DE1767634C - Process for processing a used alkaline cooking liquor from pulp production - Google Patents

Description

The invention relates to a method for processing a used alkaline cooking waste liquor, as it occurs in the manufacture of wood pulp, in particular for the recovery of chemicals from used cooking solution with a high sulfur content, which mainly consists of Na ₂ S and optionally at least one of the compounds NaHS, NaOH and Na ₂ CO ₃ consists.

The chemical processes for making pulp can be divided into two groups, namely alkaline cooking, in which NaOH and Na ₂ S are used as the main cooking agents, and the sulphite liquor process, in which sulphites such as Na ₂ SO and NaHSO ₃ , be used as a cooking agent. The alkaline processes include, in particular, the manufacture of kraft paper. The cooking liquor consists essentially of sodium sulfide and sodium hydroxide, in contents of 20 to 30% or 80 to 70% with a sulfidity of 20 to 30%.

The sulphidity is defined by the following formula:

55

Sulphidity - .. _- ** _ "· 100,
Na ₂ S l · NaOH

in which Na ₂ S and NaOH are expressed in molar numbers as Na ₂ O. A cooking liquor has a sulfidity of 100% if it does not contain NaOH. If this cooking liquor contains Na ₂ CO ₃ , this component has no effect on the sulphidity. A cooking liquor with a sulfidity of 100% therefore does not require causticization.

The sulfidity is adjusted in the manufacture of Kraft paper by chemical recovery. In this process, the used cooking liquid is withdrawn from the autoclave, collected and evaporated, after which the organic substances leached out of the wood during cooking and the inorganic substances added as cookers are burned out in a furnace, so that sodium and sulfur remain in the form of a melt. In the melt, sodium and sulfur are in the form of Na ₄ CO ₃ and Na ₂ S. In this form they are dissolved in an aqueous solution and then causticized in order to convert the sodium carbonate into sodium hydroxide and in this way to regenerate the chemical substances in the cooking liquid for the manufacture of Kraft paper. Since some of the sodium and sulfur are lost during cooking and regeneration, NasSOi is added to compensate for this in the regeneration oven. Most of the sodium sulphate is reduced in the regeneration furnace and is then present as sodium sulphide in the melt. The sulphidity of the regenerated cooking liquor to which sodium nitride has been added is at most 20 to 30 ° ₀ in the conventional methods. If the sulphidity exceeds this value, special process steps are required. The main reason that the sulphidity does not exceed the aforementioned value is that, although the molar loss of sodium in t'-fr form of sodium sulphide and sulfur compounds is essentially the same on cooking and regenerating, as can be seen from the fact that the sodium and sulfur loss is compensated by the addition of sodium sulfate, the sulfur loss is considerably greater than the sodium loss and that this sulfur loss is either via compounds with Na ₂ O, such as Na ₂ S, Na ₂ SO ₄ or Na ₂ SO ₃ , or gaseous, via Na ₂ O-free compounds, such as in the form of SO ₂ , H ₂ S or CH ₃ SH, and the loss via the gas phase is a multiple of the loss due to compounds with NaS ₂ O. The sulfur loss in particular affects the Formation of gaseous sulfur dioxide in the regulating furnace. Therefore, in order to increase the sulphidity of the regenerated cooking substances, the process must be adjusted to minimal sulfur losses. It is therefore extremely important to catch the sulfur leaving the gas phase and to bind it in hormone with sodium sulfide.

The object on which the invention is based is now to provide a method for production alkaline cooking liquors with high sulphidity by regenerating and setting the via the gas phase otherwise lost sulfur in the form of sodium sulphide and the sulphidity of the melt to increase.

This object is achieved according to the invention by a method for processing a used alkaline cooking liquor from pulp production, which essentially contains Na ₂ S and optionally at least one of the compounds Na ₂ CO ₃ , NaOH and NaHS, by concentrating the used waste liquor and burning it in a regeneration furnace _{, which is characterized in that gaseous SO 2} formed in the regeneration furnace is absorbed in the aqueous solution of the melt produced during firing or in the aqueous solution of Na ₂ CO ₃ separated from the melt and the solution is reintroduced into the circuit before the regeneration furnace .

According to an advantageous embodiment of the method according to the invention, the simultaneous

Processing of alkaline and sulphite waste liquor, the aqueous solution of NagSO ₃ , which was formed by absorption of gaseous SO ₈ in an aqueous solution of Na ₂ CO ₃ separated from the melt, partly used as a reagent for sulphite boiling and the mixed liquid of sulphite waste liquor and alkaline Waste liquor burned together with the rest of the aqueous Na ₂ SO ₃ -LoSUiIg in the regeneration furnace.

