CN109280561B

CN109280561B - Method for preparing propylene and coproducing aromatic hydrocarbon through naphtha or light hydrocarbon low-temperature catalytic reaction

Info

Publication number: CN109280561B
Application number: CN201811440380.5A
Authority: CN
Inventors: 龚小燕; 张丰豪; 丁艳明; 张芳; 孙艳茹; 郭金宝
Original assignee: BEIJING HUIERSANJI GREEN CHEM-TECH CO LTD
Current assignee: BEIJING HUIERSANJI GREEN CHEM-TECH CO LTD
Priority date: 2018-11-29
Filing date: 2018-11-29
Publication date: 2020-11-27
Anticipated expiration: 2038-11-29
Also published as: CN109280561A

Abstract

A process method for preparing propylene and coproducing aromatic hydrocarbon by using naphtha or light hydrocarbon as raw material and adopting low-temperature catalytic reaction. The method comprises the following steps: raw material naphtha or light hydrocarbon enters a fixed bed reactor after being subjected to heat exchange by a heat exchanger and/or heated by a heating furnace, low-temperature catalytic reaction is carried out under the action of a specific catalyst, ethylene propylene, C-V hydrocarbon and byproduct aromatic hydrocarbons such as toluene and xylene are obtained after reaction products pass through a separation system, and a part of C-V hydrocarbon is circularly returned to the reactor. The process method is carried out in a fixed bed reactor, and the catalytic reaction temperature is lower than that of the traditional naphtha catalytic cracking process and far lower than that of the traditional naphtha steam cracking process; the method adopts a recycling mode of self-produced carbon four-carbon five-hydrocarbon, and fully utilizes the reaction heat; the product distribution of the method is adjustable, and higher yields of propylene and aromatic hydrocarbon can be obtained simultaneously.

Description

Method for preparing propylene and coproducing aromatic hydrocarbon through naphtha or light hydrocarbon low-temperature catalytic reaction

Technical Field

The invention relates to a process method for preparing propylene and coproducing aromatic hydrocarbon by taking naphtha or light hydrocarbon as a raw material through low-temperature catalytic reaction. In particular to a method for producing high-yield propylene products and coproducing aromatic hydrocarbon by naphtha or light hydrocarbon cracking reaction in a fixed bed reactor under the action of a lower reaction temperature and a characteristic catalyst.

Background

Propylene is one of the most important raw materials of the most basic in the field of modern petrochemical industry. In recent years, the demand for propylene is rapidly increasing worldwide, and at the same time, non-renewable petroleum resources are becoming scarce. At present, about 60 percent of propylene is sourced from the traditional naphtha steam thermal cracking technology, but the traditional naphtha steam thermal cracking technology has high reaction temperature, large energy consumption and low propylene yield. In order to relieve the increasingly outstanding contradiction between the supply and demand of propylene and the contradiction between the gradual shortage of naphtha resources and the low yield of steam thermal cracking, naphtha catalytic cracking technology is produced.

Compared with the traditional steam thermal cracking technology, the naphtha catalytic cracking technology reduces the reaction temperature from 800-1000 ℃ by 50-200 ℃, and the propylene yield is also improved from about 10% to 15-38%. The application of the technology not only avoids the high-temperature energy consumption of steam cracking and the damage of high-temperature conditions to equipment and the like, but also makes full use of naphtha resources, and more propylene products can be produced by using the same amount of naphtha. Catalytic cracking technology has been receiving increasing attention from researchers in various countries in the last two years.

Like propylene, aromatics are also important basic organic synthesis feedstocks, especially the triphenyl species (i.e., benzene, toluene, and xylene, i.e., BTX). At present, the main production approach of aromatic hydrocarbon is naphtha catalytic reforming to obtain an aromatic hydrocarbon mixture, and the aromatic hydrocarbon mixture is subjected to processes of adsorption, freezing, rectification and the like to obtain a byproduct, and then subjected to processes of isomerization, disproportionation and the like to obtain an aromatic hydrocarbon product meeting quality requirements.

At present, the research on the preparation of ethylene and propylene by naphtha catalytic cracking is more, but the research on the preparation of ethylene and propylene by naphtha catalytic cracking is less, and high-yield aromatic hydrocarbon can be co-produced. The existing process capable of simultaneously co-producing high-yield aromatic hydrocarbon is only a combined process for preparing aromatic hydrocarbon by catalytic reforming or a coupling process technology adopting two or more raw materials.

