Term project
Process Plant Design Lab PPE-403L
1
Problem statement
The biodiesel production process produces two products: methyl ester (biodiesel) and glycerol. Most
biodiesel production process use excess methanol to get high yield. After the biodiesel process is complete, a lot of
methanol is available for recovery and reuse. To meet ASTM1 D6751 or EN2 14214 standards the removal of excess
methanol becomes a vital step. Almost every biodiesel standard allows 0.2% methanol in the final product Methanol
recovery can make the biodiesel productionprocess more effcient from both economical and environmental point of view.
To design an efficient and cost-effective methanol recovery system the study of the effects of different design parameters
of the process as well as its energy requirement is very important. Investigate the energy requirementas well as
separation behavior of methanol from the biodiesel and glycerol mixture using a distillation column.
FFA + Alcohol
Biodiesel + Water
Oil/Fat + Alcohol
Biodiesel + Glycerol
Chemical reaction
Abstract
This report is about excess methanol recovery in a biodiesel production process using a distillation
column. Methanol recovery analysis along with the required heat duty is simulated using Aspen plus
by varying different design and operating parameters involved in the separation. This analysis
This
report is considering a biodiesel
production process for which excess
methanol recovery is simulated using Aspen
plus. Renewable energy has attracted more
attention recently and biodiesel is one of it
that substituted diesel oil produced from
petroleum, reducing the dependency of
petroleum oil which leads to an increase oil
prices,
also
reducing
environmental
pollutants. Worldwide increasing oil crisis
and reducing fossil fuel reserve is a makor
problem cause the major portion of the total
energy consumed worldwide is now coming
from fossil fuel sources which are nonrenewable, and are depleting. So biodiesel
can be a wonderful replacement to
conventional petro-diesel fuel cause of its
production from a renewable domestic
resource.
Objective
Simulation to investigate the energy requirement
as well as separation behavior of excess
methanol from the biodiesel and glycerol
mixture using a distillation column.
Chemical process
Biodiesel is produced through a chemical
reaction known as transesterification in
which vegetable oil or animal fat (i.e
Triglyceride) react in presence of a catalyst
with a primary alcohol to give the
corresponding alkyl esters. that is found in
Group#20 M. Mohsin Maqbul 2015-PE-18 Tayyaba Irfan 2015-PE-24
17th of December, 2018
Term project
the parent vegetable oil or animal fat.
Triglyceride is a glyceride in which the
glycerol is esterfied with long chain acids,
known as fatty acids. It is the main
constituent of vegetable oil and animal fats.
Biodiesel can be produced from different
types of feedstock, with a various level of free
fatty acids (FFAs) content. The amount of free
fatty acid in triglyceride plays a very
important role in its production. FFAs act as a
potential contaminant (giving soap formation
so making glycerol phase separation difficult)
so it requires a pretreatment to convert the
FFAs to ester (i.e biodiesel) and it is known as
esterification. So, the production of biodiesel
process from low-quality feedstock consists
of
two
steps-esterification
and
transesterification.
Esterification Reaction (Acid Catalyst)
FFA + Methanol
Biodiesel + Water
Transesterification Reaction (Base Catalyst)
Oil/Fat + Methanol Biodiesel + Glycerol
Widely used base catalyst is sodium
hydroxide, while the acid catalyst is generally
sulfuric acid. Methanol is widely used
primary alcohol for producing to other
alcohols as it is not expensive, prevent soap
formation, reactivity is high, recovery
comparatively is easier. The biodiesel
production process produces two products:
methyl ester (biodiesel) and glycerol. Most
biodiesel production process use excess
methanol for getting high yield. This excess
methanol is distributed between the two
products so after the biodiesel process, a lot
of methanol is available for recovery and
reuse. To meet ASTM1 D6751 or EN2 14214
standards the removal of excess methanol
becomes a vital step for which almost every
biodiesel standard allows 0.2% methanol in
the final product cause residual methanol in
the biodiesel fuel is a major environmental
and health safety issue because methanol is
toxic so the excess methanol emission from
the use of biodiesel can be hazardous for life
and environment. Excess methanol can also
make the fuel flammable and more dangerous
to handle and store. Also it may corrode metal
components of engine. So most conventional
biodiesel manufacturers waste a lot of unused
Process Plant Design Lab PPE-403L
methanol through washing the final product
but some manufacturers are now using
distillation column and flash evaporation for
methanol recovery that can make the
biodiesel production process more effcient
from economical and environmental point of
view by saving the input costs for the process
& helping to maintain the specific standard.
