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Teknik Bioseparasi Dina Wahyu Genap/ Maret 2014
Outline
Chemical Reaction Engineering 1
Pendahuluan
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Teknik Pemisahan Secara Fisika 1
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Teknik Pemisahan Secara Fisika 2
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Teknik Pemisahan Secara Fisika 3
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Koagulasi dan flokulasi
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Adsorpsi
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Adsorpsi 2
mempelajari ruang lingkup teknik bioseparasi dan teknik “cel disruption”
Mempelajari teknik sentrifugasi pada bioseparasi Mempelajari teknik pemisahan sedimentasi
Mempelajari teknik filtrasi pada bioseparasi
Mengetahui teknik pemisahan dengan cara koagulasi dan flokulasi Proses adsorpsi pada cairan dan gas, serta pengetahuan bahan adsorpsi Kinetika Adsorpsi, Isotherm Adsorption
Adsorpsi ≠ Absorbsi •
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Absorbsi – fase fluida ditransfer dari satu medium ke medium lain (air diabsorpsi oleh spon) Adsorpsi – komponen fase fluida (cairan atau gas) tertentu ditransfer dan dipertahankan pada bagian permukaan padatan (partikel kecil terikat pada karbon)
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Absorbsi masuknya solut ke dalam bahan padat (pada tingkat molekuler) Adsorpsi proses dengan solut terakumulasi pada antarmuka cair-padat atau gaspadat Sorpsi = Adsorpsi + Absorbsi
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Aplikasi adsorpsi dalam proses di industri: Dehumidifikasi Penghilangan bau/warna/rasa Penghilangan polutan gas (H2S) Pelunakan dan deionisasi air Fraksionasi hidrokarbon
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Konsep Dasar: Melibatkan dua fase 1) Fluida yang mengandung solut produk dan kontaminan 2) Padatan berpori (adsorben) yang secara selektif mengikat solut atau kontaminan Proses melibatkan transfer komponen dalam fase cair ke permukaan padatan. Melibatkan transfer massa dan kesetimbangan pada antarmuka padatan/fluida
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Adsorbat Senyawa yang dihilangkan dari fase cair/gas Adsorben Fase padat tempat akumulasi terjadi Contoh Warna dapat dihilangkan dari air menggunakan karbon aktif. Warna adalah adsorbat dan karbon aktif adalah adorben
Adsorbat • •
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Rasa dan Bau Senyawa Organik Sintetik - Solven aromatik (benzen, toluen) - Pestisida , herbisida Humic substances Senyawa organik alami, umumnya pembentuk warna, dengan ukuran molekul berkisar antara beberapa ratus sampai ratusan ribu Halometan dapat terbentuk jika air yang mengandung humic substances diklorinasi. Molekul metan dengan halogen (Cl, Br,...) menggantikan H, beberapa bersifat karsinogen
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Adsorbat •
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Logam Arsen, perak, merkuri Virus Senyawa anorganik lainnya Klorin, bromin
Adsorben •
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Karbon Aktif Mampu menghilangkan semua adsorbat Adsorben paling populer Resin Sintetik Zeolit Tanah pemucat dengan sifat Adsorpsi Silika gel
Karbon Aktif •
Karbon yang telah dipirolisis (dipanaskan dengan sedikit oksigen) Membakar tar, menguapkan gas Menghasilkan bahan dengan banyak pori sehingga mempunyai luas permukan besar (500 - 1000 m2/g) Menghasilkan bagian Adsorpsi aktif
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Karbon bersifat non-polar, baik untuk Adsorpsi senyawa non-polar
Activated Carbon Picture
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Source: solomon.bond.okstate.edu/thinkchem97/experiments/lab7.html
Tipe •
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PAC: Powdered activated carbon A fine powder, < 0.05 mm dia. GAC: Granular activated carbon 0.3 - 3 mm
Silica gel •
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Paling banyak digunakan sebagai adsorben dalam kromatografi kolom dan lapis tipis Dibuat dengan mengasamkan sodium silikat dengan asam sulfat diikuti dengan pencusian dengan air dan pengeringan Sisi aktif silika gel merupakan kelompok hidroksil yang terikat pada atom silikon. OH Si---------O-------Si
OH
Tipe Adsorpsi •
Adsorpsi fisik Hasil dari gaya intermolekuler yang menyebabkan pengikatan senyawa tertentu pada adsorben tertentu Bersifat reversibel dengan penggunaan panas (uap air, gas inert panas, oven) Pengikatan lapisan luar dari adsorben
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Adsorpsi kimia (kemisorbsi) Hasil dari interaksi kimia Sejumlah panas dilepaskan Irreversibel Terdapat dalam katalisis
Adsorpsi Fisik •
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Ikatan Elektrostatik Partikel bermuatan berlawanan Interaksi Dipol-Dipol Ikatan antara Dua Senyawa Polar Senyawa polar mempunyai distribusi muatan yang tidak sama (satu ujung mempunyai muatan + yang lain bermuatan -)
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Ikatan Hidrogen Interaksi dipol-dipol, melibatkan atom hidrogen dengan muatan positif Ikatan Van der Waals Ikatan yang lemah disebabkan oleh dua molekul non polar yang berdekatan menyebabkan perubahan dalam distribusi muatan, menghasilkan ikatan dipol-dipol
Tahap Separasi Adsorpsi Preadsorpsi: adsorben dalam fluida bebas solut 2. Menambahkan aliran proses termasuk solut produk dan solut lain 3. Adsorpsi terjadi, solut produk berikatan dengan adsorben sedangkan yang lainnya lewat 1.
