WO1993015833A1

WO1993015833A1 - Oil-absorbent fiber pellets

Info

Publication number: WO1993015833A1
Application number: PCT/NO1993/000020
Authority: WO
Inventors: Arne Nicolai Soteland; Einar BØHMER
Original assignee: COGITO CONSULTING AS
Current assignee: COGITO CONSULTING AS
Priority date: 1992-02-07
Filing date: 1993-02-03
Publication date: 1993-08-19
Anticipated expiration: 1994-08-07
Also published as: AU3576693A; NO920499D0; CA2127252A1; NO175804B; NO175804C; NO920499L

Abstract

An oil absorbent material having a rounded, spherical shape, consists of thermo-mechanical pulp or another high-yield pulp containing at least 2 % by weight, based on the weight of the wood, of the native, extractive components of the wood, which components are utilized to make the material hydrophobic and oil-absorbing by artificially curing the material at a temperature above 100 °C in less than 5 min.

Description

OIL-ABSORBENT FIBER PELLETS.

By the use and transport of different oil products it is 5 almost impossible to avoid some contamination of the envi¬ ronment under different conditions. Small amounts of oil from land-based plants can normally be handled easily and efficiently, but the situation grows much worse when for instance, ocean-going tankers run aground with big leakages

10 as a consequence. Such incidents have previously occurred both in Alaska and on the coast of Britanny, France and in addition to the enormous costs involved in cleaning up the beaches and the shorelines, said incidents can also result in detrimental long-term effects on the vegetation and the

15 life of marine animals and birds.

It is obvious from the serious consequences that there is a need for more efficient tools to handle oil spills at open sea, and preferably before the oil products have had the

20 time to spread over large areas. Today, lenses are mostly used to keep the oil within a certain area, but they have their limitations when the wind is strong and the sea is heavy, that is, weather conditions when ships are most likely to be wrecked.

25

Chemicals with surface-active agents added, are also used and they will help to dissolve or disperse the oil in the water. Among the experts there are mixed opinions about the merits of these products since they are organic in charac-

30 ter and may have toxic effects. In order to have a signifi¬ cant effect great quantities will also be needed, and the

<_. weather conditions are sometimes so extreme that the chemi¬ cals cannot be distributed on the ocean surface. All these limitations indicate that this is not a completely satiε-

35 factory solution to the the problem considering the requirements regarding environmental control. There are also known fiber products which may be used to absorb oil and similar products, and such products are also sold on a commercial scale. According to the government authority, responsible for these matters in Norway, these products mostly consist of bark, but they have the drawback that they cannot be used in open sea, but only in the beach zone. A difficulty with bark is also that it contains a significant amount of water-soluble substances, and also under mechanical stress they will break down to very small particles, being difficult to collect without very expen¬ sive procedures. The bark products can be mechanically strengthened by being compressed into briquets, but this will reduce the porosity of the material and hence also the amount of oil being absorbed.

Products of unbleached and bleached cellulose (chemical pulps) have also been suggested for this purpose. These products are mostly hydrophylic by nature, and therefore it has been necessary to add significant amounts of chemicals like wax emulsions, resins, alum etc. in order to make the product hydrophobic. This is absolutely necessary if the product is intended for use in open sea. Such products are mentioned in NO Patent No. 117.169, and the application of organic materials like saw dust with a particle size pre- ferably from 0,25 to 2 mm is described therein. In this case chemicals like methyl-trichloro-silane are used in order to achieve a hydrophobic effect, and no attempt is made to utilize the chemicals which is present in the wood itself.

