GB2489207A

GB2489207A - Waste Treatment

Info

Publication number: GB2489207A
Application number: GB1104315.5A
Authority: GB
Inventors: Martin Osment
Original assignee: ZYSTUR Ltd
Current assignee: ZYSTUR Ltd
Priority date: 2011-03-14
Filing date: 2011-03-14
Publication date: 2012-09-26
Anticipated expiration: 2031-03-14
Also published as: GB2489207B; WO2012123736A1; GB201104315D0; EP2686479A1

Abstract

A method for the production of cellulose from a waste material 5 comprises: providing a waste material comprising organic material; homogenising the waste material; passing steam 28 through the homogenised waste material to hydrolyse at least a portion of the waste material; and retrieving cellulose from the hydrolysed waste. The hydrolysis is catalysed by the addition of urea or a urea derivative. The waste material is fed into the top 30 of a vertical reaction chamber 21 and retrieved from the base 31. The steam is introduced in to a central portion of the chamber to establish a spiral flow to stir the waste. A heat exchange system is provided for retrieving heat from the cellulose to produce steam. The waste may comprise wood, sewage or packaging materials.

Description

Waste Treatment The present invention relates to a method for the treatment of organic waste, in particular, to the production of cellulose from a waste material that comprises organic material. In addition, the present invention relates to a waste treatment apparatus for use in the method described herein.

Various techniques are known for use in the remediation or processing of waste.

Common techniques include the combustion of waste to obtain energy and may involve the recycling of useful non-combustible components of the waste. When material cannot be processed or cannot be processed further, either for practical or commercial reasons, the material can often be dumped in landfill sites. It is highly desirable to avoid the use of landfill and to, where possible, process the waste to obtain useful materials therefrom.

It is known to treat fibres produced by the thermal treatment of waste materials with pressurised steam (W004018767A1). The application discusses the steam treatment of waste between 1300 and 200°C and at a pressure of 3 to 8 Bar. This process damp cellulose fibres but does not disclose the direct treatment of a mixed waste stream.

Furthermore, EP1438459A1 discloses a method for treating diverse pulp and paper materials, including such products contained in municipal solid waste, to produce a homogeneous cellulosic product. The method involves steam treatment of the feed-stock by saturating it with steam at sufficient temperature and pressure to expand the physical and chemical structure of the materials. The vessel is then depressurised to further enhance the physical and chemical expansion of the materials. The method can be performed in the range of about 140 °C to about 160 °C, and a pressure in the range of about 275 to 450 kPa.

Accordingly, it is an object of the present invention to provide an alternative waste treatment method that tackles at least some of the problems associated with the prior art. Furthermore, there is a desire for a method that will overcome, or at least mitigate, some or all of the problems associated with the prior art or at least provide a useful or optimised alternative.

In a first aspect, the present invention provides a method for the production of cellulose from a waste material, the method comprising the steps of: providing a waste material comprising organic material; homogenising the waste material; passing steam through the homogenised waste material to hydrolyse at least a portion of the waste material; and retrieving cellulose from the hydrolysed waste; wherein the hydrolysis is catalysed by the addition of urea or a urea derivative.

The present invention will now be described further. In the following passages different aspects/embodiments of the invention are defined in more detail. Each aspect/embodiment so defined may be combined with any other aspect/embodiment or aspects/embodiments unless clearly indicated to the contrary. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature or features indicated as being preferred or advantageous.

The present inventors have discovered that the use of a urea-catalysed (or urea derivative-catalysed) hydrolysis reaction can be used to obtain useful cellulose from a waste material comprising an organic material. While some of the cellulose will be freed from the organic material and was present before processing, the present inventors have discovered that the present processing techniques further produces cellulose by decomposition and reforming of components present in the organic waste.

Advantageously the process allows for the extraction and purification of cellulose from a mixed waste so that a sterile cellulose fibre which is up to 99.99% pure can be produced.

