FIELD OF INVENTION
The present invention generally relates to a process for recovery of organic
solvent after extraction of coal. More particularly, the present invention relates to
a process to separate out coal from multiple-type organic solvent in a corrosive-
resistant membrane device.
BACKGROUND OF THE INVENTION
The organic refining process is primarily an energy intensive process. Huge
amount Heat energy is used in extraction and solvent regeneration process.
Particularly solvent regeneration consumes 70% of total consumable energy of
the entire process. Evaporation followed by distillation is the conventional root of
solvent regeneration. Membrane separation technology is an energy saving
process. Solvent extraction followed by membrane based separation technology
is considered to be an improved process compared to the existing distillation
technique.
Membrane excludes the evaporator from the process entirely and also reduces
the distillation load to 50%. Thus a great amount of heat energy is saved
adopting membranes as a separator.
PCT/IN2009/00381 of 06.07.2009 discloses a technique for recovery of solvent
via membrane technology. The prime benefit has been emerged from the
disclosure that a membrane can be used instead of an evaporator. This
alternative solvent regeneration technique has decreased the heat consumption
of the entire process drastically. So a huge amount of energy can be conserved
by applying the membrane technology.

The conventional processes of organo refining have many disadvantages,
namely:
1. At least one evaporator required to separate out the solvent from dissolved
solid solvent mixture, and that the evaporator is to be heated for separation
which consumes an enormous heat energy.
2. After specified degree of liquid concentration of the mixture the thick volume
of the viscous slurry can't be further transported, and the evaporator
becomes disabled to concentrate the remaining mixture. At this juncture, a
substantial amount of solvent still remains present in the mixture which
ultimately enhance the avoidable load on the distillation during distillation
step. In this way distillation load is nearly gets doubled.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a fabrication process to
produce defect-free inorganic ultra filtration range ceramic membrane cells,
which eliminates the requirement of providing and heating an evaporator to
separate out solvent from dissolved solid solvent mixture.
A still another object of the invention is to propose a fabrication process to
produce defect-free inorganic ultra filtration range ceramic membrane cells,
which reduces the load on the distillatory and enhances the life of the device.
A further object of the invention is to propose a process for separation of coal
from organic solvent.

SUMMARY OF THE INVENTION
In a first aspect of the invention, there is provided a new inorganic formulation
for the fabrication of a defect-free inorganic ultra filtration range ceramic
membrane having an average pore diameter around 0.5 urn. Characterization
procedure have been applied and tested for the fabricated membrane at
different sintering temperatures. Thermal characterization and XRD study reveal
that the preferred sintering temperature for a selected composition of materials
used for the inorganic formulation is around 850°C. The membranes provide a
chemical stability. The present invention thus provides significant opportunities
to produce ceramic ultrafiltration range membrane with flexible pore sizes for
industrial processing of separating coal from organic solvents. The fabricated
ceramic membrane is enabled to separate carbon from N-methyl pyrrolidone-
ethylene diamine (NMP-EDA) mixture. Normally, the NMP is used as a solvent for
coal extraction. Different compositions of the solvent are used for the extraction.
It is seen that 50 ml of NMP is the most preferred value for the extraction of 5
gm coal. The reusability of the solvent is checked by a three stage extraction
process. The extract of each stage is recovered in a membrane separation device
adapting a defect-free inorganic ultra filtration range ceramic membrane. The
performance of solvent recovery is found to be 71%, 68% and 66.4%,
respectively, for the extraction stages 1, 2 and 3. The FTIR result shows that
permeate of all the remains free of coal. This signifies the effectiveness of the
ceramic membrane of the invention for the solvent recovery during extraction of
coal using strong organic solvent like NMP.
In a second aspect of the invention, there is provided a process for separation of
coal from organic solvent by adapting a defect-free inorganic ultra filtration

range ceramic membrane device, the process comprising the steps of providing a
coal-batch including a quantity of NMP and EDA in a ratio of 1:9:1 to form an
extraction mixture in an extraction vessel; connecting a reflux condenser to the
vessel; heating the mixture by a heater having a control means to implement the
extraction step for a predefined duration, the predefined duration depending on
the selected capacity of the heater, size of the extraction vessel and the quantity
including the ratio of the selected composition; filtering the hot extracted mixture
through at least two mesh screens at two stages, the residue being dried,
weighted separately, the hot filtrate fed to the membrane batch cell; and
separating the filtrate in the membrane batch cells in multiple stages for
predetermined period at specified transmembrane pressure differential (AP) with
a determined stirring speed, the said parameters being dependent on the batch-
size of coal mixture including configuration of the membrane batch ceils.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Schematically shows a separation process of coal from organic solvent
in a membrane device
Figure 2 - Graphically represents variation of solvent recovery with extraction
stages
Figure 3 - Shows a FTIR results of pure solvent, pure coal and permeate
collected after ultra filtration.

