阅读说明：本技术 一种中密度纤维板及其制备方法 (medium-density fiberboard and preparation method thereof ) 是由 白富栋 张跃 严生虎 陈代祥 李政 张通 于 2018-05-29 设计创作，主要内容包括：本发明涉及一种中密度纤维板及其制备方法,首先利用纤维乙醇发酵废水制得30%～40%甲醛溶液,利用NaOH、纤维乙醇发酵废水、纤维乙醇发酵废渣制得碱调节液,再将上述甲醛溶液和碱调节液用于制备脲醛树脂胶液；然后将纤维素乙醇发酵废渣与木材纤维混匀,并施加脲醛树脂胶液和固化剂；最后在模具中,经压缩成型,制得中密度纤维板。本发明在资源化利用纤维素乙醇发酵废水、废渣的同时,制备的中密度纤维板满足使用标准,游离甲醛释放量低,解决了木材资源紧缺、甲醛含量超标、产品不满足使用要求如强度差等技术问题,促进了资源有效利用和清洁生产的发展。(The invention relates to a medium density fiberboard and a preparation method thereof, which comprises the steps of firstly preparing 30-40% of formaldehyde solution by using cellulosic ethanol fermentation wastewater, preparing alkali regulating solution by using NaOH, cellulosic ethanol fermentation wastewater and cellulosic ethanol fermentation waste residues, and then using the formaldehyde solution and the alkali regulating solution for preparing urea-formaldehyde resin glue solution; then evenly mixing the cellulosic ethanol fermentation waste residue with wood fibers, and applying urea-formaldehyde resin glue solution and a curing agent; and finally, in a mould, carrying out compression molding to obtain the medium-density fiberboard. According to the invention, while the cellulosic ethanol fermentation wastewater and waste residues are recycled, the prepared medium-density fiberboard meets the use standard, the free formaldehyde release amount is low, the technical problems that wood resources are in short supply, the formaldehyde content exceeds the standard, and products cannot meet the use requirements such as poor strength are solved, and the development of effective resource utilization and clean production is promoted.)

1. a preparation method of a medium-density fiberboard is characterized by comprising the following steps:

(1) Adopting cellulosic ethanol fermentation wastewater to replace process water to absorb formaldehyde gas to prepare 30-40% formaldehyde solution;

(2) Uniformly mixing NaOH, cellulosic ethanol fermentation wastewater and cellulosic ethanol fermentation waste residues, heating to boil, stopping, cooling and filtering to obtain filtrate, namely the alkali regulating solution;

(3) Adding a first batch of urea, polyvinyl alcohol and a defoaming agent into the formaldehyde solution obtained in the step (1), uniformly mixing, adding the alkali regulating solution obtained in the step (2) to adjust the pH to 8-9, heating to 70-80 ℃, and reacting for 30-40 min; adjusting the pH value of the system to 4-5, reacting for 30-40 min, sampling, dripping into water to form a mist, and adding a second batch of urea and melamine; when a sample is dripped into water in a cloud state, regulating the pH value to be 5-6 by using an alkali regulating solution, adding a third batch of urea, and carrying out heat preservation reaction at 80-90 ℃ for 30-40 min; cooling the system to 70-75 ℃, adding a fourth batch of urea, adjusting the pH to 8-9 with an alkali adjusting solution, cooling, and discharging to obtain a urea-formaldehyde resin glue solution;

(4) Uniformly mixing the cellulosic ethanol fermentation waste residue and wood fibers, and applying the urea-formaldehyde resin glue solution and the curing agent obtained in the step (3);

(5) And (5) putting the mixture obtained in the step (4) into a mould, and performing compression molding to obtain the medium-density fiberboard.

2. The method of claim 1, wherein: the cellulosic ethanol fermentation wastewater obtained in the step (1) is fermented mash from a cellulosic ethanol distillation tower, and is mainly characterized in that: insoluble solid matter is 1% -10%; the temperature is 90-100 ℃; the chroma is large; the wastewater is acidic wastewater, and the pH value is 3.0-6.0; COD (Cr method) is about 10-13 ten thousand mg/L, and mainly comprises soluble xylose, glycerol, acetic acid, volatile phenol, lactic acid, lignin, furfural and various fermentation intermediate products; BOD5/COD is 0.5-0.55, wherein the difficultly biochemically degraded substances and the color development degree substances are mainly aromatic compounds; the content of inorganic salt is more than 2 percent, sodium sulfate is taken as the main component, and sulfate radical is more than 1 percent; and carrying out solid-liquid separation on the fermented mash to obtain the cellulosic ethanol fermentation wastewater.

