Paraffin hydrofining catalyst and preparation method thereof
Technical Field
The invention relates to a paraffin hydrofining catalyst and a preparation method thereof.
Background
The paraffin takes normal paraffin as a main component, is solid at normal temperature, has a large average molecular weight of generally 300-500 and has carbon number of C20-C30. The hydrorefining of paraffin wax includes mixing material wax with hydrogen in certain proportion at certain temperature, reaction of hydrogen with S, N, O and other hetero atoms in the material wax to produce H 2S、NH3、H2O, etc. to remove impurities. As for the paraffin hydrofining catalyst, molybdenum is generally used as a main metal component, and tungsten is also used as a main metal component. In addition to the primary metal component, the hydrotreating catalyst employs a secondary metal component such as nickel or cobalt.
CN111097489A discloses a paraffin hydrofining catalyst and a preparation method thereof. The carrier of the catalyst comprises alumina, layered clay and a Y-type molecular sieve, wherein nickel and molybdenum are used as active metal components, the mass of the catalyst is taken as a reference, the content of the molybdenum oxide is 2.0-35.0%, the content of the nickel oxide is 0.5-20.0%, the dispersity of the active metal components is that IMo/IAl is 0.15-0.30, and INi/IAl is 0.07-0.15. The paraffin hydrofining catalyst improves the utilization rate of active metals from the angle of improving the dispersion degree of the active metals.
CN1393528A discloses a paraffin hydrofining catalyst and a preparation method and application thereof. The carrier is characterized in that titanium dioxide is contained on the surface of alumina through chemical treatment, so that the characteristic of the carrier is improved; the active components of the catalyst adopt a W-Mo-Ni solution one-time impregnation method, and the metal components achieve common competitive adsorption, so that the special paraffin hydrorefining catalyst with higher activity is prepared.
When applied to industrial units, paraffin hydrofinishing catalysts often suffer from reduced catalyst life due to the deposition of carbon deposits. Therefore, the development of the carbon deposition resistant paraffin hydrofining catalyst with long service life is of great significance.
Disclosure of Invention
The invention aims to provide a paraffin hydrofining catalyst and a preparation method thereof, which can prolong the service life of the paraffin hydrofining catalyst and improve the operation period of a paraffin hydrogenation device.
In the hydrogenation process of the existing paraffin hydrofining catalyst, with the prolonging of the service time of the catalyst, the deposited carbon blocks the pore channels to cover active sites, thereby reducing the utilization rate of active metals and shortening the service life of the catalyst.
The invention provides a paraffin hydrofining catalyst, which comprises a catalyst body consisting of a carrier and active components loaded on the carrier, wherein a layer of macroporous alumina layer is arranged on the outer surface of the catalyst body. The pore volume difference value between the catalyst body and the macroporous alumina is more than 0.40cm3Per g, preferably 0.45 to 0.55 cm3/g。
The pore volume of the macroporous alumina layer is more than 0.80cm3Per g (mercury intrusion method), preferably 0.85 to 0.95 cm3The pore volume of pores with the pore diameter of more than 30nm accounts for 20-60 percent of the total pore volume, preferably 40-55 percent, and can contain more carbon deposition.
The thickness of the macroporous alumina layer is 1-400 mu m, and preferably 60-180 mu m.
The catalyst body is characterized as follows: the pore volume is more than 0.35cm3The catalyst comprises, by mass, 2.0-25.0% of tungsten oxide, 2.0-20.0% of molybdenum oxide and 0.4-8.0% of nickel oxide.
In another aspect, the present invention provides a method for preparing a catalyst for hydrorefining paraffin, comprising the following steps:
(1) preparing a paraffin hydrofining catalyst as a catalyst body;
(2) adding the catalyst body obtained in the step (1) into macroporous pseudo-boehmite gel, stirring and soaking, wrapping the surface with gel, taking out, and drying;
(3) and (3) roasting the catalyst particles obtained in the step (2) to prepare the paraffin hydrofining catalyst.