CN104927915A discloses a method for producing olefin and aromatic hydrocarbon by taking naphtha as a raw material. The method comprises the steps of extracting naphtha liquid to obtain extract oil and raffinate oil, carrying out steam cracking on the raffinate oil containing alkane and cycloalkane to obtain pyrolysis gasoline, carrying out hydrofining on the obtained pyrolysis gasoline to obtain hydrofined gasoline, and carrying out catalytic reforming on the hydrofined gasoline and the extract oil containing arene and cycloalkane obtained by liquid-liquid extraction to produce light olefin and arene. As described in the examples, the yield of BTX was 35.7%, the yield of total aromatic hydrocarbons (containing C8C9 aromatic hydrocarbons) was 45.4%, the yield of ethylene was 22.5%, and the yield of propylene was 11.6%. The process has low propylene yield and complex flow, and relates to liquid-liquid extraction, hydrofining, steam cracking, catalytic reforming and the like.

CN101759513A discloses a method for utilizing naphtha. The method uses an adsorption separation method to separate naphtha into a component containing normal paraffin and a component containing non-normal paraffin, wherein the normal paraffin is cut into a C5C6 fraction and a fraction which is equal to or more than C7, the C5C6 fraction is isomerized to obtain C5C6 isoparaffin, the fraction which is equal to or more than C7 is catalytically cracked to obtain ethylene propylene, and the component containing the non-normal paraffin is catalytically reformed to obtain aromatic hydrocarbon. The embodiment shows that the aromatic hydrocarbon yield of the method is up to 59.2 percent, and the total yield of the ethylene and the propylene can reach 20.8 percent. The process has low propylene yield and complex flow, and relates to distillation, fraction cutting, isomerization, catalytic reforming and the like.

CN1721510A discloses a method and a device for producing low-carbon olefin and aromatic hydrocarbon. The method comprises the steps of carrying out catalytic cracking on raw material low-carbon olefins after hydrotreating, carrying out selective hydrogenation and solvent extraction on obtained naphtha to obtain aromatic hydrocarbon and raffinate oil, and sending the raffinate oil to a steam cracking device to obtain low-carbon olefins such as ethylene, propylene and the like. Wherein the catalytic cracking reactor is a moving bed, a fluidized bed and the like. The method has the advantages that the propylene yield can reach 30 percent, and the method can co-produce aromatic hydrocarbon rich in toluene and xylene. The process unit comprises a hydrotreating unit, a catalytic cracking unit, a steam cracking unit, a selective hydrogenation unit, a solvent extraction unit and the like.

CN102803184A discloses "production of light olefins and aromatics". The method comprises the steps of firstly dehydrogenating a raw material containing paraffin to obtain a material flow containing olefin, then introducing the material flow containing olefin into an olefin cracking zone, reacting to generate ethylene, propylene, aromatic hydrocarbon and heavy hydrocarbon by-products, and selectively hydrogenating the diolefins with the range of C5-C11 in the heavy hydrocarbon by-products and then introducing the diolefins into the olefin cracking zone. The method has no specific examples, but the computer simulates that the method can achieve the propylene yield of 50.38% and the triphenyl yield of 16% under the premise of no catalytic reforming. The process at least comprises a dehydrogenation unit, an olefin cracking unit, a selective hydrogenation unit and the like.

CN108017496A discloses a device and a method for producing olefin and aromatic hydrocarbon. The method has two raw materials, namely a light hydrocarbon raw material and an oxygen-containing compound raw material. The two raw materials are reacted separately in two reactors. The light hydrocarbon raw material reacts in the riser reactor to obtain a product rich in ethylene and propylene, and the oxygen-containing compound raw material produces a product rich in aromatic hydrocarbon in the fluidized bed reactor. The method has the advantages that the yield of propylene is not more than 13.6 percent, and the yield of aromatic hydrocarbon is 28.2 percent.

Disclosure of Invention

The invention aims to provide a process method for preparing propylene and coproducing aromatic hydrocarbon by taking naphtha or light hydrocarbon as a raw material through low-temperature catalytic reaction. The method fully utilizes the reaction heat effect, greatly reduces the energy consumption of the device, can simultaneously obtain the propylene and aromatic hydrocarbon products with high yield and high added value, and improves the economic benefit of oil refining enterprises.

