ITMI20082333A1 - PRECURSORS OF CATALYZERS OF OXYLORURATION OF ETHYLENE TO DICHLOROETHANE. - Google Patents

Description

"PRECURSORS OF ETHYLENE DICHLOROETHANE OXYCHLORURATION CATALYSTS"

DESCRIPTION

The present invention relates to catalyst precursors for the fixed bed oxychlorination of ethylene to 1,2-dichloroethane (EDC) having high selectivity to EDC and their preparation method.

Dichloroethane is the important intermediate for the production of vinyl chloride and therefore of PVC, one of the most widely used plastics.

Various technologies are used in the oxychlorination reaction. The reactors can be fixed bed or fluidized bed and air or oxygen are used as oxidizing agent.

In both fixed and fluid bed processes, catalysts based on copper salts are used, preferably CuCl2 in a mixture with different promoters such as salts of alkali metals, alkaline earth and / or salts of rare earths.

Catalysts are supported; the most used support is alumina, of a suitable shape: microspheroidal for the fluid bed, granules of various shapes and sizes in the case of a fixed bed.

The fixed bed technology covers, as an industrial application, a lower share than the fluidized bed, which is still interesting. Normally the process is carried out with the use of three reactors in which the total load is divided by partializing the oxidizer (air or 02). Furthermore, if 02 is used, the gases at the outlet of the third reactor are recycled for the recovery of the unconverted ethylene.

The reactors are of the shell and tube type with a cooling fluid, circulating in an external jacket, which can be pressurized water or diathermic oil.

An advantage that this technology offers compared to the fluidized bed is the higher specific productivity: in fact, by expressing the productivity as tons of EDC produced in an hour compared to the ton of catalyst used, it is possible to obtain productivity of 1-3 against productivity of 0, 3-0, 9 in the fluidized bed. In addition, the consumption of catalyst in the fixed bed technology is lower than that of the fluidized bed technology (0.01-0.06 Kg catalyst / ton of EDC, against 0.05-0.15).

Finally, in the fixed bed technology, there is no passage of catalyst in the cooling section (quench), while in the fluid bed the fines not retained by the cyclones pollute the quench waters in the cooling section.

However, the fixed bed has some problems compared to the fluidized bed:

- A hot spot area is formed, close to the gas inlet in which the temperature can be even 100 ° C higher than that of the thermostatic fluid. In this zone the phenomena that affect the stability of the catalyst are extremely pronounced, in particular the loss of active elements, (especially Cu), due to the high temperature and, probably, also to the high reducing capacity of ethylene in conditions of high productivity. An irreversible transformation of alumina into alumina of lower mechanical strength can also occur.

- In the hot spot area, in consideration of the high temperature, there is also a loss of selectivity due to the greater formation of carbon oxides;

- The pressure drop across the reactors is high: generally it is 1-3 atmospheres and increases over time due to the formation of fines that accumulate at the bottom of the catalytic bed. The duration of the catalyst (and therefore the consumption) is very often linked to the pressure drop.

It is therefore evident that a fixed bed catalyst, in particular to be used in the first of the three reactors used, in order to be used on an industrial level and must demonstrate good stability even at high temperatures and in conditions of high productivity, must also be equipped with high DCE selectivity. Finally, it must also ensure, by adopting suitable geometric shapes, the lowest possible pressure drop.

Various catalysts with satisfactory performances are described in the patent literature. All these catalysts have a chlorine content corresponding to that of the chlorides of the various metals used for their preparation.

From patent EP 209732 catalysts obtained by impregnating gamma AI2O3 with aqueous solution of salts forming the components of the catalyst and subsequent drying at temperatures of at most 210 ° C and then forming of the dried powder are known.

The obtained cylindrical granules do not have satisfactory mechanical properties, acceptable for use in a fixed bed.

Targets

It is an objective of the present invention to provide precursors of ethylene oxychlorination catalysts to EDC in a fixed bed with considerable selectivity to EDC and mechanical properties acceptable for use in a fixed bed.

