Academic Journal of Science and Technology ISSN: 2771-3032 | Vol. 1, No. 3, 2022 91 Process Design of Isopropyl Alcohol Synthesis Section of 80,000 Tons/Yea Junfei Zhou, Xiaoguang Wang* School of Chemistry and Chemical Engineering, Zhoukou Normal University, Zhoukou Henan, 466001, China. Abstract: 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. Keywords: Synthesis of isopropanol, Acetone hydrogenation, Process planning. 1. 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. 2. 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 nickel- based catalyst. 3. Technological Process Acetone mixed with hydrogen, heated and pressurized into the reactor for reaction, reaction mixture through condensate 30℃, and then into the air and liquid separator for separation, the main component of the gas is hydrogen, so we cycle hydrogen and hydrogenation, liquid phase of the liquid separator contains a small amount of water, acetone, pressure to atmospheric pressure, flow into the next section. According to the general situation of the annual operation time of the chemical plant continuous production unit, the operation time of this project is determined to be 8000 h/a. Simulated by Aspen Plus, the flow chart is as follows: 92 Figure 1. Schematic diagram of isopropyl alcohol synthesis section 4. Material Balance Process simulation was carried out through Aspen Plus Dynamics V11 and material balance was calculated in the following table: Table 1. Total material balance of isopropanol synthesis section Project Unit Imported material Export material Acetone feed Hydrogen feed Backflow of acetone Component after flash Phase Liquid phase Vapor phase Vapor phase Liquid phase Temperature ℃ 20.000 20.000 55.729 29.993 Pressure Mpa 0.101325 0.101325 0.101325 0.12159 Volume flow m3/hr 12.8033 4210.733 654.571 25.051 Mass flow rate kg/hr 10168.1 352.876 1382.190 11903.196 C3H6O-1 kg/hr 10168.1 0.000 1368.707 1370.044 H2 kg/hr 0.000 352.876 0.9544 0.9543 C3H8O-2 kg/hr 0.000 0.000 12.174 10256.317 C6H14O-3 kg/hr 0.000 0.000 0.1324 234.360 H2O kg/hr 0.000 0.000 0.2224 41.520 C2H6O2 kg/hr 0.000 0.000 0.000 0.000 C3H6O2-2 kg/hr 0.000 0.000 0.000 0.000 Total kg/hr 11903.166 11903.196 5. Material Balance The heat balance of reactor calculated by Aspen in the following table: Table 2. Flow enthalpy change calculation table Unit Input Output Moore flow kmoL/hr 501.084 326.036 Mass flow rate kg/hr 12306.835 12306.835 Volume flow m3/hr 2359.921 1535.482 Temperature ℃ 180.008 180.000 Pressure Mpa 0.800 0.800 Gas fraction / 1.000 1.000 Liquid fraction / 0.000 0.000 Solid fraction / 0.000 0.000 Molar enthalpy J/kmoL -78476790.721 -152138712.345 Quality enthalpy J/kg -3195253.822 -4030499.677 Moore entropy J/kmoL-K -76127.696 -170464.818 Quality entropy J/kg-K -3099.608 -4516.000 Flow enthalpy Watt -10923183.735 -13778526.202 6. Material Balance 6.1. Kinetics of Acetone Hydrogenation Through the reaction of the established kinetic model data determination, the final measured parameters. The reaction rate constant of acetone hydrogenation [10] is Ka = 2.98 × 1012exp(-70.7/RT) moL/ ( m3∙h) . The catalyst density we used is 800 kg/m3, so the reaction rate constant based on catalyst mass can be obtained: ka = 2.98×1012exp(-70.7/RT)÷800 93 = 3.725×109exp(-70.7/RT) mol/(kg∙h) = 1.03×103exp(-70.7/RT) kmol/(kg∙s) The adsorption equilibrium constant of gas phase acetone on Ni-Cu/SiO2 catalyst is: Ka=3.30×10-8exp(58.7/RT) kPa-1 ln(Ka) = -17.227 + 7060.4/T The adsorption equilibrium constant of hydrogen on Ni- Cu/SiO2 catalyst is: Kb = 1.83×10-11exp(82.2/RT) kPa-1 ln(Kb) = -24.724 + 9886.9/T Therefore, the kinetic factor of the reaction is: K = ka . Ka .Kb= 6.249×10-16 exp(70.2/RT) kmol/(kg∙s) 6.2. Reaction Condition Selection 6.2.1. 