Improved process for synthesizing thiophene from butadiene and sulfur

Abstract

The invention belongs to the technical field of chemical synthesis, provides an improved process for synthesizing thiophene from butadiene and sulfur, solves the environmental protection problem of the existing production device, and improves the yield. Excessive fed sulfur in the prior art is changed into excessive butadiene, and the generation amount of byproduct tar is reduced by 2 / 3. The reaction tail gas is subjected to pressurized rectification separation, so that the problem of recovery of excessive butadiene is solved, the problem of purification of the byproduct hydrogen sulfide is also solved, and the byproduct sodium hydrosulfide is odorless. Products of crude thiophene and yellow water respectively enter a product degassing tower and a yellow water degassing tower before going out of a reaction system, hydrogen sulfide and mercaptan are evaporated by heating, and the problem of pollution during rectification and yellow water treatment is solved. According to the cooling tower of the reaction device, backflow liquid enters the bottom of the cooling tower and does not return to the tar kettle like before, so that formation of a sulfur wall is avoided, and the reaction device can run for a long time.

Description

An improved process for synthesizing thiophene from butadiene and sulfur Technical Field

[0001] The invention relates to the technical field of chemical product preparation, and in particular to an improved process for synthesizing thiophene from butadiene and sulfur. Background Art

[0002] Thiophene, also known as thiolene and thiofuran, is the most important sulfur heterocyclic compound and a vital organic chemical raw material. Natural thiophene is abundant in petroleum and coal tar. However, due to the coexistence of natural thiophene with benzene, the boiling point difference between thiophene and benzene is only 4°C. The thiophene obtained by distillation contains benzene, making it unsuitable for pharmaceutical use. Pharmaceutical intermediates, thiophene derivatives, such as thiophene formaldehyde, thiopheneacetyl chloride, and thiophene ethanol, were previously produced using synthetic thiophene. These derivatives can be used to synthesize hundreds of pharmaceuticals, including cephalosporins and cephalosporin. In recent years, coking plants have isolated thiophene from coal tar, achieving a purity of 99.5% and a benzene content of 0.05%, meeting pharmaceutical standards. However, the yield of this thiophene derivative synthesis is 10-20% lower than that of synthetic thiophene, and the production process produces an odor. Therefore, it is only used when synthetic thiophene is in short supply, which in turn drives down its price.

[0003] The world's first industrial thiophene production plant used a gas-phase catalytic process (the Nobiloil process, developed by Soccong-Vaccum) using butane and sulfur, achieving a yield of 40%. This process, patented in 1950, was discontinued in the 1960s due to low yields, severe equipment corrosion, and environmental pollution. Other methods include: ① The gas-phase catalytic method involves the continuous reaction of butene, butadiene, n-butanol, and crotonaldehyde with carbon disulfide or sulfur dioxide in the presence of a base-promoted metal oxide catalyst at 500°C to produce thiophene and its derivatives; ② The reaction of furan or methylfuran with carbon disulfide at 400°C in the presence of a heteropolyacid to produce thiophene and methylthiophene, with yields reaching 93%. The catalyst has a long lifespan and does not require periodic regeneration; ③ Butane is mixed with sulfur vapor for a rapid reaction at 600°C; ④ Acetylene reacts with pyrite heated to 300°C in the presence of iron oxide; and ⑤ Anhydrous sodium succinate reacts with phosphorus trisulfide at high temperatures in a stream of carbon dioxide. Industrially, thiophene is prepared by reacting butane with sulfur. Butane is first dehydrogenated and then cyclized with sulfur to form thiophene.

[0004] Before 2001, thiophene was synthesized using the furan-hydrogen sulfide process, produced by Shell in the UK and Bayard in France. Furan and hydrogen sulfide reacted in the gas phase at 300-400°C using a metal oxide treated with a heteropolyacid as a catalyst to produce thiophene. This resulted in high product quality, high yield, long catalyst life, and no regeneration required. DuPont in the US used a gas-phase reaction of butadiene and sulfur at high temperatures (US Pat. No. 2,410,401), using nitrogen as a diluent. However, the reaction produced coke, which quickly clogged the pipes and condenser, making the reaction unsustainable. Nippon Steel Chemicals Co., Ltd. solved the coke accumulation problem in DuPont's patented reactor (Patent Publication No. 54-76574) by adding water to the reactants. The reaction of butadiene, sulfur, and water was carried out at atmospheric pressure and 420-470°C, with the reaction lasting for over 14 days. As olefins are known to polymerize easily at high temperatures, water is often used to de-coke the catalyst in catalytic reactions. Therefore, adding water to the reaction system can address the coke accumulation issue. In 2001, Yang Shunli cooperated with Shenzhen Xinghua Company to build the world's first butadiene-sulfur method for synthesizing thiophene (CN 101654450). The device designed by Yang Shunli used water heating and electromagnetic (medium frequency) heating to solve the problem of high-temperature heating of materials. It used cold shock steam, water spray direct cooling, and blocking valves to solve the problems of reaction heat extraction and unreacted sulfur blocking the cooler. The reactor can operate for 7 to 10 days at a time, with a unit consumption of 1.6 butadiene (1.6 tons of butadiene / ton of thiophene, the same below). After the device was put into production, the thiophene unit of the French Bayard Company was shut down in 2003, and the British Shell Company sold the thiophene unit to the German Degussa Company, a thiophene derivative manufacturer. In 2006, Yang Shunli designed a thiophene production unit with a vertical reactor and seven-stage indirect cooler for Lianyungang Hongye Chemical Company. After it was put into production, the unit consumption of butadiene dropped to 1.25. In 2008, further improvements were made to reduce the unit consumption of butadiene to 1.05. The unit operated for 14 days (CN 101654449). CN 101654449 discloses a method for producing thiophene by synthesizing butadiene and sulfur, comprising reaction, separation, distillation, and tail gas desulfurization. The reaction process is as follows: (1) heating liquid sulfur and water A together to 450-550°C to obtain water A-sulfur gas; heating vaporized butadiene and water B together to 250-350°C to obtain water B-butadiene gas; (2) mixing water A-sulfur gas and water B-butadiene gas, reacting at 360-460°C and normal pressure for a residence time of 1-5 seconds to obtain a reaction gas product; wherein the molar ratio of the raw sulfur to butadiene is 1.1-1.7, and the molar ratio of water to butadiene is 0.5-3. Subsequently, the thiophene unit of Degussa GmbH in Germany was shut down, and the furan-hydrogen sulfide thiophene synthesis method was replaced by the butadiene-sulfur method, leaving China as the world's only thiophene producer.

