Method for cleaning oil sludge with high water content and cleaning agent

Abstract

The application discloses a high-water-content oil sludge cleaning method, which comprises the steps of centrifugation, primary sedimentation, cleaning, secondary sedimentation and drying, wherein the cleaning agent used in the cleaning step comprises the following components: chitin-based surfactant, zero-water sodium metasilicate, fatty alcohol polyoxyethylene ether, sodium percarbonate and sodium chloride. The application has the advantages of simple cleaning method, small equipment investment, high cleaning efficiency when treating high-water-content oil sludge, and oil removal rate of more than 90%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oily sludge treatment, and particularly relates to a high-water-content oily sludge cleaning method and a cleaning agent. BACKGROUND

[0002] Oily sludge is one of the main solid wastes generated in the process of crude oil exploitation, transportation, storage and refining. Oily sludge belongs to a multiphase system, which is generally composed of oil-in-water (O / W), water-in-oil (W / O) and suspended solids. They are fully emulsified and have high viscosity, and thus are not easy to settle, so it is difficult to treat. Due to the limitation of existing treatment processes, currently, sludge from different sources is usually piled together. With the increase of the piled quantity, not only the land is occupied, but also the surrounding soil, atmosphere and water body are polluted due to the large amount of hydrocarbons contained in the oily sludge, which will pose a threat to human health and the environment. With the increasingly stringent pollution regulations in various places, oily sludge has been listed in the National Hazardous Waste List of China. In order to solve this problem, technologies such as pyrolysis, solvent extraction, thermal chemical cleaning, ultrasonic assisted treatment and combination of different treatment methods have appeared.

[0003] In the above disposal methods, thermal chemical cleaning is to clean oily sludge with a solution prepared by using a surfactant having hydrophilic and lipophilic groups. Through the interfacial tension reduction and special adsorption performance of the surfactant, and under the assistance of heating, mechanical stirring and sedimentation, the separation of oil, solid and water three phases is realized. Compared with other existing treatment methods, thermal chemical cleaning has the advantages of wide application range, relatively mature technology, simple process, high automation degree and low equipment investment, and is thus applied more.

[0004] However, for tank bottom sludge, oily sludge of a refinery and the like, due to the complex source, there are problems such as high water content and serious oil-water emulsification, and direct use of thermal chemical cleaning has problems such as low cleaning efficiency, large amount of reagent used, secondary pollution caused by cleaning reagent and the like.

[0005] In summary, there are many shortcomings and deficiencies in the current treatment of high-water-content oily sludge by using thermal chemical cleaning method, and therefore it is of practical significance to develop a high-water-content oily sludge cleaning method and a cleaning agent which are simple in process and friendly to the environment. SUMMARY

[0006] The present application is aimed at the deficiencies of the prior art, and provides a high-water-content oily sludge cleaning method.

[0007] The second object of the present application is to provide a cleaning agent for high-water-content oily sludge cleaning.

[0008] In order to achieve the object of the present application, the technical solution adopted by the present application is as follows: a high-water-content oily sludge cleaning method, comprising the following steps:

[0009] Step S1: preparing chitin-based surfactant and preparing cleaning agent;

[0010] Step S2: centrifuging high water content sludge in a tank to separate oil, water and solid;

[0011] Step S3: including two parallel steps S3-1 and S3-2;

[0012] Step S3-1: primary settling, placing oil layer and water layer separated from step S2 in another tank, and standing for 10-20 hours to obtain oil layer, water layer and solid layer;

[0013] Step S3-2: cleaning, adding cleaning agent prepared in step S1 and water into solid obtained from step S2, and stirring at constant temperature to make oil residues in the solid fully mix and react with the cleaning agent, and standing for 10-30 minutes after cleaning;

[0014] Step S4: secondary settling, placing oil layer and water layer separated from step S3-2 in another tank, and standing for 10-20 hours to obtain oil layer, water layer and solid layer;

[0015] Step S5: drying, pouring away oil layer and water layer after standing in step S3-1 and step S4, and drying the obtained solid layer to obtain oil-removed soil.

[0016] Preferably, the mass ratio of cleaning agent to solid layer in step S3-2 is 1:(20-30), and the mass ratio of solid layer to water is 1:(50-100).

