Abstract:
A method for enhancing solvent extraction of organic wastes from contaminated waste mixtures. A contaminated waste mixture is contacted with a solvent with high driving force for solvation of water, and most preferably with a solvent which is both anhydrous and which has an appreciable affinity for solvation of water. While the solvent is in contact with the contaminated waste mixture, a portion of the organic waste is dissolved in the solvent. Then, the solvated organic waste and residual solvent is removed from the contaminated waste mixture. Solvent is recovered, preferably by distillation, and is then dehydrated, prior to repeating the cycle. The technique substantially improves the degree of removal of certain organic wastes from contaminated waste mixtures, and has been demonstrated to be particularly useful for removal of pesticides from organic waste mixtures.

Description:
FIELD OF THE INVENTION 
     This invention relates to the removal of contaminants such as pesticides from contaminated media, especially in the process of environmental remediation. 
     BACKGROUND OF THE INVENTION 
     Many industrial operations such as refineries, steel mills, chemical factories, electrical distribution, and other operations result in the formation of by-products consisting of oily liquids, or organic contaminated sludges, sediments, soils, and solids. The aforementioned oily liquids, oily sludges, and organic contaminated sludges, soils, and solids, comprise various mixtures of oils (including a multitude of oily organic compounds) and water. These oily and organic matter containing wastes have been found to be environmentally damaging and in many cases--notably when the contaminant includes pesticides or polychlorinated biphenyls (PCBs)--is dangerous to human health. The aforementioned oily and organic material containing wastes have proven difficult and expensive to separate into components. They have also proven difficult to remove the undesirable components or to render them environmentally acceptable. In consequence, in the past, the oily and organic material containing wastes were often simply impounded in ever enlarging ponds, lagoons, or dumps. Many such contaminated sites now exist, are deemed hazardous and undesirable, and Environmental Protection Agency regulations require their clean-up. Clearly, there exists a requirement for an oil and organic material waste treatment procedure which is both effective and economical. 
     A large number of techniques have been proposed, tried, and even patented to deal with the above described problem. These techniques may be divided into various types. One of the most favored technique types is incineration. Another highly favored technique type is solvent extraction. Both of these technique types have been classified by the Environmental Protection Agency as Best Available Technology (BAT). 
     The present invention consists of an improvement to solvent extraction methods. The improvement is particularly advantageous when practicing a hot solvent extraction, wherein the oily or organic material contaminated soil, sludge, or liquid is extracted with a solvent at temperatures above about 100° F., with the solvent at that temperature possessing a limited solvent capability for water. Hot solvent extraction is frequently used for final cleaning of organic material contaminated solids which have been dewatered and partially organic material extracted by the B.E.S.T.(R) solvent extraction process. The B.E.S.T. process is described in U.S. Pat. No. 3,899,419, issued to Emmanual, the disclosure of which is incorporated herein by reference. Improvements on the Emanual process are disclosed in U.S. Pat. No. 3,925,201 to Ames, U.S. Pat. No. 4,056,466 to Peters, U.S. Pat. No. 4,830,754 to Nowak et al, and U.S. Pat. No. 5,047,153 to Nowak et al, each of which is incorporated, in its entirety, by reference. 
     The B.E.S.T. process consists of: 
     1) mixing the oily waste to be treated with an adequate amount of solvent having an inverse critical solution temperature such as triethylamine at a temperature below the inverse critical solution temperature (15.5° for triethylamine). The oily material, water, and solvent will form one homogeneous liquid phase. 
     2) Separating the solid phase (if one exists) from the liquid phase which contains the oily material, water, and solvent. 
     3) Heating the liquid phase above the inverse critical solution temperature of the solvent. Two phases will form--a water phase in which a small amount of solvent is soluble--and a solvent phase in which the oily material is soluble along with a small amount of dissolved water (about 2% at 60° C. for triethylamine). 
     4) Separating the water phase by stripping and recovering the solvent. The water can be discharged. 
     5) Purifying the water phase by stripping and recovering the solvent. The water can be discharged. 
     6) Separating the oily material from the solvent phase, usually by distilling the solvent away. The oily material can be reused, incinerated, or otherwise treated. The solvent is reused. The solvent, unless specially treated, will contain the water which was dissolved in the solvent phase. 
     7) The solid can be dried to recover solvent and discharged if sufficiently cleaned of the oily or organic material contaminant. If more oily contaminant must be removed, the solid is treated again with solvent using a Hot Solvent Extraction process. However, in this solvent treatment step hot solvent (above the inverse critical solution temperature) is used since essentially all the original water has been separated from the solid and since solubility of the oily material in the solvent is enhanced at high temperature. 
     The B.E.S.T. process described above works well to achieve its purpose of dewatering and removing oily or organic material contaminant material from oily wastes. However, problems sometimes occur in the subsequent solid cleanup using the hot solvent extraction process (Step 7 above), especially with clay or clay-like or clay containing solids. Solids separated from the cold extraction (below the inverse critical solution temperature) are mixed with hot solvent (above about 100° F.) in the hot solvent extraction process (Step 7 above), especially with clay or clay-like or clay containing solids. When the solids separated from the cold extraction (below the inverse critical solution temperature) are mixed with hot solvent (above about 100° F.) in the hot solvent extraction Process, agglomeration of the solids occurs and either a sticky, doughy mass or a multitude of hard spheres about the size of small peas to marbles is formed. Mixing and handling of the solids becomes difficult, power requirements are increased as is equipment strength requirements, and extraction efficiency is reduced. Solids of similar characteristics (clay, clay-like or clay containing solids which are oil or organic material contaminated and containing water in amounts from about 1% to about 50%) produced by treatment processes other than B.E.S.T. or naturally occurring react in the manner described above when treated by the hot solvent extraction process and present the problems described above. 
