DE3305988A1 - Agent and process for eliminating odours in cellulose production - Google Patents

Abstract

The present invention relates to an agent and process for eliminating odours during working up of the black liquor obtained after the cellulose/alkali digestion process, which is characterised by a content of cyanamide and/or cyanamide salts. The addition of the agent according to the invention is preferably carried out before evaporation and/or combustion of the black liquor, with the result that the odour emission is effectively eliminated.

Description

JT-

SKW Trostberg Trostberg, February 3, 1983

Aktiengesellschaft _{Our mark} . pAT / Dr Schm-ka

8223 Trostberg SKW 196

Means and methods for eliminating odors in the production of cellulose

The present invention relates to a means and a method to remove odors in cellulose production, especially using the sulfate or Kraft process.

The sulphate pulp process has gained considerably in technical importance in the last few decades, because almost all types of wood - including those of inferior quality - can be broken down, the chemicals can be recovered after the waste incineration and the energy obtained from this waste incineration covers almost the entire heat requirement of the pulp mill. In the sulphate pulp process, the wood is pulped; H. the separation of cellulose from lignin and hemicelluloses by pressure reaction with sodium hydroxide solution, sodium sulfide and sodium carbonate as well as small amounts of sodium sulfate. The addition of sodium sulfide activates the alkaline ether cleavage of the lignin and thus increases it its rate of dissolution, however, this sodium sulfide is, on the other hand, a major source of odor emission various points in the processing of the waste liquor ("black liquor"), because odor-intensive substances such as hydrogen sulfide, methyl mercapto and dimethyl disulfide are formed from it.

The black liquor is usually worked up in such a way that this liquor with a solids content of approx. 12-18 % is concentrated in a two-stage process before it is burned. In the first step, the black liquor is fed into a special evaporator, in which a concentration of 40 - 50 % solids is achieved. The concentration is then usually increased in a direct evaporator to a solids content of 60 - 70% before the thick liquor is fed to the incineration.

Because the odor nuisance is precisely at these three points of reprocessing occurs particularly strongly, attempts have been made to remove the excess sodium sulfide by air oxidation prior to concentration to convert to sodium thiosulfate. That way will Although a certain reduction in odor emissions is achieved, only a part of the odorous substances can be eliminated will. In addition, wood with a high resin content easily forms foam, so that oxidation does not occur or cannot be carried out quantitatively.

The use of other oxidizing agents such as. B, chlorine or Chlorinated wastewater is not an optimal solution to this problem because this compound itself is an air polluting gas, so that when it is used, new environmental problems are created will.

The present invention therefore had the object to provide a means and method for odor removal in the preparation of the products obtained after the cellulose alkali pulping process black liquor or zo develop which does not have said disadvantages and which makes it possible without great technical effort, the odor in effective way to reduce.

According to the invention, this object was achieved by a means which is characterized by a content of cyanamide and / or cyanamide salts.

Surprisingly, it has been shown that the odor emission is caused by the addition of cyanamide and / or cyanamide salts the concentration and combustion of the black liquor can be significantly reduced or practically eliminated.

It is known from DE-PS 22 61 124 that cyanamide can prevent the formation of odors during the enzymatic breakdown or decomposition of organic waste, but it was able to. it is not expected that such small additions of cyanamide and / or cyanamide salts result in the emission of odorous substances, which occur during alkaline wood digestion and during processing of the cooking liquor, reduce or eliminate.

The agents according to the invention on cyanamide and / or cyanamide salts are added to the black liquor in an amount of 10-10,000 ppm, preferably 100-5,000 ppm, based on the black liquor. This quantity range corresponds to the fluctuating sulphide content in the black liquor, but the minimum quantity is 1/100 equivalent of cyanamide and / or cyanamide salts based on the 2-valent sulfur should be contained in the black liquor. The addition can take place before the two evaporation stages and / or before combustion. The cyanamide can be introduced into the black liquor treatment cycle either as a solid or as an aqueous solution, the solution being easier to dose has certain technical advantages.

In principle, all salts of cyanamide, in particular mono- and disodium, mono- and dipotassium and calcium cyanamide, are equally suitable as cyanamide salts. Technical calcium cyanamide (calcium cyanamide), which essentially still contains carbon and calcium oxide as impurities, is also suitable as an odor inhibitor without having a disruptive influence on the work-up process. Of course, units made from cyanamide and cyanamide salts can also be used for the purpose according to the invention.

Due to the easy availability and the small amount of the invention Means as well as the small additional technical effort required to carry out the process according to the invention is required, this method represents a particularly inexpensive solution to the problem of odor nuisance Cellulose production.

