Environment-friendly multi-carbon alcohol fuel additive and preparation method thereof

Abstract

The invention discloses an environment-friendly multi-carbon alcohol fuel additive and a preparation method thereof. The preparation method comprises the steps of raw material pretreatment, catalytic conversion and separation, multi-carbon alcohol synthesis reaction, rectification purification, fuel additive compounding and the like. According to the invention, naphtha and methanol are used as compound raw materials, a denaturation additive is used as an auxiliary material, multi-carbon alcohol with low cost and high content is prepared by a specific process route, main components comprise isobutanol and isooctanol as core components, the main product multi-carbon alcohol can optimize the acting force between fuel oil molecules and promote fuel oil atomization, and the fuel oil atomization effect is improved. The multi-component (derived from the denatured additive) contained in the fuel oil additive has the effects of combustion supporting, dissolution assisting, oxidation resisting and octane number increasing, compatibility of all the components can be guaranteed, oxidative deterioration of the fuel oil is inhibited, the cleanliness, the dynamic property and the anti-knock property of the fuel oil are integrally improved, and emission is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel additives, and in particular to an environmentally friendly polyol fuel additive and a preparation method thereof. Background Art

[0002] With the development of the automotive industry, the development of high-performance, environmentally friendly fuel additives has become a key focus in the energy and chemical industry. Traditional fuel additives rely heavily on petroleum-based raw materials (such as MTBE and ethanol) or organometallic compounds (such as MMT), which present challenges such as non-renewable raw materials, high costs, metal residue contamination, and poor biodegradability.

[0003] Polyols (such as isobutanol and isooctyl alcohol) are considered ideal clean fuel components due to their high octane number, oxygen-supported combustion, and excellent fuel compatibility. However, their industrial production still faces challenges: 1) Raw material dependence and cost issues: Polyols are mainly produced through Fischer-Tropsch synthesis, olefin carbonylation or biofermentation. They have problems such as limited raw material sources (such as synthesis gas), expensive catalysts (such as rhodium-based catalysts), high process energy consumption or complex product separation, making it difficult to meet the cost requirements of the large-scale fuel additive market.

[0004] 2) Insufficient compounding functionality: Single polyol components are prone to phase separation and weak antioxidant properties in fuel, requiring the addition of functional additives such as cosolvents and explosion-proof agents. However, existing compounding technologies often lead to poor synergistic effects between components and even introduce harmful substances (such as chlorine-containing compounds).

[0005] 3) Environmental defects: Some metal-containing additives (such as lead salts) have been banned, while the cleanliness of ash-free additives (such as carbon deposit inhibition and exhaust emission reduction) still needs to be improved.

[0006] On the other hand, methanol, as a cheap renewable raw material, has defects such as corrosiveness, high vapor pressure and difficulty in cold start when directly blended into fuel, which limits its application in fuel.

[0007] In recent years, researchers have tried to use methanol and low-carbon olefins to couple to prepare high-carbon alcohols, but there are generally bottlenecks such as lengthy process routes (such as methanol to olefins + olefin carbonylation requires multiple sets of equipment), complex catalyst systems (such as poor compatibility of multi-stage catalysts), and low product selectivity (large amounts of alkanes or water are produced as by-products).

[0008] Therefore, there is an urgent need to develop a fuel additive and its preparation method that features readily available raw materials, a highly integrated process, high polyol yields, and multifunctional, environmentally friendly properties, in order to overcome the limitations of existing technologies. Traditional fuel additives suffer from a single ingredient and limited effectiveness, including insufficient cleaning capacity and an inability to effectively balance power enhancement and emission reduction requirements.

[0009] Due to their unique molecular structure, polyol compounds have the potential to improve fuel atomization and enhance combustion efficiency. However, the existing polyol preparation process is complex and the product purity and performance are difficult to control, which restricts their application in fuel additives. Therefore, it is necessary to develop new preparation methods and high-efficiency fuel additives based on them. Summary of the Invention

