Yoshizo Suzuki

Developing an innovative method, HyPr-RING, to produce hydrogen from hydrocarbons

Abstract A new innovative hydrogen-production method, HyPr-RING (hydrogen production by reaction-integrated novel gasification), using hydrocarbon and water has been proposed. Experimental results show that, using one reactor, 1 mol of carbon generates 2 mol of hydrogen with no pollutants and no carbon oxides being detected in the product gas phase. Water reduction by the hydrocarbons and the CO2 absorption reaction are the key reactions in this method. The absorption of CO2 from the gas phase improves the yield of hydrogen production from water. A feasible hydrogen production process was designed by applying the above-mentioned method, and the thermodynamic efficiency was calculated accordingly. Theoretically, the calculated cold-gas efficiency of this process exceeds 90%, and no clean-up system is required. This process potentially reduces hydrogen production costs compared to conventional hydrogen production methods.

Hydrogen production from coal by separating carbon dioxide during gasification

Hydrogen generation during the reaction of a coal/CaO mixture with high pressure steam was investigated using a flow-type reactor. Coal, CaO and CO reactions with steam, and CO2 absorption by Ca(OH)2 or CaO occurred simultaneously in the experiment. It was found that H2 was the primary resultant gas, comprising about 85% of the reaction products. CO2 was fixed into CaCO3 and CO was completely converted to H2. Pyrolysis of the coal/CaO mixture carried out in N2 was also examined. The pyrolysis gases were compared with gases produced by general coal pyrolysis. While general coal pyrolysis produced about 14.7% H2, 50.5% CH4, 12.0% CO and 12.0% CO2, the gases produced from coal/CaO mixture pyrolysis were 84.8% H2, 9.6% CH4, 1.6% CO2 and 1.1% CO.

Theoretical study on the thermal decomposition of pyridine

Semi-empirical PM3 molecular orbital calculations have been used to investigate the reaction pathways of pyrolysis of pyridine. All the transition states and intermediates of the reaction path were optimized. The probable pathways are estimated from the activation energies calculated and compared with known experimental results. The heats of formation of pyridine radicals are calculated to be 76.1, 80.6, and 79.5 kcal/mol for 2- (2A), 3- (3A) and 4-pyridyl radicals (4A), respectively. The weakest bonds on the radicals were assumed to be broken and gave the decomposition fragments successively.

Coal gasification with a subcritical steam in the presence of a CO2 sorbent: products and conversion under transient heating

Pulverized Taiheiyo coal (Japanese subbituminous coal) was gasified with steam in the presence of CO2 sorbent (Ca(OH)2) under relatively high pressure (approximately 20 MPa; subcritical condition) using a tubing-bomb microreactor (TB reactor). The transient characteristics in the conversion of coal and the formation of gaseous products during the gasification were investigated. During initial heating period, 40–50 wt.% of the coal initially loaded was rapidly converted to gas or tar. In the presence of Ca(OH)2, the yield of gaseous products was apparently increased owing to the catalytic effects of Ca(OH)2 on coal gasification. No CO2 was observed in the produced gas at any soaking time in the gasification with Ca(OH)2, suggesting that CO2 sorption by Ca(OH)2 took place effectively under high-pressure conditions. A rigid agglomeration of char and CO2 sorbent was observed at relatively high temperature, which is attributed to the formation of melts of the CO2 sorbent.

Experimental evidence for three rate-controlling regions of the non-oxidative methane dehydroaromatization over Mo/HZSM-5 catalyst at 1073 K

Mo/HZSM-5 catalyst offers high selectivity for the non-oxidative dehydroaromatization of methane to benzene. This strongly suggests the deep involvement of the zeolite channels in controlling of the overall reaction rate. Therefore, two 5 wt% Mo/HZSM-5 catalysts based on two zeolite samples of different average crystal sizes were tested for the methane dehydroaromatization reaction over a wide range of space velocities (from 3500 to 60 000 mL g−1 h−1) at 1073 K to examine the effect of superficial velocity on the benzene formation rates. Additionally, a recently developed on-line sampling and off-line analysis approach was employed to follow the maximum outlet benzene concentrations reached over very short time frames. Multiplying the obtained maximum outlet benzene concentrations by the corresponding inlet gas flow rates that were corrected for a temperature factor allowed approximate estimation of the maximum benzene formation rates. Consequently, two rate–space velocity curves were obtained to reveal that three rate-controlling regions exist for the title reaction: 40 000 mL g−1 h−1. Moreover, some specifically designed tests and detailed data analysis were performed to further reveal that these three rate-controlling regions correspond, respectively, to the external mass transfer, intracrystalline diffusion and kinetic desorption controlling steps of the reaction.

Pressure effect on char combustion in different rate-control zones:: initial rate expression

Effect of pressure on the initial rate of coal char combustion was studied in a fixed bed and analyzed in terms of theoretical rate equations. Char particles of 0.25–0.5 mm diameter were combusted over temperature and pressure ranges of 559–1273 K and 0.1–1.6 MPa, respectively. Char combustion proceeded in first order with respect to oxygen. The combustion rate increased proportionally with pressure in the chemical-kinetics control zone (Zone I), exhibited a nonlinear increase with pressure in the internal-diffusion control zone (Zone II), and was invariant with pressure in the external-diffusion control zone (Zone III). Theoretical rate equations involving explicit pressure terms were developed for predicting the combustion rate under elevated pressure. For given properties of char (dp,ρc,e and kv) and operating conditions (C0,ug,0,T and P), the combustion rate estimated from the developed rate equations agreed well with the experimental results.

