CN107540509B

CN107540509B - Method for reducing alkyne content in butadiene product in oxidative dehydrogenation process

Info

Publication number: CN107540509B
Application number: CN201710847802.XA
Authority: CN
Inventors: 常仁杰; 孙成贤; 李延生; 刘国云; 孙世谦; 高文涛; 赵强; 苗安然; 李云生
Original assignee: Wison Engineering Ltd
Current assignee: Wison Engineering Ltd
Priority date: 2017-09-19
Filing date: 2017-09-19
Publication date: 2020-11-03
Anticipated expiration: 2037-09-19
Also published as: CN107540509A

Abstract

The invention relates to a method for reducing alkyne content in butadiene product in oxidative dehydrogenation process, crude butadiene from a butadiene preparation device by oxidative dehydrogenation enters a front de-weighting tower, heavy components are cut off at the tower bottom and discharged, and tower top material enters an extraction unit to obtain the butadiene product. Compared with the prior art, the invention removes heavy components in the crude butadiene feed by increasing the heavy component removal process of the front heavy component removal tower, can obviously improve the stability of the operation of the extraction unit of the process for preparing butadiene by oxidative dehydrogenation and the product percent of pass, greatly reduces the fluctuation of the purity of butadiene products, reduces the remill of unqualified products, ensures the continuous and stable production of a device, and simultaneously reduces the energy consumption of the device.

Description

Method for reducing alkyne content in butadiene product in oxidative dehydrogenation process

Technical Field

The invention relates to the technical field of chemical product separation, in particular to a method for reducing alkyne content in butadiene products in an oxidative dehydrogenation process.

Background

Butadiene is an important petrochemical basic raw material, is mainly used for producing butadiene rubber, styrene-butadiene rubber, nitrile rubber, ABS resin and the like, and is also an important coating and organic chemical raw material. The butadiene can be produced by two methods, namely, four-carbon fraction separation and synthesis (including butane dehydrogenation, butene oxidative dehydrogenation and the like). The added butadiene in the extraction method is difficult to meet the requirement under the influence of light raw materials of the cracking device. Oxidative dehydrogenation of butene is becoming one of the major routes to butadiene production with higher conversion and selectivity.

In the oxidative dehydrogenation butadiene preparation process before 80 years (1980) in China, because the process only has requirements on carbon four total alkynes, the extraction part has no secondary extraction process flow, and a secondary extraction separation process is added in an extraction unit along with the knowledge and requirements of downstream devices on alkynes, particularly vinyl acetylene. However, since the oxidative dehydrogenation reactant needs carbon six oil absorption, the crude butadiene has a small amount of carbon six component. According to the gas-liquid balance of the carbon four and the carbon six oil, a small amount of the carbon six oil still enters the extraction system along with the carbon four, is accumulated in the extractant in the operation process, is mutually soluble with the extractant and is difficult to remove, the separation of the secondary extraction is affected, and the content of vinyl acetylene in the butadiene product at the top of the secondary extraction tower exceeds the standard. According to the operation of the similar device, no real reason is found for the fluctuation of the vinyl acetylene at the top of the second extraction tower, and the influence of absorbed oil accumulation on the pollution of the solvent is not recognized; under the condition that alkyne exceeds the standard, the general operation is to increase the load of a second extraction tower, increase a solvent and increase the reflux ratio; the first extraction and the second extraction system are repeatedly circulated and purified to meet the requirement of the purity of the product, which invisibly increases the running cost of the device. Another treatment method is to remove alkynes by a butadiene de-heavy column in an extraction unit. Increasing the load of a butadiene de-weighting tower, increasing the reflux ratio, and adjusting the reflux ratio to be even 2-2.5 times larger than the original design value; the operation energy consumption of the device is increased, and the butadiene de-heavy tower is the last separation tower in the whole process, so that the unqualified products in the tank area are easily caused, and the quality control risk of the products is greatly increased; and the subsequent operation load is high, the operation risk is large, and the stable and continuous production of the device is influenced.

Disclosure of Invention

The acetylene hydrocarbon content of the top of the secondary extraction tower of the extraction unit exceeds the standard, mainly the problem that the vinyl acetylene hydrocarbon content exceeds the standard, according to the national standard GB/T13291, the vinyl acetylene hydrocarbon content in the butadiene product is required to be less than 5PPM, in a plurality of sets of devices for preparing butadiene by oxidative dehydrogenation, due to the pollution of an extracting agent, the vinyl acetylene hydrocarbon of the top of the secondary extraction tower often exceeds the standard in actual operation, the difficulty in adjusting the devices is large, the circulation time is increased, and the operation cost is high.

The purpose of the invention can be realized by the following technical scheme:

a method for reducing alkyne content in butadiene product in oxidative dehydrogenation process comprises the steps of feeding crude butadiene from a butadiene preparation device by oxidative dehydrogenation into a front de-heavy tower, cutting heavy components at the tower bottom and discharging, and feeding tower top material into an extraction unit to obtain the butadiene product.