[0010] The purpose of the present invention is to solve the shortcomings of the prior art and to propose an environmentally friendly polyol fuel additive and a preparation method thereof.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention first proposes a method for preparing an environmentally friendly polyol fuel additive, comprising the following steps: 1) Raw material pretreatment Methanol, naphtha, and a denaturing additive are added to a stirring tank in proportion, heated and stirred to mix uniformly, and then transported to a tubular reactor via gear pump a. In the absence of oxygen, at 260±5°C, and under the action of a Mo2C / HZSM-5 catalyst (from the Shandong Research Institute of Tianjin University, Professor Bai Peng's team), the naphtha is cracked to produce C2-C4 alkenes. At 260°C, the naphtha cracking efficiency is less than 50%. Increasing the temperature increases the risk of aromatic alkylation and other side reactions. Therefore, the present invention only adopts a low-temperature partial cracking combined with a cyclic reaction. 2) Catalytic conversion and separation The product from the tubular reactor enters catalytic reactor a, where methanol is converted into dimethyl ether under the conditions of 260±10°C using an Al-DME-1 catalyst (referring to the DME-1 catalyst labeled A1 in the present invention and produced by Sheng'an Biotechnology). After cooling in cooler a, the gas phase (containing H2, CO, etc.) enters a gas collecting tank, where C1-C3 hydrocarbons are separated by a vacuum compressor unit, and the liquid phase (containing dimethyl ether, etc.) is temporarily stored in buffer tank a. 3) Polyol synthesis reaction The material in buffer tank a is heated to 300°C via gear pump b and heat exchanger a, and then enters catalytic reactor b. Methanol / dimethyl ether reacts with olefins to form polyols over a B2-ZnZSM-5 catalyst (designated B2 in this invention and produced by Zoran Environmental Protection) at 280±10°C. After the reaction, the material is cooled in cooler b, the non-condensable gas is separated, and the liquid polyols enter buffer tank b. 4) Distillation and purification The material in the buffer tank b is processed by the gear pump c, the intermediate tank, the gear pump d, and the heat exchanger b and then enters the distillation tower. The temperature is controlled by the coolers c and d, and the polyol products such as the 108°C fraction (isobutanol) and the 184°C fraction (isooctanol) are collected in the finished product tank a and the finished product tank b, respectively, to obtain high-purity polyol components.

[0012] Preferably, the mass ratio of naphtha, methanol and denaturing additive in the stirring tank is 10: (2-4): (0.3-0.6), which can be fine-tuned according to the raw material purity and reaction efficiency to ensure effective cracking of naphtha and sufficient raw materials for subsequent reactions.

[0013] Preferably, the denaturing additive comprises the following components in parts by weight: 100 parts of acetone (cosolvent), 20-25 parts of toluene (explosion-proof agent), 10-15 parts of benzoic acid (metal passivator, protecting catalyst stability), 25-30 parts of ferrocene (de-iron treatment, i.e., removing excess residual iron oxides, co-catalyst), 3-5 parts of zinc oxide (desulfurizer, adsorbing sulfides to prevent catalyst poisoning); Preferably, the oil fraction (mainly alkylate oil) at the bottom of the distillation tower is returned to the stirring tank to continue the cracking reaction as a partial substitute for naphtha; Preferably, the non-condensable gas in the buffer tank a, buffer tank b, finished product tank a and finished product tank b is collected in a gas collecting tank. After being cooled by circulating water at -7°C, the liquid part (mainly C4-C6 hydrocarbons) enters the condensate tank, and the gas part is introduced into the vacuum compressor unit. At a pressure of 10-15MPa, the small molecular gas components (mainly H2 and CO) are removed to obtain liquid low-carbon hydrocarbons (mainly C1-C3 hydrocarbons).

[0014] Preferably, part of the non-condensable gas in the buffer tank a, buffer tank b, finished product tank a and finished product tank b can also be compressed and then enter the gas incineration system.

[0015] The present invention also proposes that the environmentally friendly polyol fuel additive obtained by the above preparation method needs to undergo the following compounding process: According to the performance requirements of fuel additives, the content of polyol components in the intermediate tank is tested. When the polyol components are too high, some of the polyols should be distilled out through a distillation tower, and the polyol content in the oil at the bottom of the distillation tower is tested. When the content meets the standard, the oil at the bottom of the distillation tower is directly taken as a fuel additive. When the polyol components are too low, the methanol content in the stirring tank should be increased, or the polyols should be enriched multiple times in the distillation tower, and the purified polyols should be directly mixed with the components in the intermediate tank to obtain the fuel additive.

[0016] In addition to the function of maintaining high octane number through polyols and high-carbon hydrocarbons (C7-C11), the fuel additive also contains denaturing additives, except for zinc oxide which is retained by the catalytic system. The remaining components still play a role in the fuel combustion process. Among them, acetone acts as a solubilizing and combustion aid, toluene has explosion-proof effects and improves the octane number, benzoic acid acts as an antioxidant and metal passivator, and ferrocene is a combustion-supporting catalyst, which can significantly reduce the CO and hydrocarbon compounds in vehicle exhaust emissions, making it an environmentally friendly fuel additive.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses naphtha and methanol as compound raw materials, supplemented with denaturing additives, and uses a specific process route to prepare low-cost and high-content polyols. The main components contain isobutanol and isooctyl alcohol as core components. Among them, the main product polyol can optimize the intermolecular forces of fuel and promote fuel atomization. The multiple components contained therein (derived from the denaturing additives) have the effects of supporting combustion, promoting solubility, resisting oxidation and improving octane number. They can ensure the compatibility of various components, inhibit the oxidation and deterioration of fuel, and overall improve the cleanliness, power and anti-knock properties of fuel, thereby reducing emissions.

