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Title:
PROCESS FOR ISOLATION OF HEMICELLULOSES FROM BIOMASS PULPING PROCESS WATERS OR SPENT LIQUORS
Document Type and Number:
WIPO Patent Application WO/2018/041488
Kind Code:
A1
Abstract:
The invention relates to a process for isolation of hemicelluloses from biomass pulping process waters or spent liquors with removal of suspended solids, concentration of the product and purification of the product by removal of inorganic salts and low molecular weight substances. It is characterized in that the hemicellulose isolation process conditions at several separation/purification stages are adjusted separately by e.g. pH adjustment. The invention further relates to a plant for carrying out the process. With such process and plant it is possible to recover most of the suspended solids, especially xylan and other hemicelluloses.

Inventors:
SHAGAEV OLEG (AT)
WIESEGGER LUKAS (AT)
Application Number:
PCT/EP2017/069032
Publication Date:
March 08, 2018
Filing Date:
July 27, 2017
Export Citation:
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Assignee:
ANDRITZ AG MASCHF (AT)
International Classes:
D21C11/00; D21C11/04; D21C11/10
Domestic Patent References:
WO2004013409A12004-02-12
WO2002040767A12002-05-23
Foreign References:
US20140163245A12014-06-12
US4470876A1984-09-11
US20120196233A12012-08-02
Attorney, Agent or Firm:
SCHWEINZER, Friedrich (AT)
Download PDF:
Claims:
Claims

1. Process for isolation of hemicelluloses from biomass pulping process waters or spent liquors with removal of suspended solids, concentration of the product and purification of the product by removal of inorganic salts and low molecular weight substances, characterized in that the hemicellulose isolation process conditions at several separation/purification stages are adjusted separately by e.g. pH adjustment.

2. Process according to claim 1 , characterized in that the pH value of the

incoming effluent stream (A) is adjusted to pH 8 - 11.

3. Process according to claims 1 or 2, characterized in that pH value of the clear fluid stream (G) after the removal of the coarse suspended solids is adjusted to pH 8-11 , preferably pH 9.0 - 9.5.

4. Process according to any of claims 1 - 3, characterized in that before removal of inorganic salts the pH value is adjusted to 4.0 - 4.5.

5. Process according to any of claims 1 - 4, characterized in that the final

product enriched with hemicellulose after separation of ashes has a dryness of 15-30%.

6. Plant for isolation of hemicelluloses from biomass pulping process waters or spent liquors with units for removal of suspended solids, concentration of the product and purification of the product by removal of inorganic salts and low molecular weight substances, characterized in that a line for adding chemicals to adjust the pH value is provided at several separation/purification units.

7. Plant according to claims 6, characterized in that the units for separation of suspended solids are mechanical separation units as e.g. centrifuges, filters or the like.

8. Plant according to any of claims 6 or 7, characterized in that as concentration unit membrane filters are provided.

9. Plant according to any of claims 6 - 8, characterized that as purification unit for e.g. ash removal membrane filters are provided.

Description:
PROCESS FOR ISOLATION OF HEMICELLULOSES FROM BIOMASS PULPING PROCESS WATERS OR SPENT LIQUORS

The invention relates to a process for isolation of hemicelluloses from biomass pulping process waters and spent liquors with removal of suspended solids, concentration of the product and purification of the product by removal of inorganic salts and low molecular weight substances.

Significant efforts to develop processes for isolation of valuable bio-products from biomass pulping process waters (TMP white water, bleaching pressates) and spent liquors (alkaline pre-hydrolysis, alkaline extraction of Kraft pulps for dissolving pulp grades) have been executed in a past couple of decades, particularly isolation of lignin and hemicelluloses. However, conventionally, extracted polymeric

hemicelluloses (e.g. xylooligosaccharides (XOS)) are further converted into sugars, which are either converted into biofuels (e.g. ethanol), or other alkaline chemicals, like succinic and lactic acids that are further used in chemical industry for polymer synthesis (e.g. polylactic acid (PLA)). For concentration of the effluent the throughput (flux) was very low in ultrafiltration process. So approx. 1 - 3% solids content could be achieved with a throughput of only 10 - 15 l/m 2 h, or less by the time this concentration could be reached. Such process could not be turned into industrial use due to the big ultrafiltration equipment necessary and the still relatively low

concentration of the product, especially for a further thermal concentration and/or treatment. Such low throughput is mainly due to fouling of the ultrafiltration units.

