RU2088725C1 - Method of removing oil pollution from water surface - Google Patents

Abstract

FIELD: oil pollution removal. SUBSTANCE: method consists in treating floating oil film with natural organic sorbent powder preliminarily subjected to heat treatment and cooling in closed state followed by mechanically removing oil floating conglomerate formed as result of selective adsorption. Such adsorbent, for instance, is carbonaceous mass prepared by carbonizing disintegrated and partially dried wood waste within temperature range 300-350 C in inert medium to carbonization degree 13-16%. EFFECT: reduced cost due to utilization of waste. 3 dwg, 1 tbl

Description

 The invention relates to sorption methods for cleaning a water surface from oil pollution and can be used to clean water objects from a film of accidentally spilled and other floating oil.

 The known method [1] for cleaning water surfaces with oil absorbers based on dry fibrous mass of natural organic materials (peat, bark and wood waste of various species, agricultural waste wheat and rice bran, straw and others). In raw form, such sorbents are characterized by limited oil intensity, high water content in the oil conglomerate and low buoyancy.

The most widely used [2] are modified sorbents, which are obtained according to a two-stage scheme: pyrolysis (500–600 ^o C), inert gas activation (800–100 ^o C) or chemical reagents.

 The disadvantage of such sorbents is their high energy intensity, complex production technology. High-quality carbon sorbents contain only 14-25 wt. charcoal from the feedstock, the combustible part of which consists practically of pure carbon, the resulting oil sludge during adsorption by such sorbents, as a rule, is not disposed of and accumulates in sludge collectors.

 The closest technical solution is the method of removing oil from the surface of the water by contacting it with a non-toxic pre-treated natural organic sorbent from the family of cereal powder of burnt rice [1]. As a result of 20 minutes of selective adsorption of the sorbent with oil, agglomerates of oil products are formed, which are removed from the surface of the water in the form suspended semi-solid mass mechanically.

 However, the known method has significant disadvantages. To obtain the sorbent, expensive raw materials are used. A low oil absorption rate is observed at the initial stage of contact. During low-temperature pyrolysis (NTP) of rice, a sintered coke residue (bead) of moderately dense form is formed. Therefore, to obtain a powdered sorbent, an additional grinding step is required. The issue of disposal of oil sludge also remains unresolved.

 The aim of the proposed method is to simplify and reduce the cost of cleaning water surfaces from oil pollution while maintaining a high absorption capacity of the sorbent.

This goal is achieved by the fact that in the known method of cleaning water surfaces from oil pollution, including the processing of a floating film of oil with a powder of a natural organic sorbent, previously subjected to heat treatment and cooled in a closed state, followed by mechanical removal resulting from the selective absorption of an oil floating conglomerate, according to the invention, the carbonaceous mass obtained by grinding carbonized and dried is used as an adsorbent wood waste in the temperature range 300-350 ^o C in an inert atmosphere to a degree of carbonization of 13-16%
The method is as follows.

 Example 1. For the experiments, we used wood sawdust (DO) of coniferous species of the Salavat wood processing plant, the fractional composition in the air-dry state is shown in Fig. 1.

Low-temperature carbonization was subjected to DO with analytical humidity of 1 to 2 wt. A portion of BS was loaded into a long-necked analytical flask, then closed with a tightly wound Panchenkov metal mesh to prevent air from entering the carbonation zone. The dog was installed horizontally in an MP-2U electric muffle furnace, in which the temperature was raised to a predetermined value at a speed of 3-4 ^o C / min. Temperature readings were controlled using a KSP-4C potentiometer with a thermocouple XA (chromel-alumel). The temperature of low-temperature carbonization was varied in the range of 100-600 ^o C. The firing time at a steady temperature was 60-70 min (depending on the amount of raw material taken), during which the flask with BS was periodically turned in the furnace around its axis and monitored the release of pyrolysis gases . After the experiment, the flask with DO was placed for cooling in a desiccator, then weighed with an accuracy of ± 0.01 g. The charred DO was stored in another flask with a ground stopper.

 After carbonization, sawdust retained its original form, completely and evenly charred throughout the mass. Depending on the temperature, the color of the carbonizate changed from light yellow to black.

The degree of carbonization TO was determined as:
R = 100 • C _τ / C _o (1)
where C ₀ and C _{τ are the} mass of BS before and after carbonization.

