生物质炭催化裂解焦油的性能研究

采用管式反应器研究了生物质炭作为焦油裂解催化剂的性能,选用白云石和石英砂作对比试验。通过对焦油转换率、裂解产物、裂解气气体组分和动力学参数的分析对比可知:在所选用的3种材料中,生物质炭作为催化剂的焦油转化率最高,裂解产物中气体所占比重最大,且可燃气体的组分较高,反应动力学参数最小。生物质炭的催化性能显著高于石英砂,稍好于白云石,是一种高效的焦油裂解催化剂。     

热解焦对生物质焦油催化裂解的影响

在小型固定床反应器上,以甲苯为模型化合物对生物质焦油在热解焦上的催化裂解反应进行了研究。重点考察了裂解温度、热解焦粒径尺寸、气相停留时间和水蒸气的流量对焦油的转化率和裂解气成分的影响。结果表明,高温条件下,热解焦对甲苯的裂解具有明显的催化作用。850℃时,所用的两种热解焦对甲苯的转化率分别达到了92.7%和97.0%,同时发现,较小粒径的热解焦和较长的气相停留时间更有利于甲苯的深度裂解。另外,随着水蒸气流量的增加,甲苯的转化率和气体中CO的产率均增大,但当蒸汽甲苯比(S/T)超过6.1时,继续增加水蒸气的流量,甲苯转化率并无明显地提高。     

生物质二次裂解制取氢气的研究

采用生物质热解及二次裂解的方法制取富氢气体.通过对生物质热解产生的气液体成份进行二次裂解,实现热解组分中焦油等含氢化合物的深度转化,提高产品气体中氢气的含量,同时解决了热解产品气中焦油不易去除的难题,得到洁净的富氢气体.实验选用稻壳为原料,分析了热解温度和物料滞留时间等因素对热解气体成份的影响,比较了热解气体和二次裂解气体成份的变化,同时分析了水蒸汽、催化剂等因素对裂解气体成份的影响.实验结果表明,热解温度和物料滞留时间的增加提高了热解气体中氢气的含量,二次裂解、水蒸汽和催化剂的引入都能在一定程度上提高产品气中H2的含量.实验最终表明,氢气体积含量可达到60%以上.     

稻壳连续热解特性研究

在自行研制的生物质连续热解反应装置上进行稻壳连续热解和二次裂解实验研究。随着稻壳热解温度的提高,炭产率降低,气体产率增加,液体产率先增加后减少;随着滞留时间的减少,炭产率、液体产率增加,气体产率减少。稻壳热解气以CO2和CO为主,且二者为竞争关系,热解温度提高,CO2产量降低,CH4、H2、C2H4、C2H6产量增加,CO的产率变化不大;滞留时间对热解气组分影响不大。二次裂解温度提高,裂解气中的H2、CH4、C2H4含量明显增加,二次裂解温度为800℃时,H2产率达到12%。稻壳500℃热解挥发物600℃二次裂解木醋液中醋酸含量高达49.44%,焦油中检测到的物质主要为丙酮和异丙醇。     

生物质热解气重整试验平台设计与试验

针对热解气焦油含量高、热值低的问题,文章基于焦油催化裂解和热解气气化重整原理,提出了生物质热解气重整工艺路线,并设计、搭建了生物质热解气重整试验平台,该试验平台主要由热解、催化重整、产品收集、控制系统等组成。以玉米秸秆为原料,在该试验平台上开展了热解气重整试验,试验结果表明:在以石英砂作为惰性材料的条件(高温裂解)下,热解气产率为33.8%,焦油转化率为64.3%;在玉米秸秆炭催化裂解条件下,热解气产率为37.8%,焦油转化率72.6%;高温裂解和催化裂解条件下生成的热解气的热值均达到了17MJ/m3以上。热解气重整试验平台达到了设计目的,为热解气重整研究提供了理论支持和技术支撑。     

热解炭在线催化玉米秆热解实验研究

为探索一种更适用的催化剂,将热解炭用于玉米秆热解挥发分的在线催化。研究结果表明,虽然生物油产率有所下降,但可降低生物油中的酸类物质含量,而酚类物质含量则显著增加。在实验条件下,酚类物质的相对含量可达55%以上。通过比较热解炭脱灰前后及不同添加量的催化效果,发现热解炭表面的碱性位能吸附挥发分中的酸类物质,使其一部分发生中和,另一部分被裂解成小分子气体,从而降低生物油中的酸类物质含量,而热解炭中的碱和碱土金属对生物油中的酚类物质的富集有明显的促进作用。     

