BG67533B1 - Metmethod for obtaining bleached microcrystalline cellulose from unbleached cellulose - Google Patents

Abstract

The present invention relates to a method for obtaining bleached microcrystalline cellulose from unbleached cellulose by means of a two-step acidic hydrolysis process, wherein the reaction product is washed with water after each step, i.e. both in the hydrolysis process and in the subsequent bleaching of the resulting microcrystalline cellulose. With this method it is possible to take unbleached paper pulp, which contains a significant amount of hemicelluloses, and obtain bleached microcrystalline cellulose with low pentosan content and with characteristics which make it suitable for use in the pharmaceutical, cosmetics, food and other industries.

Description

The present invention relates to a method for obtaining microcrystalline cellulose from unbleached cellulose by two-stage acid hydrolysis with intermediate washing with water and removal of dissolved pentose sugars, as well as subsequent bleaching of the resulting microcrystalline cellulose. This method allows from unbleached paper pulp, which contains a significant amount of hemicelluloses, to obtain bleached microcrystalline cellulose with a low content of pentosans and with indicators suitable for use including in the pharmaceutical, cosmetic and food industries.

Prior art

It is known from literature and practice that microcrystalline cellulose (MCC) is partially depolymerized cellulose with a low degree of polymerization (DP). When free from organic and inorganic impurities, microcrystalline cellulose has a white powder structure, tasteless and odorless, insoluble in water, dilute acids and most organic solvents.

Its production from plant fibers, its lack of toxicity, its high hygroscopicity and physiological inertness ensure not just harmlessness, but rather a beneficial effect on the human organism, as an excipient for healthy foods and a source of dietary fiber. As a non-absorbable and non-digestible ballast substance, it helps to reduce the caloric content of food products without affecting their organoleptic properties, it has been proven to normalize metabolic processes in the body and even reduce the risk of the appearance of neoplasms.

Due to the mentioned and other qualities due to its chemical nature, microcrystalline cellulose is a multifunctional product with an extremely wide and varied application in the food industry, the pharmaceutical industry and biotechnology, in the cosmetic industry, in the chemical industry and in agriculture.

From the literature, various methods are known for obtaining MCC by a combination of acid hydrolysis and various other processes, in which bleached cellulose is usually used for chemical processing, which is characterized by a low content of pentosans and which is subjected to post-bleaching with specific oxidants to achieve of high whiteness.

US Patent US 9469695 B2 describes a method for the production of microcrystalline cellulose comprising acidifying and purifying the fibrous cellulosic material of heavy metals, followed by washing and hydrolysis of the washed cellulosic material at elevated temperature to obtain a mixture of microcrystalline cellulose and hydrolyzate, followed by separation of the microcrystalline cellulose from the hydrolyzate, wherein the mixture or the separated hydrolyzate or microcrystalline cellulose may be subjected to neutralization. The proposed method does not take into account the whiteness of microcrystalline cellulose, which decreases significantly at the high hydrolysis temperature.

From BG 19462, with analogous US patent 3,954,727, a method for obtaining microcrystalline cellulose is known, in which the hydrolysis of the cellulose is carried out with dilute sulfuric acid at a temperature of

120 to 160°C, with simultaneous chemical disaggregation of the product, which is then subjected to additional bleaching, cleaning, washing and drying.

International patent application WO 2016182867 describes a method that allows to obtain bleached microcrystalline cellulose, both from pulp for chemical processing and from pulp for paper, which involves neutralizing or alkalizing a suspension of an acidic microcrystalline reaction mixture, usually obtained by acid hydrolysis or by electron beam irradiation followed by addition of an oxidant to such reaction mixture.

From the patent RU 2298562 C1 is known a method for the production of microcrystalline cellulose from unbleached cellulose with an initial whiteness of up to 65%, which is subjected to one-step hydrolysis with sulfuric acid and subsequent bleaching of the obtained microcrystalline cellulose with chlorine dioxide in one step. As a result, a maximum whiteness of 80% is achieved. The whiteness problem of microcrystalline cellulose in this method is mainly due to absorption of chromophoric structures on the cellulose in the one-step acid hydrolysis process.