     Clearly, a method is needed to prevent agglomeration of solids and to prevent loss of extraction of oily or organic containing material from solids during the aforesaid hot extraction steps of the B.E.S.T. process. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a method for controlling agglomeration of solids during hot solvent extraction of oily or organic materials from oily or organic material containing sludges, oily or organic material containing solids, and oily or organic material containing soils where the extraction solvent is a solvent possessing some but limited solvent capacity for water; the desired range of water solubility being 1/2 to 15% and a preferred range of water solubility being 1 to 5%, and the temperature of the solvent is above about 100° F. and preferably about 130° F. and where the temperature is above the inverse critical solution temperature of the solvent, if such inverse critical solution temperature exists. 
     It is a further object of the present invention to improve to lower levels the oily or organic material content of multiply extracted solids when hot solvent extracting oily or organic material containing sludges, oily or organic material containing solids, and oily or organic material containing soils with a solvent possessing some but a limited solvent capacity for water, the desired range of water solubility being 1/2 to 15%, and a preferred range of water solubility being 1 to 5%, and the solvent is at a temperature above 100° F. and preferably above 130° F. and the solvent is above the inverse critical solution temperature of the solvent, if such exists. 
     Briefly stated, one embodiment of the present invention provides a method for prevention of agglomeration of solids from oily or organic material containing oily or organic material containing solids, and oily or organic material containing soils (which may have been previously dewatered and partially deoiled by solvent extraction) and wherein said solids are now being mixed for oil or organic material with a hot extraction solvent possessing some but limited solvent hot capacity for water (range 1/2 to 15% and preferred range 1 to 5%) and the temperature is above 100° F. and preferably above 130° F., and where the temperature is above the inverse critical solution temperature of the solvent, if such exists, by using a sufficient quantity and water content of solvent such that all the water content of the solid is absorbed by the solvent and no free water is left in or on the solid, the result being a prevention of agglomeration of said solids. 
     In another embodiment, the present invention provides a method to reduce to very low levels the oily or organic material content of solids from oily or organic material containing sludges, or organic material containing solids, and oily or organic material containing soils which have been previously dewatered and partially decontaminated by solvent extraction and wherein said solids are now being mixed for further oil or organic material extraction with a solvent having some but a limited solvent capacity for water, the desired range of water solubility being 1/2 to 15% and the preferred range being 1 to 5%, and at a temperature above 100° F. and preferably above 130° F., and where the solvent is above the inverse critical solution temperature of the solvent if such inverse temperature exists, by using essentially dry solvent (i.e., solvent substantially free of water) rather than the commonly used solvent having an equilibrium content of water, regardless of whether the solids tend to agglomerate or not. 
     In yet another embodiment the present invention provides a method for controlling the rate of settling of solids form oily or organic material containing sludge, oily or organic material containing solids, and oily or organic material containing soils which have been previously dewatered and partially decontaminated by solvent extractions and wherein said solids are now, for further oil or organic material extraction, being mixed with a solvent having some but a limited solvent capacity for water and at a temperature of 100° F. or above, and where the temperature is above the inverse critical solution temperature, if such exists, and wherein the solvent is essentially dry (i.e., substantially free of water) by adding an effective amount of water to the mixture when settling of the solids is desired thus causing partial agglomeration of the solids, the degree of agglomeration being controlled by the amount of water added and the desired rate and amount of settling thereby achieved. In addition, the above described embodiments of the present invention provides a method for control of dusting of the final dried solids product by adjusting the amount of water added to the dry solvent-solids mixture during settling of the solids. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic description of a prior art production of a solid matter containing residual oily or organic material containing matter (and amine) in the dewatering of a sludge containing oil or organic material, water and solids using an amine solvent having some but limited solvent capacity for water at a final temperature above 100° F. and having an inverse critical solution temperature with water. The technology used is based on the previously referenced Emanual &#39;419, Ames &#39;201, Peters &#39;466, Nowak &#39;754, and Nowak &#39;153. An exemplar of the aforementioned amine solvents is triethylamine. 
     FIG. 2 is a schematic depiction of a prior art production of a solid matter containing a reduced content of oily or organic matter (when compared to the oily or organic matter content of the solid matter produced by the process of FIG. 1) by washing the solid matter produced in a FIG. 1 process with a recycled solvent having some but limited solvent capacity for water at 100° F. or above, and having an inverse critical solution temperature with water. With some types of solids, especially clay or clay containing or clay-like solids, agglomeration of the solids occurs leading to difficulty in mixing and handling, increased power consumption, increased equipment strength requirements, and decreased organic material extraction. 