Comparison of the activities of binder-added and binder-free Mo/HZSM-5 catalysts in methane dehydroaromatization at 1073 K in periodic CH4-H2 switch operation mode

Three industry-supplied, well-shaped Mo/HZSM-5 catalysts, two binder-added and one binder-free, were tested for the first time in methane dehydroaromatization to benzene at 1073 K and 10000 mL/(gh) in periodic CH4-H2 switch operation mode, and their catalytic performances were compared with those of three self-prepared, binder-free powder Mo/HZSM-5 catalysts. XRD, 27Al NMR, SEM, BET and NH3-TPD characterizations of all the catalysts show that the zeolites in the two binder-added catalysts are comparable to those in the three binder-free powder catalysts in crystallinity, crystal size, micropore volume and Bronsted acidity. The test results, on the other hand, show that the catalytic performances of the two binder-added catalysts are worse than those of the four binder-free catalysts on both catalyst mass and zeolite mass bases. Then, TPO and BET measurements of all spent samples were conducted to get a deep insight into the negative effects of binder addition, and the results suggest that the binder additives functioned mainly to enhance the polyaromatization of formed aromatics to coke on their external surfaces and consequently lower the benzene formation activity and selectivity of the catalyst.

Effect of superficial velocity on the coking behavior of a nanozeolite-based Mo/HZSM-5 catalyst in the non-oxidative CH4 dehydroaromatization at 1073 K

The lifetime benzene and naphthalene productivity of a nanosized zeolite-based 5%Mo/HZSM-5 catalyst in the non-oxidative CH4 dehydroaromatization has been investigated at 1073 K and three different space velocities (4500, 10 000 and 30 000 mL g−1 h−1, corresponding to the superficial velocities 1.3, 3.0, and 9.0 cm s−1, respectively). The aim is to demonstrate that diffusion limitations do exist and have a strong influence on the coking behaviour and the lifetime aromatics productivity. The results showed that the catalyst deactivation rate increased with increasing CH4 superficial velocity, leading to decreased productivity. On the other hand, TPO and BET measurements of the spent samples revealed that the amount of coke accumulated in the spent samples decreased with increasing velocity, whereas their microporosity varied essentially depending upon the coke amount. Putting these observations together thus leads to a fact that less coke forms at a higher velocity but results in a more rapid deactivation and reduced productivity. As this may suggest the occurrence of non-uniform coke formation across catalyst particles, physical powdering of all spent samples and re-evaluation of the activity of all powdered samples were conducted to confirm this. It was found that the benzene formation activities of all powdered samples exhibited considerable but different degrees of recovery, and the most rapidly deactivated sample provided the greatest recovery. Thus, it is reasonably concluded that the preferential coke formation in the near-surface outer layers of catalyst particles and/or of crystal agglomerates inside the particles does occur in the nanozeolite-based catalyst at the test superficial velocities, particularly at 30 000 mL g−1 h−1. The essential cause for this occurrence is discussed in detail in the article.

Mechanism of Fe additive improving the activity stability of microzeolite-based Mo/HZSM-5 catalyst in non-oxidative methane dehydroaromatization at 1073 K under periodic CH4–H2 switching modes

The catalytic stabilities of Fe-modified and -unmodified 5% Mo/HZSM-5 catalysts in non-oxidative methane dehydroaromatization were compared at 1073 K and three reaction/H2-regeneration cycle periods: 5 min CH4–5 min H2, 5 min CH4–10 min H2, and 5 min CH4–20 min H2. Fe addition proved capable of remarkably increasing the catalyst stability over the cycles of 5 min CH4–20 min H2 but was hardly effective over the cycles of 5 min CH4–5 min H2. On the other hand, SEM observation of all spent samples revealed that Fe addition causes a massive accumulation of carbon nanotubes under the latter cyclic condition but little in the former. Thus several sets of comparative tests were specially designed and performed to gain an insight into the role of Fe-catalyzed cyclic formation of carbon nanotubes in stabilizing the activity under the cyclic condition of 5 min CH4–20 min H2. The results further confirmed that at this condition, cyclic formation of carbon nanotubes enhances cyclic evolution of H2 and increases the H2 concentration of the system, which is thermodynamically beneficial for suppression of formation of the activity-deactivating surface coke. Finally, it was further confirmed that at least a 20 min H2 exposure is required to remove most of the carbon nanotubes and surface coke formed during a 5 min CH4 exposure and reactivate most of the Fe nanoparticles and make them available again for formation of catalytic carbon nanotubes with an enhanced H2 evolution, i.e., with a controlled formation of the surface coke in the next CH4 exposure.

Reduction of N2O emissions from circulating fluidized bed combustors by injection of fuel gases and changing of coal feed point

Abstract This paper describes the reduction techniques of N 2 O emitted from circulating fluidized bed combustion (CFBC) of coal. Two methods, injecting the fuel gases into the riser and changing the position where coal was supplied, were tried to decrease N 2 O emission. A small lab-scale CFBC whose whole parts were made of quartz was used. In the first method, methane, propane and hydrogen were used as a fuel gas. By injecting these gases into the riser, N 2 O emission was decreased remarkably. Reduction rate was almost in proportional to the volumetric flow rate of injected gas. At this time, NO emission did not increase. Required flow rate of injected gas to achieve the same N 2 O reduction was different among the above gases. N 2 O emission was able to be decreased remarkably by changing the position where coal was supplied. When coal was fed to the top of the downcommer, devolatilization took place and volatile matters were burnt in the cyclone. As the results, the temperature in the cyclone became high enough to reduce N 2 O.