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. 6.2.2. 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 ℃. 6.2.3. Reaction Pressure Selection Referring to Yang Qingquan's study on acetone normal- pressure gas phase hydrogenation reaction and catalyst [11] and based on Aspen simulation, the inlet pressure of reaction gas was selected as 0.8mpa. Figure 2. Simulation results of Aspen pressure 6.2.4. 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. Figure 3. The simulation results (N (hydrogen)/ N (acetone) = 1.5:1) 6.3. Reactor Structure Design 6.3.1. 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 = Pw × 1.1 = 0.8 × 1.1 = 0.88 Mpa T = 180 + 20 = 200 ℃ 6.3.2. 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: 94 Db= 4V0 3600πu = 4×2354.77415 3600×π×0.095 ≈2.96m After rounded, 3.0m bed diameter is taken. 6.3.3. 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. n D d 3.0 0.03 10000 6.3.4. 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 = 1.25d0, d0is 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. Figure 4. Sensitivity analysis results of reactor length Volume of catalyst bed: VR = nπd 4 × H1 = 10444 × π0.032 4 × 8.5 =62.75 m3 Taking 800 kg/m3 as the filling density of catalyst, the amount of catalyst can be obtained: m = ρV = 800 × 62.75 = 50200 kg Ratio of catalyst diameter to reactor tube diameter :D/d = 6~12 6.4. Reactor Heat Transfer Calculation 6.4.1. Overall Profile Aspen Plus is used to simulate the reaction of the mixture system, and it can be obtained that when the reaction reaches the set goal, the heat transfer load is Q = 2846.61 ÷ 4 = 711.65 kW, the heat transfer area is: A = nπdoL = 10444 ÷ 4 ×π × 0.038 ×8.5 = 2649.472 m2 6.4.2. Estimation of Reactor Heat Transfer Coefficient 1)Design and calculation of heat transfer coefficient between cooling medium and wall surface. α0 = 0.36 λ0 de deu0ρ0 μ0 0.55 Cpμ0 λ0 1 3 μ μw 0.14 μ0= 0.219cP, λo= 0.6845W/(m⋅K), Cp= 4788.78J/(kg⋅K); μ μw 0.14 =1.05 ρ0 = 891.30kg/m³ , de= 4 √3 2 t2- π 4 d0 2 πdo , de= 4( √3 2 ×0.04752- π 4 ×0.0382) π×0.038 =0.02750 m αo=0.36× 0.219 0.02750 × 0.02750×1.25×891.3 0.219×10-3 0.55 × 4788.78×0.219×10-3 0.6845 1 3 ×1.05=2347.31W/(m⋅K) 2)Design and calculation of heat transfer coefficient between bed and wall surface αtdt λ =3.5 dpG μ 0.7 exp -4.6 dp dt dt = 0.03m, λ = 0.0894 W/(m⋅K), μ = 0.01433 cP, G = 0.4598 kg/(m2 ⋅s)；αi=3.5× 0.003×0.4598 0.01433×10-3 0.7 × exp -4.6× 0.003 0.03 × 0.0894 0.03 =161.035 W/ m∙K As the fouling thermal resistance is related to heat transfer medium and cleaning cycle, it is impossible to calculate the precise value, 0.00072 m2⋅K/W[14]. 3)Design and calculation of the total heat transfer coefficient K = 1 1 α0 + b λ ∙ do dm + 1 αi ∙ d0 di +Rso+Rsi∙ do di Plug in and calculate the total heat transfer coefficient, K = 97.4926 W/(m⋅K). 6.4.3. Calculation of Heat Exchange Area The heat transfer driving force can be calculated as 55℃ through the temperature calculation of import and export 95 materials. The heat exchange area is: A = Q ∆tm∙K Plug in and calculate the heat transfer area, A =132.714 m2. The actual heat exchange area is 1870.215 m2, which meets the heat exchange requirements. 6.4.4. Total Reactor Height The total height is divided into five parts, namely, the height of the cylinder,H1= 8.5 m; Skirt is highH2 = 4 m: For the head high, H3 = 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. The total reactor height: H = H1+H2+H3+H4+H5= 8.5+4+0.705+1+1.5 =15.705 m 7. Conclusion Isopropanol is a chemical product with great application value, which can be used as chemical raw materials and organic solvents. 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