     FIG. 3 is a schematic depiction of the present invention production of a solid matter containing a reduced content of oily or organic matter (when compared to the oily or organic matter content of the solid matter produced by the process of FIG. 1 and FIG. 2) and wherein agglomeration of the solid matter is prevented and settling of the solid matter can be controlled by utilizing dry amine solvent (such as triethylamine) for washing the solid matter rather than wet amine solvent as shown in FIG. 2 and by adding controlled amounts of water in the step of separation of solvent and solid. 
     FIG. 4 is a solubility diagram for triethylamine-water. Triethylamine is one solvent among many, of the type which can be used for the process of the present invention. The limited water solubility is shown. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention discloses, in a first embodiment, a process for controlling and preventing the agglomeration of oily or organic material containing solids particularly clay or clayey solids, which have been dewatered and partially decontaminated when said oily or organic material containing solids are treated with a solvent having some but limited solvent capacity for water in the range of 1/2 to 15% and preferably 1 to 5% and at temperatures above 100° F. and preferably above 130° F. to further reduce the oil or organic matter content. This aspect of the invention is represented at points 2 and 3 of FIG. 2 controlling and preventing agglomeration of said solids results in greater efficiency in solvent extraction of the organic compounds, a reduction in the power required for mixing, and easier handling of the solvent solid mixture. The desired result described above is achieved by using an adequate amount of solvent such that, accounting for the water content of the solvent and the absorbed and retained water content of the solid, all of the absorbed and retained water content of the solid is taken up by the solvent thus drying the solids, and rendering them non-agglomerating. The solvent can now extract oil and organic matter from the solid unimpeded by the physical barriers of agglomerated and wet solid particles. 
     Of course, if the solvent contains the equilibrium amount of water, in other words is saturated with water at the temperature of operation, no drying of the solids can take place and agglomeration is unimpeded. Most commercial grade solvents and most recycled solvents from solvent extraction operations are at or nearly saturated with water and thus cannot be used for the process of the present invention. However, many solvents of the limited water solubility type described above, can be rendered dry by simple fractional distillation and thus would be suitable for the process of the present invention. Among these solvents are the aliphatic amine solvents, particularly solvents such case triethylamine. &#34;Dry&#34; solvents usually contain no more than 0.2% water by weight. 
     As a practical matter, dry solvents are used in practicing the present invention. The amount of solvent is adjusted to achieve the prevention of agglomeration desired. The process of the present invention may be repeated multiple times in order to reduce the oil or organic matter content of the solids to as low as a level as possible, and such multiple repetitions are facilitated due to the prevention of solid agglomeration occasioned by the present invention. 
     This first embodiment of the present invention is shown schematically in FIG. 3 at point 3) where dry amine solvent 2) is added to and mixed with solid matter containing residual oil or organic matter 1). Agglomeration of the solids 1) in the mixing step 3 is prevented. The solid matter 1) could be the product of a prior practice solvent extraction, shown in FIG. 1, or could be a matter composition containing solids, oily or organic material, and water which had not previously been subjected to solvent extraction. Step 4) is a separation step where the solids and solvent are separated. Step 5) is a step where the separated solids are dried giving off solvent and water vapor mixed. The remaining process steps, except for 7), 16) and 17 represent prior practice and are not part of the present invention. Dry solvent, in this case amine, is recovered from the still after the water content of the still feed 8) and 10) is exhausted by removing the water-amine azeotrope 14). In the present invention, the dry solvent 16) is kept separate from the recovered azeotrope 14) and is reused 17) in the present invention at 2). [all triethylamine/water azeotrope is routed to the solvent decanter, then the water goes to the water stripper] The recovered azeotrope is reused in a FIG. 1 process or some other use. Such reuse is not part of the present invention. 
     Note the difference from prior practice shown schematically in FIG. 2. In the prior practice of FIG. 2, no dry solvent (amine) is used nor is any dry solvent recovered from the still. Instead, wet solvent (in this case amine) 2) is mixed with the solids 1) to form a wet solvent-solids mixture 3). Agglomeration of solids is not prevented. Note also that only azeotrope 14) is recovered from the still for reuse. Any dry solvent formed in the still is mixed with the azeotrope and lost as far as reuse as dry solvent is concerned. 
     The present invention also discloses in a second embodiment a process for control of solids settling during the solids-solvent separation step following mixing of the solids with dry solvent and for control of solids dusting in the drying step following the solids-solvent separation step. This embodiment of the present invention is shown in FIG. 3 where water 7) is added to the mixture of solids 1) and dry solvent 2) in the separation step 4). According to the practice of the present invention the solids were rendered non-agglomerating and were hot solvent extracted by mixing with dry hot solvent at step 3) of FIG. 3. Separation of these non-agglomerating solids from the hot solvent at Step 4) of FIG. 3 may now be difficult. Accordingly, water 7) is added to the separator in appropriate amounts to cause agglomeration to the extent necessary for the ease of separation desired. 
     In addition adequate amounts of water 7) can be added to the separation device 4) such that dusting of solids in the subsequent drying step 5) is held to acceptable levels. 
     EXAMPLE 1 
     A sample of soil consisting of a mixture of clay, loam, and sand and containing solids (91%), water (7.1%), and oil and grease (2.4%) and containing 20,000 ppm of polychlorinated biphenyls (PCB) was solvent extracted and the concentration of PCB remaining after each extraction step measured. Triethylamine was used as the solvent. 
     
