WO2013002742A1

WO2013002742A1 - Method for preparing powdered cellulose

Info

Publication number: WO2013002742A1
Application number: PCT/SK2011/000014
Authority: WO
Inventors: Ján ĎURIAN; Peter MELNÍK; Ján HUBAL'
Original assignee: Bukocel, A.S.
Priority date: 2011-06-27
Filing date: 2011-06-27
Publication date: 2013-01-03

Abstract

The present invention relates to a new method for preparing powdered cellulose. An innovation lies in complete or partial substitution of paper grade cellulose or dissolving grade cellulose by waste lignin-cellulosed materials rising from known processes of pulp and paper production and those contained in wastepaper. While subjecting to acid hydrolysis or alkaline degradation processes in reduction of cellulose chain the requested degree of polymerization is achieved. The method of invention describes a possibility of adjustment of raw materials by alkaline mediums actuation. The powdered cellulose obtained has many industrial applications - wide scale of using in construction chemistry, petrochemical and food industry.

Description

METHOD FOR PREPARING POWDERED CELLULOSE

Technical Field

The present invention relates to a new method for preparing powdered cellulose. Prior State of Art

The cellulose is a natural polymer derived from D-glucose units, which are fused through β(1-→4) glycosidic bonds, and which confer to it a linear structure. Many properties of cellulose depend on the chain length, i.e., on the number of glucose molecules forming the polymer. Said length is also known as the degree of polymerization, sometimes abbreviated as DP (Degree of Polymerization). The cellulose from wood pulp generally has a DP comprised between 300 and 1700; cotton and other plant fibers as well as celluloses of a bacterial origin have chain lengths comprised between 800 and 10000 units, which corresponds to a DP between 800 and 10000.

Powdered cellulose, also known as PC, is a product obtained from cellulose, primarily by mechanical procedures as grinding is. PC is purified, partially depolymerized cellulose which is presented in white (white to grey color scale), odorless, tasteless powder.

Various methods for obtaining powdered cellulose of different grades have been described in the state of art. In all these methods, the cellulose chains are partially degraded, enzymatically or thermally, or by means of using chemical reagents. The amorphous portions of the cellulose, which are dissolved and removed, are hydrolyzed with these treatments.

A treatment with acid hydrolysis for obtaining powdered cellulose is described in document RU 2 050 362 CI, where raw material consisting cellulose is used in hydrolysis process with using hydrochloric acid, sulphuric acid or alcohol.

Document GB 799 715 describes method for preparing powdered cellulose where as a raw material a waste from paper production is used - such as waste water or lixivium. Also a waste from different paper production levels as well as waste from washing raw cellulose and from pulp bleaching process.

A process for obtaining microcrystalline cellulose where raw materials as wood, cotton linter, waste from textile industry or cotton are subjected to hydrolysis with nitric acid, is described in document RU 2 141 484 CI.

Document GB 2 285 979 A describes a standard process of powdered cellulose production where sheets of cellulose are cut, loaded subsequently into reactor where being heated and blended and finally mineral acid is added. After hydrolysis the product is being filtered. A method for obtaining microcrystalline cellulose is described in US patent US 2005/0145351 Al . Here is presented a method with using hydrolysis pulp while sufficient amount of active oxygen compound is used and after the microcrystalline cellulose is being isolated.

In US patent nr. US 2006/0020126 Al is described method for preparing microcrystalline cellulose where cellulose material is being subjected to elevated temperature and pressure with using an oxygen reagent and thus a reduction of degree of polymerization is achieved. As oxygen compound is hydrogen peroxide being used.

In patent US 2004/0074615 is described method for preparing microcrystalline cellulose, which comprises alkaline hydrolysis process, washing cellulose, subsequently process of acid hydrolysis and next step of washing. For alkaline hydrolysis is lye being used, for acid hydrolysis is acid sulphuric chosen.

In document JP 6316535 is described a method of preparing material, which is a white powdered cellulose, produced with acid or alkaline hydrolysis process.

A subject of document EP 1 634 908 Al is powdered cellulose, produced by hydrolysis process and its using in tablets production. Hydrolysis might be acid, alkaline or oxidative or might come out from hydrothermal degradation process.

In document RU 2 1 19 986 CI is described a method for preparing powdered cellulose wile wood pulp is being subjected to hydrolysis in mineral acid, as acid hydrochloric or nitric is. Final product is bleached with hydrogen peroxide.