The paraffin hydrofining catalyst in the step (1) has a pore volume of more than 0.35cm3Catalyst for hydrorefining paraffin wax/g catalyst for hydrorefining paraffin waxThe active metal in the catalyst is preferably tungsten, molybdenum and/or nickel, and based on the mass of the catalyst body, the content of tungsten oxide is 2.0-25.0%, the content of molybdenum oxide is 2.0-20.0%, and the content of nickel oxide is 0.4-8.0%.
Preferably, the catalyst body is soaked in a binder solution before being added to the macroporous pseudo-boehmite gel in step (2). The adhesive solution is composed of an adhesive and purified water. The mass content of the binder in the binder solution is 1% to 80%, preferably 2% to 30%. The adhesive can be one or more of starch, dextrin, polyvinyl alcohol or carboxymethyl cellulose.
Preferably, the catalyst body is soaked in the adhesive solution for 10-50 seconds, excessive adhesive solution is drained, and the catalyst body is placed at room temperature for 15-60 minutes.
The property of the macroporous pseudo-boehmite gel converted into macroporous alumina in the step (2) is as follows: the pore volume is more than 0.80cm3The mercury vapor compression method has through-holes, the pore volume of the pores with the pore diameter larger than 30nm accounts for 20-60% of the total pore volume, and the carbon deposition can be accommodated. Wherein the macroporous pseudo-boehmite gel is converted into macroporous alumina by roasting at the temperature of 450-650 ℃ for 3-6 hours. The macroporous pseudo-boehmite gel can be obtained by adopting an inorganic aluminum source as a raw material, adding no template agent, adjusting the pH value to 2.8-3.2, and performing hydrothermal treatment at 180-300 ℃ for 3-6 hours. The concentration of the alumina in the macroporous pseudo-boehmite gel is 20 g/L-100 g/L, and the preferred concentration of the alumina is 20 g/L-70 g/L.
And (3) adding the catalyst particles in the step (2) into the macroporous pseudo-boehmite gel, stirring, soaking for 10 s-20 min, wrapping the surface with the gel, taking out, centrifuging by using a centrifugal machine to remove the redundant gel on the surface, and drying for 2-12 hours at the temperature of 80-150 ℃. The thickness of the alumina film layer can be controlled by controlling the concentration of alumina in the macroporous pseudo-boehmite gel, the soaking time and the centrifugation time.
In the step (3), the roasting adopts temperature programming. The roasting conditions are as follows: the heating rate is 1-3 ℃/min, the roasting temperature is 450-650 ℃, and the roasting time is 3-6 hours. After roasting, an alumina coating layer with the thickness of 1-400 mu m, preferably 60-180 mu m, can be formed on the surface of the catalyst.
The method has the advantage that the surface of the paraffin hydrofining catalyst body is coated with macroporous alumina. In the hydrogenation process, the generated carbon deposit is firstly deposited in the alumina pore channels on the surface, and the membrane layer has the through pore channels, so that the carbon deposit can not block the pore channels, wax materials can enter the catalyst body to carry out hydrogenation reaction, the carbon deposition resistance of the catalyst is improved, the stability of the catalyst is good, and the service life of the catalyst is prolonged.
The pore volume of the macroporous alumina on the outer layer of the catalyst body needs to be 0.40cm larger than that of the catalyst body3The catalyst has the advantages that the catalyst can ensure that even if carbon deposit occurs in the macroporous alumina, pore channels of the macroporous alumina at the outer layer cannot be blocked, and wax materials can normally enter the catalyst body to carry out hydrogenation reaction.
Detailed Description
The following examples are given to further illustrate the effects and effects of the method of the present invention, but are not limited thereto.
The pore volume and the pore diameter of the alumina with the macroporous outer surface related in the examples and the comparative examples are obtained by mercury intrusion method tests, and the pore volume, the pore diameter and the specific surface area of the desulfurization catalyst and the carrier are obtained by nitrogen adsorption and desorption experiments.