From international application WO 2019095024, a method for obtaining microcrystalline cellulose by two-stage acid hydrolysis and washing with water after each of the hydrolysis stages is known, which allows from bleached paper pulp to obtain microcrystalline cellulose with a sufficiently high whiteness, (i.e. without the need for additional bleaching) and with indicators suitable for use in the pharmaceutical, cosmetic and food industries, in agriculture and the chemical industry.

Based on the above, it can be summarized that most of the known methods for obtaining microcrystalline cellulose by acid hydrolysis of cellulose are not suitable for treating cellulose with a high content of hemicelluloses. Carrying out acid hydrolysis in one degree leads to a significant absorption of chromophoric structures on the cellulose and is accompanied by a significant increase in the Kappa number and a decrease in the whiteness of the cellulose. All this determines the need to develop efficient production processes by which unbleached cellulose can be obtained from microcrystalline cellulose with high whiteness and low content of pentosans, which is suitable for use in the pharmaceutical, cosmetic and food industries.

The technical essence of the invention

It is an object of the present invention to develop an efficient method for the production of microcrystalline cellulose by acid hydrolysis of unbleached paper pulp, so as to obtain as a final product a bleached microcrystalline cellulose with a low content of pentosans, characteristic of pulp for chemical processing.

The problem of the invention is solved by a method for the production of bleached microcrystalline cellulose from unbleached paper pulp, which includes two separate stages of acid hydrolysis, each of which is followed by washing with water and removing the dissolved pentose sugars, as well as subsequent bleaching of the microcrystalline cellulose to a high degree of whiteness.

The method according to the invention includes the following operations:

a) First degree of acid hydrolysis, in which mainly hemicelluloses and to a lesser extent cellulose are dissolved;

b) Washing the cellulose after the first stage of acid hydrolysis, in which the dissolved sugars are removed;

c) A second stage of acid hydrolysis, in which the degree of polymerization of the cellulose is reduced to a particle size characteristic of microcrystalline cellulose, and the content of pentosans is reduced to levels characteristic of cellulose for chemical processing;

d) Washing the microcrystalline cellulose obtained after the second stage of acid hydrolysis;

e) Bleaching of the microcrystalline cellulose obtained after two-step acid hydrolysis with oxidative bleaching reagents.

f) Washing after each bleaching step and isolation of the resulting high whiteness microcrystalline cellulose.

The essence of the method according to the invention is that, as a first stage of processing, the starting material - unbleached cellulose (as absolutely dry) with a concentration of 5% to 30% relative to the total weight of the reaction mixture, is subjected to acid hydrolysis, during which the acid is added in an amount of 1.0 to 5.0 percent by weight, based on the weight of the absolutely dry cellulose. The hydrolysis is carried out at temperatures from 125°C to 180°C, preferably at a temperature from 130°C to 160°C and even more preferably from 135°C to 150°C. The reaction time in the first step of acid hydrolysis is from 10 to 180 min, preferably from 20 to 150 min, and even more preferably from 40 to 120 min.

Between the two stages of acid hydrolysis, an intermediate washing of the cellulose with distilled water takes place without the need for neutralization.

In the second stage of the method according to the invention, acid hydrolysis of the cellulose washed after the first stage (as absolutely dry) is carried out with a concentration of 5% to 30% relative to the total weight of the reaction mixture. The acid is added in an amount of 0.5 to 5.0 percent by weight, based on the weight of the absolutely dry cellulose. The hydrolysis is carried out at temperatures from 100°C to 180°C, preferably at a temperature from 120°C to 160°C and even more preferably from 130°C to 150°C. The reaction time in the second stage of hydrolysis is from 10 min to 180 min, preferably from 20 min to 150 min, and even more preferably from 40 to 120 min.

The unbleached microcrystalline cellulose obtained after the second stage of acid hydrolysis is washed with distilled water.

