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I. Hydrofining 4 W$ |2 v1 P/ H, E S( n% ^ Hydrofining is primarily used in the refining of oils, with the aim of removing sulfur, nitrogen, oxygen-containing atoms, and metal impurities from the oil, thereby improving its performance. Thanks to the development of reforming processes, large amounts of by-product hydrogen can be generated, creating favorable conditions for the development of hydrofining processes. As a result, hydrofining has become a widely used processing method in refineries, and it is also replacing other types of oil refining methods. / e+ e; O8 v A ㈠ The main reactions in hydrorefining % ?6 X D" Z8 }! N+ N v9 { The main reactions in hydrorefining include: . X7 }7 S, ^$ U9 ^8 ] D1 – Hydrodesulfurization! A, c$ c# M' Z" U& h 2 – Hydrodenitrogenation L; w: J) c8 s, 3 – Hydrodeoxygenation5 |& v+ |/ l' ]+ ]7 u 4 – Hydrodemetallization of heavy oils 8 l1 d9 B6 Y$ K5. Among various hydrocarbons, naphthenes and alkanes rarely undergo reactions, while most olefins react with hydrogen to form alkanes. ! F# k! Z+ H+ R% a4 H( @In hydrorefining, hydrodesulfurization occurs more easily than hydrodenitration; among various heteroatom-containing compounds, those containing nitrogen are the hardest to hydrogenate. For example, during the hydrorefining of coker diesel, when the desulfurization rate reaches 90%, the denitration rate is only 40%. & Features of hydrogenated refining products: good quality, including stability, non-corrosiveness, and high liquid yield – all of which are determined by the hydrogenation refining reaction itself. ( o: R% P& y; ^, D1 n* p) J ㈡ Hydrofining process unit 4 G0 q! j4 j9 \8 m, S$ The hydrofining process varies depending on the feedstock, but the basic principles remain the same. As shown in Figure 3-10, it consists of three parts: a reaction system, a heat exchange unit for the product oil, a cooling system, a separation system, and a recycled hydrogen system. 0 _* E9 m; I/ t0 M5 p1 a/ a3 | 1. In the reaction system, “J- _: P7 u% i; ?5 S; W”, the crude oil is mixed with fresh hydrogen and recycled hydrogen, and after exchanging heat with the reaction products, it enters the heater in a gas-liquid mixture state before being heated to the reaction temperature and then fed into the reactor. The reactor feed can be a gas phase (for refining gasoline) or a gas-liquid mixture (for refining diesel). The catalyst in the reactor is generally filled in layers to facilitate the injection of cold hydrogen for controlling the reaction temperature (hydrofining is an exothermic reaction). The mixture of recycled hydrogen and oil undergoes hydrogenation reaction through each catalyst bed. 9 m7 i* N" R$ R7 ? The hydrogenation reactor can be one or two. The former is called the one-stage hydrogenation method, while the latter is called the two-stage hydrogenation method. The two-stage hydrogenation method is suitable for the refining of certain straight-run kerosenes to produce high-density jet fuel. At this stage, the first stage is primarily hydrogenation refining, while the second stage is aromatic hydrogenation saturation. 8 x! v6 H7 K5 2. A oil heat exchange, cooling, and separation system is generated; 2 u$ ~6 i$ r, I9 U" h. The reaction products emerge from the bottom of the reactor, undergo heat exchange and cooling, and then enter the high-pressure separator. High-pressure washing water must be injected into the product in front of the cooler to dissolve the ammonia and part of the hydrogen sulfide generated by the reaction. The reaction products are separated into oil and gas in a high-pressure separator; the gas obtained is recycled hydrogen, which contains, in addition to hydrogen as its main component, small amounts of gaseous hydrocarbons (non-condensable gases) and hydrogen sulfide that is insoluble in water. The liquid product obtained is hydrogenated oil, which also contains small amounts of gaseous hydrocarbons and hydrogen sulfide. This oil is then subjected to depressurization before being fed into a low-pressure separator to further separate components such as gaseous hydrocarbons. The resulting product is sent to a distillation system to be separated into qualified products. ; R0 U# ^) Y$ i$ i 3. The recycled hydrogen system: The recycled hydrogen separated from the high-pressure separator passes through storage tanks and a recycled hydrogen compressor; a small portion of it (about 30%) goes directly into the reactor as cooling hydrogen, while the rest is sent to be mixed with the feed oil for reuse within the plant. To ensure the purity of the recycled hydrogen (not less than 65% by volume) and prevent the accumulation of hydrogen sulfide in the system, hydrogen sulfide recovery systems are commonly used; the desorbed hydrogen sulfide is sent to sulfur production units for sulfur recovery, while the purified hydrogen is reused. * _9 R3 D, X, g: l To maintain the hydrogen concentration in the recycled hydrogen, a fresh hydrogen compressor is used to continuously supply fresh hydrogen to the system. - Q1 }' n5 C' {! l, @# q4 V The operating conditions for the hydrogenation refining of petroleum fractions vary depending on the feedstock. Generally speaking, the hydrogenation refining conditions for straight-run distillates are relatively mild, while more stringent operating conditions are required for heavy