In order to achieve the above object, the present invention comprises the steps of:

(1) raw material naphtha or light hydrocarbon and the reacted oil-gas mixture flowing out of the bottom of the reactor exchange heat and/or are directly heated to reach the preheating temperature;

(2) naphtha or light hydrocarbon is mixed with self-produced carbon four-carbon five-hydrocarbon and then enters from the top of the reactor;

(3) under the action of a characteristic catalyst filled in a fixed bed reactor, olefin components in the self-produced carbon four-carbon five-hydrocarbon undergo polymerization, cyclization and aromatization reactions to generate macromolecular hydrocarbon, and the temperature of oil gas is raised due to reaction heat release; absorbing a large amount of heat by naphtha or light hydrocarbon, and carrying out dehydrogenation, cracking, superposition, cyclization, aromatization and other reactions to generate a hydrocarbon mixture containing target products of propylene and aromatic hydrocarbon;

(4) and (3) allowing the hydrocarbon mixture to flow out of the bottom of the reactor, allowing the hydrocarbon mixture to enter a subsequent separation system, recovering ethylene, propylene and aromatic hydrocarbon generated by the reaction, and circulating part of the carbon four-carbon five-hydrocarbon generated by the reaction to the step (2) to enter the reactor together with the raw material.

The raw material naphtha of the invention is one or more of straight-run naphtha, catalytic cracking naphtha, oil field condensate oil and hydrocracking naphtha.

The raw material light hydrocarbon is a hydrocarbon mixture which takes alkane and cycloalkane with four to ten carbons as main components.

The reactor of the invention is a fixed bed reactor, and can also be a fluidized bed reactor.

The raw material naphtha or light hydrocarbon is subjected to cracking reaction instead of cracking reaction at a lower reaction temperature under the action of a characteristic catalyst, and still needs to absorb a large amount of heat. In the invention, a part of the self-produced carbon four-carbon five-hydrocarbon is circulated back to the reactor, olefin polymerization, cyclization and aromatization are carried out under the action of the catalyst to generate macromolecular hydrocarbon, and simultaneously a large amount of reaction heat is released, and the part of the reaction heat provides heat for the cracking reaction of naphtha, thereby greatly reducing the energy consumption required by the whole process.

Two reactions, namely the cracking of naphtha and the aromatization of recycled olefins, are carried out in one reactor. The aromatization reaction provides heat for the cracking reaction, and the heat is absorbed by the cracking reaction, and simultaneously, temperature runaway and the like caused by the aromatization reaction are avoided.

The self-produced carbon four-carbon five-hydrocarbon is recycled to the reactor, so that not only can the reaction heat be fully utilized, but also the yield of the target products of propylene and aromatic hydrocarbon can be greatly improved.

The invention can control the reaction temperature by adjusting the circulation amount of the self-produced carbon four-carbon five-hydrocarbon and regulate the distribution of reaction products to obtain the ideal yield of the target product. When the circulating amount is increased, the yield of aromatic hydrocarbon is increased, and the yield of propylene is influenced; when the amount of recycle is reduced, the propylene yield increases and the aromatics yield is affected. The circulating amount of the self-produced carbon four-carbon five-hydrocarbon is 0.01 to 0.5 time of the feeding rate of the raw material.

In the present invention, in order to satisfy the heat required for cracking the raw material, methanol and/or other organic oxygen-containing compounds can be added into the raw material, or other technical routes can be adopted to couple with the reaction process with exothermic effect.

In the invention, in order to reduce coking and deactivation of the catalyst, proper amount of steam can be added into raw material naphtha or light hydrocarbon, and the weight ratio of proper water to naphtha is 0.01-0.5.

In the step (1), raw material naphtha or light hydrocarbon and the reacted oil-gas mixture exchange heat and/or are directly heated to reach a preheating temperature.

In the step (2), naphtha or light hydrocarbon is mixed with the self-produced carbon four-carbon five-hydrocarbon and then enters from the top of the reactor.

In the step (3), the catalytic reaction conditions in the reactor are as follows: the reaction temperature is 460-540 ℃, the reaction pressure is 0.1-0.25 MPa, and the weight hourly space velocity is 0.2-1.5 h^-1。

In the step (4), the oil-gas mixture generated by the reaction flows out from the bottom of the reactor, and enters a separation system after heat exchange of a heat exchanger and cooling of a water cooler. Separation systems are well known to those skilled in the art and include absorption stabilization systems and rectification systems. The target products of the method, namely propylene, aromatic hydrocarbon and carbon four-carbon five-hydrocarbon, can be obtained through a separation system, one part of the carbon four-carbon five-hydrocarbon is led out to a gas separation system or a tank area, and the other part of the self-produced carbon four-carbon five-hydrocarbon is circulated back to the reactor and directly enters between catalyst bed layers of the reactor or is mixed with raw materials before entering the reactor and enters the reactor together.

