PSD

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The separation is based on fact: a simple change in pressure can alter relative volatility of the mixture with close boiling point or forming azeotrope. Pressure-swing distillation (PSD) is the process to be utilized to separate the mixture with close boiling point or forming azeotrope, but no new additive added. PSD is an environment-friendly process contact: abubackersiddieq@gmail.com

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PRESSURE SWING DISTILLATION:

PRESSURE SWING DISTILLATION ABUBACKER SIDDIEQ K K 500015447 UPES

What is psd?:

What is psd? Special distillation process Pressure-swing distillation (PSD) is the process to be utilized to separate the mixture with close boiling point or forming azeotrope, but no new additive added. PSD is an environment-friendly process Principle (When it can be used?) The separation is based on fact: a simple change in pressure can alter relative volatility of the mixture with close boiling point or forming azeotrope.

Effect of pressure on composition of azeotrope:

Effect of pressure on composition of azeotrope

Min-boiling homogeneous azeotropes :

Min-boiling homogeneous azeotropes Acetonitrile-Water system

T-x-y:

T-x-y

Examples of psd binary azeotropes:

Examples of psd binary azeotropes

OPERATION:

OPERATION THREE TYPES OF OPERATION MODE IN PRESSURE SWING DISTILLATION CONTINOUS OPERATION BATCH OPERATION SEMI CONTINOUS OPERATION

Min & max boiling azeotropes:

Min & max boiling azeotropes

CONTINOUS OPERATION:

CONTINOUS OPERATION In continuous operation the separation is performed using two columns maintained at two different pressure. The distillate which approach the azeotropic composition at low and high pressure are recycled between two columns.

batch OPERATION:

batch OPERATION Batch operation single column is used for separation First feed charged to column operated at pressure P1 and bottom B is removed Collected distillate D1 approached to azeotropic composition and column recharged with distillate D1 and operated at pressure P2 to get bottom A as pure product removed

Batch rectifier and stripper:

Batch rectifier and stripper

semi-CONTINOUS OPERATION:

semi-CONTINOUS OPERATION In semi continuous operation single distillation column used but column operated continuously and periodically It is not recharged or emptied Liquids levels are maintained, reboiler and condenser in charged condition The advantages is lower the investment cost and shorter downtime when the mixture to be separated is changed

Design of psd:

Design of psd Column Sequence Sequence of column in order of increasing pressure is found to be economical for Water-THF since recycle flow rate is much larger than sequence in pressure decreasing order Number of columns required: N col = N P + N B – 1 Where, N P = number of pure components N B = number of boundaries crossed by PSD that doesn’t include the boundaries that disappear as the pressure changes

ECONOMICAL CONSIDERATION :

ECONOMICAL CONSIDERATION The smaller the variation of azeotrope composition over the pressure range, the larger will be the recycle streams between the two columns. For minimum-boiling azeotropes, the pressure-swing distillation approach requires high energy usage and high capital costs (large-diameter columns) because both recycled azeotropic compositions must be taken overhead . However, the lower the pressure in the low-pressure column, the larger the diameter and the coolant required in the condenser. The higher the pressure in the high-pressure column, the higher the pressure of the steam that must be used in the reboiler and other problems with high temperature at reboiler.

Comparison of ed and PSd:

Comparison of ed and PSd Energy demand of ED is lower than PSD Higher recovery is achieved by ED than the process by the PSD ED needs much more operation steps than the PSD The control of the PSD is easier than that of the ED since the columns are operating practically in steady state The capital costs of the PSD (requiring two columns) are obviously higher than that of the ED .

advantages:

advantages Energy saving by heat integration of the system No need to add an entrainer or a solvent for the separation Environment friendly

Reference:

Reference Separation Process Principles, J.D.Seader , Ernest J. Henley (419-421) Special Distillation Processes, Zhigang Lei, Biaohua Chen, Zhongwei Ding (320-327) Process Design of Distillation Columns, S.B.Thakore , B.I.Bhatt (520-522) Hungarian Journal of I ndustrial chemistry, VESZPREM, vol.36(1-2) pp.89-94 (2008)

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