Microsoft Word - 19Venkatesan.docx CHEMICAL ENGINEERING TRANSACTIONS VOL. 80, 2020 A publication of The Italian Association of Chemical Engineering Online at www.cetjournal.it Guest Editors: Eliseo Maria Ranzi, Rubens Maciel Filho Copyright © 2020, AIDIC Servizi S.r.l. ISBN 978-88-95608-78-5; ISSN 2283-9216 Modelling and Simulation of Methanol and Biodiesel Production Processes using Innovative Technologies Letitia Petrescu*, Stefan C. Galusnyak, Dora A. Chisalita, Calin C. Cormos Babes-Bolyai University, Faculty of Chemistry and Chemical Engineering, Arany Janos 11, Postal code: RO-400028, Cluj- Napoca, Romania letitiapetrescu@chem.ubbcluj.ro Biodiesel is considered to be a promising alternative or additive to fossil fuel. Biodiesel, fatty acid methyl esters (FAME), is produced by transesterification of triglycerides or fatty acids with alcohols (i.e. methanol or ethanol, in the presence of a suitable acidic or alkaline catalyst. The present work is focused on process modelling and simulation of biodiesel production using: i) an innovative method for methanol synthesis, methanol being an important raw-material for biodiesel, as well as ii) an intensified method for biodiesel production (i.e. reactive distillation – RD). Methanol production from CO2 and H2 is considered to be an interesting method for CO2 utilization. The main advantages of this method are the reduction of greenhouse gas emissions and the production of one valuable chemical, methanol. The H2 for the methanol synthesis is obtained from wood chips through chemical-looping gasification. Beside methanol, other raw-materials for biodiesel production are triglycerides and the catalyst. The classical acid method, consisting in reaction and separation, and the intensified method based on RD for biodiesel production are investigated and compared from technical and environmental point of view. The study also considers as benchmark cases biodiesel production using classical and intensified methods, methanol deriving from syngas, syngas being obtained from natural gas (NG) steam reforming (SR). A productivity of 100,000 t/year of biodiesel is set for all cases. Purities higher than 99% are obtained both for the main product, biodiesel, and for the by-product, glycerol. The results of the simulations lead to the conclusion that RD for biodiesel production gives superior performance in terms of raw materials consumption, biodiesel purity, by-product flow-rate and CO2 emissions but energy and steam consumption should be reduced in order to make this technology competitive at industrial scale. 1. Introduction A sustainable future calls for sustainable fuels. A percentage of 30% of the total greenhouse emissions drives from the transportation sector with CO2 being the main contributor (Awad et al., 2018). The best way to reduce the CO2, CO and NOx emissions is to use sustainable fuel alternatives such as biodiesel (Erdiwansyah et al., 2019). Biodiesel sustainability depends on feed stocks, the character of lands for bioenergy crops and the production process (Piemonte et al., 2014). Biodiesel production in 2017 was around 36 billion liters with the European Union generating 13.5 billion liters of biodiesel (OECD-FAO, 2018). The most relevant methods for biodiesel production are: pyrolysis, transesterification, dilution and usage of supercritical methanol. The advantages and disadvantages of the above mentioned methods, the conditions involved in each case as well as a classification of transesterification is offered by Atabani and co-authors (Atabani et al., 2012). Methanol, as well, can be generated starting from various feed stocks (i.e. natural gas, coal, heavy oil) and using various technologies (i.e. reforming, gasification). In the last decade the attention was focused on methanol production from renewable sources. Green methanol can be produced from CO2 and H2. In order to be green H2 should be generated from water electrolysis using wind, solar or biomass electricity. Other green technologies for H2 generation are: biomass pyrolysis or steam/oxygen gasification and reforming of biomass-derived products (Bozzano and Manenti, 2016). CO2 can be captured from energy intensive processes (i.e. cement, steel, chemical or power generation plants) reducing in this way their emissions into the atmosphere. The novelty of the present research consists on the comparison between classical method of biodiesel production and the DOI: 10.3303/CET2080031 Paper Received: 21 November 2019; Revised: 12 February 2020; Accepted: 10 April 2020 Please cite this article as: Petrescu L., Galusnyak S.