In industrial implementation, an oil-gas mixture flowing out of the bottom of the reactor enters an absorption and desorption system after passing through a heat exchange and liquid separation tank, and dry gas and heavier components are separated. Emptying dry gas or recycling. The heavy components and the material flowing out of the bottom of the liquid separating tank enter a stabilizing tower together to separate liquefied gas containing propylene and aromatic oil, and the liquefied gas containing propylene is further separated into propane, propylene, C4 and C5 hydrocarbon through a depropanizing tower and the like. The C4 hydrocarbon is divided into two parts, one part is led out to be directly used as product liquefied gas, and the other part is returned to the reactor for recycling. The C5 hydrocarbon is also divided into two parts, most of which is returned to the reactor for recycling, and the small part is led out to be directly used as a product. And (3) the aromatic hydrocarbon oil from the bottom of the stabilizing tower goes to an aromatic hydrocarbon separation system, and an aromatic hydrocarbon product is obtained through isomerization, disproportionation and the like.

The catalyst used in the invention is a metal modified molecular sieve catalyst, and the catalyst comprises 0.1-10% of modified metal oxide, 40-90% of molecular sieve and 10-50% of alumina. The molecular sieve used is preferably one, two or more of HZSM-5, HZSM-11, mordenite and USY molecular sieve, and more preferably HZSM-5, mordenite or a mixture of the two. The molecular sieve and the alumina adhesive are jointly used as a carrier of metal, and the metal is loaded on the catalyst by adopting an impregnation method.

The supported modified metal comprises (1) a group VIII or IIB element, preferably one or more of Fe, Co, Ni, Zn, Ga and Cd, (2) a group VA element, preferably one or more of P, As and Sb, and (3) a rare earth element, preferably one or two of La and Ce.

The invention can obtain proper reaction product distribution by adjusting the content of the modified metal in the catalyst, thereby obtaining ideal target product yield.

The shaping method of the catalyst of the present invention is known to those skilled in the art, such as extrusion, tabletting, spheronization, dropping ball. Mixing the molecular sieve, aluminum hydroxide, sesbania powder and other solid uniformly, adding proper amount of water and acid (hydrochloric acid, nitric acid or acetic acid), extruding and kneading, and finally extruding, drying and breaking into strips or rolling the strips into balls; or mixing all the raw materials to obtain colloid, and dropping the colloid in hot oil or oil ammonia bath to form balls. Drying the formed catalyst at room temperature to 150 ℃, depositing metal on the catalyst by using a metal soluble salt (generally nitrate) impregnation method after drying, and roasting for 1-12 hours in air or steam atmosphere at the temperature of 400-600 ℃ to obtain the catalyst.

The invention has the following effects:

(1) compared with the traditional propylene preparation technology by catalytic cracking, the invention adopts a fixed bed reactor, the reaction temperature is not more than 600 ℃, the raw material naphtha or light hydrocarbon is in cracking reaction after contacting with the catalyst, and the cracking reaction is not high-temperature cracking reaction, so a large amount of dry gas, CO and CO can not be generated₂And the raw material naphtha or light hydrocarbon is selectively converted to generate the low-carbon olefin and the aromatic hydrocarbon with high yield under the action of the characteristic catalyst.

(2) Compared with the combined process of catalytic cracking and catalytic reforming/or steam cracking, the invention only needs one set of reaction system and one set of separation system, is simple and easy to operate, has strong operability, and does not need to increase more separation devices such as extraction, adsorption and the like for the coupling of two or more raw materials or the coupling of two or more processes. The method provided by the invention can simultaneously obtain high-yield propylene and high-yield aromatic hydrocarbon.

(3) Can simultaneously obtain higher yields of propylene and aromatic hydrocarbon, the yield of the propylene can reach 28 percent after reaction conditions are optimized, and the yield of the coproduced aromatic hydrocarbon can reach 24 percent.

(4) By optimizing the content of modified metal in the catalyst, adjusting the low-temperature cracking reaction condition, the circulating amount of the self-produced carbon four-carbon five-hydrocarbon and the like, the proper product distribution and the required target product yield can be obtained.