Part of the wash water from the second acid step can be used in the intermediate wash.

The two stages of acid hydrolysis can be carried out in the same reactor or separately, as a batch or continuous process.

Unobviously to the person skilled in the art, it was found that when the first stage of acid hydrolysis is carried out early in the process, but at a different duration, as a function of the reaction temperature, a point is passed where the Kappa number drops sharply and a significant amount is dissolved part of the hemicelluloses and related chromophoric structures. Completion of the first stage of hydrolysis at this point ensures their removal from the system through the intermediate wash. Thus, in the second stage of acid hydrolysis, destructive processes with dissolved sugars leading to the formation of new chromophoric structures are significantly limited and the possibility of their absorption on cellulose is reduced to a minimum. The resulting unbleached microcrystalline cellulose has a significantly lower Kappa number than the original unbleached cellulose and that obtained only after one-step acid hydrolysis, which in turn is a prerequisite for more efficient bleaching with a lower consumption of reagents. The content of pentosans is also significantly lower, which is comparable to the levels in cellulose for chemical processing.

The bleaching of the resulting unbleached microcrystalline cellulose is carried out with classic oxidative bleaching reagents such as: hydrogen peroxide in an alkaline environment; oxygen under pressure in an alkaline environment (alone or together with hydrogen peroxide); chlorine dioxide and peracetic acid. Bleaching conditions are standard for the respective reagents. The bleaching temperature is in the range of 50°C to 110°C, preferably at a temperature of 60°C to 100°C and even more preferably from 70°C to 100°C. The duration of bleaching in the individual stages is from 10 min to 240 min, preferably from 20 min to 180 min and even more preferably from 30 to 120 min. The consumption of bleaching reagent and added NaOH is from 0.2 to 5.0 percent by weight, based on the weight of absolutely dry cellulose. The pressure when carrying out oxygen bleaching is from 0.2 to 7.0 atm. The number of bleaching stages and the consumption of bleaching reagents is less than that required for bleaching the starting cellulose, which is determined by the substantial reduction in the Kappa number, as a result of acid hydrolysis. After each degree of bleaching, a water wash is carried out.

The final washing of the obtained bleached microcrystalline cellulose is carried out with desalted water. Part of the washing water can be used for washing after previous stages.

According to the invention, unbleached or oxygen-delignified cellulose is used as the starting fiber material, obtained by boiling either by sulfate, or by sulphite, or by sodium method, or after boiling with organic solvents, or after processing of waste paper.

The cellulose used as a starting material can be from coniferous wood, from broad-leaved wood, from non-wood plant raw materials, such as from straw, hemp, kenaf, ramie, bamboo and other cellulose-containing agricultural plant waste.

The cellulose used may have a high content of pentosans above 15%.

Hydrolysis in the first and second stages of acid hydrolysis in the method according to the invention can be carried out with dilute organic acids (oxalic, formic, acetic, etc.), sodium bisulfite and sodium bisulfate solutions, with dilute inorganic acids, preferably mineral acids such as hydrochloric (hydrochloric) acid, sulfuric acid and nitric acid.

The advantages of the method according to the invention are:

- production of microcrystalline cellulose with high whiteness by acid hydrolysis of unbleached cellulose and subsequent bleaching at a significantly lower consumption of reagents and at a shortened number of stages compared to those that would be necessary for the bleaching of the starting cellulose;

- carrying out the acid hydrolysis in two stages and washing the cellulose after the first stage leads to limiting the destructive processes with the dissolved sugars and the formation of chromophoric structures, as a result of which the possibility of absorption of these structures on the cellulose is reduced to a minimum;

- the resulting unbleached microcrystalline cellulose has a significantly lower Kappa number than the original cellulose, which also determines the more efficient course of the bleaching process;

- through an appropriate temperature-time regime of the two-stage acid hydrolysis and after additional bleaching, bleached microcrystalline cellulose with a low content of pentosans is obtained, characteristic of cellulose for chemical processing and with indicators suitable for use in the pharmaceutical, cosmetic and food industries;

- between the two stages of acid hydrolysis, the reaction product is washed without pH correction;

- an additional significant advantage of the two-stage management of the acid hydrolysis process is its much more even course.