distillates and secondary processed products. ' d# H5 _7 y5 n4 B, W& x II. Hydrocracking 5 s) ~& `2 r4 Q# G, D8 n Hydrocracking is a catalytic processing method in which heavy feedstocks are processed in the presence of a catalyst and hydrogen to produce various light fuel oils. , z# i V& x" p2 S2 P* A7 q4 a The most fundamental principle behind using heavy crude oil to produce light fuel oils is to change the molecular weight and hydrocarbon ratio of the heavy crude oil; these two changes often occur simultaneously. There are two ways to change the carbon-hydrogen ratio ； One is decarbonization, and the other is hydrogenation. Thermal processing processes such as thermal cracking, coking, and catalytic cracking fall under the category of decarburization. Their common feature is that they increase the hydrocarbon ratio of certain oils; as a result, it is inevitable that some gaseous hydrocarbons as well as condensed products with a high hydrocarbon ratio are generated, along with coke and residue. Therefore, the yield of light oil in the decarbonization process cannot be very high. 8 t# ]9 ?3 F8 V0 L) D/ o Hydrocracking is a form of hydrogenation; hydrogen is introduced from the outside in the presence of a catalyst to reduce the hydrocarbon ratio of the feed oil. % Hydrocracking is essentially a combination of hydrogenation and catalytic cracking. Therefore, it can not only prevent the formation of large amounts of carbon deposits during processes such as catalytic cracking, but also remove nitrogen, oxygen, and sulfur-containing organic impurities from crude oil through hydrogenation. It can also saturate the unsaturated hydrocarbons formed during the reaction; thus, hydrocracking enables the conversion of low-quality crude oil into high-quality light oils. . w, O; g! ]* S ㈠ The chemical reactions in the hydrocracking process “i; Z. k O. n9 R0 E6 P”. Under high temperature and pressure, along with the presence of hydrocracking catalysts, petroleum hydrocarbons undergo a series of chemical reactions that convert heavy oils into lighter ones. The main reactions include cracking, hydrogenation, isomerization, cyclization, as well as desulfurization, denitration, and demetallization. 4 y7 Z/ @4 h/ Y’ @; f2 F! O+ ]3 a4 q1. Alkanes; {: |% D3 @* e9 ^4 B. The hydrocracking reaction of alkanes involves two steps: the breaking of C-C bonds in the reactant molecules, and the hydrogenation of the resulting unsaturated fragments. For example: C16H34 → C8H18 + C8H16. Y4 O) Q8 \ H2 {0 |7 M- @. ~ C8H18 : u’ y9 N9 {* \5 M7 J/ J. The olefins produced in this reaction are first isomerized and then hydrogenated to form isomeric alkanes. The hydrogenation rate of alkanes increases as the molecular weight of the alkanes increases, and the isomerization rate also increases with rising molecular weight. - q. _7 ^4 h- e 2, Alkenes. Both the decomposition of alkanes and the cleavage of cyclic hydrocarbons with side chains yield alkenes. Under hydrocracking conditions, the hydrogenation of olefins to saturated hydrocarbons occurs at the fastest rate. In addition, polymerization and cyclization reactions are also carried out. R-CH2CH=CH2 + H2¾® R-CH2CH2CH3 / V3 n+ h2 W D+ n0 S3; cycloalkanes * U4 h7 F0 H5 S5 I* `0 V. Single-ring cycloalkanes undergo isomerization, ring opening, dealkylation, and minor dehydrogenation reactions during this process; bifunctional cycloalkanes and polycyclic cycloalkanes first undergo isomerization to form pentacyclic derivatives before ring opening occurs. The reaction products mainly consist of cyclopentane, cyclohexane, and alkanes. g% S2 r(i9 j4 b4); Aromatic hydrocarbons $s7 q0 C5 M3 W” J9 ?$ The hydrocracking of monocyclic aromatics differs from that of monocyclic naphthenes. When there are three or more carbon atoms in the side chain, isomerization does not occur first – instead, the side chain is broken off, resulting in the formation of corresponding alkanes and aromatics. In addition, a small portion of the aromatics may undergo hydrogenation and saturation to form naphthenes, which then continue to react according to the reaction patterns of naphthenes. 8 O; E: V1 _( A6 v0 |, ]6 k) n$ The hydrocracking of bicyclic, polycyclic, and fused aromatic hydrocarbons occurs in stages: typically, one aromatic ring is first hydrogenated to form a cycloalkane, after which the cycloalkane ring breaks apart to yield a monoalkylaromatic compound, and subsequent reactions proceed according to the rules applicable to monocyclic aromatic compounds. In the presence of hydrogen, the condensation reaction of polycyclic aromatics is inhibited, so coke products are not easily formed. / 5. Non-hydrocarbon compounds: Sulfur, nitrogen, and oxygen-containing compounds in the crude oil undergo hydrogenation under hydrocracking conditions, resulting in the formation of hydrogen sulfide, ammonia, and water, which are then removed. Therefore, the hydrogenated product does not require further purification. 2 d5 ^' o: V' j8 o, E& p! L N In the aforementioned hydrocracking reaction, the hydrogenation reaction is an exothermic process, while the cracking reaction is endothermic; these two effects partially offset each other, but the overall result remains an exothermic process. & m* l* y! _, c" J Based on these various chemical reactions, the hydrocracking process exhibits the following characteristics: 3 x4 `5 @1 |: T. j (1) Production flexibility ( R W" L, ~0 @% q/ A" ^ Hydrocracking has a high degree of adaptability to different feedstocks; it can process a wide range of materials, including straight-run diesel, coker wax oil, catalytic cycle oil, deasphalted oil, atmospheric residue, and vacuum residue. 