Preferably, the heavy components cut off by the front de-heavy tower comprise five carbon components and more than five carbon components, mainly six carbon components and seven carbon components. The heavy components are removed through the front heavy component removal tower, so that the heavy components are prevented from being accumulated in the extracting agent, the extracting agent is polluted, and the second extraction and rectification system is unstable in operation, so that the content of alkyne in a butadiene product exceeds the standard.

More preferably, the heavy component mainly comprises pentane, pentene, hexane, hexene, heptane, heptene and the like.

Preferably, the operation pressure of the front de-weighting tower is 0.3-0.6 MPaG, and the operation temperature is 40-60 ℃.

Preferably, a separation tank is arranged between the front de-weighting tower and the extraction unit, and the top discharge of the front de-weighting tower is extracted firstly and enters the separation tank, and then enters the extraction unit after being evaporated.

Preferably, the overhead condensing mode of the front de-heavy tower is partial reflux or no reflux,

when the mass content of carbon six in the heavy components of the crude butadiene is less than 1000ppm or the mass content of carbon five collected from the side of a second extraction tower in the extraction unit is less than 5%, the tower top does not flow back, and all gas phase at the tower top is collected and enters a subsequent extraction unit;

when the mass content of carbon six in the heavy components of the crude butadiene is more than or equal to 1000ppm or the mass content of carbon five collected from the side of a second extraction tower in the extraction unit is more than or equal to 5 percent, the top of the tower partially refluxes, part of refluxes are increased, the mass transfer and heat transfer of gas and liquid phases in the tower are increased, and the heavy components are further removed.

Preferably, the butadiene content in the crude butadiene is 50% by mass or more.

The heat source of each device of the invention preferentially utilizes the heat of the circulating solvent or the heat of the steam condensate in the process system.

Compared with the prior art, the invention finds the reasons that the content of vinyl acetylene at the top of the second extraction tower exceeds the standard and the quality of butadiene products is influenced through the research of a plurality of sets of operation devices, and confirms that the accumulation of heavy components such as carbon six and the like is the main reason through a large amount of comparison experiments and analysis data, so that the problem that acetylene hydrocarbon of the existing operation device influences the fluctuation of butadiene products is effectively solved by adding a heavy component removal process flow and removing heavy components before an oxidative dehydrogenation process extraction unit through the optimization of the flow, the flow is simple, and the operation and investment cost is low, thereby improving the operation benefit of the butadiene device.

Drawings

FIG. 1 is a process flow diagram of the present invention;

FIG. 2 is another process flow diagram of the present invention;

FIG. 3 is a process flow diagram of a prior art butadiene extraction unit;

in the figure, T-1 is a front heavy component removal tower, T-2 is a first extraction tower, T-3 is a second extraction tower, T-4 is a butadiene light component removal tower, T-5 is a butadiene heavy component removal tower, T-6 is an alkyne flash tower, V-1 is a separation tank, and V-2 is a feeding evaporation tank.

Detailed Description

The invention is described in detail below with reference to the figures and specific embodiments.

In a preferred embodiment of the invention, the heavy components cut off by the front de-heavy tower comprise five carbon components and more than five carbon components, mainly six carbon components and seven carbon components. More preferably, the heavy component mainly comprises pentane, pentene, hexane, hexene, heptane, heptene and the like.

In a preferred embodiment of the present invention, the pre-de-heavy column is operated at a pressure of 0.3 to 0.6MPaG and at a temperature of 40 to 60 ℃.

As a preferred embodiment of the invention, a knockout drum is arranged between the front de-weighting tower and the extraction unit, the top discharge of the front de-weighting tower is firstly extracted and enters the knockout drum, and then enters the extraction unit after being evaporated.

As a preferred embodiment of the invention, the overhead condensation mode of the front-end de-heavy column is partial reflux or no reflux,

In a preferred embodiment of the present invention, the crude butadiene is butene, butane, butadiene or the like, wherein the butadiene content is 50% or more.

Example 1

Crude butadiene from upstream is used as feed carbon four S1, enters a front de-weighting tower T1 from the middle upper part, the operating pressure of the front de-weighting tower T1 is controlled to be 0.5MPaG, the operating temperature is 53 ℃, partial condensed reflux material S4 is adopted at the tower top according to the content of heavy components, gas phase S3 extracted at the tower top enters a first extraction tower T2 and then enters a subsequent second extraction tower for treatment, the tower bottom is heated by solvent waste heat or steam condensate, and the heavy components at the bottom are discharged out intermittently according to the accumulation condition, as shown in figure 1.

