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The effects of pH upon methane production from anaerobic digestion of dairy cattle manure were investigated. One liter digesters were maintained by daily adjustment at the following pH levels: 7.6, 7.0, 6.0, 5.5, and 5.0. After 33 weeks of incubation the working volume of the digesters was increased to 3 liters. Digesters were incubated on a rotary shaker at 37°C. Digesters were loaded at the desired volatile solids concentrations, without an inoculum, and maintained from day one by daily additions and withdrawals to achieve a 3 day retention time. After 50 weeks of operation the manure from a second dairy was utilized as substrate. Active digestion was achieved at all pH levels except pH 5.0. Biogas production was evident in 4 to 6 days after incubation. Biogas production was highest at pH 7.0 with manure from both dairies (3.047 ± 0.403 liters per liter of digester per day with Dairy II manure and 1.43 ± 0.09 liters per liter per day with Dairy I manure). Methane production was also highest at pH 7.0 (1.43 ± 0.292 liters per liter of digester per day with Dairy II manure and 0.611 ± 0.057 liters per liter per day with Dairy I manure although the highest percentages of methane in the biogas occurred at pH 7.6 (65.9 ± 5.2 from Dairy I manure and 50.4 ± 4.6 from Dairy II manure). Dairy II manure produced significantly more biogas and methane at all pH levels. This increased production could not be attributed solely to differences in volatile solids concentrations of the two substrates. Total volatile acid concentrations were highest at the highest pH levels and were higher with Dairy II manure as a substrate. Digesters at all pH levels had volatile acid concentrations above 2000 mg/liter normally considered inhibitory for methane bacteria (2314-2890 mg/liter with Dairy I manure and 5.708-7.434 mg/liter with Dairy II manure). The results reported here indicate that stable methane digestion of dairy cattle manure can be established maintained at 37°C with a 3 day retention time. Digestion at pH levels as low as 5.5 continued for periods up to 24 months without a failure. High levels of volatile acids did not cause digester failure. Characteristics of the manure have significant effects on biogas and methane production.

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN. / Vita. / Bibliography : leaves 176-192. / Ph.D.

Freshwater ecosystems cover about 4 % of the Earth’s surface. Yet they are important components in the global C cycle, as they in addition to their within-lake primary production, receive and process organic matter loads originating from terrestrial environments. The boreal forest biome has the highest density of lakes globally. In general, lakes in the boreal forest biome are shallow with high proportions of littoral sediments and are considered methane hotspots in the landscape. The major pathway of methane (CH4) from lakes (depth ≤ 10 m) to the atmosphere is via CH4 ebullition (i.e., gas bubbles). Moreover, CH4 ebullition is highly irregular in space and time. While enhanced CH4 ebullition rates have been reported to coincide with temporal forces (e.g., pressure drop) and showed a spatial variability with higher CH4 ebullition rates at lake inlets, none of the present models can currently represent the variability of CH4 ebullition over space and time. To improve the understanding behind spatial drivers of CH4 ebullition, sediment characteristics in relation to CH4 ebullition were investigated in Lake Alsta, a shallow and eutrophic lake in Sweden. In-situ CH4 ebullition rates were analysed along with sediment TN, TOC, C:N ratio and potential CH4 production rates. Sediment TN could explain CH4 production (R20.39, p-value<0.001), while the degree of explanation of CH4 ebullition rate was low yet significant (R2=0.14, p-value=0.03). However, the combination of fine sediments, together with high loads of aquatic- and terrestrial organic matter and nitrogen are likely spatial factors driving the high CH4 ebullition rates at both inlets in Lake Alsta, Sweden. The CH4 ebullition at its deepest point cannot be distinguished from the ebullition rates at the inlets, and the outlet has a significantly lower CH4 ebullition rate than all other sites. This highlights that the distribution of sediment and the quality of organic matter (i.e., C:N ratio) within the lake affects CH4 ebullition. In addition, including littoral vegetation into CH4 ebullition models and analysing sediment redox potentials might further give explanation to spatial differences.