(5) Can be flexibly coupled with other raw materials and/or other processes according to the reaction heat effect and the characteristics of products.

Drawings

FIG. 1 is a schematic process flow diagram of the method of the present invention, but the present invention is not limited thereto.

The method comprises the following process flows: the raw material naphtha and the self-produced carbon four-carbon five-hydrocarbon are mixed, and enter the fixed bed reactor after heat exchange of a heat exchanger and heating of a heating furnace. Under the action of the characteristic catalyst, the self-produced carbon four-carbon five-hydrocarbon is subjected to olefin polymerization, cyclization and aromatization reaction to generate macromolecular hydrocarbon, and the temperature of oil gas is increased due to the reaction heat; naphtha or light hydrocarbon absorbs a large amount of heat to carry out dehydrogenation, cracking, superposition, cyclization, aromatization and other reactions to generate a hydrocarbon mixture containing target products of propylene and aromatic hydrocarbon. The hydrocarbon mixture flows out from the bottom of the reactor, and enters a subsequent separation system after being cooled by a heat exchanger and a water cooler to obtain the target products of propylene, aromatic hydrocarbon and carbon four-carbon five-hydrocarbon of the method, wherein one part of the carbon four-carbon five-hydrocarbon is taken as a product leading-out device to go to a tank area, and the other part of the self-produced carbon four-carbon five-hydrocarbon is circulated back to the reactor and directly enters from the catalyst bed layer of the reactor or is mixed with the raw material before entering the reactor and enters the reactor together.

Detailed Description

The present invention will be further described with reference to the following examples, but the present invention is not limited thereto.

Specification of raw materials

(1) The test feedstock was a hydrocarbon mixture of naphtha, carbon four and carbon five in a ratio of 70: 25: 5, respectively. Wherein the naphtha is obtained from Yanshan petrochemical, and the properties are shown in Table 1; carbon four is taken from ether rear carbon four of a Ningxia petrochemical catalytic cracking device, and the composition is shown in table 2; the carbon five is taken from raw material carbon five obtained by etherifying Ningxia petrochemical light gasoline.

(2) The catalyst is CC-17, the appearance is a strip with a butterfly-shaped section of 2.1mm multiplied by 3.2mm, and the length is 4-10 mm. This type of catalystThe preparation is prepared from green chemical technology of Beijing Huiltrigi, and contains 56.8% ZSM-5 and 1.5% P₂O₅、5.6％La₂O₃、0.46％Fe₂O₃And the balance of Al₂O₃. The ZSM-5 molecular sieve is synthesized by an in-situ crystallization method, and the silica-alumina ratio is 200.

Example 1

The experimental data show the implementation effect of the process method for preparing propylene and coproducing aromatic hydrocarbon by using naphtha or light hydrocarbon as raw materials through low-temperature catalytic reaction.

The test device is a 200mL fixed bed reactor, raw oil and water are respectively pumped into a preheating furnace by a metering pump, then enter the fixed bed reactor from the upper part of the reactor, the oil-gas mixture generated by the reaction is subjected to heat exchange, the pressure is controlled by a regulating valve, liquid generated by the reaction is separated and weighed by a condensation and gas-liquid separator, gas is metered by a wet flowmeter, the liquid and the gas are sampled and then analyzed by gas chromatography to form the product, and the yield (based on the weight of raw naphtha) is calculated.

The reactor was charged with 90g of catalyst. The flow rate of the raw oil is 30g/h, and the water flow rate is 20 g/h. The preheating temperature is 540 ℃, the average temperature of the catalyst bed layer is 520 ℃, and the reaction pressure is 0.1MPa (gauge pressure). Continuously reacting for 7 days, balancing the clamped materials every day, taking 2 times of cracked gas for composition analysis, and collecting 1 time of liquid for composition analysis; after 7 days of reaction, the coke yield was calculated by discharging the coke. Tables 3 and 4 are the average data for 7 days.

