INTEGRATED PROJECT BKF 3463 UNIT OPERATION SEM 1 2013/2014 NAME
TAN YONG CHAI LIM SOON YEE ROSSHILA BINTI IDRIS ZAKIRAH BINTI MOHD ZAHARI
MATRIC NO KA11206 KA11195 KA11186 KA11188
CONTENTS
CONTENTS Chapter 1(INTRODUCTION)
1.1 Introduction of product 1.2 Application of product 1.3 Market Survey 1.4 Economic Potential 1.5 Screening of Synthesis Route Chapter 2( PROCESS SYNTHESIS AND FLOW SHEETING)
2.1 Process Flow Diagram 2.2 Manual Material & Energy Balance 2.3 Simulation Using Aspen Plus V12.1 Chapter 3 (PROCESS EQUIPMENT SIZING)
3.1 Determine the number of stages required 3.2 Determine the Height of the Distillation Column 3.3 Simulation Using Aspen Plus 4.Conclusion 5.Reference 6. Appendix
PAGE
CHAPTER 1 : INTRODUCTION
1.1
INTRODUCTION OF ETHANOL
Ethanol (ethyl alcohol, grain alcohol) is a clear, colourless liquid with a characteristic, with a pleasant smell. Ethanol, C2H5OH, is an alcohol, a group of chemical compounds whose molecules contain a hydroxyl group, OH, bonded to a carbon atom. Ethanol has a formula weight of 46.0 g/mol. Figure 1 Structure of ethanol
Ethanol melts at -144.1 °C, boils a t 78.5°C, and has a density of 0.789 g/ml at 20°C. Its low freezing point has made it useful as the fluid in thermometers for temperatures below - 40°C, the freezing point of mercury, and for other low temperature purposes, such as for antifreeze in automobile radiator. There are 2 processes for production of ethanol which are fermentation and from ethane and steam. FERMENTATION
Ethanol has been made by fermentation of sugar. All beverages ethanol and more than half of industrial ethanol is still made by this process. Simple sugar are the raw material. Zymase (enzyme from yeast), changes the simple sugars into ethanol and carbon dioxide. The fermentation reaction, represented by the simple equation which is : C6H12O6
2 CH3CH2OH + 2CO2
It is impure cultures of yeast produce varying amounts of other substances, including glycerine and various organic acids. In the production of beverages, such as whiskey, the impurities supply the flavour. Starches from potatoes, corn, wheat, and other plants can also be used production of ethano l by fermentation. However, firstly, the starches must be broken into a simple sugar. An enzyme released by germinating barley and converts starches into sugars. The production of ethanol from fermentation has ranges in concentration until up to 14 percent. Above this 40 percent, the ethanol will destroy the enzyme and stop fermentation. Ethanol is normally concentrated by distillation of aqueous solutions, but the composition of the vapour from the aqueous ethanol is 96 percent ethanol and 4 percent water. Thus, pure water cannot be obtained by using distillation.
Ethanol is used as an automotive fuel by itself and can be mixed with gasoline to form gasohol. Ethanol is miscible in all proportions with water and with most organic solvents. It is useful as a solvent for many substances and in making perfumes, paints, lacquer, and explosives.
MAKING ETHANOL FROM ETHENE AND STEAM
Ethanol can be made by reacting ethane (from cracking crude oil fractions) with steam. A catalyst of phosphoric acid is used to ensure a fast reaction. Ethane + steam C2H4 + H2O
ethanol C2H5OH
Ethanol is the only product. The process is continuous process as long as ethane and steam are fed into one end of the reaction vessel, ethanol will be produces. These features make it an efficient process, but since ethane is made from crude oil, which is a non- renewable resources. It cannot be replaced once it is used up and it will run out in a one day. (Prof.Shakhashiri, 2009) 1.2
APPLICATION OF ETHANOL
Ethanol has been used by humans since pre-historical time. It is obtained from natural raw materials or produced from industrial chemical processes. It can be used in many ways, either ethanol is used as it is or it is used as solvent to dissolve other substances. 1.2.1
Consumable Ethanol
This type of ethanol is usually obtained from natural raw materials and is used in many products consumed by humans. It also acts as a solvent to dissolve other substance for consumption or used by humans. For example, food colouring in baking, flavouring in manufactured or processed food and natural preservation such as vinegar. 1.2.2
Household Ethanol
Household ethanol can be either produced from natural raw materials or from industrial chemical processes. It is presented as solvent in many non-consumable products that we humans used daily. For example, it acts as a solvent for glass cleaning liquids, paint strippers and hand-wash detergents. It also can be used as a type of fuel for heating, cooking and lighting. 1.2.3
Biofuel Ethanol
Ethanol is a renewable alternative source to traditional fossil fuels for motors vehicles and industries, and also in some aircraft type. Brazil, the World’s second biggest sugar cane producer, uses ethanol produced from sugar cane as biofuel. While the United States is the World’s biggest producer of ethanol as biofuel, the States mainly uses corn as the natural raw material for the production of ethanol. It is known that ethanol as a biofuel has many advantages over traditional fossil fuels such as coal and petroleum. Ethanol rely on raw materials which can be grown year-after-year, thus, it is a renewable energy source. 1.2.4
Beverage Ethanol
Ethanol is also used as a base-spirit for the production of distilled alcohol beverages, commonly known as spirit. Spirit may be produced from any natural raw materials which can produce ethanol. For example, grains such as rice, fruits such as grape, vegetables and other sources that is consumable. 1.2.5
Medical Ethanol
Ethanol is used for processing and the production of a wide range of medicines and pharmaceutical products. It acts as a solvent to dissolve other substances and as colouring or flavouring agents. For example, ethanol is used in decongestant elixirs, cough preparation (syrups and medicines), mouthwash, iodine solution and liquid medicines. The pharmaceutical industry uses ethanol in processing many types of antibiotics, vaccines, tablets and liquid medicines. The most common seen is the use of ethanol in antibacterial and antiseptic products.