Example 1
(1) 200g of a catalyst for hydrorefining of paraffin was prepared, the pore volume of the catalyst being 0.40cm3In the catalyst, the content of tungsten oxide is 10.5 percent, the content of molybdenum oxide is 18.0 percent, and the content of nickel oxide is 4.5 percent
(2) Preparing a binder solution: dissolving 20 g of starch in 500 g of purified water under the condition of heating and stirring, and stirring and dissolving uniformly;
(3) preparing macroporous pseudo-boehmite gel: 20 g of aluminum sulfate is weighed, the pH value is adjusted to be 3.0, and the mixture is subjected to hydrothermal treatment for 3 hours at 180 ℃. The concentration of alumina in the macroporous pseudo-boehmite is 25 g/L.
(4) And (3) soaking the dried catalyst particles obtained in the step (1) in the binder obtained in the step (2) for 20 seconds, taking out, draining off excessive binder solution, and standing at room temperature for 30 minutes.
(5) Adding the catalyst particles obtained in the step (4) into the macroporous pseudo-boehmite gel obtained in the step (3), stirring for 2min, wrapping the gel on the surface, taking out, centrifuging for 3min by using a high-speed centrifuge, and drying for 5 hours at 120 ℃.
(6) Roasting: heating to 500 deg.C at a temperature rise rate of 1 deg.C/min by temperature programming, and calcining for 4 hr to obtain paraffin hydrorefining catalyst A with a macroporous alumina film layer thickness of 117 μm and pore volume of 0.87cm3The pore volume of pores with a pore diameter of more than 30nm accounts for 45 percent of the total pore volume. The pore volume difference value of the macroporous alumina membrane layer and the paraffin hydrofining catalyst body is 0.47cm3/g。
Example 2
Same as example 1 except that the pH was adjusted to 2.9 in step (3), and the mixture was subjected to hydrothermal treatment at 180 ℃ for 3.5 hours. The concentration of alumina in the macroporous pseudo-boehmite is 70 g/L, thus obtaining the catalyst B for hydrorefining the paraffin wax wrapping the alumina, wherein the thickness of a macroporous alumina film layer is 165 mu m, and the pore volume is 0.90cm3The pore volume of pores with the pore diameter of more than 30nm accounts for 49 percent of the total pore volume. The pore volume difference between the macroporous alumina and the catalyst body is 0.50cm3(ii) in terms of/g. Other properties were the same as in example 1.
Example 3
As in example 1, except that 20 g of dextrin was dissolved in 100 g of purified water under heating and stirring in step (2) to prepare a binder solution, and the binder was soaked in the solution for 10S in step (4) and left at room temperature for 50 minutes. The pH was adjusted to 3.1 in step (3), and hydrothermal treatment was carried out at 250 ℃ for 5 hours. The concentration of alumina in the macroporous pseudo-boehmite is 40g/L, namely the catalyst C for hydrorefining the paraffin coated with the alumina is obtained, the thickness of a macroporous alumina membrane layer is 135 mu m, and the pore volume is 0.89cm 3The pore volume of pores with the pore diameter of more than 30nm accounts for 47 percent of the total pore volume. The pore volume difference between the macroporous alumina and the catalyst body is 0.49cm3(ii) in terms of/g. Other properties were the same as in example 1.
Example 4
Same as the embodiment1, only immersing the catalyst particles in the step (5) into the macroporous pseudo-boehmite gel in the step (3), stirring for 2min, wrapping the gel on the surface, taking out, centrifuging for 6min by using a high-speed centrifuge, and drying for 8 hours at the temperature of 90 ℃. Heating to 600 deg.C at a rate of 2 deg.C/min, and calcining for 5 hr to obtain alumina-coated paraffin hydrorefining catalyst D with a macroporous alumina film layer thickness of 84 μm and pore volume of 0.88cm3The pore volume of pores with a pore diameter of > 30nm is 46% of the total pore volume. The pore volume difference between the macroporous alumina and the catalyst body is 0.48cm3(iv) g. Other properties were the same as in example 1.