[0005] In 2011, inventor Yang Shunli modified a thiophene plant for Zibo Shuanglian Chemical Company, improving the equipment for producing sodium hydrosulfide by absorbing hydrogen sulfide with liquid caustic soda. This system employed a three-stage bubbling absorption system, with valve switching to change the number of stages. The three inlet (hydrogen sulfide) valves and three outlet valves for the three caustic soda tanks were arranged in sequence, with each tank opening the same number (1, 2, 3) as the inlet and outlet valves for the corresponding stages (1, 2, 3). This solved the problem of tank and stage reversal in the three-stage absorption process. This solidified the thiophene production technology. After years of accumulated production experience and continuous improvement, the reactor can now operate for 30 to 60 days at a time. Currently, thiophene production plants are primarily concentrated in Shandong Province, with one each in Zibo, Xintai, and Binzhou: Zibo Chenbo Chemical Co., Ltd., Tai'an Kesaier Chemical Technology Co., Ltd., and Yangxin Huichang Chemical Co., Ltd.

[0006] In 2012, Zibo Shuanglian Chemical Company was shut down after dumping tar and sulfur residue into a landfill, resulting in the deaths of two nearby residents. In 2015, Lianyungang Hongye Chemical Company was reported by CCTV for dumping tar in the mountains of Hebei, leading to the cessation of production at its thiophene plant. Since then, thiophene tar has been designated a key hazardous chemical, prohibiting manufacturers from privately disposing of it. Professional environmental protection companies charge up to 6,000 yuan per ton for incineration. All thiophene production plants have abandoned exhaust gas absorption systems. Half of the thiophene produced in the reaction enters the alkaline washing unit along with the hydrogen sulfide. This portion is manually recovered from the liquid sodium hydrosulfide tank through liquid separation, resulting in thiophene losses. Each plant's butadiene consumption per unit is 1.2 to 1.3 units. This also creates a problem: trace amounts of byproduct mercaptans end up in the liquid sodium hydrosulfide, making the product stinky and difficult to sell. It is often given away for free or sold at a loss. Because crude thiophene and yellow water contain trace amounts of mercaptans, distillation processes often result in complaints, and the plant is filled with foul odors when yellow water is processed. Furthermore, while the purity of thiophene separated from coal tar meets pharmaceutical standards, while it has inherent drawbacks and cannot generally replace synthetic thiophene, it does lower the price of synthetic thiophene. Therefore, improving the synthetic thiophene production process to increase yield, reduce costs, and address environmental concerns is imperative.

[0007] Summary of the Invention

[0008] The purpose of the present invention is to provide an improved process for synthesizing thiophene from butadiene and sulfur, so as to solve the technical problems of many by-products, low synthesis efficiency, high cost and pollution in the current thiophene synthesis process.

[0009] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0010] The present invention provides an improved process for synthesizing thiophene from butadiene and sulfur, comprising reaction, gas separation and tail gas absorption. The reaction is:

[0011] (1) heating butadiene and water B to 250-270° C. to obtain water-butadiene gas;

[0012] (2) heating sulfur A and water A to 490-510° C. to obtain water-sulfur gas;

[0013] (3) heating sulfur B to 350-400°C to obtain high-temperature liquid sulfur;

[0014] (4) passing the heated material into a reactor for reaction;

[0015] (5) The reaction products pass through a cooling tower, a condenser, and a separator in sequence to separate the liquid product crude thiophene, liquid yellow water, and tail gas. The crude thiophene and yellow water are sent to a degassing tower and a yellow water degassing tower respectively. The evaporated hydrogen sulfide and mercaptan gas are returned to the condenser.

[0016] The gas separation is:

[0017] (1) The tail gas from the condenser is compressed and condensed into liquid and then enters three series-connected distillation towers;

[0018] (2) Hydrogen sulfide is discharged from the top of tower 1, butadiene is discharged from the top of tower 2, carbon disulfide is discharged from the top of tower 3, and crude thiophene is discharged from the bottom of tower 3;

[0019] The tail gas absorption is:

[0020] A four-stage alkali washing device is used to absorb hydrogen sulfide, wherein the mass concentration of the alkali solution is 28-32%.

[0021] Furthermore, in the reaction, the inlet temperature of the reactor is 360-420°C, and the outlet temperature of the reactor is 410-430°C.

[0022] Furthermore, in the reaction, the molar ratio of butadiene to the total amount of (sulfur A+sulfur B) is 1.1 to 1.3.

[0023] Furthermore, during the reaction, the top temperature of the cooling tower is 60-65°C, the bottom temperature is 104-108°C; and the outlet temperature of the condenser is 20°C.

[0024] Furthermore, the separator is a three-phase separator, and the separated liquid product crude thiophene and liquid yellow water enter the product degassing tower and the yellow water degassing tower respectively; the gas evaporated from the product degassing tower and the yellow water degassing tower returns to the condenser, the bottom product of the product degassing tower goes to the crude thiophene tank, and the bottom product of the yellow water degassing tower goes to the sewage pool.

[0025] Furthermore, the gas exiting the condenser enters the gas compressor and is compressed to 3.0-3.2 MPa. The compressed gas enters the cooler and the gas condenser in sequence. The outlet temperature of the cooler is 60-65°C, and the outlet temperature of the gas condenser is 40-45°C.

[0026] Furthermore, the condensed liquid enters three distillation towers connected in series, namely a hydrogen sulfide distillation tower, a butadiene distillation tower and a carbon disulfide distillation tower; the hydrogen sulfide distillation pressure is 3.0-3.2 MPa, the tower top temperature is 45-47°C, the tower bottom temperature is 145-155°C, the purity of hydrogen sulfide at the tower top is ≥99.9%, and the hydrogen sulfide content at the tower bottom is ≤1.1%.

