Method for water remediation

BTEX and other hydracarbons are removed from oil field and refinery waste streams by countercurrent extraction techniques. The contaminated waste water is contacted with adsorbent particles, selected to adsorb BTEX and other hydrocarbons, circulating in counter current fashion to the waste water stream.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to methods of removing unwanted impurities from 
water. In particular this invention relates to methods of removing 
unwanted hydrocarbons, especially low molecular weight monocyclic aromatic 
hydrocarbons, from water. 
2. State of the Art 
Oilfield-produced waters, remediation site waters, and refinery runoff 
streams all contain high concentrations of hydrocarbons. These petroleum 
processing derived waste waters contain particularly high concentrations 
of several classes of organic compounds due to the high water solubility 
of these classes of compounds. The low molecular weight monocyclic 
aromatic hydrocarbons, and some other structurally related non-hydrocarbon 
monocyclic aromatic compounds, for example, benzene, toluene, 
ethylbenzene, and the three isomers of xylene, styrene, and pyridine (a 
mixture of at least three of the above named components will hereinafter 
referred to as BTEX), comprise one such class of relatively highly water 
soluble hydrocarbons. However, other less soluble hydrocarbons, such as 
aliphatic hydrocarbons found in diesel and jet fuels and in gasoline, also 
pollute water and must be removed. Because of health concerns, regulators 
reduced the maximum acceptable concentration of BTEX in water to below 5 
ppmw. Consequently, producers of BTEX contaminated water need to remove or 
greatly reduce the concentrations of all these polluting hydrocarbons in 
produced aqueous runoff streams. 
Several technologies allow treatment of water to reduce the concentrations 
of BTEX and other hydrocarbons. These technologies include UV/ozone 
oxidation, UV/peroxide oxidation, high intensity UV destruction, powdered 
activated carbon adsorption coupled with biological treatment, granular 
activated carbon adsorption, air/gas stripping followed by carbon 
adsorption, various membrane processes, and supercritical water oxidation. 
While all of these technologies work acceptably well, they all require a 
fairly large physical plant to treat water produced on an industrial 
scale. For that reason, space-critical producers, for example, off shore 
oil platforms and the like, require different techniques to process the 
water they produce. A need exists for an effective water remediation 
method easily usable in space-critical areas. 
Countercurrent technology presents a candidate for a small, space-critical 
water remediation unit since countercurrent installations typically have a 
small "footprint", that is, they are installations that require little 
plant area. Conventionally, countercurrent units soften and deionize 
water. In these conventional units, a countercurrent ion exchange resin 
removes inorganic components, for example, cations such as magnesium, iron 
or calcium, or inorganic anions. However, no countercurrent adsorption 
method has been designed to remove organic components, such as BTEX, 
diesel and gasoline components. 
It would be advantageous to have a small footprint countercurrent unit that 
removes BTEX and other hydrocarbons from water to a maximum concentration 
of less than 5 ppmw. The inventor has found that countercurrent technology 
can provide a unit that removes at least 75% of the total BTEX from a 
waste water stream. The unit also provides a means to remove other, 
non-aromatic hydrocarbons from a waste water stream. 
SUMMARY OF THE INVENTION 
BTEX and other unwanted hydrocarbon components of diesel fuel and gasoline 
are removed from oil field and refinery waste streams by countercurrent 
adsorption techniques. The contaminated waste water is contacted with 
adsorbent particles, selected to adsorb BTEX and other hydrocarbons, that 
circulate counter current to the flow of the waste water stream. 
A first aspect of the invention is a method for removing BTEX from produced 
waste water streams. The waste water stream containing BTEX is contacted 
with and flows through a moving bed of adsorbent particles. The adsorbent 
particles form a bed moving counter current to the waste water flow and 
interact with BTEX to preferentially remove at least 75% of the total BTEX 
from the waste water stream. 
