HCN and NH₃Released from Biomass and Soybean Cake under Rapid Pyrolysis

Abstract

HCN (hydrocyanic acid) and NH 3 (ammonia) (including HNCO (isocyanic acid)) released during rapid pyrolysis of three biomass samples (rice straw, chinar leaves, pine sawdust) and a nitrogen rich material (soybean cake) were measured. The pyrolysis runs were conducted at 600-1200 °C using a high-frequency furnace. Much more HCN than NH 3 was released in the biomass runs while the reverse was observed in the soybean cake runs. Because lignin was a common constituent of biomass cells and nearly absent in soybean, the effect of its content on HCN release from the biomass was determined. A strong correlation was established for each biomass sample suggesting that lignin may promote formation of heterocyclic nitrogenous compounds which then decompose to form HCN. HCN release and char/tar-N formation decreased at a higher pyrolysis temperature. Pyrolysis at >1000 °C is desirable since most nitrogen in the biomass will be converted to N 2 with <7% released as HCN and NH 3 .

A Review of Thermal Co-Conversion of Coal and Biomass/Waste

“…Minor amounts of isocyanic acid (HNCO) have been measured in fluidized bed pyrolysis [201] where the heating rate is usually low, while it has not been detected in entrained flow reactor experiments where the heating rate is usually high [199]. Contradicting results are however observed in literature where the dominant nitrogen specie during pyrolysis of biomass is HCN [202]. These authors (Yuan et al [202]) investigated the fast pyrolysis of rice straw, chinar leaves, pine sawdust and soybean cake in a high frequency furnace.…”

“…Contradicting results are however observed in literature where the dominant nitrogen specie during pyrolysis of biomass is HCN [202]. These authors (Yuan et al [202]) investigated the fast pyrolysis of rice straw, chinar leaves, pine sawdust and soybean cake in a high frequency furnace. Volatile nitrogen of rice straw, chinar leaves and sawdust was dominated by HCN while that of soybean cake was dominated by NH 3 .…”

Fuel-N Evolution during the Pyrolysis of Industrial Biomass Wastes with High Nitrogen Content

“…However, nitrogen functionalities in biomass are different from those in coal [6]. Nitrogen in coal mainly exists in heteroaromatic ring systems as pyrrolic and pyridinic N, while nitrogen in biomass mainly exists as proteins (and amino acids) together with some other forms such as DNA, RNA, alkaloids, porphyrin, and chlorophyll [13,14]. Moreover, some biomass fuels produce more NOx than coal on the basis of the heating value [15], especially for those typical industrial biomass wastes with high nitrogen content mentioned above.…”

“…Thus some researchers [2,6,8,13] have been devoting their efforts to investigate the Fuel-N evolution during the pyrolysis of biomass. It is well known that during the pyrolysis of biomass, the main NOx precursors are ammonia (NH 3 ) and cyanide (HCN).…”

“…However, the Char-N can form NO directly by a heterogeneous process (and from HCN) during combustion. In some studies [13,16,19], although the characteristics of NO x precursors (HCN/NH 3 ) produced from certain biomass with relatively high nitrogen content such as thermally thick samples (3.0-4.0 wt %, dry ash free basis) and soybean cake (4.45 wt %) were well investigated, not enough information about other nitrogen-containing products was indicated. In a word, the situation necessarily calls for comprehensive observation of Fuel-N migration and distribution among every part of the nitrogen containing products using typical industrial biomass wastes whose nitrogen content are high enough so that an innovative low NO x emission technology can be developed to treat these industrial biomass wastes with high nitrogen content.…”