It is also possible to check the sulphidity after a Regeneration process of the conventional Kraft process by greatly reducing the collection speed to improve the used cooking liquor while increasing the sodium loss, whereby however, more sodium sulfate must be added accordingly. However, this procedure is because of it exceptionally high cost of the sodium sulfate additive practically hardly applicable.

!) The influence of sulphidity in alkaline cooking arises from the following: The only method of traditional cooking has so far been the so-called soda boiling, in which the only active substance used is irium hydroxide, until the process of recovering the chemicals required in the manufacture of kraft paper emerged. Nowadays as w! around the latter method carried out primarily in that the bcJingte by the above mentioned chemicals sulfidity 20 to 30 / m ° _0th In alkaline cooking, the lignin of the wood is known to be subject to alkaline hydrolysis and dissolves in the Korhlauge, whereby in the case of the sole use of sodium hydroxide condensation of the lignin can take place, in the presence of sodium sulfide this re-condensation is suppressed and the solution des Iignins extracted from the wood The table below shows the influence of sulphidity when cooking Pinus Den under alkaline conditions; 'flora.

40

io ° /. 1 Sulfidity 50 "/", j 100%, 18th 30 »/" 18th ; 30th 18th Permanganate number (25 ml) .. 18th Effective alkali (as ° / ₀ 16 14th 12th Na ₂ O per OD span) .. 43.5 15th 45.5 : i70 46.0 Total yield (V ₀ ) ·· ■ · 45.0 Viscosity of the ■ bleaching 17th ; 60 36 th pülDe (C P S 1 25th [ Cooking conditions ¹ 90 Maximum temperature 170 170 ( ⁰ C) 170 4th Time to the maximum 60 , 60 temperature (min.) ... ! ⁶⁰ i Hold time at maximum 90 I 90 temperature (min.) ... I 90 Liquid / wood ratio 4th I 4 nis (/ kg-O. D. wood) .. I ⁴

The test results on which the invention is based are shown in the table. At a Increasing the sulphidity can achieve the desired delignification by adding a small amount an effective alkali can be achieved for the above-mentioned purpose. The data resulted from the Reducing the losses during cooking, the carbohydrates irt> Wood, resulting in a high viscosity pulp. The yield was also improved. It is also of great advantage that you get such excellent results when cooking with Allow alkalis of high sulphidity to reach.

The process according to the invention enables the recovery of process-effective chemicals from used alkaline cooking liquor with high sulphidity. As mentioned earlier, it is with It is impossible to regenerate cooking defrost from the manufacture of Kraft paper using cooking chemicals regain high sulfidity without increasing the addition of sodium sulfate and thus the The economy of the process is worsened. According to the invention, however, it is possible to reduce the sulfidity limit, that is achieved with conventional regeneration processes, to much higher values Shift.

In the method according to the invention, the spent cooking waste is concentrated and then in a known regeneration furnace burned out and some or all of the sodium carbonate becomes separated from the resulting melt. Thereafter, the aqueous solution of the melt or this sodium carbonate with the sulfur dioxide produced in the exhaust gas and, if necessary, additional Sulfur dioxide is sulphided and the sodium sulphite formed is fed to the regeneration furnace. in the The regeneration furnace will then use up the sodium sulfite along with! Cooking liquid burned out, whereby the sulfur released in the furnace is bound in the melt and increases its sulphidity, so that ultimately a regenerated alkaline cooking liquid with high sulfidity results.

With the method according to the invention, a regenerated alkaline cooking liquor with any desired sulfidity can be achieved by selecting the circulating amount of sodium carbonate through which the sulfur dioxide contained in the exhaust gas is absorbed. Some of the sodium and sulfur introduced as active substances into the alkaline cooking liquor are lost when the unbleached pulp is washed. In some cases, the sulfur also forms a small proportion of volatile organic compounds such as CH ₃ SH and is also lost when the unbleached pulp is cooked and washed. The predominant part of the sodium and sulfur is, however, contained in the collected used cooking liquor. If used cooking liquor with organic substances dissolved from the wood during cooking and sodium and sulfur compounds of the cooking liquor is concentrated and burned out in the regeneration furnace, then a melt with sodium sulfide and soda as the main components is produced. Experiments have shown that a change in the sulphidity of the cooking liquor during alkaline cooking leads to a corresponding change in the composition of the melt. However, this relationship has not yet been fully elucidated, as the structural formula of sodium and sulfur in the spent cooking liquor is still unclear, as is the nature of the reactions taking place in the regeneration oven, with the exception of some experimental findings on the consumed cooking liquor, its sulphidity 20 to 30 ° / ₀ has not yet been finally clarified. The relationship in question is still unexplained with regard to the high sulfidity of the used cooking liquor.