Description of the invention

It has now unexpectedly been found that it is possible to obtain precursors of EDC ethylene oxychlorination catalysts to be used in a fixed bed, comprising oxides and / or oxygenated compounds of copper and preferably also oxygenated potassium compounds in quantities expressed as metal of 2-10 % by weight for copper and 0.5-3% by weight for potassium, with particularly high selectivity and satisfactory mechanical properties (axial and radial breaking load).

The precursors may also comprise oxides and / or oxygenated compounds of metals selected from alkali metals other than potassium, alkaline earth metals and rare earth metals in quantities expressed as metal of 0.5-3% by weight for alkali metals, 0.05-2% by weight for alkaline earth metals and 0.1-3% by weight for rare earth metals.

In these precursors the chlorine content is 0-4% by weight.

It is surprising that the catalysts obtained from the precursors according to the invention are endowed with greater selectivity to EDC with respect to the corresponding catalysts of the same composition expressed as metal, prepared by impregnating a pre-formed support with an aqueous solution of the salts of the metal components of the catalyst .

A higher selectivity in EDC of even 1% by moles means hundreds of tons of unburned ethylene in plants producing thousands of tons / year of EDC.

The precursors according to the invention are obtained by calcining in the air products of impregnation of boehmite with copper salts, and of at least one alkaline, alkaline earth and / or rare earth metal.

The preparation of the precursors is carried out by impregnating boehmite or its mixtures with microspheroidal gamma alumina or with Al silicates with an aqueous solution of the salts of the metal components of the catalyst, preferably using a volume of solution lower than the porosity of the boehmite or its mixtures, then drying the product impregnation at temperatures of 100-150 ° C for a few hours, finally calcining everything at temperatures starting from 500 ° (i.e. from the minimum temperature to transform boehmite into gamma alumina) and up to 850 ° C, until obtaining the desired transformation of the salts used during the preparation.

Salts other than chlorides can be used which are soluble and decomposable in the corresponding oxides or other compounds by heating to the calcination temperatures. Salts used are nitrates, formates, acetates or other soluble salts of organic acids which are decomposable by heating at calcination temperatures. If chlorides are used, the residual chlorine content after calcination is less than 3-4% by weight.

In the precursors, the Cu compounds, expressed as metal, are present in quantities of 2-10% by weight, preferably 3.5-8% by weight. Preferred precursor compositions expressed as percent by weight of metal are: Cu = 3.5-8%; K = 0.6-3%; Cs = 0.15-3%; Mg = 0-1%.

The Cu / K atomic ratio is 1: 0.01-1, the Cu / Cs ratio is 1: 0.01-0.5, the Cu / Mg ratio is 1: 0.01-1.1. Preferred atomic ratios are Cu / K = 1: 0.01-1; Cu / Cs = 1: 0.1-0.2; Cu / Mg = 1: 0.1-0.5. The surface area of the precursors is 80-210 m <z> / g, the pore volume of 0.2-0.6 ml / g, which results in an average radius of 2-15 nm.

The precursors prepared according to the methodology object of the present invention differ from the catalysts having the same content of active phase expressed as copper and other metals, prepared by impregnating a pre-formed support with the solution of the salts using the dry ~ impregnation, incipient methods wetness impregnation, dipping, by having a uniform distribution of the active phase and of the compounds of the other metals through the section of the precursor tablet (absence of concentration gradients).

The boehmite used for the preparation of the precursor is preferably the boehmite SASOL Pural SCC 150, which is transformed by heating into gamma-Al203 at the calcination temperatures. The precursor granules have a defined geometric shape.

As already mentioned, the shape of the catalyst is important. A particularly advantageous shape is that of the cylindrical type, provided with one or more through holes or with a three-lobed circular cross-section with through holes with axes generally parallel and equidistant from each other. This particular shape is obtained with the tableting technique. The extrusion technique can also be used, except for a more complex and expensive set-up for obtaining pellets with constant shape and size.

Tablets having the three-lobed geometric configuration indicated above are described for example in USP 5,905,054. The advantages offered by these forms are:

- minimum resistance to diffusion, due to very low wall thicknesses;

- minimum resistance to the passage of gases, which allows to operate with lower pressure drops in the reactors.

The following examples are provided for illustrative but not limitative purposes of the scope of the invention.