1.3
MARKET SURVEY
The production of ethanol in the world fuel of ethanol showed the competition between the other country through the world.If we can see in the production route for synthetic ethanol,the largest portion producers that contribute is come from SASOL industry which produce around 35 billion tonnes/year.It is followed by the SADAF,BP,Equistar,Sodes,Mossgas,Japan Ethanol,Jilin Chemicals,Neftochim,Chempetrol and Aprechim industry that shows the increment that reach around 10 billion tonnes/year. The production of ethanol by type which are in industrial,beverage and fuel shows that the increment in year 1975 which is 100000 tonnes/year,in 1985 which is 250000 tonnes/year and have a dramatically increase in the year 2005 which is reach to 600000 tonnes/year.(Christoph Berg,F.O.Licht) The ethanol production by feedstock shows the sugar crops contribute the large amount compared to grains in the market world which is 61 percent and 39 percent respectively.In the USA,the production of corn reached 350000 litres/tones and the cost per litre of fuel ethanol reached to the 24 billion US Cents/litre while in Brazil shows 75000 litre/tones of cane production in the feedstock and 8 billion US Cents/litre in the fuel of ethanol.The demanding of ethanol production are increased and unlimited through the year since ethanol are good for the environment and also good for rural areas.In Brazil,the economics of ethanol vs sugar shows the ups and down in their market demand.But,in the year 2003 it shows that more than 50 percent of domestic sugar/ethanol production are produced. (Christoph Berg,F.O.Licht)
Graph of Ethanol production by type A more diverse global ethanol market has started to take form in recent years in terms of an internationality traded commodity.According to F.O.Licht,about 700 million litres of ethanol were traded internationally in 2004,reduces 20 percent of total traded volumes and relatively low volume given by the global market potential.Further development of an international ethanol market will require a larger number of producers and exporters,a more feedstock types and an increased number of global producing and exporting countries. World production of ethanol from all possible starch and sugar feedstock increased 30 billion litres to 46 billion litres between year 2000 and 2005.A global consumption of ethanol is expected to reach 54 billion litres in the year 2010 which is equivalent to about one percent of world oil consumption(World Energy Council).The consumption and trade of fuel ethanol have increased significantly in recent years nearly doubling between 2000 and 2005.Brazil and the United States are the largest producers and consumers of fuel ethanol,with Brazil the primary consume for production,trade and consumption of sugar-based fuel ethanol.Global demand for fuel ethanol has increased significantly over the past few years.The global supply of fuel ethanol is expected to increase by 45 percent over the same period which is increased output in the Japan,China,India,Thailand and EU. (Christoph Berg,F.O.Licht)
1.4
ECONOMIC POTENTIAL
The market price of ethanol Species Ethene Ethanol
Price (US $/MT) 1287 1300
The EP calculation (level 1) for the market survey The reactions just only need one condition and can be conducted without any catalyst. According to the literature, the production of side product can be neglected for a rough calculation at this level as compared to other species. The prices of products and raw materials in the global market are listed accordingly. 1 Metric Ton (MT) = 1000kg Since the demand of ethanol in the world is in the range of 541300 tons per year,so we assumed to produce 27065 tons per year for our production at the first level due to world production of ethanol by hydration of ethene is just 5 percent of the total production of ethanol. Therefore,in order to produce 27065 tons per year,we assume operation hour is 8000 hours per year. Economic Potential (EP1) = Revenue – Raw Material costs EP = Price of product (ethanol) – Price of reactant(ethene)
- = $351,845/year x
x
1.5
SCREENING OF SYNTHESIS ROUTES
Fermentation
This is the oldest and most widely used biological method of producing drinkable ethanol. This process uses yeast under anaerobic condition to convert sugar into ethanol and carbon dioxide.The common sugar source are sugar cane, barley, corn, grape or coconut juice which are fermented to produce various kind of alcoholic drink such as beer, wine and liquor. The overall chemical formula for alcoholic fermentation is: C6H12O6 + Zymase → 2 C2H5OH + 2 CO2 Theoretically 10 kg of sugar will produce 6.5 L (5.1 kg) of ethanol and 4.9 kg (4900L) of carbon dioxide. In doing so, some energy is released too (about 2.6 MJ/kg of ethanol). Yeasts are single-cell fungi organisms. The most important ones used for making ethanol are members of the Saccharomyces genus, bred to give uniform, rapid fermentation and high ethanol yields, and be tollerant to wide ranges of temperature, pH levels, and high ethanol concentrations. Yeasts are facultative organisms - which means that they can live with or without oxygen. In a normal fermentation cycle they use oxygen at the start, then continue to thrive once it has all been used up. It is only during the anaerobic (without oxygen) period that they produce ethanol.