A subject of document US 3 954 727 is method of preparing microcrystalline cellulose with means of acid hydrolysis with acid. Primarily acid sulphuric is being used.

In document US 2 978 446 is described treatment with acid, in which purified wood pulp containing amorphous and crystalline forms of cellulose are being used as started materials. These are hydrolyzed with 2,5 N hydrochloric acid at temperature of no less than 105°C.

In document CS is described method of preparing microcrystalline cellulose by acid heterogenic hydrolysis of fiber pulp with mineral acid using, where mostly sulphurychloride or glycerin is being used. In this method also non-beneficiated wood pulp might be used. For hydrolysis an acid hydrochloric is preferred.

Document CS 213 442 Bl describes a method for preparing microcrystalline cellulose by acid heterogenic hydrolysis with using 0,5 - 3 M of acid hydrochloric. This solution is prepared for powdered cellulose being implicated in food and pharmaceutical industry.

From article Tropical Journal of Pharmaceutical Research from March 2007 is possible to know the results of powdered cellulose AVICEL PH 101 gained from waste paper and cellulose. Therefore, there is a need to provide a method for preparing powdered cellulose which would save the raw materials entering the process of production and which would bring environmental benefits as well while waste fibers are being used. Object of the Invention

The inventors have discovered a new method for preparing powdered cellulose from a less expensive and more available raw material. Said method allows reducing the consumption of manufacturing costs in process of powdered cellulose production. A discovered method describes a process of preparing powdered cellulose from waste lignin-cellulosed materials which rise from known processes of pulp and paper production and which are contained in wastepaper. These are subsequently subjected the acid hydrolysis or alkaline degradation so that the degree of polymerization may be adjusted in accord to cellulose viscosity while being reduced.

In comparison to known mechanical methods of preparing the powdered cellulose said method allows preparing of powdered cellulose with wide scale of polymerization degree in final product as well as obtaining the powdered character of cellulose in acid hydrolysis or alkaline degradation phase already. In respect of previous said conditions, all the process can be carried out without prior step of blending.

The main advantage of new method is an easy control of acid hydrolysis or alkaline degradation technological process. On basis of raw materials quality analyses (as pH, ash content, and degree of polymerization are) are manufacturing conditions - reagent concentration, hydro module, temperature and pressure chosen.

With different combination ratio of raw materials - waste lignin-cellulosed materials rising from processes of pulp and paper production and those contained in waste paper is possible to prepare powdered cellulose with wide scale of industrial applications - in construction chemistry, petrochemical and food industry.

The Inventors consider as substantial also an environmental benefit outstanding - as long as the primary fibers from pulp production are being substituted by secondary and waste fibers.

The object of invention is therefore a method for preparing powdered cellulose from waste lignin-cellulosed materials. Description of the Drawings

No drawings are enclosed.

Detailed Description of the Invention

The method for preparing powdered cellulose comprises:

1. Choice and preparation of raw materials.

2. Acidification, alkaline ennoblement and reducing the degree of polymerization of raw materials.

3. Isolating the powdered cellulose obtained in step 2.

In the method of invention the first key step is using the waste lignin-cellulosed materials as raw materials and subsequently reducing the degree of polymerization on requested level by subjecting the acid hydrolysis or alkaline degradation so that the powder character of cellulose is obtained already in these processes. The resultant degree of polymerization of powdered cellulose is determined by cellulose viscosity and comprises between 100 - 400 (depending on sort of raw material used and requirements given on final products' quality characteristics).

Raw materials for preparing powdered cellulose

The raw materials which are used in the method of invention are following waste lignin- cellulosed materials rising from known processes of pulp and paper production and those contained in wastepaper:

1. Waste fibers rising from process of pulp chipping following the process of non- bleached pulp washing.

2. Waste fibers rising from process of pulp chipping following the oxygen delignification process.

3. Mixture of waste fibers described in points 1) and 2) together with non-bleached pulp using a ratio comprised between 100:0 to 0:100.

4. Waste fibers rising from process of pulp chipping following the pulp bleaching process.

5. Waste fibers rising from bleaching pulp processes which are captured in sewerage waters.

6. Waste fibers rising from drying technology at pulp and paper machines.

7. Mixture of waste fibers described in points 4) to 6) together with bleached pulp using a ratio comprised between 100 : 0 to 0 : 100. 8. Mixed waste fibers described in points 1) and 2) and 4) to 6) captured in sewerage waters.