-C., Chisalita D.-A., Cormos C.-C., 2020, Modelling and Simulation of Methanol and Biodiesel Production Processes Using Innovative Technologies, Chemical Engineering Transactions, 80, 181-186 DOI:10.3303/CET2080031 181 intensified one based on RD, biodiesel being produced from two different sources, a fossil fuel source (i.e. NG) and a renewable one (i.e. biomass). 2. Plants configurations and models assumptions The cases investigated in the present paper are presented in Table 1. Table 1: Cases investigated in the present research Case name Final product Technology for biodiesel production Intermediate Key component Raw-material for intermediate key component production Technology for converting the raw-material into intermediate key component Case 1 Biodiesel Classic Methanol NG Steam reforming Case 2 Biodiesel Intensified Methanol NG Steam reforming Case 3 Biodiesel Classic Methanol Biomass Chemical-looping gasification Case 4 Biodiesel Intensified Methanol Biomass Chemical-looping gasification Classic - reaction and separation for biodiesel production, Intensified – RD for biodiesel production Case 1 refers to biodiesel production by means of classical method using NG as raw-material, Case 2 refers to biodiesel production by means of intensified method using NG as raw-material; Case 3 is represented by biodiesel production through classical method using biomass as raw-material and Case 4 is the biodiesel production by means of intensified method using biomass as raw-material. Methanol is the intermediate key component for all cases. Methanol production from syngas, which is obtained from NG by SR, is a common part for the first two cases. In the latter cases methanol production from CO2 and H2 were considered, CO2 and H2 being obtained from biomass through chemical-looping gasification technology. Biomass-derived chemical-looping gasification is a novel technology to convert biomass into renewable hydrogen-enriched syngas (Hu et al., 2020). All cases were modeled using ChemCAD and Aspen Plus software packages. Most methanol industrial processes use syngas as raw material, syngas being produced from different fossil fuels. In the present study syngas is obtained from NG. Methanol production process from syngas is presented in Figure 1A while methanol production process from CO2 and H2 is presented in Figure 1B. S11 5 76 9 10824 12 13 2123 22 15 14 17 18 1920 Methanol Water Flue gases S6 S7 S5 S8 S9 S17S18 S10 S12 S13 S19 S14 S16 S15 S18 S20 1 3 2 Natural gas Water S2 S1 S3 S4 16 11 4 2 4 6 9 11 27 20 22 15 1 3 5 10 14 12 18 8 28 CO2 16 H2 21 13 19 23 Water 26 Air 24 Methanol 7 Flue Gases 17 S1 S2 S3 S4 S7 S5 S6 S12 S8 S10 S9 S11 S13 S14 S15 S16 A B Figure 1: A) Methanol production from syngas derived from NG (sub process for Case 1 and Case 2) B) Methanol production from CO2 & H2 derived from biomass (sub process for Case 3 and Case 4) NG, stream S1 is converted to syngas in the SR technology. Syngas, S4, is compressed to 108 atm, in a two- stage compressor with intermediate cooling, furthermore mixed with two recycled streams, S18 and S19, and preheated up to the reactor inlet temperature. The reactions occurring in the methanol production are: + 2 ↔ (1) + 3 ↔ + (2) The output stream of the reactor, S8, leaves the reactor at 267°C and enters the heat exchanger (Unit 10) which is used to preheat the reactor inlet flow. After this thermal integration, the flow is cooled down to 38°C. The liquid and gaseous phases are separated using a separator (Unit 13). S11 is divided into two streams, S18, which is compressed and recycled, and S17 which is removed from the system as a purge. The liquid phase, S10, is sent to another separation unit to remove the remaining gases and then fed to the distillation 182 column (Unit 16). Methanol is obtained in the top of the column, as S16, whilst water, collected at the bottom, can be used to generate the steam required in the syngas production. The methanol production process from CO2 and H2 is presented in Figure 1B. CO2 feed, S1, is compressed up to 78 atm through a four-stage compressor with intermediate cooling. H2 feed stream, S2 is also compressed to the same pressure. Compressed