The invention is characterized in that the hemicellulose isolation process conditions at several separation/purification stages are adjusted separately by e.g. pH

adjustment. By these means it is possible to achieve high flux flow throughput rates and product concentrations while each stage can work at its optimal conditions.

An advantageous embodiment of the invention is characterized in that the pH value of the incoming effluent stream is adjusted to pH 8 - 11. With such measure a good separation of fibers, suspended solids and hemicelluloses is possible.

A further improvement of the invention is characterized in that pH value of the clear fluid stream after the removal of the coarse suspended solids is adjusted to pH 8-11 , preferably pH 9.0 - 9.5. With this adjustment the fouling of filter surfaces, especially membranes, is reduced significantly.

A further development of the invention is characterized in that before removal of inorganic salts the pH value is adjusted to 4.0 - 4.5. Such pH adjustment allows that no sodium ions are bound to the hemicelluloses and thus can be separated easily.

An advantageous improvement of the invention is characterized in that the final product enriched with hemicellulose after separation of ashes has a dryness of 15- 30%. This allows cheaper thermal isolation treatment afterwards.

The invention further relates to a plant for isolation of hemicelluloses from biomass pulping process waters or spent liquors with units for removal of suspended solids, concentration of the product and purification of the product by removal of inorganic salts and low molecular weight substances. This is characterized in that a line for adding chemicals to adjust the pH value is provided at several separation/purification units. By this means it is possible to achieve high throughput rates and

concentrations and the optimal pH value for separation and purification can be set.

An advantageous development of the invention is characterized in that the units for separation of suspended solids are mechanical separation units as e.g. centrifuges, filters or the like. So the main portion of fibers can be separated and possibly reused easily.

A further development of the invention is characterized in that as concentration unit membrane filters are provided. These filters can separate the suspended solids at a high ratio.

An advantageous improvement of the invention is characterized that as purification unit for e.g. ash removal membrane filters are provided the corresponding product purity can be achieved according to the desired level.

A further improvement of the invention is characterized in that a thermal separation unit is provided to concentrate the product. Depending on the demands the product can be sold and transported with a little portion of water only. Process description

The block diagram in Fig. 1 shows the typical setup of the preferred process.

This process for isolation of hemicelluloses can be used for mechanical pulping lines, semi-chemical and chemical pulping plants. It can be implemented in either existing installations or rebuild projects. The process applies for biomass, hardwood (xylans) and softwoods (galactoglucomannans (GGM)) pulping lines process waters and spent liquors treatment where alkaline treatment or high temperature water extraction of biomass is used.

Typical pulping lines for isolation of hemicelluloses from process waters, bleach plants and spent liquors are:

- Hardwood Kraft mills with alkaline pre-hydrolysis

- Hardwood Kraft mills with alkaline extraction stage before, or after

bleaching

- Hardwood NSSC semi chemical pulping lines

- Hardwood green liquor semi-chemical pulping lines

- Annual plants mechanical and semi-chemical pulping lines (bagasse,

kenaf, etc.)

- TMP process white water

- APMP hardwood lines

- BCTMP hardwood pulping lines.

The incoming stream A in Fig. 1 can be any effluent of any mechanical or semi- chemical pulping line containing hemicellulose, which can be e.g. white water or pressate, or filtrate, or black liquor from pulp washing equipment normally at a temperature of e.g. 60 - 90°C. The incoming stream A loaded with a high amount of COD (chemical oxygen demand) as "effluent" is usually sent to an effluent treatment station, which is the current state-of-the-art.

For the process according to the invention the pH is adjusted to pH 8-11 by stream B. After the first pH adjustment - stream C - containing coarse suspended solids, such as fibers and fiber particles and particles greater than > 10 pm that are not retained during washing are removed in the first process step I, whereby some separation equipment allows to remove particles greater than > 5 pm. Process step I can be performed by mechanical separation equipment such as filtration units or centrifuges (e.g. decanter centrifuge). The necessity to use for example a decanter centrifuge is suitable for the APMP lines without existing fiber recovery system (e.g. fiber recovery disc filter) that is capable to remove fiber fragments, fines and other suspended solids from screw press pressate after an alkaline peroxide bleaching stage. In this case, the decanter centrifuge is used to remove suspended solids. For the APMP lines with existing fiber recovery system (e.g. having the fiber recovery disc filter) that is capable to remove efficiently fiber fragments, fines and other suspended solids from pulp washing equipment (e.g.

screw press) pressate after alkaline peroxide bleaching stage the usage of decanter centrifuge is optional, or can be eliminated.