烟秆裂解实验研究

系统地研究了以烟秆为原料裂解制备生物质焦油的工艺参数,以及原料粒径、裂解温度、添加剂用量对裂解产物组成的影响。结果表明,当裂解温度在550℃左右,原料粒径为0.425～1.000 mm,添加剂凹凸棒土用量为烟秆的100%时,生物质焦油产率最高,为47.9%,而残焦及气体得率分别为17.6%和34.5%。烟秆裂解得到的生物质焦油,其成分复杂。分离提纯生物质焦油中的较大组分尼古丁,可用于医药、食品和饲料、日用化工、染料及电镀等行业,应用前景相当广泛,烟秆裂解具有巨大的开发利用潜力。     

整体式焦油裂解催化剂的制备及性能研究

以堇青石为载体,采用真空浸渍法制备整体式镍基催化剂,研究了不同干燥方法对整体式催化剂内表面活性组分轴向分布的影响及不同工艺条件下的催化性能。结果表明:微波干燥法所得催化剂内表面活性组分轴向分布最均匀;重时空速对焦油裂解率的影响较大,当重时空速为177kg/(h.m3)时,焦油裂解率高达92.62%,H2的体积分数为46.53%;在较低温度条件(700~800℃)下,催化温度对焦油裂解的影响较小,当催化温度上升到900℃时,焦油裂解率大幅上升,单位质量生物质气体产率高达1.22Nm3/kg。     

快速外热式热解工艺对生物质热解产物的影响

焦油一直是生物质热解技术发展的瓶颈。文中研究了快速外热式热解工艺对生物质热解产物的影响。研究表明:快速外热式热解工艺可以有效地避免常规热解过程中出现的原料夹生问题,缩短从加料到开始热解的时间,减少温度上升期间焦油的产生;由于热解温度高,速度快,大分子芳香族化合物发生二次热解,支链断裂生成小分子的烷、氢等物质,提高了热解气的产率和热值;焦油中CmHn等较大分子通过热解和重整的方式变成生物质气,降低了热解产物中焦油含量;热解过程中,由于生物质炭中的芳香族化合物分解成小分子的烷烃、烯烃等进入生物质燃气中,剩余的主要是固定碳,所以生物质炭的产率较低,其它物相与灰烬的相同。     

焙烧温度对球状Ni-Al纳米催化剂结构及生物质催化热解的影响研究

采用水热法制备三维Ni-Al纳米结构催化剂,并利用多种表征手段和稻壳催化热解实验研究焙烧温度（500~800 ℃）对催化剂的整体结构及催化性能的影响。结果表明：催化剂为球状结构,活性位点分布均匀,焙烧温度对材料结构有显著影响,800 ℃焙烧条件下球状结构有向内塌陷的趋势。相较于无催化条件下的稻壳热解产物,催化热解后焦油产率明显减小,产气量大幅提高。500 ℃焙烧制备的Ni-Al催化剂作用条件下,稻壳热解气体产物中H₂/CO最大可达2.66,600 ℃焙烧条件下可获得最大合成气产量737 mL/g,而700 ℃焙烧条件下可获得最低的焦油产率（13.5%）。材料表征发现,反应后的催化剂仍具有稳定的球状结构与活化性能。     

Two-step steam pyrolysis of biomass for hydrogen production

In this study, different char based catalysts were evaluated in order to increase hydrogen production from the steam pyrolysis of olive pomace in two stage fixed bed reactor system. Biomass char, nickel loaded biomass char, coal char and nickel or iron loaded coal chars were used as catalyst. Acid washed biomass char was also tested to investigate the effect of inorganics in char on catalytic activity for hydrogen production. Catalysts were characterized by using Brunauer–Emmet–Teller (BET) method, X-ray diffraction (XRD) analyzer, X-ray fluorescence (XRF) and thermogravimetric analyzer (TGA). The results showed that the steam in absence of catalyst had no influence on hydrogen production. Increase in catalytic bed temperature (from 500 °C to 700 °C) enhanced hydrogen production in presence of Ni-impregnated and non-impregnated biomass char. Inherent inorganic content of char had great effect on hydrogen production. Ni based biomass char exhibited the highest catalytic activity in terms of hydrogen production. Besides, Ni and Fe based coal char had catalytic activity on H₂ production. On the other hand, the results showed that biomass char was not thermally stable under steam pyrolysis conditions. Weight loss of catalyst during steam pyrolysis could be attributed to steam gasification of biomass char itself. In contrast, properties of coal char based catalysts after steam pyrolysis process remained nearly unchanged, leading to better thermal stability than biomass char.     

