Process Design of Isopropyl Alcohol Synthesis Section of 80,000 Tons/Yea

: Isopropanol is a chemical product with great application value and can be used as a chemical raw material and organic solvent. This design is a synthesis section of 80,000 tons/year isopropanol, using acetone hydrogenation synthesis process. At a temperature of 180 °C, a pressure of 0.8 MPa, n (hydrogen)/n (acetone) = 1.5 : 1, performed in a column tubular fixed bed reactor. This design uses a 4-stage tubular fixed-bed reactor with an effective length of 8.5 m, a total length of 15.705 m, and a housing diameter of 2.9 m. The total number of 4-segment column tubes is 10,444, and the column tubes are made of seamless stainless steel pipes with a diameter of 38 mm and a thickness of 4 mm. The design improves production safety and reduces energy losses. The design results have certain guiding significance for actual production and application.


Introduction
Isopropanol has many applications. As chemical raw materials, acetone, hydrogen peroxide, isopropyl chloride, fatty acid isopropyl ester, and chlorinated fatty acid isopropyl ester can be produced [1].
Before 2010, the production of isopropanol in China was far from meeting the demand and needed to be imported to make up for it. However, since 2020, due to the serious impact of the epidemic, the demand for isopropyl alcohol has been increasing, so it is the general trend to build factories producing isopropyl alcohol and optimize the production process [2].
At present, there are three main production routes of isopropyl alcohol, namely propylene water method, acetone hydrogenation method and transesterification method [3]. However, due to the limitation of the existing technological level and product value, this project plans to build a new isopropanol production project for a factory. With acetone from a factory as the main raw material, isopropanol is prepared through synthesis, separation and other processes, and data are simulated by Aspen software.

Determination of Design Scheme
Hydrogenation of acetone to produce isopropanol mainly includes three sections, namely, synthesis section of isopropanol, separation section, extraction of by-products and recovery of azeotrope section [4]. Among these three sections, only synthesis section involves chemical reactions.
At present, isopropyl alcohol has achieved industrial production in the world in two categories: acetone hydrogenation and propylene hydration, and propylene hydration can be divided into liquid phase direct hydration, gas phase direct hydration and gas liquid miscible hydration [5]. The gas phase direct water method has a high utilization rate for propylene. Most of propylene can be converted into target products, and only a small part can be converted into by-products. But at the same time, the disadvantages should not be ignored: in order to prevent the dissolution of phosphoric acid, water must be converted from liquid to gas, resulting in low propylene conversion rate [6]. The liquid phase direct water catalyst has high activity. Compared with the gas phase direct water catalyst, the reaction speed is several times higher under the same concentration of hydrogen ion, and the product selectivity is good, the service life is long, and there is no pollution. However, the heat ratio of hydroene is large, the heat consumption of distillation is large, the reaction pressure is too high, and the equipment investment is high [7].
The application of acetone hydrogenation method in isopropanol production process is not as wide as that of direct water method, because the method has high requirements for raw materials and large demand, which is not conducive to its economic benefits. However, this method still has advantages, low energy consumption is more important, and acetone hydrogenation has less corrosion to production equipment [8].
From the perspective of catalyst, nickel catalyst is expensive, but long life, and waste catalyst can be recycled, environmental protection pressure is low; The price of acidic catalyst is relatively low, but the service life is short and loss occurs in the reaction process. The catalyst needs to be continuously supplemented during the reaction, which also corrodes the reactor [9]. Acetone hydrogenation reaction conditions are mild, and the one-way conversion rate is high, and the reaction process is not complicated. Therefore, this project adopts the acetone hydrogenation process with nickelbased catalyst.

Material Balance
Process simulation was carried out through Aspen Plus Dynamics V11 and material balance was calculated in the following

Determination of Catalyst
Referring to Yang Qingquan's study on acetone constant pressure gas phase hydrogenation reaction and catalyst [11], we selected the following properties of catalyst: shape: spherical, particle size: 3 mm, bulk density: 800 kg/m3, life: 5 years.

Reaction Temperature Selection
According to the suitable range of active temperature of catalyst and Yang Qingquan's Study on Gas Phase Hydrogenation of Acetone under normal Pressure and Catalyst [13], the inlet temperature of reaction gas was selected as 180 ℃.

Reaction Pressure Selection
Referring to Yang Qingquan's study on acetone normalpressure gas phase hydrogenation reaction and catalyst [11] and based on Aspen simulation, the inlet pressure of reaction gas was selected as 0.8mpa.

