Advances in Aromatics Production Technology in Refining & Chemical Integration
Aromatic hydrocarbons mostly use naphtha as raw material and are produced by aromatic hydrocarbon complexes. The main products are benzene, toluene and xylene. Aromatic products come from catalytic reforming oil, hydrocracking gasoline by-product of steam cracking and C6~C8 aromatics in coking crude benzene.
The production of aromatic hydrocarbons can be increased by using liquefied gas (LPG), light olefins, reforming raffinate and other raw materials through light hydrocarbon aromatization technology; heavier resources such as heavy pyrolysis gasoline and heavy FCC light cycle oil can also be used. Aromatic hydrocarbons are increased by lightening, hydrocracking and other reactions.
At present, typical aromatics production technologies include catalytic reforming, pyrolysis gasoline hydrogenation, light hydrocarbon aromatization, toluene/benzene disproportionation and transalkylation, xylene isomerization, and coal (methanol) to aromatics, etc.
1. Catalytic Reforming
Catalytic reforming is the leading device for producing aromatics, and it is also one of the main devices in the modern refining and chemical industry. The production of aromatics accounts for about 30% of the global aromatics production.
Typical catalytic reforming technologies currently include:
(1) The Continuous Reforming (CCR) Platforming process developed by UOP Company in the United States.
(2) The CCR process developed by French Axens Company, which includes the Aromizing process for producing aromatic hydrocarbons and the Octanizing process for producing high-octane gasoline blending components.
(3) The ultra-low pressure CCR process (SLCR) developed by Sinopec.
(4) Countercurrent moving bed CCR process (SCCCR) developed by Sinopec.
2. Hydrogenation of Pyrolysis Gasoline
When pyrolysis gasoline is used as the raw material for aromatic extraction to produce high-purity aromatic products, it must first undergo selective hydrogenation and hydrorefining to remove diolefins, aromatic hydrocarbons, olefins, and impurities such as sulfur, nitrogen, and oxygen.
At present, the two-stage hydrogenation process is widely used in the industry:
The first-stage hydrogenation mainly removes diolefins and olefinic hydrocarbons, and the low-temperature liquid-phase selective hydrogenation technology is the main method;
The second-stage hydrogenation mainly removes monoolefins and impurities such as sulfur, nitrogen, and oxygen, and usually adopts high-temperature, gas-phase hydrotreating technology, and the process conditions are relatively harsh.
The main pyrolysis gasoline production aromatics technologies are:
(1) The pyrolysis gasoline hydrogenation process developed by PetroChina.
(2) APUSM process developed by SK Company in South Korea.
(3) The pyrolysis gasoline hydrogenation process developed by Sinopec.
3. Aromatization of Light Hydrocarbons
Light hydrocarbon feedstocks such as LPG, light olefins, and reforming raffinate can be converted into aromatic hydrocarbons through aromatization. According to the form of reactor, the aromatization technology for producing aromatic hydrocarbons can be divided into fixed bed process and moving bed process. According to the type of catalyst used, it can be divided into two process routes:
One is the use of metal-modified ZSM-5 molecular sieve acid catalyst technology. The processing raw materials are mainly C2~C5 light hydrocarbon components, which have the advantages of simple process flow, wide applicability of raw materials, no need for strict refining, and low construction costs. The rate can reach more than 60%;
The other is the use of Pt/KL basic molecular sieve catalyst technology, which mainly processes C6~C7 alkanes. The yield of aromatics is higher than that of the traditional reforming process, but it has strict requirements on the refining of raw materials, especially the desulfurization of raw materials, so it has not been obtained. widely used.
Light hydrocarbon aromatization technology mainly includes:
(1) The C4 hydro-aromatization technology developed by PetroChina to produce high-octane gasoline components (LAG).
(2) The Alpha process jointly developed by Japan's Asahi and Sanyo.
(3) The Cyclar process developed by UOP in the United States and BP in the United Kingdom.
