CN102247876B - A method for the selective catalytic hydrogenation of acetylene to produce ethylene - Google Patents

Abstract

The invention relates to a method for preparing ethylene through selective catalytic hydrogenation of acetylene, using molybdenum phosphide (MoP) as a catalyst. For pure-phase MoP catalysts, at normal pressure, 200-240°C, H ₂ /C ₂ H ₂ =4-8, and space velocity 36,000h ^-1 , the catalytic hydrogenation conversion rate of acetylene is still more than 99.5%. 76% ethylene selectivity; for supported molybdenum phosphide catalyst (20-35wt% MoP/SiO ₂ ), the ethylene selectivity still exceeds 70% when the acetylene catalytic hydrogenation conversion rate is 99.8%. Compared with traditional noble metal catalysts (such as palladium catalysts), molybdenum phosphide catalysts have the advantages of high catalytic hydrogenation activity and selectivity, simple preparation methods, and low prices.

Description

A method for the selective catalytic hydrogenation of acetylene to produce ethylene

technical field

The invention relates to a method for preparing ethylene by selective catalytic hydrogenation of acetylene, using molybdenum phosphide as a catalyst, and using the catalyst for selective catalytic hydrogenation to remove a small amount of acetylene in ethylene.

Background technique

The process of producing ethylene in industry mainly involves the cracking of hydrocarbons to ethylene and the selective catalytic hydrogenation of acetylene to ethylene. The ethylene gas produced by these processes still contains a small amount of acetylene. The presence of trace amounts of acetylene will poison and deactivate the ethylene polymerization catalyst, which will deteriorate the performance of the final polymer. Therefore, the trace amount of acetylene must be removed from the ethylene feed gas before the polymerization reaction. From the current research results, the selective hydrogenation of acetylene to ethylene by selective catalytic hydrogenation is the most feasible and valuable method. However, the hydrogenation reaction of acetylene is a series reaction (C ₂ H ₂ →C ₂ H ₄ →C ₂ H ₆ ), and the ethylene formed during the hydrogenation reaction is very easy to be further hydrogenated to ethane, which leads to a decrease in the selectivity of ethylene with With the increase of acetylene conversion rate, it decreases sharply, even for Pd catalysts with high trace acetylene removal capacity (US 20090326288; US 20040074220; CN 1317367; CN 1657513; CN 1151908; A.Sarkany, A.Beck, L. Guczi. Appl. Catal. A, 2003, 253: 283; W. Huang, JRMcCormick, JG Chen. J. Catal., 2007, 246: 40). Among numerous researches at present, mainly still concentrate on the research to Pd catalyst system, and Ag, Co, Cu, Cr, alkali metal, metal oxide and lead acetate are known auxiliary agents (US 7247760B2 that can improve palladium catalyst performance; W. Huang, W. Pyrz, JG Chen. Appl. Catal. A, 2007, 333: 254; JHKang, EW Shin, SH Moon. Catal. Today, 2000, 63: 183; Y. Jin, AK Datye, J. Blackson, J. Catal., 2001, 203:2001). Judging from the current research results, the high catalyst cost is one of the important factors that limit the further application of this technology, and the research on non-precious metal catalysts is still rare. Therefore, how to reduce the cost of catalysts and improve the selectivity and activity of catalysts has always been the focus of this research, and it is imperative to develop a catalyst with low cost, high activity and high selectivity. For this reason, researchers at home and abroad are still actively exploring new catalyst systems for selective catalytic hydrogenation to remove trace acetylene from ethylene.