Examples of implementation of the invention

The invention is illustrated by the following examples, which clarify it without limiting its scope of protection.

The tests were carried out with unbleached and oxygen-delignified broadleaf cellulose, which is characterized by a content of pentosans in the cellulose above 18%.

Acid hydrolysis in the first and second stages is carried out in rotating 2 liter stainless steel laboratory autoclaves, which are isolated by a heat-resistant polymer from possible contact of the acid with the metal.

The autoclaves were charged with a pre-disintegrated cellulose pulp containing 30 g of abs. dry cellulose, with a certain mass concentration and the necessary amount of diluted acid added to it.

The autoclaves are placed in a polyethylene glycol bath that is preheated to the required temperature. The time for tempering the autoclaves is 5 min. After completion of the hydrolysis process, the autoclaves are removed and cooled with cold water.

The resulting microcrystalline cellulose is washed on a Buchner funnel with a vacuum pump through a filter with pore sizes of 2-3 μm. The first filtrate was separated for analysis for sugars and furfural on an HPLC Dionex liquid chromatography system according to NREL Technical Report (NREL/TP-510-42623). Each sample was washed with distilled water. A partial intermediate wash is also carried out between the stages of acid hydrolysis, in which the mass is diluted with distilled water to a concentration of 5%, then filtered.

Bleaching with CO2, hydrogen peroxide and peracetic acid is carried out under appropriate conditions in polyethylene bags placed in a water bath. Oxygen bleaching is carried out under pressure in rotating autoclaves.

The wash after each bleaching stage is done with distilled water and the final wash with deep desalted water.

Particle size and size distribution was characterized on a Fritsch Analysette 22 Micro Tec Plus laser analyzer. The average degree of polymerization of the cellulose DP was determined according to the pharmacopoeia standard and the whiteness according to ISO 2470. The content of pentosans in the cellulose was determined according to TAPPI T223 cm-10 and the Kappa number according to ISO 302:2004. The yield of MSS is determined by weight.

Example 1

Table 1 presents the results of one-stage and two-stage acid hydrolysis of oxygen-delignified cellulose, characterized by a Kappa number of 8.83% and pentosan content of 19.7%. Acid hydrolysis was carried out with dilute sulfuric acid at an acid consumption relative to absolutely dry cellulose of 3.0% for the first stage and 2.0% for the second stage. The reaction temperature is 150°C and the mass concentration is 12.5% for both stages. The duration of the process is 60 min for the first degree and 60 and 90 min for the second. The cellulose was washed after the first acid step with distilled water.

Under the conditions of conducting the process before the second stage of acid hydrolysis, no absorption of caramels and degradation products of sugars on MCC was observed. At this temperature after 60 min, the content of pentosans decreases to 11%, and the Kappa number to 4.6. The average degree of polymerization is lowered to 460.

Table ! Acids >>113 hnlrolnli Oi PiiirmJ 1'ks.i>rch11np-de.1i1nm4 ^> NPNryNj Sh.Plish at coiciggratspp of the mass IJ.5% c gemier* At T 150'C

With Li V· II31 ON kNDryL! 1st frontal. % You're gliding. % UI lsc. KSNLOZFor % IFI BCLL furfur% FROM AS-Ci UP IIO SCAN PG Pharm, LV1TT-LVD|P % knid h n g;ro First gtsisp acid 1 elevated on itaη,ΐιψ 1 c _l acid-dslcgnificnrd salui»y prιι μιιΐΰ,ι pi k-Nya 3%; 1gri'1u,1zhpslnps100 invi gemiusip ura T 15Q C Nj rank 82.4 1 l* K.lb 0.45 S77 4(11 10.98 4.58