raw-materials streams are mixed with the recycle stream, S7, and fed to the heat exchanger (Unit 10), where they are heated up to reach the reactor inlet temperature, 210°C. S5 from the reactor is divided into two streams one is used to preheat the reactor feed, while the other is used to preheat the column feed. After heat integration, the streams are mixed again and cooled down to 35°C and then separated in two gas-liquid separators (Unit 15 and Unit 20). The liquid stream, S11, is preheated and sent to the distillation column, Unit 22. Liquid methanol is obtained in S13. Hydrogen requested for methanol synthesis can be obtained from biomass using gassification or chemical- looping gassification technologies. Gasification of biomass and production of high yields of clean syngas is very challenging (Volpe et al., 2016). Chemical-looping gasification is a promising technology that uses two interconnected fluidized bed reactors with a solid oxygen carrier circulating between them (see Figure 2). In the first reactor (i.e. fuel reactor) gassification of biomass takes place using oxygen from the oxygen carrier and steam as gassifying agent, while in the second reactor (i.e. air reactor) the oxygen carrier is regenerated. Compared to other gassification technologies, chemical-looping gasification presents some advantages (Ge at al., 2016), such as: i) no nitrogen dillution leading to higher quality syngas as well as minimizing the energy penalty of CO2 separation, ii) lower enegy penalty by removing the air separation unit (ASU) used for O2 production, iii) autothermal operation – heat for endothermic gasification and reduction reactions supplied by the oxygen carrier returning from the air reactor. The proposed hydrogen production technology, represented in Figure 3, was simulated using Aspen Plus software package. The main characteristics of biomass used for chemical-looping gasification as well as the design assumptions of this technology are listed in Table 2. Table 2: Main design and modelling assumptions for hydrogen production from biomass Process Unit Assumption Ultimate and Proximate analyses of wood chips (Pala et al., 2017) Moisture (wt.%): 20.00. Proximate analysis (wt.% dry): volatile matter – 80; fixed carbon - 18.84; ash - 1.16. Ultimate analysis (wt.% dry): C - 51.19; H - 6.08; O - 41.30; N - 0.20; S - 0.02; Cl - 0.05; Ash - 1.16. Chemical-looping gasification Property method: PR with BM modification; Tar formation notconsidered; Operating conditions: P = 1 atm; TAR = 950°C; TFR ≈ 800°C; Oxigen carrier: Ilmenite (0.50 wt.% Fe2O3 + 0.50 wt.% TiO2) Fluidization agent: Steam at 150°C , 1 atm. AR – Air reactor; FR – Fuel reactor; PR- Peng-Robinson; BM – Boston-Mathias Figure 2: Chemical-looping gasification of biomass Figure 3: Conceptual design of hydrogen production from biomass Biodiesel is produced via a transesterification reaction, in which triglycerides react with a primary alcohol to generate two products. The main product is the fatty acid methyl ester (FAME) or methyl oleate, while glycerol is obtained as a by-product. Figure 4 illustrates the process flow diagram for biodiesel production process through the classic method. 183 1 2 3 8 4 7 9 11 12 13 10 CaO Methanol Oil Calcium sulfate Vent Unconverted Oil Methanol & Water Glycerol Methyl Oleate S1 S2 S3 S4 S6 S5 S7 S8 S9 S10 S12 S14 S13 S11 S15 S16 S17 S19 S18 5 6 14 16 Water 15 Figure 4: Biodiesel production through classic method (sub-process for Case 1 and Case 3) Methanol, oil (i.e. rapeseed oil) and sulfuric acid feed streams are all brought to a pressure of 4 atm and mixed before entering the transesterification reactor, Unit 5. A distillation column, Unit 6, installed after the transesterification reactor, aims to separate and recycle the unconverted methanol S7. The residue from the column, S5, is cooled down to 60°C and mixed with calcium oxide (S8) in order to neutralize the catalyst (i.e. H2SO4); the resulting calcium sulfate is removed from the system in Unit 12. The mixture is sent to an extraction column (Unit 14) and washed with water, S12, separating the biofuel and the unconverted triglyceride from methanol and glycerol. S13 stream, containing biofuel and unconverted triglyceride, is sent into another distillation column (Unit 15). Biodiesel is obtained in stream S16. The water, glycerol and methanol mixture that is obtained after the