With regard to the recovery of chemicals from used cooking liquor with high sullidity

5 °

55

-JT -, - -ti

In connection with the invention, experiments were carried out on the sulphidity of the melt obtained during the burning of the used cooking liquor obtained with high sulphidicity during cooking. It was found that with increasing sulphidicity of the waste liquor, represented by the percentage molar ratio of S / Na ₂ O, the amount of gaseous sulfur and the difference between the sulphidity of the melt and that of the waste liquor also increase

enlarged. For example, it was found that the Sull'idi ™ ⁱ » ^5Dren ™ _{d give the} predominant part of the sodium, * ^ to which the Ue B _{315 melts the melt}

and b-jwe ew _N ° _lrium sulphide and sodium m ^ ™ «^ ^ ^ ^ _{rium sulphal}

_{in e} r i _ne appropriate amount of the Regcner.erungs-

· «« Ne jf _Ab f _beigescngl around the

oie s procedural stages occurring

^ wanreno ^^. ^ _{Dje Aur8chwe} f | uiig is not

_{If the} use of sodium sulfate is restricted,

but can also be done with sodium sulfate or similar

It follows that there is sulfur egg waste liquor in one of the difference between the SuIMiUt the Waste liquor and the melt «W mainly in the form of

Dioxyd imgas.de. '^^ KX ^ SK , so that the sulphidity of the melt is always under aer

the waste liquor remains. Sulfidity is

In alkaline cooking, the temperature set in the regeneration ^{oven is very high} . so large that the Aufschweflung mu Natr umsu a in an amount to compensate for the de N ^a sufficient cores Sulfid.ta _ £ of

which is sufficiently high for an alkaline oil to have high sulfidity. Accordingly, w, rd najh the MJN dung part or GESAM ^e soda _b chmeize separated to deren'Sulfiditat to 'dioxya "^" f ° ^a "freißesetzte, severity in the exhaust gas, where appropriate supplemented by"™' 2 this soda absorbed _n ^s0Wie _pr ^d _p ^a _r ^s sodium sulfite added to the Rf ^, ^ to adjust the ratio of the sodium content of the melt to a melt with noner Sulfiditat _"rf i _Erlich off _the

It is not absolutely necessary ^ that a Dge separated nitrium carbonal from the melt

direct absorption of the exhaust gas sulfur with li-hen the same effect can be used. The inventive method is on the basis of the in the drawing ^ «' provided the procedural tree of the

The waste liquor is made from a for that Cooking with high ^ 'X ^ deducted and in «Λ from which it is in a mixer 3

rauon _a ^S hafllichfe heat guide at _Economics

be de ^ subsequent crystallization be as high as possible, preferably as close as possible to the Sätt.gungs- "P" held 'kt The solution of the melt J ^^^, ^ · _{η ejnp Krista} i |. _isa tionsslufe 7 in which they fn a Kristallkomponenle, which is mainly separated _{beslelUi and which consists} of Nalrium _{substantially} mother liquor from _{soda soda wjrd erneul. | n ejnem Lösungsta} nk 8

_{A lö Tei, the solution} then passes into the ^ß _{Kauslifizierungsstufe "currency} rend the rest of the Sclnvcfzugeführt is. The causalization IJ g 8 amount of soda is determined on the basis of the suIIi-

_de ,%, _calic cooking in the cooker 1 is determined. _In alkaline cooking with a sulphidity of 100 _{%, do not add any soda to the} causation channels

U. "The" remaining soda solution reaches the swelling stage 9, in which it is brought into contact with a mixed solution of sodium carbonate and sodium _{bisuiru from g tion stage 10 for} sulfur dioxide

^^ ^^ ^ _{Sodium carbonate is} consumed in a reaction according to the following formula (1) releasing β carbon dioxide for the production of sodium, which is returned to the mixer 3 ^ :

essential- Na ₂ CO ₃ i 2 NaHSO ₃ -> 2 Na ₂ SO ₃ \ H ₂ O \ CO.