A second aspect of the invention is a method for removing a mixture of 
dissolved hydrocarbons that includes BTEX from waste water streams. The 
waste water stream containing the mixture of hydrocarbons contacts 
adsorbent particles that adsorb hydrocarbon compounds to remove at least 
75% of the total hydrocarbons from the waste water stream. 
Another aspect of the invention is a method of regenerating adsorbent 
particles used as adsorbents in a system having a waste water stream 
flowing with a plurality of particulate adsorbent particles moving counter 
current to the flow of the waste water. The particles are selected to 
interact with BTEX to selectively remove them from the aqueous stream. The 
particles move through a regeneration zone which contains a regenerant 
which contacts the particles and flows over the particles contacting the 
particles counter current to the direction of particle flow. The 
regenerant is selected from the group consisting of organic solvents and 
steam.

DETAILED DESCRIPTION OF THE INVENTION 
Two challenges face the designer of a countercurrent water remediation 
unit. First, a useful candidate adsorbent must extract all the unwanted 
components from an aqueous waste stream. Second, the unit must regenerate 
the candidate adsorbent. Any conventional countercurrent unit can be 
adapted for use in removing organic components from waste water streams. 
Manufacturers currently market several "countercurrent" loops. The Figure 
shows the details of one, but any of the others could be substituted. The 
critical details of the invention are a) that the adsorbent remove a 
substantial amount, preferably at least 75%, of the contaminating 
hydrocarbon from the waste water stream, b) that the method of 
regeneration remove substantially all the contaminants from the adsorbent 
particles, and c) that the particles to circulate through the system 
rather than occupy a stationary bed. A brief analysis of one 
countercurrent system will illustrate how the system works to remove 
organic components from water. 
The phrase "preferentially remove at least 75% of the total BTEX from the 
waste water stream," as used herein, means that the adsorbent system must 
remove at least 75% of all BTEX from the waste water stream. If other 
hydrocarbons are present, however much of the other hydrocarbons are 
removed, at least the 75% of BTEX present will be removed. BTEX is by its 
definition a mixture, and the three or more components that comprise any 
BTEX will form a composition ratio. After the waste water has passed 
through he moving bed of this invention, the amount of reduction in 
concentration of each of the components will form a reduction ratio. In 
this invention BTEX will not be substantially partitioned by the 
particles, that is, the reduction ratio of the component reduced the least 
to the component reduced the most will not change by more than 50% from 
its relative amount in the composition ratio. It is preferred that the 
ratio not change by more than 25%. For example, if a particular BTEX 
mixture contains benzene, toluene, paraxylene and metaxylene in a 1:1:1:1 
ratio (in dimensionless concentration), the freshened water can contain 
those same components in a reduced concentration in a ratio of 0.5: 0.5: 
0.5: 0.25, but not, for example, 0.5: 0.5: 0.5: 0.1. The 75% reduction in 
BTEX will not come about because all of several components have been 
removed, leaving only one behind that originally was only 25% of the 
original composition. 
Referring to FIG. 1, the waste water feed containing BTEX enters a 
countercurrent loop 10 in the waste water introduction line 11. The waste 
water fills the exchange zone 12, and moves downwardly through it (as 
shown in the drawing). The moving bed of adsorbent particles is stationary 
while the unwanted organic components are adsorbed by the particles. The 
freshened waste water effluent leaves the zone through the waste water 
effluent line 14. At predetermined intervals, the some portion of the 
contaminated particles leave the exchange zone through the particle 
removal line 16. The contaminant laden adsorbent particles circulate 
through the counter current loop 10 in a direction counter current to the 
direction taken by the waste water stream. The contaminant laden particles 
are then pumped through a regeneration zone 18. 