Cellulosic ethanol
Cellulosic ethanol is a biofuel produced from wood, grasses, or the inedible parts of plants. Cellulose are composed of long chain of sugar molecule which can be broken down into individual sugar molecule by enzymes. Cellulose is hydrolyzed into sugar which then can be fermented into ethanol. This is a very important renewable technology because any usable part of plants can be turn into biofuel. For example, wild grass which grows fast without care, wasted wood chips from wood industrial, wither leaves can all turn into renewable biofuel. Unlike fermentation process, cellulosic ethanol doesn’t have to compete with food supply in order to produce ethanol fuel because it uses inedible part of plant rather than sugar.
Ethylene hydration
Ethanol can be produced by synthetic route based on ethene, water and phosphoric acid in vapor phase. Phosphoric acid is used as catalyst which usually absorbed onto a porous support(usually silica gel or diatomaceous earth) Only 5% of the ethene is converted into ethanol at each pass through the reactor. By removing the ethanol from the equilibrium mixture and recycling the ethene, it is possible to achieve an overall 95% conversion. Since ethene’s boiling is considerable low at -103.7°C compared to ethanol (78.37°C) and water(100°C ), it can be easily separate by condensing water and ethanol into liquid phase and ethene in the gas phase. The unreacted ethene is then recycle back to the reactor. The condense ethanol and water mixture is distilled using fractional distillation until distillate is about 95% ethanol which approach azeotropic point of ethanol-water mixture. Further purification of ethanol required more advanced method such as Molecular sieves, Extractive Distillation using Ethylene glycol, Azeotropic Distillation using Benzene.
In molecular sieves method, ethanol-water mixtures is pass through 3A zeolite which the zeolite will adsorb the remaining water to produce nearly pure ethanol.
In Extractive Distillation using Ethylene glycol, Ethylene glycol is used as solvent to extract ethanol which utilize partial vaporization process in the presence of a non-volatile and high boiling point entrainerwhich does not form any azeotropes with the original components of the azeotropic mixture.
In Azeotropic Distillation using Benzene, benzene is added to ethanol-water mixture and formed a new azeotropic point which is lower than ethanol boiling point. The benzene, water and ethanol can be separated with fractional distillation where most of ethanol is obtained in the distillate with trace amount of benzene and water. However, this system is very sensitive to other component. Syngas Fermentation Ethanol is produced through thermochemical pathways involve the gasification of biomass into synthesis gas or syngas (a mixture of CO and H2), and then converting the syngas to biofuels by using chemical catalysts process or by using microbial catalysts known as syngas fermentation.Biological catalysts (such as Clostridium ljungdahlii, Clostridium autoethanogenum, Acetobacteriumwoodii, Clostridium carboxidivoransand Peptostreptococcusproductus) are able to ferment syngas into liquid fuel more effectively than the use of chemical catalysts(e.g., iron, copper or cobalt) (Heiskanen et al., 2007; Henstra et al.,2007).Syngas-fermenting microorganisms use acetyl-CoA pathway to produce ethanol, acetic acid and other byproducts such as butanoland butyrate from syngas.
The overall biochemical reactions that take place in the reductive acetyl-CoA pathway are shown in Eqs. (1) – (4). 6CO + 3H2O → C2H5OH + 4CO2
ΔH =-217.9 kJ mol-1 (1)
2CO2 + 6H2 →C2H5OH + 3H2O
ΔH =-97.3 kJ mol-1
4CO + 2H2O→CH3COOH + 2CO2
ΔH=-154.9 kJ mol-1 (3)
2CO2 + 4H2 → CH3COOH + 2H2O
ΔH=-75.3 kJ mol-1
(Pradeep ChamindaMunasinghe, Samir Kumar Khanal)
(2)
(4)
1.5.1 Comparison of the synthesis route:
Raw Material
Effectiveness
Advantage
Disadvantage
Type of Reactor
Fermentation Hydration of ethene 1. Sugar 1.Ethene gas from 2. Yeast(Saccharomyces petroleum cracking cerevisiae) 2. Steam (price from sigma3. phosphoric(V) acid aldrichcatalog) coated onto a solid silicon dioxide support
Cellulosic ethanol 1. xylose-extracted corncob residue 2. βglucosidase(enzymes for breaking the cellulose into sugar)
1. Maximum glucose 1.5% of the ethene is conversion is 14% converted into ethanol because the yeast cannot per pass through the grow under high ethanol reactor. concentration. 2.By recycling the ethanol, overall 95% conversion of ethanol can be achieved 1. Low pressure and low 1. Continuous process temperature. and high production rate. 2. Carried out in 2. Produces 100% anaerobic conditions percentage yield 3. Uses renewable 3. Few worker is needed sources of material. to monitor the process. 4. Notreatment is needed to get rid of impurity.
