M. Helal Uddin

Bio: M. Helal Uddin is an academic researcher from University of Nevada, Reno. The author has contributed to research in topics: Lignocellulosic biomass & Hydrothermal carbonization. The author has an hindex of 9, co-authored 13 publications receiving 826 citations. Previous affiliations of M. Helal Uddin include University of Minnesota & Kansas State University.

Hydrothermal carbonization: Fate of inorganics

Abstract: Hydrothermal carbonization (HTC) is a pretreatment process for making a homogenized, carbon rich, and energy-dense solid fuel, called biochar, from lignocellulosic biomass. Corn stover, miscanthus, switch grass, and rice hulls were treated with hot compressed water at 200, 230, and 260 °C for 5 min. Mass yield is as low as 41% of the raw biomass, and decreases with increasing HTC temperature. Higher heating values (HHV) increase up to 55% with HTC pretreatment temperature. Up to 90% of calcium, magnesium, sulfur, phosphorus, and potassium were removed with HTC treatment possibly due to hemicellulose removal. At a HTC temperature of 260 °C, some structural Si was removed. All heavy metals were reduced by HTC treatment. The slagging and fouling indices are reduced with HTC treatment relative to that of untreated biomass. Chlorine content, a concern only for raw and HTC 200 switch grass, was reduced to a low slagging range at 230 °C, and 260 °C. Alkali index was medium for raw biomass but decreased by HTC.

Hydrothermal carbonization of loblolly pine: reaction chemistry and water balance

Abstract: Hydrothermal carbonization (HTC) is a thermochemical process to convert lignocellulosic biomass into lignite-like HTC biochar. In this study, chemical reactions occurring during a relatively short HTC reaction time are discussed (5–30 min), and reaction mechanisms are examined at temperatures between 200 and 260 °C. Solid HTC biochar products were analyzed by attenuated total reflectance (ATR)/Fourier transform infrared spectroscopy (FTIR), elemental analysis, and gas chromatography-mass spectrometry (GC-MS), while liquid products were analyzed with GC-MS and ion chromatography (IC) to predict the reaction schemes. HTC reactions for whole biomass (loblolly pine) were proposed in the context of HTC reactions for individual biomass fractions. Hydrolysis, dehydration, and decarboxylation reactions are the major reactions of HTC, though condensation, polymerization, and aromatization also occur. An experimental procedure was developed to determine the net water production, a balance between consumption by hydrolysis reactions and production by dehydration reactions. Net production of water is evaluated. At lower HTC temperature (200 °C), water was consumed. However, at higher HTC temperatures, water was produced and the production increases with increasing reaction time.

Engineered pellets from dry torrefied and HTC biochar blends

Abstract: Dry torrefaction and hydrothermal carbonization (HTC) are two thermal pretreatment processes for making homogenized, carbon rich, hydrophobic, and energy dense solid fuel from lignocellulosic biomass. Pellets made from torrefied biochar have poor durability compared to pellets of raw biomass. Durability, mass density, and energy density of torrefied biochar pellets decrease with increasing dry torrefaction temperature. Durable pellets of torrefied biochar may be engineered for high durability using HTC biochar as a binder. In this study, biomass dry torrefied for 1 h at 250, 275, 300, and 350 °C was pelletized with various proportions of biomass HTC treated at 260 °C for 5 min. During the pelletization of biochar blends, HTC biochar fills the void spaces and makes solid bridges between torrefied biochar particles, thus increasing the durability of the blended pellets. The engineered pellets' durability is increased with increasing HTC biochar fraction. For instance, engineered pellets of 90% Dry 300 and 10% HTC 260 are 82.5% durable, which is 33% more durable than 100% Dry 300 biochar pellets, and also have 7% higher energy density than 100% Dry 300 biochar pellets.

Effects of water recycling in hydrothermal carbonization of loblolly pine

Abstract: Hydrothermal carbonization (HTC) is a process to densify, homogenize, and stabilize diverse biomass feedstocks. The water requirements of HTC need to be assessed to determine commercial feasibility. This current research work focuses on the effects on HTC of using recycled process water for multiple process cycles. Loblolly pine was treated in hot, compressed water at 200, 230, and 260°C for 5 min with a 5:1 water:biomass mass ratio. Liquid product was separated and recycled for reuse in HTC, nine cycles at 200 and 230°C and five cycles at 260°C. The solid products (biocarbon) were characterized by their mass yields, higher heating values (HHVs), and equilibrium moisture content (EMC), whereas in the liquid samples, total organic carbon (TOC) content and pH were determined. With successive recycling, biocarbon mass yield increases by 5–10% above the yield recorded for the initial cycle at each temperature investigated, whereas biocarbon HHV is essentially unchanged. The aqueous TOC is increasingly concentrated with the number of cycles and reaches an equilibrium. The EMC results suggest that the effects of recycling process water on hydrophobicity of the biocarbon are negligible. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 1309–1315, 2014

A comparative review of biochar and hydrochar in terms of production, physico-chemical properties and applications

Abstract: Slow-pyrolysis of biomass for the production of biochar, a stable carbon-rich solid by-product, has gained considerable interest due to its proven role and application in the multidisciplinary areas of science and engineering. An alternative to slow-pyrolysis is a relatively new process called hydrothermal carbonization (HTC) of biomass, where the biomass is treated with hot compressed water instead of drying, has shown promising results. The HTC process offers several advantages over conventional dry-thermal pre-treatments like slow-pyrolysis in terms of improvements in the process performances and economic efficiency, especially its ability to process wet feedstock without pre-drying requirement. Char produced from both the processes exhibits significantly different physiochemical properties that affect their potential applications, which includes but is not limited to carbon sequestration, soil amelioration, bioenergy production, and wastewater pollution remediation. This paper provides an updated review on the fundamentals and reaction mechanisms of the slow-pyrolysis and HTC processes, identifies research gaps, and summarizes the physicochemical characteristics of chars for different applications in the industry. The literature reviewed in this study suggests that hydrochar (HTC char) is a valuable resource and is superior to biochar in certain ways. For example, it contains a reduced alkali and alkaline earth and heavy metal content, and an increased higher heating value compared to the biochar produced at the same operating process temperature. However, its effective utilization would require further experimental research and investigations in terms of feeding of biomass against pressure; effects and relationships among feedstocks compositions, hydrochar characteristics and process conditions; advancement in the production technique(s) for improvement in the physicochemical behavior of hydrochar; and development of a diverse range of processing options to produce hydrochar with characteristics required for various industry applications.

A review on the current status of various hydrothermal technologies on biomass feedstock

Abstract: Hydrothermal processing, a thermochemical approach, is an excellent method of converting energy-rich biomass into useful products. This approach offers the advantage of handling biomass with relatively high moisture content by precluding an energy-intensive pretreatment step. Hydrothermal processing is of world-wide interest in view of depleting fossil-fuel reserves and increased environmental greenhouse gas emissions. There is potential to develop this novel technology at demonstration scale. This paper reviews the three hydrothermal technologies, namely hydrothermal liquefaction, gasification and carbonization, to provide insight into the likelihood of commercialization. The study discusses the role of different process parameters that have key impacts on the quality and yield of the desired products. This study also identifies the gaps in the literature including the need to establish a baseline to develop key process models and to perform a techno-economic assessment to get a better sense of the viability of the technology in future.