         ______________________________________                PCBExtraction     Solvent    RemainingStep      Condition  ppm         Observation______________________________________1         Cold       1,100       mixes to     triethylamine          uniform     (&lt;60° F.)       suspension2         Hot, wet   190         solid forms     triethylamine          gooey mass     (140° F., 2%    sticks to     H.sub.2 O)             wall3         Hot, wet   83          solid forms     triethylamine          gooey mass                            sticks to                            wall4         Hot, wet   210         solid forms     triethylamine          gooey mass                            sticks to                            wall5         Hot, wet   92          solid forms     triethylamine          gooey mass                            sticks to                            wall6         Hot, wet   73-100      solid forms     triethylamine          gooey mass                            sticks to                            wall7         Hot, dry   150         gooey mass     triethylamine          breaks up to     (140° F., 0.2%  fine     H.sub.2 O)             particles8         Hot, dry   46          fine     triethylamine          particles     (140° F., 0.2%     H.sub.2 O)9         Hot, dry   34          fine     triethylamine          particles     (140° F., 0.2%     H.sub.2 O)______________________________________ 
    
     This example illustrates agglomeration of solids when hot (140° F.), wet (2% water) triethylamine is used for extraction, and how use of hot, dry triethylamine overcomes agglomeration of solids. Also illustrated is the increase in Extraction efficiency using hot, dry triethylamine rather than hot, wet triethylamine. 
     EXAMPLE 2 
     A sediment sample with a high oil and grease (2.0%), and clay content containing solids (51%), water content (47%) and 670 ppm of polychlorinated biphenyls (PCB) was solvent extracted and the concentration of PCB remaining after each extraction step measured. Triethylamine was used as the solvent. 
     