[0027] Furthermore, the butadiene distillation tower pressure is 0.7 MPa, the tower top temperature is 61-62° C., the tower bottom temperature is 140-145° C., and the purity of the butadiene at the tower top is ≥97.3%;

[0028] The carbon disulfide distillation tower has a pressure of 0.1 MPa, a tower top temperature of 66-68° C., a tower bottom temperature of 107-109° C., a tower top carbon disulfide content of ≥99.75%, and a tower bottom thiophene content of ≥99.6%.

[0029] Furthermore, in the tail gas absorption, the alkali solution is a sodium hydroxide solution, and after alkali washing, a liquid sodium hydrosulfide product is obtained with a standard content of 28-35%.

[0030] Furthermore, the improved process for synthesizing thiophene from butadiene and sulfur is used to synthesize thiophene derivatives from butadiene derivatives having the following general formula and sulfur:

[0031] X1, X2, X3, and X4 are independently hydrogen, methyl, ethyl, or halogen.

[0032] Beneficial effects of the present invention:

[0033] The present invention makes the following improvements to the design of the thiophene synthesis device:

[0034] (1) Change the feeding method

[0035] The previous process used excess sulfur to replace excess butadiene to reduce the production of heavy tar. This was previously done because of its low cost and to simplify the process, avoiding butadiene recovery. Furthermore, to ensure complete butadiene reaction, the reaction temperature was raised, which inevitably resulted in increased byproducts, including heavy components and carbon disulfide. Today, thiophene production plants are relatively large and have the investment capacity to recover butadiene from liquefied petroleum gas. With excess butadiene, the reaction temperature drops by 20-30°C, with the reactor's peak temperature dropping from 440-450°C to 410-430°C. This reduces tar and carbon disulfide production, ensuring complete sulfur reaction and virtually eliminating sulfur slag. The design assumes a 20% excess butadiene, with optimization adjustments made in actual production. Excess butadiene requires butadiene separation and recovery equipment, with excess butadiene recycled and pressure distillation separating hydrogen sulfide, butadiene, carbon disulfide, and thiophene—all mature technologies in the petrochemical industry.

[0036] Excess butadiene requires pressure separation to recover unreacted butadiene. This process not only minimizes production costs but also generates additional economic benefits and is environmentally friendly. The pressurized distillation process utilizes three distillation towers in series: tower one produces greater than 99.9% pure hydrogen sulfide, tower two produces butadiene, and tower three produces carbon disulfide. Alkali absorption of the pure hydrogen sulfide yields petrochemical-grade sodium hydrosulfide, which is odorless and marketable. Carbon disulfide recovery avoids air pollution caused by previously hidden carbon disulfide emissions while also increasing economic benefits.

[0037] (2) Liquid sulfur feed

[0038] In 2001, the inventors designed a direct-cooled thiophene production device (CN 101654450). The reaction feedstock consisted of four streams: sulfur, butadiene, water A, and water B. Three medium-frequency electromagnetic heating furnaces were used. Butadiene and water B were fed together into the butadiene heating furnace. Water A entered from the top of the water heating furnace and exited from the bottom. Water A, heated to 600°C, entered the bottom of the sulfur furnace. Liquid sulfur at 140°C entered from the top of the sulfur furnace and flowed down the furnace walls. The gaseous sulfur-water mixture, heated to 500-550°C, was combined with the gaseous butadiene-water mixture exiting from the top of the butadiene furnace to form a mixer. The indirect-cooled thiophene production device (CN 101654449), designed by the inventors in 2005, also employed this feed system. Sulfur is the best heat medium, with a melting point of 120°C and a boiling point of 444°C. If a separate stream of sulfur is heated to 350-400°C and fed into the reaction mixer, it will vaporize upon entering the reactor. This absorbs heat, solving the exothermic reaction problem, and also saves heating electricity. Previously, this method was not used because sulfur was fed using a plunger metering pump, requiring two sulfur metering tanks. The present invention uses an internal gear pump to feed sulfur, a target flowmeter for metering, and variable frequency automatic control. The sulfur is then divided into two streams: one to the sulfur vaporizer and the other to the liquid sulfur heating furnace, where it is heated to 350-400°C before entering the reactor.

[0039] (3) Enlarge the reaction mixer

[0040] The cracking (bond breaking) of the compound is an endothermic process, while the chain growth and cyclization (bond bonding) are exothermic processes. The reaction between butadiene and sulfur is a highly exothermic reaction. Heat extraction is a difficult problem. The methods of injecting water and steam into the reactor have been used, but coking is serious. Reducing or removing the reactor insulation will cause coke accumulation on the inner wall of the reactor. The present invention has increased the volume of the feed mixer at the top of the reaction tube in the reactor, so that about half of the reaction is completed in the mixer. Firstly, it can reduce the feed preheating temperature - saving electricity, and secondly, it can solve the problem of heat extraction from the reaction - the heat released is used for heating the raw materials themselves. This concept has been verified in production and the effect is very obvious. The liquid sulfur feed increases the volume of the reaction mixer, which completely solves the problem of heat extraction and temperature control in the reactor.

[0041] (4) Cooling tower improvement

[0042] The previous reactor was not opened for a long time and could only be opened for a month at most. The unreacted sulfur from the cooling tower reflux formed a wall (sulfur wall), which blocked the tar kettle outlet. The reactor was pressurized and forced to stop production. In order to solve the problem of tar kettle blocking, the present invention canceled the product cooler (CN 101654449) in the original intercooling reaction device. The liquid coming off the cooling tower no longer enters the tar kettle, fundamentally eliminating the possibility of forming a sulfur wall. The cooling tower is designed as a cooling-stripping integrated tower. The cooling tower top is an internal reflux condenser. The gaseous product coming out of the tar kettle enters the cooling tower, flows back into the kettle (bottom) of the cooling tower, and the cooling tower kettle enters steam. The cooling tower kettle can deposit solid sulfur and block the liquid discharge control valve. The ball valve between the cooling tower kettle and the settling tank V146 (Fig. 2) is normally open and regularly cleaned. During cleaning, steam is used to clear the blockage and purge. The diameter of the cooling tower's packing section must be smaller than that of the tar kettle (Figure 2), and the upper section must extend beyond the inclined tube on the right side of the cooling cylinder to prevent condensate from entering the tar kettle. This allows the cooling tower to serve both product cooling and vapor cooling functions, eliminating the need for the stripping tower used in previous processes. Since the reflux tar from the cooling tower does not enter the tar kettle, the long-standing problem of tar kettle blockage is resolved, enabling the production unit to operate for extended periods of time, increasing its operating time from one month to four to six months.