3. The method according to claim 1 or 2, characterized in that: the preparation process of the formaldehyde solution in the step (1) is to directly use the cellulosic ethanol fermentation wastewater to replace process water in an absorption tower of the existing device or build a side line absorption tower and is specially used for producing the formaldehyde solution by using the cellulosic ethanol fermentation wastewater as absorption liquid.

4. The method of claim 1, wherein: the cellulosic ethanol fermentation waste residue in the step (2) is residue obtained by pretreating, performing enzymolysis, fermenting ethanol and performing distillation separation on lignocellulose biomass, wherein the lignocellulose biomass is straw, wood chip or energy plant containing cellulose, hemicellulose and lignin, and the straw is preferably selected.

5. The method according to claim 1 or 4, characterized in that: in the dry residue obtained after dehydration of the cellulosic ethanol fermentation waste residue in the step (2), the mass content of lignin is 50-65%, the mass content of cellulose is 10-20%, the mass content of hemicellulose is 0.5-3%, the mass content of soluble components is 15-20%, and the mass content of ash is 10-15%.

6. The method of claim 1, wherein: in the step (2), 10-30 parts by weight of NaOH, 50-85 parts by weight of cellulosic ethanol fermentation wastewater and 5-20 parts by weight of cellulosic ethanol fermentation waste residue are respectively calculated; the concentration of the prepared alkali conditioning solution is 10-50%, preferably 15-25%.

7. The method of claim 1, wherein: in the step (3), the total adding amount of the urea is determined according to the molar ratio of formaldehyde to urea of 0.95-1.25; the adding amount of the first batch of urea is 50 to 60 percent of the total adding amount of the urea, the adding amount of the polyvinyl alcohol is 0.1 to 0.6 percent of the weight of the formaldehyde solution, and the adding amount of the defoaming agent is 0.01 to 0.05 percent of the weight of the formaldehyde solution; the adding amount of the second batch of urea is 10-20% of the total adding amount of the urea, and the adding amount of the melamine is 1-5% of the weight of the formaldehyde solution; the addition of the third batch of urea is 10 to 30 percent of the total addition of urea; the adding amount of the fourth batch of urea is 5-10% of the total adding amount of urea.

8. The method of claim 7, wherein: the defoaming agent is one or more of a fatty acid amide defoaming agent, an organic silicon defoaming agent and a polyether defoaming agent; the acid for adjusting the pH value to 4-5 is formic acid solution with the mass concentration of 10% -30%.

9. The method of claim 1, wherein: in the step (4), 10-40 parts by weight of cellulosic ethanol fermentation waste residues and 60-90 parts by weight of wood fibers are uniformly mixed; the addition amount of the urea-formaldehyde resin glue solution is 8-20% of the total fiber weight, and the addition amount of the curing agent is 1-5% of the total fiber weight.

10. The method according to claim 1 or 9, characterized in that: the curing agent is at least one of ammonium chloride, ammonium persulfate, potassium persulfate and the like, and ammonium chloride is preferred.

11. The method of claim 1, wherein: in the step (5), the mixture is placed into a die, and is subjected to cold pressing to form a plate shape, and then hot pressing is performed for 10-20 s; the hot pressing temperature is 100-180 ℃, the hot pressing pressure is 2-10 MPa, and the hot pressing time is 10-20 min; and (5) drying after pressure relief and cooling.

12. A medium density fiberboard is characterized by being prepared by the method of the invention.

Technical Field

The invention belongs to the technical field of artificial boards, and particularly relates to an environment-friendly composite medium-density fiberboard prepared by using cellulosic ethanol fermentation wastewater and waste residues and a preparation method thereof.