[0017] Preferably, the cleaning temperature in step S3-2 is 70-80℃, and the cleaning time is 30-60 minutes.

[0018] Preferably, the drying temperature of the solid layer in step S5 is 110-120℃, and the drying time is 6-12 hours.

[0019] A cleaning agent for high water content sludge is prepared by mixing modified chitin-based surfactant, zero-water metasilicate sodium (anhydrous metasilicate sodium), fatty alcohol polyoxyethylene ether, sodium percarbonate, sodium chloride and water in the following proportions. The weight ratio of chitin-based surfactant, zero-water metasilicate sodium, fatty alcohol polyoxyethylene ether, sodium percarbonate, sodium chloride and water is 1:(0.08-0.15):(0.03-0.10):(0.03-0.10):(0.01-0.10):(100-500).

[0020] Preferably, the chitin-based surfactant is obtained by modifying chitin, and the preparation method of the chitin-based surfactant comprises the following steps: first, chitin is added into a sodium hydroxide solution with a concentration of 0.5-0.8 mol / L at a mass ratio of chitin to sodium hydroxide solution of 1:(20-30), and then heated at 60-70 DEG C for 8-12 hours to remove part of the acetyl groups; then, the product with a deacetylation degree of more than 70% is reacted with propylene oxide at a mass ratio of the product to propylene oxide of 1:(8-10) to obtain a hydrophilic surfactant; and then, the hydrophilic surfactant is subjected to an alkylation reaction with hexadecyl trimethyl ammonium bromide at a mass ratio of the hydrophilic surfactant to hexadecyl trimethyl ammonium bromide of 1:(5-7) to introduce carbon chain structures with different lengths at the amino sites, so as to finally obtain a chitin-based surfactant with amphiphilic properties. The deacetylation degree of the removal of part of the acetyl groups is preferably 70-80%.

[0021] The high water content oil sludge in the application is oil sludge with a water content of more than 30%, in particular, tank bottom sludge and oil sludge in oil refineries.

[0022] Compared with the prior art, the application has the following beneficial effects:

[0023] (1) The main component of the cleaning agent is an amphiphilic surfactant obtained by modifying chitin through deacetylation and etherification, and the cleaning efficiency is high, and the oil removal rate can reach more than 90%; chitin is the second most abundant biopolymer in nature and is widely distributed, and is an important component of the shells of many lower animals, especially arthropods such as shrimps, crabs and insects, so the cleaning agent used is a natural high molecular polymer with low toxicity, biodegradability and good biocompatibility, and has environmental friendliness, and the raw material is easy to obtain, thereby reducing the use cost of the oil sludge cleaning agent; (2) The application can effectively improve the cleaning efficiency of high water content oil sludge by coupling heat chemical cleaning with centrifugation and sedimentation, and the process is simple, the equipment investment is small, and the application has great popularization and application potential.

[0024] Other advantages, objects and features of the application will be apparent from the following description, and will be understood by those skilled in the art through the study and practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 It is a process flow diagram of the oil sludge cleaning method of the application.

[0026] Figure 2 It is a conductivity graph of the main component, amphiphilic surfactant, in the cleaning agent at different pH values. DETAILED DESCRIPTION

[0027] The application is further described below in connection with specific examples, it should be noted that the examples do not constitute a limitation on the scope of the application.

[0028] Embodiments 1-4 of a cleaning agent for high water content oily sludge are shown in the following table:

[0029]

[0030] The cleaning agent for high water content oily sludge obtained in Example 1 above was used to measure the conductivity of the surfactant at different pH values by the conductivity-pH method, the detection method and specific operation steps are as follows: a series of aqueous solutions with different pH values were prepared from the prepared chitin-based surfactant, and were placed in a constant temperature bath at 25°C for uniform dispersion, and the conductivity was measured by a DDS-11A conductivity meter, and the conductivity was plotted against pH. The detection results are shown in Figure 2 The isoelectric point is ph 4.5-7.5, and the entire molecular charge balance results in low conductivity in this pH range. When pH > 7.5 and pH < 4.5, the surfactant has high conductivity, indicating that the entire molecule has strong ionic properties. When pH < 4.5, it mainly exhibits cationic properties, and when pH > 7.5, it mainly exhibits anionic properties, as shown in the attached figure. Figure 2 The conductivity of the surfactant at different pH values can be seen from the isoelectric point property of the conductivity graph, and the prepared surfactant has the characteristics of amphiphilic surfactants.

