RECOVERY,CONCENTRATION AND PURIFICATION

OF PHENOLICCOMPOUNDS BY

ADSORPTIONDiego Alonso Martínez

Filip AmbrozJavier Marqués de Marino

Substances who contains phenol  are very dangerous to the environment at high

concentration, so therefore there are very unwanted things in nature. They are not harm in

low concentrations like 0,002 mg/L, but higher conc. can cause unpleasant taste in drinking water, they

can even adsorbed through the skin.  They are also very useful, we use them in medicine, for example

as disinfectants or medical preparations, they have chemopreventive properties too, so they can be

useful in treatments of cancer.

TECHNOLOGIES Like we heard before, phenols are not environmental friendly so

therefore we need some technologies  to sustained water quality. We divide these techn. to three groups. biological, chemical and physically operations.

In physically operations we have: sedimentation, flotation, filtration, flow equalization…

In chemically operations there are: adsorption, disinfection, dechlorination…

In biological operations: trickling filters, pond stabilization, anaerobic digestion, biological nutrient removal…

The most widely used treatment is biological because is the most cheapest, here is very  important fact that bacteria is able to accumulate and degrade different pollutants but, these treatment is incapable to remove phenol from process. This is a big problem so therefore we have to use also chemical techniques which remove phenols, but these techniques are very expensive. They are so expensive because we need a lot of electrical energy for them and also we need a lot of chemical reagent.  We have also some alternatives like oxidation processes but this is still very costly. We have also physical techniques, which are widely used but here we also have a problem. In this technique we have membrane processes but this processes don’t have a long lifetime so we have to change them a lot of times and this is costly.

Because of all this things adsorption is the most popular method for removal pollutants.

ADSORPTION

Is also very efficient. Here we use activated carbon for adsorbent, because it has very good adsorption properties for organic pollutants. Activated carbon has high-surface area, pore volume and porosity. But here we again have an economic problem. Activated carbon has high cost for an expensive regeneration system. In adsorption there is also important ionic strength and pH.  At acid pH the uptake of phenolics is enhanced, but alkaline pH  decreases adsorption. In adsorption is very important also the temperature, if we have high temperature then we have irreversible interactions, which favores adsorption.

Adsorption is also very important for practical operations, because of the interactions of adsorbate-adsorbent. Here we have Langmuir isotherm, this isotherm is wifely used equation. We use it when we have uniform adsorption energies at the adsorbent surface. When we have nonideal system we use the Freundlich isotherm. This isotherm is also very important, because it gives

good interpretation of concentration range.

EQUATIONSFreundlich equation:ln(q)= ln(Kf) + 1/nCe

Langmuir equation:Ce/Qe=1/Kl +(b/Kl) Ce

Dubinin-Radushkevic equation:E= R T e*(1/Ce)

These equation is very important, because information was obtained from the adsorbtion experience with p-CP and p-NP.  We use connection between Freundlich and Dubinin-Radushkevic to interpret the result. Another important thing is Lewis acid-base theory, which modified clays including metal cations can be considered as Lewis acids, while phenolic compounds can be regarded as Lewis bases and Bronsted acids.  Her is very tough to predict adsorption capacity, because it depends on the adsorbent property, the solution conditions and the interactions at the solid-liquid interface.  We get majority informations from the experiments of adsorption.

Here we have also reversible and irreversible adsorption.  Reversible adsorption we have, when we have physical adsorption, because here are important van der Waals forces, which are very weak so this thing has affect on the adsorption.  If we have chemisorptions and oxidative polymerization of phenolics we have irreversible adsorption.

  Imoportant method to control adsorption is electrosorption. Here

we have electrostatic field, which is applied to the surface of the electrodes and it is immersed in an electrolyte solution.

Activated Carbon

Waste materials by-products Coal Coal-iron

-nitric acid Mechanims control

Low-cost waste materials

Ozonation of activated carbons

High toxicity for human beings and aquatic life. Biological treatment not allowed.

Activated carbons (GAC) adsorb phenols.

Ozone treatments: used to fix SOG.

Description: phenolic compounds

SOG refers to Surface Oxygen Groups on the GAC.

Improvement on the phenol adsorption: - Bonds between carbonyl groups and OH groups of phenols.

Ozone produce SOG on the GAC surface.

What is SOG?

Two different GAC (F400, AQ40) at two temperatures (25 and 100 ºC).

Four experiments with ozonation, four without it.

Compounds : phenol (P), chlorophenol (PCP) and nitrophenol (PNP).

Experimentation

Enlarging of micropores: gasification.

Microporosity blockage: SOG fixed.

Temperature as an important factor: - 25ºC: only C=0 SOG. - 100ºC : different kinds of SOG.

RESULTS AFTER OZONATION

Adsorption of P, PNP and PCP depends on: - Chemistry of adsorbates. - Porosity and surface of adsorbent. - Temperature

Ozonation decrease the adsorption capacity:

- Create more bonds with water. - This blocks the access for the phenols.

Conclusions

Carbon Nanotubes Materials Results

◦ diameter◦ Effects

Aromaticy -OH hydrogen bonds

Polymeric adsorbents

GAC capacity is higher than the polymeric one : its hydrophobic surface produces low contact with aqueous solutions.

1990: “Hypercrosslinking Technique”:

- More easily wetted. - Higher adsorption

Comparison GAC- Polymeric

Two resins:

- XAD-4: polystyrene-based. - NJ-8: hypercrossed.

Four adsorbates:

- Phenol -P-chlorophenol. - P-cresol -P-nitrophenol.

Experiment

Four steps: 1. Synthesis of macroporous polymer. 2. Chlorometylation. 3. Crosslinking. 4. Filtration and drying.

Elaboration of NJ-8

Adsorption capacity - Two times higher for NJ-8 than for XAD-4.

Physical adsorption in all the experiments. - Negative values of isosteric enthalpies.

NJ8 does not trap phenol molecules - The amount of desorbant remains

constant.

RESULTS

Natural Materials

Clay Classes Price Physical properties Improvements Clarion vs vlinoptylolite

Ciliceous, Zeolite & Biadsorbents Ciliceous

◦ Physics properties◦ Improvements

Zeolite◦ Physics properties◦ Improvements

Biadsorbents◦ Physics properties◦ improvements

Peat & biomass Peat

◦ Limitations◦ Pre-treatments

Biomass◦ Affinity with microbial species◦ Working Specifics conditions

Wastes materials Agricultural

◦ Sawdust◦ Bark

Industrial◦ Fly ash◦ Sludge◦ Red mud

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