MOLEX (Molecular Extraction) process in LAB Plant (Gujarat Refinery). Working & Principle of Multi port Rotary Valve.

1. Pratik Patel
pratik19121994@gmail.com
Advanced Chemical Technology
(Multi-port Rotary Valve)

2. In 2004, the world's largest single train Linear Alkyl Benzene
(LAB) Plant was set up in the Gujarat Refinery marking Indian Oil’s
big-ticket entry into the Petrochemicals field. Today, the Gujarat refinery
holds the 2nd largest market share of LAB in India and exports to over 20
countries.
This Document give the basic information about technological most
advanced the multi-port rotary valve in MOLEX unit at LAB
Plant (Gujarat Refinery).
In FRONT END section of LAB plant having final MOLEX (Molecular
Extraction) process.
The Molex process is a liquid state separation of normal paraffins from
branched and cyclic components (i- paraffins) using Sorbex technology.
The simulated moving bed adsorptive separation results from using a
proprietary multi-port rotary valve. The extract stream is a high-purity
normal paraffins stream.

3. Process
Feed
Feed contains Nonlinear & linear
Hydrocarbons, but we need only linear
hydrocarbons for production of Linear
Alkyl Benzene (LAB) because Nonlinear
Alkyl Benzene is not bio- degradable.
Feed enters the bed of Carbon Molecular Sieves (CMS). CMS is solid
adsorbent having pores shape as shown in figure (a). Nonlinear
hydrocarbons are fits in pores as shown in figure (b). Nonlinear
hydrocarbon molecules shape restrict to fits in pores & the
only half of molecule occupy in the space of pores just like
hanging outside of pores as shown in figure (b).
Linear Hydrocarbons are fits perfectly in the pores
because of their linear chain geometry as shown in
figure (c)…

4. n-pentane
n- Pentane is added after feed…
n- Pentane molecule replace itself with adsorbed linear hydrocarbon
molecule in pores & the downstream is extract having linear
hydrocarbons…This is how pure linear hydrocarbon separates….
Now, in bed there are nonlinear Hydrocarbon & n-pentane molecules….
i-octane
i-octane added after n- pentane…i-octane takes all the nonlinear
hydrocarbons in the downstream…downstream contains i-octane & non-
linear hydrocarbon….that is the Raffinate stream…
Now, in bed pores there is only n- pentane molecules..

5. Desorbent
The desorbent is a liquid mixture of a different boiling point than the feed
components.
Desorbent added after i-octane
Desorbent takes all the n-pentane molecules in the bed. Desorbent just
wash out whole bed.
So now bed pores are empty & ready for repeat the same operation as
above 4 steps.
Now, this is the batch process but we need to convert it into continuous
process for the industry. In LAB plant this is the most advanced
technology I ever seen in the industry.
Just one Multi port Rotary Valve make this process continuous &
doing job of 300 individual valves.

6. In this whole process
Inlet streams are 1) Feed 2) n-pentane 3) n-octane 4) Desorbent in
Outlet streams are 5) Extract 6) Raffinate 7) Desorbent out
The Process having Two Verticals Adsorbent Columns having 12 beds
each

7. Total of 24 separate beds of CMS…as
shown in figure.
The Control valve shown in center of
two columns
Control valve has two plates
1) Rotating plate (above)
2) Static plate or Track Plate (below) as shown in figure.

8. Below plate have total 24 holes. All 24 holes are connecting to 24 beds
with 24 different connecting lines as shown in figure…
Above plate have 8 holes total….4 holes nearer to center connecting with
net stream tracks as shown in figure…other 4 holes are just co
eccentric with below plate’s holes….as shown in figure….The above
plates 8 holes are connected with connecting lines shown with different
color lines….
Both plates are connected with central shaft…There is a hydraulic
arrangement to rotate the above plate…

9. Working
At time t=t
Only 7 beds are in operation….Bed no.1, 3, 7, 10, 14, 17 & 21
Inlet streams are 1) Feed 2) n-pentane 3) n-octane 4) Desorbent in (1, 3,
7, 10 respectively)
Outlet streams are 5) Extract 6) Raffinate 7) Desorbent out (14, 17, 21
respectively)
In Operation Desorbent stream is called Zone Flush Stream…
There is also a Line flush in & out stream…Line Flush is to flush the
whole Connecting lines with Feed Liquid…
After Cycle time of 2.5 minute Rotor plate rotates anticlockwise & the
other 7 beds in operation….Bed no. 2, 4, 8, 10, 15, 18 & 22
So after every interval of 2.5 minutes rotor plate rotating & the process
become continuous.