FI127900B

FI127900B - A method for reducing phosphorus load in effluent from a pulp production process

Info

Publication number: FI127900B
Application number: FI20145479A
Authority: FI
Inventors: Ines Eluen; Los Santos Ernesto De; Gastón Cubas; Luciana Costabel
Original assignee: Upm Kymmene Corp
Priority date: 2014-05-27
Filing date: 2014-05-27
Publication date: 2019-05-15
Also published as: WO2015181442A1; FI20145479A; UY36139A

Abstract

The invention relates to a method for reducing the phosphorus load in effluent from a pulp production process, which process comprises the steps of: a) digesting lignocellulosic material for forming cooked pulp, b) washing the pulp, and c) bleaching the pulp in acidic conditions, wherein digesting the lignocellulosic material in step a) is carried out in the presence of at least one chelating agent for preventing the formation of insoluble salt containing calcium and/or magnesium and phosphorus.A) digesting lignocellulosic material for forming cooked pulp, b) washing the pulp, and c) bleaching the pulp in acidic conditions, digesting the lignocellulosic material in step a) is carried out in the presence of at least one chelating agent.

Description

A METHOD FOR REDUCING PHOSPHORUS LOAD IN EFFLUENT FROM A PULP PRODUCTION PROCESS

FIELD OF THE INVENTION

The invention relates to a method for reducing the phosphorus load in effluent from a pulp production process. The invention further relates to uses of at least one chelating agent.

BACKGROUND OF THE INVENTION

The content of compounds harmful for the environment in effluent or waste water coming from a pulp production process is nowadays rather strictly controlled for environmental reasons in order to pro15 vide a sustainable production process. Plants have different kinds of solutions that are used for waste water treatment in order to ensure that environmental regulations are fulfilled for the plant.

Traditional solutions for phosphorus removal 20 are mainly for the effluent treatment plant, including tertiary treatment, use of phosphorus concentrating (P-concentrating) microorganisms, precipitation with different chemicals, etc. A drawback of tertiary treatment is a high investment and operating cost. P25 concentrating microorganisms work in anaerobic media, which complicates the needed operations and requires specific treatments for the effluent to be used. Precipitation with chemicals involves a high operating cost and depending on the precipitation chemical used 30 can pose challenges for non-process elements accumulation in the recovery cycle when biosludge is burnt in a recovery boiler.

The inventors have recognized the need for a method to reduce the phosphorus load in the effluent 35 coming from the pulp production process so that less

20145479 prh 27-05- 2014 phosphorus needs to be dealt with in e.g. a waste water treatment plant.

PURPOSE OF THE INVENTION

The purpose of the invention is to provide a new type of method for reducing the phosphorus load in effluent from a pulp production process. Further, the purpose of the invention is to provide new uses of at least one chelating agent.

SUMMARY

The method according to the present invention is characterized by what is presented in claim 1.

The uses according to the present invention 15 are characterized by what is presented in claims 7 and 8 .

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing, which is included to provide a further understanding of the invention and constitutes a part of this specification, illustrates an embodiment of the invention and together with the description helps to explain the principles of the invention. In the drawing:

Fig. 1 is a flow chart illustration of a method for reducing the phosphorus load in effluent from a pulp production process.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for reducing the phosphorus load in effluent from a pulp production process, which process comprises the steps of a) digesting lignocellulosic material for forming cooked pulp, b) washing the pulp, and c) bleaching the pulp, wherein digesting the lignocellulosic material

20145479 prh 27-05- 2014 in step a) is carried out in the presence of at least one chelating agent for preventing the formation of insoluble salt containing calcium and/or magnesium and phosphorus .

The expression pulp production process should be understood in this specification, unless otherwise stated, as referring to a manufacturing process that converts lignocellulosic material into a fibrous material, which is also referred to as pulp. In 10 step a), the lignocellulosic material is cooked, whereby heat and chemicals break down preferably lignin. In step b) the pulp is washed, whereby breakdown products are washed out from fibrous material. In step c), i.e. bleaching, the brightness of fibrous material 15 is increased. The fibrous material produced can be e.g. further processed into paper.

The expression pulp should be understood in this specification, unless otherwise stated, as a lignocellulosic fibrous material prepared by chemically 20 and/or mechanically separating cellulose fibres from a lignocellulosic material. So-called kraft or sulphate processes can be used for producing pulp.

In this specification, unless otherwise stated, the expression lignocellulosic material should 25 be understood in as any plant derived organic matter that includes cellulose, hemicellulose, and lignin. Lignocellulosic material can originate from virgin biomass from trees, bushes and grass or waste biomass from various sectors like straw, sugarcane bagasse, 30 corn stover etc. from the agricultural sector as well as saw mill and paper mill discards from the forestry sector .