The regeneration zone 18 of the loop, the lower portion of the counter 
current loop as shown, regenerates the circulating contaminant laden 
adsorbent particles by removing the adsorbed organic material. In the 
regeneration zone the contaminant laden adsorbent particles contact a 
second fluid to remove the adsorbed BTEX. Organic solvents such as water 
miscible acetone or water immiscible light hydrocarbon, for example 
hexane, or an inorganic regeneration media, such as steam, circulate 
counter current to the adsorbent particles. The regeneration solvent, 
i.e., regenerant, enters the counter current loop through the regenerant 
line 20 and flows past the particles contacting them in countercurrent 
fashion before exiting through the regeneration solvent effluent line 22. 
The regenerated adsorbent particles leave the regeneration zone via the 
regenerated particle line 24. It is preferred that the length of the line 
24 be as short as possible before the particles are reintroduced into the 
exchange zone 12. The adsorbent particles move through the entire loop, 
adsorbing BTEX at the exchange zone, and being regenerated at the 
regeneration zone. 
The regenerant leaving the regeneration zone through line 22 goes to the 
organic holding tank 26. Although the amount of organics typically removed 
from the contaminant laden adsorbent particles is small, a two phase 
system will eventually form in the organic holding tank as the solubility 
of organics in water is exceeded. The organic layer can be removed for 
processing into refined products or other proper disposal. It is preferred 
that a positive disposal technique for utilizing the organic layer be 
used, that is, the organic layer not merely be disposed of. The 
contaminated aqueous solution formed in the holding tank can be recycled 
back, through the super-loading recirculation line 28, to the waste water 
feed to "super-load" the waste water feed with excess BTEX and other 
hydrocarbons. A small amount of contaminated water having nearly a 
saturation concentration of BTEX will always be left behind for disposal. 
However, the volume of concentrated contaminated water will be much less 
than the volume of less concentrated contaminated water that traversed 
through the exchange zone. 
The adsorbent particles are propelled through the loop, out of the exchange 
zone and on to the regeneration zone, by the adsorbent particle pumping 
means 30. The adsorbent particle pumping means moves particles around the 
counter current loop from the exchange zone to the regeneration loop. The 
pumping means comprises not only the mechanical pump but the vanes and 
associated hardware required to maintain the flow of the particles. 
Conventional disclosures such as J. Newman, "Water Demineralization 
Benefits from Continuous Ion Exchange Process," Chemical Engineering, Dec. 
18, 1967, pages 72-74, and M. E. Gilwood, "Saving Capital and Chemicals 
with Countercurrent Ion Exchange," Chemical Engineering, Dec. 18, 1967, 
pages 83-88, both references hereby incorporated in full by reference, 
disclose the details of the pumping mechanism of several different kinds 
of countercurrent systems. A full discussion of the details of these 
conventional mechanisms is beyond the scope of this disclosure. Among the 
different countercurrent schemes discussed in these articles are the 
Degremont-Cottrell continuous ion-regeneration process, the Asahi process, 
the Chemical Separations process, and the Permutit CCIX system. These 
systems, and variations of these systems, can all be used in the 
invention. For example, the flow rate of the waste water stream through 
the exchange zone is at least 12 gallons per minute per square foot. 
However, any pumping mechanism that moves fluidized particles, as opposed 
to system where the waste water flows over a stationary bed of particles, 
is intended to be encompassed by the scope of the claims. 
It should be realized that, although the particles are conventionally 
referred to as having "counter current" flow compared to the waste stream, 
in the systems identified above, the particles are generally stationary 
while the waste water flows through the particle bed to contact the 
particles. Then at preset intervals, the waste water flow momentarily 
stops while the pump moves a portion of the particles around the counter 
current loop in a direction opposite (counter current) to the direction of 
waste water flow. The particles therefore form what is defined herein as a 
"moving bed." Although the amount of particles removed from the contact 
zone is an inherent feature of the system used, and not critical for the 
operation of the invention, usually from 10 to 50% of the particles in the 
contact zone are removed and replaced by fresh particles. The advantage to 
this flow scheme is that the least processed waste water contacts the 
particles having the greatest loading of BTEX and other hydrocarbons, and 
the cleanest waste water contacts the freshest particles. 