A single compressor station site along a gathering line network was monitored for fugitive methane emissions to quantify long-term emissions in Appalachia Virginia. Continuous monitoring was conducted from January 2021 to April 2021. The compressor station undergoing monitoring operated two CAT3516 Tale and one CAT3516 B engines operating at 80% of max output flow. Data presented on methane emissions during this period was gathered with an eddy covariance monitoring station. This station was equipped with an LI-7700 methane analyzer, LI-7500A - CO_2/H_2 O analyzer as well as a sonic anemometer these sensors could be observed remotely through cellular connection. The data is represented in flux output ((µmol)/(s m^2 )) as well as kg CO_2 equivalence of methane outlined by the EPA greenhouse gas inventory. The average daily emissions for this compressor station are estimated to be 136 kg CO_2 equivalent emissions. This study shows that the site during the observational period the compressor station emitted on average are estimated to be 5.43 kg of CH_4 per day. / Master of Science / There has been an increased interest in quantifying and recording methane (CH_4) emissions among all sectors. A main focus of interest among methane is to understand fugitive gasses and emissions resulting from the natural gas sector. Leaks along pipelines are most likely occurring at connection points between components. This study aimed to continuously monitor a pipeline compressor station in Appalachia Virginia. Compressor stations are just one component of the pipeline network as well as the natural gas production and delivery chain attributed with CH_4 emissions. To monitor methane emissions at the site a stationary eddy covariance monitoring station was installed that was equipped with an open path methane analyzer, open path CO_2 and H_2 O analyzer, and a sonic anemometer. The data gathered was used to calculate the flux of methane which is the amount of methane being generated or absorbed by the area of interest. The goal of this study was to continuously monitor methane emissions of a natural gas compressor station. Data presented in this study was collected from January 2021 to April 2021. Data was presented in the flux output ((µmol)/(s m^2 )) as well as kg CO_2 equivalence of methane outlined by the EPA greenhouse gas inventory.

The present thesis has focused on the intensive study of the methane dehydroaromatization process under non-oxidative conditions for producing benzene and H2 in a direct way. Nevertheless, MDA process is thermodynamically limited and, moreover, the catalyst quickly accumulates large amounts of carbonaceous deposits, which hinders its commercialization. Therefore, this thesis has as fundamental purposes the improvement of the catalytic activity and the stability of the catalyst on MDA reaction. The catalysts widely used on MDA reaction are Mo/zeolite, which are bifunctional, i.e., Mo sites are involved in the methane dehydrogenation and formation of CHx species, which are dimirized to C2Hy species, and Brønsted acid sites of the zeolite oligomerize these C2Hy species, forming mostly benzene and naphthalene. Thereby, different Mo/zeolite catalysts were prepared using commercial zeolites as well as zeolites synthesized on the laboratory. Thus, observing that the zeolite and the Mo content employed on the catalyst affected significantly the MDA performance. The topology and the channel dimensions of the zeolite as well as its Si/Al ratio and crystal size were also important on the MDA results obtained. Concretely, the best MDA performance was achieved by the 6%Mo/MCM-22 catalyst. Different catalyst activation procedures were tested, achieving the best MDA performance and catalyst stability using a gas mixture of CH4:H2, 1:4 (vol. ratio) during 1 h up to 700 ºC and maintaining this temperature for 2 h. This catalyst activation leads to the pre-carburization and pre-reduction of the Mo species, obtaining the most active and stable on MDA reaction. Moreover, the effect of the space velocity was studied in the present thesis. The best MDA results were reached at 1500 mL¿h-1¿gcat-1, as at higher space velocities methane barely can interact with the catalytic sites. While at lower space velocities the condensation of the heavy aromatic hydrocarbons is facilitated, causing higher coke accumulation on the catalyst. Furthermore, higher catalyst stability was obtained by co-feeding H2O, H2 and CO2 separately using the 