Inhibition of steam gasification of biomass char by hydrogen and tar

The influence of hydrogen and tar on the reaction rate of woody biomass char in steam gasification was investigated by varying the concentrations in a rapid-heating thermobalance reactor. It was observed that the steam gasification of biomass char can be separated into two periods. Compared with the first period, in the second period (in which the relative mass of remaining char is smaller than 0.4) the gasification rate is increased. These effects are probably due to inherent potassium catalyst. Higher hydrogen partial pressure greatly inhibits the gasification of biomass char in the first and second periods. By calculating the first-order rate constants of char gasification in the first and second periods, we found that the hydrogen inhibition on biomass char gasification is caused by the reverse oxygen exchange reaction in the first period. In the second period, dissociative hydrogen adsorption on the char is the major inhibition reaction. The influence of levoglucosan, a major tar component derived from cellulose, was also examined. We found that not only hydrogen but also vapor-phase levoglucosan and its pyrolysates inhibited the steam gasification of woody biomass char. By mixing levoglucosan with woody biomass sample, the pyrolysis of char proceeds slightly more rapidly than with woody biomass alone, and gas evolution rates of H₂ and CO₂ are larger in steam gasification.     

催化剂粒径与质量对生物质热解焦油催化裂化反应的影响

针对催化裂化条件对生物质热解焦油处理的影响,以秸秆热解产生的焦油为原料,在固定床焦油催化裂化反应试验台上研究了催化剂作用下焦油催化裂化的过程,并对催化剂粒径和质量等参数对焦油转化效果和催化裂化产物的影响进行了分析．结果表明：减小催化剂的粒径或者增加催化剂质量能促进燃气中高热值大分子气体转化为低热值的小分子轻质气体,从而有效促进焦油裂化,提高燃气产率,降低燃气热值．     

Synergistic effects during co-pyrolysis of biomass and plastic: Gas,tar, soot,char products and thermogravimetric study

Synergistic effects of biomass and plastic co-pyrolysis on gas, tar, soot and char production and pyrolysis kinetics were studied using a fixed-bed reactor and a thermogravimetric analyzer, respectively. These pyrolysis products' yields and compositions were measured during the individual pyrolysis of biomass and plastic at 800–1100 °C, and synergistic effects were explored under non-sooty (900 °C) and sooty (1100 °C) conditions. Results shows that the soot starts to form from tar at 900–1000 °C for both biomass and plastic and that the soot from plastic pyrolysis is of greater yield and size than the biomass pyrolysis. Under non-sooty conditions, the synergistic effect of co-pyrolysis results in higher char yields but lower tar yields, while under sooty conditions co-pyrolysis inhibits the gas and soot formation, resulting in higher tar yields and different soot morphologies. The synergistic effect observed by the thermogravimetric analysis agrees with that in a fixed-bed reactor.     

Degradation of rubber waste into hydrogen enriched syngas via microwave-induced catalytic pyrolysis

Microwave-induced catalytic pyrolysis of end-of-life tires was conducted for the purpose of producing hydrogen-enriched syngas. Tire derived char (TDC) was employed as the catalyst due to its superiorities of excellent microwave-absorbing ability, remarkable catalytic effect, and cost-effectiveness. The effects of the carbon structure, microwave power, and tire-to-catalysts ratio on the hydrogen yield and conversion rate were investigated. TDC had two functions in promoting the production of hydrogen in microwave-induced pyrolysis (MP). One was facilitating the degradation of tar into gas, and the other was initiating the catalytic reforming of light hydrocarbons into hydrogen. The highest hydrogen yield (27.81 mmol/g) and conversion rate (85.57%) were obtained under optimal experimental conditions. The as-generated TDC in MP could be reused as a catalyst for MP, thus improving the economics of this method significantly. This research provides an efficient and economical strategy for the microwave-induced pyrolysis of end-of-life tires to produce hydrogen-rich syngas.     

Exergy analysis of biomass staged-gasification for hydrogen-rich syngas

Using Aspen Plus simulations, exergy analyses of hydrogen-rich syngas production via biomass staged-gasification are carried out for three configurations, namely, staged-gasification with pyrolysis gas combustion and char gasification (C-1), staged-gasification with pyrolysis gas reforming and char gasification (C-2), and staged-gasification with pyrolysis gas reforming and char combustion (C-3). The results show that, for the gasification and reforming processes, the exergy loss of pyrolysis gas with tar reforming is less than that of char gasification. As for the system, it is conducive to generating hydrogen by making full use of the hydrogen element (H) in biomass instead of the H in water. The benefits of C-1 are that it removes tar and produces higher yield and concentration of hydrogen. However, C-2 is capable of obtaining higher exergy efficiency and lower exergy loss per mole of H₂ production. C-3 theoretically has greater process performances, but it has disadvantages in tar conversion in practical applications. The appropriate gasification temperature (T_G) are in the range of 700–750 °C and the appropriate mass ratio of steam to biomass (S/B) are in the range of 0.6–0.8 for C-1 and C-3; the corresponding parameters for C-2 are in the ranges of 650–700 °C and 0.7–0.8, respectively.     