Background

At present, the technology for preparing fuel ethanol by taking cellulose as a raw material is basically mature, and the principle is that lignocellulose raw materials, such as straw and other plant raw materials rich in cellulose, are pretreated to obtain reducing monosaccharides, such as glucose, xylose and the like, the reducing monosaccharides are fermented and rectified to obtain the fuel ethanol, and the residual rectified waste liquid is subjected to solid-liquid separation to obtain the cellulosic ethanol fermentation waste water and waste residues. The water quality characteristics of the wastewater are analyzed by Zhang-Kung et al (contemporary chemical, 2015, 44 (4): 691-694), which indicates that the wastewater contains certain hydrophilic acid and the pH value is about 4. In addition, the wastewater also contains high-concentration inorganic salt, saccharides, lignin and other metabolites in the fermentation process, and the components are complex, so that the difficulty of wastewater treatment is increased. The dry residue after the waste residue is dehydrated is mainly a mixture of lignin (50-65%), cellulose (10-20%), hemicellulose (about 0.5-3%), soluble components (15-20%) and ash (10-15%). Currently, each fuel ethanol enterprise generally directly discards waste residues (stacking in the open air or landfill treatment) or burns the waste residues, so that not only is the production cost increased, but also certain pollution is brought to the environment. If the method can realize effective and comprehensive utilization of the fermentation wastewater and the waste residue, the method has important significance for improving the economy of the cellulosic ethanol technology and accelerating the industrialization pace of the cellulosic ethanol industry.

Patent CN104987225A discloses a culture medium for cultivating morchella by using cellulosic ethanol fermentation waste residues and a preparation method thereof; patent CN105399473A discloses the preparation of bio-organic fertilizer by using cellulose ethanol fermentation waste residue, and provides a method for comprehensive utilization of cellulose ethanol fermentation waste residue. However, the amount of the waste cellulosic ethanol residues provided by the method is limited, and a new way for comprehensively utilizing the waste cellulosic ethanol residues is still required to be actively sought.

The artificial board is a general name of non-natural boards such as plywood, shaving board, fiberboard, wood chip board and the like, and has extremely wide application and huge demand in the fields of building materials, home decoration, furniture manufacturing and the like. The existing production of artificial board uses wood or its processed product and processing by-product as raw material, and adopts the manufacturing process of adhering by using urea-formaldehyde resin and other adhesive, and then pressing and forming. China is the first major producing and consuming nation of artificial boards, wood resources are in short supply, and raw materials for producing artificial boards need to be expanded. Along with the rapid promotion of the environmental protection consciousness and the health consciousness of the public, people pay more and more attention to the free formaldehyde emission of indoor furniture and decoration materials. GB/T16217-1995 "hygienic Standard for Formaldehyde in the air of Living rooms" was also issued in China, which stipulates that the maximum allowable concentration is 0.08mg/m 3. In addition, because the artificial board is the main reason for the overproof formaldehyde in indoor air, the formaldehyde emission value of the artificial board is strictly regulated in many countries in the world, and the perforation test value of the artificial board which can be directly used indoors is not more than 9mg/100g (standard E1) according to the national standard GB 18580-2001.

CN101786286 discloses that enzymatic hydrolysis lignin in a fuel ethanol fermentation production process is used as a raw material, is mixed with lignin in the paper industry or the enzymatic hydrolysis lignin after being modified, and is pressed into an enzymatic hydrolysis lignin composite board through drying, so that the production cost of the composite board is greatly reduced, and the application approach of the enzymatic hydrolysis lignin in cellulose ethanol fermentation waste residues is widened. CN 101786286A discloses a method for manufacturing a modified enzymatic hydrolysis lignin composite board, firstly, under alkaline conditions, formaldehyde is added for hydroxymethylation reaction to obtain modified lignin; and then uniformly mixing the modified lignin and the enzymatic hydrolysis lignin, drying, and carrying out hot-pressing crosslinking to obtain the composite board material. Maxinyue et al (Chinese Adhesives, 2015,24 (12), 15-18.) use laccase activated cellulose ethanol lignin to prepare biomass-based wood adhesives, and the prepared modified lignin is used as an adhesive to synthesize plywood. Hujianpeng and the like (influence of oxidation conditions on the performance of an environment-friendly fiberboard prepared by modified lignin, university of northeast forestry, proceedings of 2012,40 (4), 55-58.) use hydrogen peroxide as an oxidant, respectively carry out oxidation modification on industrial lignin under acid and alkali conditions by adopting an oxidation modification method, mix the modified lignin with wood fibers, and prepare the environment-friendly fiberboard material by adopting a flat pressing method.