Transition metal phosphides are another catalyst material with good hydrogenation performance after nitrides and carbides. They have good hydrogen-related reaction performance in catalytic hydrogenation reactions. In recent years, they have been used in hydrodenitrogenation and desulfurization of fuel oil. Good results have been obtained in the research (D.C.Phillips, S.J.Sawhill, R.Self, M.E.Bussell.J.Catal., 2002, 207:266; F.Sun, Z.Jiang, C.Li.J.Catal. , 2004, 228: 298). For the first time, our research group carried out the research on the gas-phase hydrogenation of acetonitrile to ethylamines using molybdenum phosphide as a catalyst, and achieved a series of significant results. The application of molybdenum phosphide catalysts in other hydrogenation reaction systems is seldom, so the application field of molybdenum phosphide as a new hydrogenation catalyst is further developed, whether it is for the development of molybdenum phosphide catalysts or the application of hydrogenation catalytic reactions. The development has important academic significance and application value, and the research on the use of molybdenum phosphide for the selective catalytic hydrogenation of acetylene to prepare ethylene has not been reported.

Contents of the invention

The purpose of the present invention is to provide a method for preparing ethylene by selective catalytic hydrogenation of acetylene using molybdenum phosphide catalyst; the preparation method of the catalyst is simple, the catalyst cost is low, the activity of acetylene hydrogenation is high, and the acetylene hydrogenation activity remains high under the condition of high acetylene conversion rate. Higher ethylene selectivity.

To achieve the above object, the technical solution of the present invention is achieved through the following steps:

A method for preparing ethylene by selective catalytic hydrogenation of acetylene, using molybdenum phosphide as a catalyst.

The molar ratio of molybdenum to phosphorus in the molybdenum phosphide is 0.9-1.1.

The reaction pressure is normal pressure, the reaction temperature is 200-240°C, the molar ratio of H ₂ /C ₂ H ₂ =4-8, and the space velocity is 33,000-38,000h ^-1 .

The molybdenum phosphide catalyst is pure phase molybdenum phosphide or supported molybdenum phosphide with _SiO2 as carrier.

In the SiO ₂ supported molybdenum phosphide catalyst, the weight percentage of molybdenum phosphide is 20-35wt%.

The pure-phase MoP is prepared by high-temperature hydrogen temperature-programmed reduction, while the supported molybdenum phosphide is prepared by loading the active components Mo and P on the _SiO2 carrier by wet impregnation method, and then by high-temperature hydrogen temperature-programmed reduction.

In the above technical solution, the molar ratio of molybdenum and phosphorus in the precursor of pure-phase MoP is 0.90-1.10. Under normal pressure, reaction temperature of 200-240°C, H ₂ /C ₂ H ₂ =4-8, the selectivity of ethylene remains above 76% when the conversion rate of acetylene reaches 99.5%.

The molybdenum and phosphorus feeding ratio of the supported MoP catalyst is 1, and the MoP loading is 20-35 wt%. Under normal pressure, reaction temperature of 200-240°C, and H ₂ /C ₂ H ₂ =4-8, the ethylene selectivity of more than 70% can still be maintained when the conversion rate of acetylene reaches 99.8%.

The raw materials used in the catalyst component of the present invention are: the molybdenum element is selected from ammonium molybdate or molybdenum trioxide. Phosphorus is selected from ammonium phosphate.

The preparation method of the catalyst involved in the present invention is: firstly, dissolving molybdenum-containing compound and ammonium phosphate salt in a certain molar ratio in distilled water and mixing them, then evaporating the liquid to dryness, drying at 120°C for 10-24 hours, and roasting at 450-650°C for 2 ~8 hours. Then, the calcined molybdenum phosphide precursor was subjected to multi-stage temperature-programmed reduction under hydrogen atmosphere. The reduction conditions are: from room temperature to 250-400°C at a heating rate of 2-10°C/min, from 250-400°C to 550-900°C at a heating rate of 0.5-2°C/min, and at the end Keep warm for 2-4 hours. After the reaction is finished, passivate the product with a passivation gas with an oxygen concentration of 0.5-1.5% at room temperature to obtain a pure-phase MoP catalyst.

The preparation process of supported molybdenum phosphide is similar to that of pure phase molybdenum phosphide, the difference is that the molybdenum-containing compound and ammonium phosphate salt with a molar ratio of 1 are dissolved and mixed, and then impregnated on the _SiO2 carrier.