Similar products are described in NO Patent No. 118.786, also based upon organic materials such as saw dust. In this case the material is treated with paraffin-like hydrocar¬ bons and/or animal or vegetable oils with an emulsifier. There is no mentioning of the use of the chemicals in the wood, nor is it described how to make particles with a suitable size and open capillaries. Fiber products are also described in NO Patent No. 137.688. Rosin sizing is here used in order to make the particles suitable for oil absorption. In the main claim it is stated that all types of pulp may be used, but in most examples kraft pulp has been used. This is a pulp manufactured by means of an alkaline process which will efficiently remove the chemicals in the wood which are utilized in accordance with the present invention. Accordingly, the idea that the chemicals in the wood might be used to attain a hydrophobic effect, has apparently not occurred to the inventors of NO patent No. 137.688. It should also be added that the density of the product are given to be in the range of 3,2 - 24 kg/m³, and this is much lower than the density of the particles made in accordance with the present inven- tion.

The problem may be expressed as how to make porous partic¬ les with sufficient strength not to disentegrate in open sea under the mechanical strains involved and with a hydro- phobic sur-face which will permit only a minimum of water to be absorbed. It should be added that it is virtually impossible to prevent water from penetrating in the vapour phase. This amount will be a function of the water tempera¬ ture, its vapour pressure and also the time the particles are in contact with the water.

In US Patent No. 4.343.680 it has been disclosed that it is possible to use wood species with a high content of extrac¬ tives such as pine, to achieve a material which is hydro- phobic, but oil-absorbing. In this case a limit of 3,0 % by weight based on the weight of the wood extractable with ether has been mentioned, and it has also been specifically mentioned that a thermo-mechanical pulp of pine might be used. It is true that in this patent the chemicals in the wood are utilized, but the examples also indicated that it has been necessary to treat the material at 105°C for 16 hours in order to get the desired effect. In this case the material is then fed to a fiberizer in order to separate the material into single fibers, and then packed in bags or pressed into bales. Accordingly, there is no comments about how to make spherical particles which are hydrophobic and oleophyllic in a single process stage with a process time in the order of minutes, and where the pulp deliberately is treated with the goal to produce particles with a suitable size.

From the technology described in US Patent No. 4.343.680 it must be regarded as surprising that it is possible to make hydrophobic and oleophylic fiber pellets in one integrated process stage, with wood chips as raw material and with a heat treatment of only a few minutes at high temperature. It is also surprising that it is possible to make pellets which are approximately spherical in form by letting the particles rotate during the drying process. Rotating driers are well known from the cement and fish industry, and they are normally arranged with a certain inclination to convey the particles by gravity from the inlet to the outlet .

In real life there will always be variations in the extrac¬ tive content of the trees, for instance between the outer layers of the tree and the core. Such variations will also normally occur from summer to winter. To compensate for these variations, which may give undesirable quality varia¬ tions in the product, it may be necessary to add small amounts of chemicals contributing to the hydrophobic effects. It should be clearly understood, however, that this amount should be much smaller than the rosin content present in the wood.

The simplest process will be to treat wood chips rich in extractives in modern refiners without use of chemicals , but at higher temperatures. In such refiners the tempera¬ tures will frequently be between 115° and 130°C, but tempe¬ ratures down to about 100° may be accepted during the defi- bration process. This thermo-mechanical pulp will be dried at higher temperature while rotating, and the pulp is natu¬ rally acidified by the organic acids liberated during the drying process and the subsequent storage. It will however, also be possible to make a satisfactory product by impreg¬ nating the chips with chemicals such as alkali and/or sul- fite. The pulp will in this case be called CTMP (Chemi- Thermo-Mechanical-Pulp) , and the advantage of this process is that the defibration will be more complete and the average fiber length greater. In order to get a hydrophobic surface in this case, it is essential that the pulp is not washed, and further that it is acidified with strong acids such as sulphuric acid or hydrochloric acid before the drying process is initiated.