Table 1 below shows the composition of the feed to a first extraction column in a post-extraction unit after a certain apparatus has been subjected to the de-weighting treatment according to the above procedure.

TABLE 1

Feed to extraction unit	Composition (wt%)
		Carbon III	0.0860
Isobutane	0.5233
		Isobutene	0.0389
1, 3-butadiene	70.9253
		N-butane	2.4187
Butene-1	0.3584
		Trans-2-butene	14.5329
Cis-2-butene	10.8041
		Vinyl acetylene	0.2535
Five and more carbons	0.0590

Comparative example 1

Crude butadiene from the upstream is taken as feed carbon four S1 and is sent into a feed evaporation tank V-2, the evaporated material is directly sent into a first extraction tower T2 in a subsequent extraction unit for starting processing, and as shown in figure 3, the extraction unit comprises a first extraction tower T-2, a second extraction tower T-3, a butadiene light component removal tower T-4, a butadiene heavy component removal tower T-5 and an alkyne flash evaporation tower T-6 which are connected in sequence.

The treatment results of comparative example 1 and comparative example 1 were analyzed as shown in table 2 below.

TABLE 2 comparison of Vinyl Acetylene (VA) content at the top of the second extraction column

	Before the weight-removing tower is added (namely comparative example 1)	After adding the de-weighting tower (i.e., example 1)
			VA(ppm)	0～50	≤5
Fluctuation frequency (times/day)	15～30	Stabilization

From the above table, it can be seen that for the same feed carbon four S1 discharged from the oxidative dehydrogenation butadiene production unit, the addition of the front de-heaving column significantly reduces the content and the fluctuation times of the vinyl ethylene at the top of the second extraction column; on one hand, the running stability of the device is increased, on the other hand, the running load of a subsequent treatment device is reduced, the running cost is greatly reduced, and the device has remarkable effects of running stability, energy conservation and consumption reduction of a butadiene device.

Example 2

The specific flow is as shown in fig. 2, except that a knockout drum V1 is provided between the front de-heaving column T1 and the first extraction column T1 of the extraction unit, as compared with the process flow of example 1.

Example 3

Compared to example 1, most of them are the same except that in this example:

the operating pressure of the front de-weighting column T1 was 0.3MPaG and the operating temperature was 40 ℃.

Example 4

Compared to example 1, most of them are the same except that in this example:

the operating pressure of the front de-weighting column T1 was 0.4MPaG and the operating temperature was 45 ℃.

Example 5

Compared to example 1, most of them are the same except that in this example:

the operating pressure of the front de-weighting column T1 was 0.6MPaG and the operating temperature was 60 ℃.

The invention provides a refining and separating process for preparing butadiene by oxidative dehydrogenation of butylene, which has remarkable economic benefit. The embodiments are described in detail, and those skilled in the relevant art can implement the technology by making appropriate changes, modifications and combinations according to the method provided by the present invention. It is expressly stated that all such modifications or alterations and subcombinations which would be apparent to persons skilled in the art by making similar changes or variations to the process flow provided by the present invention are deemed to be within the spirit, scope and content of the invention.

Claims

1. A method for reducing alkyne content in butadiene product of oxidative dehydrogenation process is to improve the stability of device operation, and is characterized in that crude butadiene from a butadiene preparation device of oxidative dehydrogenation enters a front de-weighting tower, heavy components are cut off at the tower bottom and discharged, and materials at the tower top enter an extraction unit to obtain butadiene product;

heavy components cut off by the front de-heavy tower comprise five carbon components and more than five carbon components;

the operation pressure of the front de-weighting tower is 0.3-0.6 MPaG, and the operation temperature is 40-60 ℃.

2. The method of claim 1, wherein the heavy components comprise pentane, pentene, hexane, hexene, heptane and heptene.

3. The method for reducing the alkyne content in a butadiene product of an oxidative dehydrogenation process according to claim 1, wherein a knockout drum is further arranged between the front de-weighting tower and the extraction unit, and the top discharge of the front de-weighting tower is firstly extracted and enters the knockout drum, and then enters the extraction unit after being evaporated.

4. The method for reducing the alkyne content in a butadiene product of an oxidative dehydrogenation process according to claim 1, wherein the overhead condensation mode of the front de-heavy tower is partial reflux or no reflux,

when the mass content of carbon six in the heavy components of the crude butadiene is less than 1000ppm or the mass content of carbon five or more extracted from the side of a second extraction tower in the extraction unit is less than 5%, the tower top does not flow back, and all gas phase at the tower top is extracted and enters a subsequent extraction unit;

when the mass content of carbon six in the heavy component of the crude butadiene is more than or equal to 1000ppm or the mass content of carbon five collected from the side of a second extraction tower in the extraction unit is more than or equal to 5 percent, the tower top part is refluxed.

5. The method of claim 1, wherein the butadiene content of the crude butadiene is greater than 50% by weight.