The clear fluid (stream G) from coarse suspended solids removed in process step I, e.g. either by a disc filter or decanter centrifuge, the effluent is collected in a buffer tank where the pH value of this spent liquor is adjusted to pH 8-11 (more

advantageously to pH 9.0-9.5) by stream H - to dissolve the high molecular weight hemicelluloses, that tend to coagulate and/or absorb on high specific surface fines/particles at pH < 6-7 after a neutralization stage that is typically performed after the bleaching stage in APMP/BCTMP processes. In some applications adjustment of the pH value may only be done with adding the basic chemicals in stream B, in other applications chemical addition to get to pH 8 - 11 , preferably 9.0 - 9.5, can be done in stream H. However it is possible also to add chemicals in both streams b and h depending on the characteristics of the effluent and of the separation equipment.

After high molecular weight hemicelluloses are desorbed and re-dissolved, this fraction is transferred to the liquid phase of the effluent - stream I - and is sent to process step II, where smaller particles in the range of > 0.5 - 10 pm are removed, e.g. very fine biomass material and colloidal suspended solids (e.g. silicates, resins).

For process step II, machines and equipment such as centrifugal disc separators (or other type of separators), or membrane type micro filtration units can be used.

After thorough suspended solids and colloidal substances removal after process steps I and II, the effluent J is sent to process step III, in which the hemicelluloses are enriched. The reject streams of process step I - stream D- and of process step II - stream E, containing fibers and other suspended solids down to approx. 0.5 pm particle size, are collected and can be sent back to the system (mechanical or semi-chemical pulping line or pulp and paper mill) - stream F.

In process step III - usually ultrafiltration membrane units are used and most of the water, salts and low molecular organics are removed and the effluent/product is concentrated to a factor of 10-20. The permeate of this process step - stream K - having much less COD (chemical oxygen demand) than stream A thus can be reused in the system (mechanical or semi-chemical pulping line or pulp and paper mill).

Following process step III the pH of the concentrated liquor / effluent L is adjusted by stream M and the resulting stream N is passing through the next process step IV, which is a membrane unit - usually diafiltration, where stream N is washed by fresh water or process condensate - stream P and inorganic salts (mostly sodium) are removed to the required product quality level and the product is concentrated further to the level of solids content sufficient for the next process step(s). Considering that most of hemicelluloses (e.g. xylans) are containing uronic acids as side chains which are relatively acidic and contain sodium ions bound by COO " -groups, the pH of stream L is adjusted to pH 4.0-4.5 by acid, e.g. sulfuric acid, hydrochloric acid etc. by stream M in order to have more efficient removal of bound sodium ions (Na + ) and, correspondingly, reduce the product ash content further if required.

Process step IV is able to produce the product (stream Q) at 20-30% solids concentration. Process step IV generates excess water / permeate O, which can be used for dilution or any further use in the system (mechanical or semi-chemical pulping line or pulp and paper mill) to substitute fresh water or any mill water. The out coming stream Q of process step IV is further processed in process step V, where the hemicelluloses are thickened further up to a solid concentration of 50 - 80 %. Process step (V) can usually be a thermal separation process such as evaporation, which generates excess water of high quality, typically condensate, - stream R, which can be used for the diafiltration stage (step IV), dilution or any further use in the system (mechanical or semi-chemical pulping line or pulp and paper mill) to substitute fresh water or any mill water. The heating of the thermal drying unit may be achieved by waste steam from the mill. The out coming stream S of process step V can be used as a product or depending on the final product concentration requirements (e.g. 80-90% dry solids) is thickened further in another process step VI, which can be a drying unit, e.g. spray dryer. The final product enriched with hemicellulose encompasses a dryness level of 50-80% as slurry/suspension, paste or gel - stream S or if necessary around 80-90% as powder - stream T.

The invention is not limited to the drawing but the process may also already end after process step IV when the stream may be further used in the system. Also excess water (stream R) of process step V may be reused instead of fresh water for stream P of process step IV.