4. Toluene/Benzene Disproportionation and Transalkylation
Toluene disproportionation and transalkylation technology is the main process unit for increasing xylene production in the aromatics complex. It plays an important role in the logistics transformation hub and effectively adjusting the aromatics feedstock and product structure in the entire aromatics complex.
This technology uses toluene/benzene and aromatic hydrocarbons of C≥9 as raw materials, and uses molecular sieve solid acid as catalyst active main body, and converts it into xylene through transalkylation reaction in a fixed bed reactor under hydrogen conditions.
According to the different raw materials can be divided into 2 categories:
One is the toluene disproportionation and transalkylation technology, which mainly uses toluene and C≥9 aromatics as raw materials to produce xylene and a small amount of benzene;
The other is the benzene and C≥9 aromatics transalkylation technology, which uses benzene and C≥9 aromatics as raw materials to produce xylene and toluene.
Toluene/benzene disproportionation and transalkylation technologies mainly include:
(1) The Tatoray process jointly developed by UOP Corporation of the United States and TORAY Corporation of Japan.
(2) TransPlus process developed by Exxon Mobil in the United States.
(3) MTDP-3 process developed by Exxon Mobil.
(4) S-TDT disproportionation process developed by Sinopec.
5. Xylene Isomerization
The core of xylene isomerization technology is the isomerization catalyst. At present, the process flow (including reaction and separation system) of the isomerization unit in most of the industrialized xylene hydroisomerization technologies in the world is basically similar.
This technology converts ethylbenzene into xylene or deethylation to generate benzene through the mutual isomerization of p-(m/o)-xylene, which can be divided into two types: ethylbenzene conversion type and ethylbenzene deethylation type.
Among them, the advantage of ethylbenzene conversion type is that it can use limited C8 aromatic hydrocarbon resources to produce PX in the largest amount, but the single-pass conversion rate of ethylbenzene is low;
The advantages of the deethylation type are high reaction space velocity and high ethylbenzene conversion rate, but the utilization rate of C8 aromatic hydrocarbon resources is relatively low.
The xylene isomerization technology mainly includes:
(1) The Isomar process developed by UOP.
(2) XyMax process developed by Exxon Mobil.
(3) LPI process developed by Exxon Mobil.
(4) The xylene isomerization process developed by Sinopec.
6. Coal Aromatics
Coal-to-aromatics technology is an emerging aromatics production technology, which can maximize the comprehensive utilization of resources while broadening the sources of raw materials for aromatics production. The technology first uses coal as the raw material to produce methanol, and then uses methanol as the raw material to use dual-function active catalysts to produce aromatic hydrocarbons through dehydrogenation and cyclization reactions.
(1) MTA
The technology uses methanol as the raw material to catalyze the conversion into products mainly composed of mixed aromatic hydrocarbons, and then separates the gas-phase product low-carbon hydrocarbons from the liquid-phase products C≥5 hydrocarbons through cooling and separation, and the liquid-phase products C≥5 hydrocarbons are extracted and separated to obtain Aromatic and non-aromatic hydrocarbons. MTA technology is a large-scale methanol downstream conversion technology. Its methanol conversion rate is higher than 99%, the liquid phase product selectivity is higher than 33%, the gas phase product selectivity is lower than 10%, and the aromatics mass fraction in the liquid phase product is higher than 60%.
(2) FMTA
The aromatization reaction was carried out under the process conditions of reaction pressure of 0.1MPa and reaction temperature of 500℃. The methanol conversion rate was close to 100%, the yield of aromatic hydrocarbon groups was 74.47%, and the unit consumption of 1 t of aromatic hydrocarbons was 3.07t.
The advantages of FMTA technology integration are obvious, and many coal-to-aromatics projects plan to adopt this technology.
(3) Alkylation of benzene with methanol
This technology not only fills the domestic technical gap of increasing xylene production from benzene, but also realizes high value-added application of coal chemical products.
(4) Alkylation of toluene with methanol
Toluene methanol alkylation technology has become an economical and efficient process route for the production of PX due to its advantages of low raw material cost, high PX product yield, low energy consumption, flexible production, and convenient optimization and adjustment.