Example 1:

An assortment of Norwegian pine (Pinus Silvestris) with an outer diameter of 20 cm and with an extractive content of 2,6% based upon the wood weight as determined with dichloro methane, was chipped in the normal way before making thermo mechanical pulp being a modern high yield pulp. The chips were moistened with steam and run through double disc refiners in two stages to a Canadian Freeness of about 150. This is a measure of the particle size of the pulp and is mainly a function of the energy consumption. The pulp left the refiner at a consistency of about 20%, and was then transferred to a cement mixer, where hot air was blown into the mixer while rotating. The main part of the pulp was converted to spherical particles of varying sizes, and after complete drying and storage at a somewhat higher temperature for some days, the particles had developed a hydrophobic surface enabling them to float on water for a couple of days. At the same time the particles willingly absorbed oil in an amount corresponding to several times the weight of the fibers. Example 2.

A load of pine from Zambia (Pinus Kesiya) was treated in the same way as described in Example 1, but the Freeness was not reduced to more than 300 CSF. Under these condi- tions it was more difficult to form the fibers into partic¬ les, and it was also more difficult to make the surface completely hydrophobic. The reason is probably the fact that tropical pine species contain less extractives than the pines growing in the temperate areas. It was also clear that the ability to form spherical particles during drying, is related to the specific surface of the fibers, and this is increased on increasing the energy consumption which also will reduce the Freeness level.

Example 3.

A load of Norwegian pine like the wood used in Example l was impregnated with 1% NaOH and 3% sodium sulfite. The impregnated chips were treated in the refiner at 115°C in two stages as mentioned in a preceding paragraph to a Freeness of 200 CSF. The solid content from the refiners was about 22%. The pulp was dried at 110"C to a solid content of 10% under slow rotation. The pulp was then stored for a few days at a slightly elevated temperature. The greater part of the particles were spherical in shape, and all of them developed a hydrophobic surface.

It should be emphasized that the curing at elevated tempe¬ rature after the drying was required due to the shortcoming of the laboratory drying equipment. On an industrial scale an optimum air temperature and drying conditions may be selected, and the after-curing will then not be necessary.

It should also be emphasized that the present invention will not be limited to the examples which are only meant to illustrate how the product can be made. On an industrial scale continuous, rotating driers will obviously be used, such as the ones used in the cement industry, but with other temperatures, because the fibers are combustible. To avoid overheating the moist material might be dried in a co-current manner with high temperature drying air, even if this is not the most effective procedure from an energy point of view. It will, however, be possible and efficient to use temperatures much higher than 100°C.

Claims

P a t e n t c l a i m s

1. Oil absorbent material of wood fibers converted to thermomechanical pulp or another high-yield pulp in which the extractive components of the wood is utilized to make the material hydrophobic, c h a r a c t e r i z e d i n particles mainly greater than 6 mm i diameter and with rounded, spherical shapes, artificially cured with a residence time less than 5 mi¬ nutes at a temperature above 100°C, and where the content of extractives in the wood is greater than 2,0 % by weight based on the weight of the wood and in which the fiber length of the wood material is greater than 2,5 mm.

2. Product according to claim 1, c h a r a c t e r i z e d i n a supplement of the wood rosins or extractives with an addition of wax emulsions or other hydrophobic-making agents with up to 25% of the amount of extractives in the wood.

3. Process for the manufacture of a product in accordance with claim 1 and 2, c h a r a c t e r i z e d i n a high-yield pulp with a freeness less than 300 CSF, optionally adjusted to a pH- value less than 5, and dried in an apparatus giving the particles a rotating motion during the drying process at a temperature below the break-down temperature of the fibers.

4. Process according to claim 3, c h a r a c t e r i z e d i n the drying of the pulp to 10% moisture content at a temperature in the range 105 - 150°C.

5. Process according to claim 3 and 4, c h a r a c t e r i z e d i n refining the pulp to a Freeness below CSF 300 and adjusting the same to a dry content between 15 and 25 % before drying the pulp.

6. Process according to claims 3-5, c h a r a c t e r i z e d i n a second drying procedure for the particles with an undesirable particle size in the presence of fresh, previously undried material.