Sn-modified Pt/SAPO-11 catalysts for selective hydroisomerization of n-paraffins

The hydroconversion of n-paraffins is a key reaction in hydrodewaxing of lubricating base oil. In this paper, we investigate the performance of Pt/SAPO-11 catalysts for isomerization of n-paraffins by the model compound of n-dodecane. Under this experimental condition, yields of feed isomers as well as cracking products are a function of the total n-dodecane conversion. Primary products are methylundecane while multi-brancheds and cracking products are formed in successive reactions. The result shows that the addition of Sn increases the selectivity for isomerization reaction. The most ideal experimental data for hydroconversion of n-dodecane is that the selectivity of isomerized products gets 90% when conversion of n-dodecane is 90% for the Sn-promoted Pt/SAPO-11 catalyst.

Diffusion of linear paraffins in nanoporous silica

The diffusion of hexane, heptane, octane, and decane in nanoporous MCM-41 silica at various temperatures is investigated by the zero-length-column method. The diffusion coefficients are derived by a complete-time-range analysis of desorption curves at different purge flow rates and temperatures. The results show that the calculated low-coverage diffusivity values decrease monotonically, and the derived Henry's law constants increase, as the carbon number of paraffins increases. The study reveals that transport is strongly influenced by intracrystalline diffusion and dominated by the sorbate-sorbent interaction. The diffusion activation energy and adsorption isosteric heat at zero loading increase monotonically with the carbon number of linear paraffins, but their ratio is essentially constant for each adsorbate compound.

Separation of n-paraffins by selective adsorption

A study has been undertaken of the vapor-phase adsorptive separation of n-alkanes from Kuwait kerosene (Kuwait National Petroleum Company, heavy kerosene) using zeolite molecular sieves. Due to the shortage of information on the adsorption of multicomponent systems in the open literature, the present investigation was initiated to study the effect of feed flowrate, temperature, and zeolite particle size on the height of mass transfer zone (MTZ) and the dynamic capacity of the adsorbent for multicomponent n-alkanes adsorption on a fixed-bed of zeolite type-5A. The optimum operating conditions for separation of the n-alkanes has been identified so that the effluent would also be of marketable quality. The effect of multicycle adsorption-desorption stages on the dynamic behaviour of zeolite using steam as a desorbing agent has been studied and compared with n-pentane and n-hexane as desorbing agents. The separation process comprised one cycle of adsorption using a fixed-bed of zeolite type-5A. The bed was fed with vaporized kerosene until saturation had been achieved whereby the n-alkanes were adsorbed and the denormalized material eluted. The process of adsorption-desorption was carried out isobarically at one atmosphere. A mathematical model has been developed to predict the breakthrough time using the method of characteristics. The results were in a reasonable agreement with the experimental values. This model has also been utilized to develop the equilibrium isotherm. Optimum operating conditions were achieved at a feed flowrate of 33.33 x 10-9 m3/s, a temperature of 643 K, and a particle size of (1.0 - 2.0) x 10-3 m. This yielded an HMTZ value and a dynamic capacity of 0.206 m and 9.6S3 x 10-2 kg n-alkanes/kg of zeolite respectively. These data will serve as a basis for design of a commercial plant. The purity of liquid-paraffin product desorbed using steam was 83.24 wt%. The dynamic capacity was noticed to decrease sharply with the cycle number, without intermediate reactivation of zeolite, while it was kept unchanged by intermediate reactivation. Normal hexane was found to be the best desorbing agent, the efficiency of which was mounted to 88.2%.

