Yamin Hu

Co-pyrolysis mechanism of seaweed polysaccharides and cellulose based on macroscopic experiments and molecular simulations

Co-pyrolysis conversion of seaweed (Enteromorpha clathrat and Sargassum fusiforme) polysaccharides and cellulose has been investigated. From the Py-GC/MS results, Enteromorpha clathrata (EN) polysaccharides pyrolysis mainly forms furans; while the products of Sargassum fusiforme (SA) polysaccharides pyrolysis are mainly acid esters. The formation mechanisms of H2O, CO2, and SO2 during the pyrolysis of seaweed polysaccharides were analyzed using the thermogravimetric-mass spectrometry. Meanwhile the pyrolysis of seaweed polysaccharide based on the Amber and the ReaxFF force fields, has also been proposed and simulated respectively. The simulation results coincided with the experimental results. During the fast pyrolysis, strong synergistic effects among cellulose and seaweed polysaccharide molecules have been simulated. By comparing the experimental and simulation value, it has been found that co-pyrolysis could increase the number of molecular fragments, increase the pyrolysis conversion rate, and increase gas production rate at the middle temperature range.

TG–FTIR–MS analysis of the pyrolysis of blended seaweed and rice husk

Pyrolysis of seaweed (Enteromorpha clathrata), rice husk, and five kinds of samples of blended Enteromorpha clathrata and rice husk (at different mass ratios as 3:1, 2:1, 1:1, 1:2, and 1:3) was investigated with thermogravimetric–infrared–mass spectrometry analysis. The results indicated that the pyrolysis of seaweed and rice husk can be divided into four stages: evaporation, depolymerization, devolatilization, and carbonization. However, due to the major pyrolysis component differences between seaweed and rice husk, the pyrolysis characteristics between them varied significantly. Through differential scanning calorimetry analysis, seaweed showed a special exothermic reaction during the stage of precipitation of main volatiles, while the rice husk showed mainly an endothermic reaction in that process. But it appeared to be an exothermic process during pyrolysis of the seaweed and rice husk mixture. We can infer that there was mutual promotion between the seaweed and rice husk, and energy coupling was realized. Meanwhile, it can be concluded that the experimental value of thermal mass loss rate turns out to be higher than that of theoretical value in the process of the main stage of pyrolysis through the comparison between the experimental data and the theoretical data for calculated DTG curves in the pyrolysis of blended sample of different proportions of seaweed and rice husk. The FTIR analysis indicated that with the increasing proportion of the rice husk, the volatile gas, sulfurous gas, and nitrogen gas are decreasingly released from the process of pyrolysis. Judging from the thermogravimetric–mass spectrometry, the pyrolysis of the blended mixture of seaweed and rice husk has been affected because of the increasing amount of rice husk. This reduced the emission of NO, NO2, and SO2 gases which are released from the above process of pyrolysis. Therefore, for the pyrolysis of mixed seaweed and rice husk, there was actually a synergistic effect rather than the simple sum of the characteristics of the pyrolysis of different components.

A comparative study on the quality of bio-oil derived from green macroalga Enteromorpha clathrata over metal modified ZSM-5 catalysts

The green macroalga Enteromorpha clathrata was pyrolyzed with or without catalysts at the temperature of 550 °C for producing high-quality bio-oil. The ZSM-5 and 1,2,3 mmol Mg-Ce/ZSM-5 catalysts were introduced to investigate the yields and components distribution of bio-oil. Increase of bio-oil production was obtained with the use of ZSM-5 and 1,2,3 mmol Mg-Ce/ZSM-5 catalysts. The 1 mmol Mg-Ce/ZSM-5 catalyst exhibited more promising property for promoting the relative content of C5-C7 compounds, and decreasing the relative content of acids in bio-oil. The results suggested that E. clathrata had potential as pyrolysis feedstocks for producing the high-quality bio-oil with large amounts of C5-C7 compounds and low relative content of acids when the 1 mmol Mg-Ce/ZSM-5 catalyst was used. Furthermore, the physicochemical properties of ZSM-5 and 1 mmol Mg-Ce/ZSM-5 catalysts were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and temperature-programmed desorption of ammonia.