4. Pencucian (tidak selalu) adsorben melepaskan impuritis yang tersisa 5. Elusi: merecover solut produk 6. Regenerasi adsorben
Adsorpsi •
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Molekul cenderung berada pada tingkat energi yang lebih rendah Molekul dapat berada pada tingkat energi yang lebih rendah dengan cara melekat pada permukaan padatan senyawa hidrofob
Kesetimbangan •
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Pada kesetimbangan: Terlarut dalam fase cair Teradsorpsi pada adsorben fase padat Adsorpsi bersifat reversibel: Desorbsi
Adsorption chromatography •
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Fase stasioner dalam adsorption chromatography disebut adsorben Jika cairan digunakan sebagai fase mobil disebut Liquid-Solid Chromatography (LSC) e.g. TLC and HPLC Jika gas digunakan sebagai fase mobil disebut Gas-Solid Chromatography (GSC) e.g. Gas Chromatography (GC)
Pada adsorption chromatography terdapat dua tipe gaya:
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Gaya tarik solut pada adsorben (fase stasioner) Gaya yang melepaskan solut dari adsorben untuk bergerak bersama fase mobil
Gaya tarik: = Adsorpsi fisik
Gaya penyebab pergerakan solut •
Elusi: Kecenderungan solut terlarut dan bergerak dengan fase mobil. Solven yang digunakan sebagai fase mobil harus mampu melarutkan solut sehingga terjadi kompetisi dengan gaya adsorpsi dari fase stasioner. Jika digunakan solven yang sangat kuat, maka akan mencuci solut tanpa pemisahan.
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Displacement: Dalam kasus molekul solven berkompetisi dengan solut pada sisi adsorpsi fase stasioner. Kompetisi ini menyebabkan solut bergerak dalam kecepatan yang berbeda
Langmuir Isotherm: This model assumes monolayer coverage and constant binding energy between surface and adsorbate. The model is:
qe Q 0a
0 K Q a Ce
1 K Ce
represents the maximum adsorption
(monolayer coverage) (g solute/g Ce has units of mg/L. K has units of L/mg
adsorbent).
capacity
BET (Brunauer, Emmett and Teller) isotherm: This is a more general, multi-layer model. It assumes that a Langmuir isotherm applies to each layer and that no transmigration occurs between layers. It also assumes that there is equal energy of adsorption for each layer except for the first layer.
K B Ce Q qe (C S C e ){1 (K B 1)(C e / C S )} 0 a
CS =saturation (solubility limit) concentration of the solute. (mg/liter) KB = a parameter related to the binding intensity for all layers. Note: when Ce << CS and KB >> 1 and K = KB/Cs BET isotherm approaches Langmuir isotherm.
Freundlich Isotherm: For the special case of heterogeneous surface energies (particularly good for mixed wastes) in which the energy term, “KF”, varies as a function of surface coverage we use the Freundlich model.
1
q e K FCe
n
n and KF are system specific constants.
Determination of appropriate model: To determine which model to use to describe the adsorption for a particular adsorbent/adsorbate isotherms experiments are usually run. Data from these isotherm experiments are then analyzed using the following methods that are based on linearization of the models.
For the Langmuir model linearization gives:
Ce Ce 1 0 0 qe K Qa Qa A plot of Ce/qe versus Ce should give a straight line with intercept
:
1 0 K Qa
and slope:
Or:
1 0 Qa
1 1 1 1 0 0 q e Qa K Qa Ce
Here a plot of 1/qe versus 1/Ce should give a straight line with intercept 1/Qao and slope
1 K Q 0a
For the Freundlich isotherm use the log-log version :
1 log q e log K F log C n A log-log plot should yield an intercept of log KF and a slope of 1/n.
