CN1336322A

CN1336322A - Method of preparing gas contg. high concn. of carbon monooxide

Info

Publication number: CN1336322A
Application number: CN 00111253
Authority: CN
Inventors: 程玉春; 郝树仁; 尹长学; 胡玉才; 李春禄; 梁卫忠; 王玲真
Original assignee: Qilu Petrochemical Co of Sinopec
Current assignee: China Petroleum and Chemical Corp
Priority date: 2000-08-01
Filing date: 2000-08-01
Publication date: 2002-02-20
Anticipated expiration: 2020-08-01
Also published as: CN1126710C

Abstract

The present invention relates to technology of preparing high carbon monooxide content gas from conversion of hydrocarbon and carbon dioxide vapor. In said method, light oil, liquified gas or refinery gas and steam and carbon dioxide are sent to reaction bed layer having hydrocarbon vapor conversion catalyst to proceed vapor conversion reaction; to separate high CO content gas from the converted gas, the residual gas is circularted as CO2 raw material; at the same time, larg quantity of external carbon dioxide is added. It is characterized in that not only the carbon in raw material hydrocarbon is converted to carbon monoxide, the added external carbon dioxide also converts into carbon monoxide. Advantages: the carbon source of carbon monoxide is expanded and also it can reduce carbon dioxide pollution to environment.

Description

Method for preparing gas with high carbon monoxide content

The invention relates to a method for preparing gas with high carbon monoxide content by hydrocarbon steam conversion, in particular to a method for preparing low H by one-step conversion reaction of heavy hydrocarbon, water vapor and externally supplied carbon dioxide₂Process for synthesis gas with/CO ratio.

COIs a basic raw material which plays a very important role in the fields of petrochemical industry, fine chemical industry and organic synthesis, in particular to the production of alcohol, aldehyde, ketone, anhydride, acyl chloride, lactone, quinone, phosgene and the like by oxo synthesis, the preparation of solvent, plasticizer and the like. In some fields pure CO is required, while in others H is used, depending on its use₂A syngas with a/CO ratio of 1.0-3.0. At present, reformed gas with relatively high CO content can be obtained by steam reforming reaction using light hydrocarbon raw material, such as light hydrocarbon, water steam and CO in U.S. Pat. No. 4,894,394₂To give H₂A converted gas with CO of 2.8-4.5. But H of such a gas₂The ratio/CO is still relatively high, the CO content is insufficient if the catalyst is used directly as oxo gas, and H is₂The content is excessive. Thus, when syngas is produced by a hydrocarbon steam reforming process, the CO content of the reformed gas must be increased.

The reaction mechanism for steam reforming of hydrocarbons is as follows:

(1)

ΔH＝-206KJ/mol (2)

ΔH＝+247KJ/mol (3)

in which reaction (1) is a strongly endothermic reaction with an increased volume, and the pressure is reduced and the temperature is increased by-41 KJ/mol (4)The reaction is favorably carried out rightwards, and the generation of CO is favorably realized; the reaction (2) is an exothermic reaction with reduced volume, and increasing the temperature, decreasing the pressure and increasing the partial pressure of water will cause the reaction (2) to move to the left, which is beneficial to the generation of CO; reaction (3) is an endothermic reaction with increased volume, increased temperature, reduced pressure and increased CO₂Partial pressure, which will cause reaction (3) to move to the right, favoring the generation of CO; the reaction (4) is an exothermic reaction with invariable volume, and the reaction (4) moves leftwards by increasing the temperature and reducing the water partial pressure, which is favorable forCO is generated. By analyzing the above mechanism of the hydrocarbon steam reforming reaction, it can be known that: increasing reaction temperature, reducing reaction pressure, reducing water-carbon ratio and increasing CO₂The concentration is an important means for increasing the content of CO in the converted gas.