[0031] Examples 2-4 above also have basically the same effect as the detection results of Example 1 above.

[0032] The oily sludge samples used in Examples 5 and 6 below are tank bottom sludge from oil fields, and the infrared spectrophotometric method is used to measure that the dry base oil content of the oily sludge is 10.8%, and the water content is 36.3%.

[0033] Example 5

[0034] A high water content oily sludge cleaning method, comprising the following steps:

[0035] Step S1: Preparation of chitin-based surfactant and preparation of cleaning agent. First, the chitin-based surfactant is prepared as follows: 20 g of chitin is added to 400 g of 0.5 mol / L sodium hydroxide solution, the mass ratio of chitin to sodium hydroxide solution is 1:20, and the reaction is carried out at 60°C for 8 h to remove part of the acetyl group. After freeze-drying at a temperature of -30°C, a product with a degree of deacetylation of 80% is obtained. 10 g of the deacetylated product is dissolved in 80 g of isopropyl alcohol and stirred uniformly. 80 g of propylene oxide is added, and the reaction is carried out at 60°C for 8 h to obtain a hydrophilic surfactant. Finally, 8 g of the hydrophilic surfactant is added to 40 g of hexadecyltrimethylammonium bromide, and the reaction is carried out at 75°C for 8 h to obtain a chitin-based surfactant with amphiphilic properties. Then, the cleaning agent is prepared: 1 g of chitin-based surfactant, 0.10 g of metasilicate sodium, 0.08 g of fatty alcohol polyoxyethylene ether, 0.07 g of sodium percarbonate, and 0.05 g of sodium chloride are dissolved in 100 mL of deionized water to prepare the cleaning agent.

[0036] Step S2: Centrifugal treatment of high water content sludge to separate oil, water and solids. 60 mL of the above high water content tank bottom sludge is added to a 100 mL centrifuge tube, and centrifugation is carried out at a speed of 8000 r / min for 10 min to separate oil, water and solids.

[0037] Step S3-1: The oil layer and water layer in the centrifuge tube of step S2 are poured into another beaker and allowed to settle for 20 h to obtain oil layer, water layer and solid layer. Since the amount of solids contained in the oil layer and water layer separated in step S2 is small after centrifugal treatment, the floating oil and water layer can be removed by pouring, and a solid layer with low oil content is obtained.

[0038] Step S3-2: 20 g of the remaining solid after centrifugation and pouring of the oil and water phases in step S2 is added with 1 g of the cleaning agent prepared in step S1, and 200 g of deionized water is added. The mixture is stirred at a constant temperature of 70°C for 30 min to allow the residual oil in the centrifuged solid to fully mix and react with the cleaning agent. After cleaning, the mixture is allowed to stand for a short time of 10 min.

[0039] Step S4: Secondary settling, the oil layer and water layer separated by cleaning in step S3-2 are poured into another beaker and allowed to settle for 20 h to obtain oil layer, water layer and solid layer.

[0040] Step S5: Drying, the oil layer and water layer after settling in step S3-1 and step S4 are poured out, and the obtained solid layer is dried to obtain the oil-removed soil.

[0041] The specific process flow is as follows: Figure 1As shown in the above, the oil content of the remaining solid after cleaning of the oily sludge is measured by infrared spectrophotometry, and the dry basis oil content is 0.80%, and the oil removal rate is 92.59%, and the cleaning effect is remarkable.

[0042] Example 6

[0043] A high water content oily sludge cleaning method, comprising the following steps:

[0044] Step S1: preparing a chitin-based surfactant and preparing a cleaning agent. First, prepare the chitin-based surfactant, the preparation method is as follows: take chitin 20g, add 400g sodium hydroxide solution with a concentration of 0.5mol / L, the mass ratio of chitin to sodium hydroxide solution is 1:20, react at 60℃ for 8h to remove part of the acetyl group, freeze dry at-30℃ to obtain a product with a degree of deacetylation of 80%, take 10g of the product with part of the acetyl group removed, dissolve it in 80g of isopropyl alcohol, stir uniformly, add 80g of propylene oxide, react at 60℃ for 8h to obtain a hydrophilic surfactant, finally take 8g of the hydrophilic surfactant, add 40g of hexadecyl trimethyl ammonium bromide, react at 75℃ for 8h to obtain a chitin-based surfactant with amphiphilic properties. Then, prepare the cleaning agent: dissolve 1g of the chitin-based surfactant, 0.15g of metasilicate sodium, 0.06g of fatty alcohol polyoxyethylene ether, 0.08g of sodium percarbonate and 0.08g of sodium chloride in 150mL of deionized water to prepare the cleaning agent.

