Ethanol Production.docx

HEAT EFFECTS ANALYSIS IN THE ETHANOL INDUSTRY

In Partial Fulfilment of the Requirements for the Course Chemical Engineering Thermodynamics 1

Submitted By: LAPUEBLA JEREMY C. MAMBA, RHEA D. OBILLO, ANA ROSE S.

Submitted To: ENGR. CAESAR P. LLAPITAN

MAY 2017

Table of Contents Abstract I.

Introduction .................................................................................................................. 1

II.

Ethanol Production Processes ...................................................................................2-6 A. Ethanol Production by Catalytic Hydration ............................................................. B. Ethanol Production by Indirect Hydration ............................................................. 6 C. Ethanol Production by Fermentation ...................................................................... 6

III.

Energy balance in the Reactor .................................................................................... 10

IV.

Conclusion .................................................................................................................. 15

V.

References ................................................................................................................. 16

HEAT EFFECTS ANALYSIS IN THE ETHANOL INDUSTRY

Abstract: Ethanol plays an important role in human life, it is used in the production of beverages and an important component in the production of fuel. In producing ethanol, four processes can be applied but the commonly used processes are the catalytic hydration of ethylene and the fermentation processes. In using catalytic hydration process in a mole of ethylene gas at 320°C the resulting product is one mole of ethanol with a temperature of 25°C, heat effects occur during the production; it starts from the furnace moving to the reactor, so that to get the amount of heat transfer energy balance from the system must be done and the resulting heat is equal to Q= -155.563 KJ which means that as the process move from furnace to the reactor heat loss occur.

I.

Introduction The world ethanol production has recently seen an incremental growth mainly due to economic and environmental security concerns, worldwide. Ethanol or ethyl alcohol (CH3CH2OH), a colorless liquid with characteristic odor and taste; commonly called grain alcohol has been described as one of the most exotic synthetic oxygen-containing organic chemicals because of its unique combination of properties as a solvent, a germicide, a beverage, an antifreeze, a fuel, a depressant, and especially because of its versatility as a chemical intermediate for other organic chemicals. Ethanol has been recognized as an important renewable and sustainable fuel source for modern industries. For example, it can be used as a replacement of gasoline for many internal combustion engines, and it can be mixed with gasoline to any concentration. Most existing car engines can run on blends of up to 15% bioethanol with petroleum/gasoline, thus it can significantly reduce the dependence on crude oil. Ethanol produced has three major applications: fuel ethanol, beverage ethanol, and industrial ethanol. Fuel ethanol is blended with gasoline for use as motor fuel. Beverage ethanol is used to produce beer, wine, and other spirits. Industrial ethanol is a chemical feedstock typically used to produce pharmaceutical products and polymers. Ethanol production had an extreme requirement globally as a fuel additive as 1.02 × 1011 liters were produced in 2010. Most of the ethanol produced is used as motor fuel or an additive in gasoline to improve its octane level. As a liquid fuel, ethanol has long-term advantages. Ethanol has good properties for spark ignition with the motor octane number and research octane number of 90 and 109, respectively that is much greater than regular gasoline which is 88. 1

II.

Ethanol Production Process

Ethylene

Catalytic Hydration

Ethanol

Fermentation

Sugar

Starchy Material Lignocellulosic Material

Hydrolysis

Pretreatment

Figure 1.0-Schematic diagram of some of the different methods for production of ethanol The economic competitiveness of ethanol has been heightened by concerns over prices and availability of crude oil as well as greenhouse gas emissions which have stimulated interest in alternatives to crude oil to provide for automotive power and also by the use of bioethanol in the production of hydrogen for fuel cells. Therefore, there is the need to explore ways of producing ethanol at competitive costs by the use of energy efficient processes. Some of the processes involved in producing ethanol are shown in Figure 1.0. Some of the several ways to produce ethanol production includes fermentation of ethanol, indirect hydration (esterification-hydrolysis) process and direct hydration of ethylene. Ethanol is produced by petrochemical through direct and indirect hydration as well as via biological processes by fermenting sugars with yeast. Most of the industrial processes were done by fermentation process but the output was not reliable.

