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AIR2-CT93-0889
Integrated Chemicals and Fuels Recovery from Pyrolysis Liquids Generated by Ablative Pyrolysis |
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Contractl No: | AIR2-CT93-0889 |
| Date Prepared: | July 1998, September 1999 | |
| Source: | Final technical report 1998 |
Summary
Five distinct areas are addressed in this report:
Pre-treatment of biomass Pre-treatment experiments have been carried out to improve the yield of chemicals from pyrolysis of treated feedstocks. Pre-treatment has concentrated on water washing and mild acid washing to reduce the ash content of biomass and hence improve the yield of certain chemicals, notably levoglucosan. Washing experiments have increased the yield of levoglucosan from the pyrolysis of poplar from 2.8 dry wt.% for untreated poplar to 3.1 wt.% for water washed poplar and 8.6 wt.% for water washed followed by mild acid washed poplar. An investigation into the effect of using different types of mineral acid has produced yields of levoglucosan in excess of 15 wt.%.
Pyrolysis of biomass, untreated and pre-treated A 150 g/h shallow fluidised bed reactor has been used to successfully pyrolyse a range of feedstocks including poplar, pine, pine bark, miscanthus, rape straw and rape meal over the temperature range 400-600'C. Mass balance closures in the range 95-100 wt.% on a dry feedstock basis are typically obtained. Bio-oil yields for woody biomass [e.g. poplar or pine] are typically about 65 wt.% with a moisture content of about l0wt.%. A one kg/h shallow fluidised bed pyrolysis system has been used to pyrolyse a variety of feedstocks, such as, poplar, pine, rape seed, pine bark and acid washed pine over a range of temperatures, 450 to 560'C. Good mass balances closures in the range of 90-100wt.% have been achieved. Continuous improvements have been made to the system since its installation to improve its operational efficiency Bio-oil yields for woody biomass are typically about 65 wt.% at a moisture content of 8 to 14 wt.%.
Chemicals extraction from bio-oil Carboxylic acids, calcium carboxylates, levoglucosan and levoglucosenone have been successfully extracted. Yields of 43.3 wt.% of levoglucosan have been achieved at a purity of 63 wt.%. Yields of 51.5 wt.% acetic acid and 19.1 wt.% of formic acid have been achieved at relatively low purities of 15.3 wt.% and 2.7 wt.%. The aqueous/water insoluble phase separation properties have been investigated as the important initial step in a chemical recovery process from a pyrolysis liquid. The physical properties of the water insoluble phase resulting from the phase separation of pyrolysis liquid and water have been investigated. Finally, proposals for integrated process routes exploiting pyrolysis liquid feedstocks are considered techno-economically.
Physical properties of bio-oil The physical properties of pyrolysis liquids have been investigated, especially pertaining to its use as a fuel. The most common properties required for its assessment as a fuel are density, viscosity, water content, thermal conductivity, specific heat capacity and the heating value, all of which have been measured for a range of liquid products over a range of temperature and storage times. It was noted that storage of the pyrolysis liquid over time adversely affects the physical properties notably viscosity. However, the use of a diluent such as ethanol or methanol can reduce this effect.
Analysis of bio-oil Procedures for the analysis of pyrolysis liquids have been developed. A range of analytical techniques have been evaluated and HPLC has been routinely used to quantitatively analyse fast pyrolysis liquids and their chemical fractions. HPLC analysis can analyse the aqueous fraction of pyrolysis liquids and can quantitatively analyse for levoglucosan, hydroxyacetaldehyde, formic acid, acetic acid, fructose, glyoxal, xylitol, acetol, methanol, 2-furoic acid, cyclotene, cellobiosan, glyceraldehyde, ethanol and glucose. Water content is measured by coulometric Karl-Fischer and FRIR techniques have been investigated for qualitative comparisons.