In the above measures for increasing the content of CO, increasing the reaction temperature and decreasing the reaction pressure are limited by the reaction itself, and the effect of increasing the relative content of CO using these reaction conditions is insignificant. While reducing the water-carbon ratio and increasing the CO content in the reaction gas₂When the concentration method is used to increase the relative content of CO, the steam reforming catalyst used must have strong anti-coking capability, and the catalyst should have high reactivity for the reaction (3).

In another patent filed concurrently herewith (title: a method for preparing oxo gas by steam reforming of hydrocarbon andcarbon dioxide), a process for preparing oxo gas by one-step reforming of heavy hydrocarbon feedstock is disclosed, wherein carbon dioxide in the reformed gas is separated and recycled as feedstock, such that carbon dioxide at the inlet and outlet is maintained in equilibrium, whereby substantially all of the carbon in the hydrocarbon feedstock is converted to carbon monoxide, no carbon dioxide emissions are produced during the entire reforming process, and H of the oxo gas produced is produced₂The ratio/CO is also relatively low, but this process has certain limitations because even if the carbon in the hydrocarbon is totally converted to carbon monoxide, the H of the resulting oxo gas is₂The limiting value of the/CO is also around 2.2 (for light oils), if H is to be produced₂Oxo gas or pure CO with/CO<2.0,this method is not very suitable.

The invention aims to provide a process method for preparing gas with high carbon monoxide content by one-step conversion of heavy hydrocarbons such as light oil and the like.

In the present invention, heavy hydrocarbons such as light oil, liquefied gas, or refinery gas, and steam, CO₂Mixing, feeding into a reformer with steam reforming catalyst, and converting in one step to obtain a mixture containing CO and CO₂、H₂And small amountConversion gas of methane; separating the converted gas to separate out gas with high CO content, wherein the rest gas is mainly carbon dioxide and contains a small amount of methane, carbon monoxide and hydrogen; recycling residual gas mainly containing carbon dioxide to the raw material inlet section as raw material CO₂Mixing with hydrocarbons and steam; meanwhile, in order to increase the content of CO, external carbon dioxide is additionally added into a raw material inlet in a large amount so as to convert the carbon dioxide into carbon monoxide.

The high CO content gas described above consists of CO and H₂Composition H₂The ratio of/CO is below 2.0. The method for separating the gas with high CO content from the converted gas can be selected from a PSA (pressure swing adsorption) method, a cryogenic method or a liquid phase method and the like.

The external carbon dioxide can be carbon dioxide exhausted by other devices, can also be carbon dioxide recovered from flue gas of the device, and can also be pure carbon dioxide products. The specific source of carbon dioxide used is determined according to the specific situation and economic benefit.

In the invention, because sufficient carbon dioxide is added as the conversion raw material, the content of carbon monoxide in the converted gas is obviously increased, simultaneously the proportion of hydrogen is obviously reduced, and correspondingly, the concentration of carbon monoxide in the gas with high content of CO prepared by separating the converted gas is also high. The high CO content gas can be used as synthesis gas directly or further separated to prepare pure carbon monoxide.

In the invention, H in the synthesis gas can be effectively adjusted by adjusting the adding amount of the carbon dioxide₂The ratio of/CO. With the increasing of the adding amount of the carbon dioxide, the content of the carbon monoxide in the converted gas is increased continuously, the content of the hydrogen is reduced greatly, and the H of the prepared gas with high CO content₂the/CO ratio is kept below 2.0 and can be gradually reduced to 1.0, 0.8 and even lower, such as about 0.6. Under the test conditions of the present invention, when the amount of carbon in the carbon dioxide added at the raw material inlet reached about 2.5 times the amount of carbon in the light oil, H was added₂The ratio of the/CO can reach about 1.0.