1. conversion efficiency with added βglucosidase was 55%, 43%, and 24% for 15%, 25%, and 35% solids loading (Z. Lewis Liua, 2012)
1. enzyme zymase stops functioning after alcohol concentration of 14% so limits concentration of ethanol made 2. If aerobic conditions introduced - can turn into toxic products. 3. Produces very impure ethanol which needs further processing 4. Uses food sources as raw material which will drive the cost of food for humans. 5. Slow Production Rate Batch
1. Renewable biomass 2. Cheap, Non-Food Feedstocks(Bothast and Saha, 1997, Wheals et al., 1999 and Zaldivaret al., 2001). 3. No Crop Displacement 4. Greenhouse Gas Reduction
Syngas fermentation 1. Carbon monoxide 2. Carbon dioxide, 3. Hydrogen gas 4.Alkalibaculumbacchi T CP11 , CP13 and CP15 Abubackar, H.N.; Veiga, M. C.; Kennes, C. (2011) 1. Conversion from 33.3% to 100%, 2. Yield from CO from 10.7% to 50% (as shown in Table. (Kan Liu et al, 2013)
1. Low Pressure and ambient Temperature Operating condition. 2. Tolerate higher amount of sulfur compound and doesn’t require specific ratio to CO2 and H2. 3.utilization of the whole biomass including lignin irrespective of the biomass quality 4. elimination of complex pretreatment steps and costly enzymes. 5. higher specificity of the biocatalysts
6. no issue of noble metal poisoning. 1. High temperatures 1. Enzymes for 1. Gas-liquid mass and pressures expend lot cellulosic ethanol transfer limitation of energy when production are projected 2. low volumetric manufacturing ethanol to cost 79.25 US dollars, productivity 2. Ethene finite source meaning they are 20-40 3. inhibition of and is made by burning times more expensive. organisms. fossil fuels Sainz, M. B. (2011). 4. Produces very impure Commercial cellulosic ethanol which needs ethanol: the role of further processing plant-expressed 5. Slow Production Rate enzymes. Biofuels (Pradeep 2. Produces very impure ChamindaMunasinghe, ethanol which needs Samir Kumar Khanal) further processing 3. Slow Production Rate Continuous
Batch
Continuous
We have chosen hydration of ethene for our synthesis route because the process is very simple and high production rate. Since no pretreatment is needed and no extra step is needed to purify the ethanol besides remove the water, the process is relatively simple to control. The overall conversion is only depend on how well ethene is able to separate from the mixtures of ethanol and water and unreacted ethene is mostly recycle back to the reactor.
Disadvantage
Type of Reactor
1. enzyme zymase stops functioning after alcohol concentration of 14% so limits concentration of ethanol made 2. If aerobic conditions introduced - can turn into toxic products. 3. Produces very impure ethanol which needs further processing 4. Uses food sources as raw material which will drive the cost of food for humans. 5. Slow Production Rate Batch
6. no issue of noble metal poisoning. 1. High temperatures 1. Enzymes for 1. Gas-liquid mass and pressures expend lot cellulosic ethanol transfer limitation of energy when production are projected 2. low volumetric manufacturing ethanol to cost 79.25 US dollars, productivity 2. Ethene finite source meaning they are 20-40 3. inhibition of and is made by burning times more expensive. organisms. fossil fuels Sainz, M. B. (2011). 4. Produces very impure Commercial cellulosic ethanol which needs ethanol: the role of further processing plant-expressed 5. Slow Production Rate enzymes. Biofuels (Pradeep 2. Produces very impure ChamindaMunasinghe, ethanol which needs Samir Kumar Khanal) further processing 3. Slow Production Rate Continuous
Batch
Continuous
We have chosen hydration of ethene for our synthesis route because the process is very simple and high production rate. Since no pretreatment is needed and no extra step is needed to purify the ethanol besides remove the water, the process is relatively simple to control. The overall conversion is only depend on how well ethene is able to separate from the mixtures of ethanol and water and unreacted ethene is mostly recycle back to the reactor.
1.5.2 Comparison Purification Method of ethanol :
Distillation
Molecular sieves
Solvent or Solid uses
-
Advantage
1. Distillation can be done up to 96% purity using the difference in boiling of water and ethanol without using any reagent.
Disadvantage
1. Unable to purified alcohol beyond 96% because water and ethanol form azeotropic mixtures.
1. 3A Zeolite(adsorption of water) 1. Easy to regenerate 2. Minimal Labor 3. The process is inert. Since no chemicals are used, there are no material handling or liability problems, which might endanger workers 4. Near theoretical recovery 5. Has very few operation parts 6. The molecular sieve desiccant material has a very long potential service life. 7. Molecular sieves can easily process ethanolcontaining contaminants 1. Zeolites is expensive
Extractive Distillation Azeotropic Distillation using Ethylene glycol. using Benzene 1.Ethylene glycol 1. Benzene 1. Smaller Distillation Column. 2. Low energy cost 3. Low equipment cost
1. Widely used in industry.
1. Need to add make-up ethylene glycol 2. The system has recycle stream which advance process control maybe needed. 3. Ethylene glycol is weakly toxic.
1. Benzene is carcinogenic and is unsafe for medical or chemical uses. 2. High Capital Cost and energy cost. 3. Unacceptable number of tower plate.