For the BET isotherm we can arrange the isotherm equation to get:
Ce K B 1 Ce 1 0 (C S C e ) q e K B Q a C S K B Q 0a Intercept =
Slope =
1 K B Q 0a
KB 1 0
K B Q a Cs
Factors which affect adsorption extent (and therefore affect isotherm) are: Adsorbate: Solubility In general, as solubility of solute increases the extent of adsorption decreases. This is known as the “Lundelius’ Rule”. Solute-solid surface binding competes with solutesolvent attraction as discussed earlier. Factors which affect solubility include molecular size (high MW- low solubility), ionization (solubility is minimum when compounds are uncharged), polarity (as polarity increases get higher solubility because water is a polar solvent).
pH pH often affects the surface charge on the adsorbent as well as the charge on the solute. Generally, for organic material as pH goes down adsorption goes up. Temperature Adsorption reactions are typically exothermic i.e., D H rxn is generally negative. Here heat is given off by the reaction therefore as T increases extent of adsorption decreases.
Presence of other solutes In general, get competition for a limited number of sites therefore get reduced extent of adsorption or a specific material.
Adsorbent: Virtually every solid surface has the capacity to adsorb solutes. From the wastewater/water treatment point of view activated carbon (AC) is the adsorbent of choice. AC prepared from many sources: •Wood •Lignite •Coal •Nutshells •Bone
These raw materials are pyrolyzed at high temperature under low oxygen conditions (so we don’t get complete combustion). This forms a “char”. The char is then activated by heating to 300 – 1000 oC in the presence of steam, oxygen or C02. Result: “Activated carbon” which is highly porous, micro-crystalline material which resembles graphite plates with some specific functional groups (e.g. COOH, OH)
Increasing magnification
Surface area of the AC is huge. Most of the surface area is interior in micro- and macropores. Typical surface area is in the range of 300-1500 m2/gram. Quality and hardness of the AC are a function of the starting material and the activation process.
Pore size distribution: micropores: <2nm dia mesopores: 2nm to 20 nm dia macropores: > 20 nm
Pore size Micro
% pore volume 30 - 60
% surface area >95
Meso
< 10
<5
Macro
25 - 30
negligible
Most of the surface area is in pores of molecular sized dimensions. This results in slower mass transfer during the adsorption process but also results in greater binding capacity of the adsorbate. Adsorption behavior is related in part to the nature of the functional groups on the carbon surface. In general carbon manufactured at: <500 oC is weakly acidic > 500 oC is weakly basic Spent AC can be regenerated at high temperatures (roughly a maximum of fifteen times).
Adsorption Kinetics. Adsorption onto AC usually is modeled as a three consecutive step process. These steps are film transport (through the stagnant boundary layer about the AC particle); transport of the solute through the internal pores; and finally adsorption to the surface site. One or more of these steps can limit the rate of solute adsorption. In most cases the actual adsorption process does not limit the process. In some cases film transport limits and in other cases (most likely) pore diffusion limits.
We can lump all the mass transport resistance terms into one term, k, and write:
C k a (C C e ) t k = overall mass transfer coefficient (cm/min) a = surface area of carbon per unit volume of reactor (1/cm) Ce = concentration that would be in equilibrium with actual amount of solute adsorbed, q (g/liter). C = actual concentration of solute in bulk solution. (g/liter).
Treated Effluent Fresh Carbon Effluent zone C approx. 0
“S” zone: C goes from C0 to approx. 0
0
C/C0
Saturated zone: C = C0 1
Waste Influent Exhausted Carbon
MANUFACTURE OF ACTIVATED CARBON: DIFFERENT RAW MATERIALS
MANUFACTURE OF ACTIVATED CARBON FROM COAL
Multiple Hearth ↑
ACTIVATION FURNACE TYPES Rotary kiln
DIFFERENT PHYSICAL FORMS OF ACTIVATED CARBON
First magnification of carbon granules
Continued magnification
Continued magnification
Continued conceptual magnification
Continued conceptual magnification
Continued conceptual magnification
Scanning Electron Microscope Photo of GAC
Area of a few grams of activated carbon
Application Methodology
Granular Activated Carbon Columns
GAC Silos
Gas Purification
Contacting Column Internals
Typical isotherm solid-phase concentration (y-axis) vs liquid phase concentration (xaxis)
This is a favorable isotherm: higher solidphase concentration at low liquid concentrations
Column Hydraulics
Adsorptive Forces
The effect of molecular size and functional groups on adsorbability
Langmuir isotherm
Freundlich isotherm (linear scale)
Freundlich isotherm, log-log scale
Freundlich isotherm, compared with real data 0 -2
-1.5
-1
-0.5
0 -0.5
Log (x/m)
-1 -1.5 -2 -2.5 -3
Log C
0.5
Four GAC columns in series
REACTIVATION OF ACTIVATED CARBON
Transport of GAC
Decentralized Multiple Hearth Regeneration Facility
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