So to design a cost-effective methanol
recovery unit energy requirement is the most
important parameter, as high energy
requirement may increase the cost of
biodiesel compared to conventional petrodiesel. Although different research groups
have done simulation and lab scale studies on
various types of biodiesel production process
using various types of feedstock and catalysts,
but no attempt has been focused on the
energy requirement for methanol recovery
unit. Distillation can do the separation very
efficiently, but its major disadvantage is the
high energy requirement. Important variables
involved in designing distillation column are
operating pressure, temperature, feed
composition, feed flow rate, total number of
stages, feed location, distillate rate, reflux
ratio etc. So to design an effcient and costeffective methanol recovery system the study
of the effects of different design parameters
of the process as well as its energy
requirement is very important.
Methanol Recovery Process
After transesterification and esterification
reactions the excess methanol is distributed
to the mixture of the products that is usually
separated by gravity separation cause of their
density differences. Methanol recovery unit
(MRU) can be used before phase separation
because unreacted methanol act as a phase
stabilizer and reducing the rate of phase
separation of biodiesel from glycerol. So
methanol recovery is carried out immediately
following the reaction to reduce the load in
downstream units, using a requirement of
distillation column is very high. So, using two
different methanol recovery units increase
the installation, operati ng costs and the cost
of production of biodiesel as well. So in this
study the simulation was done for Methanol
Group#20 M. Mohsin Maqbul 2015-PE-18 Tayyaba Irfan 2015-PE-24
17th of December, 2018
2
Term project
Recovery Unit before the phase separation to
achieve as much greater methanol recovery
so there may no need of further methanol
separation after the phase separation of the
products. distillation column before phase
separation. After the phase separation of
methyl ester (Biodiesel) and glycerol they still
contain excess methanol so two different
methanol recovery units are used to separate
methanol from biodiesel and glycerol after their
phase separation in most conventional
biodiesel production processes. But the
energy requirement of distillation column is
very high. So the use of two different
methanol recovery units may increase the
installation, operating costs and the cost of
production of biodiesel as well. So the
simulation is done for Methanol Recovery
Unit before the phase separation to have a
maximum
recovery,
in
less
energy
requirement, so there may no need of its
further separation from the products after
their phase separation.
Simulation
It is a widely used tool to design, test and
optimize a chemical process and it is used by
most process designer for investigating the
effects of different design parameters of the
chemical process during operation. To study
the effect of methanol to oil ratio and
different design parameters of distillation
column on energy requirement for methanol
recovery before phase separation a process
simulation was performed using Aspen plus.
in chemical process industries. Aspen plus
can be used for sensitivity analysis,
profitability
analysis,
and
process
optimization
Methodology
Drawing the process flowsheet
Specifying the components involved in the
process
Selecting a thermodynamic model
Specifying the operating condition such as
flow rate, temperature, pressure, composition
etc.
Process Plant Design Lab PPE-403L
UNIFAC thermodynamic model is chosen for
this simulation, as it can be used when
experimental data is not available. In process
simulation, biodiesel production from
comparatively moderate feedstock with 15%
free fatty acid (FFA) is assumed. Triolein
(C57H104O6) is used to represent the
triglyceride for biodiesel production & major
free fatty acid found in vegetable oil and
animal fat is oleic acid (C18H34O2), is chosen to
represent the free fatty acid (FFA). So,
produced biodiesel is methyl oleate
(C19H36O2). One RStoic reactor is used for
both reactions (transesterification and
esterification) to simplify the process
flowsheet & this reactor is used in Aspen plus
Simulation when the detail kinetic
information of a chemical reaction is not
available. Different studies have reported 9597% & 98-100% conversion for base
catalyzed transesterification & acid catalyzed
esterification as a pretreatment process for
converting FFA to ester respectively. So due
to lack of detailed kinetic information, 97%
and 100% conversion of reactant are
assumed in the simulation for base catalyzed
transesterification
and
acid
catalyzed
esterification reactions respectively. Rad-Frac
column is chosen for distillation, as it provide
much more rigorous calculations, give more
freedom to specify almost all the design
parameters.
The
selected
operating
temperature and pressure of reactor is 65 oC
and 1 atm respectively. To increase the inlet
feed temperature in distillation column a
preheater is used between the reactor and
distillation column. The top product of
column represents the recovered excess
methanol from product. This excess methanol
is recycled for reuse. A stream multiplier can
be used to control the amount of methanol in
feed to maintain the desired alcohol to oil ratio.
The bottom product of the column is the mixture
of biodiesel, glycerol and residual methanol.
