Lignin: Difference between revisions
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[http://www.ligninplatform.wur.nl/NR/rdonlyres/AFA06812-6F05-4D07-92A1-3BAA88D2318A/112993/ZakseksietalChemRev2011.pdf The Catalytic Valorization of Lignin for the Production of Renewable Chemicals] by Zakzeski et al (2009) reviews the available information on using lignin as source of basic chemical structures for value adding. Lignin acts as a glue holding together the cellulose and hemicellulose in the cell wall and is composed of three phenylpropane subunits namely, coniferyl, sinapyl, and p-coumaryl. There are three strategies to utilizing lignin for chemical materials: 1. pyrolysis to simple component molecules that can be purified and used to build desired complex molecules (based on petrochemical processes) 2. removal of functional groups and isolation of aromatics which can be used to build desired complex molecules (based on petrochemical processes) 3. Use of highly selective catalysts for the direct production of desired chemicals by interrupting targeted functional groups (based on novel biorefinement processes). Purification technology is a essential to all three strategies and needs further development. < br /> | [http://www.ligninplatform.wur.nl/NR/rdonlyres/AFA06812-6F05-4D07-92A1-3BAA88D2318A/112993/ZakseksietalChemRev2011.pdf The Catalytic Valorization of Lignin for the Production of Renewable Chemicals] by Zakzeski et al (2009) reviews the available information on using lignin as source of basic chemical structures for value adding. Lignin acts as a glue holding together the cellulose and hemicellulose in the cell wall and is composed of three phenylpropane subunits namely, coniferyl, sinapyl, and p-coumaryl. There are three strategies to utilizing lignin for chemical materials: 1. pyrolysis to simple component molecules that can be purified and used to build desired complex molecules (based on petrochemical processes) 2. removal of functional groups and isolation of aromatics which can be used to build desired complex molecules (based on petrochemical processes) 3. Use of highly selective catalysts for the direct production of desired chemicals by interrupting targeted functional groups (based on novel biorefinement processes). Purification technology is a essential to all three strategies and needs further development. < br /> | ||
Pretreatment of biomass is essential to the start of biorefinement techniques and pretreatment of lignin is enhanced by proper pairing of pretreatment with the lignin structure. Pretreatments can be split into 4 broad categories physical, chemical, solvent, and biological. Pretreatment parameters must also be carefully selected including temperature, pressure, pH, etc. The authors reference polyoxometalate as an alternative to the chlorine based pulping process. The Kraft process is the main industrial treatment utilized in pulping mills and involve high temperatures between 423-453 K, high pHs and sodium hydroxide and sodium sulfide, however to be economical lignin is used for combustion for energy and not all recalcitrant (5-5) linkages are broken. Organosolv pretreatment utilizes an organic solvent extraction to produce streams of cellulose, hemicellulose, and lignin fractions and has been demonstrated industrially, however the process is hampered by the high cost of solvent and their recovery. Pyrolysis is another pretreatment but consumes carbon in the process and needs high temperature. A related treatment is steam explosion in which steam at 453-503 K is introduced under pressure 1.38-3.45 MPa for 1-20 min and then rapidly vented resulting in the separation of lignin fibers. | Pretreatment of biomass is essential to the start of biorefinement techniques and pretreatment of lignin is enhanced by proper pairing of pretreatment with the lignin structure. Pretreatments can be split into 4 broad categories physical, chemical, solvent, and biological. Pretreatment parameters must also be carefully selected including temperature, pressure, pH, etc. The authors reference polyoxometalate as an alternative to the chlorine based pulping process. The Kraft process is the main industrial treatment utilized in pulping mills and involve high temperatures between 423-453 K, high pHs and sodium hydroxide and sodium sulfide, however to be economical lignin is used for combustion for energy and not all recalcitrant (5-5) linkages are broken. Organosolv pretreatment utilizes an organic solvent extraction to produce streams of cellulose, hemicellulose, and lignin fractions and has been demonstrated industrially, however the process is hampered by the high cost of solvent and their recovery. Pyrolysis is another pretreatment but consumes carbon in the process and needs high temperature. A related treatment is steam explosion in which steam at 453-503 K is introduced under pressure 1.38-3.45 MPa for 1-20 min and then rapidly vented resulting in the separation of lignin fibers. | ||