[0043] (5) Degassing tower

[0044] Before the product and yellow water leave the reaction system, they enter the product degassing tower and the yellow water degassing tower respectively. The product degassing tower evaporates hydrogen sulfide, butadiene, and mercaptan, which solves the problem of distilling hydrogen sulfide to pollute the atmosphere. Current thiophene production equipment is often complained about and fined for this reason.

[0045] (6) Alkali washing improvement

[0046] In the production of sodium hydrosulfide by alkali absorption, an additional stage is added to the original three-stage absorption process. When the third stage is saturated, the fourth stage is activated, which completely eliminates the chance of hydrogen sulfide escaping.

[0047] (7) Reactor design method

[0048] Due to the high number of reaction byproducts, reactor design also involves thermodynamic and reactor heat dissipation issues, making the calculations too complex. Therefore, the inventors' previous reactor designs and improvements relied on empirical and crude calculations. This improvement involved a significantly more complex process, with continuous gas separation and product distillation, and significantly more equipment required, making empirical estimation and design impossible. The reaction was assumed to be a single, first-order reaction, with the reaction rate proportional to the concentrations of butadiene and sulfur. Product composition was calculated based on the set yield (selectivity) and a simplified product mass spectrometry analysis (Table 1). Thermodynamic data such as the heat of formation, as well as data for the raw materials and main products, can be found in manuals, while data for byproducts were estimated using the group method. Reactor heat dissipation was calculated using conventional methods, and a correction factor was derived based on production data. A mathematical model based on the above method was developed and programmed in Excel. Using this model, the constants in the reaction rate equation (frequency factor A and activation energy E) were derived from Shuanglian Chemical's thiophene production data (60% selectivity). The results were applied to reactors at Hongye Chemical and Chenbo Chemical, and were close to production data, demonstrating the feasibility of this calculation method. Using the resulting mathematical model and calculation program, various reactor designs were calculated with a selectivity of 80%. The calculations involved vapor-liquid equilibrium and three-phase equilibrium (liquid product oil phase - liquid water phase - gas phase), which would be too lengthy to describe here.

[0049] Table 1 Mass spectrometry analysis results of reaction products

[0050] The reaction of butadiene with sulfur involves high reaction temperatures and numerous side reactions. Mass spectrometry analysis of the reaction products revealed over 40 products, as shown in Table 1. The underlined boiling points are estimated values, calculated using interpolation due to the linear relationship between boiling point and retention time. The data in Table 1 illustrate the strong odor during product stripping and distillation of light components, particularly the tar odor. When the tar is spilled, the odor can be felt up to 100 meters away.

[0051] The liquid product is primarily thiophene, and the gaseous product is primarily hydrogen sulfide. Due to the high reaction temperature, many side reactions occur. The light component with the highest content is carbon disulfide (CS2), while the heavy components are primarily dihydrothiophene, 2-thiothiophene, butadiene-thiophene sulfide (C8H8S2), 3-thiophene mercaptan, and 3-thiophene disulfide (C8H6S4). The butadiene-sulfur method for synthesizing thiophene has a 22-year history. None of the light components remain at all thiophene production plants; they are evaporated and vanish. Repeated distillation of the light components yields light components stored in barrels, which emit steam in the summer. The heavy component tar is a black liquid that bubbles when heated to approximately 300°C and becomes a foamy solid upon cooling. Emission spectrometry analysis revealed 50.8% sulfur in the tar, while the heavy sulfur content was 37.1% dihydrothiophene, 36.3% tetrahydrothiophene, 55.1% thiophene mercaptan, 54.1% thiothiophene, 38.0% butadiene-thiophene sulfide, and 55.6% thiophene disulfide. This indicates that the light components of the reaction are carbon disulfide and trace amounts of butadiene mercaptan, while the heavy tar is primarily the product of further reaction between thiophene and sulfur, which is consistent with the mass spectrometry analysis results in Table 1.

[0052] To achieve material equilibrium by eliminating components with very low content, the structures of individual by-products obtained by mass spectrometry analysis were adjusted according to the actual reaction conditions. The main reaction formula is:

[0053] C4H6+S2=C4H4S+H2S (thiophene, hydrogen sulfide)

[0054] The main side reaction formula is:

[0055] C4H6+5.5S2=4CS2+3H2S (carbon disulfide)

[0056] C4H6+0.5S2=C4H6S(butadiene mercaptan)

[0057] 2C4H6+3.5S2=C6H6+2CS2+3H2S(benzene)

[0058] C4H6+0.5S2=C4H6S(cyclobutenethiol)

[0059] 2C4H6+2S2=C7H8+CS2+2H2S(toluene)

[0060] 2C4H6+5S2=C5H6S+3CS2+3H2S(3-methylthiophene)

[0061] C4H6+0.5S2=C4H6S (dihydrothiophene)

[0062] 2C4H6+0.5S2=C8H 10 +H2S (ethylbenzene)

[0063] C4H6+1.5S2=C4H4S2+H2S(3-thiophenethiol)

[0064] C4H6+1.5S2=C4H4S2+H2S(2-thiothiophene)

[0065] 2C4H6+2S2=C8H8S2+2H2S (butadiene thiophene sulfide)

[0066] 2C4H6+3.5S2=C8H6S4+3H2S (thiophene disulfide)

[0067] The structures of thiophene and thiothiophene compounds (tar) are as follows: BRIEF DESCRIPTION OF THE DRAWINGS

[0068] FIG1 is a flow chart of the overall production process of the present invention;

[0069] FIG2 is a schematic diagram of a reaction apparatus of the present invention, comprising a reactor, a tar kettle, and a cooling tower;

[0070] FIG3 is a process flow diagram of a reaction system of the present invention;

[0071] FIG4 is a process flow diagram of the separation system of the present invention, including gas separation and product distillation.