From the prior art disclosed above, the purification and modification processes of enzymatic hydrolysis lignin are complex, and various solvents are used in the separation and modification processes, which easily causes discharge of a large amount of three wastes, and the cellulosic ethanol waste residue also contains 40-50% of cellulose, hemicellulose, ash and other components which can not be effectively utilized, so that solid waste residue is formed to pollute the environment. In addition, due to the heterogeneity of the lignin structure and the polydispersity of molecular mass, the modified product is a complex mixture, which affects the stability of the properties of the modified product of lignin as a whole. Compared with urea-formaldehyde resin or phenolic resin adhesives, the modified lignin adhesives still have the problems of few reactive functional groups and low crosslinking density, so that the strength of the fiberboard is low.

disclosure of Invention

Aiming at the problems of wood resource shortage, excessive formaldehyde content, poor strength of the fiberboard prepared after purification and modification and the like, the invention provides an environment-friendly composite medium-density fiberboard prepared by using cellulosic ethanol fermentation wastewater and waste residues and a preparation method thereof. According to the invention, while the cellulosic ethanol fermentation wastewater and waste residues are recycled, the prepared medium-density fiberboard meets the use standard, the free formaldehyde release amount is low, and the development of effective resource utilization and clean production is promoted.

The invention provides a preparation method of a medium-density fiberboard, which comprises the following steps:

(1) in the preparation process of the formaldehyde solution, cellulosic ethanol fermentation wastewater is adopted to replace process water to absorb formaldehyde gas, so as to prepare 30-40% formaldehyde solution;

(2) Uniformly mixing NaOH, cellulosic ethanol fermentation wastewater and cellulosic ethanol fermentation waste residues, heating to boil, stopping, cooling and filtering to obtain filtrate, namely the alkali regulating solution;

(3) Adding a first batch of urea, polyvinyl alcohol and a defoaming agent into the formaldehyde solution obtained in the step (1), uniformly mixing, adding the alkali regulating solution obtained in the step (2) to enable the pH value to be 8-9, heating to 70-80 ℃, and reacting for 30-40 min; adjusting the pH value of the system to 4-5, reacting for 30-40 min, sampling, dripping into water to form a mist, and adding a second batch of urea and melamine; when a sample is dripped into water in a cloud state, regulating the pH value to be 5-6 by using an alkali regulating solution, adding a third batch of urea, and carrying out heat preservation reaction at 80-90 ℃ for 30-40 min; cooling the system to 70-75 ℃, adding a fourth batch of urea, adjusting the pH to 8-9 with an alkali adjusting solution, cooling, and discharging to obtain a urea-formaldehyde resin glue solution;

(4) Uniformly mixing the cellulosic ethanol fermentation waste residue and wood fibers, and applying the urea-formaldehyde resin glue solution and the curing agent obtained in the step (3);

(5) And (5) putting the mixture obtained in the step (4) into a mould, and performing compression molding to obtain the medium-density fiberboard.

The main source of the cellulosic ethanol fermentation wastewater in the step (1) of the invention is wastewater generated in the cellulosic ethanol preparation process, such as fermentation mash of a cellulosic ethanol distillation tower, and the main characteristics are as follows: the insoluble solid matter is 1-10%; the temperature is high and is about 90-100 ℃; the chroma is large; the wastewater is acidic wastewater, and the pH value is 3.0-6.0; COD (Cr method, the same below) is about 10-13 ten thousand mg/L, and mainly comprises soluble xylose, glycerol, acetic acid, volatile phenol, lactic acid, lignin, furfural and various fermentation intermediate products; BOD5/COD is 0.5-0.55, wherein the difficultly biochemically degraded substances and the color development degree substances are mainly aromatic compounds; the inorganic salt content is above 2%, mainly sodium sulfate, and sulfate radical is above 1%. And (3) carrying out solid-liquid separation on the fermented mash to obtain the cellulosic ethanol fermentation wastewater.