Second eggs, acid and pi stliirtii knsl«rolil-leli in ifnci paitu unyy-iou ·φμ rshthi nl k-nl 2%, practlantalvos1 66 and Mlshn k irMucpanoi 15DC 60 Mail 75.5 11 Hi 3.99 (8 IfrU.M) 11).78 (1.75 400 111 0 7(1 4.48 9u UMI 71.9· ί.Ι.Μ+130ι 3.9a 10+2.95) 1 in U.79 377 JOI 6.4? J .89

BG 67533 Bl

After the second stage of hydrolysis, the content of pentosans further decreases to 6%. The average degree of polymerization is slightly above 300. The Kappa number after the second stage of acid hydrolysis reaches levels of 4 units, which is a prerequisite for more effective bleaching.

Bleaching with peroxide was carried out at mass concentration 10%, temperature 70°C, duration 120 min, consumption of peroxide 1.0% and consumption of NaOH 2.5%.

Bleaching with CO2 was carried out at mass concentration 10%, temperature 70°C, duration 60 min, consumption of HCl 2.0% and 2.5%.

Microcrystalline cellulose obtained after two-step acid hydrolysis of oxygen-delignified unbleached cellulose was bleached to high whiteness in two bleaching stages (Table 2), with an additional slight decrease in the content of pentosans and the average degree of polymerization of cellulose.

Bleaching rates and consumption of bleaching reagents is less than that required for bleaching the original cellulose, which is determined by the substantial reduction in Kappa number as a result of acid hydrolysis.

It was found that carrying out the bleaching steps with CO2 in an acidic medium as the last step provides the required low ash content of the microcrystalline cellulose.

A higher bleaching rate of microcrystalline cellulose was observed compared to the bleaching of paper pulp.

Ta&i. 2 Bleached* is SU _A n HjOi hi MCC obtained a slm lnspichnic acid hydrolysis of LlL-lV.'IOM and Kat.i'

NZ C13MD31

Uvdpnnya IL shLs. Shyie white o1 a, *4 [Ml COURT OF COURT, GST IICIICJI, % ΙΙβΗΠηίΗΗ' % epejch size MCC _t .ym-- Чссд second ГГСПГИ kpgechchill HNDrШШЗЙ І stshiyartny KRG.|ProD11O-,1<^ШП11|fiPIrj1P1 at κπΉΐΐΕίΓΓΠϋίΠΜ of mass T 15О'С _D duration Ml rank n rlnad pa kpselnsh 2% 1 year whitening 1.0*4 expenditure 2.5% decomposition N1OH 120 mln., ZS, 1P% mlzt Pet Hiitaaiui k s C Ju j 2.0% p gdalSh 6(1 min!.. 70'C 10 ^c oK*ep]. 507 SS.5 chambers* 6.27 Al .3 stell acid wirimIIU NL Etdnlirgma ............. ................. ηρη KUicurrlW-ilUii of the iaedta 12.5%, ttapgrlptlT ! WC, prtilzhngslpoST WJ mvp in riTzDOa Mite-Tadi !% 1 p (pba.chadne 1.0% consumption H;Oj 2.5% ra.iad Νζϋί 1 1ID MinI.. 7ΪΙΤ, 10% drink II l. иххпшзг with L'lU; 2.5% rapod aP 00 nin., 70 S. 10% SHISH 256 9| .II 0.U44S 5, «8 51.6

BG 67533 Bl

The presented example shows that from oxygen-delignified unbleached cellulose, by two-step acid hydrolysis and subsequent bleaching, microcrystalline cellulose can be obtained, meeting the requirements of the European Pharmacopoeia and characterized by a pentosan content comparable to that of commercial microcrystalline cellulose products, which are obtained from bleached pulp for chemical processing.

Example 2

Table 3 presents the results of one-step and two-step acid hydrolysis of unbleached broadleaf cellulose, characterized by a Kappa number of 18.01% and pentosan content of 19.9%. Acid hydrolysis was carried out with dilute sulfuric acid at an acid consumption relative to absolutely dry cellulose of 3.5% for the first stage and 2.0% for the second stage. The reaction temperature is 150°C and the mass concentration is 12.5% for both stages. The duration of the process is 60 min for the first degree and 60 and 90 min for the second. The cellulose was washed after the first acid step with distilled water.