EXAMPLE 1

Preparation of precursor in the form of a perforated cylinder

769.2 g of SASOL Pural SCO 150 boehmite with the following characteristics:

Weight loss at 1000 ° C = 22.4%

Granulometry :

Particles larger than 250 microns = 0.7% weight;

Particles between 100 and 250 microns 56.3% by weight;

Particles between 63 and 100 microns = 27.3% by weight;

Particles smaller than 63 microns = 15.7% by weight;

Loose bulk density = 0.66 g / ml;

were impregnated in a rotating jar, at room temperature, with 300 ml of an aqueous solution containing:

CUC12 * 2H20 = 115.6 g;

Kcl 24.1 g;

CsCl = 23.5 g;

MgCl2 * 6H20 = 9.3 g.

The impregnated powder is dried at 100 ° C for 16 hours in an oven, previously brought to the desired temperature.

480 grams of dried powder is mixed with 20 grams of Aluminum tri-stearate (tableting aid) and subsequently tableted in the form of a perforated cylinder.

This is followed by calcination at 800 ° C in a muffle for the transformation of boehmite into gamma alumina.

The pads obtained are in the form of a perforated cylinder having a height of 4.9 mm, an external diameter of 4.9 mm and an internal diameter of 2.5 mm.

The chemical-physical characteristics of the precursor Al are reported in Table 1.

EXAMPLE 2

Preparation of the trilobate precursor with three through holes

768.2 g of SASOL Pural SCO 150 boehmite, having the same characteristics mentioned in example A1, were impregnated in a rotating jar, at room temperature, with 300 ml of an aqueous solution containing:

CUC12 * 2H20 115.8 g;

Kcl 24.5 g;

CsCl 23.8 g;

MgCl2 * 6H20 9.4 g.

The impregnated powder is dried at 100 ° C for 16 hours in an oven, previously brought to the desired temperature.

480 grams of dried powder is mixed with 20 grams of Aluminum tri-stearate (tableting aid) and subsequently tableted in the form of a trilobate having three through holes.

This is followed by calcination at 800 ° C in a muffle to transform the boehmite into gamma alumina and to obtain the catalyst precursor.

The pads obtained are cylindrical-shaped, 4.5 mm high, with a trilobal cross section in which there are three through and equidistant holes with a diameter of 1.7 mm in correspondence with the lobes. The diameter of the circumscribed circumference is 6 mm.

The physico-chemical characteristics of the precursor A2 are reported in Table 1.

COMPARISON EXAMPLE 1

Preparation of the catalyst in the form of a perforated cylinder

100 g of basic support tablets of γ-

AI2O3 are impregnated in a rotating jar with 52 ml of an aqueous solution containing:

CUC1Z * 2H20 = 20.3 g;

Kcl ~ 4.2 g;

CsCl = 4.1 g;

MgClz * 2H20 2, 2 g;

HC1 37% weight = 3 ml.

The tablets obtained were dried in an oven at 100 ° C for 16 hours.

The alumina tablets used are prepared by tableting in the form of a perforated cylinder of a mixture of Boehmite SASOL Pural SCC 150 and aluminum-stearate (3% by weight) and their subsequent calcination at a temperature of 700 ° C for 4 hours. The morphological characteristics of the substrate used are as follows: a specific BET surface of 188 m <2> / g, a pore volume of 0.50 cm <3> / g, an apparent density of 1.24 g / cm <3>, real density of 3.28 g / cm <3>; the mean pore radius was 53 A.

COMPARISON EXAMPLE 2

Commercial catalyst

Commercial catalyst composed of CuClz-KCl-CsCl-MgO / gamma-Al203 having the shape of a perforated cylinder (single through hole), the dimensions of which are: height = 4.7 mm; outer diameter = 4.7mm, inner diameter = 2.1mm.

COMPARISON EXAMPLE 3

Commercial catalyst

Commercial catalyst composed of CuCl2-KCl-MgO / gamma-Al203 having the shape of a perforated cylinder (single through hole), the dimensions of which are: height = 5.0 mm; outer diameter = 5.0 mm; internal diameter = 2.4 mm.