Urea, also known as carbamide, has the chemical formula (NH2)2C0. Urea derivatives have the structural formula R1R2N-CO-NR3R4, wherein R1-R4 are independently selected from the group consisting of H and C1-C6. Urea is the most preferred catalyst although blends of urea and urea derivatives may also be used.

In addition to the urea, the hydrolysis is driven by the addition of heat and/or pressure, and/or by a reduction in the waste material size and/or a steam explosion treatment. In addition to the urea, a pH modifier may be included to help the processing proceed at a faster rate.

The method comprises providing a waste material comprising an organic material.

Advantageously, this can arise from almost any source and be in almost any form: solid, such as MS\N (Municipal Solid Waste) or industrial residues; or liquid, such as agricultural slurry. Preferably the waste comprises board, card, paper, wood, sewage and/or packaging materials. More preferably the organic material comprises one or more of cellulose, hemi-cellulose, pectin and lignin.

Firstly, the organic material is homogenised prior to introduction to the steam treatment.

"Homogenous" indicates that the waste should have one or more properties which do not vary to a great extent throughout the bulk of the waste or from batch to batch. Hence the value of the property in question does not vary to a great extent in the waste. Such properties that preferably do not vary to a great extent include the calorific value, the size of constituents, moisture content, ash content, pH, and density of the waste material.

Preferably one or more of these properties varies by 20% or less, preferably 15% or less, more preferably 10% or less. Preferably, the calorific value and the moisture content of the waste being fed to the steam treatment are relatively consistent during the process.

The consistency of the property/properties of interest may be measured by taking samples of the same weight from a given number of batches of the feedstock over a period of time.

Sampling methods known to the skilled person may be used to measure the consistency of the waste feedstock.

Various processes may be used to homogenise various properties of the waste material, for example: picking, shredding, screening, mixing and blending. Apparatus for performing these steps is well known in the art and readily available.

Picking is an Initial treatment to remove objects which are not organic, often described as the "heavy fraction" or "heavies", such as aggregates, glass, stone, concrete, metal, old tyres etc. Objects having a size in excess of 100mm or more may also be removed. The process can be carried out on a stationary surface, such as a picking floor. Alternatively or additionally, the waste may be loaded onto a moving surface such as a conveyor and passed through a picking station in which mechanical or manual picking of the material takes place. Preferably the method further comprises an initial screening step to remove non-organic components from the waste.

Shredding is a highly preferred step. In a preferred embodiment, the waste material is homogenised and size reduced. Shredding is carried out to reduce the average particle size. It can also be used to increase blending of waste from different sources. lt also makes the treatment process more effective. Preferably the homogenised waste material has a mean particle size of 20 mm or less. Most preferably the particles are of 12mm of less. The particle size is measured based on the longest particle diameter.

Preferably the step of homogenising the waste material comprises a size reduction of the waste by shredding and macerating.

The waste may be mechanically screened to select particles with size in a given range.

The given range may be from 1 mm to 20mm. The waste may be treated to at least two screening processes in succession, each ensuring that only desired fractions of particles are treated. Material removed in the screening process as being too large may be shredded to reduce its average size. Material which is classified by the screen as being of acceptable size and, where applicable, shredded material, can then be fed to the treatment vessel. The organic waste stream may also be fluidised and macerated.

Metal separation may be carried out so that relatively small metal particles such as iron or aluminium are removed from the system. They can be removed, for example by a magnetic or electromagnetic remover in a subsequent step. Metal particles removed from the system may then pass to a suitable recycling process.

Once the waste has been homogenised, and after the requisite additives (such as urea) have been introduced, steam is passed through the homogenised waste material to hydrolyse at least a portion of the waste material. Preferably the steam passes through the homogenised waste material at a temperature of from 164°C to 174°C.

More preferably the steam passes at a temperature of from 168 to 172°C. That is, the steam is provided at that temperature and the waste being treated attains the same temperature during the processing technique. A broader range of temperatures may additionally be used, such as from 80 to 330°C, depending on the material to be treated and this may be used to treat the waste before and or after the addition of the urea catalyst.

