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FS532 > Unit operation #2 > Flashcards

Unit operation #2 Flashcards

1
Q

Distillation def

A

A process of separating the component substances from a
liquid mixture by selective evaporation and condensation.

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2
Q

Based on what concept

A

differences in volatility

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3
Q

composition on vapor

A

Vapors produced contain the components of the original
mixture, but in different proportions (determined by the
relative volatilities).

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4
Q

Applications of Distillation
in Food Processing

A
  • Manufacture of alcoholic beverages
  • Recovery of solvents after oil extraction
  • Concentration of aroma compounds from juices
    and extracts
  • Extraction of essential oils from seeds and leaves
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5
Q

Azeotropes

A
  • Constant boiling mixture
  • Mixture of two or more liquids whose proportions
    cannot be altered by simple distillation
  • The vapor and liquid composition lines in the
    boiling point diagram come together
  • It is not possible to separate the components by
    fractional distillation
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6
Q

Azeotropes ex

A

The ethanol-water mixture
* Has a minimum boiling-point azeotrope

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7
Q

Distillation Methods

A
  • Simple Distillation
    (Batch Distillation)
  • Equilibrium (Flash)
    Distillation
  • Distillation with Reflux
  • Vacuum Distillation
  • Molecular Distillation
    (Short Path)
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8
Q

Batch Distillation

A

Equilibrium Distillation
or Flash Distillation
All components are present in
both phases (liquid, vapor)
The composition of the vapor is
different from the liquid
Production of vapor by
boiling liquid mixture in a single
stage
Recovering and condensing vapors
No liquid allowed to return to the still to contact the vapor

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9
Q

Equilibrium (Flash) Distillation

A

Mass Balances
F = V + L
F xF = L x + V y

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10
Q

Distillation Equipment of batch

A

Pot Stills

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11
Q

Distillation Equipment properties

A

Contaminants from materials
used to build the system
Lead
Antifreeze (use of car radiators
as condensers)
Methanol (adulteration)
“Foreshot” may contain
methanol, acetone

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12
Q

Risk of distillation

A

High alcohol concentrations:
Flammable
Alcohol vapors may
accumulate in the air
Poor ventilation
Federal law strictly prohibits
individuals from producing
distilled spirits at home

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13
Q

Fractional Distillation

A

Distillation with Reflux or
Rectification
A series of flash distillation
stages
A portion of the condensate
is returned to the still
Vapors rise through a series of
trays or stages
Part of the condensate flows
downwards

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14
Q

Fractional equipments

A

internal plates

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15
Q

Ex whiskey

A
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16
Q

Steam Distillation

A

At atmospheric pressure high boiling liquids cannot be purified by distillation
The components of the mixture may decompose at the high temperature required
Often those high-boiling substances are insoluble in water
Steam distillation may sometimes be used to effect the separation at safe temperatures.

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17
Q

Steam Distillation boiling

A

Boiling temperatures can be reduced by reducing the pressure on the system
Boiling under a vacuum or by adding an inert vapor
Inert vapor contributes to the vapor pressure and allows the liquid to boil at a lower temperature.
Easily removed from the distillate
Must not react with any of the products

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18
Q

Ex gin production

A

steam disillation + reflux

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19
Q

Vacuum Distillation

A

Reduction of the total
pressure = distilling at
lower temperatures
Vacuum distillation is
tending to supplant steam distillation
In some instances, the two
methods are combined in
vacuum steam distillation.

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20
Q

Molecular Distillation (Short Path)

A

Carried out under a high vacuum
* Molecules escaping from the warm liquid reach the cooled surface of the condenser
* Used in the purification of substances of low volatility

21
Q

Molecular Distillation fonctionnement

A

Feed liquid is admitted into
still under high vacuum
* Immediately spread into a
very thin film
* Forced quickly down the
evaporation surface.
Heated walls (orange)
and high vacuum (yellow) drive the more volatile components
(distillate) to the closely positioned internal condenser
* The less volatile components (residue) continue down the
cylinder
* The resulting separated fractions exit through individual discharge outlets
* Depending on application, the desired product is either the distillate or the residue fraction

22
Q

Molecular Distillation
(Typical Applications

A

ü Esters, Fatty Acids, Mono, Di, Omega 3 & Triglycerides
ü Vitamin, Nutraceuticals
ü Essential Oil Isolation
ü Oil Deodorization
ü Water Removal (ppm Level)
ü Solvent Recovery

23
Q

Concentration (Unit Operations)

A
  • Filtration
  • Centrifugation
  • Membrane separation
  • Evaporation
24
Q

Filtration def

A

Filtration is an operation by which solid particles are
separated from a liquid or gas by forcing the mixture through a porous medium that retains the
particles
* The purpose of filtration may be:
üThe removal of undesirable solid particles from a liquid
product (e.g., clarification of wine)
ü The recovery of a solid product from a solid/liquid mixture
(separation of sugar crystals from mother liquor)