8 w7 q' ~3 K* h; Q1 @( f: The hydrocracking product scheme can be adjusted as needed. It is possible to focus on the production of gasoline, or on the production of jet fuel with a low freezing point and high smoke point; it is also possible to prioritize the production of diesel with a low pour point. In short, by changing the catalysts and adjusting the operating conditions according to needs, different production processes can be employed to obtain the desired products. ( h4 u9 |- F8 q (2) The product quality is good and the yield is high. + x( h, A2 x" d The main characteristics of hydrocracking products are low levels of unsaturated hydrocarbons and low amounts of non-hydrocarbon impurities; as a result, these oils have good stability, do not cause corrosion, and contain plenty of naphthenes, making them suitable as feedstock for reforming processes. $ s! ]6 ]7 {0 C+ J" n$ D0 L( W㈡ Hydrocracking process units # i8 o2 u# Q2 o0 I8 Q1 Q- V. The hydrocracking process can be designed as a single-stage process, a two-stage process, or a cascade process, depending on the properties of the feedstock, the requirements for the products, the volume of material to be processed, and the performance of the catalysts. The following mainly introduces one-stage and two-stage hydrocracking processes. _' X3 d7 @) X0 W, P1 – A hydrocracking process: 1 @’ N3 Q/ p* K3 j/ x! a% K! E’ U7 F. The feed oil is pressurized to 16.0 megapascals using a pump, after which it is mixed with fresh hydrogen and recycled hydrogen. It is then heated to a temperature of 320°C–360°C by exchanging heat with the hydrocracking product at around 420°C, before being fed into the heater. The reactor feed temperature ranges from 370°C to 450°C. The reaction conditions of the raw materials in the reactor are maintained at a temperature of 380°C to 440°C, with a space velocity of 1.0 h⁻¹ and a hydrogen-to-oil volume ratio of 2500. To control the reaction temperature, cold hydrogen is injected into the reactor in layers. The reaction product is cooled to 200°C by heat exchange with the raw materials, and after further cooling to 30°C–40°C, it enters the high-pressure separator. Soft water is injected into the reaction products before they enter the air cooler to dissolve substances such as NH3 and H2S, thereby preventing the formation of hydrates that could block the pipes. Cyclic hydrogen is taken out from the top of the high-pressure separator; after being pressurized to the reactor inlet pressure by a cyclic hydrogen compressor, it is returned to the system for reuse. The hydrogenation product oil is obtained from the bottom of the high-pressure separator; it is depressurized to 0.5 MPa via a pressure reduction system and then enters the low-pressure separator, where water is removed and dissolved gases are released. This gas, which is rich in hydrocarbons, is sent out as fuel gas. The produced oil is heated and fed into a stabilizer column, where liquefied gas is distilled at a pressure of 1.0 MPa to 2.0 MPa. The liquid at the bottom of the column is heated in a furnace and then sent to a distillation column, where light gasoline, aviation kerosene, low-flashpoint diesel, and residual oil from the bottom of the column are finally separated. The tail oil can be used in part or in its entirety as recycled oil, returning to the reaction system after being mixed with the raw material, or it can be sent out of the plant as fuel oil. $ V1 W1 e8 y’ t0 O2 t; N9 Y2 – two hydrocracking processes) z) L) {1 w6 f6 b8 l0 I3 g’ { The feed oil is pressurized by a high-pressure pump and mixed with recycled hydrogen and fresh hydrogen; it first exchanges heat with the product oil, and then is heated to the reaction temperature in a heating furnace before entering the first hydrofinishing reactor. Desulfurization and denitration reactions are carried out using catalysts with high hydrogenation activity, during which the heavy metals in the feed oil are also removed. The reaction products are cooled through heat exchange before entering a high-pressure separator, where the recycle hydrogen is separated out. The produced oil enters the deammoniation (desulfurization) tower; after NH3 and H2S are removed, it is used as feed for the second stage of hydrocracking. After being mixed with recycled hydrogen, the second feed enters the second heating furnace where it is heated to the reaction temperature. It then undergoes cracking in the second hydrocracking reactor, which is equipped with highly acidic catalysts. The reaction products are subjected to heat exchange, cooling, and separation; after the dissolved gases and recycled hydrogen are separated, they are sent to the stabilization system. # The characteristics of the two-stage hydrocracking process of n! x- O5 ^/ ]- I are its strong adaptability to feedstocks; by changing the catalyst in the first stage, it is possible to process various types of feedstocks, such as heavy crude oils with high nitrogen and aromatic content. The second stage can employ different operating conditions to alter the product distribution of the produced oil. 0 T4