[0018] 2. The product of the present invention can be added to fuel to effectively clean engine carbon deposits. Continuous use can reduce carbon deposits in the fuel injector and combustion chamber; improve fuel combustion efficiency and reduce fuel consumption; enhance anti-knock performance and adapt to a variety of engine compression ratios; and significantly reduce emissions of pollutants such as CO and hydrocarbons in exhaust gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a process flow chart of the preparation method of the environmentally friendly polyol fuel additive proposed by the present invention. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the existing known technologies. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0021] 1. Preparation process Reference Figure 1 The present invention first proposes a method for preparing an environmentally friendly polyol fuel additive, comprising the following steps: 1) Raw material pretreatment Methanol, naphtha, and denaturing additives are added to a stirring tank in proportion, heated and stirred to mix evenly, and then transported to a tubular reactor via a gear pump a. In the absence of oxygen, at 260±5°C, and under the action of a Mo2C / HZSM-5 catalyst, the naphtha is cracked to produce C2-C4 olefins. 2) Catalytic conversion and separation The product from the tubular reactor enters catalytic reactor a, where methanol is converted into dimethyl ether under the conditions of Al-DME-1 catalyst and 260±10℃. After cooling in cooler a, the gas phase (containing H2, CO, etc.) enters the gas collecting tank, where C1-C3 hydrocarbons are separated by a vacuum compressor unit and reused as fuel gas. The liquid phase (containing dimethyl ether, etc.) is temporarily stored in buffer tank a. 3) Polyol synthesis reaction The material in buffer tank a is heated to 300°C by gear pump b and heat exchanger a, and then enters catalytic reactor b. Under the conditions of B2-ZnZSM-5 catalyst and 280±10°C, methanol / dimethyl ether reacts with olefins to produce polyols. After the reaction, it is cooled in cooler b, the non-condensable gas is separated, and the liquid polyols enter buffer tank b. 4) Distillation and purification The material in the buffer tank b is processed by the gear pump c, the intermediate tank, the gear pump d, and the heat exchanger b and then enters the distillation tower. The temperature is controlled by the coolers c and d. The 108°C fraction (isobutanol) and the 184°C fraction (isooctanol) and other polyol products are collected and respectively collected in the finished product tank a and the finished product tank b to obtain high-purity polyol components.

[0022] The mass ratio of naphtha, methanol and denaturing additive in the stirring tank is 10: (2-4): (0.3-0.6), which can be fine-tuned according to the raw material purity and reaction efficiency to ensure effective cracking of naphtha and sufficient raw materials for subsequent reactions.

[0023] The denaturing additive comprises the following components by weight: 100 parts of acetone (cosolvent), 20-25 parts of toluene (explosion-proof agent), 10-15 parts of benzoic acid (metal passivator, protecting catalyst stability), 25-30 parts of ferrocene (de-iron treatment, i.e., removing excess residual iron oxides, co-catalyst), and 3-5 parts of zinc oxide (desulfurizer, adsorbing sulfides to prevent catalyst poisoning). The oil at the bottom of the distillation tower (mainly alkylate) is returned to the stirring tank to continue the cracking reaction as a partial substitute for naphtha; Among them, the non-condensable gas in the buffer tank a, buffer tank b, finished product tank a and finished product tank b is collected in a gas collecting tank. After being cooled by circulating water at -7°C, the liquid part (mainly C4-C6 hydrocarbons) enters the condensate tank, and the gas part is introduced into the vacuum compressor unit. At a pressure of 10-15MPa, the small molecular gas components (mainly H2 and CO) are removed to obtain liquid low-carbon hydrocarbons (mainly C1-C3 hydrocarbons).

[0024] Part of the non-condensable gas in the buffer tank a, buffer tank b, finished product tank a and finished product tank b can also be compressed and then enter the gas incineration system.

[0025] The following examples and comparative examples are designed according to the above preparation method: Example 1

[0026] Raw material ratio: Naphtha: 100kg; Methanol: 30 kg (mass ratio 3:10); Denaturing additive: 3.4 kg (based on 100 parts of acetone), including: Acetone: 3.0 kg; Toluene: 0.9 kg (22.5 parts); Benzoic acid: 0.6 kg (15 parts); Ferrocene: 1.35 kg (30 parts); Zinc oxide: 0.15kg (5 parts).

[0027] Process parameters: Cracking reaction: Tubular reactor temperature 260 ° C, catalyst Mo2C / HZSM-5, C2-C4 olefins accounted for 15.6% of the cracking products; Dimethyl ether synthesis: catalytic reactor a temperature 260 ° C, Al-DME-1 catalyst, methanol conversion rate 92.1%; Polyol synthesis: Catalytic reactor b temperature 280 ° C, B2-ZnZSM-5 catalyst, polyol yield 41.5% (calculated as olefins); Distillation purification: 108℃ fraction (isobutanol): purity ≥98%; 184℃ fraction (isooctanol): purity ≥97%; By-product treatment: The oil fraction (alkylate) at the bottom of the distillation tower is recycled to the mixing tank to replace 15% of the naphtha; The non-condensable gas is compressed and circulated as the reaction driving gas phase, reducing raw material loss by 5%; if the local natural gas supply is insufficient, it can also be mixed with natural gas.