Under the conditions of conducting the process before the second stage of acid hydrolysis, no absorption of caramels and degradation products of sugars on MCC was observed. At this temperature after 60 min, the content of pentosans decreased to 10% and the Kappa number to 13. The average degree of polymerization decreased to 460.

Table 5 Acidic lidrolnzz ni son to pi pa ngnzbolsna cellulose at kohuphi ricin on the table

uslorshn tld hydrtl Ilia yield, % GLMKPL, % IPI MSC- kgnpshya, % PG jasp· furfur. *'o N DP then SCAN DP jin firm. ΙΙ£ΙΙΤ0·Ί3ΗΗ % h'^EId ΊΙΚ.ΊΠ The first stage of the N Kneeshan kondrolnta pa standard cens belen a cglu.usi and pit split at 3.5%: po.tkljn1gl|1ОС1 ¢0 min n tempgeraturl T 150'С Κ-Ή3 3.5% ] 1 jSO· 60 mnn 7S.2 1.4+ 7.65 0.43 581) 461 him In case of wall knee tnyarolysis C1yP.1irti< and specific 1#UbbL1SHY celluloma at RINSHIM K-nl 2%, noujuiiKHir.LifCrl ¢0 * 96 Ini a gemlEfacura J50/C __ CrfJ min bb.4 (].44' 1.341 , 2. S3 (7.65+1 7 Y 9.43 6.6 L 4HJ 328 5.85 L2.2S 411 min #0 1 1.44Article 2) 3.26 (7 65-2.1 1 1 4.76 U 67 369 1 2W 5.73 11.56

It can be seen that after the second stage of acid hydrolysis, the content of pentosans further decreases to levels below 6%. The average degree of polymerization is about 300. The Kappa number decreases after the second stage of acid hydrolysis to levels of about 12 units, which is a prerequisite for more effective bleaching.

Bleaching with peroxide was carried out at mass concentration 10%, temperature 70°C, duration 120 min, consumption of peroxide 2.0% and consumption of NaOH 2.5%.

Bleaching with SU ₂ was carried out at mass concentration 10%, temperature 70°C, duration 60 min, consumption of HCI 0.5%, 1.0% and 2.0%.

BG 67533 Bl

Tu6.1l-4 Ntbslians with ΟΟχΗ H.tlj our MCC obtained schel lvust#cpy knssdppii chnlrolizy pa naled cellulose

Uslpnn-i on 1p6ëlv1is DP on pharynx. whiteness, % ISO SUDER^!. IID Inaccuracy % % average size MSS, ct SlGl Spra Ci'eUcIi of chiesLpshi androsigza Of standard psibsLsna cellulose at »his|ggra|||i not IOM-go 12.5%; teitterv-google 1 1 30C, ProGGA-TZTSTS-LC IT MNP II RYPP.1 at 2% E st. eyelid 2.0¾ r&zcode H _; Oj 2.5% rathod NbOEE [20 Sh1n. _d 70 ^d C, 10% k+sh;. JL Ct. Ptbslisshte G SU; 2 11% rpmtl iC1 60 MIN-. TO'C, KPVkWiU. Ill is; sale with _S.U. 311 40J i. 1094 5.52 31.8 After ator· C1SPEL pd shn. single kidrishsh of syndartai iepzbsdip nelulii at cash.ts.-|<[early t|a cieai 12.5%, j cm I icpiiTvpu T 150'С pro.t đjn ι el post 9v mnp and ραιχο,τιυ kngelni· 2% 1 Ct jllSewne Л1% |Х«0dЦ.О' 2.5% rimiMg,™ 120 kiiil.. 70'C, 10% water._______ II century itbeyaaape with SU; 2.0% pLmij.il and C1 60 inn , 70'С, 1 Q% tu»HtL [11 st bleaching with SU- 0.5% seedling lC1 60.win., 70'С, ΐθ%popi 11 Yu 39.9 0.0293 5 +14 32.4

Microcrystalline cellulose with high whiteness and with indicators meeting the requirements of the European pharmacopoeia is obtained by bleaching microcrystalline cellulose, which was obtained after two-stage acid hydrolysis of unbleached cellulose (table 4).