[0045] Step S2: centrifugal treatment of high water content oily sludge to separate oil, water and solid. Take 60mL of the above high water content tank bottom oily sludge and add it to a 100mL centrifuge tube, centrifuge at 8000r / min for 10min to separate oil, water and solid.

[0046] Step S3-1: pour the oil layer and water layer in the centrifuge tube of step S2 into another beaker and stand for 20h to obtain oil layer, water layer and solid layer. Since the amount of solid contained in the oil layer and water layer separated in step S2 is small after centrifugal treatment, the floating oil and water layer in the upper layer can be removed by pouring, and a solid layer with lower oil content is obtained.

[0047] Step S3-2: add 1g of the cleaning agent prepared in step S1 to 20g of the remaining solid after centrifuging and pouring off the oil and water phases in step S2, add 200g of deionized water, and stir at a constant temperature of 70℃ water bath for 30min to make the residual oil in the solid after centrifugation fully mix and react with the cleaning agent. After cleaning, stand for a short time of 10min.

[0048] Step S4: secondary settlement, pour the oil layer and water layer separated by cleaning in step S3-2 into another beaker, and stand for 20h to obtain oil layer, water layer and solid layer.

[0049] Step S5: drying, the oil layer and water layer after settling in step S3-1 and step S4 are poured away, and the obtained solid layer is dried, thereby obtaining the oil-removed soil.

[0050] The specific process is shown in the following Figure 1 The oil content of the remaining solid after cleaning of the oil-containing sludge is measured by infrared spectrophotometry, and the dry basis oil content is 0.70%, and the oil removal rate is 93.52%, and the cleaning effect is remarkable.

[0051] The oil-containing sludge sample used in the following examples 7 and 8 is oil-containing sludge from a domestic refinery, and the dry basis oil content of the oil-containing sludge is measured by infrared spectrophotometry, and the dry basis oil content is 9.6%, and the water content is 40.2%.

[0052] Example 7

[0053] A high water content oil sludge cleaning method, comprising the following steps:

[0054] Step S1: preparing a chitin-based surfactant and preparing a cleaning agent. First, prepare a chitin-based surfactant, the operation method is as follows: take chitin 20g, add it into sodium hydroxide solution with 400g, the mass ratio of chitin to sodium hydroxide solution is 1:20, react at 60℃ for 8h to remove part of the acetyl group, freeze dry at -20℃ to obtain a product with a degree of deacetylation of 80%, take 10g of the product, dissolve it in 80g of isopropyl alcohol, stir uniformly, add 80g of propylene oxide, react at 60℃ for 8h to obtain a hydrophilic surfactant, finally take 8g of the hydrophilic surfactant, add 40g of hexadecyl trimethyl ammonium bromide, react at 75℃ for 8h to obtain a chitin-based surfactant with amphiphilic properties. Then, prepare the cleaning agent: dissolve 1g of the chitin-based surfactant, 0.12g of metasilicate sodium, 0.05g of fatty alcohol polyoxyethylene ether, 0.05g of sodium percarbonate, and 0.08g of sodium chloride in 100mL of deionized water to prepare the cleaning agent.

[0055] Step S2: centrifugal treatment of high water content oil sludge to separate oil, water and solid. Take 60mL of the above high water content tank bottom oil sludge and add it to a 100mL centrifuge tube, centrifuge at 8000r / min for 10min to separate oil, water and solid.

[0056] Step S3-1: pour the oil layer and water layer in the centrifuge tube of step S2 into another beaker and stand for 20h to obtain oil layer, water layer and solid layer. Since the amount of solid contained in the oil layer and water layer separated in step S2 is small after centrifugal treatment, the floating oil and water layer can be removed by pouring, and a solid layer with lower oil content is obtained.