The most common linkage in lignin is B(eta)-O-4 which are readily cleaved by current processes and releases phenylpropane subunits. Certain configurations are not readily broken down. Carbon carbon bonds are the most difficult to break and are an area where catalysis research is necessary. The most recalcitrant configurations are crosslinked aromatics, particularly pentoses with a 5-5 linkage. The p-coumaryl subunit is the least substituted and removal of the para-alkene via reduction produces phenol. Coniferyl subunit's R substituent can be oxidized yielding vanillin a high value fragrance and taste additive. Sinapyl alcohol subunits also can serve as a model for numerous desirable molecules and is not susceptible to repolymerization due to the occupation of the 3 and 5 positions. The authors catalogue a huge variety of chemicals that can be derived from the model subunits and reported protocols for their preparations (see figures 12-14). | |||
[http://www.google.com/patents/US4647704 US patent 4,647,704] issued to Engel et al on March 3, 1987 describes a method of hydrocracking lignin using a tungsten/nickel catalyst supported on a mildly acidic base, notably alumina, silica, alumina phosphate or a combination. The catalyst has superior due to the combination of a cracking catalyst tungsten and a hydrogenating catalyst nickel. The products are phenol or cresols, a methyl phenol, a benzene with a hydroxyl and methyl substitution. The process is conducted in a reactor under a hydrogen atmosphere at pressures of 500 - 3500 psig and temperatures of 300-450 C. Yield is improved with the use of a low weight aliphatic alcohol, namely methanol, in a percentage of up 25% but usually between 7-15%. Inclusion of methanol increases the yield of cresols. A water content of up to 25% wt lignin is found to have optimal yields and additional process improvements include the inclusion of a lewis acid/friedel-crafts (alkylates and acylates benzene) catalyst, namely AlCl3. Lignin from the kraft process or any nonbasic form is suspended in a nonreactive solvent but phenol was found to have the best performance.<br /> | [http://www.google.com/patents/US4647704 US patent 4,647,704] issued to Engel et al on March 3, 1987 describes a method of hydrocracking lignin using a tungsten/nickel catalyst supported on a mildly acidic base, notably alumina, silica, alumina phosphate or a combination. The catalyst has superior due to the combination of a cracking catalyst tungsten and a hydrogenating catalyst nickel. The products are phenol or cresols, a methyl phenol, a benzene with a hydroxyl and methyl substitution. The process is conducted in a reactor under a hydrogen atmosphere at pressures of 500 - 3500 psig and temperatures of 300-450 C. Yield is improved with the use of a low weight aliphatic alcohol, namely methanol, in a percentage of up 25% but usually between 7-15%. Inclusion of methanol increases the yield of cresols. A water content of up to 25% wt lignin is found to have optimal yields and additional process improvements include the inclusion of a lewis acid/friedel-crafts (alkylates and acylates benzene) catalyst, namely AlCl3. Lignin from the kraft process or any nonbasic form is suspended in a nonreactive solvent but phenol was found to have the best performance.<br /> | ||
Revision as of 15:18, 10 June 2012
Background
Lignin is a complex and heterogeneous polymer found in wood. It composed of aromatics crosslinked with carbohydrates. If is the second largest component of biomass on Earth and has many applications. Lignin is difficult to decompose in the wild and a dense source of energy when combusted. Lignin may be an a source of aromatic compounds for OSE.
OSE context
Aromatics from lignin
Phenols and benzenes can be produced from lignin using catalytic hydrocracking, high heat with a hydrogen feed. A variety of valuable chemicals are produced by the decomposition of lignin but the challenge lies in purification.