We have chosen to use molecular sieve as our purification method o f ethanol because it doesn’t use any solvent which may contaminate the ethanol. Furthermore, once zeolites is saturated with water, it can be easily regenerated by heating it to remove the water molecule.
1.5.2 Comparison Purification Method of ethanol :
Distillation
Molecular sieves
Solvent or Solid uses
-
Advantage
1. Distillation can be done up to 96% purity using the difference in boiling of water and ethanol without using any reagent.
Disadvantage
1. Unable to purified alcohol beyond 96% because water and ethanol form azeotropic mixtures.
1. 3A Zeolite(adsorption of water) 1. Easy to regenerate 2. Minimal Labor 3. The process is inert. Since no chemicals are used, there are no material handling or liability problems, which might endanger workers 4. Near theoretical recovery 5. Has very few operation parts 6. The molecular sieve desiccant material has a very long potential service life. 7. Molecular sieves can easily process ethanolcontaining contaminants 1. Zeolites is expensive
Extractive Distillation Azeotropic Distillation using Ethylene glycol. using Benzene 1.Ethylene glycol 1. Benzene 1. Smaller Distillation Column. 2. Low energy cost 3. Low equipment cost
1. Widely used in industry.
1. Need to add make-up ethylene glycol 2. The system has recycle stream which advance process control maybe needed. 3. Ethylene glycol is weakly toxic.
1. Benzene is carcinogenic and is unsafe for medical or chemical uses. 2. High Capital Cost and energy cost. 3. Unacceptable number of tower plate.
We have chosen to use molecular sieve as our purification method o f ethanol because it doesn’t use any solvent which may contaminate the ethanol. Furthermore, once zeolites is saturated with water, it can be easily regenerated by heating it to remove the water molecule.
̇
2.1 Production rate of Ethanol ( 8) 27065 tons 1000kg 1 year 1 kmol year 1 tons 8000hours 46.07kg = 73.4348 kmol/day *Assume 8000 operating hours.
2.2 Material & Energy Balance
2.2.1 Assumption 1. 2. 3. 4.
Composition of Top distillate is 95%ethanol and 5% water. Molecular sieve is able to fully separate ethanol and water to 100% purity. 90% of the ethanol is recover from steam 4 at distillate stream 5 at Separator 2 Separator 1 is able to fully separate ethane into vapour phase and ethanol-water mixture into liquid phase. 5. Single Pass Conversion is 5% of ethane, since all the ethene is being recycled. Overall Conversion is 100% 6. No heat to surrounding and pressure drop in all the components. 7. Based on the rule of thumb, reflux ratio is set to 1.5R m. Aspen calculate the minimum reflux is 0.9131. We assume the reflux ratio is 1.3697.
8. Composition of reactor outlet stream 2 is calculated based on conversion and stoichiometry ratio. 9. Assume Feed condition entering the Separator 2 is q=1
̇
2.1 Production rate of Ethanol ( 8) 27065 tons 1000kg 1 year 1 kmol year 1 tons 8000hours 46.07kg = 73.4348 kmol/day *Assume 8000 operating hours.
2.2 Material & Energy Balance
2.2.1 Assumption 1. 2. 3. 4.
Composition of Top distillate is 95%ethanol and 5% water. Molecular sieve is able to fully separate ethanol and water to 100% purity. 90% of the ethanol is recover from steam 4 at distillate stream 5 at Separator 2 Separator 1 is able to fully separate ethane into vapour phase and ethanol-water mixture into liquid phase. 5. Single Pass Conversion is 5% of ethane, since all the ethene is being recycled. Overall Conversion is 100% 6. No heat to surrounding and pressure drop in all the components. 7. Based on the rule of thumb, reflux ratio is set to 1.5R m. Aspen calculate the minimum reflux is 0.9131. We assume the reflux ratio is 1.3697.