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A. Ethanol production by catalytic hydration

Light Product

Water

Hydrogen

Hydrogenerator

Pump

Scrubber

Light Distillation Column

Acetaldehyde separator

Separator Feed Pump

Feed Preheater

Furnace `

Pump Reactor

Purifier

Figure 2.0-Process flow diagram for catalytic hydration of ethylene

Ethanol can be manufactured industrially by reacting ethane with steam. This reaction is reversible and the formation of ethanol is exothermic. At normal conditions, the equilibrium is positioned to the left and the amount of ethanol formed is quite small, therefore, to significantly increase the yield of ethanol, the reaction is carried out at 300C and about 60-70 atmospheric pressure using catalyst compounds such as phosphoric acid (H3PO4) which acts as the catalyst. The reaction for the process is

CH 2  CH 2 ( g )  H 2 ( g )  C2 H 5OH ( g )

(H  45 kj / mol )

In the petrochemical industry, ethanol is produced via direct and indirect hydration of ethylene. Catalytic direct ethylene hydration was first introduced by Shell in 1947. In this process, ethanol is produced by a reversible exothermic reaction between ethylene and water vapor. The process consists of three different steps including reaction, recovery and purification. The ethylene is mixed with steam with a molar ratio of 0.6 at 250–300 ºC and 70– 80 bar and then passes over an acidic catalyst in a fixed bed reactor. The water-to-ethylene ratio should be less than one to avoid catalyst losses. The ethylene conversion is about 4–25% and it is recycled. The ethanol selectivity is 98.5mol%. Phosphoric acid coated onto a solid silicon dioxide has been used mainly as the catalyst. 3

A simple process diagram of catalytic direct hydration of ethylene is presented in Figure 2.0. The feed stream (ethylene and water) preheated by effluent is heated up to 300 ºC in the furnace. Thereafter, it enters into a packed bed catalytic reactor at 70 bar. Phosphoric acid is used as catalyst and conversion is 4–25%. Acetaldehyde is produced as a by-product, which can either be sold or further hydrogenated to produce ethanol. The unreacted reactants are separated from the outlet vapor mixture of the reactor in a high pressure separator and then scrubbed with water to dissolve the ethanol. The recycled vapor from the scrubber contains ethylene, and the molar ratio of water to ethylene is maintained as 0.6:1. The bottom streams of the scrubber and the separator are then fed to the hydrogenator, where acetaldehyde is converted into ethanol on a nickelpacked catalyst. In the acetaldehyde separator column, the unreacted acetaldehyde is removed and recycled to the hydrogenator, and the bottom stream is fed to the light and the heavy (purifier) columns to increase the ethanol concentration.

a. Reactors used in catalytic hydration The reactor used in this process is a fixed bed reactor in which a stationary solid catalyst is used to carry out reactions whereby the reactant is in mobile fluid phase that takes place on the surface of the catalyst. The reactant diffuses, adsorbs and reacts on the active surface of the catalyst. Catalytic fixed bed reactors are the most widely used reactor for gas phase reactants as well as in the production and synthesis of large scale basics chemicals and intermediates. Fixed bed reactor is usually modelled and optimised using the continuum models that are grouped in two categories namely; pseudo-homogeneous and heterogeneous model. If the differences between the fluid and solid phase conditions are significant, heterogeneous model has to be considered in spite of the pseudo-homogeneous model with average properties. The pseudo-homogeneous model does not take into account explicitly for the presence of the catalyst in contrast to heterogeneous model which, in turns leads to the separate conservation equations for fluid phase in the catalyst pores.

b. Catalysts used in catalytic hydration The direct hydration of the ethylene has been carried out since about 60 years ago in the chemical industry over catalyst consisting of the silica gel with a high loading of phosphoric acid. Catalyst is characterised as the supported liquid phase and the catalytic active bound on a carrier as the concentrated liquid acid. Phosphoric acid on silica gel is more resistant to leaching than the acid on metal phosphate. The Silica gel-supported phosphoric acid catalyst (H3PO4/SiO2) is used in the industry as it has high selectivity in excess ethylene. The ethanol 4

production rate increases remarkably with increasing phosphoric acid loadings. Phosphoric acid present in liquid like form on silica gel has a pure acidic nature. The higher condensed phosphates take longer time to be hydrolysed.