The following examples are intended to explain the invention in more detail without, however, restricting it thereto.

Example 1: 1 1 black liquor each of the composition Solids content ( ^{dried at 150 °} C. in vacuo): 41 % Total sodium content,

calculated as Na ₃ O: 11.3 %

Total sulfur content,

calculated as elemental sulfur: 1.1 %

Sulphide sulfur, determined and

calculated as hLS: 1.0 %

PH value; 14th

was with cyanamide in the form of the 50 $ aqueous technical cyanamide solution (SKW-Cyanamid L 500) in increasing amounts (0; 0.5; 2 and 5 ml of 50% cyanamide solution) are added at room temperature. Then the appropriate solutions were added to an open beaker Atmospheric pressure (953 mbar) evaporated to dryness. During the evaporation, the odor development was determined by sensory testing determined continuously with 10 test persons each. The test persons had to assess the odor according to 5 relative levels:

1 = very faint odor

2 s faint odor

3 = moderate odor

4 = strong odor

5 = extremely strong odor

The untreated black liquor served as a comparison. In table 1 the results of these tests are given.

Table 1: Test results for example 1.

Assessment of the odor development during the evaporation of a black liquor of the named composition
with and without the addition of cyanamide as a 50% aqueous cyanamide solution (SKW-Cyanamid L 500). The odor was determined by sensory means by 10 test persons. The tests were carried out until an internal temperature of 150 ° C. was reached.

))
t )
" 1
) t
»>
»>
)>
) 3
> attempt
> No. treatment number
reviews
all in all Percentage distribution
in stages 2 3 1 = very faint odor
2 s faint odor
3 s moderate odor of reviews
1 - 5 5 Evaluation by
Averaging calculation
(medium rating) J) YY
J
)
>>>> '. 1 untreated 100 1 - 5 4th 87 4.8 >
1>
> > 2 Addition of 0.5 ml, 5Q
A solution of cyanamide
(265 mg cyanamide)
1 black liquor per 1 100 - 18th 66 8th 4th 2.9 3 Add 2 ml of 50
j & Lge cyanamide solution
(1.06 g cyanamide)
1 black liquor per 1 100 3 9 4th 9 1.2 4th Add 5 ml of 50
^ ige cyanamide solution
(2.65 g cyanamide)
1 black liquor per 1 100 87 6th 2 1.1 Rating levels: 92 4 = strong odor
5 s extremely strong odor

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Example 2:

σ) In each case 1 liter of black liquor of the composition heated to 80 C.

Solids content (at 150 ^° C. in vacuo, dried): 16 % Total sodium content, 4.4 %

calculated as Na ₀ O:

Total sulfur content, 0.4 %

calculated as elemental sulfur:

Sulphide sulfur, determined and

calculated as H ₀ S : ^; 0.06 %

was with 0.1; 0.4 and 1 ml of 50% aqueous cyanamide solution are added and then in an open beaker (air pressure 1002 mbar) up to evaporated to an internal temperature of 130 C. During the evaporation process, the odor was rated by 5 test persons, the test question being:

Do you judge the smell as reasonable, partially reasonable or unreasonable? . The untreated black liquor served as a comparison.

The test results are shown in Table 2.

b) The residues obtained after evaporation were in an open Crucible (with access to air) burned over a propane / butane gas flame. The odor emissions occurring during the combustion of the individual samples were rated by 5 test persons. The test results are compiled in Table 3.

Table 2:

Test results for example 2. σ).

Unpleasant odor during the evaporation of the black liquor of the composition mentioned without
and with the addition of SKW-Cyanamid L 500 (50% aqueous solution) until an internal temperature of 130 ° C. was reached. The odor was rated by 5 test persons.

'/ request
No.

treatment

untreated

Addition of 0.1 ml of 50 Jfcige cyanamide per 1 1 black liquor

Add 0.4 ml of 50 yS cyanamide solution per 1 liter Black liquor

Add 1 ml of 50
Cyanamide solution per 1 liter of black liquor

number

reviews

all in all

50 50

50 50

Percentage distribution of the ratings

reasonable

conditionally reasonable

18th

32

16

unreasonable %

78

22nd

CO CO CO

Table 3:

Experimental results for example 2. b).