Hydrogen Acetone Feed Ratio
Referring to Yang Qingquan's study on acetone normally pressurization gas phase hydrogenation reaction and catalyst [11] and based on Aspen simulation, acetone hydrogenation reactor of this project was selected: n (氢气) /n (丙酮) = 1.5 : 1.

Design Conditions
The pressure in the reactor can be obtained from the Aspen flow simulation information Pw = 0.8 Mpa. The design pressure is generally selected as P = (1 ~ 1.1)Pw, because the design temperature is generally higher than the maximum temperature. P = P w × 1.1 = 0.8 × 1.1 = 0.88 Mpa T = 180 + 20 = 200 ℃

Determination of Catalyst Bed Diameter
Firstly, the diameter of the catalyst bed was calculated in an ideal tubular reactor. For the operating pressure of 0.8 Mpa, under the premise of ensuring the conversion rate and pressure drop, the empty bed flow rate of the compressed gas was 0.095 m/s, so the bed diameter was calculated as follows: After rounded, 3.0m bed diameter is taken.

Design of Tube Size and Number of Roots
In order to ensure adequate heat dissipation, the inner diameter of the reaction tube should be minimum, so the inner diameter of the reaction tube should be 30 mm. Refer to GBT17395-2008 Dimensions, Shape, Weight and Allowable Deviation of Seamless Steel Tube [12]. The specifications of the seamless stainless steel tube selected are 38×4mm, and the material used is 12Cr2Mo1.
The number of tubes in the reactor should conform to the diameter of the catalyst bed, so the number of tubes needed is as follows. The number of tube roots was 10444 after rounding.

Determination of Inner Diameter of Shell
The inner diameter of the shell is calculated by the following formula: D = 2e +(b-1)× t In the formula, t is the distance between the tubes , t = 1.25d 0 , d 0 is the outer diameter of the tubes.
The reactor was designed to be composed of four reactors, arranged in staggered equilateral triangle, with 10,444 tubes in total.
Shell inner diameter ： D = =0.045×2+(59-1)×0.0475=2.845m After being rounded, it is 2.9m. The appropriate reactor volume was selected based on the simulation and improvement data of Aspen Plus acetone hydrogenation reactor and various factors (see figure). At the same time, when the catalyst bed porosity of 0.4 and density of 800 kg/m3 are filled, the one-way yield of isopropanol is 85.3% and the selectivity is 97.4% [13], so it can be calculated that the conversion rate of acetone under such conditions is 87.6%. When the length of the reactor was 0.85m, the corresponding conversion rate was 87.56%. Therefore, the length of the reactor was 8.5 m.  As the fouling thermal resistance is related to heat transfer medium and cleaning cycle, it is impossible to calculate the precise value, 0.00072 m 2 ⋅K/W [14].
3)Design and calculation of the total heat transfer coefficient

Calculation of Heat Exchange Area
The heat transfer driving force can be calculated as 55℃ through the temperature calculation of import and export materials.
The heat exchange area is: Plug in and calculate the heat transfer area,  A =132.714 m 2 . The actual heat exchange area is 1870.215 m 2 , which meets the heat exchange requirements.

Total Reactor Height
The total height is divided into five parts, namely, the height of the cylinder,H 1 = 8.5 m; Skirt is highH 2 = 4 m: For the head high, H 3 = 650 + 40 +15= 705 mm = 0.705 m. At the same time, the height of the reactor also includes the top and bottom of the cylinder. According to literature [15], the top space is 1m and the bottom space is 1.5m.

Conclusion
Isopropanol is a chemical product with great application value, which can be used as chemical raw materials and organic solvents. The design of 80,000 tons/year isopropanol synthesis section, using acetone hydrogenation synthesis process. Under the conditions of temperature 180 ℃, pressure 0.8 MPa, N (hydrogen)/ N (acetone) = 1.5:1, the experiment was carried out in a tubular fixed-bed reactor. In this design, a four-section tubular fixed-bed reactor was adopted, with an effective length of 8.5m, a total length of 15.705m and a shell diameter of 2.9m. There are 10,444 tubes in 4 sections, and the tubes are seamless stainless steel tubes with a diameter of 38 mm and a thickness of 4 mm. The design improves production safety and reduces energy loss. The design result has certain guiding significance for practical production and application.