B. Ethanol production by indirect hydration Sodium Hydroxide Solution

Ethyl Ether Ethyl Alcohol

Sulfuric Acid Ethylene

Steam

Absorption tower

Hydrolyzer

Stripping Column

Scrubber

Spent Caustic

Water

Diluted Acid

Ether Column

Fractionating Column Water

Concentrator

Figure 3.0- Process flow diagram for indirect hydration of ethylene Gas containing ethylene with a C2H4 percentage variable from 35% to 95% reacts in adsorption towers at 55-80°C and 10-35 bars with sulphuric acid and H2SO4 percentage varying from 94 to 98%; eventually, the reaction is catalysed by Ag2SO4. The reaction is exothermic and gives mono and diethylsulphate. Both esthers are hydrolysed to ethanol in towers with antiacid coating at 70-100°C. During the hydrolysis at high temperatures, the by-product diethylether is obtained. The sulphuric acid is later concentrated from 50 to 98%. The process efficiency is of 86%. The indirect hydration uses as principal raw material ethylene from different sources: coke production, cracking gas of ethane/propane mixtures, cracking gas of heavy gasoline or naphtha. The gases have to be enriched in ethylene and made free from superior olephines. The natural resources necessary to produce ethylene are: natural gas, petroleum, and carbon. The others raw materials are sulphuric acid and the sulphur or pyrites. During the process a small quantity of NaOH and water are used. As far as energy consumption is concerned, it is necessary to consider the following steps: ethylene production, sulphuric acid production, concentration of ethylene, heating ethylene and sulphuric acid, compressing ethylene, 5

distillation of ethanol, and concentration of sulphuric acid. The total energy consumption can be calculated in about 29 MJ/kg.

C. Ethanol production by fermentation

Water Molasses

Water

Condenser

Sulfuric Acid

Ammonium Sulfate

Scrubber

Mixing Tank

Fermenter

Sterilizer

Aldehhyde Column

Beer

Yeast Tub

Yeast Culture Machine

Carbon Dioxide Aldehydes

Beer Still

Fuel Oil

Water

Rectifying Column

Water

Benzene Slop

Aldehhyde Column

Ethyl Alcohol (absolute)

Figure 4.0- Process flow diagram for catalytic fermentation

A distinction must be made from raw materials. Those which are specifically grown for ethanol production (sugar substrates such as sugar beet, fodder beet, sugar cane, starch products such as potatoes) and the residues: industrial and food processing wastes (waste sulphite liquors, whey, food industry wastes); agricultural and domestic residues. A different treatment is necessary, of course, to prepare the culture broth with different energetic and environmental impact. Once the culture broth is prepared, the process is common. The resulting wine, at a maximum ethanol concentration of about 10% by volume is decanted and centrifuged to separate the non-fermentable matter and the yeasts. The obtained liquor is distilled, rectified and dehydrated to obtain absolute alcohol. The scheme of the process is illustrated in Figure 4.0. The raw materials for ethanol fermentation are various: sugar substrates, starchy products, cellulose material, and industrial residues. Other materials and utility requirements are sulphuric acid and ammonium sulphate with a much reduced consumption of natural 6

sources and water. As far as energy consumption is concerned, the following steps have to be considered: operation of agricultural machinery, irrigation, chemical products, preparation of worth, fermentation and distillation. The total energy consumption can be calculated in about 21 MJ/kg.