Both the adsorbent selectivity and the adsorbent particle size must be 
correct for the system to remove unwanted organic material from a waste 
water feedstock. Organic resins that adsorb organic components or 
inorganic adsorbents that adsorb organic components comprise the family of 
candidate adsorbent particles having the correct adsorbent selectivity. 
Examples of organic adsorbents are polymeric resins, carbonaceous resins 
(essentially cooked ion exchange resins), activated charcoal, and examples 
of inorganic adsorbents are hydrophobic silicas and zeolites. The 
adsorbent particles preferably easily transit through the loop. Easy 
transit is assured by proper particle size; preferably the particles are 
between about 4 and 150 mesh sized particles, and more preferably between 
6 and 120 mesh. This selected dimension prevents particle packing in the 
counter current loop insuring that the particles will be pumped throughout 
the loop. The particles can be made of any suitable material to adsorb the 
particular combination of BTEX known to be in the water, but it is 
essential that the adsorbent particles not partition the BTEX, that is be 
preferential for adsorbing one component of BTEX while not adsorbing 
another. Furthermore, the adsorbent must adsorb at least 75 % of the BTEX 
(and other hydrocarbons if present) from the waste aqueous stream. 
In the counter current loop concept, organic pollutants load on the 
adsorbent while the adsorbent particles are simultaneously stripped and 
regenerated. The adsorbent materials must be sufficiently hydrophobic to 
adsorb organic molecules preferentially over water. Steam, inexpensive 
organic solvents or even salt solutions strip the organic molecules from 
the adsorbents. However, the strip solutions must be compatible with loop 
operation. Furthermore, it is greatly preferred that the strip solution 
not adversely affect the easy disposal of the organic layer by injection 
into oil fields, solvent refinery operations, or similar positive disposal 
techniques. Table 1 lists the adsorbents chosen for comparative study in 
the examples that follow and include activated carbons, molecular sieves, 
chromatographic-type adsorbents, carbonaceous beads and polymeric beads. 
The Examples show that the carbonaceous beads, polymeric beads and 
granulated carbon seem to be more efficient at removing the undesirable 
components from waste water streams. 
TABLE 1 
______________________________________ 
Name Description 
______________________________________ 
Darco 12-20 .RTM. 
Darco GAC.sup.1 12-20 mesh 
Darco 100-325 .RTM. 
Darco .sup.2 100-325 mesh 
Alpha 6-8 Alpha GAC.sup.1 6-8 mesh pellet form 
Ambersorb 563 .RTM. 
Rohm & Hass hydrophobic 
carbonaceous resin 
Ambersorb 572 .RTM. 
Rohm & Haas mildly hydrophobic 
carbonaceous resin 
Amberlite XAD 4 .TM. 
Rohm & Haas polymeric resin low pore 
size 
Amberlite XAD 16 .TM. 
Rohm & Haas polymeric resin higher 
pore size 
C4092 ZSM-5 Zeolite 
Porous hydrocracking catalyst 
-20 mesh 
ZSM-5 CA-1472B 
Conteka zeolite powder 
Silicalite C-2296 
Union Carbide molecular sieve 
Amorphous silica 
Baker silicic acid hydrate 
Florisil Baker mag-silicate chromatographic 
grade powder 60-100 mesh 
Filter Cake Unocal geothermal iron silicate flour 
______________________________________ 
.sup.1 GAC means Granulated Activated Carbon 
.sup.2 means Powdered Activated Carbon 
EXAMPLES 
The following examples further describe the invention. These examples 
illustrate various aspects of the invention, and should not be considered 
to limit the scope of the appended claims. 