[0057] Step S3-2: 20g of the remaining solid after the oil and water phases were centrifuged and poured off in step S2 was added with 1g of the washing agent prepared in step S1, 250g of deionized water, and constant temperature stirring at 70°C for 30min in a water bath to allow the oil remaining in the centrifuged solid to fully mix and react with the washing agent. After washing, the mixture was allowed to stand for 10min.

[0058] Step S4: secondary sedimentation, the oil layer and water layer separated by washing in step S3-2 were poured into another beaker and allowed to stand and sediment for 20h to obtain an oil layer, a water layer, and a solid layer.

[0059] Step S5: drying, the oil layer and water layer after sedimentation in step S3-1 and step S4 were poured off, and the obtained solid layer was dried to obtain the oil-removed soil.

[0060] The specific process is shown in Figure 1 The oil content of the remaining solid after washing of the oil-containing sludge was measured by infrared spectrophotometry, and the dry basis oil content was 0.84%, and the oil removal rate was 91.25%, and the washing effect was remarkable.

[0061] Example 8

[0062] A high water content oil sludge washing method, comprising the following steps:

[0063] Step S1: preparation of chitin-based surfactant and preparation of washing agent. First, chitin-based surfactant was prepared, and the operation method was as follows: chitin 20g was added into sodium hydroxide solution with a concentration of 0.5mol / L, the mass ratio of chitin to sodium hydroxide solution was 1:20, and the product with a degree of deacetylation of 80% was obtained by removing part of the acetyl group at 60°C for 8h and freeze-drying. 10g of the product was dissolved in 80g of isopropyl alcohol and stirred uniformly, and 80g of propylene oxide was added and reacted at 60°C for 8h to obtain a hydrophilic surfactant. Finally, 8g of the hydrophilic surfactant was added with 40g of hexadecyl trimethyl ammonium bromide, and the reaction was carried out at 75°C for 8h to obtain a chitin-based surfactant with amphiphilic properties. Then, the washing agent was prepared: 1g of chitin-based surfactant, 0.13g of metasilicate sodium, 0.07g of fatty alcohol polyoxyethylene ether, 0.08g of sodium percarbonate, and 0.05g of sodium chloride were dissolved in 200mL of deionized water to prepare the washing agent.

[0064] Step S2: centrifugal treatment of high water content oil sludge to separate oil, water and solid. 60mL of the above high water content tank bottom oil sludge was added to a 100mL centrifuge tube, and centrifuged at a speed of 8000r / min for 10min to separate the oil, water and solid.

[0065] Step S3-1: The oil layer and the water layer in the centrifugal tube in step S2 are poured into another beaker and allowed to stand and settle for 20 h to obtain an oil layer, a water layer and a solid layer; since the oil layer and the water layer separated in step S2 contain less solids, the upper floating oil and the water layer can be removed by pouring, and a solid layer with a lower oil content is obtained.

[0066] Step S3-2: 1 g of the cleaning agent prepared in step S1 is added to 20 g of the remaining solid after the oil and water phases are centrifuged and poured away in step S2, 250 g of deionized water is added, and constant temperature stirring is performed at 70 DEG C in a water bath for 30 min, so that the residual oil in the solid after centrifugation is fully mixed and reacted with the cleaning agent; after cleaning, the mixture is allowed to stand for 10 min.

[0067] Step S4: Secondary settling, the oil layer and the water layer separated by cleaning in step S3-2 are poured into another beaker and allowed to stand and settle for 20 h to obtain an oil layer, a water layer and a solid layer.

[0068] Step S5: Drying, the oil layer and the water layer after settling in step S3-1 and step S4 are poured away, and the obtained solid layer is dried to obtain the oil-removed soil.

[0069] The specific process flow is shown in Figure 1 The oil content of the remaining solid after cleaning of the oily sludge is measured by infrared spectrophotometry, and the dry basis oil content is 0.76%, and the oil removal rate is 92.08%, and the cleaning effect is remarkable.

[0070] From the above examples, it can be seen that the oily sludge with high water content and high oil content is difficult to dispose, and the cleaning effect is remarkable, and the oil removal rate can reach more than 90%.