Reduction of the odor nuisance when burning the evaporation residues of the black liquor mentioned Composition by adding cyanamide before evaporation. The smell was determined by 5 test subjects rated.

attempt treatment number of Percentage distribution of the ratings conditionally reasonable
% unreasonable
% No. reviews
all in all reasonable
% 18th 74 1 untreated 50 8th 42 20th 2 Add 0.1 ml of 50%
Cyanamide solution (53 mg
Cyanamide) per 1 1 black
lye 50 38 14th 4th 3 Addition of 0.4 ml 50%
Cyanamide solution (212 mg
Cyanamide) per 1 1 black
lye 50 82 8th 2 4th Addition of Ί ml 50 / Sige
Cyanamide solution (530 mg
Cyanamide). Per 1 1 black
lye 50 90

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Example 3:

Lime cyanamide (cyanamide content, calculated as free cyanamide = 29.5 %) was added in increasing amounts (0, 1, 4 and 10 g) to 1 kg of black liquor of the composition given in Example 1.

The mixture was then evaporated to an internal temperature of 120 ° C. in an open beaker (air pressure 986 mbar) and the resulting odor development was determined by sensory means by 5 test persons.

The odor had to be assessed according to 4 relative levels:
Faint odor to extremely strong odor.

The test results can be found in Table 4.

Table 4:

Test results for example 3.

Reduction of the odor development when concentrating (up to 120 C internal temperature) a black liquor the composition given in Example 1 as a function of the amount of calcium cyanamide added. 5 people were available for the sensory odor determination.

1
¹ , attempt
"""' No.
<
«
<
C <
C (
f (
C.
[ t treatment number of
reviews
all in all Percentage
weaker
odor
% Apportion
in 4 p
more moderate
odor
% g the ev
step
stronger
odor
% »Guards
extremely strong
odor
% t C
• ι untreated 50 - 6th 12th 82 2 Addition of 1 g of lime stick
substance (295 mg cyanamide) per
kg black liquor 50 26th 58 14th 2 3 Addition of 4 g of lime stick
substance (1.18 g of cyanamide) per
kg black liquor 50 92 8th - - 4th Added 10 g of lime stick
substance (2.95 g cyanamide) per
kg black liquor 50 94 6th

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1S

Example 4:

A 1 kg black liquor of the composition

Solids content (dried at 150 ° C / 20 °): 18 %

Total sodium content,. 4.9 %

calculated as Na "0:

Total sulfur content, 0.51 %

calculated as elemental sulfur;

Sulphide sulfur, determined and calculated 0.44 %

as H ₂ S:

was treated with 2 g of 50 ^ strength Cyanamid | .Ösung (1 g Cyanamid) was added at 70 C and (mbar 1012) as long as concentrated at atmospheric pressure to dryness, until the internal temperature reached 180 C.

The black residue so obtained was then in a combustion tube at 850-900 ⁰ C:

a) in the deficit of LuftsauersHroff

b) burned in excess of atmospheric oxygen.

In the same way an untreated sample was evaporated and burned

While the typical ScJi Caustic odor occurred, was the result of the incineration of the evaporation residue Cyanamide-treated sample this characteristic odor disappeared. (Table 5)

Table 5:

Test results for example 4

Reduction of odor emissions when incinerating the evaporation residue by adding cyanamide
before evaporation of the black liquor. The incineration took place at 850 - 900 ° C.

a) in the deficiency of atmospheric oxygen

b) in excess of atmospheric oxygen

Type of treatment typical black liquor smell untreated
Addition of 2 g of 50% aqueous
Cyanamide solution (Ig Cyanamid) per
kg black liquor before evaporation a) strongly present
b) strongly present
a) disappeared
b) disappeared

CD OO OO

SKW Trostberg A ^ t Trostberg, February 3, 1983 Aktiengesellschaft _{Our mark} . pAT / Dr Schm-ka

8223 Trostberg SKW 196

Means and methods for eliminating odors in cellulose production

Claims (7)

Patent claims: (λ.) Means for eliminating odors in the processing of the black liquor obtained after the cellulose alkali digestion process, characterized by a content of cyanamide and / or cyanamide salts. 2.) Means according to claim 1 characterized by a content of 10 10,000 ppm, in particular 100-5,000 ppm, of cyanamide and / or Cyanamide salts based on the black liquor. 3.) Means according to claims 1 and 2, characterized in that an aqueous cyanamide solution is used. 4.) Means according to claims 1 to 3, characterized in that the cyanamide salts are calcium cyanamide, sodium cyanamide, potassium cyanamide, Sodium hydrogen cyanamide and potassium hydrogen cyanamide begins. 5.) Means according to claims 1 to 4, characterized in that calcium cyanamide is used as the cyanamide salt. 6.) Process according to claims 1 to 5, characterized in that that one adds cyanamide and / or cyanamide salts to the black liquor before evaporation and / or incineration. 7.) Process according to claims 1 to 7, characterized that the cyanamide and / or the cyanamide salts are added to the black liquor in such an amount that the proportion of cyanamide is at least 1/100 equivalent based on the amount of negatively divalent sulfur in the black liquor.