Investigation On The Upgrading Of Pyrolytic Liquid Of Biomass Based On The Key Step Of Etherification Of Phenolic Oil

The more and more serious environmental problems, caused by the long-term consumption of fossil fuels, force people to explore the renewable energy resources. One option is to utilize biomass, which is the only renewable resource containing carbon with CO2 neutral characteristics. Among the conversion technologies, pyrolysis of biomass attracted much attention, because of its advantages in high liquid yield and feasible to variety of feedstocks. However, the high content of water and oxygen, lower PH and heating values of the biooil with highly instability hamper the direct use of it. Thus, it is of essential importance to upgrade the pyrolytic liquid for a better application of pyrolysis of biomass.The pyrolytic liquid consists of two phases:aquous phase and oil phase. The oil phase can be further divided into phenolic oil and neutral oil. The neutral oil may be directly used as fuels of boilers. Whereas, the phenolic oil may neither be used directly as an automobile fuel, nor a component of a blended fuel with gasoline or diesel, due to its high acidity, corrosivity, and polarity, though the heating value is not so low. Thus, the upgrading of the phenolic oil may be one of the key steps for application of the pyrolysis of biomass.Therefore, we put forward a novel approach of etherification of phenolic oil as the key step in the upgrading of pyrolytic liquid. Through the conversion of etherification by gas phase reaction at high temperature, the polar hydroxy group of the phenol derivatives was replaced by alkoxy group in weak polarity, and the active hydrogen atom was substituted by methyl group, and thus the acidity and corrosivity of the phenolic oil can be mitigated, and its solubility in gasoline or diesel can be remarkable augmented. The idea is opened for the frst time and no report has be found till now, so the research is a work with distinct creativity and significance.In this work, phenol as the model compound of phenolic oil was firstly used for reaction with methanol, through which the catalysts were screened and the reaction conditions were optimized. It was found that the catalysts with supported potassium salts on active alumina (AA, γ-AbO3) revealed good performance, among which KH2PO4/AA is the best. A best phenol conversion of 84.23% and a highest anisole selectivity of 93.26% were reached under the optimized conditions at a temperature range of 400-450℃, with a mole ratio of phenol to methanol of 15, reaction time of 3 hours, and a space velocity of 0.20 h-1. The best preparation conditions for the catalyst synthesis are:the catalyst was calcined at 700℃ for 8 hours with a load of 7.53% of KH2PO4 on the γ-AbO3 support. The activity of the used KH2PO4/AA catalyst was still nearly fully recovered after regeneration for 8 times. The XRD analysis showed that K.3Ab(PO4)3 was formed in solid phase reaction after calcination of KH2PO4/AA. This fact may indicate that K.3Ab(PO4)3 is the active component of the catalyst. The reaction mechanism was deduced that the anion of OH was removed from methanol under the effect of acidic alumina, and the cation of H+ was replaced by K+. The remained CH3+ of methanol and Ph-O- of phenol then combined to the aim product of anisole, and water was also generated by the bind of H+ to -OH. Thus, the catalysis was a ’metal-acid’ bi-functional process.The effects of five types of potassium salts on the etherification of phenolic oil were then examined. It was found that under the optimized conditions of 450℃ and mass ratio of phenolic oil to methanol of 1:1, the content of phenolic derivative decreased from 76.68% to 35.52% and the anisole increased from 0.46% to 27.41%, with an increased PH value from 3.27 to 5.44 by using the KH2PO4/AA catalyst. The activity of the catalyst was not remarkably decreased after 4 times of regeneration. In addition, an important phenomenon was found that almost all alkoxy phenols disappeared after reaction, while the alkcyl phenols including phenol remained in the product oil. In order to explain the results, the interaction between the major components in the phenolic oil were investigated. It was found that the reactivity of alkoxy phenol is higher than that of alkyl phenol, and the alkcoxy phenol may hinder the reactivity of alkyl phenol by reactive competition, when the two types of phenols exists simultaneously. Besides, acetic acid was found promotive to the reactivity of the phenolic oil.In consideration of the facts that alkoxy phenols restrain the reactivity of alkyl phenols and that the separation from each other was rather hard, an idea of catalytic pyrolysis for high selective alkyl phenols was studied. The corn straw fermentation residue was pyrolyzed with different catalysts at different temperatures in a fixed bed reactor. The results showed that the yield of oil phase of the pyrolytic liquid is about 16% at the non-catalytic conditions, which contains around 30% of phenols. When pyrolysis was catalyzed by ZSM-5 or Y zeolite, the yield of aromatics increased remarkably. The aromatics yield increased with increasing temperature for the both catalysts. When KH2PO4/AA is used as the catalyst, the content of alkyl phenols in the oil phase reached 49.15%, while almost no alkoxy phenols were observed. The high selectivity of alkyl phenols by catalytic pyrolysis of the residues from fermentation of straw is faverable for the down stream etherification. This provides a new path for value-added utilization of the fermentation residue.In addition to the oil phase, the aqueous phase is another major pyrolytic products from pyrolysis of biomass. The aqueous phase contains a low amount of small acids, alcohols, aldehydes, and ketones, besides water. Such characteristics of the aqueous phase make it difficult to be upgraded in conventional route. A diluted aqueous phase used for growth of Saccharomyces Cerevisiae (S.C.) was investigated by considering the fact that carbon source is a necessary nutrition for the growth of microorganisms. It was found that the diluted aqueous phase can be used as a sob carbon source for the cultivation of S.C., particularly the solution in the concentration of 10 voL% is the best. The components of formic acid, acetic acid, and propionic acid can be consumed by S.C. during growing. However, phenol, p-cresol, and furfural are not suitable for the growth of S.C. Comparatively, the promoting effect of the carboxylic acids for the growth of S.C. is more distinct than the hindering effect of phenols and furfural. As a result, the microorganism can be still cultivated by the diluted aqueous phase of pyrolic liquids from biomass.