Preferably the steam is passed through the homogenised waste material at a pressure of from 5 to 10 Bar. More preferably the pressure is about 7 Bar. The pressure provides a balance to ensure good reaction conditions without undue complexity or strengthening required for the reaction vessel.

Preferably the homogenised waste material is stirred while the steam is passed through it. This ensures thorough mixing of the waste material and ensures that all of the waste material is heated and steam treated.

Following the processing technique, cellulose is retrieved from the reaction chamber.

This is preferably obtained in suspension in the water present in the reaction vessel.

Alternatively the cellulose may be obtained as a precipitated solid. The material may then be obtained as a pure product by drying and dewatering the material. Such techniques allow for the easy separation of more dense or heavy fractions that remain from the waste by filtration. Accordingly, an extremely pure cellulose material is obtained. Cyclones, dryers and other separation machines are well known in the art.

Preferably the method further comprises a step of retrieving and recycling non-organic material from the hydrolysed waste material. This material, which is often rich in metal components, may be usefully recycled. Plastics may also be similarly recovered and recycled. On one embodiment, some components from the treated material may be fed back into the process to help ensure homogeneity of the waste being treated and to ensure a maximum recovery rate for the cellulosic material.

Preferably the urea is provided in the form of urine. This is advantageously mixed with the waste before treatment and during the homogenisation step. Urine provides a cheap and readily available source of catalyst. Suitable urine may be obtained from farm animals. Where the organic waste comprises a higher percentage of Lignin, e.g. wood, addition of an additional stronger may be desirable. This can be determined by simple experiment to find the Ph necessary to decompose a sample.

Preferably further additives may be added to the homogenised waste material.

Preferred additives include buffering salts. Preferably the homogenised waste is provided at a pH of from S to 14. More preferably the pH is from 9 to 10. This alkaline condition encourages the urea-catalysed alkaline hydrolysis of the waste material to occur.

In an alternative embodiment, an acidic additive may be used in place of, or in addition to the urea. This may have a pH of from 6 to 0, more preferably from 5 to 4. The use of this alternative allows for the treatment of more diverse waste materials.

Further preferred additives include bioflavinoids. These can be used to mask the smell of certain waste products, such as sewage. Alternatively, they can be used as a detection tool to determine whether the processing system is water-tight.

Preferably the process is carried out in a batchwise manner. The present method is ideally suited to being performed in a batchwise manner. This is because the individual batches of material to be processed can be pre-prepared to ensure that they have identical balances of the components therein, For example, preferably the step of homogenising the waste material comprises supplementing the waste material to ensure that the batch has sufficient organic material. For example, steps can be taken to ensure that sufficient lignin is present, or other material, dependent upon the grade of cellulose sought, if desired, by the addition of waste wood products, or other lingo-cellulosic biomass. Suitable batches may be around 5000kg per treatment process.

Furthermore, batchwise treatment allows for long residency times. Preferably the steam is passed through the homogenised waste material for up to three hours, more preferably from one to three hours. This ensures complete hydrolysis and maximum yields. More preferably the treatment duration is for about one hour. This provides a sufficient yield without requiring too much heat energy to process the material.

Preferably before passing steam through the homogenised waste material, the homogenised waste material forms a slurry comprising from 5 to 15 litres of water per 1 kg of solid waste material, more preferably from 6 to 12 litres of water per 1 kg of solid waste material. Preferably the slurry comprises about 101 per 1 kg of solid waste. The slurry is easy to handle and/or pump and ensures that sufficient water is present to ensure full hydrolysis of the batch.

Preferably the method further comprises the addition of a dye to the waste material to enable visual confirmation of the extent of homogeneous mixing. Thus, once the dye is evenly distributed with no concentrated patches, the waste material can be considered sufficiently homogenised for treatment.

Preferably after steam treatment the hydrolysed waste material is passed through a condenser to recover heat for use in the production of the steam. This saves on the energy costs of the treatment process. In addition, the heat can be used to simply pre-warm the next batch of material to be heated, Preferably the waste material is not subjected to enzymatic treatment. Enzymatic treatment is not required to provide the substantially pure cellulose material and is preferably avoided to reduce the process complexity.