Due to the large amount of carbon dioxideThe process of the invention can be carried out at a lower water-to-carbon ratio (H)₂O/C) performed well. Since carbon dioxide can to some extent play the same role as water in terms of carbon resistance and carbon elimination (compare the following reactions):

(5)

(6) the large amount of carbon dioxide is beneficial to preventing carbon deposition of the catalyst, and the carbon dioxide reacts with hydrocarbon after the water-carbon ratio is reduced

(7) Is greatly increased, and the hydrocarbon is converted with the steam

(8) Thus, the use of a smaller water-to-carbon ratio in the present invention does not affect the performance of the shift catalyst, but is beneficial for reducing H₂The ratio of/CO. Under general operation conditions, the water-carbon ratio of the invention is in the range of 3.0-1.0, and the preferable water-carbon ratio is in the range of 2.5-2.0.

The choice of conversion catalyst is also important to the process of the present invention. Catalyst and process for preparing sameBesides the catalytic active metal elements and the anti-carbon components, the catalyst also contains the components capable of catalyzing the reaction And in addition, selecting proper catalyst carrier. Wherein the catalytically active metal element may be nickel and/or cobalt, preferably nickel; the anti-carbon composition may be a compound or mixture of alkali and/or alkaline earth metals, preferably a potassium compound; the support of the catalyst may be a refractory metal oxide or a mixture thereof, preferably calcium aluminate cement and/or iron cement; catalysis The components of (A) can be selected from iron and/or rare earth elements and the like.

The reduction of the reformer pressure is not only beneficial to increase the content of carbon monoxide in the reformed gas, but also to increase the content of hydrogen in the reformed gas, but also to increase the content of H₂The ratio of/CO does not vary much. However, choosing a lower pressure where permitted can reduce the residual methane content of the reformed gas, making the reforming process more complete and beneficial for the production of high CO content gases. In industrial applications, the pressure is selected in relation to the pressure rating of the system before and after the conversion process, and is generally selected between 1.0MPa and 4.0 MPa.

Although the higher the reaction temperature, the higher the concentration of carbon monoxide in the product gas from the viewpoint of thermodynamic equilibrium, the choice of the reaction temperature is limited by various factors such as the heat resistance of the reformer and the catalyst used. If the reformer tube has good heat resistance, the reaction temperature can be increased accordingly. In the conversion reaction of the invention, the outlet temperature is generally selected within the range of 800-950 ℃, which is beneficial to improving the concentration of carbon monoxide and ensuring that the conversion furnace tube and the catalyst have longer service life.

The process of the invention is used for preparing the gas with high CO content, and has good economic benefit and social benefit. When CO is produced by the conventional light oil steam conversion method, the carbon source is only hydrocarbon, 1 standard cubic meter of CO is produced, and about 1.2Kg of light oil is consumed, but the method of the invention is adopted to produce COWhen producing CO, the carbon source is not only hydrocarbon but also carbon dioxide from the outside, if H is controlled₂The light oil of about 0.4Kg is needed to produce 1 standard cubic meter of CO, which is 1.0/CO. In addition, the added carbon dioxide raw material can utilize carbon dioxide exhausted by other devices or the device, so that an additional carbon source is provided for producing gas with high CO content, and the pollution to the atmosphere can be reduced.

The present invention is further illustrated by the following examples, but the scope of the present invention should not be construed as being limited to the following examples.

Example 1

Filling 10-20 meshes/inch of small catalyst particles in a conversion reaction tube, wherein about 50% of Z405G (volume ratio) is filled in the lower part of the reaction tube, and about 50% of Z409 (volume ratio) is filled in the upper part of the reaction tube; in the reaction tubeThe thermocouple tube is provided, and the thermocouple can move up and down in the thermocouple tube so as to measure the temperature of different positions of the reaction tube; then the catalyst is reduced and heated up, and the temperature is raised under the nitrogen atmosphere, hydrogen and water (H) for reduction₂O/H₂3.0), inlet temperature about 500 deg.c, outlet temperature about 800 deg.c, hydrogen space velocity 1000h^-1The time is about 8 hours.

