WO1994021392A1

WO1994021392A1 - Soil treatment process

Info

Publication number: WO1994021392A1
Application number: PCT/CA1994/000164
Authority: WO
Inventors: Zdzislaw Janusz Kozlowski
Original assignee: E.R.T. Environmental Research Technology K.S.P.W. Inc.
Priority date: 1993-03-22
Filing date: 1994-03-22
Publication date: 1994-09-29
Also published as: CN1097149A; NO941014D0; NO941014L

Abstract

A process for recovering a liquid from a particulate solid which comprises mixing the solid containing the liquid with a particulate polyurethane liquid sorbent, in the presence or absence of water for a time and at a temperature sufficient for the liquid to be sorbed by the particulate liquid sorbent. Thereafter the mixture of sorbent, solid, and liquid is diluted with water, at a suitable temperature, and the sorbent containing the sorbed liquid separated from the water-solid mix. The liquid is recovered from the sorbent by a centrifugation step. The process is applicable to the recovery of liquids spilt onto the ground. It is also applicable to the recovery of oil from deposits such as the Athabasca Tar Sands.

Description

SOIL TREATMENT PROCESS

This invention relates to methods of removing a liquid from a particulate solid, such as soil. It is of particular relevance to the clean-up and recovery of inadvertently spilled liquids. It is also of considerable relevance to the recovery of hydrocarbons from soils and the like, including both clean-up procedures, and primary recovery from deposits such as the Athabasca Tar Sands.

For most spilled liquids, methods of clean-up and disposal are available, even for relatively difficult and environmentally unacceptable ones such as crude oil and PCB's. However, in order to be able to dispose of a spilled liquid, two factors are important. First, it is necessary to be able to recover the spilled liquid. Second, it is desirable to be able to carry out the recovery step in such a way that the spilled liquid can be easily, efficiently, and preferably relatively simply, separated from any agent used in the recovery step. For example, an oil spill can be cleaned up with a water-detergent mixture, but that only transforms the problem into one of disposing of an oil-water-detergent mixture. This problem is particularly acute when the spilled liquid itself is initially in an inaccessible form, such as crude oil on a beach, or fuel hydrocarbon leakages from buried storage tanks. In both of these cases, and many other spillage situations, the first problem is to devise a means whereby access can be achieved reliably to the spilt liquid, without spreading the problem further.

Very similar problems arise in recovering crude oil from the oil deposits typified by the Athabasca Tar Sands. Once the oil and "sand" have been separated, processing the crude oil to afford useful products is straight forward: what is still very difficult is the initial separation step.

In Canadian Application 2,085,951 is disclosed a new class of particulate liquid sorbents which are described therein as being particularly useful in cleaning up a wide range of spilled liquids. These liquid sorbents are primarily a particulate polyurethane product. One of the main advantages of these liquid sorbents is that separation of the absorbed liquid from them is relatively straight forward, requiring only a centrifugation step. A further advantage is that once the sorbed liquid has been removed in the centrifuge the particulate liquid sorbent can be re-used. As described, the particulate liquid sorbent is used by spreading it onto the spilt liquid, a prime example being an oil slick on water. There is no suggestion in Canada 2,085,951 that these liquid sorbents will function at all when blended into a liquid system.

This invention seeks to extend the range of usefulness of these liquid sorbents by using them to recover a liquid contained within an essentially particulate solid medium.

Thus in a first broad embodiment this invention seeks to provide a process for recovering a liquid from a particulate solid medium comprising the following steps:

(i) mixing the particulate solid containing the liquid to be recovered with an effective amount of particulate polyurethane liquid sorbent;

(ii) continuing mixing the particulate solid-liquid sorbent mix for a time sufficient to disperse the sorbent therein;

(iii) transferring the particulate solid-liquid sorbent mix to a sedimentation tank containing a volume of water;

(iv) agitating the contents of the sedimentation tank to cause the mass of polyurethane particulate liquid sorbent to rise to the surface of the mixture in the tank;

(v) recovering the floating mass of liquid sorbent, containing liquid separated from the particulate solid, from the water surface in the tank; and if desired

(vi) separating the recovered liquid from the liquid sorbent. In a second broad embodiment, especially applicable when the liquid content of the particulate solid medium is not very high, this invention seeks to provide a process for recovering a liquid from a particulate solid medium comprising the following steps:

(a) mixing the particulate solid containing the liquid to be recovered with sufficient water for a time and at a temperature adequate to provide an essentially homogenous mixture of liquid bearing particulate solid in water;

(b) adding to the homogenous mixture an effective amount of particulate polyurethane liquid sorbent;

(c) continuing mixing the particulate solid-water- liquid sorbent mix for a time sufficient to disperse the sorbent therein;

(d) transferring the particulate solid-liquid sorbent mix to a sedimentation tank containing a further volume of water;

(e) agitating the contents of the sedimentation tank to cause the mass of polyurethane particulate liquid sorbent to rise to the surface of the mixture in the tank;

(f) recovering the floating mass of liquid sorbent, containing liquid separated from the particulate solid, from the water surface in the tank; and if desired

(g) separating the recovered liquid from the liquid sorbent.