Compared with known technology, the present invention has the following advantages:

This method uses non-noble metal MoP catalysts for the selective catalytic hydrogenation of acetylene to produce ethylene. When the reaction space velocity is high (36,000h ^-1 ), for the MoP and MoP/SiO ₂ catalysts, the conversion rate of acetylene hydrogenation and the hydrogenation product ethylene The selectivity can reach 99% and 70% respectively. Compared with traditional noble metal catalysts (such as palladium catalysts), molybdenum phosphide catalysts have the advantages of simple preparation method, low price and high catalytic hydrogenation activity and selectivity.

For pure-phase molybdenum phosphide, it exhibits good acetylene catalytic hydrogenation activity at high reaction space velocity (36,000h ^-1 ) and wide reaction temperature range (200-240°C). High ethylene selectivity can still be maintained. For the supported molybdenum phosphide catalyst with SiO ₂ as the carrier, it has higher catalytic hydrogenation activity of acetylene and selectivity of product ethylene, and can obtain high catalytic hydrogenation at lower molar ratio of H ₂ /C ₂ H ₂ Hydrogen activity and selectivity. Compared with traditional noble metal catalysts (such as palladium catalysts), molybdenum phosphide catalysts have the advantages of simple preparation method, low price and high catalytic hydrogenation activity and selectivity.

Under the operating conditions, the catalyst can be used to obtain an acetylene conversion rate higher than 99.5% and an ethylene selectivity higher than 70%.

Detailed ways

The present invention uses the above catalyst to carry out selective catalytic hydrogenation, the main steps are: a certain amount of MoP or MoP/ _SiO2 catalyst is loaded into a fixed-bed reactor, and the The catalyst is pretreated for 1 hour; after the pretreatment is completed, it is naturally cooled to the set reaction temperature, and the reaction raw material gas is fed according to a certain ratio of H ₂ /C ₂ H ₂ . The catalytic hydrogenation performance of acetylene was investigated under normal pressure, 200-240°C, H ₂ /C ₂ H ₂ =4-8, and space velocity of 33,000-38,000 h ^-1 .

In order to further illustrate the present invention, the following examples are given without limiting the scope of the invention defined by the appended claims.

Example 1

The pure-phase molybdenum phosphide prepared with a molar ratio of molybdenum to phosphorus of 1 is used as a catalyst, and the hydrogenation reaction of acetylene is carried out in a miniature fixed-bed reactor. Feed gas composition: 1.0vol% acetylene and 99.0vol% Ar mixed gas, reaction conditions: 0.10g catalyst, temperature 200°C, normal pressure, H ₂ /C ₂ H ₂ =8, feed gas flow rate 60mL/min, Airspeed 36,000h ^-1 . Product analysis was performed using Agilent gas chromatography with a hydrogen flame detector.

Example 2

Same as in Example 1, using pure-phase molybdenum phosphide with a molar ratio of molybdenum to phosphorus of 0.9 as the catalyst, the reaction results are listed in Table 1.

Example 3

Same as in Example 1, using pure-phase molybdenum phosphide with a molar ratio of molybdenum to phosphorus of 0.95 as the catalyst, the reaction results are listed in Table 1.

Example 4

Same as in Example 1, using pure-phase molybdenum phosphide with a molar ratio of molybdenum to phosphorus of 1.05 as the catalyst, the reaction results are listed in Table 1.

Example 5

Same as in Example 1, using pure-phase molybdenum phosphide with a molar ratio of molybdenum to phosphorus of 1.10 as the catalyst, the reaction results are listed in Table 1.

Example 6

As in Example 1, the hydrogenation activity of acetylene was investigated at a reaction temperature of 200° C., and the reaction results are listed in Table 1.

Example 7

As in Example 1, the hydrogenation activity of acetylene was investigated at a reaction temperature of 220° C., and the reaction results are listed in Table 1.

Example 8

As in Example 1, the hydrogenation activity of acetylene was investigated at a reaction temperature of 240° C., and the reaction results are listed in Table 1.