Combustion mathematical simulation of single seaweed particle in a bench-scale fluidized bed

In this study, combustion experiments of green algae granulations (Enteromorpha clathrata) (EN) were carried out in a bench-scale fluidized bed. The particle diameter was kept constant during the combustion process and combustion model was described as a shrinking core model. Model was divided into water ball, volatile-matter ball, and carbon ball. Ash ball radius was assumed to be the same during the combustion and carbon ball was burned layer by layer. Simulation of single-particle combustion process consists of process of water evaporation, release of volatile matters and combustion, and the process of char combustion. Finally, a mathematical model was established for the combustion of EN single particle in the fluidized bed, validated by the experiment data. The model can be applied for the design of the combustion devices for the combustion of seaweed particles with high content of ash.

Study of pyrolytic mechanisms of seaweed based on different components (soluble polysaccharides, proteins, and ash)

The pyrolysis mechanisms of the main components of seaweed (soluble polysaccharides, proteins, and ash) were investigated in this study using characterization analysis and thermogravimetric analysis–mass spectrometry. XPS analysis indicated that most of the metal ions existed in the ash, while substituents of Na and K ions were found in polysaccharides. Oxygen-containing functional groups in Enteromorpha were found to exist mainly in the following forms: -OH/C-O in polysaccharides, COO- in proteins, and inorganic oxygen in the ash. Pyrolysis thermogravimetric (TG) curves of the components of Enteromorpha indicated that the thermogravimetric analysis ranges of polysaccharides and proteins were 175–310 °C and 300–350 °C, respectively. During the pyrolysis process, due to the effects of metal ions, the maximum thermal weight loss rate was found to increase, while the pyrolysis temperature also increased. CO2 was generated from the decarboxylation of uronic acids and the decomposition of inorganic carbonates ...

Co-pyrolysis of macroalgae and lignocellulosic biomass: Synergistic effect, optimization studies, modeling, and simulation of effects of co-pyrolysis parameters on yields

Synergistic effect of co-pyrolysis of macroalgae [Enteromorpha prolifera (EP)] and lignocellulosic biomass [rice husk (RH)] in a fixed bed reactor for maximum and enhanced biofuels yield has been investigated. The main and interaction effects of three effective co-pyrolysis parameters (pyrolysis temperature, feedstock blending ratio, and heating rate) were also modeled and simulated to determine the yield rates of bio-oil and bio-char, respectively. Optimization studies were, then, performed to predict the optimal conditions for maximum yields using the central composite circumscribed experimental design in Design Expert® software 8.0.6. Analysis of variance was carried out to determine whether the fit of the multiple regressions is significant for the second-order model. Normal pyrolysis oils from EP, RH, and co-pyrolysis oils obtained from different feedstock blending ratios were examined using the gas chromatography-mass spectrometry to identify their compositions. Some vital properties of oils and bio-chars such as the heating value, water content, elemental compositions, and specific gravity were also determined, which unveiled that synergistic effect exists between EP and RH during co-pyrolysis, and this led to increase in products’ yields and improved co-pyrolysis products’ quality.

Comparative Study of Combustion Properties of Two Seaweeds in a Batch Fluidized Bed

ABSTRACT In the present study, combustion of two seaweeds, Enteromorpha clathrate and Sargassum natans, was carried out in a bench-scale fluidized bed. According to the shrinking core model, combustion of E. clathrate particles resulted in dehydration and release of volatile components first, followed by char combustion. While combustion of S. natans particles resulted in scraps formation due to the rapid release of large amounts of volatiles, followed by expansion and fragmentation. The cross sections of E. clathrate particles and the cokes collected after different combustion durations were analyzed with a scanning electron microscope. Some micro-pores were generated with a rougher surface after being burned for 30 s. When combustion continued for 3 min, a cotton wool-like structure was obtained due to complete release of volatiles. After 4 min of burning, internal surface of the ash particle became cohesive, due to partial melting of ash particles. In addition, the released gases were studied during the combustion process. Results showed that SO2, NOx, and other gases emitted spontaneously as soon as seaweed particles were fed into the fluidized bed, indicating that both pyrolysis and oxidation reactions rapidly take place within the seaweed particles. In general, the heat transfer rate was accelerated by increasing bed temperature and led to an earlier release of volatile components with shortened burnout time. Moreover, increasing air velocity and raising the bed height also enhanced, to some extent, the combustion and shortened the burnout time.