In one embodiment a portion of the hydrolysed waste material is contacted with further steam to produce ethanol. The inventors have discovered that by subjecting the hydrolysed material, before it is recovered as cellulose, to further steam treatment, particularly steam explosion by decompression, it is possible to obtain ethanol as a by-product of the present invention.

Preferably the method of the present invention is for the retrieval of substantially pure hemicellulose. The cellulosic material that is obtained may be usefully used as a building material and is especially desirable due to its high purity.

According to a second aspect of the present invention there is provided an apparatus for the hydrolysis of waste to produce cellulose, the apparatus comprising a reaction chamber arranged substantially vertically so that waste material fed into the top of the chamber and is retrieved from the base, and means for introducing steam into a central portion of the reaction chamber and establishing a spiral flow of steam within the vessel to thereby, in use, stir the waste; and a heat exchange system for retrieving heat from the cellulose for the production of steam, wherein the apparatus is configured to operate at a temperature of from 164 to 174°C and a pressure of from 5 to 10 Bar.

The present invention will now be described further with reference to the accompanying drawings, provided by way of example, in which:-Figure 1 shows a flow-chart of the process steps used in the method described herein.

Figure 2 shows an example of the preferred processing unit for use in the process described herein.

The method shown in figure 1 comprises providing a material (1) to be processed. The material (1) will comprise organic material and takes the form of a residue or waste.

The material (1) is homogenised (2) in a shredder to ensure that it contains sufficient organic matter and to ensure a mean particle size of 12mm or less. This shredded material (3) then has additives (4) added. The additives (4) include sufficient water to ensure that for every 1 kg of solid material (1) there is 101 of water present.

Furthermore, urea is added together with turmeric as a bioflavinoid and buffering salts, and an additive to act as a leak detector, such as an alcohol based aftershave. The addition of additives provides a processable batch (5) of material (1).

The batch (5) is passed into a steam sterilisation vessel and steam (6)is added so that the batch (5) is treated at 170°C for one hour at 7 Bar. This produces a hydrolysed material (7).

The hydrolysed material (7) is passed through a heat exchanger to recover heat (8) which is used to produce further steam. The hydrolysed material is then cooler and easier to handle as cooled material (9).

The cooled material (9) is then separated with a cyclone to obtain pure cellulose (11) and by-products (10) for further treatment.

Figure 2 shows an example of the treatment device (20) suitable for use in the present method. The device comprises a reaction chamber (21) for holding a batch (5) of waste material. The chamber (21) has an inlet hopper (30) which is sealed in use and forms part of the top of the chamber (21). The chamber (21) has an outlet (31) which is opened after processing for retrieval of the processed material (7). The chamber (21) has means (27) for allowing steam (28) to enter the chamber (21) so as to establish a spiral flow of steam within the chamber (21). The means (27) are preferably angled vents configured in substantially the centre of the chamber (21).

The present invention will now be explained with relation to the following worked

examples.

A batch of waste material was prepared having a total weight of 5000kg. This was formed from 500kg of shredded paper and 4500 kg of water. The waste was homogenised by sequential size reduction by shredding followed by adding a dye and then macerating to ensure that the following characteristics of the waste were homogeneous throughout: colour, texture, moisture.

The homogenous material was then sampled, a random sample of 500g being drawn off for testing. The testing was used to determine the necessary additives and catalysts to be blended: the principle of A+B=C were followed, i.e. the Arisings + the Blendings = a Constant. Sampling was normalised for standard atmospheric temperature and pressure for this type of evaluation, i.e 25C, and 1013.25 mB.

Additives and catalysts were added to the 5000kg batch in the following amounts: Reagent -Urea in an amount sufficient to be present at 1% by volume of the whole; Bio-flavinoid -turmeric was added as a dye to be sufficient in order to be visible; 10 g in the 5000L was observed to be sufficient.

Leak detector -aftershave was added in an amount of 1 OmI, this being sufficient to be detected in the mix by the operator; Table salt was added in an amount of 10 g.