DETAILED DESCRIPTION OF THE INVENTION
1. Membrane preparation and characterization
The membrane fabrication process is initialized by a thorough mixing of a group
of dry inorganic raw material comprising Kaolin, Quartz, calcium carbonate,
sodium carbonate, Boric acid, sodium metasillicate respectively at a wt% 40,15,
25, 10 5, and 5, followed by addition of distilled water of 25.92% wet basis, to
prepare a paste (see Table 1). The paste is then cast cover a circular compact
disk made of gypsum. The disk may preferably have diameter between 50-
60mm, and thickness around 3 to 8mm. A stainless steel ring having inner
diameter and thickness corresponding to that of the disk is adapted for casting.
Subsequently, the ring is carefully removed and the paste is kept under a
distributed pressure of 2 kg/cm2 for 24 hours to prevent propagation of
deformation and drive homogeneity in the inorganic matrix. The paste is then
subjected to two different sequential heat treatment steps. Firstly, the circular
mold is fried at room temperature for 24 hours. After that it is dried at 100 °C for
12 hours in a hot air oven followed by drying at 250 °C, a low heating rate is
maintained in order to eliminate the induction of thermal stresses generated due
to loss of moisture. The second heat treatment step involves heating of the
membrane from 250 °C to desired sintering temperature at a heating rate of 2
°C per minute. Then the membrane is kept for 5 hours for sintering. Sintering of
the membranes at four different temperature 850 °C, 900 °C, 950 °C and 1000
°C are done in a muffle furnace to verify the effect of sintering temperature on
the membrane properties. Subsequent cooling of the membrane is conducted by

atmospheric cooling procedure adopted by switching off the muffle furnace that
is previously maintained at said desired sintering temperature. After sintering,
the membranes achieved hardness, rigidity, and porous texture. Finally, the
fabricated membrane is polished with silicon carbide abrasive paper (C-220) to
obtain a smooth, flat ultrafiltration membrane of a diameter of around 52.5 mm
and a thickness of approximately 4.5 mm.
Table 1: Composition of raw materials used for the fabrication of inorganic
membrane

2. Process for separation of coal from organic solvent
A coal sample is collected and an extraction process is carried out in three stages

as shown in Fig. 1. A measured amount of coal, NMP and EDA are placed in a
round bottom flask of 500 ml capacity. The flask is connected to a reflux
condenser and is electrically heated by means of a heating mantle control by a
Variac. The extraction is carried out in three stages for one hour under total
reflux conditions.
After extraction, the hot extracted mixture is filtered through a first mesh SS
screen (not shown). The hot filtrate is further filtered using a second mesh SS
screen. The filtrate is the "extract" liquid and the residues are the solid retained
on the mesh SS screens. The residues are dried and weighted separately and the
hot filtrate is feed to the membrane cell.
Composition of stage 1 extraction is shown in Table 2. It may be concluded from
the extraction efficiency (Ref: Table 4a) that the composition as in process
numbers 3 and 4 of Table 2 are preferable. The permeate collected after UF
(using stage 1 extract) are used for stage 2 extraction (Ref: Table 2) for both the
compositions (process numbers 3 and 4)). Extract of stage 2 extraction is used
for further UF experiment and the permeate is collected and used to stage 3
extraction. Details of schematic is shown in Fig. 4b
Table 2: Composition of extraction mixture (stage 1)

Membrane cleaning
Membrane separation are carried out with filtrate (after extraction) of three
different stages (stage 1, stage 2 and stage 3) using batch cell. The processes
are conducted for about 120 minutes. Transmembrane pressures differential (AP)
of 203 kPa and 500 rpm stirring speed are used to observe the permeate flux
and coal rejection efficiency of the membrane separately using extract of three
different stages. Permeate from the bottom of the cell is collected and its
cumulative weight can be measured with the help of an electronic balance.
Permeate are collected at 10 minutes interval for measurement of its coal
content and flux measurement.
At the end of each process run, the membrane is dried and cleaned with a
ordinary brush to remove coal particle deposited over the membrane surface.
After that, the membrane is reversely placed on the membrane cell and pure
NMP (~50ml) is passed the membrane. The permeate contained a minute
amount of coal particle which may be processed in the extraction stage number
1 in order to recycle the NMP. Therefore, the membrane cleaning does not
increase additional cost except the negligible amount of membrane experimental
cost.
OBSERATIONS
The extraction results are shown in Tables 3a to 3c for three different stages of

extraction. From table 3a it may be concluded that the compositions in process
number 3 and 4 (stage 1) are most suitable with respect to solvent requirement
and coal extraction efficiency. Therefore, these compositions are considered for
cascade type extraction in order to ensure reusability of the solvents. The
extraction performance of stage 2 and stage 3 are shown in Tables 3b and 3c,
respectively. Both the tables show a satisfactory coal extraction performance.
Table 3a : Extraction results (stage 1: used pure NMP as solvent)