The preparation process of the formaldehyde solution in the step (1) of the invention adopts a conventional process and a process for preparing the formaldehyde solution, and the formaldehyde solution is prepared by absorbing formaldehyde gas with process water in the preparation process, for example, the domestic process for preparing formaldehyde by silver method methanol oxidation is adopted, so that the process water can be directly replaced by cellulosic ethanol fermentation wastewater in an absorption tower of the existing device or a side-stream absorption tower can be built for the production of the formaldehyde solution by taking the cellulosic ethanol fermentation wastewater as the absorption liquid.

The cellulosic ethanol fermentation waste residue in the step (2) is residue obtained by pretreating, performing enzymolysis, fermenting ethanol and separating by distillation of lignocellulosic biomass, wherein the lignocellulosic biomass is straw, wood chip or energy plant containing cellulose, hemicellulose and lignin, and the straw is preferred. In the dry residue after the waste residue is dehydrated, the mass content of lignin is 50-65%, the mass content of cellulose is 10-20%, the mass content of hemicellulose is 0.5-3%, the mass content of soluble components is 15-20%, and the mass content of ash is 10-15%. The cellulosic ethanol fermentation wastewater in the step (2) is the same as that in the step (1).

In the step (2), the NaOH, the cellulosic ethanol fermentation wastewater and the cellulosic ethanol fermentation waste residue are respectively 10-30 parts, 50-85 parts and 5-20 parts by weight. Cooling, standing overnight, and filtering to obtain filtrate as alkali regulating solution. The concentration of the prepared alkali conditioning solution is 10-50%, preferably 15-25%.

In the step (3), the total addition of the urea is determined according to the molar ratio of the formaldehyde to the urea of 0.95-1.25. The adding amount of the first batch of urea is 50 to 60 percent of the total adding amount of the urea, the adding amount of the polyvinyl alcohol is 0.1 to 0.6 percent of the weight of the formaldehyde solution, and the adding amount of the defoaming agent is 0.01 to 0.05 percent of the weight of the formaldehyde solution. The defoaming agent is one or more of fatty acid amide defoaming agent, organic silicon defoaming agent, polyether defoaming agent and the like. And (3) dripping a small amount of urea-formaldehyde resin glue solution into water every 3-6 min, observing the state of the glue solution in the water, and carrying out the next operation when the sample is in a cloud state in the water. The acid for adjusting the pH value to 4-5 can be acid used in the reaction process, and preferably a formic acid solution with the mass concentration of 10% -30%. The adding amount of the second batch of urea is 10-20% of the total adding amount of the urea, and the adding amount of the melamine is 1-5% of the weight of the formaldehyde solution. The addition of the third batch of urea is 10-30% of the total addition of urea. The adding amount of the fourth batch of urea is 5-10% of the total adding amount of urea. In the urea-formaldehyde resin glue solution prepared by the invention, the content of free formaldehyde is less than or equal to 0.1%, the solid content is 45-65%, the viscosity is 50-100 mPa.s, and the curing time is less than 70 s.

In the step (4), 10-40 parts by weight of cellulosic ethanol fermentation waste residues and 60-90 parts by weight of wood fibers are uniformly mixed. The wood fiber is wood board fiber used for preparing the fiber board conventionally, and the cellulose ethanol fermentation waste residue is obtained in the same step (2). The addition amount of the urea-formaldehyde resin glue solution prepared in the step (3) is 8-20% of the total fiber weight, and the addition amount of the curing agent is 1-5% of the total fiber weight. The curing agent is at least one of ammonium chloride, ammonium persulfate, potassium persulfate and the like, and ammonium chloride is preferred.

In the step (5), the mixture is placed into a die and is cold-pressed into a plate shape, and then hot pressing is carried out, wherein the cold pressing time is 10-20 s; the hot pressing temperature is 100-180 ℃, the hot pressing pressure is 2-10 MPa, and the hot pressing time is 10-20 min. And (5) drying after pressure relief and cooling, wherein the drying adopts a mode of airing or drying at a natural ventilation position.