9. All existing sorts of wastepaper.

Before starting degree of polymerization reduction are the basic raw materials qualities parameters assessed so that these subsequently subject the process of acid hydrolysis or alkaline degradation.

All said raw materials contain as basic compound cellulose. Depending on sort of raw material used, the chain length is given in degree of polymerization that usually comprises between 400 - 1300 and is determined by cellulose viscosity.

Ash content is defined as a ratio between cellulose content and content of inorganic additions. Its amount is determined by method of preparing final product and by place where it was separated. The usual ash content by said raw materials is comprised between 0,2 - 50%. pH value depends is determined by method of preparing final product and by place where raw material was produced. The usual values comprise between 4 - 10.

Acidification, alkaline ennoblement and reducing the degree of polymerization of raw materials

The degree of polymerization is a parameter which indicates the number of glucose units forming the cellulose chains. It can be determined from the viscosity of cellulose. Reducing the degree of polymerization in process of preparing powdered cellulose as described in this invention is being subjected to heterogeneous hydrolysis treatment in presence of mineral acids.

Important parameters that directly influence reducing the degree of polymerization and process of hydrolysis are as following:

1. Type of mineral acid

2. Elevated temperature by hydrolysis

3. Pressure

4. Other parameters in hydrolysis and alkaline degradation technological process. Type of mineral acid

The method of invention describes the using of following types of mineral acids - described on preferable application:

1. Hydrochloric acid (HC1)

2. Sulphuric acid (H₂S0₄)

3. Phosphate acid (H₃P0₄) The amount of acid used is determined by its concentration. Acid concentration in hydrolysis process depends on quality of raw material. In accord to method of this invention it is recommended to choose acid concentration in ratio between 0,5 - 10%.

In respect of raw materials quality characteristics (mainly ash content and pH value) a prior step of acid hydrolysis is an acidification, where the lower H value is being achieved - neutral or slightly acid (4-7).

Hydrolysis temperature

In process of hydrolysis is temperature's scale chosen in respect of raw materials quality characteristics, in respect of degree of polymerization and acid concentration in solution. In the described method the temperature used comprises between 90 - 180°C.

Pressure

In process of hydrolysis is pressure determined by used temperature. In method of this invention the pressure comprises between 1 - 12 bars.

Other parameters in hydrolysis and alkaline degradation technological process

Raw material - water ratio

Said method of invention allows using a wide scale of raw material - water ratio during the reduction of degree of polymerization. This ratio is determined by hydro module used and water consistence.

By hydrolysis process in accord to this method of invention is hydro module chosen as 1 :4 to 1 :6 ratio what corresponds with water consistence 16 - 20% w. While this hydro module ratio is used, there is an important heat savings achieved.

Raw material dryness comprises between 3,5 - 90%w and really depends on sort of raw material used. In acid hydrolysis process - while reducing degree of polymerization - can be thus hydro module 1 :30 ratio used. When hydro module ratio is needed to be cut down the raw material must be subjected to drainage process. Depending on quality characteristic required on final powdered cellulose product, in method of this invention can be used following types of water - filtrated river water, decarbonised water or demineralised water. Time of hydrolysis process

The usual time for reaching a required degree of polymerization comprises between 30 minutes to 8 hours, depending on raw material quality characteristics. The time depends also on temperature and pressure used.

Said method of invention describes a time regulation in reducing degree of polymerization what is performed through monitoring of cellulose viscosity in material that is being subjected to hydrolysis process. When required viscosity is reached, the process stops.

Blending

This method of invention describes a possibility of a static process in reducing degree of polymerization. After a required degree of polymerization is reached, final product has a powdered character what minimizes a need of blending before following phases.

In case of performing all process in high hydro module ratio (higher than 1 :10), blending is sufficient for homogenization.

Warming up

Warming up the material in a reactor is being performed through:

Entering a direct steam to water suspension, where also blending is provided through pressure of steam

- Indirect warming of water suspension.

Alkaline ennoblement

In case of using a lignin-cellulosed material which includes a higher amount of lignin and other extractive compounds, prior to reducing the degree of polymerization the process of alkaline ennoblement is integrated. Following alkaline mediums can be used: NaOH, KOH, and NA₂C0₃.