Table 3b: Extraction results (stage 2: using permeate of stage 1 extraction as
extracting solvent)

Table 3c: Extraction results (stage 3: using permeate of stage 2 extraction as
extracting solvent)


Ultra filtration (UR results
The results obtained from UF of the extract obtained from three different stages
are shown in Tables 4a - 4c. Table 4a, which shows the UF performance of
stage 1 extract at 203 kPa. It is seen that more than 70% NMP is recovered. The
permeate collected is used for stage 2 extraction and again it is used for UF
steps and the result is shown in Table 4b. The permeate obtained is further used
for stage 3 extraction and the extract is used for implementation of the UF steps
and the result is shown in Table 4c. From both Tables 4b and 4c it may be been
that performance of solvent recovery remains at 67.9% and 66.4%, respectively,
for second and third time of use for the composition of process number 4 of
Table 2.
Table 4a : Ultrafiltration results (using extract of stage 1)


Table 4b: Ultrafiltration results (using extract of stage 2)

The variations of percentage solvent recovery with number of stages (use) are
shown in Fig. 2 for the two different compositions of experiment number 3 and 4
f Table 2. It may be seen that the decrease in percentage recovery is marginal
(remains within 66% to 71% for both the cases. Again, a slight higher (~1%)
solvent recovery is observed in case of experiment number 4.

WE CLAIM
1. A fabrication process to produce defect-free inorganic ultra filtration range
ceramic membrane cells, comprising the steps of:
- providing a group of dry inorganic raw materials comprising kaolin, Quartz,
calcium carbonate, sodium carbonate, boric acid, and sodium calcium
carbonate, respectively at a weight present of 40,15, 25,10, 5 and 5;
- mixing the dry inorganic raw materials with distilled water of 28.92%, wet
basis, to form a paste;
- casting the paste over a compact disk adapting a metal ring;
- removing the metal ring and allowing the casted paste under a distributed
pressure for a predetermined time period;
- subjecting the paste to undergo at least two different sequential heat
treatment phases;
- cooling the formed membrane through atmospheric coding procedure; and
- polishing the membrane with silicon carbide abrasive paper.
2. The process as claimed in claim 1, wherein the compact disk is substantially
circular-shaped having a diameter between 50to 60 mm with thickness
around 3 to 8mm, and wherein the disc is preferably formed of gypsum.

3. The process as claimed in claim 1, wherein the metal ring is made of stainless
steel and having an inner diameter and thickness corresponding to that of the
disk.
4. The process as claimed in claim 1, wherein said distributed pressure is around
2kg/cm2, and wherein said predetermined time period is about 24 hours.
5. The process as claimed in claim 1, wherein said two differential heat
treatment phases comprises a first phase in which the mold is dried in room
temperature for about 24 hours followers by around 12 hours of drying in a
hot air oven at 100°C, and further drying for 24 hours at 250°C, and wherein
the second phase of heat treatment comprises heating the membrane from
250°C to a desired sintering temperature at a heating rate of 2°C per minute
at four different temperature of 850°C, 900°C, 950°C, and 1000°C in a
muffle furnace 5 hours.
6. A process for separation of coal from organic solvent by adapting a defect-
free inorganic ultra filtration range ceramic membrane device, the process
comprising the steps of:

- providing a coal-batch including a quantity of NMP and EDA in a ratio of 1:9:1
to form an extraction mixture in an extraction vessel;
- connecting a reflux condenser to the vessel;

- heating the mixture by a heater having a control means to implement the
extraction step for a predefined duration, the predefined duration depending
on the selected capacity of the heater, size of the extraction vessel and the
quantity including the ratio of the selected composition;
- filtering the hot extracted mixture through at least two mesh screens at two
stages, the residue being dried, weighted separately, the hot filtrate fed to
the membrane batch cell; and
- separating the filtrate in the membrane batch cells in multiple stages for
predetermined period at specified transmembrane pressure differential (AP)
with a determined stirring speed, the said parameters being dependent on
the batch-size of coal mixture including configuration of the membrane batch
cells.
7. A fabrication process to produce defect-free inorganic ultra filtration range
ceramic membrane cells as substantially described and illustrated herein with
reference to the accompanying drawings.

The invention relates to a fabrication process to produce defect-free inorganic
ultra filtration range ceramic membrane cells, comprising the steps of providing a
group of dry inorganic raw materials comprising kaolin, Quartz, calcium
carbonate, sodium carbonate, boric acid, and sodium calcium carbonate,
respectively at a weight present of 40, 15, 25, 10, 5 and 5; mixing the dry
inorganic raw materials with distilled water of 28.92%, wet basis, to form a
paste; casting the paste over a compact disk adapting a metal ring; removing the
metal ring and allowing the casted paste under a distributed pressure for a
predetermined time period; subjecting the paste to undergo at least two
different sequential heat treatment phases; cooling the formed membrane
through atmospheric coding procedure; and polishing the membrane with silicon
carbide abrasive paper.