[0071] In summary, the cleaning method provided by the present application can effectively solve the problems of high water content, serious oil-water emulsification and low cleaning efficiency of the oily sludge with high water content and high oil content by coupling simple process procedures such as centrifugation and settling, and the cleaning effect is remarkable; the main component of the cleaning agent, modified chitin, is a natural high polymer derived from the shells of arthropods such as shrimps, crabs and insects, and is easy to be degraded, has environmental friendliness, and the raw material is easy to obtain, and the cost is low, and has remarkable practical application value.

[0072] The above is only a preferred embodiment of the present application, and cannot limit the scope of the present application, that is, any simple equivalent changes and modifications made according to the scope of the patent application and the content of the present application are still within the scope of the present application.

Claims

1. A high water content sludge cleaning method characterized by, It comprises the following steps: Step S1: preparing chitin-based surfactant and preparing cleaning agent; the cleaning agent is prepared by chitin-based surfactant, zero-water sodium metasilicate, fatty alcohol polyoxyethylene ether, sodium percarbonate, sodium chloride and water in the proportion of 1: (0.08-0.15): (0.03-0.10): (0.03-0.10): (0.01-0.10): (100-500) by weight; Step S2: centrifugal treatment is carried out on the high-water-content oil sludge in a tank to separate oil, water and solid; Step S3: comprising two parallel steps S3-1 and S3-2; Step S3-1: primary settling, the oil layer and water layer separated by centrifugal separation in step S2 are placed in a tank, and static settling is carried out for 10-20h to obtain oil layer, water layer and solid layer; Step S3-2: cleaning, the cleaning agent prepared in step S1 and water are added to the solid obtained by centrifugal separation in step S2, constant-temperature stirring is carried out, and static setting is carried out for 10-30min after stirring; the mass ratio of the cleaning agent to the solid is 1: (20-30), and the mass ratio of the solid to water is 1: (50-100); Step S4: secondary settling, the oil layer and water layer separated by cleaning in step S3-2 are placed in a tank, and static settling is carried out for 10-20h to obtain oil layer, water layer and solid layer; Step S5: drying, the oil layer and water layer after settling in step S3-1 and step S4 are poured off, and the obtained solid layer is dried; The preparation method of the chitin-based surfactant comprises the following steps: first, chitin is added into sodium hydroxide solution with a concentration of 0.5-0.8mol / L in the proportion of 1: (20-30) by mass ratio of chitin to sodium hydroxide solution, and heating is carried out at 60-70℃ for 8-12h to remove part of acetyl groups; then, the product with a deacetylation degree of more than 70% is reacted with propylene oxide in the proportion of 1: (8-10) by mass ratio of the product to propylene oxide to obtain a hydrophilic surfactant; finally, the hydrophilic surfactant is subjected to alkylation reaction with hexadecyl trimethyl ammonium bromide in the proportion of 1: (5-7) by mass ratio of the hydrophilic surfactant to hexadecyl trimethyl ammonium bromide to introduce carbon chain structures with different lengths on the amino sites.

2. The high water content sludge cleaning method according to claim 1, characterized by: The cleaning temperature in step S3-2 is 70-80℃, and the time is 30-60min.

3. The method of claim 1, wherein the high water content sludge is a mixture of water and oil.

3. The method of claim 1, wherein the high water content sludge is a mixture of water and oil. The solid layer drying temperature in step S5 is 110-120℃, and the drying time is 6-12h.

4. A cleaning agent for use in the method of claim 1, characterized in that: Chitin-based surfactant, zero water sodium metasilicate, fatty alcohol polyoxyethylene ether, sodium percarbonate, sodium chloride and water are prepared into 1: (0.08-0.15): (0.03-0.10): (0.03-0.10): (0.01-0.10): (100-500) by weight parts; the preparation method of the chitin-based surfactant comprises the following steps: first, chitin is added into sodium hydroxide solution with a mass ratio of 1: (20-30), and heated at 60-70 ℃ for 8-12 h to remove part of acetyl groups; then, the product with a deacetylation degree of more than 70% is reacted with propylene oxide with a mass ratio of 1: (8-10) to obtain a hydrophilic surfactant; finally, the hydrophilic surfactant is subjected to alkylation reaction with cetyltrimethylammonium bromide with a mass ratio of 1: (5-7) to introduce carbon chain structures with different lengths at the amino sites.

5. The cleaning agent of claim 4, wherein: The deacetylation degree of the removal of part of acetyl groups is 70-80%.

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