As will be discussed in more detail below, which one of these processes is used depends on the amount of liquid contained in the particulate solid to be treated. If it is high enough, the solid can be contacted with the sorbent without added water. If it is low, then it is desirable to use water in the contacting step. It is also within the concepts of this invention to subject a given mass of particulate solid to the process more than once.

As is disclosed in Canada 2,085,951, the particulate solid liquid sorbent is readily separable from the absorbed liquid, and reusable. The solid sorbent comprises a particulate polyurethane liquid sorbent prepared by a process comprising :

(i) reacting together at a temperature of from 180° to 200°, for a time of less than 10 minutes, a prepolymer of the formula A:

^NC0

^{NC0 A}

^NC0

with a prepolymer of the general formula B:

in the presence of a lower alkyl ester of the general formula C:

RjCOOR₄ C

in which: n represents 1,2, or 3;

R-_L represents a lower alkyl group having 1 to 6 carbon atoms;

R₂ represents hydrogen or a lower alkyl group having 1 to 4 carbon atoms; and

R₃ and R₄ represent a lower alkyl group having

1 to 3 carbon atoms, and when R₂ is other than hydrogen, it is in the meta or para position relative to the -NH- linkage; and wherein the weight ratio of prepolymer of formula A to prepolymer of formula B is about 3:1, and the reaction mixture contains from 22% to 25% by weight of ester solvent;

(ii) cooling the thus formed polymer;

4

SUBSTITUTESHEET (iii) adding thereto an alcoholic medium chosen from the group consisting of:

(a) ethanol; or

(b) a mixture of ethanol, methanol, and water containing 85% by weight ethanol, up to 15% by weight methanol, remainder to 100% water, or

(c) ethanol containing from 4% to 6% by weight isopropanol;

(iv) adding thereto with mixing hexamethylene tetramine,

(v) allowing the spontaneous reaction to proceed thereafter during which a temperature in the range of 55° to 65° is developed, and during which at least some of both the lower alkyl ester solvent, the alcoholic medium, and any water present, evaporate and

(vi) recovering the particulate polyurethane product.

Preferably microspheres consisting of aluminosilicate shells containing gas having a diameter of from 10 um to 100 um are added to the reaction mixture between steps (ii) and (iv) .

Preferably: (i) the prepolymer has the formula A^

CH₂

CH₃CH₂ C A_*.

CH₂

(ii) the prepolymer B has the formula Bj:

5

SUBSTITUTESHEET and (iii) the lower alkyl ester solvent is ethyl acetate, and the alcoholic medium is ethanol.

These particulate liquid sorbents are more particularly described in Canadian Application 2,085,951. Hereafter, they will be referred to as RPA.

The time and temperature required for the dry mixing of step (i) and the wet mixing of steps (a) and (c) to a degree depend on the liquid being recovered. Generally it has been found that a mixing time of less than 30 minutes is sufficient. The temperature is much more dependant on the physical properties of the liquid being recovered: it must be high enough for the liquid to be fluid enough to be absorbed by the RPA. In recovering hydrocarbons such as fuel oil, gasoline, and diesel fuel from soil a temperature of from 5°C to 15°C has been found effective. In separating crude oil from an oil sand a temperature of from about 30°C to about 40°C has been found to be effective.

The amount of RPA added in the dry mixing of step (i) , and in step (b) will depend on the amount of liquid to be recovered, as the capacity of the RPA is not infinite. Generally, for particulate solids that appear to be "dry" an amount of RPA in the range of 0.75% to 20%, by weight based on the amount of solid to be treated, has been found sufficient. In most applications an amount of RPA in the range of from 2% to 15% appears to be sufficient. However it is to be noted that the amount of RPA is not critical, as all of the liquid does not have to be recovered in one pass. A particulate solid containing a high amount of liquid, for example sand recovered from around a ruptured buried storage tank, can be treated first with dry RPA, and then reprocessed with wet RPA.

During the initial mixing steps the temperature of the mixture desirably is maintained relatively constant. The water in the sedimentation tank conveniently is at a temperature in the range of from 5°C to 40°C, again depending to a large degree on the properties of the liquid being recovered. The amount of agitation used in the sedimentation tank is enough to free the RPA from the particulate solids mass. It has been found that air and water pressure agitation is effective. The mass of RPA together with the absorbed liquid then floats to the top of the mixture in the sedimentation tank. The RPA is separated from the water by any convenient means, such as a porous net or gravity separation, to provide a reasonably water free mass of RPA.