8. Composition of reactor outlet stream 2 is calculated based on conversion and stoichiometry ratio. 9. Assume Feed condition entering the Separator 2 is q=1 Overall material balance: n0 = n9 + n8 x0n0 = x9n9 + x8n8 y0n0 = y9n9 + y8n8 z0n0 = z9n9 + z8n8
Material Balance at Separator 1: n2 = n3 + n4 x2n2 = x3n3 + x4n4 y2n2 = y3n3 + y4n4 z2n2 = z3n3 + z4n4
Material Balance at Mixer: n0 + n3 = n1 x0n0 + x3n3 = x1n1 y0n0 + y3n3 = y1n1 z0n0 + z3n3 = z1n1 Material Balance at Reactor: n1 = n2 x1n1 = x2n2 y1n1 = y2n2 z1n1 = z2n2
Material Balance at Separator 2: n4 = n5 + n6 x4n4 = x5n5 + x6n6 y4n4 = y5n5 + y6n6 z4n4 = z5n5 + z6n6 Material Balance at Molecular Sieve: n5 = n7 + n8 x5n5 = x7n7 + x8n8 y5n5 = y7n7 + y8n8 z5n5 = z7n7 + z8n8
Assumption Information: Ethanol produced is 73.4348kmol/h. Therefore n9=73.4348kmol/h, since all ethanol is fully recover with molecular sieve. Ethanol is fully separated. x9=1 y8=1 Ethanol is 90% recover from stream 4 at stream 5. 0.9x4n4=x5n5 Ethane is fully separated at the separator 1. z3=1 z4=
2.2.2 Mole Balance for reactor From literature review, http://www.chemguide.co.uk/physical/equilibria/ethanol.html Single pass Conversion of the reaction is 5%, ethene to water ratio is 1:0.6 Mole Balance on the Reactor Species Initial feed Change Outlet Ethene FA0 - FA0X Water
0.6FA0
-FA0X
Ethanol Total
0 1.6 FA0
FA0X - FA0X
FA0X=P
P=amount of ethanol produce by the reactor= n2x2. Solving composition for n2 stream. Outlet Mole Faction of ethanol=
canceling the P, substitute X=0.05
X2=0.03226 Outlet Mole Faction of water =
canceling the P, substitute X=0.05
Y2=0.3235
Outlet Mole Faction of Ethene=
canceling the P, substitute X=0.05
Z2=0.6129
Solving all the material balance using Excel and Goal Seek, all stream data is tabulate as below. Stream Data 0 Temperature(°C) Pressure(atm) Total Mass flow(kg/hr) Total Mole flow(kmol/hr)
1
2
3
4
5
6
8
9
300 300 300 30 30 78.75 99.62 25 25 65 65 65 1 1 1 1 1 1 16457.4 56319.082 56822.97 39860.88 18462.15 3452.789 15009.42 178.0606 1323.295 897.6661 2318.7312 2318.592 1421.065 897.527 77.2998 820.2272 3.865 73.4348
Mass Fraction Water Ethene Ethanol
0.952035 0.2782152 0.237864 0.047965 0.7217848 0.701492 0 0 0.060643
0 0.796392 0.020171 1 0 0 0 0.203608 0.979829
0.97495 0 0.02505
0 0 1
1 0 0
Mass flow(kg/hr) Water Ethene Ethanol
15668.02 15668.826 13516.16 0 14703.11 69.64712 14633.43 0 1323.295 789.3784 40650.256 39860.88 39860.88 0 0 0 0 0 0 0 3445.934 0 3759.044 3383.142 375.9893 178.0606 0
Mole Fraction Water Ethene Ethanol
0.9686 0.03135 0
0.375 0.625 0
0.3235 0.6129 0.03226
0 1 0
0.90909 0 0.09091
0.05 0 0.95
0.99005 0 0.00995
0 0 1
1 0 0
869.5242 750.0645 0 815.9328 3.86499 812.0659 1449.207 1421.065 1421.065 0 0 0 0 74.79778 0 81.59418 73.43481 8.161261
0 0 3.865
73.4348 0 0
Mole flow(kmol/hr) Water Ethene Ethanol
869.4794 28.14183 0
2.2.3 Energy Balance Reactor:
T=300°C C2H5OH
T=300°C C2H2+ H20
T=25°C C2H2 + H20
T=25°C C2H5OH
Figure : Calculation Path for Hydration of Ethene Production
ΔH˚f 298°C Ethanol (gas)
: -235100 J/mol
ΔH˚f 298°CEthene(gas)
: 52510 J/mol
ΔH˚f 298°C Water (gas)
: -241818 J/mol (J.M.Smith, 1925)
ΔH˚298°C = ΔH˚f 298°C Ethanol (gas) - ΔH˚f 298°CEthene(gas) - ΔH˚f 298°C Water (gas)
= (-235100) – 52510 - (-241818) = - 45792 J/mol
Species
n
a
n*a
b
n*b
c
n*c
d
n*d
state
Ethene
1
4.08E-02
4.08E-02
1.15E-04
1.15E-04
-6.89E-08
-6.89E-08
1.77E-11
1.77E-11
g
Ethanol
0
6.13E-02
0.00E+00
1.57E-04
0.00E+00
-8.75E-08
0.00E+00
1.98E-11
0.00E+00
g
Water
1
3.36E-02
3.36E-02
6.88E-06
6.88E-06
7.60E-09
7.60E-09
-3.59E-12
-3.59E-12
g
Sum
7.44E-02
Where
1.22E-04
-6.13E-08
1.41E-11
〈 〉 (∑ 〈〉)[∑ ∑ ∑] and
Table: Heat Capacities of Components for ΔH˚R (J.M.Smith, H. V., 1925).