6%Mo/HZSM-5 catalyst as well as the 6%Mo/MCM-22, due to the partial suppression of coke deposited. However, the catalytic activity was worsen by adding these co-reactants because of, on one hand, thermodynamically the addition of H2O, H2 or CO2 to the methane feed is detrimental and, on the other hand, H2O and CO2 partially re-oxidize the Mo species of the catalyst. Thermodynamically, H2 causes an equilibrium shift and, therefore, a decrease on the methane conversion; H2O favors the methane reforming reaction and coke gasification; and CO2 promotes the methane reforming reaction and the reverse Boudart reaction. The development and implementation of a catalytic membrane reactor (CMR) that integrates the 6%Mo/MCM-22 catalyst and the BZCY72 tubular membrane has been carried out on the present thesis. The MDA performance and the stability of the catalyst were exceptionally improved using this CMR by imposing a current to the electrochemical cell, changing or not the standard operating conditions. These good results were obtained due to the simultaneous H2 removal from MDA reaction side and O2 injection to this side through the BZCY72 tubular membrane. Thus, the H2 extraction results in the thermodynamic equilibrium displacement of MDA reaction, which causes the increase of the methane conversion and in turn of the aromatics yield. Moreover, the O2 injection involves the formation of H2O in low concentration, which reacts with coke accumulated (coke gasification), rising the stability of the catalyst. / La presente tesis se ha centrado en el estudio intensivo del proceso de deshidroaromatización de metano en condiciones no oxidativas para producir benceno e hidrógeno de forma directa. Sin embargo, el proceso de MDA está limitado termodinámicamente y, además, el catalizador acumula rápidamente grandes cantidades de depósitos carbonosos, lo que dificulta su comercialización. Por tanto, esta tesis tiene como objetivos fundamentales la mejora de la actividad catalítica y la estabilidad del catalizador en la reacción MDA. Los catalizadores Mo/zeolita son ampliamente utilizados en la reacción MDA, los cuales son bifuncionales, es decir, los sitios de Mo están involucrados en la deshidrogenación del metano y la formación de las especies CHx, las cuales se dimerizan a especies C2Hy, y los sitios ácidos de Brønsted de la zeolita oligomerizan éstas especies C2Hy, formando principalmente benceno y naftaleno. Por lo que, diferentes catalizadores Mo/zeolita se prepararon utilizando zeolitas tanto comerciales como sintetizadas en el laboratorio. Observando así que la zeolita y el contenido de Mo utilizados en el catalizador afectan significativamente el rendimiento de la reacción MDA. Tanto la topología y las dimensiones de los canales de la zeolita como su relación Si/Al y su tamaño de cristal son también importantes en los resultados obtenidos de la reacción MDA. Concretamente, el mejor rendimiento de MDA fue obtenido por el catalizador 6%Mo/MCM-22. Se probaron diferentes procedimientos de activación del catalizador, obteniendo el mejor rendimiento de la reacción MDA y estabilidad del catalizador usando una mezcla gaseosa de CH4:H2, 1:4 (relación en volumen) durante 1 h hasta 700 ºC y manteniendo esta temperatura durante 2 h. Esta activación del catalizador provoca la pre-carburización y pre-reducción de las especies de Mo, obteniendo las más activas y estables en la reacción de MDA. Los mejores resultados de MDA se obtuvieron con 1500 mL¿h-1¿gcat-1, ya que con mayores velocidades espaciales el metano apenas puede interaccionar con los sitios catalíticos. Mientras que con menores velocidades espaciales la condensación de los hidrocarburos aromáticos pesados se ve favorecida, provocando una mayor acumulación de coque en el catalizador. Por otra parte, co-alimentando H2O, H2 y CO2 por separado se obtuvo una mayor estabilidad tanto del catalizador 6%Mo/HZSM-5 como del 6%Mo/MCM-22, debido a la supresión parcial del coque depositado. Sin embargo, la actividad catalítica empeoró al añadir estos co-reactivos ya que, por un lado, la adición de H2O, H2 y CO2 a la alimentación de metano es perjudicial termodinámicamente y, por otro lado, el H2O y el CO2 re-oxidan parcialmente las especies Mo del catalizador. Termodinámicamente, el H2 provoca un cambio en el equilibrio y, por tanto, una disminución de la conversión de metano; el H2O favorece la reacción de reformado de metano y la gasificación de coque; y el CO2 promueve la reacción de reformado de metano