Environmental Engineering Reference
In-Depth Information
TABLE 8.2
Effect of TDS on Partition Coeficients of Toluene and Methanol
Partition Coeficient
Methanol
a
TDS, NaCl (ppm)
Toluene
b
0
1.0
3.9 × 10
3
5800
2.1
-
11,000
2.6
-
24,000
5.2
-
58,000
31
-
100,000
49
4.0 × 10
4
a
5000 ppm, extraction with 2.0% w/v Osorb,
T
= 25°C.
b
125 ppm, extraction with 0.5% w/v Osorb,
T
= 70°C.
volatilization or partitioning into a nonmiscible nonpolar solvent. The high TDS of briny
produced water is ideal for the use of Osorb to remove dissolved organics.
Changes in hydrogen ion concentration do not lead to signiicant changes in swellable
organosilica surface chemistry or an inherent ability to bind organics. The lack of sensi-
tivity to pH is attributed to hydrophobicity and lack of acidic or basic functional groups
that can be protonated or deprotonated. At pH >9.5, the organosilica matrix will begin to
degrade due to the attack of hydroxide ions on the silica groups leading to dissolution of
the material. The hydroxide reaction is relatively slow, allowing for applications at high pH
if the contact time is limited to <8 h. The pH of the solution can have the greatest affect on
the solute ionization state, which can change the afinity for absorption into the nonpolar
Osorb matrix. For example, absorption of fatty acids is decreased by >60% at neutral pH
compared with acidic conditions owing to the deprotonation of the carboxylic acid group
above pH 4. Control of pH can thus be used to improve either the afinity or the selectivity
of the extraction of organics by Osorb.
8.2.4 Variants of Osorb for Polar Water Contaminants
Typically, Osorb is synthesized using precursors and derivatizing groups that are nonpo-
lar and lead to an oleophilic surface chemistry. For instance, surface derivatization with
trimethylchlorosilane is useful in making the material hydrophobic and oleophilic. Such
functionality is ideal in capturing hydrocarbons from produced water. On the other hand,
there are a number of polar organic species in the produced water that need to be removed
before discharge in certain regulatory environments. Some of these chemical species are
naturally occurring, such as aliphatic organic acids. Phenol and alkyl phenols are common
dissolved organics in steam-assisted gravity-drain water resulting from oil sand recovery
operations. Finally, there are many biocides (e.g., glutaraldehyde), friction reducers (e.g.,
polyacrylamide), and other production chemicals that are highly water soluble and become
part of some produced water streams. Removal of polar species is particularly challeng-
ing because of high water solubility and, in some cases, the ability to form azeotropes
with water. These properties make the separation or extraction of polar organics thermo-
dynamically dificult and the use of alternative methods such as biodigestion attractive.
Unfortunately, the high TDS (and sometimes the presence of biocides) prohibits the use of
biodigestion, limiting treatment options.
Osorb, in its standard form, has some ability to extract polar organics from water to
various degrees depending the polarity of the target (Table 8.3). The afinity of more polar
