Patent Application
20100152505
The present invention relates to catalysts usable in fixed-bed oxychlorination of ethylene to 1.2-dichloroethane (DCE) in form of granules having hollow geometrical configuration endowed with a particular pore volume distribution and to the hollow carriers used for said catalysts.
The oxychlorination of ethylene to DCE is carried out, as it is known, either in fluid bed or in fixed bed. In the first case, more uniform distribution of the temperatures in the reactor is obtained, in the other case, the management of reaction parameters is easier but, due to the low exchange coefficient among the catalyst granules and between the granules and the reaction gas, localized hot spot temperatures can occur having detrimental effects on the selectivity and useful life of the catalyst.
Hollow cylindrical granules are normally used which, thanks to S/V ratio (geometric surface to volume ratio) higher than that of the spheres and solid cylinders allow to obtain more efficient heat exchange and lower pressure drop through the catalytic bed, and consequently better temperature control along the bed and increased productivity of industrial reactors.
In spite of the above advantages, a hollow cylindrical granule has to be designed carefully since, otherwise several disadvantages become evident.
For example, if the ratio of the external to internal diameter (De/Di) of the hollow cylinder is greater than a certain value, the granules become too fragile and the bulk density of the catalyst decreases resulting in a decreased conversion per unit volume of the catalytic bed due to the lower presence of total content of the active catalyst phase.
A too high increase of De or the length of the cylinders maintaining constant the De/Di ratio can cause an inhomogeneous loading of the catalyst inside the tubes of the reactor and possible breakage of the granules with consequent increase of the pressure drop.
A catalyst in form of cylinders having De from 4 to 7 mm, Di from 2.0 to 2.8 nm, height from 6.1 to 6.9 mm is described in EP 1 053 789 A1.
This catalyst is reported to be advantageous with respect to the catalysts in form of cylinders having length shorter than the external diameter described in U.S. Pat. No. 4,740,644 and the catalysts having longer length than the external diameter (U.S. Pat. No. 5,166,120).
The catalysts of the latter cited U.S. patent are also characterized by a total pore volume of 0.6 to 1.0 ml/g, wherein no pores smaller than 4 nm are present and at least 80% of the pore volume is formed of pores with a diameter of 8 to 20 nm, the remainder being pores with diameter of more than 20 nm and up to 200 nm. The catalysts are more active than those wherein the total pore volume is prevailingly formed of pores with diameter of less than 8 nm.
The catalyst of U.S. Pat. No. 5,166,120, according to the consideration made in EP 1 053 789, has the disadvantage of a too high bed void fraction which implies a lower amount of catalytic material present in the bed and consequently a lower specific productivity to DCE (g DCE/g catalyst.h) combined with high pressure drop due to breakage of the catalyst granules during the loading step.
It is an object of the present invention to provide catalysts for the oxychlorination of ethylene to DCE performed in fixed bed, in form of hollow granules comprising copper chloride and chlorides of the metals selected from the alkali metals, the alkaline earth metals and the rare earth metals supported on gamma alumina hollow cylindrical granules, endowed with satisfactory performance in terms of selectivity and conversion and capable of providing specific productivity to DCE (g DCE/g catalyst.h) higher than that of catalysts having the same geometrical parameters (shape and size), and composition.
Other objects will be apparent from the following description of the invention.
The catalysts of the present invention, which are in form of hollow granules having definite geometrical configuration and comprise copper chloride and at least one or more chlorides of the metals selected from the group of the alkali metals, alkaline earth metals and rare earth metals supported on alumina hollow cylindrical granules, are characterized by a macropore volume fraction of the granules of at least 20% of the total pore volume and up to 40%, wherein the diameter of the pores at the maximum of the macropore volume distribution curve is from 800 nm up to 1500 nm. The bulk density preferably is comprised from 0.80 g/ml to 0.65 g/ml, more preferably from 0.7 g/ml to less than 0.78 g/ml.
Further benefits and advantages of the invention will become apparent from a consideration of the following detailed description, given with reference to the accompanying drawings.
The catalysts are endowed with productivity of DCE per g catalyst/h higher than that of the known catalyst granules having similar geometrical configuration (shape and size) and composition, but having diameter of the macropores measured at the maximum of the macropores distribution curve lower than that of the catalysts of the present invention. This means a greater activity (conversion and selectivity) of the catalysts with respect of the known catalysts.
The boehmite used for preparing the catalysts of the invention has d50 of at least 100 μm and up to 170 μm and a fraction of particles of less than 100 μm lower than 50 wt %.
An example of usable boehmite is the commercial boehmite Pural SCC 150 manufactured by SASOL AG—Germany.
This boehmite has particle size distribution (wt %) evaluated by ponderal sieve screening as follows:
The d50 value (average) is 130 μm, the d90 (average) 209 μm. The volume of particles having diameter less than 100 μm is 30%; the volume of particles with diameter less than 250 μm is 98%.