y la reacción inversa de Boudart. En la presente tesis se ha llevado a cabo el desarrollo y la implementación de un reactor catalítico de membrana (CMR) que integra el catalizador 6%Mo/MCM-22 y la membrana tubular BZCY72. El rendimiento de la reacción MDA y la estabilidad del catalizador fueron excepcionalmente mejorados usando este CMR imponiendo una corriente a la celda electroquímica, cambiando o no las condiciones de operación estándar. Estos buenos resultados fueron obtenidos debido a la simultánea extracción de H2 del lado de reacción y la inyección de O2 a este lado mediante la membrana tubular BZCY72. Así, la extracción de H2 se traduce en un desplazamiento del equilibrio termodinámico de la reacción MDA, lo que causa el aumento de la conversion de metano y a su vez del rendimiento de aromáticos. Además, la inyección de O2 implica la formación de agua en baja concentración, la que reacciona con el coque acumulado (gas / La present tesi s'ha centrat en l'estudi intensiu del procés de deshidroaromatització de metà en condicions no oxidatives per produir benzé i hidrogen de forma directa. No obstant això, el procés de MDA està limitat termodinàmicament i, a més, el catalitzador acumula ràpidament grans quantitats de dipòsits carbonosos, el que dificulta la seva comercialització. Per tant, aquesta tesi té com a objectius fonamentals la millora de l'activitat catalítica i l'estabilitat del catalitzador en la reacció MDA. Els catalitzadors Mo/zeolita són àmpliament utilitzats en la reacció MDA, els quals són bifuncionals, és a dir, els llocs de Mo estan involucrats en la deshidrogenació del metà i la formació de les espècies CHx, les quals es dimeritzen a espècies C2Hy, i els llocs àcids de Brønsted de la zeolita oligomeritzan aquestes espècies C2Hy, formant principalment benzè i naftalè. Per tant, diferents catalitzadors Mo/zeolita es van preparar utilitzant zeolites tant comercials com sintetitzades al laboratori. Observant així que la zeolita i el contingut de Mo utilitzats en el catalitzador afecten significativament el rendiment de la reacció MDA. Tant la topologia i les dimensions dels canals de la zeolita com la seva relació Si/Al i el seu tamany de cristall són també importants en els resultats obtinguts de la reacció MDA. Concretament, el millor rendiment de MDA va ser obtingut pel catalitzador 6%Mo/MCM-22. Es van provar diferents procediments d'activació del catalitzador, obtenint el millor rendiment de la reacció MDA i estabilitat del catalitzador usant una mescla de gasos de CH4: H2, 1: 4 (relació en volum) durant 1 h fins a 700 ºC i mantenint aquesta temperatura durant 2 h. Aquesta activació del catalitzador provoca la pre-carburització i pre-reducció de les espècies de Mo, obtenint les més actives i estables en la reacció de MDA. A més, en la present tesi es va estudiar l'efecte de la velocitat espacial. Els millors resultats de MDA es van obtindre amb 1500 mL¿h-1¿gcat-1, ja que amb majors velocitats espacials el metà gairebé no pot interaccionar amb els llocs catalítics. Mentre que amb menors velocitats espacials la condensació dels hidrocarburs aromàtics pesants es veu afavorida, provocant una major acumulació de coc en el catalitzador. D'altra banda, co-alimentant H2O, H2 i CO2 per separat es va obtindre una major estabilitat tant del catalitzador 6%Mo/HZSM-5 com del 6%Mo/MCM-22, a causa de la supressió parcial del coc dipositat. No obstant això, l'activitat catalítica empitjorà en afegir aquests co-reactius ja que, d'una banda, l'addició d'H2O, H2 i CO2 a l'alimentació de metà és perjudicial termodinàmicament i, d'altra banda, el H2O i el CO2 re-oxiden parcialment les espècies Mo del catalitzador. Termodinàmicament, el H2 provoca un canvi en l'equilibri i, per tant, una disminució de la conversió de metà; l'H2O afavoreix la reacció de reformat de metà i la gasificació de coc; i el CO2 promou la reacció de reformat de metà i la reacció inversa de Boudart. En la present tesi s'ha dut a terme el desenvolupament i la implementació d'un reactor catalític de membrana (CMR) que integra el catalitzador 6%Mo/MCM-22 i la membrana tubular BZCY72. El rendiment de la reacció MDA i l'estabilitat del catalitzador van ser excepcionalment millorats usant aquest CMR imposant un corrent a la cel¿la electroquímica, canviant o no les condicions d'operació estàndard. Aquests bons resultats van ser obtinguts a causa de la simultània extracció d'H2 del costat de reacció i la injecció d'O2 a aquest costat per mitjà de la membrana tubular BZCY72. Així, l'extracció d'H2 es tradueix en un desplaçament de l'equilibri termodinàmic de la reacció MDA, el que causa l'augment de la conversió de metà i alhora del rendiment d'aromàtics. A més, la injecció d'O2 implica la formació d'aigua en baixa concentració, la qual reacciona amb el coc acumulat (gasificació de coc) / Zanón González, R. (2017). Intensification of methane dehydroaromatization process on catalytic reactors [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/83124