25
Application of filtration in food processing
ü Clarification of fruit juices ü Clarification of wine ü Bleaching of edible oils ü Sugar refining ü Preparation of brines and syrups for canned foods ü Treatment of drinking water, and of water used in the preparation of soft beverages and beer ü Air filtration
26
Types of filtration
* Depth Filtration * Surface Filtration
27
Depth Filtration
ü The mixture flows through a thick layer of porous material of fibrous (glass wool, rock wool) or particulate (sand) structure ü The solid particles of the mixture are retained as a result of the collision with the fibers or particles of the filter medium, or by adsorption ü The passages available to flow are much larger than the retained particles. Retention is probabilistic and not absolute ü The size range of the particles retained is very wide, from 0.1 μ m (microorganisms) to 0.1 mm (dust and fine powder).
28
Filtration of the depth equipment
Depth filters Cartridge filters
29
Depth filters
The most common depth filter is the sand filter, used for water purification Range in size from very large tanks or boxes used for municipal water treatment to small portable vessels used in swimming pools
30
Cartridge filters
ü Perforated metal surface, cloth, canvas, paper, mesh, porous ceramic, or a series of discs with a very narrow gap between them Cartridges placed in housings with flowdiverting elements ü Most cartridge filters can be cleaned in-place ü The filtering elements are replaceable or even disposable
31
Cartridge filters uses
Used to continuously separate small quantities of suspended solids from a fluid in flow. Some of their most common uses are: ü Filtration of compressed air ü Filtration of steam (steam strainer) ü Filtration of clean water before spray nozzles
32
Surface Filtration
ü The fluid is forced through a porous medium (filter medium) that retains the particles on its surface ü Also known as barrier filtration ü The most common type of filtration in the food industry ü Particles larger than the openings of the porous surface are retained ü There is a definite cut-out size (maximum size of particles passing through), and retention of particles above the cut-out size is absolute
33
Surface filtration
Dead-end filtration Cross-flow filtration
34
Dead-end filtration
ü The direction of suspension flow is normal to the filter surface ü The particles are stopped (come to a dead-end) on the filter surface and accumulate (filtration cake)
35
Cross-flow filtration
ü The direction of suspension flow is parallel (tangential) to the filter surface ü The retained particles are carried forwards by the flowing suspension
36
Membrane definition
* Membrane: thin film or material with selective permeability.
37
types of membrane
– Microfiltration (MF) – Ultrafiltration (UF) – Nanofiltration (NF) – Reverse Osmosis (RO)
38
Membrane processes def
* The driving force for material transport is a pressure difference * MF and UF are filtration processes (particle size is the criterion for permeation or rejection) * RO membranes separate particles at molecular level (based on their chemical nature)
39
Membrane materials
(cellulose and its derivatives) * Polyolefines * Polysulfones * Polyamides * Cl and F substituted hydrocarbons * Ceramic membranes (oxides of Zr, Ti, Si and Al)
40
Membranes for food processing
* High permeate flux * Good retention capability * Good mechanical strength * Chemical stability and inertness * Bio-inertness * Thermal stability * Resistance to cleaning and sanitizing agents * Resistance to microbial action * Smooth, fouling resistant surface * Long service life * Affordable cost
41
Membrane configurations
– Plate and frame – Spiral wound – Tubular – Hollow fiber
42
Plate and frame
* Membranes are square or circular * Vertical or horizontal stacks * Cannot withstand high pressures (limited to MF and UF)
43
Plate and Frame Ultrafiltration
* Dairy: Cultured milk concentration * Gums: Xanthan and pectin concentration * Protein: Concentration of soy, whole egg, gelatin etc. * Beer: Beer yeast concentration * Sugar: Clarification of saccharification liquid (HFCS) * Juice: Clarification of orange juice, apple juice etc.
44
* Spiral wound
* Two large sheets of membrane are heat sealed forming a bag * A flexible spacer is inserted into the bag * The sandwich assembly is wounded spirally (cylindrical module
45
Tubular
* Resembles a shell and tube heat exchanger * The membrane is cast on the inner wall of rigid porous tubes * The tubes are connected to end plates and installed as parallel bundles
46
Hollow fiber
– Tubes are thin (diameters from 1 mm down to capillary size) – An external rigid support is not necessary – Many hollow fibers are connected to perforated end plates – The entire bundle in inserted in a vessel or jacket – Oxygen concentrators, hemodialysis
47
Microfiltration
– Clarification of fruit juices, wine, vinegar, sugar syrups – Purification of drinking water – Water for soft beverages – Pretreatment, before UF or RO
48

FS532 (6 decks)

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