[0028] Final product performance: Fuel additive octane number (RON): 118 Engine bench test: Fuel consumption reduced by 7%, exhaust CO emissions reduced by 42%, and carbon deposit reduction rate reduced by 89%. Example 2

[0029] Raw material ratio: Naphtha: 100kg; Methanol: 40kg; Denaturing additive: 6 kg (based on 100 parts of acetone), including: Acetone: 3.68 kg; Toluene: 0.92 kg (25 parts); Benzoic acid: 0.37 kg (10 parts); Ferrocene: 0.92 kg (25 parts); Zinc oxide: 0.11 kg (3 parts).

[0030] Process parameters: Cracking reaction: Tubular reactor temperature 255°C, catalyst Mo2C / HZSM-5, C2-C4 olefins account for 14.1% of the cracking products; Dimethyl ether synthesis: catalytic reactor a temperature 250 ° C, Al-DME-1 catalyst, methanol conversion rate 92%; Polyol synthesis: Catalytic reactor b temperature 270 ° C, B2-ZnZSM-5 catalyst, polyol yield 41% (calculated as olefins); Distillation purification: 108℃ fraction (isobutanol): purity ≥98%; 184℃ fraction (isooctanol): purity ≥97%; By-product treatment: The oil fraction (alkylate) at the bottom of the distillation tower is recycled to the mixing tank to replace 15% of the naphtha; The non-condensable gas is compressed and circulated as the reaction driving gas phase, reducing the raw material loss by 5%; Final product performance: Fuel additive octane number (RON): 123 Engine bench test: Fuel consumption reduced by 8%, exhaust CO emissions reduced by 41%, and carbon deposit reduction rate reduced by 84%. Example 3

[0031] Raw material ratio: Naphtha: 100kg; Methanol: 20kg; Denaturing additive: 3 kg (based on 100 parts of acetone), including: Acetone: 1.83 kg; Toluene: 0.37 kg (20 parts); Benzoic acid: 0.24 kg (12 parts); Ferrocene: 0.50 kg (27 parts); Zinc oxide: 0.06 kg (3.3 parts).

[0032] Process parameters: Cracking reaction: Tubular reactor temperature 265°C, catalyst Mo2C / HZSM-5, C2-C4 olefins account for 17.1% of the cracking products; Dimethyl ether synthesis: catalytic reactor a temperature 270 ° C, Al-DME-1 catalyst, methanol conversion rate 94%; Polyol synthesis: Catalytic reactor b temperature 290 ° C, B2-ZnZSM-5 catalyst, polyol yield 43.1% (calculated as olefins); Distillation purification: 108℃ fraction (isobutanol): purity ≥98%; 184℃ fraction (isooctanol): purity ≥97%; By-product treatment: The oil fraction (alkylate) at the bottom of the distillation tower is recycled to the mixing tank to replace 15% of the naphtha; The non-condensable gas is compressed and circulated as the reaction driving gas phase, reducing the raw material loss by 5%; Final product performance: Fuel additive octane number (RON): 116 Engine bench test: Fuel consumption reduced by 6%, exhaust CO emissions reduced by 43%, and carbon deposit reduction rate reduced by 87%.

[0033] Comparative Example 1 (no catalyst) Based on Example 1, no Mo2C / HZSM-5 catalyst was added to the tubular reactor. result: Naphtha cracking efficiency is only 10.5%, and the proportion of C2-C4 olefins has dropped to 2.9%; The yield of polyols plummeted to 4.3%; The octane number (RON) of the distillation product is only 101.

[0034] Comparative Example 2 (without denaturing additive) Based on Example 1, the denaturing additive was removed from the stirred tank. The results were: Iron oxides were deposited in the reaction system, and the catalyst activity decreased by 50% after 3 hours; Sulfide poisoned the B2-ZnZSM-5 catalyst, and the yield of polyols dropped to 22%. After 7 days of storage, the product separated and precipitated.

[0035] Comparative Example 3 (Temperature out of control) Based on Example 1, the temperature of catalytic reactor b was raised to 310°C (outside the range of 280±10°C). The results were as follows: Excessive cracking causes the proportion of C1-C3 hydrocarbons to increase to 40%; The isooctyl alcohol content in the target polyol product is less than 50%, and the proportion of fusel oil increases; The fuel additive anti-knock rating (RON) is only 105.

[0036] Comparative Example 4 (by-products not recycled) On the basis of Example 1, the oil content and non-condensable gas at the bottom of the distillation tower were directly discharged without being reused. The results were as follows: Raw material utilization rate decreased by 28%, and the additional amount of naphtha and methanol required increased; Alkylate losses lead to a 20% increase in naphtha usage; The economic efficiency has deteriorated significantly, and the cost has increased by 35%.

[0037] 2. Products The obtained environmentally friendly polyol fuel additive needs to undergo the following compounding process: According to the performance requirements of fuel additives, the content of polyol components in the intermediate tank is tested. When the polyol components are too high, some of the polyols should be distilled out through a distillation tower, and the polyol content in the oil at the bottom of the distillation tower is tested. When the content meets the standard, the oil at the bottom of the distillation tower is directly taken as a fuel additive. When the polyol components are too low, the methanol content in the stirring tank should be increased, or the polyols should be enriched multiple times in the distillation tower, and the purified polyols should be directly mixed with the components in the intermediate tank to obtain the fuel additive.