No / Methane reforming in the presence of hydrogen sulfide (H2SMR) is not only conspicuous in terms of producing valuable material but also because of its advantages in obtaining hydrogen as a clean fuel. Substitution of traditional hydrogen production processes such as methane steam reforming (MSR), elimination of natural gas amine–based H2S removal, and sulfur recovery processes have attracted much attention. The current hydrogen production is associated with consuming energy that is usually supplied by burning fossil fuels. Thus, producing hydrogen by current high greenhouse gas emitter methods seems not to be a rational approach to benefit from this clean energy source. Additionally, H2SMR with the potential of producing four moles of hydrogen and one mole of CS2 from methane could be a promising alternative as providing the opportunity to benefit from producing cleaner fuels and simultaneously making CS2 that is used for the production of more valuable products. This chapter reviews the recent progress in CS2 production from methane reforming in the presence of H2S and brings the effect of dominant parameters on this process.

Volatile fatty acids (VFA) are important products of ruminal fermentation. The VFA are not only the major source of energy to the ruminant animals but also influence methane production in the rumen. Therefore it is important to understand mechanism controlling VFA production and to depict VFA production in a model. This will allow us to devise strategies to enhance energy utilization and reduce methane production in ruminant livestock. An evaluation of a mechanistic model in predicting VFA production was conducted and equations were introduced into the model to improve the predictions. Later a continuous culture experiment was conducted to test the hypothesis on which those equations were based on. A mechanistic model -" Molly, was evaluated using a dataset with reported VFA production rates. The results of residual error analysis indicated that the root mean square prediction errors (RMSPE) were 63, 63, and 49% for acetate, propionate and butyrate, respectively. An assessment from two studies reporting VFA production revealed a potential of reducing errors of prediction by representing interconversion among VFA. In the second study, equations based on thermodynamics influence of pH and VFA concentration were introduced in the model to represent interconversion among VFA. The parameters for de novo VFA production and VFA absorption were re derived with (VFAInt) and without (BASE) the new interconversion equations. There were some improvements in the VFA concentration predictions but the improvements were both in VFAInt and BASE models. The RMSPE of VFA production were still above 50% for acetate, propionate and butyrate. The larger errors of predictions were attributed to measurement variation in VFA production literature, or possible incorrect rate constants for interconversion equations. Finally, a third study was conducted to assess the effect of pH, and VFA concentration on VFA and methane production in continuous culture. The treatments consisted of control, 20 mmol/d acetate infusion (INFAC), 7 mmol/d propionate infusion (INFPR), and low pH (LOWPH). Individual isotopes of acetate, propionate and butyrate were infused in the fermenters to estimate interconversions among VFA. With LOWPH treatment methane emission was reduced whereas production of propionate was increased. Hydrogen production was higher in INFAC indicating that some of the acetate could have been degraded to CO2 and H2. It was estimated that around 3 % of de novo acetate was converted to propionate and 9 % to butyrate. Exchange between propionate and butyrate was insignificant and below 1% of de novo production of either VFA. However, treatments did not affect interconversion rates among VFA. These results indicated that pH and VFA concentration do not have thermodynamic influence on VFA interconversion as hypothesized. / Ph. D.