[0072] In the accompanying drawings: R130 Reactor V131 Tar Kettle V132 Liquid Storage Tank C140 Cooling Tower C150 (Product) Degassing Tower C160 Yellow Water Degassing Tower V110 Butadiene Metering Tank V121 Sulfur Feeding Tank V122 Sulfur Melting Tank V123 Sulfur Metering Tank F143 Three-Phase Separator F311 Oil-Water Separator V144 Product Intermediate Tank V145 Yellow Water Intermediate Tank V146 Sedimentation Tank V300 Crude Thiophene Tank V161 Yellow Water Tank V134 Tar Storage Tank E112 Chiller E112 Butadiene Heat Exchanger E113 Butadiene Preheater E124 Sulfur-Water Preheater E114 Butadiene Heating Furnace E125 Water Heating Furnace E126 Sulfur Vaporization Furnace E127 Sulfur Heating Furnace E141 Condenser E142 chiller, B200 compressor, C210 hydrogen sulfide tower, C220 butadiene tower, C230 carbon disulfide tower, C310 light component tower, C320 debenzene tower, C330 thiophene tower, K reflux ratio controller, E heat exchanger, V210 liquefied gas tank, V220 crude butadiene tank, V230 crude carbon disulfide tank, V211 hydrogen sulfide tank, V221 butadiene recovery tank, V231 carbon disulfide intermediate tank, V213 hydrogen sulfide storage tank, V233 carbon disulfide storage tank, V311 light component intermediate tank, V321 debenzene liquid intermediate tank, V331 thiophene intermediate tank, V313 light component tank, V323 debenzene liquid tank, V333 thiophene finished product tank, V334 heavy component tank, V301 pan-tower buffer tank, R410-440 alkali absorption tanks DETAILED DESCRIPTION

[0073] The present invention provides an improved process for synthesizing thiophene from butadiene and sulfur, comprising reaction, gas separation and tail gas absorption. The reaction is:

[0074] (1) heating butadiene and water B to 250-270° C. to obtain water-butadiene gas;

[0075] (2) heating sulfur A and water A to 490-510° C. to obtain water-sulfur gas;

[0076] (3) heating sulfur B to 350-400°C to obtain high-temperature liquid sulfur;

[0077] (4) The heated material is passed into a reactor for reaction.

[0078] (5) The reaction products are sequentially passed through a cooling tower, a condenser, and a separator to separate the liquid product crude thiophene, liquid yellow water, and tail gas. The crude thiophene and yellow water are sent to a degassing tower and a yellow water degassing tower respectively. The evaporated hydrogen sulfide and mercaptan gas are returned to the condenser.

[0079] The gas separation is:

[0080] (1) The tail gas from the condenser is compressed and condensed into liquid and then enters three series-connected distillation towers;

[0081] (2) Hydrogen sulfide is discharged from the top of tower 1, butadiene is discharged from the top of tower 2, carbon disulfide is discharged from the top of tower 3, and crude thiophene is discharged from the bottom of tower 3;

[0082] The tail gas absorption is:

[0083] A four-stage alkali washing device is used to absorb hydrogen sulfide, wherein the mass concentration of the alkali solution is 28-32%.

[0084] In the present invention, the sulfur is basically reacted completely, and the product yield (selectivity) calculated based on butadiene is 70-90%.

[0085] In the present invention, the purity of liquid hydrogen sulfide obtained by gas pressure distillation separation is 99.0-99.99%, which can be sold as a commodity or can be made into petrochemical-grade liquid sodium hydrosulfide by alkali absorption and sold.

[0086] In the present invention, during the reaction, the inlet temperature of the reactor is 360-420°C, preferably 370°C; the outlet temperature of the reactor is 410-430°C, preferably 420°C.

[0087] In the present invention, the temperature at which butadiene and water B are heated is preferably 260°C; the temperature at which sulfur A and water A are heated is preferably 500°C; and the temperature at which sulfur B is heated is preferably 400°C.

[0088] In the present invention, the mass concentration of the alkali solution is preferably 28 to 32%, more preferably 32%.

[0089] In the present invention, the molar ratio of butadiene to the total amount of (sulfur A + sulfur B) is preferably 1.2.

[0090] In the present invention, the top temperature of the reaction cooling tower is 60-65°C, preferably 63°C; the bottom temperature is 104-108°C, preferably 105°C; and the outlet temperature of the condenser is 20°C-20°C, preferably 20°C.

[0091] In the present invention, the gas exiting the condenser includes the gas of the cooling tower top product that has not been cooled down after passing through the condenser and the gas that has not been cooled down after the gas evaporated from the degassing tower returns to the condenser. The gas enters the gas compressor and is compressed to 3.0-3.2 MPa. The compressed gas enters the cooler and the gas condenser in turn. The outlet temperature of the cooler is 60-65°C, and the outlet temperature of the gas condenser is 40-45°C. Preferably, the gas is compressed to 3.1 MPa and the outlet temperature of the gas condenser is 42°C.

[0092] In the present invention, the condensed liquid enters three series-connected distillation towers, namely a hydrogen sulfide distillation tower, a butadiene distillation tower and a carbon disulfide distillation tower; the pressure of the hydrogen sulfide distillation tower is 3.0-3.2 MPa, preferably 3.1 MPa, the top temperature is 45-47°C, preferably 46°C; the bottom temperature is 145-155°C, preferably 148°C; the purity of hydrogen sulfide at the top is ≥99.9%, and the hydrogen sulfide content at the bottom is ≤1.1%.

[0093] In the present invention, the pressure of the butadiene distillation tower is 0.7 MPa, the tower top temperature is 61-62° C., preferably 61.8° C.; the tower bottom temperature is 140-145° C., preferably 142° C.; and the purity of butadiene at the tower top is ≥97.3%.

[0094] In the present invention, the pressure of the carbon disulfide distillation tower is 0.1 MPa, the top temperature is 66-68°C, preferably 67.6°C; the bottom temperature is 107-109°C, preferably 108°C; the carbon disulfide content at the top is ≥99.75%, the thiophene content at the bottom is ≥99.6%, and the purity of thiophene is ≥99.9%.