Activities
The project work included the following activities:
Task 1 Operate and optimise an existing ablative pyrolyser to produce liquid fuels and chemicals from biomass at biomass feed rates up to 5 kg/h with supplementary work on a small fluid bed reactor to study co-processing. The ablative pyrolysis reactor has been operated and information provided which will be used in the assessment of a scaled up version of the reactor. Problems have occurred in the liquids collection system which have been resolved, and an improved system devised. Two fluid bed reactors [lkg/h and 150g/h] have been commissioned and successfully operated with good mass balance closures. Testing has been carried out on the following feedstocks: poplar, pine, pine bark, miscanthus; oil seed rape, rape straw and rape meal.
Task 2 Develop a reliable and efficient product collection systems that might include an electrostatic precipitator and selective condensation at high temperature to minimise water condensation. This resulted in an electrostatic precipitator fitted to a small fluid bed reactor [150 g/h and larger reactors [1 kg/h fluid pyrolysis reactor and 5 kg/h ablative pyrolysis reactor].
Task 3 Evaluation of the influence of process parameters such as particle size, moisture content, reactor temperature, particle pressure, relative motion and vapour product residence time on performance parameters and product quality. The effects of each parameter have been investigated although further experimental work is required in view of the number of variables. The key parameters investigated were reactor temperature, gas/vapour product residence time, particle size and moisture content. The liquid product quality in terms of its physical properties has been evaluated although more work is required.
Task 4 Test and compare different feeds of agricultural materials and biomass. The 150g/h and 1 kg/h fluid bed reactors have been used to test a number of feedstocks. Results were obtained for poplar, pine, pine bark, miscanthus, oil seed rape, rape straw and rape meal.
Task 5 Comparison of performance and products with other flash pyrolysis reactors. An assessment of the product yields and composition has been made and reported.
Task 6 Derive a model or models of ablative pyrolysis. The activities of one partner did not did not evolve as an ablative pyrolyser. One process was modelled.
Task 7 Provide samples of liquid products and assess the potential for chemicals recovery, upgrading to chemicals and/or higher value hydrocarbons. Liquid samples have been provided as required.
Task 8 Determine a range of physical properties from pyrolysis liquids produced under a variety of conditions and compare the variation in the main physical properties and study the problems of stability. The range of physical properties to be investigated included:
In addition, a simple method of assessing product quality was to be developed. Considerable work was carried out on pyrolysis liquids to validate test methods and devise satisfactory methods for characterisation of the liquid physical properties. The key parameters investigated have been density and viscosity and their variation with time, temperature, water content, ethanol and methanol content. Methods for the determination of the specific heat capacity, surface tension, enthalpy of vaporisation, enthalpy of combustion and the saturated vapour pressure were investigated and a thermal conductivity rig tested. Methods for assessing an "instability index" were attempted but require further work.
Task 9 Analysis of the liquid products with HPLC and other techniques including GCMS and FTIR methods. An in-house HPLC system was developed following of several types of column and a library developed, specific to fast pyrolysis liquids is ongoing. Advice on this matter has been sought from the University of Waterloo (Canada), the Institute of Wood Chemistry and specialist equipment suppliers.
Task 10 Extraction of chemicals using orthodox solvent separation techniques including water, oxygenates, aliphatic solvents, aromatic solvents, and chlorinated solvents. Functional and specific solvents were used in order to maximise yields of designated products. Orthodox purification methods were also used. Upgrading of extracted products was studied but not developed unless there was clear evidence of significant potential. Work was carried out on batch extraction methods and a system has been tested.
Task 11 Identification of the most interesting chemicals in terms of their yield, market value and ease of recovery, with suitable physical and chemical recovery schemes for the most interesting chemicals, based on orthodox chemistry and chemical engineering practice. Speciality chemicals which may be of commercial interest were identified and noted. Extraction, recovery and purification systems have been developed.
Task 12 This will be the design and evaluation of chemical recovery processes in terms of cost and performance, in order to establish the technical feasibility and economic viability of chemicals production. This will be carried out in collaboration with the other contractors. Chemical extraction and recovery routes have not been sufficiently developed, although some schemes have been devised.
Task 13 Characterisation of residual liquid, to determine its suitability as a fuel including upgrading methods. The residue of the pyrolysis liquids after an initial phase separation has been determined. The development of an overall pyrolysis to chemicals and fuel processing system has not been evaluated although sufficient information is now available for this to be carried out.
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