[0038] In addition to the function of maintaining high octane number through polyols and high-carbon hydrocarbons (C7-C11), the fuel additive also contains denaturing additives, except for zinc oxide which is retained by the catalytic system. The remaining components still play a role in the fuel combustion process. Among them, acetone acts as a solubilizing and combustion aid, toluene has explosion-proof effects and improves the octane number, benzoic acid acts as an antioxidant and metal passivator, and ferrocene is a combustion-supporting catalyst, which can significantly reduce the CO and hydrocarbon compounds in vehicle exhaust emissions, making it an environmentally friendly fuel additive.

[0039] 3. Reaction principle description: 3.1 Catalytic reaction process After the raw materials are denatured, methanol and naphtha are preheated and gasified, mixed with the circulating gas, and after reaching the reaction temperature, they are cracked and enter the catalytic reactor a, where they are converted into a hydrocarbon mixture product mainly composed of dimethyl ether, C5-C10 and water under the action of the catalyst; after the etherification reaction, they enter the catalytic reactor b, and the outlet materials are cooled and separated to obtain crude gasoline, LPG and dry gas. The dry gas mainly consists of methane, ethane, and a small amount of hydrogen, CO, etc. Part of the dry gas leaves the system as purge gas, and part is compressed and recycled, mixed with methanol and then re-enters the reactor.

[0040] The product composition in the intermediate tank of Example 1 is shown in Table 1 below: Table 1. Composition of naphtha and methanol reaction products

[0041] 3.2 Product distribution of the obtained crude gasoline components after alkylation reaction Using isobutane and three different olefins, i.e., isobutylene, 1-butene, and 2-butene, as raw materials and acidification as catalyst, the alkylation products obtained are shown in Table 2 below: Table 2. Analysis of crude gasoline alkylation reaction products

[0042] As can be seen from Table 2: 1) The alkylation reaction of isobutane with C4 olefins produces not only C8 compounds, but also C6, C7, and heavy components above C9. From this, it can be inferred that the reaction mechanism is relatively complex; 2) In the distribution of alkylation reaction products, C8 compounds account for the majority, and among C8 compounds, 2,2,4-trimethylpentane accounts for the largest proportion, followed by 2,3,4-trimethylpentane and 2,3,3-trimethylpentane; 3) The types of reaction products in sulfuric acid alkylation are more than those in hydrofluoric acid alkylation, which may be because sulfuric acid alkylation involves more reaction processes.

[0043] 3.3 Alkylation chain reaction mechanism The main product of various butene-isobutane alkylation reactions is 2,2,4-trimethylpentane. In the alkylation reaction of propylene and isobutane, trimethylpentane also accounts for a considerable amount of the reaction products.

[0044] The alkylation reaction based on the carbonium ion theory can be summarized as the following chain reaction mechanism: Any chain reaction generally includes three steps, namely chain initiation, chain growth, and chain termination.

[0045] 3.3.1 Chain initiation In the alkylation reaction of isobutane with olefins, the olefin obtains hydrogen protons H+ to form positive carbon ions as the initiation process of the chain. The positive carbon ion on the tert-butyl group generated in the following formula plays a vital role in the alkylation reaction.

[0046] ; There are a few points to note about chain initiation: The dissociation of the acid generates hydrogen protons, which provide a positive ion source for the positive carbon ion. However, when the acid is in a completely non-dissociable state, such as under relatively dry conditions, that is, when there are no highly polar water molecules, the acid cannot dissociate and the alkylation reaction cannot occur.

[0047] Only the tert-butyl carbonium ion can serve as a chain carrier. If other straight-chain alkenes accept hydrogen protons, the situation is more complicated: either the straight-chain olefin itself isomerizes to the tert-butyl carbonium ion; or the carbonium ion of the straight-chain olefin abstracts the hydrogen anion of isobutane, turning isobutane into a tert-butyl carbonium ion to initiate the alkylation reaction.

[0048] Macromolecular carbon ions (available R + Indicates), especially acid-soluble hydrocarbons, are highly ionized and can abstract the hydrogen anion of olefins or isobutane to generate new tert-butyl carbonium ions.

[0049] The primary source of tert-butyl carbenium ions is isobutene. The carbenium ion formed by protonation of n-butene can also be converted to tert-butyl carbenium ions through hydrogen transfer. However, studies of the alkylation reaction mechanism have revealed that at least a portion of the traced n-butene is converted to isobutane, indicating that under acidic conditions, n-butene isomerizes to isobutene, which then undergoes hydrogen transfer to isobutane. Furthermore, the alkylation of isobutene with isobutane does not significantly increase the trimethylpentane content. When hydrogen transfer plays a primary role, it accelerates the dimerization and polymerization of isobutene, indicating that n-butene undergoes an isomerization process before the alkylation reaction. This is also the main reason why the product distributions obtained from the alkylation of isobutane with different olefins are generally similar.

