Brief description of the benzene hydrogenation process using coke oven gas as a hydrogen source
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Brief description of the hydrogenation process for crude benzene using coke oven gas as a hydrogen source: (1) Desulfurization and hydrogen production. The raw coke oven gas is subjected to wet desulfurization, and the sulfur removed is exported as a by-product for packaging. The desulfurized coke oven gas is used to produce hydrogen via a pressure swing adsorption hydrogen production unit, and then sent to the benzene hydrogenation process. Fresh hydrogen, after being pressurized and heated by a compressor, enters the main reactor as supplemental hydrogen. (2) Raw material pretreatment process (100#): The crude benzene coming from the tank area is pumped into the middle of the diphenyl tower by the raw material pump, where separation of light and heavy benzene takes place. The BTX mixture vapor escaping from the top of the tower enters the diphenyl tower condenser; after cooling, it goes to the oil-water separator in the diphenyl tower. The oil obtained after water separation is pumped by the diphenyl tower reflux pump – part of this oil is used as reflux in the diphenyl tower, while the rest is sent to the storage tanks in the tank area as raw material for hydrogenation. The heavy benzene extracted from the bottom of the diphenyl tower passes through an oil-water separator and is then pumped to the heavy benzene storage tanks in the tank area using underground pumps. (3) Hydrogenation process (200#): The pretreated light benzene is pumped from tank farm 600# (V604) by the hydrogenation feed oil pump into the feed oil heat exchanger, where it exchanges heat with the hydrogenation reaction gas; thereafter, it enters the bottom of the evaporator together with the heated recycled hydrogen to undergo mixed vaporization. The hydrogen gas, after being pressurized by the compressor, first enters the hydrogen heat exchanger to exchange heat with the hydrogenation reaction gas; it is then heated in a hydrogen heater. After that, it is mixed with the preheated light benzene oil and fed into the lower part of the evaporator to vaporize the light benzene. After the filter residue containing polymers from the evaporator bottom is removed, it is sent to the 100# heavy benzene oil water separator. The mixed gas of benzene vapor and hydrogen is discharged from the top; it enters the pre-reactor from there, where the unsaturated compounds are hydrogenated and saturated under the action of a CoMo catalyst. The mixture of oil gas and hydrogen resulting from this reaction exits the pre-reactor from the bottom and enters an oil gas heat exchanger. After being heated, it goes into the main reactors, where it undergoes desulfurization, decarburization, deoxygenation, dealkylation, and non-aromatic hydrocarbon cracking reactions under the action of CrMo-based catalysts. To control the temperature rise in the reactor, cold hydrogen is introduced between the two series-connected main reactors. The hydrogenated gas mixture exiting the main reactor is cooled to 40°C after passing through a series of heat exchangers, and both the gas and liquid phases then enter a high-pressure separator for gas-liquid separation. 90% of the separated gas phase is sent to the recycle compressor for reuse. After heat exchange, the oil enters the middle section of the stabilizer tower. The stabilizer bottom is continuously heated by a steam-heated stabilizer reboiler; the hydrogenation oil is distilled within the tower, and hydrocarbons below C5 as well as acidic gases such as H2S dissolved in the hydrogenation oil are vaporized and discharged from the top of the tower. The overhead distillate is cooled by the stabilizer tower cooler before entering the oil-water separator of the stabilizer tower. Part of the condensed liquid obtained after separation is pumped back to the top of the tower using a stabilizer tower reflux pump, while the other part is sent to the storage tank area. The non-condensable gases emitted from the oil-water separator of the stabilizer tower are routed to the flare pipeline. The oil phase goes through a 400# pretreatment process, or is stored in a 600# hydrogenated oil tank ； The wastewater enters the level control tank to achieve control of the oil-water interface; it is then sent to the wastewater treatment system, where the hydrogenated oil separated out is sent for distillation and purification. To inhibit the polymerization of unsaturated hydrocarbons in crude benzene, the inhibitor is added in a controlled amount from the inhibitor storage tank into the pipeline that transports light benzene oil; a pump is used to feed the inhibitor into the inhibitor storage tank. The carbon disulfide storage tank and the carbon disulfide metering pump are used to pre-sulfurize the hydrogenation catalyst during its hydration process. The carbon disulfide metering pump delivers the C2S liquid from the storage tank into the system in a measured amount, thereby achieving the purpose of pre-sulfurizing the catalyst. The soft water in the soft water storage tank is pumped into the soft water high-level tank using a soft water pressure pump; after measurement, it is added to the hydrogenation products to dissolve and remove some impurities ； To achieve the hydrogen concentration required for the cyclohydrogen reaction (>80%), a portion of the cyclohydrogen (10% V) must be continuously discharged into the gas pipeline, while fresh hydrogen is supplied to the system via a compressor to maintain equilibrium. (4) Heat transfer oil heating process (300#): A new heat transfer oil furnace is installed, and heat transfer oil circulation