In one embodiment of the present invention the lignocellulosic material originates from at least 35 one wood species. In one embodiment of the present invention the lignocellulosic material originates from at least one hardwood species. In one embodiment of

20145479 prh 27-05- 2014 the present invention, the lignocellulosic material originates from at least one eucalyptus species.

In one embodiment of the present invention the lignocellulosic material comprises wood chips. In 5 one embodiment of the present invention the wood chips comprise chips of at least one hardwood species. In one embodiment of the present invention the wood chips comprise chips of at least one eucalyptus species.

The present invention further relates to the 10 use of at least one chelating agent in a pulp production process, which process comprises the steps of a) digesting lignocellulosic material for forming cooked pulp, b) washing the pulp, and c) bleaching the pulp, for preventing the formation of insoluble salt con15 taining calcium and/or magnesium and phosphorus.

The present invention further relates to the use of at least one chelating agent in a pulp production process, which process comprises the steps of a) digesting lignocellulosic material for forming cooked 20 pulp, b) washing the pulp, and c) bleaching the pulp, for reducing the phosphorus load in effluent from the pulp production process.

In one embodiment of the present invention the step c) of bleaching the pulp comprises at least 25 one step of bleaching the pulp in acidic conditions. In one embodiment of the present invention the step c) of bleaching the pulp comprises at least one step of bleaching the pulp in conditions with neutral pH.

The expression effluent should be under30 stood in this specification, unless otherwise stated, as referring to waste water discharged from a pulp production process. The waste water discharged from a pulp production process is usually purified at a waste water treatment plant before being conveyed further to 35 e.g. a river, a lake or the sea.

20145479 prh 27-05- 2014

The expression phosphorus load in effluent should be understood as referring to the amount of phosphorus in the effluent.

Especially a phosphorus load in the effluent 5 reaching territorial waters may be harmful to the surrounding environment. Thus regulatory agreements in certain countries are becoming increasingly strict. One of the main sources for the phosphorus load coming from a pulp production process or plant is the bleach10 ing stage. The phosphorus of the pulp production process mainly originates from the lignocellulosic material, e.g. wood, used in the process. The inventors of the present invention found out that the phosphorus content together with the calcium content of the used 15 lignocellulosic material affects the amount of phosphorus that will pass through the pulp production process and end up in the effluent thereof and especially in the effluent from the bleaching step. Magnesium, and possibly also other elements, may also precipitate 20 in the same manner as calcium. It was found out that calcium and possibly also magnesium present in the step of digesting the lignocellulosic material is able to precipitate phosphates from the lignocellulosic material. This formed precipitate is then carried fur25 ther through the fiberline process until it is dissolved under the acidic or neutral conditions used e.g. in the step of bleaching the pulp. As the phosphorus is being dissolved during the bleaching step, it will end up in the effluent received from this 30 step.

The inventors of the present invention surprisingly found out that the use of at least one chelating agent in the step of digesting the used lignocellulosic material is able to bind the calcium and/or 35 magnesium present in a manner that the formation of insoluble salt containing calcium and/or magnesium and phosphorus is decreased or prevented.

20145479 prh 27-05- 2014

In one embodiment of the present invention the insoluble salt containing calcium and/or magnesium and phosphorus comprises calcium phosphate precipitate. In one embodiment of the present invention the 5 insoluble salt containing calcium and phosphorus consists of calcium phosphate precipitate. The insoluble salt may also contain other components, such as magnesium phosphate and other calcium and/or magnesium salts .

The inventors of the present invention found out that the use of the method according to the present invention can result in effluent, coming from the pulp production process and especially from the bleaching step thereof, with a reduced phosphorus load 15 compared to a corresponding process, where no chelating agent is used in step a) of digesting the lignocellulosic material.

A chelating agent or a complexing agent is a substance capable of forming a complex compound with 20 another material in solution. It was found out that when using at least one chelating agent in the step of digesting the lignocellulosic material the calcium and/or magnesium will be part of the complexes formed with the chelating agent instead of forming calcium 25 and/or magnesium phosphates.

The amount of the at least one chelating agent in step a) may be selected e.g. depending on the amount of calcium present in the wood raw material species. For example, in Eucalyptus species with low 30 calcium contents of up to 500mg/kg od wood, the effective dosage of a commercial industrial chelating agent could range from 0,5 to 8 kg/ADt depending on the desired effect (e.g. how large a percentage of the phosphorus in effluent should be removed). For commonly 35 occurring calcium contents of about 1000mg/kg od wood dose, the amount may be e.g. about 15kg/ADt. For high calcium containing species, the amount may be even

20145479 prh 27-05- 2014 higher. Further, a stoichiometric excess of chelating agent may be added with respect to the stoichiometric amount of calcium and/or magnesium.