Example 1 
In this example various adsorbents were tested for their ability to remove 
aromatics from Coalinga Nose Unit (CNU) produced water having a 
concentration of BTEX in the range of 20-30 ppm. Eight different 
adsorbents were examined for removal of BTEX and total organic carbon 
(TOC) by passing samples of CNU produced water through packed columns of 
samples of adsorbent. The eluent was tested for the presence of aromatics 
by ultra-violet (UV) absorption, and standard EPA methods 418.1 and 8020. 
CNU produced water passed through two-inch diameter columns each containing 
100 g of one of the adsorbents tested. The CNU water passed through at a 
rate of 3 gpm/ft.sup.2. The effective bed contact time was about one 
minute. The relative efficiencies at removing BTEX are shown in Table 2. 
TABLE 2 
______________________________________ 
B&T B&T 
Loading Breakthrough 
regeneration, 
Regeneration 
adsorbent 
mg @ 5 ppm, BV 
mg efficiency, % 
______________________________________ 
Darco 3138 200 3660 116 
GAC 
Alpha 3629 3 4940 136 
AC 
Amber- 5896 590 5236 89 
sorb 536 
Amber- 8598 1160 9360 109 
sorb 572 
XAD 4 1744 190 1390 80 
XAD 16 1211 150 926 76 
Silicalite 
830 55 630 76 
Filter 1076 75 716 16 
Cake 
______________________________________ 
Ambersorb 572 and 563, both carbonized ion exchange resins, removed the 
most benzene and toluene of all the adsorbents tested. These resins also 
exhibited the best breakthrough characteristics. After treating over 600 
volumes of water, only 10 ppb BTEX was observed in the eluent from the 
Ambersorb 572 column. Furthermore, at that time, the Ambersorb 572 had not 
achieved 50% loading. It was observed that Ambersorb tended to load 
toluene in preference to benzene. 
Darco and Alpha are granulated activated carbons (GAC) and are only about 
half as efficient at removing BTEX as the Ambersorb resins from the CNU 
produced water. The XAD resins (Rohm and Haas) performed well. They were 
particularly efficient at removing oil and grease (aliphatic hydrocarbons) 
from the water. 
The hydrophilic silicas, silicalite catalyst and filter cake obtained from 
the Salton Sea Geothermal operations performed poorly. 
Example 2 
In this experiment the adsorbents of the first Example were regenerated 
with acetone. 
About 2 1 of technical acetone flowed through the columns holding the 
adsorbents after the adsorption tests. The ratio of acetone to treated 
water was about 1:150. The results are shown in Table 2, columns 3 and 4. 
It can be seen that Ambersorb and GAC regenerated well, while the 
regeneration of XAD polymeric resins and silicalite was acceptable. The 
regeneration of the geothermal silicate was unacceptably difficult. 
Example 3 
This Example shows laboratory studies of the ability of different 
adsorbents to remove gasoline components. 
Distilled water containing an average of about 94 ppm of dissolved unleaded 
gasoline passes through 4 ml of a respective adsorbent contained in 1 inch 
columns. In each experiment, the adsorbents contacted 1,000 bed volumes of 
gasoline-contaminated water at high flow rates ranging from 2-3 
gpm/ft.sup.2 (effective bed contact times of 0.4-0.6 minutes). Typical 
flow rates below 2 gpm/ft.sup.2 used in carbon adsorption applications 
minimized leakage of contaminants from the adsorbent. Effluent samples 
were monitored "on-line" for UV adsorption and also for smell. After 
collection, analysis of the effluent by several different methods allowed 
determination of loading and chromatographic characteristics of the 
adsorbents. 
The synthetic adsorbents, Ambersorb 572 and XAD-4 appeared to remove 
gasoline efficiently from water. Even after treating 1,000 bed volumes of 
water at abnormally high flow rates, the effluents contained only very low 
concentrations of gasoline components. However, a small amount of methyl 
tertiary butyl ether, MTBE (octane booster), in the effluent was detected. 