is utilized to provide heat for the distillation process. (5) Pretreatment process (400#): The BTX fraction discharged from the bottom of the stabilization tower is fed into the pretreatment tower via a feed pump. After being heated in two stages, it enters the middle part of the pretreatment tower where it is separated into XS and BT components. The XS component at the bottom of the tower is cooled through heat exchange before being sent to the storage area, while the BT component at the top of the tower is sent to the BT storage tank for use as a raw material in extractive distillation. (6) In the processing step (500#), the BT component is pumped into the middle section of the extraction distillation tower via a feed pump for distillation. The benzene column is continuously heated by two benzene reboilers heated by steam; hydrocarbons such as cyclohexane, which form azeotropes with benzene, are discharged from the top of the tower. After being cooled by the benzene column air cooler and the benzene column cooler, they enter the benzene column oil-water separator. Part of the condensed liquid obtained after separation is pumped back to the top of the tower using a benzene reflux pump as reflux, while the other part is sent to the middle section of the extraction tower for further purification. The residue oil from the pure benzene tower, after being cooled in the cooler, is sent to the underground tank of the pure benzene tower for storage. The liquid from the pure benzene reflux pump enters the feed heater of the extraction tower, and then proceeds to the middle section of the extraction tower. The distillate from the top of the extraction tower is cooled by the extraction tower cooler before entering the oil-water separator of the tower. After separation, part of the condensed liquid is pumped back to the top of the tower using the extraction tower reflux pump for reflux purposes, while the other part is cooled by the extraction tower cooler and then sent to the storage tank area for storage. The solvent and benzene from the bottom of the extraction tower enter the feed pump of the solvent tower, where they are pressurized and sent to the solvent tower for solvent recovery. The bottom of the solvent tower is continuously heated by a steam-heated solvent tower reboiler; formylmorpholine and benzene liquid are distilled inside the tower, with the product benzene and water being discharged from the top of the tower. The distillate from the top of the solvent tower is cooled by the solvent tower air cooler and the solvent tower cooler before entering the oil-water separator of the tower. The pure benzene obtained after separation is partially pumped using a pure benzene product pump to the top of the tower for reflux, while the other portion is cooled by the solvent tower cooler and then sent as a product to the storage tank area for storage. The condensed liquid aqueous phase is buffered and then pumped by a solvent pump to the top of the tower for reflux. The solvent at the bottom of the solvent tower is pumped by a solvent pump into the reboiler of the extraction tower to recover heat; it then enters the feed heater of the extraction tower to recover more heat. After passing through the solvent cooler in the solvent tower, the solvent is sent to the upper part of the extraction tower for circulation. The ratio of formylmorpholine (the solvent) to benzene is 4:1. The liquid from the underground tank of the pure benzene tower is pumped to the middle section of the toluene tower using a toluene tower feed pump. The toluene bottom stream is continuously heated by a steam-heated reboiler in the toluene column; the crude toluene liquid is distilled within the column, with toluene being discharged from the top of the column. The overhead distillate is cooled by the first and second coolers of the toluene column before entering the oil-water separator of the toluene column. It is then pumped back to the top of the column using a toluene reflux pump to maintain pressure; part of this stream is used for reflux, while the rest is sent as a product to the storage tank area. The liquid from the bottom of the toluene tower is sent to the underground tank of the toluene tower for storage. The liquid from the underground tank of the toluene column is pumped to the middle section of the xylene column using a xylene column feed pump for feeding. The xylene bottom stream is continuously heated by a steam-heated reboiler in the xylene column; xylene and the directly introduced steam are distilled inside the column, with the xylene being discharged from the top of the column. The overhead distillate from the xylene tower is cooled in the first and second coolers of the xylene tower before entering the oil-water separator of the same tower. The condensed liquid phase obtained after separation is pumped back to the top of the tower using a xylene reflux pump for reflux purposes, while the oil phase is sent to the storage area as a product. The xylene bottom residue is sent to the tank area for storage. This post was last edited by ryn on 2009-2-6 11:32]