         ______________________________________Extraction   Solvent    PCB RemainingStep    Condition  ppm           Observation______________________________________1       Cold       72            mixes to   triethylamine            uniform   (&lt;60° F., 2%      suspension   H.sub.2 O)2       Hot, wet   9.1           severe   triethylamine            agglomer-   (140° F., 2%      ation large   H.sub.2 O)               spheres,                            adheres to                            walls3       Hot, wet   2.7           severe   triethylamine            agglomer-   (140° F., 2%      ation large   H.sub.2 O)               spheres,                            adheres to                            walls4       Hot, wet   1.5           similar to   triethylamine            step 3,   (140° F., 2%      solids very   H.sub.2 O)               heavy,                            doesn&#39;t want                            to stay                            suspended5       Hot, wet   1.3           No water at   triethylamine            first,   (140° F., 2%      mixing   H.sub.2 O)               difficult.                            Added water                            after 2 min                            solids                            adhere to                            wall6       Hot, wet   1.2           wet   triethylamine            triethylamin   (140° F., 2%      e. Solids   H.sub.2 O)               adhere to                            wall7       Hot, wet   0.9           wet   triethylamine            triethylamin   (140° F., 2%      e. Solids   H.sub.2 O)               adhere to                            wall8       Hot, wet   1.0           wet   triethylamine            triethylamin   (140° F., 2%      e. Solids   H.sub.2 O)               adhere to                            wall9       Hot, dry   0.5           Solid balls   triethylamine            begin to   (140° F., 0.2%    break up to   H.sub.2 O)               fine                            particles10      Hot,       0.5           All solid   drytriethylam            balls break   ine (140° F.,     up to fine   0.2% H.sub.2 O)          particles______________________________________ 
    
     This example illustrates the agglomeration of solids when using hot (140° F.), wet (2% water) triethylamine for extraction and how use of hot, dry triethylamine overcomes agglomeration of solids. Also illustrated is improvement in extraction efficiency when using hot, dry triethylamine as opposed to using hot, wet triethylamine. 
     EXAMPLE 3 
     A high water content clay sample containing 390 PPM of toxaphene (a pesticide) was solvent extracted and the concentration of toxaphene remaining after each extraction step measured. Triethylamine was used as the solvent. 
     