 Example 2. The absorption capacity of the sorbents was determined under conditions close to emergency situations of oil spills on the water surface. The experimental setup scheme (FIG. 2) and the experimental procedure do not fundamentally differ from the known ones [3] Weighed previously wetted with water, a plastic bucket 1 with a mesh filter with a particle size of 0.08 mm, mounted the installation by attaching a quick disconnect connection 2 and a glass 3, manipulating the equalization flask 4, set the water level above the strainer by 3 cm.

Carefully pouring a known amount of oil into the bucket, an oil film was formed on the surface of the water. Next, a known amount of the sorbent was uniformly sprayed onto the contaminated water surface until it was completely wetted. After 20 minutes of contact of the sorbent with oil, water was drained and the bucket with the filter and oil conglomerate was again weighed. Absorption capacity was calculated per 1 kg of sorbent, and water cut from the material balance. The experimental results are shown in the table. The data were obtained for the DO fraction with a size of 1≅ FR <3.2 mm at an oil and ambient temperature of 25-27 ^o C. Oil was used from the Salavat-Orsk trunk pipeline with a density of 0.87 g / cm ³ and a viscosity of 38.76 MPa • from.

It is known that during firing of lignocellulosic material in an inert medium, the ratio of which is determined by the temperature and time of the process, humidity, particle size of the material, etc. With increasing temperature of the STC, the yield of volatiles increases (the degree of carbonization), the yield of liquid hydrocarbons decreases, and thus the carbon content in coal, which makes the main contribution to the adsorption capacity of the oil scavenger. Rational is the degree of carbonization in the range of 13-16% at 300-350 ^o C firing.

In the temperature range 200-300 ^o C, the capacity of the considered oil absorbers (g) is 3.0-3.7 kg / kg (table 1). These values are significantly less than the oil intensity of known sorbents: from reed inflorescences (g 19.9), hydrophobized vermiculite (g 20.0); comparable to modified peat (g 7.5); are at the level of crushed chalk impregnated with stearic acid (g = 2.3 4.6), crushed rubber (g = 3.0), heat-treated bark, peat, fibrous materials or mixtures thereof (g≥1.8 kg / kg) [ 1] Oil intensity of sorbents 3.0 4.5 kg / kg can be considered as economically viable.

 Purification of the water surface from the oil film consists in the fact that the phase separation occurs due to the selective wettability of the capillary structure at the interface of the three phases (dispersed phase dispersed medium - capillary structure). The interaction of two phases with different hydrophilic (the ability of a material to be wetted by water), hydrophobic oleophilicity (a solid material is not wetted by water repels it, but is well wetted by hydrocarbons) by the nature of the capillary structure is accompanied by complex surface phenomena that manifest themselves through adsorption processes on a solid surface and capillary suction of liquids.

As these processes proceed, the ability of the sorbent-oil absorbent to retain on the surface of a dispersed medium (water) also changes. There is a danger of sedimentation of the resulting oil mousse to the bottom of the reservoir. The ability of a solid to stay on the surface of a liquid or at a certain level inside it (buoyancy) is determined by the ratio of two forces: the gravity of the particle and the lifting (Archimedean) force. This condition can be written as:
r _r ≅ ρ _c (2)
where ρ _r particle density (conglomerate sorbent-oil);
ρ _{c is the} density of the dispersed medium.

The data in the table show that the process of oil absorption from the water surface is accompanied by water absorption of the studied sorbents. In this case, the degree of water cut of oil sludge with an increase in the temperature of sorbent firing at NTC in comparison with air-dry BS first sharply decreases (1.74 times at 200 ^o C) and then changes slightly.

 The significant oil content in the oil conglomerate (more than 70% of the table), as well as the high initial rate of its absorption by the capillary structure of the lignocellulosic material, provide a high duration of conservation of buoyancy of the oil conglomerate (up to 15-20 days), sufficient to remove it from the water surface.

 However, when spraying an oil sorbent over a contaminated surface, part of it may be in direct contact with a dispersed medium.

Example 3. The process of water absorption of sorbents in the conditions of their complete immersion was modeled in laboratory conditions. 2-3 g of the studied sorbent were loaded into a measuring cylinder with a diameter of 30 cm and 70 ml of tap water was poured with vigorous stirring of the suspension with a glass rod. After 10 minutes, the sorbent layer height h _{0 was} measured. Then, after 1-2 days, the entire mixture, including the precipitate, was stirred again and after 1 h, the precipitate height h _{τ was} measured. The deposition rate was determined as h _τ / h _o = f (τ).

Figure 3 shows the kinetic deposition curves of up to 1.0 ° F <3.2 mm heat-treated at 250, 300 and 350 ^o C: curves A (pyrolysis 1.0 ° F <3.2 mm at 250 ^° C); B the same at 300 ^o C; C is the same at 350 ^o C.