The compression-shaped hollow cylindrical granules obtained from the above boehmite, calcined at 650° C., 700° C. and 800° C. to obtain conversion to gamma alluminia, have the following characteristics:
surface area (BET) of 239, 208 and 183 m2/g calcined at the above mentioned temperatures, respectively;
pore volume (BET) 0.41-0.43 ml/g;
total pore volume=0.48-0.52 ml/g (calculated as difference between the reciprocals of the particle density (PD) and the real density (RD)=1/PD−1/RD);
macropore volume=0.1 ml/g (Hg porosimetry);
pore diameter (MPS) at the maximum of the macropore volume distribution curve=1068 nm. Diameters up to 1600 nm can be obtained using boehmite having d50 higher than 150 μm. The catalysts obtained from this boehmite are endowed with satisfactory good performance and sufficient mechanical properties (axial and radial crush resistance).
The boehmite usable in preparing the catalysts of the invention is obtainable according to know methods, by dissolution of aluminum in hexanol via a modified Ziegler alcohol process: the obtained boehmite slurry is then dried by spray drying.
The characteristics of the hollow cylindrical gamma alumina granules prepared from boehmite Pural SCC 150 hollow granules, having external diameter (De) about 5 mm, internal diameter (De) 2.5 mm, height about 5 mm, as reported in Table 1, wherein the characteristics are also reported of gamma alumina granules having the same size and shape as the granules of gamma alumina from boehmite Pural SCC 150, obtained from SASOL Pural SB1 boehmite having d50 (average) 43 μm and d90=(average) 119 μm, volume of the particles having diameter less than 100 μm of 83.9% and having diameter less than 250 μm=100%.
The granules are prepared by compression-shaping mixtures of powder boehmite with a lubricant such as for example aluminum stearate in amount of 3-6 wt %.
The obtained shaped granules are calcinated at temperature from about 600° to 800° C. to convert the boehmite into gamma alumina, which are then impregnated with an aqueous solution of the metal chlorides-catalyst components. The impregnation is preferably carried out using a s volume of solution equal or lower than the total pore volume of the alumina granules.
The amount of the chlorides present in the catalyst expressed as metal is 3-12 wt % Cu, 1-4 wt % alkali metal, 0.05-2wt % alkaline earth metal, 0.1-3 wt % rare earth metal.
Preferably the amount of Cu is from 4 to 10 wt %, and the alkali metal is potassium and/or cesium used in amount of 0.5 to 3 wt %, the alkaline earth metal is magnesium in amount of 0.05 to 2 wt % and the rare earth metal is cerium in amount of 0.5 to 3 wt %.
The hollow granules comprise at least one through bore parallel to the axis of the granule. In the case of cylindrical granules, the De diameter is from 4 to 6 mm, the Di diameter of 1 to 3 mm and the height of 4 to 7 mm.
Pellets having trilobed cross-section with the lobes provided with through bores parallel to the axis of the granules are conveniently used.
Representative properties of the catalyst granules of the invention are reported in Table 2, while in Table 3 the results are reported of the catalysis tests obtained with the catalysts of the examples.
In
The oxychlorination of ethylene to DCE using the catalysts granules of the invention is carried out in fixed bed according to known methods using air or oxygen as oxidizer, at temperatures from 200° C. to 300° C., using overall feed molar ratios C2H4/HCl/O2 of 1:1.99:0.51 when using air and of 1:0.71:0.18 when using oxygen.
Preferably, the molar ratios HCl/C2H4, O2/C2H4 and HCl/O2 are respectively 0.15 to 0.50, 0.04 to 0.1 and 3.20 to 5.8 when using oxygen and the process is carried out in three reactors in series, wherein the third reactor is loaded with a fixed bed formed or comprising the catalyst granules according to the invention.
The macropore volume is measured by Hg-porosimetry: the micro and the meso pores by BET nitrogen adsorption-desorption.
The bulk density (called also apparent packing density) is measured according to ASTM method D 4164-82.
The following examples are given to illustrate but not to limit the is scope of the invention.
400 g of alumina hollow cylinders with De=5 mm, Di=2.5 mm and height=5 mm obtained by calcination at 700° C. of cylinders prepared by compression-shaping of a powder of boehmite Pural SCC 150 mixed with 6 wt % of aluminum tristearate, having S.A. (BET) of 208 m2/g, total pore volume of 0.51 ml/g, are impregnated in rotating jar of 5 l at room temperature up to 50° C., with 200 ml of an aqueous solution containing
Remaining=demineralized water up to 200 ml.
The impregnated granules were dried in an oven with the following cycle=1 h at 60° C., 2 hs at 80° C., 3 hs at 100° C. and 16 hs at 150° C.
The characteristics of the granules are reported in Table 2 wherein the characteristics of the catalysts of comparative Example 1 and 2 are also reported.
The results of the catalysis test are reported in Table 3.
300 g alumina hollow cylinders having the same size and shape as the cylinders of Example 1, obtained by calcination of crude cylindrical granules prepared by compression-shaping of boehmite Pural SB1 mixed with 4 wt % of aluminum tristearate were impregnated in rotating jar of 5 l at r.t. with 150 ml of an aqueous solution containing:
The impregnated granules are dried as described in Example 1.
The results of the catalysis test carried out under the same conditions as of Example 1 are reported in Table 3.
Two commercial catalysts having similar size and shape as the catalyst of Example 1 and similar composition were used under the same catalysis test conditions as in Example 1.
The results of the test are reported in table 3.
The disclosures in European Patent Application No. 08172023.7 from which this application claims priority are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08172023.7 | Dec 2008 | EP | regional |