[0050] 3.3.2 Chain Growth The following reaction equation explains the chain growth process. The tert-butyl carbonium ion captures the hydrogen ion to generate the product and ensures the continued existence of the tert-butyl carbonium ion.

[0051] ; 3.3.3 Chain Termination The growing carbenium ion usually extracts a hydrogen ion from isobutane, thus stopping the growth process. This is the way most alkylation chains terminate. However, it is rare for a growing carbenium ion to lose its hydrogen ion to form an olefin, as olefins are rarely found in alkylation product analysis. Moreover, if olefins are formed, they are immediately protonated under the alkylation conditions and re-enter the reaction.

[0052] ; The chemical reaction formula for the alkylation reaction between isobutane in the C4 fraction and isobutylene to produce 2,2,4-trimethylpentane is as follows: ; Alkylation principle: Alkylation is a chemical addition reaction between alkanes and alkenes. In this reaction, the active hydrogen atoms of the alkane molecule are replaced by alkenes. The raw materials for the alkylation unit are mainly isobutane, isobutylene, and butene-1 from catalytic cracking liquid hydrocarbons, and 98% concentrated sulfuric acid is used as a catalyst. The basic reaction formula is: C4H8 + H2SO4 → (C4H9)HSO4 (sulfate), (C4H9)HSO4 + C4H 10 →C8H 18 (isooctane) + H2SO 4。 The catalytic alkylation reaction of isoparaffins and alkenes can be explained by the carbenium ion mechanism, and its main reaction process is: 1) Addition reaction of olefins with hydrogen ions (provided by acid catalysts) (first, the proton on the catalyst adds to the double bond of the olefin) to form a carbenium ion: ; 2) Olefin carbenium ions react with isobutane to generate new carbenium ions ; 3) Addition reaction of tert-butyl carbenium ion with olefins The addition of the tert-butyl carbenium ion to the double bond is the decisive step in the alkylation reaction: ; 4) C n+4 H 2n+9 + The ion reacts with isobutane to produce alkylate oil (the generated carbocation reacts with isobutane to undergo hydrogen transfer to produce alkylate oil and tert-butyl carbocation, which maintains the carbocation bond and continues the reaction). The reaction formula is: ; The above reactions are the desired primary reactions in the alkylation process. However, side reactions such as cracking, cyclization, polymerization, disproportionation, self-alkylation, and the formation of catalyst complexes and esters can also occur. The extent of these reactions depends on the reaction conditions. Therefore, strict control of reaction conditions to enhance the primary reactions and minimize side reactions is crucial to the alkylation process.

[0053] 3.4 Types of Alkylation Reactions It can be seen from the composition table of alkylation products that the alkylation reaction process is much more complicated than the above-mentioned chain reaction mechanism. The reactions in the general process are as follows.

[0054] 3.4.1 Isomerization Alkylation with n-butene yields more 2,2,4-trimethylpentane than with isobutylene. Even with propylene, a considerable amount of 2,2,4-trimethylpentane is produced. A plausible explanation is that under acidic conditions, n-butene undergoes isomerization to form isobutylene, which then undergoes hydride ion transfer to form isobutane.

[0055] Note: C14 is a tracer atom commonly used in studying alkylation reactions.

[0056] ; The theory of isomerization reaction in alkylation reaction is generally accepted and confirmed by the following facts: At the reaction temperature of alkylation, the thermodynamic equilibrium among several butenes is in favor of isobutylene. Considering the thermodynamic advantage, the percentage of isobutylene is the highest.

[0057] According to research, the composition of the alkylation products obtained from various butenes is generally similar. This means that different butenes undergo isomerization reaction before entering the alkylation reaction, and different butenes are isomerized into a balanced olefin mixture with similar composition dominated by isobutylene, so the alkylation products of different olefins have similar compositions.

[0058] If n-butene directly participates in the chain initiation reaction, a considerable amount of n-butane will be produced. In fact, no significant amount of n-butane is produced in the alkylation reaction, which indicates that n-butene does not directly participate in the initiation of the alkylation reaction.

[0059] 3.4.2 Isobutylene dimerization or polymerization At low temperatures, isobutylene can polymerize under the action of an acidic catalyst to form a high polymer, polyisobutylene. At high temperatures, however, isobutylene dimerizes to produce isooctene, which can be hydrogenated to produce isooctane. Therefore, it is thought that the alkylation of isobutylene with isobutane does not involve the alkylation of one isobutane molecule with another, but rather the dimerization of isobutylene followed by the extraction of a hydrogen atom from the isobutane molecule.

[0060] Since dimerization occurs, trimerization and polymerization are inevitable, especially polymerization of isobutylene, resulting in the alkylation product always containing a certain amount of high-boiling products. Increasing the isobutane concentration in the alkylation reactor can reduce the chance of isobutylene collisions, thereby reducing the formation of high-boiling products. This is why the alkylene to olefin ratio in industrial production is controlled within the range of 15-20.