COMPARISON EXAMPLE 4

Preparation of catalyst according to patent application EP 0209732

600 g of alumina powder range SASOL Puralox SCCA 30/210 from a fluidized bed, having the following characteristics:

Surface area 214 m <2> / g

Total Pore Volume = 0.49 cm <3> / g

Granulometry :

Particles with a diameter greater than 125 microns = 0.7% weight;

Particles with a diameter between 90 and 125 microns = 3.7% weight;

Particles with a diameter between 63 and 90 microns = 25.5% by weight;

Particles with a diameter between 40 and 63 microns = 35.0% by weight;

Particles with a diameter of less than 40 microns = 35.8% weight.

Loose Bulk density = 0.71 g / ml.

were impregnated in a rotating jar, at room temperature, with 300 ml of an aqueous solution containing:

CuCl2 * 2H20 = 118.7 g;

Kcl = 25.2 g;

CsCl = 25.3 g;

MgClz * 6H20 = 6.2 g.

The impregnated powder was dried at 80 ° C for 1 night, then at 120 ° C for 3 hours and finally at 210 ° C for 3 hours in an oven.

500 grams of dried powder was mixed with 20 grams of Aluminum tri-stearate (tableting aid) and subsequently tableted in the form of a perforated cylinder.

The pads obtained are in the form of a perforated cylinder having a height of 5.0 mm, an external diameter of 5.2 mm and an internal diameter of 2.5 mm.

The physico-chemical characteristics of the catalyst precursor Comparative Example 4 are reported in Table 1.

The catalyst has NOT satisfactory mechanical resistance characteristics; Axial Breaking Load = 22.3 / - 10 kg / plt vs the acceptable value> 40 kg / plt; Radial Breaking Load = 0.7 / - 0.2 kg / plt vs acceptable values> 1.2 kg / plt; dust a lot.

Since the catalyst had NOT satisfactory mechanical qualities, it has not been tested in a pilot plant at the moment.

COMPARISON EXAMPLE 5

Preparation of the trilobate catalyst having three through holes

200 g of AI2O3-based support tablets are impregnated in a rotating jar with 100 ml of an aqueous solution containing:

CUC12 * 2HzO = 38.6 g;

Kcl = 8.2 g;

CsCl 7.9 g;

MgCl2 * 2H20 = 3.1 g;

HCl 37% by weight 6 ml.

The tablets obtained were dried in an oven at 100 ° C for 16 hours.

The support tablets used are prepared by tableting in trilobate form with three through holes of a mixture of Boehmite of Boehmite SASOL Pural SCC 150 and aluminum-stear ato (3% by weight) and their subsequent calcination at a temperature of 700 ° C for 4 hours. The morphological characteristics of the substrate used are as follows: a specific BET surface of 194 m <2> / g, a pore volume of 0.48 cm <3> / g, an apparent density of 1.28 g / cm <3>, real density of 3.27 g / cm <3>; the average pore radius was 4.9 mm.

The chemical, physical and morphological characteristics of the comparative precursors and of the catalysts obtained from them are reported in Table 1.

Catalytic tests and durability tests in a pilot plant.

- Loading the catalyst into the reactor

64 ml of cylindrical graphite and 23 ml of previously weighed catalyst (approximately 14 g) are measured in a 100 ml glass cylinder. It is mixed in a plastic bag in order to homogenize the mixture. The mixture is then loaded into the reactor to a height of 16 cm on a foot of approx. 30 cm of irregular graphite. Above the catalytic bed, approx. 66 ml of soapstone rings. The reactor has a height of 129 cm and a useful section of 5.23 cm <2>. The reactor is equipped with a thermostating jacket in which oil circulates and, internally and in a coaxial position, with a sheath in which it houses a bundle of thermocouples for measuring the temperature.

- Test conditions.

The reagent gases are sent when the reactor has reached the temperature of 250 ° C in the sequence: N2, HC1, C2H4 and lastly 02. The test conditions include:

- Linear speed = 5.7 cm / s (speed calculated with the reactor empty and under process conditions);

- Pressure = 1.3 ata;

- Contact time = 2.8 seconds;

- Total reagent flow = 66.5 Nl / h;

- Molar ratio Cl / C = 0.69;

- Molar ratio O2 / C2H0 = 0.35.

