Hydrothermal carbonization (HTC) of loblolly pine using a continuous, reactive twin-screw extruder

Abstract

Hydrothermal carbonization (HTC) has become an accepted means of converting a wide variety of lignocellulosic feedstocks into solid hydrochars, which have improved physical and chemical properties compared to raw biomass. To date, HTC applications have involved batch or semicontinuous process systems, which has limited their economic viability. The work presented here describes a fully-continuous HTC process, made possible by use of a specially modified twinscrew extruder (TSE). The reaction time within this fast HTC (FHTC) reactor system is very short (20-30 sec.) as compared to a typical batch reactor. Therefore, the concept of reaction "severity factor" is used when comparing the FHTC products with those produced in other reactor systems. While solid hydrochar produced in the FHTC system has different physical properties than hydrochar from batch reactor systems, these materials exhibit similar energy densification and pelletization behavior, when produced under comparable severity conditions. However, total hydrochar yields are considerably higher from the FHTC reactor compared to batch reactor systems. This is a consequence of the de-pressurization process in the FHTC system, whereby most water-soluble organic products are retained in the hydrochar, rather than exiting the process in a separate aqueous product stream. FHTC treatment of loblolly pine at a severity factor of 5.3 (290 °C) produced a hydrochar yield of nearly 85% (based on dry feedstock mass). Condensation of the flashed vapor products provided a relatively clean water stream, containing only 1.2% organicsprimarily furfural and acetic acid. Recovery of these organics and recycling of the condensed water would further improve the cost-effectiveness of FHTC operations.

In Deep Analysis on the Behavior of Grape Marc Constituents during Hydrothermal Carbonization

“…Table 3 reports the results of the ICP analyses performed on the HTC liquid produced processing grape seeds, grape skins and grape marc respectively. The value of 8-13% of C in the aqueous phase for experiments with seeds is in agreement with literature [37,40]. At 180 • C, it seems to be clear that the carbon content decreases in the liquid phase for HTC experiments with seeds.…”

“…When predicting the solid mass yields of the hydrochars for the three substrates with the trend lines, the absolute errors range between 0.02 and 9.39%, while the predictions for both the liquid and the gaseous phases seems to be less accurate in some cases, presenting absolute errors higher than 10%. Hoekman et al [40] proposed a different severity factor (hereinafter SFR0) shown in Equation 3, where t is expressed in min and T in • C, and applied it to hydrothermally carbonized loblolly pine:…”

Hydrothermal Carbonization: Modeling, Final Properties Design and Applications: A Review

“…This severity factor equation has been used by other researchers for describing the HTC process as applied to various biomass feedstocks. For example, Gao et al [17] analysed the effect of water to biomass ratio on the HC yield of HTC of corn stalk and longan shell, and Hoekman et al [18] studied the HTC of loblolly pine in a continuous, reactive twin-screw extruder. Janga et al [19] applied a more complex severity model for the prediction of the monosaccharide yield via hydrolysis of different wood by concentrated sulfuric acid.…”

Hyperspectral Imaging to Determine the Properties and Homogeneity of Renewable Carbon Materials

“…Although most publications in the hydrothermal field still discuss laboratory results, several pilot facilities and continuous process alternatives have recently been reported. [26] Hyperspectral imaging can be performed next to ap roduction line potentially allowing real-time process monitoring and control. In principle, images can also be recorded to the level of af ew microns after which the wavelengthi tself restricts furtheri ncreases in image detail.…”