In one embodiment, the amount of the at least one chelating agent in step a) is at least 0,5 kg/ADt. kg/ADt should be understood as referring to kilograms of the chelating agent per air dry tonne of pulp. Thus 0,5 kg/ADt corresponds to 0,05 % (w/w) of the at least one chelating agent based on the weight of air dry 10 pulp.

In one embodiment of the present invention the amount of the at least one chelating agent in step a) is 0,5 - 15 kg/ADt.

In one embodiment, the amount of the at least 15 one chelating agent in step a) is 0,5 - 8 kg/ADt.

In one embodiment, the amount of the at least one chelating agent in step a) is 8 - 15 kg/ADt. In one embodiment, the amount of the at least one chelating agent in step a) is at least 15 kg/ADt.

In one embodiment, the at least one chelating agent is present in stoichiometric excess in comparison to the amount of calcium and/or magnesium in step a) . In one embodiment, the at least one chelating agent is present in frank or large stoichiometric ex25 cess relative to calcium and/or magnesium in step a) .

In one embodiment, the molar ratio of the at least one chelating agent to calcium and/or magnesium in step a) is in the range of 1:1 to 10:1, or in the range of 2:1 to 6:1, or in the range of 3:1 to 5:1.

In one embodiment of the present invention the chelating agent is selected from a group consisting of ethylenediaminetetraacetic acid (EDTA), 2,3dimercaptopropanesulfonic acid (DMPS), thiamine tetrahydrofurfuryl disulfide (TTFD), diethylene triamine 35 pentaacetic acid (DTPA), tri (carboxymethyl) amine (NT), and 2,3-dimercaptosuccinic acid (DMSA).

20145479 prh 27-05- 2014

In one embodiment of the present invention a further amount of at least one chelating agent is added before step c), and preferably in step b).

The embodiments of the invention described hereinbefore may be used in any combination with each other. Several of the embodiments may be combined together to form a further embodiment of the invention. A method, or a use, to which the invention is related, may comprise at least one of the embodiments of the 10 invention described hereinbefore.

An advantage of the present invention is that the content of phosphorus in effluent coming from a pulp production process can be reduced by the method according to the present invention. This results in 15 less phosphorus being needed to be treated in e.g. a waste water treatment plant, which may have a beneficial effect also for the waste treatment plant.

An advantage of the present invention is that the method enables the use of different kinds of lig20 nocellulosic material in the pulp production process as it diminishes the effect of different elements contents, such as the phosphorus and calcium and/or magnesium content thereof, of the source material.

An advantage of the method according to the 25 present invention is that it does not require significant investments for equipment of the pulp production plant.

EXAMPLES

Reference will now be made in detail to the embodiments of the present invention, an example of which is illustrated in the accompanying drawing.

The description below discloses some embodiments of the invention in such a detail that a person 35 skilled in the art is able to utilize the invention based on the disclosure. Not all steps of the embodiments are discussed in detail, as many of the steps will be obvious for the person skilled in the art based on this specification.

Figure 1 illustrates a method according to one embodiment of the present invention for reducing 5 the phosphorus load in effluent from a pulp production process. The pulp production process comprises, in step a), digesting or cooking lignocellulosic material for forming cooked pulp material. Step a) of digesting the used lignocellulosic material is carried out in 10 the presence of at least one chelating agent. The use of the chelating agent in step a) prevents the formation of insoluble salt containing calcium and/or magnesium and phosphorus, such as calcium phosphate precipitate, during the cooking step. The at least one

15	chelating agent 15 kg/ADt.	may	be used e.g	. in	an amount of 0	,5 -
	After	step	a) of forming	cooked pulp,	the
	pulp is washed	in	step b) followed by step c)	of
	bleaching the pulp	in e.g. in	acidic conditions.	The
20	effluent coming	from the pulp	production process	and
	especially from	the	bleaching	step	thereof has a	re-
	duced phosphorus load compared	to a	corresponding	pro-
	cess, where no	chelating agent	has	been used in	step

20145479 prh 27-05- 2014

a) of digesting the lignocellulosic material.