The test was carried out continuously at a constant cooling fluid temperature of 250 ° C, measuring the temperatures of the six thermocouples placed inside the catalytic bed every 6 hours, in order to check the progress of the activity. The TC1 and TC6 thermocouples are placed 1 cm from the inlet of the reagents and at the end of the catalytic bed, the others 4 and 3 cm away from each other.

The 1 hour DCE sampling was performed after approximately 75 hours. The results are reported in Table 2.

Table 1 Characteristics of precursors and their catalysts used *

• By catalysts used we mean the precursors transformed into catalyzed use in the oxychlorination reactor.

Table 2 Results of the tests in the pilot plant

Claims (16)

R I V E N D I C A Z I O N I 1. Precursors of catalysts usable in the fixed bed oxychlorination of ethylene to 1,2-dichloroethane in the form of hollow granules having a defined geometric configuration, comprising oxides and / or oxygenated compounds of copper in quantities expressed as metallic copper of 2-10% by weight, supported on alumina granules, said precursors having a content of chlorinated compounds expressed as chlorine of 0 to 4% by weight and having uniform distribution of the copper compounds in the cross section of the granules of the precursor. 2. The precursors of claim 1, comprising oxygenated potassium compounds in quantities expressed as potassium metal of 0.5 to 3% by weight, and optionally oxides and / or oxygenated compounds of the metals selected from the alkali metals, in quantities as alkali metal of 0.5-3% by weight, alkaline earth metal of 0.05-2% by weight and rare earth metal of 0.1-3% by weight, wherein the content of chlorinated compounds expressed as chlorine is 0 to 3% by weight. 3. The precursors of claim 1, having a chlorine content after use in the oxychlorination process of 3-10% by weight. The precursors of each of claims 1 to 3, wherein the content of the supported compounds expressed as metal is 3-8% by weight for copper, 0.6-3% by weight for potassium, 0.1- 1% by weight for magnesium and 0.15-3% by weight for cesium. 5. The precursors of each of claims 1 to 4, wherein the surface area (BET) is 80-210 m <2> / g, the pore volume 0.2-0.6 ml / g and the mean pore radius from 2 to 15 nm. 6. The precursors of any one of claims 1 to 5 supported on gamma alumina granules. The precursors of any one of claims 1 to 6 wherein the hollow granules have a cylindrical configuration with at least one through hole. 8. The precursors of claim 7, in which the granules have a circular cross section having in correspondence of the lobes three through holes parallel to the axis of the granule. 9. The precursors according to claim 7, wherein the granules have an axial breaking strength of 40 to 80 kg / part. and radial breaking strength of 1.2 to 3 kg / part. 10. A method for the preparation of the precursors of each of claims 1 to 9 comprising the step of impregnating powdered boehmite or its mixtures with smaller proportions of gamma alumina and / or aluminum silicate with a solution of a salt of the metals forming the components of the precursor as defined in claims 1 to 9, drying of the impregnated boehmite followed by calcination carried out at a temperature from 500 ° C to 850 ° C to obtain the transformation of the boehmite into gamma alumina. The method according to claim 10, wherein the soluble salts used are decomposable by heating at the calcination temperature into the corresponding oxides and / or oxygenated compounds and carbon dioxide when the salts derive from organic carboxylic acids or other volatile compounds. 12. The method according to claim 11, in which the impregnation is carried out using the chlorides of the metals indicated in claim 9 and the calcination is prolonged until a chlorine content of less than 3% by weight is obtained. 13. A process for the oxychlorination of ethylene to 1,2-dichlor cetane carried out using three reactors in series, in which the first reactor is loaded with a precursor according to claims 1 to 9. 14. The process according to claim 13, wherein it is carried out at a temperature from 200 ° C to 300 ° C using oxygen as oxidant and molar ratios HC1 / C2H0, 02 / C2H4 and HCl / 02 respectively of 0.15 to 0.50 0.04 to 0.10 and 3.2 to 5.8. The catalysts obtained from the precursors of claims 1 to 9 using the precursors in oxychlorination processes according to claims 13 and 14. 16. The catalysts of claim 15, wherein the chlorine content is 3-10% by weight.