 300 to 400 mm3/g. The zeolite from Example 5, employed for comparison, exhibits a specific volume of 41 mm3/g in the range from 10 to 100 nm.
The zeolites obtained in Examples 1, 5 and 9 were analyzed for their pore radius distribution by nitrogen porosimetry to DIN 66134. The experimental conditions were selected as follows according to the manufacturer's instructions and the evaluation was carried out by the method of “Dollim./Heal”.
The values found for the samples are reported in Table 6.
Nitrogen porosimetry in the 10-200 Å range clearly shows the differences in the two structures. In the region of very small pores having a pore radius in the range of 10-30 Å, which are characteristic of compact-structure agglomerates, both the inventive zeolite (Examples 1 and 9) and the zeolite from Example 5 employed as a comparison have a volume of about 0.04 cm3/g. However, the inventive zeolite has in this range only approx. 15% of the total volume for the range of 10-200 Å under consideration, while the volume of 0.04 cm3/g in this range for Example 5 corresponds to a fraction of the total pore volume (10-200 Å) of 76%. In agreement with the mercury porosimetry, the differences between the inventive zeolite (Examples 1 and 9) and Example 5 become clear in the pore radius range of 30-200 Å in particular. In nitrogen porosimetry in the range of 30-200 Å, the calcined inventive zeolite exhibits a specific volume in the range of about 0.18-0.21 cm3/g. In the Example 5 employed as a comparison, a specific volume of only 0.014 cm3/g was found in this range, which means that the zeolite for Example 5 exhibits a distinctly smaller fraction of cavities between the primary crystals.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10314753.5 | Apr 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP04/03283 | 3/27/2004 | WO | 00 | 1/17/2007 |