Thus, it is apparent from these experiments that the synthetic adsorbents 
chromatographically separate gasoline components--BTEX and other "true" 
hydrocarbons are successfully adsorbed on the materials, while MTBE 
continuously leaks through the columns. 
Darco granular activated carbon removed gasoline less efficiently from 
water than the synthetic adsorbents. Various gasoline components quickly 
broke through the column including MTBE. 
Regeneration of the resin columns with acetone produced a significant 
gasoline "cut". A 100:1 water to solvent concentration ratio at a flow 
rate of .about.0.3 gpm/ft.sup.2 facilitated regeneration. Steam also 
regenerates the synthetic adsorbents. Thermal incineration of the adsorbed 
gasoline allows one other method to regenerate carbon adsorbents. 
Synthetic adsorbents remediated water more efficiently than GAC. For 
remediation of gasoline-contaminated waters using pump and treat systems, 
the adsorbents may be excellent alternatives to GAC application. The 
adsorbents exhibit higher loading capacities, can tolerate very high flow 
rates and can be more easily regenerated at lower energy cost than GACs. 
The adsorbents employed in a CCA loop arrangement will outperform 
fixed-bed GAC systems. 
Example 4 
This Example shows laboratory studies of the ability of different 
adsorbents to remove diesel components. 
Studies similar to those reported above for gasoline were conducted with 
dieselcontaminated water. Mixtures of diesel in water in a concentration 
of about 195 ppmw flowed through laboratory columns loaded with the 
synthetic adsorbents and activated carbon. The Darco GAC carbon was nearly 
completely loaded (saturated) with diesel after 1000 bed volumes of 
diesel-contaminated water flowed through the column containing the 
adsorbent. The loading capacity for the carbon approached 340 mg 
contaminant/g carbon. After 400 bed volumes of diesel contaminated water 
flowed through the column at high flow rate, breakthrough of diesel 
through the carbon column was excessive. 
By contrast, even after 500 bed volumes at a very high flow rate, the 
synthetic adsorbents were not saturated with diesel. Although the 
adsorbents were not saturated, they appear to load more diesel than GAC. 
Ambersorb 572 "leaked" diesel early in the test, but later reduced the 
diesel concentration from 195 ppmw to only 5 ppmw at the end of the test. 
Lower flow rates of water through the column reduce leakage considerably. 
As in the gasoline case study described above, the synthetic adsorbents 
appeared to remove diesel from water more efficiently than GAC. Diesel 
adsorbed on the columns was completely stripped employing acetone. Steam 
regenerates the synthetic adsorbents. 
Example 5 
This example shows field and laboratory adsorption studies of real 
contaminated waters. 
Applicant tested the adsorbents for complete loading and breakthrough 
employing an "on-line" field test kit at CNU. The field tests produced 
results similar to those conducted earlier in that Ambersorb 572 exhibited 
the highest loading capacity of the eight different materials tested. 
Steam regenerated the adsorbents in the laboratory. 
In small laboratory columns, Darco GAC, Ambersorb 572 and XAD-4 removed 
organic contaminants from hydrocarbon-contaminated groundwater obtained 
from the Union Oil Company of California Carson Refinery. Each adsorbent 
was compared to the others. The three adsorbents remove BTEX from the 
water similarly. Oddly, in this test, the GAC apparently remove other, as 
yet unidentified, organics more efficiently than the synthetic adsorbents. 
The resins were then regenerated as above using acetone. 
It can be seen that countercurrent exchange technology, in conjunction with 
the correct adsorbent particles and regenerant, offers convenient method 
that uses only a small amount of plant area to remove unwanted organic 
contaminants from waste water streams. 
Although this invention has been primarily described in conjunction with 
examples and by references to embodiments thereof, it is evident that the 
foregoing description will suggest many alternatives, modifications, and 
variations to those skilled in the art. Accordingly, the spirit and scope 
of the appended claims are intended to embrace within the invention all 
such alternatives, modifications, and variations.