The recovered liquid is separated from the RPA by a centrifugation step, as is more fully described in Canada 2,2085,951. If necessary, a diluent can be added to the RPA to aid in the centrifugation step. For example, in treating tar sand materials, it is desirable to add a light hydrocarbon such as naphtha. The RPA freed from recovered liquid can be returned to the process for re-use.

If necessary, the solid containing the liquid to be recovered can be comminuted to a suitable particle size before treatment. Such a step is usually necessary with many tar sands.

In the preceding discussion, an essentially batch-wise procedure is described. However, this invention is not so limited, and can be operated as a continuous process as is well understood by those of skill in this art.

The invention will now be described by way of the following Examples.

Example 1: Spill Simulation in Soil.

A plexiglass reservoir approximately 45.7 cm square and 61 cm deep was provided with a simulated soil comprising a layer of gravel, at the bottom, with a compacted layer of humid sand from 29 to 43 cm thick on top; 18.5 kg of gravel and 170.6 kg of humid sand were used. To this simulated soil 17 litres of crude petroleum were added slowly over a period of several days. A was then taken and an analysis of the contaminated soil made to determine hydrocarbon content. Three sets of tests were then carried out on the contaminated soil. The results are summarised in the Table.

Test #1: performed on the top layer of soil. Test #2: performed on the soil from Test #1. Test #3: performed on the bottom layer of soil.

TEST DATA

PARAMETER #1 #2 #3

Concentration of HC, 21,000 1,100 2,300 ppm

Wt. of soil, kg 71.5 60.7

RPA added, g. 1,832 (a) 2,909(b) 2,836(c) Water added,litres. 12.5 12.5 12.0

Mixing time, mins. 45 28 31

HC in feed water,ppm. below 0.5 below 0.5

HC in water after 150 9.7 5.8 test,ppm.

Oil recovered,litres. 2.25 1.75 0.20

RPA recovered,g. (d) 1,944 3,456 2,328

HC left in soil,ppm. 1,100 660 250

Notes:

HC: hydrocarbons.

(a) Reused RPA.

(b) Mixed fresh and reused RPA, ratio about 2:1 by weight.

(c) Fresh RPA.

(d) RPA recovered from centrifuge somewhat humid and dark in colour.

In addition to the soil testing, a total hydrocarbon balance was made as follows (the amounts are in litres) (i)pumped from the reservoir surface .... 11.5 (ii) Recovered from top layer of soil- in first wash .... 2.25 in second wash .... 1.75 (iii) Recovered from bottom layer .... 0.20 (iv) Remaining in contaminated soil in reservoir .... 1.3

The water used in the recovery process was also analysed for hydrocarbon content. The effluent water from the washing steps contains from 5.8 to 150 ppm hydrocarbons.

Example 2: Spill Simulation in Sand.

This example simulates a common situation, namely the consequences of a ruptured fuel storage tank. Such tanks are normally sunk into the ground, and bedded in sand on installation. A reservoir as described in Example 1 was set up, and after all of the hydrocarbon had been added contained 17 litres of diesel fuel, and 159.3 kg of humid sand over 18.6 kg of gravel. The sand was sampled and treated using the same procedure as in Example 1.

Before being subjected to the recovery procedure, the sand contained 15,000 ppm of diesel fuel. After treatment with 5% by weight RPA, the sand contained less than 100 ppm diesel fuel. The same result was obtained when using 2% by weight RPA

Example 3: Oil Recovery from Tar Sands.

A number of oil recovery experiments were carried out on a number of samples of tar sands solids. These were essentially rocky materials, which had to be powdered before treatment. Depending on the amount of hydrocarbon, the amount of water used in the mixing step ranged from 30% to 50% by weight. Also depending on the amount of hydrocarbon, the amount of RPA used ranged from 0.75% to 15% by weight of the solids being treated. Recoveries of crude oil in a single pass process ranged from 93% to 96%. From these test results it can be seen that quite surprisingly, in addition to acting as an efficient sorbent when placed onto a spilt liquid, the RPA described in Canada 2,085,951 also functions as an efficient sorbent in a situation where it is exposed to a much larger amount of water than the material being recovered. It is not known why the sorbent should apparently selectively sorb the nonaqueous liquid in preference to becoming water logged.