Example 5
The same as example 1, except that the concentration of alumina in the macroporous pseudo-boehmite is adjusted to be 50 g/L in the step (3), meanwhile, the catalyst particles in the step (5) are immersed in the macroporous pseudo-boehmite gel in the step (3) and stirred for 18min, the gel is coated on the surface of the gel and taken out, the gel is centrifuged by a high-speed centrifuge for 6min, and the alumina-coated paraffin hydrofining catalyst E is obtained, wherein the thickness of the macroporous alumina membrane layer is 141 mu m, and the pore volume is 0.87cm 3The pore volume of pores with a pore diameter of more than 30nm accounts for 45 percent of the total pore volume. The pore volume difference between the macroporous alumina and the catalyst body is 0.47cm3(ii) in terms of/g. Other properties were the same as in example 1.
Example 6
In the same way as example 1, only the steps (1), (3), (5) and (6) are carried out, and the steps (2) and (4) are not carried out, thus obtaining the alumina-coated paraffin hydrofining catalyst F, wherein the thickness of the macroporous alumina membrane layer is 27 mu m, and other properties are the same as example 1.
Comparative example 1
And (3) directly taking the paraffin hydrofining catalyst obtained in the step (1), and marking the catalyst as a paraffin hydrofining catalyst D1.
Comparative example 2
The same as example 1, except that in the aluminum sulfate process using the conventional cocurrent flow method in step (3), 2L of an aqueous solution of sodium metaaluminate (as Al)2O3Concentration of 15g/100 mL) and 3L of aluminum sulfate (as Al)2O3Measured concentration of 3g/100 mL) is gelled under the conditions that the gelling temperature is 60 ℃ and the gelling pH value is 7.3, thus obtaining the productThe obtained alumina film layer has no through pore canal. Finally, pseudo-boehmite gel is obtained, and the paraffin hydrofining catalyst D2 is prepared. The thickness of the macroporous alumina membrane layer is 127 mu m, and the pore volume is 0.65cm3The pore volume of pores with the pore diameter of more than 30nm accounts for 14 percent of the total pore volume, and the pore volume difference value of the macroporous alumina and the catalyst body is 0.25cm 3/g。
The catalysts in the above examples were evaluated by a small paraffin hydrofining evaluation device under the following reaction conditions: the reaction pressure is 6.5MPa, the reaction temperature is 255 ℃, and the LHSV is 1.0h-1The hydrogen wax ratio was 300. The raw wax and corresponding hydrofinished product properties after 2000 hours on stream are shown in table 1.
TABLE 1 raw wax and hydrofinished product Properties
Catalyst numbering
|
Raw material wax
|
A
|
F
|
D1
|
D2
|
Melting point of
|
59.55
|
59.45
|
59.45
|
59.40
|
59.35
|
Oil content, wt%
|
0.20
|
0.20
|
0.21
|
0.23
|
0.24
|
Color (Sai's), number
|
-13
|
+30
|
+29
|
+28
|
+27
|
Penetration (25 deg.C)/10-1mm
|
15
|
15
|
15
|
16
|
17
|
Light stability No.
|
7
|
2~3
|
2~3
|
4
|
4
|
Heat stability No. 1
|
-16
|
29
|
28
|
27
|
26
|
Easily carbonized substance
|
Fail to be qualified
|
Qualified
|
Qualified
|
Qualified
|
Qualified |
As can be seen from Table 1, the paraffin hydrofining catalyst prepared by the invention has better hydrogenation performance than a contrast agent, the reduction of hydrogenation activity is slow after 2000 hours of operation, and the catalyst still has better hydrogenation performance, thereby providing guarantee for prolonging the operation period of a device.