The Catalytic Valorization of Lignin for the Production of Renewable Chemicals by Zakzeski et al (2009) reviews the available information on using lignin as source of basic chemical structures for value adding. Lignin acts as a glue holding together the cellulose and hemicellulose in the cell wall and is composed of three phenylpropane subunits namely, coniferyl, sinapyl, and p-coumaryl. There are three strategies to utilizing lignin for chemical materials: 1. pyrolysis to simple component molecules that can be purified and used to build desired complex molecules (based on petrochemical processes) 2. removal of functional groups and isolation of aromatics which can be used to build desired complex molecules (based on petrochemical processes) 3. Use of highly selective catalysts for the direct production of desired chemicals by interrupting targeted functional groups (based on novel biorefinement processes). Purification technology is a essential to all three strategies and needs further development. < br /> Pretreatment of biomass is essential to the start of biorefinement techniques and pretreatment of lignin is enhanced by proper pairing of pretreatment with the lignin structure. Pretreatments can be split into 4 broad categories physical, chemical, solvent, and biological. Pretreatment parameters must also be carefully selected including temperature, pressure, pH, etc. The authors reference polyoxometalate as an alternative to the chlorine based pulping process. The Kraft process is the main industrial treatment utilized in pulping mills and involve high temperatures between 423-453 K, high pHs and sodium hydroxide and sodium sulfide, however to be economical lignin is used for combustion for energy and not all recalcitrant (5-5) linkages are broken. Organosolv pretreatment utilizes an organic solvent extraction to produce streams of cellulose, hemicellulose, and lignin fractions and has been demonstrated industrially, however the process is hampered by the high cost of solvent and their recovery. Pyrolysis is another pretreatment but consumes carbon in the process and needs high temperature. A related treatment is steam explosion in which steam at 453-503 K is introduced under pressure 1.38-3.45 MPa for 1-20 min and then rapidly vented resulting in the separation of lignin fibers. The most common linkage in lignin is B(eta)-O-4 which are readily cleaved by current processes and releases phenylpropane subunits. Certain configurations are not readily broken down. Carbon carbon bonds are the most difficult to break and are an area where catalysis research is necessary. The most recalcitrant configurations are crosslinked aromatics, particularly pentoses with a 5-5 linkage. The p-coumaryl subunit is the least substituted and removal of the para-alkene via reduction produces phenol. Coniferyl subunit's R substituent can be oxidized yielding vanillin a high value fragrance and taste additive. Sinapyl alcohol subunits also can serve as a model for numerous desirable molecules and is not susceptible to repolymerization due to the occupation of the 3 and 5 positions. The authors catalogue a huge variety of chemicals that can be derived from the model subunits and reported protocols for their preparations (see figures 12-14).
US patent 4,647,704 issued to Engel et al on March 3, 1987 describes a method of hydrocracking lignin using a tungsten/nickel catalyst supported on a mildly acidic base, notably alumina, silica, alumina phosphate or a combination. The catalyst has superior due to the combination of a cracking catalyst tungsten and a hydrogenating catalyst nickel. The products are phenol or cresols, a methyl phenol, a benzene with a hydroxyl and methyl substitution. The process is conducted in a reactor under a hydrogen atmosphere at pressures of 500 - 3500 psig and temperatures of 300-450 C. Yield is improved with the use of a low weight aliphatic alcohol, namely methanol, in a percentage of up 25% but usually between 7-15%. Inclusion of methanol increases the yield of cresols. A water content of up to 25% wt lignin is found to have optimal yields and additional process improvements include the inclusion of a lewis acid/friedel-crafts (alkylates and acylates benzene) catalyst, namely AlCl3. Lignin from the kraft process or any nonbasic form is suspended in a nonreactive solvent but phenol was found to have the best performance.
The catalyst consists of 2-20% weight tungsten component preferably the zerovalent metal but tungsten sulfide may be used. Tungsten by itself may be used (has both cracking and hydrogenation activity) but a second hydrogenating catalyst enhances action. Preferably nickel (but also palladium) is an effective cocatalyst in the zerovalent metal state and should be combined with the tungsten in a molar ratio nickel:tungsten of 5:1-20:1. Friedel craft catalysts used include iron, antimony, zinc, tin, and aluminium as particularly bromides or chlorides but also fluorides and phosphates and are included in 0.5-5.0% wt lignin. A Fluidized bed reactor has superior performance compared to fixed bed reactors.
After further R&D the examples should be reviewed for optimal performance and adherence to OSE product ecologies.
Basic Studies on the Pyrolysis Products of Lignin by Hwang and Obst utilized model lignin compounds for pyrolysis and analyzed the products by GC-MS. Arylglycerol-ß-arylether (substituted aromatics linked through two carbons one as a C-C bond with hydroxyl group and one ether linkage) linked compounds served as model lignin structures and were pyrolysized at 250-500 C. Pyrolysis at 315 C was found to be optimal. Products were dimethoxyacetonophenone (DMAP), trimethoxyacetonphenone (TMAP), and dimethoxyphenol (DMP) and their exact yields were dependent on the starting material. The yield of aromatic products were higher in veratryl than trimethoxyphenol possibly due to pyrolysis being easier.
http://www.google.com/patents/US3105095
http://www.cellulosechemtechnol.ro/pdf/CCT9(2010)/P.353-363.pdf
http://www.google.com/patents/US4420644