[0095] In the present invention, the production process for synthesizing thiophene from butadiene and sulfur is used to synthesize thiophene derivatives from butadiene derivatives and sulfur having the following general formula:

[0096] X1, X2, X3, and X4 are independently hydrogen, methyl, ethyl, or halogen. Preferably, 1,3-butadiene, piperylene, isoprene, and 3-chloroprene are reacted with sulfur to produce, in order, thiophene, 2-methylthiophene, 3-methylthiophene, and 3-chlorothiophene. The most commonly used thiophene derivative is 3-methylthiophene, which has a density of 1.016 g / ml at 20°C and a density of 1 g / ml at 20°C. The two are very close in density, and production is best carried out during the coldest winter months, as otherwise the two are difficult to separate.

[0097] In the present invention, approximately half of the reaction is completed in the mixer, which allows the reaction heat to be used to heat the reaction feed and solves the problem of difficult reaction temperature control. The present invention also adds a stream of liquid sulfur feed, utilizing its vaporization to absorb the reaction heat, saving electricity required for feed heating.

[0098] The process of the present invention is:

[0099] reaction

[0100] (1) Butadiene enters the tube side of the chiller E111 through the metering tank V110 and exchanges heat with the water entering the shell side of the heat exchanger. The butadiene is decompressed and vaporized to cool the water to 15°C.

[0101] (2) Butadiene discharged from the chiller enters the tube side of the butadiene heat exchanger E112 and exchanges heat with the water entering the shell side of the heat exchanger. The butadiene is completely vaporized and heated to a temperature close to the water temperature, and the water temperature drops by ~0.5℃.

[0102] (3) The butadiene vaporized by water enters the butadiene preheater E113 together with the water vapor (water B), is heated to 140°C by steam, and then enters the butadiene heating furnace E114 and is heated to 260°C.

[0103] (4) Liquid sulfur is pumped into the sulfur intermediate tank V121 and intermittently into the sulfur metering tank V122. The sulfur intermediate tank, metering tank, and pipeline are insulated with steam at a steam jacket pressure of 0.45-0.5 MPa to maintain the sulfur temperature at 140-150°C.

[0104] (5) Sulfur is pumped from the sulfur metering tank using an internal gear pump and sent to the sulfur vaporization furnace E125 and the sulfur heating furnace E126 in two ways. The ratio of the amount entering E125 to the amount entering E126 is approximately 2 / 1.

[0105] (6) Water vapor (water A) enters the water preheater E123 and is heated to 140°C by steam. It then enters the water heating furnace E124 and is heated to 600°C. It then enters E125 and carries the vaporized sulfur to 500-540°C.

[0106] (7) Butadiene, sulfur and water enter the mixer of reactor R130. The mixer inlet temperature is 360-380°C and the mixer outlet temperature is 390-410°C.

[0107] (8) Adjust the sulfur water feed rate and the sulfur vaporization furnace outlet temperature to make the reactor operate at the optimal state.

[0108] (9) The reaction product is cooled to ~300°C in a cooling drum and then to ~150°C in a tar kettle V131. The condensed tar and part of the yellow water (water containing sulfur powder) are regularly placed in the liquid storage tank V132. The tar and yellow water in the liquid storage tank are placed in the tar tank V133. Before being placed in the tar tank, steam is passed through for 3 minutes to drive away the dissolved hydrogen sulfide.

[0109] (10) Uncondensed products, including thiophene, hydrogen sulfide, and water, enter cooling tower C140. Steam enters the bottom of the tower and is cooled and refluxed by the partial condenser at the top of the tower. The top temperature is 60-65°C and the bottom temperature is 104-108°C. The cooling tower also functions as a stripping tower, eliminating the need for a stripping tower in existing thiophene units. Moreover, the reflux does not enter the tar kettle as before, thus avoiding the formation of a sulfur wall at the tar kettle outlet - the cause of tar kettle blockage and forced shutdown in existing thiophene units. The tar and condensed water at the bottom of the cooling tower enter the discharge box tar kettle V133.

[0110] (11) The gas from the cooling tower enters condenser E141, with cooling water coming from butadiene heat exchanger E112. Uncondensed gas enters chiller E142, with cooling water coming from chiller E111. The liquid condensed from both condensers enters phase separator F143, where it is automatically separated by gravity into the oil (crude thiophene) and water (yellow water) phases. The gas temperature from condenser E141 is 40°C, and the gas temperature from chiller E142 is 20°C. If the chiller is clogged with deposited sulfur powder, activate the gas phase bypass and the condenser isolation valve, use steam to melt and purge the sulfur, and then resume chiller use after cleaning. These bypasses and spare pipe valves are omitted in Figure 2.

[0111] (12) The lower oil phase of phase separator F143 enters product intermediate tank V144, and the upper aqueous phase enters yellow water intermediate tank V145. The product enters product degassing tower C150, and the yellow water enters yellow water degassing tower C160. The gases at the top of both towers go to condenser E141, and the bottom products enter crude thiophene tank V300 and sewage tank, respectively. The bottom products of both towers are free of hydrogen sulfide, carbon disulfide, and mercaptans, and no atmospheric pollution is generated during the distillation and water treatment processes.

[0112] Gas separation:

[0113] (1) The gas from freezer E142 enters gas compressor B200 and is compressed to 3.1 MPa. After compression, the temperature rises to ~215°C, enters gas cooler E201 and is cooled to ~60°C, and then enters gas condenser E202 and is cooled to ~45°C. The condensate enters liquefied gas tank V210 and then enters hydrogen sulfide distillation tower C210. ​​The bottom of the tower is heated with 0.8 MPa steam, and the top of the tower is controlled by a rotary reflux ratio controller to maintain a reflux ratio of 0.55. The top temperature is 46°C and the bottom temperature is 150°C. The purity of hydrogen sulfide at the top of the tower is 99.9%, and the hydrogen sulfide content at the bottom of the tower is 1.1%. The hydrogen sulfide product at the top of the tower enters hydrogen sulfide tank V211 and is then absorbed by the de-alkali system to produce sodium hydrosulfide. If the hydrogen sulfide can be sold as a commodity, it enters hydrogen sulfide storage tank V213.

[0114] (2) The product exiting the bottom of the hydrogen sulfide tower contains a small amount of water, which is immiscible with the oil phase and has a greater density than the oil phase. Due to the small amount of water, it is cooled in cooler E212 and then enters the crude butadiene tank V220. After sedimentation and water separation, it is charged into the butadiene distillation tower C220 at an operating pressure of 0.7 MPa. The bottom of the tower is heated with 0.8 MPa steam, and the reflux ratio at the top of the tower is controlled at 1.4. The top temperature is 61.8°C and the bottom temperature is 142°C. The top product contains 97.3% butadiene and enters the butadiene recovery tank V221. It then returns to V110 for recycling.