TABLE 1 essential properties of naphtha

Item	Analyzing data
		Density, g/mL	0.718
Sulfur content, ppm	26
		Alkane content, wt.%	78.4
Naphthene content wt%	18.7
		Aromatic content, wt.%	1.8
Olefin content, wt.%	1.1
		Distillation range, deg.C
Initial boiling point	38
		10％	58
50％	105
		90％	138
Dried cake	164

TABLE 2 post C four composition of ether

Name (R)	Volume composition, v%
		Carbon III	0.45
N-butane	12.62
		Isobutane	39.23
N-butene	16.62
		Isobutene	0.84
Butene of trans-butene	17.06
		Cis-butenediol	12.8
Carbon five	0.38
		Total of	100

TABLE 3 reaction conditions and product distribution of the examples

Test number	Example 1
		Catalyst and process for preparing same	CC-17
Reaction temperature of	520
		Reaction pressure, MPa	0.1
Space velocity of feed, h^-1	0.33
		Proportion of water vapor in wt%	66.7
Distribution of reaction products in wt%
		Hydrogen gas	0.32
Methane	1.39
		Ethane (III)	2.01
Ethylene	7.07
		Propane	3.68
Propylene (PA)	27.42
		N-butane	1.50
Isobutane	3.01
		N-butene	1.32
Isobutene	3.13
		Cis-butenediol	1.27
Butene of trans-butene	1.34
		C5+ aromatic oil	46.48
Coke	0.06
		Total of	100

TABLE 4 Properties of aromatic oils

Name (R)	Properties of
		Density (20 deg.C), g.cm^-3	0.7326
Octane RON	97.5
		Distillation range, deg.C
First run	38
		10％	79
50％	135
		90％	175
The content of each component is wt%
		Benzene content	11.8
Toluene content	21.6
		Xylene content	20.9

Claims

1. A method for preparing propylene and coproducing aromatic hydrocarbon by taking naphtha or light hydrocarbon as a raw material through low-temperature catalytic reaction comprises the following steps:

(2) naphtha or light hydrocarbon is mixed with self-produced carbon four-carbon five-hydrocarbon and then enters from the top of the reactor; the catalytic reaction temperature in the reactor is 460-540 ℃;

(3) under the action of a characteristic catalyst filled in a fixed bed reactor, olefin components in the self-produced carbon four-carbon five-hydrocarbon undergo polymerization, cyclization and aromatization reactions to generate macromolecular hydrocarbon, and the temperature of oil gas is raised due to reaction heat release; absorbing a large amount of heat by naphtha or light hydrocarbon to perform dehydrogenation, cracking, superposition, cyclization and aromatization reactions to generate a hydrocarbon mixture containing target products of propylene and aromatic hydrocarbon; the characteristic catalyst is a molecular sieve catalyst modified by three types of elements together, the molecular sieve is HZSM-5, mordenite or a mixture of the HZSM-5 and the mordenite, and the loaded three types of modified elements are as follows: VIII group or IIB group elements, VA group elements and rare earth elements;

2. The method of claim 1, wherein the raw naphtha is one or more of straight run naphtha, catalytically cracked naphtha, oil field condensate, hydrocracked naphtha.

3. The method of claim 1, wherein the raw light hydrocarbon is a hydrocarbon mixture containing four to ten carbon paraffins and naphthenes as main components.

4. The method according to claim 1, wherein the process of cracking naphtha to produce propylene in step (3) requires a large amount of heat, and the olefin polymerization, cyclization and aromatization reactions of the self-produced C-V hydrocarbons release a large amount of heat, and the two reactions are performed in the same reactor by the circulation of the self-produced C-V hydrocarbons, and the aromatization reaction provides heat for the cracking reaction, thereby greatly reducing the energy consumption required by the whole process.

5. The method of claim 4, wherein the desired yield of the target product is obtained by controlling the reaction temperature by adjusting the amount of the self-produced hydrocarbons recycled and by controlling the distribution of the reaction products.

6. The method according to claim 4, wherein the amount of the self-produced carbon four-carbon five-hydrocarbon is 0.01 to 0.5 times the feed rate of the raw material.

7. The process according to claim 1, wherein in step (2) and step (4), part of the self-carbon-producing tetracarbon pentahydrocarbons is recycled to the reactor directly between the catalyst beds in the reactor or is mixed with the feedstock before entering the reactor and then enters the reactor.

8. The process according to claim 1, characterized in that the reactor is a fixed bed reactor.

9. The process according to claim 1, characterized in that in step (3), the catalytic reaction conditions in the reactor are: the reaction temperature is 460-540 ℃, the reaction pressure is 0.1-0.25 MPa, and the weight hourly space velocity is 0.2-1.5 h^-1。

10. The process of claim 1, wherein in step (1), a suitable amount of steam is added to the raw naphtha or light hydrocarbon to reduce coking and deactivation of the catalyst, the weight ratio of water to naphtha being 0.01 to 0.5.