One-step synthesis of biochar-supported potassium-iron catalyst for catalytic cracking of biomass pyrolysis tar

In this work, K–Fe bimetallic catalyst supported on porous biomass char was synthesized via a one-step synthesis method by pyrolysis of biomass (peanut shells) after impregnation of a small amount of potassium ferrate (PSC–K₂FeO₄), and was evaluated for the cracking of biomass pyrolysis tar. Control experiments using the pure char (PSC) and char-supported catalysts after impregnation of KOH (PSC–KOH) and FeCl₃ (PSC–FeCl₃) were also performed for comparison. The as-prepared PSC-K₂FeO₄ possessed a porous structure with the dispersion of particles/clusters of Fe metal, K₂CO₃ and KFeO₂ on the char support. Tar cracking experiments showed that the PSC-K₂FeO₄ exhibited excellent catalytic activity on the cracking of biomass pyrolysis tar in the temperature range of 600–800 °C, and the obtained tar conversion efficiencies were obviously higher than that in the control experiments, particularly at relatively lower temperatures (600 and 700 °C). The yields of combustible gas compounds including CO, H₂ and CH₄ increased significantly using PSC-K₂FeO₄ as the catalyst due to the enhanced tar cracking and reforming reactions. The porous structure and the active crystal structures of the spent catalyst were well retained, indicating the potential for efficient and long-term utilization of the catalyst in tar cracking. PSC-K₂FeO₄ exhibited excellent reusability during the five times reuse under the same conditions without regeneration, which showed almost no obvious decrease in the tar conversion efficiency and gas yields.     

Reduction of primary tar vapor from biomass by hot char particles in fixed bed gasification

This study investigated the reduction of primary tar vapor from biomass pyrolysis over a bed of hot char particles, focusing on the effect of different operating conditions and char properties. The char samples were prepared from wood, paddy straw, palm kernel shell, and activated carbon. The primary tar was produced from fir wood by pyrolysis at 500 °C and passed through a reactor filled with char particles with different lengths and temperatures.The tar cracking reactions became active above 700 °C, and the presence of hot char particles promoted more tar reduction compared with thermal cracking alone. The mass yield of the primary tar was reduced from 24.8% by pyrolysis to 13.7% by thermal cracking at 800 °C, and further to 7.7% by hot char particles in a reactor volume of 1.48 cm³/g_wood. In terms of carbon yield, these values correspond to 32.1%, 19.9% and 11.8%, respectively. The tar with smaller molecular weights was quickly decomposed to gases, whereas the heavy tar was resistant to cracking, even when the reactor volume was increased to 6.90 cm³/g_wood. The tar cracking behaviors were similar for four char types despite differences in microscopic surface areas, pore-size distributions, and inorganic contents. The results suggest that creating a tar-cracking zone using char particles situated between the pyrolysis and gasification zones could be helpful in converting the primary tar vapor in a downdraft fixed-bed gasifier, but the degree of conversion is not high enough to eliminate tar issues completely.     

Novel hydrogen‐rich gas production by steam gasification of biomass in a research‐scale rotary tubular helical coil gasifier

The concept of biomass steam gasification offers platform for production (i) of hydrogen, (ii) hydrocarbons and (iii) value added chemicals. Majority of these developments are either in nascent or in pilot/demonstration stage. In this context, there exists potential for hydrogen production via biomass steam gasification. Gaseous products of biomass steam gasification consist of large percentage of CO, CH₄ and other hydrocarbons, which can be converted to hydrogen through water‐gas‐shift reaction, steam reforming and cracking respectively. Although there are many previous research works showing the potential of production of hydrogen from biomass in a two stage process, challenges remain in extended biomass and char gasification so as to reduce the amount of carbon in the residual char as well as improve conversion of heavy hydrocarbon condensates to hydrogen rich gas. In the current work, the characteristics of biomass steam gasification in an in‐house designed rotary tubular helical coil reactor at temperatures less than 850 °C, in the presence of superheated steam, were presented. The objectives were to obtain high carbon conversion in the primary biomass steam gasification step (upstream) and high product gas yield and hydrogen yield in the secondary fixed bed catalytic step (downstream). The influence of temperature, steam‐to‐biomass ratio and residence time on product gas yield in the rotary tubular helical coil gasifier was studied in detail using one of the abundantly available biomass sources in India‐rice husk. Further, enhancement of product gas yield and hydrogen yield in a fixed bed catalytic converter was studied and optimized. In the integrated pathway, a maximum gas yield of 1.92 Nm³/kg moisture‐free biomass was obtained at a carbon conversion efficiency of 92%. The maximum hydrogen purity achieved under steady state conditions was 53% by volume with a hydrogen yield of 91.5 g/kg of moisture‐free biomass. This study substantiates overall feasibility of production of high value hydrogen from locally available biomass by superheated steam gasification followed by catalytic conversion. Copyright © 2016 John Wiley & Sons, Ltd.