The total production capacity of the
continuous biodiesel production plant is 7500
tonnes
of
biodiesel
per
year.
Group#20 M. Mohsin Maqbul 2015-PE-18 Tayyaba Irfan 2015-PE-24
17th of December, 2018
3
Term project
Process Plant Design Lab PPE-403L
Procedure
4
Firstly with creating a new file on aspen plus, there we come up with the window asking component id,
with typing there name of our components mentioned in the problem i.e. methanol, glycerol & water, the
component type, and name will be appeared there by aspen, and type there C57H104O6, C18H34O2, &
C19H36O2 and name them as TRIGL, FFA & BDIESEL respectively, there component and type will be
appeared there by aspen Then with Next command from the Home ribbon go to the methods folder
where choose ’Chemical’ under Method filter option while ‘UNIFAC’ under the Base method. Make a flow
sheet by going bottom left there will find simulation icon where the flowsheet of our process is drawn
using the arrows and equipment shown down there. With using RStoic from reactors option and place
two input streams one for methanol as ‘Methanol’ while the other one for oil as ‘OIL’ and one output
stream for the product as ‘PRODUCT’. Then put a heater from exchanger option down there and for its
feed stream connect the product stream of the reactor (with right clicking on the PRODUCT arrow and
then choosing the reconnect and then reconnect destination option from the drop down menu; connect
its inlet stream with the outlet PRODUCT stream of the reactor), while put out one outlet stream as
‘FEED’. Put a ‘RadFrac’ distillation column from column option down there after the heater, for its inlet
stream take the outlet stream of the heater (with right clicking on the FEED arrow and then choosing the
reconnect and then reconnect destination option from the drop down menu; connect its inlet stream
with the outlet FEED stream of the heater) and put out two streams distillate as ‘DIST’ & bottoms as
‘BOTTOMS’ as its outlet streams. Then on clicking the Next command from the Home ribbon go to the
specifications folder where choose ‘mass’ as the flow basis and its flow rate ‘5250’ and for units ‘kg/hr’
and for composition choose ‘mole-frac’ with value of methanol ‘1’ & ‘0’ for resting one and temperature
’25 0C’ and pressure ‘1 atm’ for the Methanol stream and choose ‘mass’ as the flow basis and its flow rate
‘875’ and for units ‘kg/hr’ and for composition choose ‘mole-frac’ with value of TRIGL ‘0.85’ & ‘0.15’ for
FFA while ‘0’ for the resting one and temperature ’25 0C’ and pressure ‘1 atm’ for the OIL stream. Then by
using the next command make specifications by going on the specifications folder for RStoic as
temperature ’65 0C’ and pressure ‘1 atm’. Next it, and specify there reaction 1 by clicking on new in the
coming window as for reactants Methanol & FFA with their coefficients as -1 & -1 and for products Water
& BDIESEL with their coefficients as 1 & 1, now specify the fractional conversion as 1 for the component
FFA down there and next it. Then click on the option reaction in series there and opt for new for a 2 nd
reaction and here in the coming window for the 2nd reaction type there for reactants Methanol & TRIGL
with their coefficients as -3 & -1 respectively and for products GLYCEROL & BDIESEL with their coefficients
as 1 & 3 respectively, now specify the fractional conversion as 0.97 for the component TRIGL down there
and next it. Enter the specifications for the heater as temperature ’80 0C’ and pressure ‘0.5 atm’. Next it
and specify for the distillation column as ‘10’ for ‘No. of stages’, ‘Partial-vapor’ for ‘Condenser’, ‘1500
kg/hr’ for Distillate rate and ‘4’ for reflux ratio and have 5 as the no. of stage for the feed. Next it and put
0.5 atm pressure for stage 1. Next it
Results and discussion
Group#20 M. Mohsin Maqbul 2015-PE-18 Tayyaba Irfan 2015-PE-24
17th of December, 2018
Term project
Process Plant Design Lab PPE-403L
5
…..
Process Flowsheet
Reference
Kusmiyati, Agung S. Production of Biodiesel from Oleic Acid and Methanol by Reactive Distillation.
Bulletin of Chemical Reaction Engineering & Catalysis, 5 (1). 2010. 1 - 6
Bipro R. D., Kawnish K. Excess methanol recovery in biodiesel production process using a distillation column: a simulation
study. Chemical Engineering Research Bulletin. 2009. 55-60
Group#20 M. Mohsin Maqbul 2015-PE-18 Tayyaba Irfan 2015-PE-24
17th of December, 2018