The composite medium-density fiberboard is prepared by adopting the method. The density of the prepared fiberboard is 0.65-0.80g/cm3, wherein the content of the cellulosic ethanol fermentation waste residue is 10% -40%, the physical and mechanical properties of the fiberboard meet the requirements of GB/T11718-.

firstly, preparing 30-40% of formaldehyde solution by using cellulosic ethanol fermentation wastewater, preparing alkali regulating solution by using NaOH, cellulosic ethanol fermentation wastewater and cellulosic ethanol fermentation waste residue, and then using the formaldehyde solution and the alkali regulating solution to prepare urea-formaldehyde resin glue solution; then evenly mixing the cellulosic ethanol fermentation waste residue with wood fibers, and applying urea-formaldehyde resin glue solution and a curing agent; and finally, in a mould, carrying out compression molding to obtain the medium-density fiberboard. The preparation method provided by the invention realizes resource utilization of cellulosic ethanol fermentation wastewater and waste residues, simultaneously, the prepared medium-density fiberboard meets the use standard, the free formaldehyde release amount is low, the technical problems that wood resources are in short supply, the formaldehyde content exceeds the standard, products do not meet the use requirements such as poor strength and the like are solved, and the development of effective resource utilization and clean production is promoted. Compared with the prior art, the method has the following advantages:

(1) The method utilizes the cellulosic ethanol fermentation wastewater to absorb formaldehyde gas to prepare formaldehyde solution, saves process water and utilizes the cellulosic ethanol fermentation wastewater to the maximum extent.

(2) Meanwhile, the cellulosic ethanol fermentation wastewater and the waste residues are adopted to prepare the alkali regulating solution, and lignin in the waste residues is utilized to modify the glue solution, so that the improvement of physical and mechanical properties and the reduction of the content of free formaldehyde are facilitated.

(3) In the preparation process, the enzymolysis lignin in the waste residue is introduced to partially replace the required auxiliary raw materials, so that the addition amount of high-cost modifiers such as polyvinyl alcohol, melamine and the like is reduced.

(4) the urea-formaldehyde resin glue solution prepared by fermenting the waste water and the waste residues by using the cellulosic ethanol is used for bonding the waste residues and the wood fibers, and has good physical and mechanical properties.

Detailed Description

The process and product properties of the medium density fiberboard of the present invention are further illustrated by the following examples. The embodiments are implemented on the premise of the technical scheme of the invention, and detailed implementation modes and specific operation processes are given, but the protection scope of the invention is not limited by the following embodiments.

The experimental procedures in the following examples are, unless otherwise specified, conventional in the art. The experimental materials used in the following examples were purchased from a conventional biochemical reagent store unless otherwise specified.

The cellulosic ethanol fermentation wastewater used in the embodiment of the invention is wastewater obtained by removing residues from fermentation mash of an ethanol distillation tower, and the water quality is as follows: the temperature is 80 ℃, the COD is 120000mg/L, the sulfate radical is 9290mg/L, the total salt content is 2.0wt percent, and the pH value is 5.0.

The cellulosic ethanol fermentation waste residue used in the embodiment of the invention is residue obtained by performing pretreatment, enzymolysis and ethanol fermentation on corn straws and performing distillation separation on the corn straws, and specifically is residue obtained by performing steam explosion pretreatment on the corn straws, performing enzymolysis on the corn straws by using cellulase to convert most of cellulose and hemicellulose in the corn straws into sugar and fermenting the sugar into ethanol, and performing distillation separation on the sugar and the hemicellulose. In the dry residue obtained after the dehydration of the cellulosic ethanol waste residue, the mass content of lignin is 50%, the mass content of cellulose is 15%, the mass content of hemicellulose is 2%, the mass content of soluble components is 17%, and the mass content of ash is 15%.

The invention adopts the process and the device for preparing formaldehyde by silver method methanol oxidation, directly uses the cellulosic ethanol fermentation wastewater to replace process water in an absorption tower of the prior device or establishes a lateral line absorption tower to be specially used for the production of formaldehyde solution by using the cellulosic ethanol fermentation wastewater as absorption liquid. The wood fibers used in the examples of the present invention had an average fiber length of 3mm and a fiber width of 40 μm.