(D

sulfur dioxide atorplionic lure 10 becomes M, gas with 1 to 0.3 percent by volume of sulfur dioxide us g regeneration furnace 5 and, if necessary, an additional u - | _cnwefe i _{di xyd} ° _aU s a Schwefeldioxv.lerzeuger 12 in contact with the mainly a-> 50 sodium sulphite and soda ash of existing, from the _{Schweflungsstufe} 9 coming into contact solution

erf alkaline scne

o Erl,

° £ _m the dan α

Sulfur compounds, in1 to ^^

^ "! '« ^. »^. I ^ SSr ^ Snd also the d, e Comnion of precedence and au

Sulfur losses ^V ^^. _J J23 must be reopened. level 2 can also be the "Ji" * er ^ nacngso

\ Vn? E \ maiS ^

^d _A 'u, ^^ nX? and eiiim cascade evaporator

Ablaugcvcrdanipfcr and a K «» JJJ ^e ' _dj

consists, the ^ »'" B ^' ^^ ³ "T SO b, 55 · / f

Si- "'

_{The solution is then 2 back into the} Schwefhmg,

level 9 given to sulphurise the soda. De ^ ^ _{Soda | ösu can also be used directly with the} exhaust gas

brought into contact to sulphurize them

To convert sodium sulfite. On the other hand, the freed from the Sodakrista.len in Kristallabscheider 7 and "substantially ai _Nat riumsulfid existing mother liquor with a Tel the soda solution directly or with the interposition ^d" Ka _"S., Nz, he _U ngsst _y re II mixed and after" with soda in sodium hydroxide as

1 7676034

",. u ι / μ,. with high sulfidity in the alkaline cooking liquor .with high buliicmai in α

Cooker 1 fed in. melt

In e.nzehen is the ^ ° ^ ^ ^the separate "" 8 ^de _u ^r J ^cl f ™ ^e ^ _r in the Kr.stall.sierunptufe 7 and m "r Schweflungsstufe 9 m ^ hweJUe soda form of sodium sulfate in the control passage : renung »» ^ « ^r , f leads, which is also ve h * H w JJ ^ ms

SSrSf _1n the ^^ AES amount of soda that Sulfidlat can melt into. " Furthermore, by AWuh en a

the in the cycle « ^rb ' ^c '^" ^de " _u ^S r ^a _de " ^ Sli-Soda amount from the melt rmtel ^ the art

s.erungsvorrichtung an alkahsche Mcja Jg a su fid. act of 25 to 100 /.

a su fid
Thereby w.rdm Sulphid fV
Cooking liquor in proportion
Soda increased.

the

ren can be a

Ö. » alkaline as well as from sulphidic waste liquor. In this case the sulphite boiling can take place during the period during which a possibly very large part of the sodium carbonate of the melt »$ ^B m, t ice dl? Exercise device 9 converted into sodium sulfite and then fed back into the mixer 3ί • As can be seen in particular from the instructions (l) a2) and (3) ._kamidu, c ^ ^

the sulphurisation rate in uu "c" v. '' -T "Vj _rt "

and sulfitic ^ηΒΐ ^ ^β ™ * Ϊ5 ^, SSTodeTefn the entwed "^ mmsulfit a ^

^Sodium ' ^u ' ^ _hp ^Un K _0C hflus _S ige with a »« '^^^ S weighing part of the sodium carbonate was _{crystallized as Na 2} CO ₃ · H ₂ O, which was then separated from the residual liquor in a centrifuge. The purity of soda obtained in this way was 95 ° / _0th The separated soda was redissolved in water, ₀ brought to a solids concentration of 15 ° / and then the Schweflungsstufe supplied in "which absorbs the sulfur dioxide contained in the exhaust gas of the regeneration furnace and the soda was transferred to Natriumsullit Lo.

The sulfur dioxide concentration in the exhaust gas was 0.4 percent by volume and its absorption rate was approximately 90 ° / ₀ . The pH of the aqueous sodium sulfite solution after absorption of the sulfur was 7.8 at a concentration of 18 ° / ₀ . / ice obtained sodium sulfite solution uiuv. in.L α ...., mixed cooking waste liquor.
The concentration of the obtained in the Kristallisationsstiife Natriumsulfitmutlerlauge was on the other hand can be so aach ao about 20 ° / _0, calculated as Na ₂ S and about 4.6 ° / _0, calculated as Na ₂ CO _3. This mother liquor can be used as alkaline cooking liquor with a sulfidity of 100% without the interposition of causticizing.

g ^

jSf ^, _the circular flow rate

a will

will,
Mixture of

contains, or

Sodium sulfite, sodium bisulfite and se are produced. In these cases, neutral sulfitic needed
sulphitic cooking liquid in the and then in the already
treated.