Bleaching rates and consumption of bleaching reagents is less than that required for bleaching the original cellulose, which is determined by the substantial reduction in Kappa number as a result of acid hydrolysis.

It was found that carrying out the bleaching stages with _C1O2 in an acidic environment, as the last stage, provides the required low ash content of the microcrystalline cellulose.

A higher bleaching rate of microcrystalline cellulose was observed compared to the bleaching of paper pulp.

Example 3

The studies were carried out with unbleached broadleaf cellulose, characterized by a Kappa number of 16.62% and a pentosan content of 19.6%.

Acid hydrolysis was carried out with dilute sulfuric acid at an acid consumption relative to absolutely dry cellulose of 3.5% for the first stage and 2.0% for the second stage. The reaction temperature is 150°C and the mass concentration is 12.5% for both stages. The duration of the process is 30, 60, 90, 120 and 150 min for the first stage and 60 and 90 min for the second (table 5). The cellulose was washed after the first step of acid hydrolysis with distilled water, and a partial intermediate wash was also carried out.

In the course of the first stage of acid hydrolysis, a significant decrease in the average degree of polymerization of cellulose and the content of pentosans was observed, and the process was accompanied by a corresponding decrease in yield.

Unexpectedly for the person skilled in the art, it was found that the Kappa number drops sharply by about 4 units at the very beginning of acid hydrolysis, and at this reaction temperature, after 60 minutes of carrying out the first stage of acid hydrolysis, it increases substantially and at 150 min reaches a value that exceeds by 2 units that of the starting cellulose. This effect can be explained by absorption of caramels and sugar degradation products on the MCC.

After the second stage of acid hydrolysis lasting 60 and 90 min, the content of pentosans further decreases to 2.8% - 3.8%, and the average degree of polymerization is 247 - 281. The Kappa number of microcrystalline cellulose practically does not change after the second stage of acid hydrolysis .

I'alL·. 5 Khcvj.

YCJIUBIIH HJ X H jp .ΙϋΟΜΗ, % glucose IP d 1Stc. K<1MOZL _Ch % ΰΐ 1NC. furfur. % 01 JSCg 1 DP P9 SCAN PR by flrm· IeNT>No.NN % κόπα chenelo First wall acid tmdrl.shzi ia siidir! of unbleached cellulose at a mass concentration of 12.5 °C: xyzngrapnia of H,S < 1 _l 3.5% tf ι gmperature Ί 150'С_________ 3D nnn. 7K.I 1.69 7.95 II 55 590 472 8.91 1319 3.5%Η;5ϋ^ jO min. 74.6 2 m 9.22 0.93 543 434 7.14 12 N| 1.5% 90 min. 72.1 J .21 9.31 129 45" 366 5.42 14.71 1.5% H _? MP 1JO min. 7ύ 9 3.86 K.% 1.Я1 416 333 4.66 17.35 3.5%L;MH 1 50 min. £7.7 4.90 Bt.K 2.5] 360 288 3.60 18.32 Brqpa сГгнгп ^Шт-'1НШ!a spreltp us spEshartyaa nsnt6s.1sni sh-|ului when wounded on continued re.HWT Ml and 91) min and temperature 1М'С__________________________ 64 ipk 1 tttegin + 90 mkn 1 degree 65.3 12 M+2 33ϊ 4.94 (9.12+1.ΙΟΙ 10.32 1.23 351 281 1.7S 12.82 9P mhil I C1 Brilliant Aiil whip 1 11 cictbh M. 5 13.2TJ-2.471 5.68 (9.11 * J. 1Я1 10.48 143 309 247 2.82 [5.|H

BG 67533 Bl

Therefore, from the point of view of the optimal bleaching of microcrystalline cellulose, it is desirable under the conditions of carrying out the two-stage acid hydrolysis with an intermediate washing with water, that the first stage of acid hydrolysis, at the indicated reaction temperature, should have an optimal duration of about 60 min, in which achieves a final microcrystalline cellulose Kappa number 4 units lower than that of the starting cellulose.