extraction step is separated in a third distillation column (Unit 16). The water-methanol mixture leaves the column at the top, while glycerol is recovered at the bottom, S19. As mentioned before, biodiesel production process was also modelled following an innovative method, RD. Instead of Unit 5 and Unit 6 from Figure 4 a single column containing a reaction zone was used. In RD both reaction and separation occur in the same unit. Beside the reaction and separation sections, the process follows the same path as described in Figure 4. The main design assumptions considered in the present study are summarized in Table 3. Table 3: Main design assumptions for various sub-processes involved in Cases 1 – 4 Modelling and simulation details and main design assumptions M e th a n o l fr o m s y n g a s, sy n g a s fr o m N G Raw materials: natural gas, water; Main product: methanol; By-product: flue gases, water; Thermodynamic package used: SRK; Assumptions: reactor isothermal 267°C; distillation column 42 stages; distillate component mole fraction 0.99 CH3OH, bottom component mole fraction 0.001 CH3OH; HE min ∆T 10˚C. M e th a n o l f ro m C O 2 a n d H 2 , C O 2 a n d H 2 fr o m b io m a ss g a si fi ca ti o n Raw materials: CO2, H2, air; Main product: methanol; By-product: flue gases, water; Thermodynamic package used: UNIFAC; Assumptions: methanol reactor isothermal 210°C; distillation column 57 stages, distillate component recovery 99.75% CH3OH, bottom component recovery 99.75% H2O; compressors efficiencies 75%; pump efficiency 75%; HE min ∆T 10˚C. B io d ie se l t h ro u g h c la ss ic m e th o d ( re a c tio n & se p a ra ti o n ) Raw materials: methanol, triglyceride, sulphuric acid, water, calcium oxide; Main product: biodiesel; By-products: glycerol, unconverted triglyceride; Thermodynamic package used: UNIFAC; Assumptions: transesterification kinetic reactor thermal mode isothermal 60°C; methanol recovery column 10 stages, RR 2, bottom component recovery 93.25% glycerol; extraction column 4 stages; biodiesel column 18 stages, top pressure 0.40 atm, RR 4, bottom component recovery 98.90% monoolein; glycerol distillation column 6 stages, RR 2, bottom product temperature 107.30°C; pump efficiencies 75%; HE min ∆T 10˚C. B io d ie se l t h ro u g h in n o va tiv e m e th o d ( R D ) Raw materials: methanol, triglyceride, sulphuric acid, water, calcium oxide; Main product: biodiesel; By-products: glycerol, unconverted triglyceride; Thermodynamic package used: UNIFAC Assumptions: reactive distillation column 30 stages, feed stages no. 8 and 19, RR 2, reaction volume stages 8 -16; extraction column 4 stages; biodiesel column 18 stages, RR 4, bottom component recovery 99% monoolein; glycerol column 6 stages, RR 2, bottom product temperature 107.3°C; pump efficiency 75%; HE min ∆T 10˚C. HE – heat exchangers, RR – reflux ratio, UNIFAC – UNIQUAC Functional-group Activity Coefficients; SRK – Soave Redlich Kwong 184 The transesterification reaction occurring either in the transesterification reactor or RD column were modelled using kinetic rate expressions for the forward and backwards reactions (Giwa and Ogunware, 2018). The parameters involved in the expressions are presented in Table 4. Table 4: Kinetic data for the transesterification reaction of triolein with methanol Reactions Expressions for reaction rate Parameters k (mol -1 litre min -1 ) E (cal/kmol) C57H104O6 + CH3OH → C39H72O5 + C19H36O2 r1=k1*CTriolein* CMethanol 1.469 × 10 8 14,040 C39H72O5 + C19H36O2→ C57H104O6 + CH3OH r2= k2 * CDiolein * CMethyl oleate 105,100 10,739 C39H72O5 + CH3OH → C21H40O4 + C19H36O2 r3= k3* CDiolein* CMethanol 1.19 × 10 10 16,039 C21H40O4 + C19H36O2→ C39H72O5 + CH3OH r4= k4* CMonoolein* CMethyl oleate 1.725 × 10 8 13,907 C21H40O4 + CH3OH→ C3H8O3 + C19H36O2 r5= k5* CMonoolein* CMethanol 2.55 × 10 10 7,173 C3H8O3 + C19H36O2→ C21H40O4 + CH3OH r6= k6* CGlycerol* CMethyl oleate 627,700 10,997 Triolein – C57H104O6; Dioelin – C39H72O5; Monoolein – C21H40O4; Methyl oleate – C19H36O2; Glycerol – C3H8O3 3. Results and discussions Based on mass and energy balances different key performance indicators were calculated and summarized in Table 5. The productivity, for all cases, was fixed at 13,333.33 kg/h of biodiesel. Analyzing the data presented in Table 5 it can be noticed that the NG flow-rate used for biodiesel production (e.g. 837.92 kg/h for Case 1 and 