〈 〉
From T0=573.15 K to T=298 K
ΔH˚R =
(∑ 〈〉)
Species
n
Ethene
0.95
4.08E-02
3.87E-02
Ethanol
0.05
6.13E-02
Water
0.95
3.36E-02
Sum
a
n*a
b
n*b
c
n*c
1.15E-04
1.09E-04
-6.89E-08
-6.55E-08
1.77E-11
1.68E-11
g
3.07E-03
1.57E-04
7.86E-06
-8.75E-08
-4.37E-09
1.98E-11
9.92E-13
g
3.19E-02
6.88E-06
6.54E-06
7.60E-09
7.22E-09
-3.59E-12
-3.41E-12
g
7.37E-02
1.23E-04
d
n*d
-6.26E-08 Table: Heat Capacities of Components for ΔH˚P (J.M.Smith, H. V., 1925).
state
1.44E-11
〈 〉 (∑ 〈〉)
From T0=573.15 K to T=298 K
ΔH˚P =
= 291.7690 + (-45792) + (-291.1637) = - 45791.39 J
2.3 Simulation Using Aspen Plus V12.1
Manual Calculation of MEB allow the rough estimate but based on many assumption. Aspen enable us to simulate close to actual unit operation and eliminate some of assumption. In real situation, it is impossible to fully recycle ethene because it is impossible to fully separate ethene from ethanol and water mixture even though the boiling point of ethene and ethanol-water mixtures is very far apart. We can compare the actual amount of reactant we suppose to used and condition needed to separate the all the component to desired composition. 2.3.1 PFD of Aspen
2.3.2 Assumption 1. Conversion of the reactor B2 is assumed to be 5% of ethene. 2. Flash Drum S1 operating condition is set to 1 atm, 30°C to condense as much ethanol and water as possible. 3. Heater H1 is set to heat Stream 6 from 30°C to Stream 95°C. 4. Recovery of Distillation Column is Light Key Recovery. Ethanol at 0.95 whereas heavy key Recovery water is set at 0.003 5. Heater H2 is set to heat Stream 4 from 30°C to 300°C and output pressure of 65atm to stream 5. 6. Based on the rule of thumb, reflux ratio is set to 1.5R m. Aspen calculate the minimum reflux is 9.95. We assume the reflux ratio is 15 2.3.3 Aspen Result Ethanol Produc tion Plant Stream ID
1
Temperature
C
Pressure
atm
Vapor Frac
2
3
4
5
6
7
8
9
300.0
293.9
300.0
30.0
300.0
30.0
95.0
80.1
101.7
65.000
65.000
65.000
1.000
65.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
1.000
0.000
< 0.001
1.000
0.000
1480.200
3084.757
3003.389
1604.586
1604.557
1398.803
1398.803
81.268
1317.535
Mole Flow
kmol/hr
Mass Flow
kg/sec
7.634
20.045
20.045
12.411
12.411
7.634
7.634
1.009
6.625
Volume Flow
cum/sec
0.245
0.563
0.555
11.023
0.315
0.008
0.009
0.637
0.007
Enthalpy
MMkcal/hr
-77.362
-55.780
-56.443
16.085
21.582
-96.282
-94.105
-4.499
-88.691
Mass Flow
kg/sec
WATER
7.000
7.248
6.841
0.248
0.248
6.593
6.593
0.020
6.573
ETHYL-01
0.634
12.682
12.048
12.047
12.047
< 0.001
< 0.001
< 0.001
trace
0.116
1.157
0.116
0.116
1.041
1.041
0.989
0.052
ETHAN-01 Mass Frac WATER
0.917
0.362
0.341
0.020
0.020
0.864
0.864
0.020
0.992
ETHYL-01
0.083
0.633
0.601
0.971
0.971
16 PPM
16 PPM
118 PPM
trace
0.006
0.058
0.009
0.009
0.136
0.136
0.980
0.008
1398.789
1448.332
1366.963
49.545
49.543
1317.418
1317.418
3.952
1313.466
81.411
1627.375
1546.006
1545.991
1545.964
0.015
0.015
0.015
trace
9.051
90.419
9.050
9.051
81.369
81.369
77.301
4.068
ETHAN-01 Mole Flow WATER ETHYL-01
kmol/hr
ETHAN-01 Mole Frac WATER
0.945
0.470
0.455
0.031
0.031
0.942
0.942
0.049
0.997
ETHYL-01
0.055
0.528
0.515
0.963
0.963
11 PPM
11 PPM
188 PPM
trace
0.003
0.030
0.006
0.006
0.058
0.058
0.951
0.003
ETHAN-01
2.3.4 Heat Duty at Each Component Reactor B2 Heat Duty= -770866.51 Watt (Cooling) Heater H1 Heat Duty= 2532425.48 Watt (Heating) Heater H2 Heat Duty= 6393769.33 Watt (Heating) Flash Drum Heat Duty= -27625919 Watt (Cooling) Reboiler heating required: 14651001 Watt Condenser cooling required: 13587693.4 Watt
CHAPTER 3: DISTILLATION COLUMN SIZING
3.1 Determine the number of stages required. Given Equilibrium Data Equilibrium Data
Vapor-Liquid Equilibria, Mass fraction of ethanol
Temperature
xa
Vapor-Liquid Equilibria, Mole fraction of ethanol
ya
Xa
Ya
100
0
0
0
0
98.1
0.02
0.192
0.049598753
0.377972007
95.2
0.05
0.377
0.118622771
0.607448676
91.8
0.1
0.527
0.221262739
0.740199725
87.3
0.2
0.656
0.389980869
0.829829708
84.7
0.3
0.713
0.522884966
0.863998008
83.2
0.4
0.746
0.630284291
0.882497159
82
0.5
0.771
0.718877758
0.895936486
81
0.6
0.794
0.793207149
0.907887433
80.1
0.7
0.822
0.856460703
0.92192965
79.1
0.8
0.858
0.910942381
0.93921371
78.3
0.9
0.912
0.958358566
0.963638472
78.2
0.94
0.942
0.975646792
0.976488286
78.1
0.96