[0115] (3) The bottom product of tower C220 enters the crude carbon disulfide tank V230 through cooler E222, and then enters the carbon disulfide distillation tower C230 with an operating pressure of 0.1 MPa. The bottom of the tower is heated with 0.5 MPa steam, and the reflux ratio at the top of the tower is controlled at 2.7. The top temperature is 67.6°C and the bottom temperature is 108°C. The top product contains 0.22% butadiene, 99.75% carbon disulfide, and 0.03% thiophene, and enters the carbon disulfide intermediate tank V231 and the carbon disulfide storage tank V233 in sequence. The bottom product contains 0.05% thiophene carbon disulfide and 99.60% thiophene, and enters the distillation raw material tank V300.

[0116] (4) Pressure control: The gas compressor controls the pressure of the reaction unit to 104 kPa (absolute pressure, slightly positive pressure). The three distillation towers use nitrogen to control the pressure, and the overpressure is discharged to the alkali washing tank.

[0117] Product distillation:

[0118] The product distillation uses three atmospheric continuous distillation towers connected in series, namely the light component tower C310, the debenzene tower C320, and the thiophene tower C330. The designed product thiophene purity is 99.9%.

[0119] Alkaline washing:

[0120] Alkali washing, also known as tail gas absorption, uses 32% liquid caustic soda to absorb hydrogen sulfide, producing a 35% liquid sodium hydrosulfide product. Hydrogen sulfide is pressure-fed into the caustic washing tank, replacing the existing three-stage caustic washing process in the thiophene unit with a four-stage process. The hydrogen sulfide is pure (99.9%), and the resulting liquid sodium hydrosulfide is high-quality and easy to sell, eliminating off-season backlogs and giveaways.

[0121] The reaction between hydrogen sulfide and sodium hydroxide is exothermic. After the reaction, the temperature of the alkali tank rises. When the temperature of the first tank drops, it proves that the first-stage reaction is complete and the switch begins. The second stage becomes the first stage, the third stage becomes the second stage, and the fourth stage becomes the third stage. The original first stage becomes the fourth stage after the alkali is replaced. Under normal circumstances, the fourth stage is not used. It is activated when the first stage is close to saturation or when the alkali is replaced.

[0122] In the present invention, the cooling tower of the reaction device is designed as a cooling-stripping integrated structure. The gaseous products from the reactor are initially cooled in the tar kettle, and the gaseous products from the tar kettle enter the cooling tower. The tar and part of the yellow water (water containing sulfur powder) condensed from the initial cooling of the tar kettle are regularly placed in the liquid accumulation tank V132; the uncondensed products, including thiophene, hydrogen sulfide and water, enter the cooling tower, and steam enters the bottom of the cooling tower; the gas from the cooling tower enters the condenser E141, and the cooling water comes from the butadiene heat exchanger; the uncondensed gas enters the freezer E142; the condensed liquid enters the phase separator F143, and the oil (crude thiophene) and water (yellow water) phases are automatically separated by gravity.

[0123] The top of the cooling tower adopts a partial condenser for cooling and reflux, the top temperature is 60-65℃, and the bottom temperature is 104-108℃. The cooling tower also has the function of a stripping tower; gas separation: the gas coming out of the freezer E142 enters the gas compressor B200 and is compressed to 3.1MPa; after compression, it enters the gas cooler E201 and the gas condenser E202, and the condensate enters the liquefied gas tank V210, and then enters the hydrogen sulfide distillation tower C210, hydrogen sulfide is discharged from the top of the tower, and the bottom product goes to C220.

[0124] The product exiting the hydrogen sulfide column contains a small amount of water, which is immiscible with the oil phase and has a higher density than the oil phase. Due to the low water content, it is cooled in cooler E212 and then enters crude butadiene tank V220. After sedimentation and water separation, it enters butadiene distillation tower C220, operating at 0.7 MPa. The tower bottom is heated with 0.8 MPa steam, and the tower top is controlled at a reflux ratio of 1.4. The tower top temperature is 61.8°C, and the tower bottom temperature is 142°C. The overhead product, containing 97.3% butadiene, enters butadiene recovery tank V221 and then returns to V110 for recycling.

[0125] The bottoms product from the butadiene distillation tower C220 passes through cooler E222 and enters crude carbon disulfide tank V230. It then enters the carbon disulfide distillation tower C230, where the bottom is heated with 0.5 MPa steam and the top of the tower is controlled at a reflux ratio of 2.7. The top product, containing 0.22% butadiene, 99.75% carbon disulfide, and 0.03% thiophene, enters carbon disulfide intermediate tank V231 and carbon disulfide storage tank V233. The bottoms product, containing 0.05% thiophene and carbon disulfide, and 99.60% thiophene, enters distillation feed tank V300.

[0126] In the present invention, the cooling tower of the reaction unit is designed as an integrated cooling and stripping structure. The gaseous product from the tar kettle enters the cooling tower, and the reflux liquid enters the bottom of the cooling tower. The integrated cooling tower, with steam entering the bottom of the cooling tower, also functions as a stripping tower.

[0127] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0128] Example 1

[0129] Thiophene production:

[0130] The structure of the reaction-coarse separation device is shown in Figure 2. Reactor size: mixer Φ530 (outer diameter mm) × 1800 (length mm), volume 0.35m 3 ; Reaction tube Φ273×8100, rear reaction tube Φ377×1900, total reaction tube volume 0.51m 3 The diameter of the cooling tower packing section is Φ325, and the diameter of the tower kettle is Φ426. Feed rate: butadiene 150kg / h, sulfur 170.9kg / h, water A 100kg / h, water B 20kg / h. Reaction products: hydrogen sulfide 82.6kg / h, butadiene 25kg / h, sulfur 1.7kg / h, carbon disulfide 17.1kg / h, butadiene mercaptan 0.05kg / h, benzene 0.14kg / h, thiophene 165.3kg / h, heavy components 28.8kg / h. The total material balance calculation results of the reaction and separation are shown in Table 2:

[0131] Table 2 Balance calculation results

[0132] Table 3 Temperature settings of various devices

[0133] The actual production results are close to the above design calculation results. The actual butadiene unit consumption is 0.71 tons and the yield is 85.7%.