Claims

I CLAIM :

1. A process for recovering a liquid from a particulate solid medium comprising the following steps:

(iv) agitating the contents of the sedimentation tank to cause the mass of polyurethane particulate liquid sorbent to rise to the surface of the mixture in the tank; and

(v) recovering the floating mass of liquid sorbent, containing liquid separated from the particulate solid, from the water surface in the tank; wherein the solid sorbent comprises a particulate polyurethane liquid sorbent prepared by a process comprising :

Ri- ^■C

11

SUBSTITUTESHEET with a prepolymer of the general formula B:

in the presence of a lower alkyl ester of the general formula C:

R_xCOOR₄ C

in which: n represents 1,2, or 3;

R_j represents a lower alkyl group having 1 to 6 carbon atoms;

R₂ represents hydrogen or a lower alkyl group having 1 to 4 carbon atoms; and

R₃ and R₄ represent a lower alkyl group having

(ii) cooling the thus formed polymer;

(iii) adding thereto an alcoholic medium chosen from the group consisting of:

(a) ethanol; or

(c) ethanol containing from 4% to 6% by weight isopropanol;

(iv) adding thereto with mixing hexamethylene tetramine,

(v) allowing the spontaneous reaction to proceed thereafter during which a temperature in the range of 55° to 65° is developed, and during which at least some of both the lower

12

SUBSTITUTESHEET alkyl ester solvent, the alcoholic medium, and any water present, evaporate and

(vi) recovering the particulate polyurethane product.

2. A process according to Claim 1 wherein microspheres consisting of aluminosilicate shells containing gas having a diameter of from 10 um to 100 um are added to the reaction mixture between steps (ii) and (iv) .

3. A process according to Claim 1 wherein

(i) the prepolymer has the formula R- :

CH₃CH₂

(ii) the prepolymer B has the formula B_{1 :}

and (iii) the lower alkyl ester solvent is ethyl acetate, and the alcoholic medium is ethanol.

4. A process according to Claim 1 wherein in each of steps (i) , and (ii) the mixture is maintained at a temperature in the range of from 5°C to 40°C.

5. A process according to Claim 1 wherein from 0.75% to 20% by weight of liquid sorbent is used in step (i) , based on the weight of liquid containing particulate solid.

13 SUBSTITUTESHEET

6. A process according to Claim 5 wherein the amount of liquid sorbent is from 1% to 15% by weight.

7. A process according to Claim 1 operated as a batchwise process.

8. A process according to Claim 1 operated as a continuous process .

9. A process according to Claim 1 further including: (vi) separating the recovered liquid from the liquid sorbent .

10. A process for recovering a liquid from a particulate solid medium comprising the following steps:

(f) recovering the floating mass of liquid sorbent, containing liquid separated from the particulate solid, from the water surface in the tank; and wherein the solid sorbent comprises a particulate polyurethane liquid sorbent prepared by a process comprising :

(i) . reacting together at a temperature of from 180° to 200°, for a time of less than 10 minutes, a prepolymer of the formula A: ⁽CH₂ ⁾ _n OCONH

R. C (CH₂)

(CH₂)_n OCONH O

with a prepolymer of the general formula B:

in the presence of a lower alkyl ester of the general formula C:

R_αCOOR₄ C in which: n represents 1,2, or 3;

Ri represents a lower alkyl group having 1 to 6 carbon atoms;

R₂ represents hydrogen or a lower alkyl group having 1 to 4 carbon atoms; and

R₃ and R₄ represent a lower alkyl group having

(ii) cooling the thus formed polymer;

(iii) adding thereto an alcoholic medium chosen from the group consisting of:

(a) ethanol; or

(c) ethanol containing from 4% to 6% by weight isopropanol;

¹⁵ SUBSTITUTE SHEET (iv) adding thereto with mixing hexamethylene tetramine,

(vi) recovering the particulate polyurethane product.

11. A process according to Claim 10 wherein microspheres consisting of aluminosilicate shells containing gas having a diameter of from 10 um to 100 um are added to the reaction mixture between steps (ii) and (iv) .

12 A process according to Claim 10 wherein

(i) the prepolymer has the formula A^

(ii) the prepolymer B has the formula B_1:

13. A process according to Claim 10 wherein in each of steps (a) , and (c) the mixture is maintained at a temperature in the range of from 5°C to 40°C.

16

SUBSTITUTESHEET

14. A process according to Claim 10 wherein from 0.75% to 20% by weight of liquid sorbent is used in step (b) , based on the weight of liquid containing particulate solid.

15. A process according to Claim 14 wherein the amount of liquid sorbent is from 1% to 15% by weight.

16. A process according to Claim 10 operated as a batchwise process.

17. A process according to Claim 10 operated as a continuous process.

18. A process according to Claim 10 further including: (g) separating the recovered liquid from the liquid sorbent.