Bleaching with peroxide was carried out at mass concentration 10%, temperature 70°C, duration 120 min, consumption of peroxide 2% and consumption of NaOH 2.5%.

Bleaching with _C1O2 was carried out at mass concentration 10%, temperature 70°C, duration 60 min, consumption of HCI 2.0%.

Table 6 Bleaching C C!O _a II HjOg 111 MCC Received C.tsl e^Hocii'iJCHin· n Two-stage acid shtrl.tnzl nl ni nchiglonz schultz

Uslpvin through bleaching 1>P llfl company Κ1ΙΠ. whiteness a, ' penkpann. % ISO % medium size MCC< cm After 60 min. 1 wall n 90 min. ΓΪ degree kmeelmppd knzfzlpi uh etlndav·^ isyzbslsna 1 CT. qtch.h shne 2.0% mix 2.5% mix NaOH 120 min., TOT. 10% Hons. I 11 gt i^s.zvaie e ravddCi ЧНН _Ч 'O'C, |Q% lepi 262 8I.2 J.J7 12.7 Article 90 of the Civil Code 1 gtchpsh a «0 rank. II degree ssalpshga hacntppv of epntshgpch· nenzbelep· iirmoii _{1 fl} . [I yr bleach vCIO2.0% fuzz! n.d 60 mnp, 71GS, 10% conc. 23S H4.7 2 75 2M C.iu.n tS6 mnn. I erentn кггишшк унцкгыпя ua tTanijpTWn ithiИнлац· ц₽.pulp m 1 er. HJoe.iBBue 2.0% pVmol H;Ui 2.5% split NaOH Ι2ϋ№Ε||.. 70'C, 10%KPH11. 11 ct. nzpe.toyans c CIO _; Ϊ 0% prnMMi 'l bOhmic , 70'C, 10% num 271 S1 2 3 46 35 4

Technological effect of carrying out bleaching after two-stage acid hydrolysis of unbleached cellulose at a reaction temperature of 150°C, with a duration of the first stage of 60 MIN and of the second 90 MIN (table 6) is the production of microcrystalline cellulose with high whiteness, low content of pentosans and with indicators meeting the requirements of the European pharmacopoeia.

The higher values of the Kappa number for the unbleached microcrystalline cellulose naturally lead to a lower whiteness after bleaching, and with a one-step acid hydrolysis process, the whiteness of the microcrystalline cellulose is 7% lower.

Claims (1)

Method for obtaining bleached microcrystalline cellulose from cellulose with a concentration of 5% to 30% relative to the total weight of the reaction mixture, by two-stage acid hydrolysis with dilute acid, for a time of 10 min to 180 min, including intermediate washing with water of the cellulose obtained after the first stage of acid hydrolysis, characterized in that unbleached or oxygen-delignified cellulose is used as a starting material, the first stage of acid hydrolysis is carried out with dilute acid in an amount of 1.0 to 5.0, based on the weight of absolutely dry cellulose at temperatures from 125°C to 180°C, after which the cellulose washed after the first stage of acid hydrolysis with a concentration of 5% to 30% relative to the total weight of the reaction mixture is subjected to a second stage of acid hydrolysis with dilute acid in an amount of 0.5 to 5.0 weight percent, based on the weight of the absolutely dry cellulose, wherein the hydrolysis is carried out at temperatures from 100°C to 180°C, followed by washing with water and bleaching of the resulting unbleached microcrystalline cellulose, after each degree of bleaching the microcrystalline cellulose is washed with water, and the final washing of the resulting bleached microcrystalline cellulose is carried out with deionized water