A high degree of water absorption was shown by sorbents from BS with a low firing temperature of 100, 160, and 200 ^o C. The capillary suction of moisture here turned out to be so great that after 1.2 hours 51.0 vol. capillary structures lost buoyancy in the first sorbent, 38.5% in the second and 23.5% in the third, respectively. Almost complete sedimentation of the sorbents occurred after 17 hours.

In sorbents obtained by firing at a temperature of 300 and 350 ^o C, the loss of buoyancy in capillary structures upon their contact with a dispersed medium is only 4 6 vol. sorbent for 5 days (figure 3). Their interaction with the disperse phase system disperse medium gives the capillary structures buoyancy due to the intensive absorption of oil hydrocarbons by them with a limited suction of moisture. Sorption capacity of oil absorbers in equilibrium in a 3-phase oil-water system (capillary dispersions are 3.70 and 4.28 kg / kg (table), respectively, at temperatures of NTK 300 and 350 ^o C. When localizing spilled oil on the surface water non-toxic biodegradable sorbents can be considered as oil absorbers with acceptable oleophilic and hydrophobic characteristics, acquired by them as a result of carbonization of BS in an inert medium.

Thus, the lower limit of NTK (300 ^o C) BS is determined by the significant water absorption of the resulting sorbents, and the upper (350 ^o C) is determined by an increase in the degree of burning without a noticeable increase in oil intensity.

Example 4. With NTK DO absorbers are obtained that are inferior in oil capacity to known sorbents. However, after saturation with oil, they can be successfully used for the preparation of solid fuels. Obtaining a high-quality hydrocarbon sorbent according to a two-stage scheme (pyrolysis, activation) leads to the formation of only 14-25% of charcoal, the combustible part of which consists practically of pure carbon. The output of charcoal after preliminary firing is 86.1% (table, 300 ^o C), while the carbon content in it increases to 16-64%, which is 90% of the energy potential of wood. This is especially important for the production of solid fuels from oil sludges currently not being utilized.

It is known that in fuel briquettes a moisture content of up to 10% is allowed; oil content of 2-10 wt. (binder at 100-200 ^o C) [4] Fuel mixed with pre-burned wood burns faster than unburnt wood, less smoke and soot is formed during its combustion, it is hydrophobic during storage.

 The cost of solid fuel from wood waste by the end of the 80s on the world market was $ 15-20, and the well-known oil scavenger (Japan) based on rice husk during the Iraq-Iran conflict was $ 1,500 per 1 ton of production.

 At the meeting on the problems of liquidation of accidents at oil pipelines (Pipeline transport of oil N 10, p.23, 1994), it was noted that the cost of sorbents BTI-1. BTI-3 based on peat crumb is about 40 thousand rubles. for 1 cubic meter (in prices as of September 1, 1994).

 The determination of the elemental composition of the obtained carbonizates during low-temperature carbonization was carried out according to the method of A.M. Kunin (Technological control of gas production. M. Gostoptekhizdat, 1958, p. 37-42).

Received, wt. at 200 ^o C (C 49.86, H 6.52), at 300 ^o C (C - 62.71, H 5.83), at 400 ^o C (C 86.51, H 3.17), at 600 ^o C (C - 87.84, H 2.38).

 The elemental composition of charcoal during roasting DO for 60–70 min did not change, which indicates the complete completeness of NTC processes.

 The use of the proposed sorbent for cleaning water surfaces reduces the cost and simplifies the cleaning method, and oil floating conglomerates formed as a result of selective adsorption are used in the form of fuel briquettes, i.e. The process of cleaning water bodies from oil pollution is a waste-free technology.

Sources of information
1. CH, patent, N 669205, class. C 09 K 3/32, 1989.

 2. JP, application N 58-140311, cl. C 01 C 31/08, 1983.

 3. Michelson H.I. The use of wood processing waste in the forest complex for the needs of its own production (Hydrolysis and wood chemical industry, 1986, N8, p. 26-27).

 4. JP, application N 59-18792, cl. C 01 G 5/48, 1984.2

Claims (1)

A method of cleaning the water surface from oil pollution, comprising treating a floating film of oil with a natural organic sorbent, which is preliminarily subjected to heat treatment and cooling in a closed state, followed by mechanical removal of the oil conglomerate formed as a result of selective adsorption, characterized in that carbon is used as a sorbent mass, which is obtained by carbonization of dried and shredded waste wood at a temperature of 300-350 ^o C in an inert the second medium to the extent of charring 13-16%

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