Lyondell’s light tar hydrogenation/cyclosulfone aromatic extraction technology in the United States: Light tar (COLO – Coke Oven Light Oil) is a by-product of the steel industry; coke is used in steel production, and light tar is produced as a by-product of coal coking. In 2006, China’s production of light tar was around 3.5 to 4 million tons, with benzene, toluene, and xylene accounting for over 90% of its composition (benzene accounting for 70–80%) ； Toluene 10 – 15% ； Xylene, styrene, and ethylbenzene account for 3–5% of its composition; COLO contains heterocyclic compounds such as pyridine (0.25%) and thiophene (0.3–0.6%), which result in sulfur and nitrogen impurity levels of several thousand, or even over 10,000 PPm. It also contains impurities such as mono- and diolefins (styrene at 1.5–2.5%). It is not practical to separate these impurities—pyridine, thiophene, and styrene—from COLO using simple distillation methods, as their boiling points are very close to those of the desired products (benzene, toluene, xylene) (see table below). This limits the economic, efficient, and effective utilization of light tar. Traditional refining and recovery methods used in China not only result in low recovery rates for benzene, toluene, and mixed xylene but also cause severe environmental pollution, thereby hindering the development and utilization of light tar. The selective hydrogenation refining and sulfolane aromatic extraction technologies developed by the American company Lyondell for light tar (COLO – Coke Oven Light Oil) effectively address these challenges. These technologies not only convert low-value light tar into products with high added value but also ensure high product recovery rates (with yields of BTX reaching 97.5%, 97.5%, and 115% respectively, as guaranteed) and high purity levels (with purities of BTX at 99.95%, 99.8%, and 98.6% respectively, as guaranteed). The benzene, toluene, and xylene produced meet the requirements for use in various applications, while cyclohexane-grade benzene, methylcyclohexane, and TDI-grade toluene can also be obtained. More importantly, these processes cause no environmental pollution, thereby promoting the development of the light tar chemical industry. Since the 1970s, Lyondell has licensed dozens of selective hydrogenation/cyclosulfone aromatic extraction technologies around the world for the hydrorefining/aromatic extraction of catalytically reformed/petrolyzed gasoline, to produce benzene, toluene, and xylene (BTX – Benzene, Toluene, Xylene). The first industrial plant to use Lyondell hydrogenation/aromatic extraction technology with COLO as raw material was operated by Japan’s Kawatetsu Chemicals company in 1982. The second set, also using COLO raw material, was produced by the Japanese company Adchemco in 1995. It is expected that industrial plants in China that will use Lyondell’s aforementioned technology with COLO as raw material will come online successively between 2008 and 2010. These users include Shanghai Baosteel, Jiangsu Shagang, Shenma Group (Pingdingshan, Henan), Shuncheng Group (Anyang, Henan), Baotou Steel, and Huaibei Mining Bureau, among others. Lyondell, drawing on its more than 20 years of experience in industrialization as well as relevant pilot-scale hydrogenation research results, is able to quantitatively adjust all major operating parameters, thereby providing new and existing customers with the latest technological advancements and catalyst improvements to bring benefits to them. Advantages of Lyondell’s selective hydrogenation technology: strong adaptability to the raw materials processed, and high flexibility. The designed unit can process different feedstocks (reformate, pyrolysis gasoline, coker light oil, and mixtures thereof). It can be designed to process 100% light tar feedstock, as well as mixtures of light tar and pyrolysis gasoline or aromatic reformate. Due to this characteristic, in plants designed using 100% light tar feedstock, the maximum proportion of pyrolysis gasoline or reformed oil in the mixed feedstock is approximately 35.0%. Unique Lyondell aromatic extraction technology: There are many different processes that can be used to extract aromatics from various light coal-tar and petrochemical products. To date, the most commonly used method is the liquid-liquid extraction technique with sulfolane as the extractant. This process has over 40 years of successful application experience and has been continuously improved; despite the introduction of other extraction processes and various solvents, the sulfolane-based systems provided by Lyondell (and UOP, etc.) remain the preferred technology. Today, there are over 30 aromatic extraction units owned by Lyondell itself or those that use its transferred technology in operation, processing feedstocks such as coker light oil, hydrogenated cracked gasoline, reformate oil, and various mixtures of these. In fact, the Japanese Kawatetsu and Adchemco plants can process light tar feedstock alone, or a mixture of it with pyrolysis gasoline. Lyondell provides customized designs for each new aromatic extraction unit, constructing more flexible production facilities as required by each customer. Contact me: James.yang@eandj-intl.com
There is also a process for benzene hydration that uses sulfolane as an extractant
Since the beginning of 2009, the price of hydrogenated benzene has defied market principles, staying at around 3,000 yuan per ton. It should logically be on par with the price of gasoline, which has hindered the operation of the benzene hydrogenation industry.
Hehe, the price of gasoline is now 6,600 per ton. Petroleum benzene is only 5500; let alone hydrogenated benzene… it’s difficult.
The chemical industry is in a downturn, what a worry! However, the original poster’s approach is worth studying carefully*, hehe
It is necessary for the poster to have relevant educational background. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Thank you, I’ve learned it. We are currently working on a benzene hydration process, and it’s very necessary to learn this.
Thank you, our benzene hydrogenation plant is under construction
Make full use of the raw materials from coking plants to produce high-value-added products. Resources were utilized to reduce environmental impact. It’s a good thing; it should be promoted.