Treatment was carried out by passing steam through the waste material for 1 hour. The temperature of the steam was not less than 165C and the pressure was maintained at 7 Bar.

Similar treatments were conducted with a wide variety of arisings. The strength of the acid / base used varied according to the A+B=C formula. The other additives and catalysts needed little variation.

When introducing elements of the present disclosure or the preferred embodiments(s) thereof, the articles "a", "an", "the" and "said" are intended to mean that there are one or more of the elements. The terms "comprising", "including" and having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.

Claims

Claims: 1. A method for the production of cellulose from a waste material, the method comprising the steps of: providing a waste material comprising organic material; homogenising the waste material; passing steam through the homogenised waste material to hydrolyse at least a portion of the waste material; and retrieving cellulose from the hydrolysed waste; wherein the hydrolysis is catalysed by the addition of urea or a urea derivative.
2. A method according to claim 1 wherein the waste comprises wood, sewage and/or packaging materials.
3. A method according to claim I or claim 2, wherein the organic material comprises one or more of cellulose, hemi-cellulose, pectin and lignin.
4. A method according to any of the preceding claims, wherein the steam passes through the homogenised waste material at a temperature of from 164°C to 174°C.
5. A method according to any of the preceding claims, wherein the steam is passed through the homogenised waste material at a pressure of from 5 to 10 Bar.
6. A method according to any of the preceding claims, wherein the homogenised waste is stirred while the steam is passed through it.
7. A method according to any of the preceding claims, wherein the urea is provided in the form of urine.
8. A method according to any of the preceding claims, wherein an additive is added to the homogenised waste material, the additive being selected from one or more of buffering salts and bioflavinoids.
9. A method according to any of the preceding claims, wherein the homogenised waste is provided at a pH of from 8 to 14.
10. A method according to any of the preceding claims, further comprising an initial screening step to remove non-organic components from the waste.
11. A method according to any of the preceding claims, wherein the step of homogenising the waste material comprises a size reduction of the waste by shredding and macerating.
12. A method according to any of the preceding claims, wherein the homogenised waste material has a mean particle size of 12 mm or less.
13. A method according to any of the preceding claims, wherein the process is carried out in a batchwise manner.
14. A method according to any of the preceding claims, wherein before passing steam through the homogenised waste material, the homogenised waste material forms a slurry comprising from 5 to 151 of water per 1kg of solid waste material.
15. A method according to any of the preceding claims, further comprising the addition of a dye to the waste material to enable visual confirmation of the extent of homogeneous mixing.
16. A method according to any of the preceding claims, wherein the step of homogenising the waste material comprises supplementing the waste material to ensure that the batch has sufficient organic material.
17. A method according to any of the preceding claims, wherein the hydrolysed waste material is passed through a condenser to recover heat for use in the production of the steam.
18. A method according to any of the preceding claims, wherein the hydrolysed waste is subjected to a dehydration and/or separation treatment to recover cellulose.
19. A method according to any of the preceding claims, wherein the steam is passed through the homogenised waste material for from one to three hours.
20. A method according to any of the preceding claims, wherein the waste material is not subjected to enzymatic treatment.
21. A method according to any of the preceding claims, wherein a portion of the hydrolysed waste material is contacted with further steam to produce ethanol.
22. A method according to any of the preceding claims, further comprising a step of retrieving and recycling non-organic material from the hydrolysed waste material.
23. A method according to any of the preceding claims for the retrieval of substantially pure hemicellulose.
24. An apparatus for the hydrolysis of waste to produce cellulose, the apparatus comprising a reaction chamber arranged substantially vertically so that waste material fed into the top of the chamber and is retrieved from the base, and means for introducing steam into a central portion of the reaction chamber and establishing a spiral flow of steam within the vessel to thereby, in use, stir the waste; and a heat exchange system for retrieving heat from the cellulose for the production of steam, wherein the apparatus is configured to operate at a temperature of from 164 to 174°C and a pressure of from 5 to 10 Bar.