         ______________________________________Extraction     Solvent    ToxapheneStep      Condition  Remaining    Observation______________________________________1         Cold       240          Mixes to a     triethylamine           uniform     (&lt;60° F.)        suspension2         Hot, wet   120          Mixes to a     triethylamine           uniform     (140° F., 2%     suspension     H.sub.2 O)3         Hot, wet   200          Mixes to a     triethylamine           uniform     (140° F., 2%     suspension     H.sub.2 O)4         Hot,       9            Mixes to a     drytriethylam           uniform     ine (140° F.,    suspension     0.2% H.sub.2 O)5         Hot, dry   8            Mixes to a     triethylamine           uniform     (140° F., 0.2%   suspension     H.sub.2 O)6         Hot, dry   3            Mixes to a     triethylamine           uniform     (140° F., 0.2%   suspension     H.sub.2 O)______________________________________ 
    
     This example illustrates a dramatic improvement in extraction efficiency when using hot, dry triethylamine as opposed to using hot (140° F.), wet (2% water) triethylamine even though agglomeration is not a problem with this sample. 
     EXAMPLE 4 
     A sample of soil consisting of mixture of clay, loam and sand containing oil and grease (0.25%), water (14%), and solids (86%), and PCB (1,100 ppm) was solvent extracted, and observations were recorded after each extraction step regarding mixing, particle agglomeration, settling, and other salient factors. The content of organic matter was not recorded at each stage. Triethylamine was used as the solvent. 
     
         ______________________________________Extraction Step       Solvent Condition                       Observations______________________________________1           Cold triethylamine                       Mixes easily and       (&lt;60° F.)                       well. Settles                       cleanly but not                       very far.2           Hot, wet        Mixes easily,       triethylamine   small spheres.       (140° F. 2% H.sub.2 O)                       beginning to                       form. Settles                       quickly.3a          Hot, Dry        Spheres breaking       triethylamine   up. A good       (140° F., 0.2% H.sub.2 O)                       amount of fine                       particles formed.3b          Water added )2% of                       All fine       triethylamine   particles       volume)         immediately                       settled______________________________________ 
    
     This example illustrates agglomeration of solids when using hot (140° F.), wet (2% water) triethylamine for extraction; prevention of agglomeration by using hot, dry triethylamine; increase in settling time using hot, dry triethylamine, and use of water addition to reduce and control settling time. 
     EXAMPLE 5 
     A oil sample consisting of a mixture of clay, (19%), loam and sand containing oil and grease (0.40%), water (19%), solids (81%) and PCB (100 ppm) was solvent extracted and observations were recorded regarding mixing, particle agglomeration, settling and other salient factors. The content or organic matter was noted and recorded at each stage. Triethylamine was used as the solvent. 
     
         ______________________________________Extraction Step       Solvent Condition                      Observations______________________________________1           Cold triethylamine                      Mixes uniformly       (&lt;60° F.)                      and easily2           Hot, wet       Mixes easily       triethylamine       (140° F., 2% H.sub.2 O)3           Hot, wet       Mixes easily.       triethylamine  Spheres beginning       140° F., 2% H.sub.2 O)                      to form.4           Hot, wet       Mixes easily but       triethylamine  a little more       140° F., 2% H.sub.2 O)                      difficult than                      step 3. Settles                      quickly. Spheres                      now evident.5           Hot, wet       Mixes the same.       triethylamine  Spheres larger       140° F., 2% H.sub.2 O)6a          Hot, dry       After 10 min       triethylamine  mixing, spheres       140° F., 0.2% H.sub.2 O)                      broken down and                      fines present.                      Settles much more                      slowly. Solids                      do not adhere to                      sides.6b          Add water (2% of                      Spheres form and       triethylamine  settles       volume)        immediately.                      After 10 min                      mixing, solids                      begin to adhere                      to sides.______________________________________ 
    
     This example illustrates agglomeration of solids when using hot (140° F.), wet (2% water) triethylamine for extraction; prevention or overcoming of agglomeration when using hot, dry triethylamine; increase in settling time when using hot, dry triethylamine; use of water addition to reduce and control settling time; adherence of solids to container walls (or sides) when using hot, wet triethylamine; and use of hot, dry triethylamine to cause solids to not adhere to container walls. 
     From the foregoing it will be appreciated that, although embodiments of the invention have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims. In particular, this invention is applicable to the removal of lewisite, nerve agent, and mustard compounds from contaminated samples.