EXAMPLE 1 - Reducing phosphorus load in effluent coming from a pulp production process; laboratory simulation

Eucalyptus wood chips were laboratory cooked 30 using an airbath digester with IL autoclaves, using an alkali dose of 20% EA as NaOH and H factor to reach kappa number in the range of 16 to 18. In the blank no chelating agent was added, while in the different experiments a chelating agent was added to the cooking 35 liquor before the beginning of the cook. Cooked chips were disintegrated, screened and thoroughly washed with water. After that an acidic extraction with sul ίο

20145479 prh 27-05- 2014 furic acid simulating a bleaching A stage was performed, using following conditions: temperature 85°C, final pH 3, consistency 5% and retention time 180 min.

In one example, wood chips were clonal Eucalyptus dun5 nii chips with a high calcium content of 9,4g/kg od wood and a phosphorous content of 110 mg/kg od wood.

Wood chips were cooked using H factor 600. Chelating agent was EDTA disodium salt ppa added in frank excess with respect to calcium content (5mol EDTA/ mol calci10 um) to prove the concept. Phosphorous extracted from A stage (simulating P carried to effluent) decreased from 34mgP/kg od wood to non-detectable (<0,5mg P/kg od wood).

EXAMPLE 2

Wood chips were mill chips taken from UPM

Fray Bentos Mill production, consisting of a mix of E.

grandis 46%, E. benthamii 20%, E. dunnii 16%, E. glob20 ulus 11% and E. maidenii 7%. Phosphorous content in chips was 100mg/kg od wood and calcium content l,0g/kg od wood. Mill chips were cooked to kappa 17, with H factor 450. The chelating agent was EDTA disodium salt ppa added in a dose of 1,0 kg/ADt. Phosphorous ex25 tracted from A stage decreased from 13mg P/kg od wood to 8mg P/kg od wood (38% phosphorous reduction to effluent) .

EXAMPLE 3

The same mill chips as in Example 2 were cooked to kappa 15 (H factor 600) and treated with commercial chelating agents: EDTA with a chelating power of lOOmg Ca/kg commercial product and DTPA with 35 a chelating power of 80mg Ca/kg commercial product, both in a dose of 2kg/ADt pulp. Commercial EDTA reduced phosphorous extracted in A stage from 21,4mg

P/kg od wood to 17,7mg P/kg od wood (17% phosphorous reduction to effluent) and DTPA to 15,3mg P/kg od wood (29% phosphorous reduction to effluent).

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims.

Claims

A process for reducing the amount of phosphorus in waste water from a pulping process comprising the steps of: a) boiling lignocellulose;

B) washing the pulp and c) bleaching the pulp, characterized in that the lignocellulosic material in step a) is carried out in the presence of at least one chelating agent to prevent the formation of an insoluble salt containing calcium and / or magnesium and phosphorus.

The process according to claim 1, wherein the amount of at least one chelating agent in step a) is at least 0.5 kg / ADt or 0.5-15 kg / ADt.

15

The process according to any one of claims 1 to 2, wherein the chelating agent is selected from the group consisting of ethylenediaminetetraacetic acid, 2,3-dimethylcaptopropane sulfonic acid, thiamine tetrahydrofurfuryl disulfide, diethylenetriamine pentaacetic acid, tri (carboxymethyl) amine and 2,3-dimethylamine.

A process according to any one of claims 1 to 3, wherein an additional amount of at least one chelating agent is added before step c) and preferably

25 in step b).

The method of any one of claims 1 to 4, wherein the lignocellulosic material is derived from at least one species of eucalyptus.

The method of any one of claims 1 to 5, wherein the lignocellulosic material comprises wood chips.

Use of at least one chelating agent in a pulping process comprising the steps of: a) cooking lignocellulosic material;

35 liters to form a cooked pulp, b) washing the pulp, and c) bleaching the pulp to prevent the formation of an insoluble salt containing calcium and / or magnesium and phosphorus.

Use of at least one chelating agent in a pulping process comprising

5) the steps of a) boiling the lignocellulosic material to form the cooked pulp, b) washing the pulp, and c) bleaching the pulp to reduce the amount of phosphorus from the waste water from the pulping process.

The process of claim 7 or claim

Use according to Claim 8, wherein the chelating agent is selected from the group consisting of ethylenediaminetetraacetic acid, 2,3-dimercaptopropanesulfonic acid, thiamine tetrahydrofurfuryldisulfide, diethylenetriaminepentaacetic acid,

15 of tri (carboxymethyl) amine and 2,3-dimercaptomeric succinic acid.

Use according to any one of claims 7-9, wherein the lignocellulosic material comprises wood chips.

Use according to any one of claims 7 to 10, wherein the lignocellulosic material is derived from at least one species of eucalyptus.