Degradation of degree of polymerization in alkaline medium

Degradation for reducing the cellulose chain in raw material may be performed through alkaline medium action. Preferably alkaline medium NaOH is used as long as the best results are observed thus. The usual concentration of NaOH in solid is 0,5 - 10%w, temperature used comprises between 140 - 180°C, pressure 4 - 12 bars during time period between 30 minutes to 8 hours. Alkaline degradation might have best effect is oxygen or peroxide is being used. Powdered cellulose isolation

After finishing hydrolysis process the powdered cellulose obtained has excellent pumping characteristics, even if hydrolysis is performed by hydro module with ratio 1:4 as well as excellent water-laid and filtration characteristics. This method of invention describes following steps by isolating the powdered cellulose.

Neutralization

After a required degree of polymerization is reached, a cake of powdered cellulose might be neutralized.

Water-laid washing

In this method of invention is washing performed through water, whose temperature needs to be lower than a temperature used in reactor. After adding water and decreasing internal temperature the process of degradation the polymerization degree is finished. In the same reactor it is possible subsequently perform a multiple powdered cellulose washing. The pH value achieved after neutralization and water-laid washing usually comprises between 3 - 5.

Acid solids from neutralization process might be consequently used for:

raw materials acidification

pH value adjustment before hydrolysis

hydro module adjustment.

While acid solids from washing are used a savings in mineral acids consumption is achieved.

Alkaline mediums

As alkaline mediums in this method of invention chemicals NaOH, NA₂C0₃ CaO, Ca(OH)₂ are being used and are added in chosen concentration to achieve requested pH value comprising between 5 - 7.

Thus neutralized product is water-laid washed and pumped into filtration process.

Filtrating the powdered cellulose

A very good characteristic of powdered cellulose to be easily filtrated is used in filtration process. Powdered cellulose is being condensed and while adding water from washing process, the inorganic impurities are being removed from final product. Final phase in preparing powdered cellulose

After finishing all previous technological phases is powdered cellulose subjected to drying, grinding and granulation processes. The particle sizes are being adjusted to requested dimensions.

Depending on sort of raw material used is proceeds in powdered cellulose preparing comprising between 40 - 90% and the achieved degree of polymerization comprises between 100 - 400.

Examples

Example 1 - Laboratory scale testing of powdered cellulose preparing

Raw material: waste fibers from paper grade pulp production, separated in mechanical sewage tank. Humidity achieved: 60%, degree of polymerization: 522 cm³/g.

Hydro module in ratio 1 :7 was loaded into laboratory reactor. Hydrolytic medium used: appropriate amount of acid hydrochloric in concentration of 1,5% or appropriate amount of acid sulphuric in concentration 3%.

The temperature of hydrolysis process comprised to 95°C.

The results outstanding from laboratory testing in quality parameters of powdered cellulose obtained are as following:

After hydrolysis was finished, pH value was modified by triple water-laid washing, then filtrated and washed for removing inorganic impurities. Subsequently was the product dried in laboratory drier and grinded to requested particle size.

Final product mining: 68% (hydrochloride acid used) or 62% (sulphuric acid used). Example 2 - Laboratory scale testing of powdered cellulose preparing

Raw material: waste fibers from paper grade pulp production, separated in mechanical sewage tank. Humidity achieved: 68%, degree of polymerization: 503 cm /g.

Hydro module in ratio 1 :5 was loaded into laboratory reactor. Hydrolytic medium used: appropriate amount of acid hydrochloric in concentration of 1,5% .

The temperature of hydrolysis process comprised to 95 °C.

Final product mining: 63% (hydrochloride acid used). Example 3 - Laboratory scale testing of powdered cellulose preparing

Raw material: separated waste paper. Humidity achieved: 8%, degree of polymerization: 405 cm³/g.

Hydro module in ratio 1 :7 was loaded into laboratory reactor. Hydrolytic medium used: appropriate amount of acid hydrochloric in concentration of 2% and 3% or appropriate amount of sulphuric acid in concentration 4%.

The temperature of hydrolysis process comprised to 95 °C.

Minutes DP - Acid DP - Acid DP - Acid sulphuric hydrochloric 2% hydrochloric 3% 4%

60 220 214 350

120 187 170 254

180 145 118 205 After hydrolysis was finished, pH value was modified by triple water-laid washing, then filtrated and washed for removing inorganic impurities. Subsequently was the product dried in laboratory drier and grinded to requested particle size. Final product mining: 82% (hydrochloride acid 2% used), 78% (hydrochloride acid 3% used), 85% (sulphuric acid 4% used).