1,043.75 kg/h for Case 2) is lower than the biomass flow-rate used to generate the same quantity of biodiesel (e.g. 2,843.48 kg/h for Case 3 and 3,541.66 kg/h for Case 4). It can be also noticed that steam consumption is higher in the NG cases compared to biomass cases. From environmental point of view the NG cases will have a higher impact due to the higher steam and energy consumption. Even if the CO2 emissions in the biomass cases are higher compared to NG cases these emissions will end up in biomass growing, lowering the environmental impact of Case 3 and Case 4 compared to Case 1 and Case 2. The innovative reactive distillation method (Case 2 and Case 4) requires smaller quantities of methanol (e.g. 36,644.48 kg/h for Case 2 and 38,854.51 kg/h for Case 4) compared to the classical method (Case 1 and Case 3). Table 5: Technical comparison among Cases 1 – 4 Parameter Units Case 1 Case 2 Case 3 Case 4 NG kg/h 837.92 1,043.75 - - Biomass kg/h - - 2,843.48 3,541.66 Methanol fresh kg/h 1,531.31 1,907.40 1,531.31 1,907.40 Methanol recycle kg/h 37331.21 34737.08 37331.21 36947.11 Methanol total kg/h 38,862.52 36,644.48 38,862.52 38,854.51 Triglyceride kg/h 21,428.00 20,990.20 21,428.00 20,990.20 Sulphuric acid kg/h 3,072.57 3,009.79 3,072.57 3,009.79 Glycerol kg/h 18.25 41.62 18.25 35.17 Biofuel purity % 99.31 99.41 99.31 99.41 Glycerol purity % 99.77 99.43 99.77 99.37 Total CO2 emissions kg/h 1,431.95 1,425.17 1,813.69 1,805.65 Total Energy consumption kW 1,373.98 4,530.98 1269,96 4,540.83 Total Steam consumption kg/h 65,896.17 89,101.48 63,279.20 87,070.57 This conclusion is the same also for the other raw-materials, triglyceride and sulfuric acid. For instance the quantity of triglyceride used in the RD method is 20,990.20 kg/h (for Case 2 and Case 4) lower than the flow- rate of triglyceride used in the classical biodiesel production process cases (e.g. 21,428.00 kg/h). The highest purities for biofuel are obtained in RD cases, Case 2 and Case 4, (e.g. 99.41%). The purities of biofuel obtained in classical method, Case 1 and Case 3, are lower than the purities of biofuel based on RD but higher than 99%. Glycerol is the by-product obtained in biodiesel process. The highest quantities of glycerol produced in the biodiesel process are obtained in Case 2 (e.g. 41.62 kg/h), followed by Case 4 (e.g.35.17 kg/h). This glycerol can be furthermore converted into methanol and recycled back to the transesterification reactor. By using this approach the quantity of fresh methanol introduced into the system, and the quantities of natural gas (NG) and biomass used for methanol production will be lower compared to the values presented in Table 5. The total CO2 emissions are also lower in the RD case compared to the classical case. The positive 185 aspects of RD mentioned above are not reflected anymore in the energy and steam consumption. The energy consumption for RD is about 3.3 times higher than the energy consumption of classical method when NG is used for biodiesel production (Case 2 vs. Case1) and about 3.6 times higher when biomass is converted to biodiesel (Case 4 vs. Case 3). The steam consumption is also higher, about 1.35 times, in the RD case compared to classical method. 4. Conclusions The present paper evaluates biodiesel production from NG and biomass using the traditional method, consisting on reaction followed by separation but also a novel process based on RD. The technical parameters outline reduced raw-materials consumption, as well as improved biofuel purity for the reactive distillation method compared to the classical method. The biofuel purity obtained in RD cases is 99.41%. The energy consumption and steam consumption are higher in the RD cases compared to classical method. Consequently, the method can to be efficient and its implementation on industrial scale can represent an attractive prospect if the energy consumption and steam consumption will be reduced. Acknowledgments This work was supported by CONVERGE Project, European Union’s Horizon 2020 Research and Innovation Programme under Grant Agreement No. 818135. References Atabani A.E., Silitonga A.S., Badruddin I.A., Mahlia T.M.I., Masjuki H.H., Mekhilef S., 2012, A comprehensive review on biodiesel as an alternative energy resource and its characteristics, Renewable and Sustainable Energy Reviews 16, 2070-2093. 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