That way you can
and alkaline cooking liquor g
Process stages are regenerated.

The invention is explained in more detail below using exemplary embodiments.

example 1 Example 2

An alkaline cooking liquor with a sulphidicity of 100% and a used, neutral sulphite semi-chemical cooking liquid with a pH value of 6.2, a solids concentration of 4.8%, a molar S / Na ₄ O ratio of 0 , 98 were mixed in a solids ratio of the alkaline cooking liquor to the neutral sulphite semi-chemical cooking liquid of 3: 1 and the mixture up

t with liquid g g

Sfture 35 brought a solids concentration of 55 ° / ₀ . The _d Mihlö b 105 to 110 Nch

the pH of the mixed solution was 10 ^ 5 to 11.0. After or the burn-out of the concentrated solution was the melt of 50 ° / ₀ sodium sulfite, 35 ° / _n sodium carbonate and 15 ° / "other materials, predominantly sodium sulfate.

Then in the same way as in the example! the melt dissolved in water and the sodium carbonate crystallized out under the same conditions as in Beivon game 1 and separated from the muttei liquor. The thereby obtained crystallized sodium carbonate had a purity of 95 ° / _0, while the mother liquor consisted essentially of NatriumsiiHU.

The separated sodium carbonate was dissolved in water

· ■ rt, »krrv-hlauee with a
A used alkaline lye mrt «^ ^ ^ _n ^ ^ _wäBrgen ^^

Sulphidity of 100 ° / ₀ , emem pH if w » ^ _{q1w {} Sodium sulphite sulphurized. The mother liquor was concentration of m, o ^, _f , _{kIih K} hl d di ßrie solution of solid

ratio S / Na, 0 of ° · ⁸⁵ * ^ L i

aqueous solution of ^Ν
l

as

Sodium-

aqueous solution ₈ ™ "J. _λ

component in the molar ^ J * ". ff ¹ ^ _Feststo and the mixture ^b '^ on _konzemrierte concentration of _55/0 ^eing" "~ I, _enofen abrannt.

Waste liquor ^^, ^ / 'Thme ^ SS S? 6V% The enamel Na ₁ S, 31 ^e / o Na ₂ CO ₃ and 8% others

predominantly Na ₁ SO *. wneasr relieved and up

The melt was then poured into water to a solids concentration of _ « _γ · ^^ Then it was poured into an iur

the evaporation Dei w v.

Sulphurized sodium sulfite. The mother liquor was used as _{alkaline cooking} liquor and the aqueous solution of sodium sulphate as a neutral sulphite, semi-chemical liquid.

According to the method according to the invention _{, the active} chemicals of an alkaline cooking waste liquor with high sulfidity can easily be recovered, si that in practice an alkali £ ^. _{hochf smmi industries carried} out

^^ ^^ TtoAbcr also allows the method according to the invention in systems in which both alkaline and sulfitic cooking takes place, _the recovery of the cooking substances from the consumed cooking liquids.

For this! Sheet drawings

207682/263

Claims (1)

I 767 ■ ·> Patent claims: 1. A method for processing a used alkaline cooking liquor from pulp production, which essentially contains Na ₂ S and optionally at least one of the compounds NaJCO ₃ , NaOH and NaHS, by concentrating the spent liquor and burning it out in a regeneration furnace, characterized in that _{gaseous SO 2} formed in the regeneration furnace is absorbed in the aqueous solution of the melt produced during firing or in the aqueous solution of Na ₂ CO ₃ separated from the melt, and this solution is reintroduced into the circuit before the regeneration furnace. 1. The method according to claim 1, characterized in that d ~ .T for the simultaneous processing of alkaline and sulfitic waste liquor, the aqueous ao solution of Na ₂ SO ₃ , which by absorption of gaseous SO ₂ in an aqueous solution of Na _{2 separated from the melt} CO _{3 was} formed, partly used as a reagent for the sulphite cooking and the mixed liquid of sulphite waste liquor and alkaline waste liquor is _{burned together with the rest of the aqueous Na 2} SO ₃ solution in the regeneration furnace.