[0134] Example 2

[0135] 3-Methylthiophene production

[0136] 3-Methylthiophene was produced using the apparatus of Example 1. Isoprene feed was 95 kg / h, sulfur feed was 85 kg / h, and 15 kg / h of isoprene was recovered. The calculated 3-methylthiophene production was 95 kg / h, and the actual production was 101 kg / h, for a yield of 89%.

[0137] As can be seen from the above examples, the present invention provides a production process for synthesizing thiophene from butadiene and sulfur, which solves the environmental problems of existing production equipment and improves the yield. By changing the existing process from excessive sulfur to excessive butadiene as feed, the amount of by-product tar generated is reduced by 2 / 3. The reaction tail gas is pressurized and distilled to separate, which not only solves the problem of recycling excess butadiene, but also solves the problem of purifying the by-product hydrogen sulfide, and the by-product sodium hydrosulfide is odorless. Before leaving the reaction system, the crude thiophene and yellow water enter the product degassing tower and the yellow water degassing tower respectively, and are heated to evaporate hydrogen sulfide and mercaptans, solving the pollution problem during distillation and treatment of yellow water. The cooling tower of the reaction unit refluxes the liquid into the bottom of the cooling tower, and no longer refluxes the liquid back to the tar kettle as before, avoiding the formation of sulfur wall, and the reaction unit can operate for a long time.

[0138] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principles of the present invention. These improvements should also be regarded as the scope of protection of the present invention.

Claims

1. An improved process for synthesizing thiophene from butadiene and sulfur, comprising reaction, gas separation and tail gas absorption, It is characterized in that The reaction is: (1) heating butadiene and water B to 250-270° C. to obtain water-butadiene gas; (2) heating sulfur A and water A to 490-510° C. to obtain water-sulfur gas; (3) heating sulfur B to 350-400° C. to obtain high-temperature liquid sulfur; (4) passing the heated material into a reactor for reaction; (5) The reaction product passes through a cooling tower, a condenser, and a separator in sequence to separate the liquid product crude thiophene, liquid yellow water, and tail gas. The crude thiophene and yellow water are sent to a degassing tower and a yellow water degassing tower, respectively. The evaporated hydrogen sulfide and mercaptan gas are returned to the condenser; The gas separation is: (1) The tail gas from the condenser is compressed and condensed into liquid and then enters three series-connected distillation towers; (2) Hydrogen sulfide is discharged from the top of tower 1, butadiene is discharged from the top of tower 2, carbon disulfide is discharged from the top of tower 3, and thiophene is discharged from the bottom of tower 3; The tail gas absorption is: A four-stage alkali washing device is used to absorb hydrogen sulfide, wherein the mass concentration of the alkali solution is 28-32%.

2. The improved process for synthesizing thiophene from butadiene and sulfur according to claim 1, It is characterized in that In the reaction, the inlet temperature of the reactor is 360-420°C, and the outlet temperature of the reactor is 410-430°C.

3. The improved process for synthesizing thiophene from butadiene and sulfur according to claim 2, It is characterized in that In the reaction, the molar ratio of butadiene to the total amount of (sulfur A+sulfur B) is 1.1 to 1.

3.

4. The improved process for synthesizing thiophene from butadiene and sulfur according to any one of claims 1 to 3, It is characterized in that During the reaction, the top temperature of the cooling tower is 60-65°C, the bottom temperature is 104-108°C; the outlet temperature of the condenser is 20°C.

5. The improved production process for synthesizing thiophene from butadiene and sulfur according to claim 4, It is characterized in that The separator is a three-phase separator, and the separated liquid product crude thiophene and liquid yellow water enter the product degassing tower and the yellow water degassing tower respectively; the gas evaporated from the product degassing tower and the yellow water degassing tower returns to the condenser, the bottom product of the product degassing tower goes to the crude thiophene tank, and the bottom product of the yellow water degassing tower goes to the sewage tank.

6. The improved process for synthesizing thiophene from butadiene and sulfur according to claim 5, It is characterized in that The gas leaving the condenser enters the gas compressor and is compressed to 3.0-3.2 MPa. The compressed gas enters the cooler and the gas condenser in sequence. The outlet temperature of the cooler is 60-65°C, and the outlet temperature of the gas condenser is 40-45°C.

7. The improved process for synthesizing thiophene from butadiene and sulfur according to claim 6, It is characterized in that The condensed liquid enters three series-connected distillation towers, namely a hydrogen sulfide distillation tower, a butadiene distillation tower and a carbon disulfide distillation tower; the pressure of the hydrogen sulfide distillation tower is 3.0-3.2 MPa, the top temperature is 45-47°C, the bottom temperature is 145-155°C, the purity of hydrogen sulfide at the top is ≥99.9%, and the hydrogen sulfide content at the bottom is ≤1.1%.

8. The improved process for synthesizing thiophene from butadiene and sulfur according to claim 7, It is characterized in that The butadiene distillation tower has a pressure of 0.7 MPa, a tower top temperature of 61-62° C., a tower bottom temperature of 140-145° C., and a purity of butadiene at the tower top of ≥97.3%; The pressure of the carbon disulfide distillation tower is 0.1 MPa, the tower top temperature is 66-68° C., the tower bottom temperature is 107-109° C., the carbon disulfide content at the tower top is ≥99.7%, and the thiophene content at the tower bottom is ≥99.6%.

9. The improved process for synthesizing thiophene from butadiene and sulfur according to claim 2, 6 or 8, It is characterized in that In the tail gas absorption, the alkali solution is a sodium hydroxide solution, and a liquid sodium hydrosulfide product is obtained after alkali washing.

10. The improved process for synthesizing thiophene from butadiene and sulfur according to claim 9, It is characterized in that The production process for synthesizing thiophene from butadiene and sulfur is used to synthesize thiophene derivatives from butadiene derivatives having the following general formula and sulfur: X 1 , X 2 , X 3 , X 4 is independently a hydrogen atom, a methyl group, an ethyl group or a halogen group.

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