Example 9

As in Example 7, the hydrogenation activity of acetylene was investigated under the condition of H ₂ /C ₂ H ₂ =8, and the reaction results are listed in Table 1.

Example 10

As in Example 7, the hydrogenation activity of acetylene was investigated under the condition of H ₂ /C ₂ H ₂ =6, and the reaction results are listed in Table 1.

Example 11

As in Example 7, the hydrogenation activity of acetylene was investigated under the condition of H ₂ /C ₂ H ₂ =4, and the reaction results are listed in Table 1.

Example 12

Same as in Example 1, with mesoporous _SiO2 as the carrier, the prepared molybdenum-phosphorus molar ratio is 1, and the supported molybdenum phosphide with the weight loading of MoP is 15% as the catalyst. At a reaction temperature of 220°C, _H2 / _{C2H 2} = 6, under which the hydrogenation activity of acetylene was examined, and the reaction results are listed in Table 1.

Example 13

As in Example 12, the acetylene hydrogenation activity of the MoP catalyst with a MoP weight loading of 20% was investigated, and the reaction results are listed in Table 1.

Example 14

As in Example 12, the acetylene hydrogenation activity of the MoP catalyst with a MoP weight loading of 25% was investigated, and the reaction results are listed in Table 1.

Example 15

As in Example 12, the acetylene hydrogenation activity of the MoP catalyst with a MoP weight loading of 30% was investigated, and the reaction results are listed in Table 1.

Example 16

As in Example 12, the acetylene hydrogenation activity of the MoP catalyst with a MoP weight loading of 35% was investigated, and the reaction results are listed in Table 1.

Example 17

As in Example 14, the hydrogenation activity of acetylene was investigated at a reaction temperature of 200° C., and the reaction results are listed in Table 1.

Example 18

With embodiment 14, reaction result is listed in table 1.

Example 19

As in Example 14, the hydrogenation activity of acetylene was investigated at a reaction temperature of 240° C., and the reaction results are listed in Table 1.

Example 20

As in Example 14, the hydrogenation activity of acetylene was investigated under the condition of H ₂ /C ₂ H ₂ =8, and the reaction results are listed in Table 1.

Example 21

With embodiment 14, reaction result is listed in table 1.

Example 22

As in Example 14, the hydrogenation activity of acetylene was investigated under the condition of H ₂ /C ₂ H ₂ =4, and the reaction results are listed in Table 1.

Table 1

It can be seen from Table 1 that the pure-phase MoP catalyst has high activity and selectivity for acetylene catalytic hydrogenation at high reaction space velocity (33,000-38,000h ^-1 ) and wide reaction temperature range (200-240°C). When the acetylene conversion rate reaches 99.5%, it can still maintain a hydrogenation selectivity of more than 76%. The supported MoP/SiO ₂ catalyst can also maintain high acetylene catalytic hydrogenation activity and selectivity in a high reaction space velocity and a wide reaction temperature range; at the same time, it has higher low-temperature acetylene hydrogenation activity and selectivity, When the molar ratio of H ₂ /C ₂ H ₂ is low, the catalytic hydrogenation conversion rate and selectivity of acetylene are higher.

Claims (3)

1. A method for the selective catalytic hydrogenation of acetylene to prepare ethylene, characterized in that: molybdenum phosphide is used as a catalyst; The reaction pressure is normal pressure, the reaction temperature is 200-240°C, the molar ratio of H ₂ /C ₂ H ₂ = 4-8, and the space velocity is 33,000-38,000h ^-1 ; The molybdenum phosphide catalyst is pure phase molybdenum phosphide or supported molybdenum phosphide with mesoporous _SiO2 as carrier. 2. The method according to claim 1, wherein the molar ratio of molybdenum to phosphorus in the molybdenum phosphide is 0.9-1.1. 3. The method according to claim 1, characterized in that: in the mesoporous _SiO2 supported molybdenum phosphide catalyst, the weight percentage of molybdenum phosphide is 20-35wt%.