Example 4 - Laboratory scale testing of powdered cellulose preparing

Raw material: rejections from last pressure classer. Humidity achieved: 15%.

The temperature of hydrolysis process comprised to 95 °C.

After hydrolysis was finished, pH value was modified by triple water-laid washing, then filtrated and washed for removing inorganic impurities. Subsequently was the product dried in laboratory drier and grinded to requested particle size. Final product mining: 86% (hydrochloride acid used).

Example 5 - Manufactory scale testing of powdered cellulose preparing

Raw material: waste fibers from paper grade pulp production, separated in mechanical sewage tank. Humidity achieved: 61%, degree of polymerization: 498 cm³/g.

Filtrated water temperatured to 90°C and hydrochloride acid were loaded into reactor with capacity of 12 m . The amount needed was calculated in respect of hydro module ratio 1 :7 to be achieved and acid concentration of 2%. Then the waste fibers from paper grade pulp production were loaded into reactor in amount of 500 kg substantially dry waste fibers. Next the reactor was closed and heated by indirect steam to temperature reached 92 - 96°C and the suspension was maintained the hydrolysis for 4 hours period. Once hydrolysis had ended, the suspension in reactor was cooled with water to temperature of 75°C. After triple water-laid washing pH value was modified, then filtrated and washed for removing inorganic impurities at vacuum filter. Subsequently was the product dried in drier and grinded to requested particle size.

The powdered cellulose obtained had degree of polymerization 230 cm³/g and the product mining achieved to 62%.

Example 6 - Manufactory scale testing of powdered cellulose preparing

Raw material: Wastepaper. Humidity achieved: 9%, degree of polymerization: 412 cm /g. Filtrated water temperatured to 90°C and hydrochloride acid were loaded into reactor with capacity of 12 m³. The amount needed was calculated in respect of hydro module ratio 1 :7 to be achieved and acid concentration of 2,5%.

Then the wastepaper was loaded into reactor in amount of 1000 kg substantially dry wastepaper. Next the reactor was closed and heated by indirect steam to temperature reached 92 - 96°C and the suspension was maintained the hydrolysis for 4 hours period. Once hydrolysis had ended, the suspension in reactor was cooled with water to temperature of 75°C. After triple water-laid washing pH value was modified, then filtrated and washed for removing inorganic impurities at vacuum filter. Subsequently was the product dried in drier and grinded to requested particle size.

The powdered cellulose obtained had degree of polymerization 147 cm /g and the product mining achieved to 83%.

Claims

A method for preparing powdered cellulose, characterized in that it comprises:

- Producing powdered cellulose from waste lignin-cellulosed rising from known processes of pulp and paper production and those contained in wastepaper

- Reducing the degree of polymerization in raw material

- Isolating the powdered cellulose obtained in previous step.

The method according to claim 1 characterized in that the powdered cellulose is being prepared from waste lignin-cellulosed rising from known processes of pulp and paper production and those contained in wastepaper in ration comprised between 100:0 and 0:100.

The method according to claim 1-2 characterized in that the reduction of degree of polymerization of raw material is carried out by means of hydrolysis process with mineral acids or alkaline degradation, while same actuation of oxygen and peroxide is possible.

The method according to claim 3 characterized in that the acid medium is generated by an acid medium selected from the group consisting of hydrochloride acid, sulfuric acid, and phosphoric acid.

The method according to claim 4 characterized in that the acid medium preferably used is hydrochloride acid, and sulfuric acid.

The method according to claim 3 characterized in that the alkaline medium is generated by an alkaline medium selected from the group consisting of NaOH, OH, and NA₂C0₃.

The method according to claim 6 characterized in that the alkaline medium preferably used is NaOH.

8. The method according to claim 5 characterized in that cellulose has powdered character with excellent water-laid and filtrating characteristics.

9. The method according to claim 8 characterized in that the acid hydrolysis process may be static (without prior step of blending raw material).

10. The method according to claim 9 characterized in that the hydrolysis process might be carried out by low hydro module ratio.

1 1. The method according to any of claims 1 to 10 characterized in that it includes as additional steps for isolating the powdered cellulose neutralization in the case of having used acid or alkaline medium for hydrolyzing the raw material, filtration of the suspension containing powdered cellulose, purification by means of washing operations with purified water, drying, grinding and granulometric classification according to particle size.