After the completion of the catalyst reduction, the test was carried out. Desalted water enters a vaporizer to be vaporized through a metering pump, naphtha is mixed with water vapor and carbon dioxide through the metering pump, enters a superheater to be overheated and heated, and then enters a conversion reaction tube to finish conversion reaction. Cooling the converted gas, performing composition analysis by chromatography, separating out gas with high CO content by a PSA method, taking carbon dioxide as the main gas and containing a small amount of methane, carbon monoxide and hydrogen, and recycling the residual gas to a raw material inlet; the carbon dioxide from the outside is sent directly to the feed inlet. The whole reaction process simulates the operation condition of an industrial device, and the bed layer temperature is heated and controlled by four sections of furnace wires outside the reaction tube so as to adjust the inlet, the outlet and the bed layer temperature and ensure the reaction heat supply. The pressure is controlled by a pressure controller, the liquid feeding is controlled and regulated by a micro pump and an electronic balance, the gas feeding is controlled by a gas mass flowmeter, and the chromatographic analysis adopts an external standard method.

The system pressure is 2.0Mpa, the inlet temperature is 480 ℃, the outlet temperature is 860 ℃, the water-carbon ratio is 2.5, and the space velocity of carbon in naphtha is 1610h^-1Under the conditions of (1), the addition of different CO is determined₂The composition of the gas was inverted in the amount, and the results are shown in Table 1. In Table 1, V_CO2/V_CIndicating CO added₂The ratio (mol/mol) of the amount of medium carbon to the amount of carbon in the raw hydrocarbon.

TABLE 1

CO₂Airspeed	CO，％	H₂，％	CO₂，％	CH₄，％	V_CO2/VC	H₂/CO
CO₂Airspeed	CO，％	H₂，％	CO₂，％	CH₄，％	V_CO2/VC	H₂/CO	324h^-1	24.8	51.3	21.5	2.36	0.201	2.07
628h^-1	26.1	47.8	24.4	1.91	0.402	1.83	324h^-1	24.8	51.3	21.5	2.36	0.201	2.07
628h^-1	26.1	47.8	24.4	1.91	0.402	1.83	1296h^-1	27.6	43.5	27.2	1.72	0.805	1.58
1512h^-1	28.9	40.8	28.6	1.68	0.939	1.41	1296h^-1	27.6	43.5	27.2	1.72	0.805	1.58
1512h^-1	28.9	40.8	28.6	1.68	0.939	1.41	2502h^-1	28.9	38.2	31.6	1.27	1.275	1.32
3996h^-1	29.8	29.8	40.0	0.44	2.482	1.00	2502h^-1	28.9	38.2	31.6	1.27	1.275	1.32
3996h^-1	29.8	29.8	40.0	0.44	2.482	1.00	5832h^-1	29.3	23.5	46.9	0.30	3.622	0.80

Note: the percentages of the components in the table are volume percentages

As can be seen from the data in Table 1, with the addition of CO₂The amount is increasing and the proportion of CO in the high CO content gas is increasing.

Example 2

The reaction conditions were changed to: the pressure is 2.0MPa, the inlet temperature is 480 ℃, the outlet temperature is 860 ℃, and the space velocity of carbon in hydrocarbon is 1610h^-1Maintaining transforming H in the gas₂/CO＝1.0，CO₂The space velocity is shown in Table 2, and the rest is the same as in example 1. Measuring the content of each component in the converted gas under different water-carbon ratios,the results are shown in Table 2.

TABLE 2

CO₂Airspeed	CO，％	H₂，％	CO₂，％	CH₄，％	V_CO2/V_C	H₂O/C
CO₂Airspeed	CO，％	H₂，％	CO₂，％	CH₄，％	V_CO2/V_C	H₂O/C	3996h^-1	29.8	29.8	40.0	0.94	2.48	2.5
3240h^-1	32.4	30.9	35.8	0.91	2.012	2.0	3996h^-1	29.8	29.8	40.0	0.94	2.48	2.5
3240h^-1	32.4	30.9	35.8	0.91	2.012	2.0	2268h^-1	34.3	33.6	30.5	1.60	1.409	1.5
1728h^-1	35.1	34.3	26.7	3.94	1.073	1.2	2268h^-1	34.3	33.6	30.5	1.60	1.409	1.5
1728h^-1	35.1	34.3	26.7	3.94	1.073	1.2	1404h^-1	34.2	35.0	26.7	4.14	0.872	1.0