0.959
0.983967194
0.98355611
78.2
0.98
0.978
0.992082431
0.991279923
78.3
1
1
1
1
Graph 1 is plotted to find the ‘pinch’ point and hence find the minimum reflux ratio using McCabe-Thiele
Method. (see appendix) Assume feed condition q=1. The chemical that leave the product is cool sufficiently to saturated liquid condition. From Graph 1, the pinch point is determined y’=0.54 , x’=0.091
Operating line is draw from xD and with slope 1.3697 at Graph 2. (see appendix) Theoretical Stage Obtained=11.5 stages
3.2 Determine the Height of the Distillation Column The entering and exiting composition of ethanol for Seperator 2 is X4=0.091 , X5=0.95 , X6=0.01
At, X =0.95, Dew Point is Solve T =78.75°C Solve T =99.62°C At , X6=0.01. Boiling Temperature is 5
W
D
= 89.19°C Using Table A.3-12 and Fig A.3-4 at 89.19°C: µ(ethanol)=0.385cp µ(water)=0.345cp µL=0.385(0.0909) +0.345(0.90909) =0.3486cp Vapour Pressure log (P_sat) = A - B/(T+C) : P_sat [torr], T [C] torr x 133.22 = Pa source: Perry 13-4 Species
A
B
C
Ethanol
8.1122
1592.864
226.184
Water
8.07131
1730.63
233.426
P(ethanol)= 152.6kPa α=(152.6/67.4)=2.2641 -0.245 E0=0.492(µLα) -0.245 =0.0492(0.3486 x 2.2641) =0.5124
P(Water)=67.4kPa
Assume Mid-size tower where 0.6m Tray Spacing for 1.0m diameter tower. HETP=(0.6/0.5124) =1.1507m/theoretical Stage number of step=11.5-condenser- reboiler =9.5 Steps Tower Tray Height=1.1507 x 9.5= 10.931m
3.3 Simulation Using Aspen Plus Distillation column Sizing D1
Assume Tray Spacing of 0.8m for 4m tower in diameter (large tower) Tower Height= 13.927(0.8)=11.1m
4.Conclusion Based on the manual MEB calculation for producing ethanol, ethanol obtained at stream 9 is 73.4348kmol/h and the feed required is 869.46kmol/h of water and 28.141kmol/h of ethene. Compared to aspen simulation, Ethanol obtained is 77.301kmol/h which is close to our targeted production rate, but the feed is required is much higher at 1398.78kmol/h of water and 81.411kmol/h. This is due to the fact that ethene cannot be fully separate from ethanol-water mixtures. Composition of feed in aspen simulation is adjusted so that distillate of separator 2 is producing nearly azeotropic mixture of water ethanol mixtures. Based on McCabe-Thiele Method, were graph were hand draw and assumption of constant molar flow rate throughout the distillation column is made, 11.5 Theorectical Stage is estimated requirement. However, from aspen result obtained, 13.927 stages were actually required to separate ethanol-water mixtures close to the azeotropic point.
5.REFERENCES:
1. Prof.Shakhashiri,2009,ethanol,retrieved from: http://scifun.org/GenChem/Enrichment/Strang[Jan09].htm 2. World Fuel Ethanol Analysis and Outlook,Dr Christoph Berg,F.O.Licht,April 2004. 3. Ethylene Highlights,Retrieved on 19 December 2013.Retrieve from: http://www.fibre2fashion.com/textile-market-watch/ethylene-price-trends-industry-reports.asp
4. Platss Global Ethylene Price Index,Retrieved on 19 December 2013. Retrieve from: http://www.platts.com/news-feature/2013/petrochemicals/pgpi/ethylene 5. Jim Clark,April 2013, The manufacture of ethanol, retrieved from: http://www.chemguide.co.uk/physical/equilibria/ethanol.html
6. Tony Ackland, 5 March 2012, Fermenting.Retrieved from: http://homedistiller.org/wash/ferment 7. Ethanol information India. Retrieved from: http://www.ethanolindia.net/molecular_sieves.html 8. Comparison of the main ethanol dehydration technologies through process simulation, Bastidas,aIván D. Gil,a Gerardo Rodrígueza
Paola A.
9. Ethanol dehydration by azeotropic distillation with a mixed-solvent entrainerA. Chianese,F. Zinnamosca. 10. C.J.Geankoplis, (2003). Transport Processes and Separation Process Principles. Fourth edition. 11. J.M.Smith, H. V. (1925). Introduction to Chemical Engineering Thermodynamics. New York: McGraw-Hill. 12. Berg, USDA. (July 2006). The Economic Feasibility of Ethanol Production from Sugar in the United States. 78. Retrieved from http://www.usda.gov/oce/reports/energy/EthanolSugarFeasibilityReport3.pdf
13. Kan Liu et al (2013). Continuous syngas fermentation for the production of ethanol, n-propanol and n-butanol. 14. Chao Fan et al . (2013). Efficient ethanol production from corncob residues by repeated fermentation of an adapted yeast
6. Appendix