[0061] 3.4.3 Fracture reaction The olefins generated by the polymerization reaction obtain protons under the action of the catalyst to form positive carbon ions. These large molecular positive carbon ions can undergo a breakage reaction before abstracting hydrogen anions. The smaller molecular weight positive carbon ions generated abstract hydrogen anions to generate alkanes. This is the reason for the formation of alkanes such as C5 and C7.

[0062] There is also some evidence that a fracture reaction occurs: ① When 2,2,4-trimethylpentene was used as the alkylation raw material, low molecular weight products such as C5 and C7 isoalkanes were found in the reaction products, indicating that a breakage reaction occurred.

[0063] ② Trimethylpentane and dimethylhexane are degraded in the presence of sulfuric acid to generate a considerable amount of low molecular weight alkanes or olefins such as C4-C7.

[0064] Research on fragmentation reactions has found that macromolecular alkyl cations generated by olefin polymerization are intermediates in fragmentation reactions. Different types of fragmentation reactions may occur under different reaction conditions.

[0065] 3.4.4 Hydrogen ion transfer reaction The carbon ion has the potential to extract a hydrogen ion from another alkane molecule, thereby making itself a stable alkane and starting a new carbon ion.

[0066] ; Carbocations can abstract hydrides from olefins and larger polymer molecules in a reaction called a hydride transfer reaction. This hydride transfer reaction explains why 2,2,4-trimethylpentane can be produced during the alkylation of propylene with isobutane.

[0067] 3.4.5 Disproportionation reaction A small amount of C7 product can also be seen in the alkylation product of butene and isobutane, which is produced by the disproportionation reaction between C4 and C8.

[0068] ; 3.5 Interpretation of reaction products 1) 2,2,4-Trimethylpentane is the most important reaction product, accounting for approximately 20-50% of the total reaction products, depending on the alkylation feedstock, process, and reaction conditions. Its formation occurs through the co-dimerization of tert-butyl carbenium with isobutene, followed by the abstraction of a hydrogen atom from the isobutane. Under alkylation conditions, n-butene can isomerize to isobutene or tert-butyl carbenium. Propylene can also abstract the hydrogen anion from isobutane, converting isobutane to tert-butyl carbenium and ultimately isobutene, thereby producing 2,2,4-trimethylpentane.

[0069] 2) It is generally believed that dimethylhexane is produced by the dimerization of isobutene and n-butene and then the extraction of hydrogen anions from isobutane.

[0070] 3) The various isomers of C7 and C8 are produced by isomerization reactions at the carbonium ion stage after dimerization. They should not be the direct dimerization skeleton of n-butene and isobutene.

[0071] 4) The heavy compounds in the alkylation reaction product should be the products of olefin polymerization.

[0072] 5) The formation of light hydrocarbons such as C5, C6, and C7 is C12 + 、C16 + The fragmentation reaction of macromolecular carbon ions and C7 + 、C8 + Produced by the disproportionation reaction of positive carbon ions.

[0073] 6) The primary product of the alkylation of propylene with isobutane is dimethylpentane. Trimethylpentane can also be produced due to the action of carbonium ions. Propylene can also undergo dimerization and polymerization, and its carbonium ions can undergo disproportionation, isomerization, and cleavage reactions.

[0074] Through product composition analysis and mechanism analysis of the alkylation reaction of crude gasoline components, it can be roughly determined that the isomerization path of carbon cations can be roughly derived. The isomerized C7-C11 hydrocarbons themselves can also be used as a small amount of additive to increase the octane number (excessive amounts are prone to carbon deposition). This also supports why the present invention returns the oil fraction for secondary cracking and why the present invention can produce high-purity polyol components.

[0075] 4. Product fractionation principle After the alkylation reaction is complete, the net effluent must be separated to obtain the desired products. Product fractionation involves physically vaporizing and condensing the net effluent (a mixture of alkylate, n-butane, and isobutane) multiple times, separating the components according to their boiling point ranges to produce alkylate, isobutane, and n-butane. This process is accomplished in a fractionating tower.

[0076] 4.1 Distillation process: The distillation process is carried out in a distillation tower equipped with many trays or packings. The raw materials enter the feed section of the distillation tower (this device uses a gas-liquid mixed feed). After entering the tower, the vapor phase of the raw materials rises and the liquid phase descends, thereby separating the components in the raw materials.

[0077] The light components flowing out of the top of the tower are condensed in the condenser and enter the reflux tank, where they are pumped out by a reflux pump. Part of the components are injected into the tower as reflux, and part of the components are sent out as the top product. A reboiler is installed at the bottom of the tower to further heat the liquid at the bottom of the tower, causing the light components in the liquid to evaporate and rise. The liquid that cannot be vaporized flows out from the bottom of the tower and is sent out as the bottom product. The temperature gradually increases from top to bottom along the tower, with the lowest temperature at the top and the highest temperature at the bottom, that is, the temperature changes in a gradient.

