Self-generated peroxyacetic acid in phosphoric acid plus hydrogen peroxide pretreatment mediated lignocellulose deconstruction and delignification

Background Peroxyacetic acid involved chemical pretreatment is effective in lignocellulose deconstruction and oxidation. However, these peroxyacetic acid are usually artificially added. Our previous work has shown that the newly developed PHP pretreatment (phosphoric acid plus hydrogen peroxide) is promising in lignocellulose biomass fractionation through an aggressive oxidation process, while the information about the synergistic effect between H3PO4 and H2O2 is quite lack, especially whether some strong oxidant intermediates is existed. In this work, we reported the PHP pretreatment system could self-generate peroxyacetic acid oxidant, which mediated the overall lignocellulose deconstruction, and hemicellulose/lignin degradation. Results The PHP pretreatment profile on wheat straw and corn stalk were investigated. The pathways/mechanisms of peroxyacetic acid mediated-PHP pretreatment were elucidated through tracing the structural changes of each component. Results showed that hemicellulose was almost completely solubilized and removed, corresponding to about 87.0% cellulose recovery with high digestibility. Rather high degrees of delignification of 83.5% and 90.0% were achieved for wheat straw and corn stalk, respectively, with the aid of peroxyacetic acid oxidation. A clearly positive correlation was found between the concentration of peroxyacetic acid and the extent of lignocellulose deconstruction. Peroxyacetic acid was mainly self-generated through H2O2 oxidation of acetic acid that was produced from hemicellulose deacetylation and lignin degradation. The self-generated peroxyacetic acid then further contributed to lignocellulose deconstruction and delignification. Conclusions The synergistic effect of H3PO4 and H2O2 in the PHP solvent system could efficiently deconstruct wheat straw and corn stalk lignocellulose through an oxidation-mediated process. The main function of H3PO4 was to deconstruct biomass recalcitrance and degrade hemicellulose through acid hydrolysis, while the function of H2O2 was to facilitate the formation of peroxyacetic acid. Peroxyacetic acid with stronger oxidation ability was generated through the reaction between H2O2 and acetic acid, which was released from xylan and lignin oxidation/degradation. This work elucidated the generation and function of peroxyacetic acid in the PHP pretreatment system, and also provide useful information to tailor peroxide-involved pretreatment routes, especially at acidic conditions. Graphical abstract

Sanitizantes clorados no setor alimentício: mini-revisão

A utilidade prática, aspectos positivos e desvantagens são mostrados nesta mini-revisão por meio da apresentação de uma fórmula prática para se calcular as dosagens de sanitizantes clorados (SC), a qual fornece a quantidade de cloro a ser utilizada na solução em grama (g) ou mililitros (ml) e duas figuras i) as concentrações cloradas já calculadas para locais que manipulam ou que processam alimentos e ii) com as vantagens e desvantagens dos SC. Os SC são muito utilizados no setor da agroindústria no mundo todo, no entanto, produzem cloramina, substância tóxica, cancerígena aos seres humanos. Alternativas ao uso do cloro se fazem necessárias como o ozônio (O3), peróxido de hidrogênio (H2O2), ácido peracético (CH3CO3H), raios ultravioletas com comprimento de onda de 250 a 275nm por apresentarem atividade germicida. Estudos são necessários para diminuir o custo de aplicação destas tecnologias nas empresas. The practical utility, positive aspects and disadvantages are shown in this mini-review by means a practical formula to calculate the dosage of chlorine sanitizers (CS), which provides the amount of chlorine being used in the solution in gram (g) or milliliters (ml) and two figuras i) concentrations as calculated for chlorinated sites that handle or process food and ii) the advantages and disadvantages of the CS. The CS are widely used in the agribusiness sector widely used in the agribusiness sector worldwide, however, produce chloramine, toxic, carcinogenic to humans. Alternatives to the use of chlorine are needed such as ozone (O3), hydrogen peroxide (H2O2), peroxyacetic acid or peracetic (CH3CO3H), ultraviolet rays with a wavelength of 250 to 275nm by presenting germicidal activity. Studies are needed to reduce the cost of implementing these technologies in business.

Iodide CIMS and <i>m</i>∕<i>z</i> 62: the detection of HNO₃ as NO₃⁻ in the presence of PAN, peroxyacetic acid and ozone

Chemical ionisation mass spectrometry (CIMS) using I− (the iodide anion), hereafter I-CIMS, as a primary reactant ion has previously been used to measure NO3 and N2O5 both in laboratory and field experiments. We show that reports of large daytime mixing ratios of NO3 and N2O5 (both usually present in detectable amounts only at night) are likely to be heavily biased by the ubiquitous presence of HNO3 in the troposphere and lower stratosphere. We demonstrate in a series of laboratory experiments that the CIMS detection of HNO3 at m/z 62 using I− ions is efficient in the presence of peroxy acetyl nitric anhydride (PAN) or peroxyacetic acid (PAA) and especially O3. We have characterised the dependence of the sensitivity to HNO3 detection on the presence of acetate anions (CH3CO2-, m/z 59, from either PAN or PAA). The loss of CH3CO2- via conversion to NO3- in the presence of HNO3 may represent a significant bias in I-CIMS measurements of PAN and PAA in which continuous calibration (e.g. via addition of isotopically labelled PAN) is not carried out. The greatest sensitivity to HNO3 at m/z 62 is achieved in the presence of ambient levels of O3 whereby the thermodynamically disfavoured, direct reaction of I− with HNO3 to form NO3- is bypassed by the formation of IOx-, which reacts with HNO3 to form, for example, iodic acid and NO3-. The ozone and humidity dependence of the detection of HNO3 at m/z 62 was characterised in laboratory experiments and applied to daytime, airborne measurements in which good agreement with measurements of the I−(HNO3) cluster ion (specific for HNO3 detection) was obtained. At high ozone mixing ratios, we show that the concentration of I− ions in our ion–molecule reactor (IMR) is significantly depleted. This is not reflected by changes in the measured I− signal at m/z 127 as the IOx- formed does not survive passage through the instrument but is likely detected after fragmentation to I−. This may result in a bias in measurements of trace gases using I-CIMS in stratospheric air masses unless a calibration gas is continuously added or the impact of O3 on sensitivity is characterised.