Note: the percentages of the components in the table are volume percentages

Example 3

The reaction conditions were changed to: the inlet temperature is 480 ℃, the outlet temperature is 860 ℃, and the space velocity of the carbon in the hydrocarbon is 1610h^-1，CO₂Space velocity is 1404h^-1，H₂O/C is about 1.0, and H in the converted gas is maintained₂The rest is the same as example 1, except that CO is 1.0. The contents of the various components in the converted gas were measured at different pressures and the results are shown in Table 3.

TABLE 3

Pressure, MPa	CO，％	H₂，％	CO₂，％	CH₄，％	H₂/CO
Pressure, MPa	CO，％	H₂，％	CO₂，％	CH₄，％	H₂/CO	2.5	31.6	32.7	30.6	5.10	1.03
2.0	34.2	35.0	26.7	4.14	1.02	2.5	31.6	32.7	30.6	5.10	1.03
2.0	34.2	35.0	26.7	4.14	1.02	1.5	35.0	38.2	23.6	3.20	1.09

Claims

1. Hydrocarbon-CO₂The process method for preparing the gas with high CO content by steam reforming comprises the following steps:

(1) feeding light oil, liquefied gas or refinery gas, water vapor and carbon dioxide into a reaction bed layer filled with a hydrocarbon vapor conversion catalyst to perform a hydrocarbon vapor conversion reaction to generate converted gas containing carbon monoxide, carbon dioxide, hydrogen and a small amount of methane in one step;

(2) separating the converted gas obtained in the step (1) to separate a gas with high CO content consisting of carbon monoxide and hydrogen, and recycling the residual gas which mainly comprises carbon dioxide and contains a small amount of methane, carbon monoxide and hydrogen to the step (1) to be used as a part of carbon dioxide raw material for hydrocarbon steam conversion reaction;

the method is characterized in that carbon dioxide raw materials required by the steam reforming reaction are not only from circulation of separated residual gas mainly comprising carbon dioxide, but also continuous carbon dioxide external supply is required, so that carbon in raw material hydrocarbon is completely converted into carbon monoxide, and simultaneously, the carbon dioxide externally supplied is also converted into the carbon monoxide.

2. The process of claim 1 wherein the high CO content gas produced has a relatively high concentration of carbon monoxide, H₂The ratio of/CO is in the range of 2.0-0.6.

3. The process of claim 2, wherein the feed in step (1) has a water to carbon ratio of H₂The O/C is controlled within the range of 1.0-3.0。

4. The process of claim 3, wherein the feed in step (1) has a water to carbon ratio of H₂The O/C is controlled within the range of 2.0 to 2.5.

5. The process according to claim 3, wherein the steam reforming catalyst used in step (1) comprises the following components:

a. a metal element having catalytic activity for steam reforming reaction;

b. alkali metal and/or alkaline earth metal compounds as anti-carbon components;

c. refractory metal oxides or mixtures thereof as catalyst supports;

d. iron and/or rare earth elements.

6. The process according to claim 5, wherein the steam reforming catalyst used in step (1) comprises the following components:

a. the metallic nickel is used as a catalytic active metal element for steam conversion;

b. potassium compound as the component for resisting carbon deposition;

c. calcium aluminate cement and/or iron cement are/is used as a carrier of the catalyst;

d. iron and/or rare earth elements.

7. The process according to claim 3 or 5, wherein the pressure in the steam reforming reaction system is controlled to be 1.0MPa to 4.0MPa when the steam reforming is carried out in the step (1).

8. The process according to claim 7, wherein the steam reforming in the step (1) is carried out while controlling the outlet temperature of the steam reforming reaction bed to be in the range of 800 to 950 ℃.