III.

Energy Analysis The region in a catalytic hydration process in which the energy balance was analyze was is shown below. Heat

Work

Furnace m0 E0 C0

Reactor

m1 E1 C1 Reactor

Figure 5.0- Region in which energy balanced was analyzed The statement of conservation of energy for this system takes the form

rate of energy  rate of energy rate of energy        entering system  leaving system  accumulated  by in flow  by outflow   

  rate of work   rate of heat     added to system done on system 

In terms of the defined variables it is written as,     dE  m0 E 0  m1 E 1  Q  W dt

(1)

wherein total work done by the system can be expressed as 







W  W f W s W b

(2)

where 

W = total work 

W f = flow stream 

W s = shaft work 

W b = boundary work

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

Work done by the flow stream W f can be also expressed in different parameters 

W

f

  0 A0 P0  1 A1 P1

(3)

f

 Q0 P0  Q1 P1

(4)



W 

W f  m0

P0

0

 m1

P1

(5)

1

Therefore the overall work of the system is 







W  W f  W s  W b  m0

P0

0

 m1

P1

1





W s W b

(6)

This energy balanced can be applied in the given problem which involved a reactor section. Ethylene gas and steam at 320 C and atmospheric pressure are fed to a reaction process as an equimolar mixture. The process produces ethanol by the reaction:

C2 H 2 ( g )  H 2 O ( g )  C2 H 5OH (l ) The liquid ethanol exits the process at 25 C. What is the heat transfer associated with this overall process per mole of ethanol produced? 1 mol of C2H4 (g) Reactor 1 mol of H2O(g)

C 2 H 2 ( g )  H 2 O ( g )  C 2 H 5 OH (l ) Energy balance:

H  Q  H R  H 298



H 298  H C 2 H 5OH  (H C 2 H 4  H H 2 O )



H 298   277690  (52510  241818) H 298  8.838  104 J / mol Reactant consists of 1 mole each of C2H4 and H2O.

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1 mol of C2H5OH

Constants: C2 H 2 ( g )

H 2O ( g )

A  1.424

A  3.470

B  14.394  10 3

B  1.450  103

C  4.392  106

C 0

D0

D0

A  ni  Ai  A  (1) (1.424  3.470)

A  4.894

B  ni  Bi  B  (1) (14.394  103  1.450  103 B  0.001584

C  ni  Ci  C  (1) (4.392  106  0) C  4.392  106

D  ni  Di  D  (1) (0.121105  0) D  1.21  104

The general formula for solving H R is

H R  R  M C PHT Solving for M C PH

M C PH  A 

B C D T0 (  1)  T0 ( 2    1)  2 2 3 TT0

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where  :



T T0

 

298.15 593.15

  0.5 M C PH  4.894 

0.0158 (4.392  106 ) 1.21 104 (593.15)(0.5  1)  (593.15)2 (0.52  0.5  1)  2 3 (0.5)(593.15)2

M C PH  11.12 Plugging in the calculated value of

M C PH gives

H R  (8.314) (11.12) (298.15  593.15)

H R  2.727  104 J / mol Solving for Q

Q  (H R  H 298 ) (n)

Q  (2.727  104  8.838  104 ) (1) Q  115653 J 

1kJ 1000 J

Q  115.563 kJ

IV.

Conclusion Producing ethanol can be done in different processes, these processes include catalytic hydration of ethylene, indirect hydration and fermentation. The process of catalytic hydration is used to logically model and solve a problem. Taking the furnace and the reactor as the system and relating it to the problem, the energy balance was performed in the region. The problem involves the reaction as shown below

C2 H 2 ( g )  H 2O ( g )  C2 H 5OH g  .The problem requires the heat transfer associated with the overall process per mole of ethanol produced, by doing some energy balance, Q is then computed with a result of 115.63 kJ. It is a negative heat transfer, thus, the system is transferring heat to the surroundings.

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V.

References

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