[0078] 4.2 Distillation principle: The distillation process is a process of combining multiple partial vaporizations of the liquid phase with multiple partial condensations of the vapor phase, or in other words, distillation is a bidirectional mass and heat transfer process in which the vapor and liquid phases come into contact with each other in opposite directions multiple times without equilibrium.

[0079] 5. Performance Analysis Some products were added to fuel for testing, and the results are shown in Table 3 below: Table 3. Properties of fuel additives

[0080] Necessity of catalysts and denaturing additives: Comparative Examples 1-2 demonstrate that the absence of these two directly leads to a collapse in reaction efficiency and product quality; Process parameter sensitivity: Comparative Example 3 shows that a temperature deviation of 10% will lead to product structural degradation; Resource recycling value: Comparative Example 4 verifies that by-product recycling is the core of cost control (e.g., Example 1 reduces raw material costs by 18%); Environmental performance: The synergistic effect of ferrocene / benzoic acid in the embodiment reduces the exhaust pollutant emissions by more than 50% below the national standard, highlighting the "environmentally friendly" nature.

[0081] The above data confirms that naphtha-methanol compound system, customized denaturing additives and closed-loop process design are key factors in achieving high-efficiency and environmentally friendly fuel additives.

[0082] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for preparing an environmentally friendly polyol fuel additive, characterized in that: The following steps are involved: 1) Raw material pretreatment Methanol, naphtha, and denaturing additives are added to a stirring tank in proportion, heated and stirred to mix evenly, and then transported to a tubular reactor via a gear pump a. In the absence of oxygen, at 260±5°C, and under the action of a Mo2C / HZSM-5 catalyst, the naphtha is cracked to produce C2-C4 olefins. 2) Catalytic conversion and separation The product from the tubular reactor enters catalytic reactor a, where methanol is converted into dimethyl ether under the conditions of Al-DME-1 catalyst and 260±10°C. After cooling in cooler a, the gas phase enters a gas collecting tank, where C1-C3 hydrocarbons are separated by a vacuum compressor unit, and the liquid phase is temporarily stored in buffer tank a. 3) Polyol synthesis reaction The material in buffer tank a is heated to 300°C by gear pump b and heat exchanger a, and then enters catalytic reactor b. Under the conditions of B2-ZnZSM-5 catalyst and 280±10°C, methanol / dimethyl ether reacts with olefins to produce polyols. After the reaction, it is cooled in cooler b, the non-condensable gas is separated, and the liquid phase material enters buffer tank b. 4) Distillation and purification The material in the buffer tank b is processed by the gear pump c, the intermediate tank, the gear pump d, and the heat exchanger b and then enters the distillation tower. The temperature is controlled by the coolers c and d, and the 108°C fraction and the 184°C fraction are collected in the finished product tank a and the finished product tank b, respectively, to obtain high-purity polyol components.

2. The method for preparing the environmentally friendly polyol fuel additive according to claim 1, characterized in that: The mass ratio of naphtha, methanol and denaturing additive in the stirring tank is 10:(2-4):(0.3-0.6).

3. The method for preparing the environmentally friendly polyol fuel additive according to claim 1, characterized in that: The denaturing additive comprises the following components in parts by weight: 100 parts of acetone, 20-25 parts of toluene, 10-15 parts of benzoic acid, 25-30 parts of ferrocene, and 3-5 parts of zinc oxide.

4. The method for preparing the environmentally friendly polyol fuel additive according to claim 1, characterized in that: The oil at the bottom of the distillation tower is returned to the stirring tank to continue the cracking reaction as a partial substitute for naphtha.

5. The method for preparing the environmentally friendly polyol fuel additive according to claim 1, characterized in that: The non-condensable gas in the buffer tank a, buffer tank b, finished product tank a and finished product tank b is collected in a gas collecting tank. After being cooled by circulating water at -7°C, the liquid part enters the condensate tank and the gas part is introduced into the vacuum compressor unit. At a pressure of 10-15MPa, the small molecular gas components are removed to obtain liquid low-carbon hydrocarbons.

6. The method for preparing the environmentally friendly polyol fuel additive according to claim 1, characterized in that: Part of the non-condensable gas in the buffer tank a, buffer tank b, finished product tank a and finished product tank b can also be compressed and circulated, mixed with methanol and then re-entered into the stirring tank to be used as the driving gas phase of the reaction system.

7. The environmentally friendly polyol fuel additive obtained by the preparation method according to any one of claims 1 to 6, characterized in that: After the following compounding process: According to the performance requirements of the fuel additive, the content of the polyol component in the intermediate tank is tested. When the polyol component is too high, some of the polyol should be distilled out through a distillation tower, and the polyol content in the oil at the bottom of the distillation tower is tested. When the content meets the standard, the oil at the bottom of the distillation tower is directly taken as a fuel additive. When the polyol component in the intermediate tank is too low, the methanol content in the stirring tank should be increased, or the polyol should be enriched multiple times in the distillation tower, and the purified polyol should be directly mixed with the components in the intermediate tank to obtain the fuel additive.

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