Liquid-phase adsorption of n-paraffins on type 5A molecular sieves

As a basis for the commercial separation of normal paraffins a detailed study has been made of factors affecting the adsorption of binary liquid mixtures of high molecular weight normal paraffins (C12, C16, and C20) from isooctane on type 5A molecular sieves. The literature relating to molecular sieve properties and applications, and to liquid-phase adsorption of high molecular weight normal paraffin compounds by zeolites, was reviewed. Equilibrium isotherms were determined experimentally for the normal paraffins under investigation at temperatures of 303oK, 323oK and 343oK and showed a non-linear, favourable- type of isotherm. A higher equilibrium amount was adsorbed with lower molecular weight normal paraffins. An increase in adsorption temperature resulted in a decrease in the adsorption value. Kinetics of adsorption were investigated for the three normal paraffins at different temperatures. The effective diffusivity and the rate of adsorption of each normal paraffin increased with an increase in temperature in the range 303 to 343oK. The value of activation energy was between 2 and 4 kcal/mole. The dynamic properties of the three systems were investigated over a range of operating conditions (i.e. temperature, flow rate, feed concentration, and molecular sieve size in the range 0.032 x 10-3 to 2 x 10-3m) with a packed column. The heights of adsorption zones calculated by two independent equations (one based on a constant width, constant velocity and adsorption zone and the second on a solute material balance within the adsorption zone) agreed within 3% which confirmed the validity of using the mass transfer zone concept to provide a simple design procedure for the systems under study. The dynamic capacity of type 5A sieves for n-eicosane was lower than for n-hexadecane and n-dodecane corresponding to a lower equilibrium loading capacity and lower overall mass transfer coefficient. The values of individual external, internal, theoretical and experimental overall mass transfer coefficient were determined. The internal resistance was in all cases rate-controlling. A mathematical model for the prediction of dynamic breakthrough curves was developed analytically and solved from the equilibrium isotherm and the mass transfer rate equation. The experimental breakthrough curves were tested against both the proposed model and a graphical method developed by Treybal. The model produced the best fit with mean relative percent deviations of 26, 22, and 13% for the n-dodecane, n-hexadecane, and n-eicosane systems respectively.

Caracterização de compostos aromáticos em gasolina comercial

A contaminação do ar e do meio ambiente por combustíveis derivados de petróleo tem sido objeto de crescente pesquisa no Brasil. Dentre os tipos de poluição ao meio ambiente, a poluição atmosférica é a que causa mais incômodo à população. Esta exerce efeitos sobre a saúde humana, causando desde simples irritações até câncer de pulmão. Dos poluentes mais perigosos encontrados nesses ambientes, são destaques os hidrocarbonetos e os compostos monoaromáticos como o benzeno, tolueno e xilenos (BTX), presentes nesses combustíveis, que são extremamente tóxicos à saúde humana. Para controle desses compostos orgânicos voláteis, é necessário quantificá-los e compará-los aos valores limites de tolerância legislados no Brasil. A utilização da técnica de cromatografia gasosa e da técnica de espectroscopia por infravermelho permite realizar essa tarefa de maneira relativamente simples e rápida. Portanto o objetivo deste trabalho foi apresentar a composição química de amostras de gasolina do tipo C comercializadas nos postos revendedores da Região Metropolitana do Estado do Rio de Janeiro. Foram feitas análises quantitativas dos principais grupos químicos (parafínicos, olefínicos, naftênicos e aromáticos) e etanol por Cromatografia Gasosa de Alta Resolução e da composição de benzeno, tolueno e xileno (BTX) pela técnica de absorção no infravermelho. Os resultados foram comparados com os limites dados pela especificação da ANP (Portaria n 309) para a qualidade da gasolina, com o objetivo de se verificar se estão em conformidade com este agente regulamentador. Os resultados mostraram que todos os teores encontrados de olefínicos e aromáticos foram abaixo do limite especificado. Alguns postos apresentaram os teores de benzeno acima do limite especificado, indicando um nível de ação por parte da ANP principalmente pela ação tóxica do benzeno

Estimation of catalyst activity profiles and deactivation parameters from reactor operating data with applications to naphtha reforming

Techniques are developed for estimating activity profiles in fixed bed reactors and catalyst deactivation parameters from operating reactor data. These techniques are applicable, in general, to most industrial catalytic processes. The catalytic reforming of naphthas is taken as a broad example to illustrate the estimation schemes and to signify the physical meaning of the kinetic parameters of the estimation equations. The work is described in two parts. Part I deals with the modeling of kinetic rate expressions and the derivation of the working equations for estimation. Part II concentrates on developing various estimation techniques.

Part I: The reactions used to describe naphtha reforming are dehydrogenation and dehydroisomerization of cycloparaffins; isomerization, dehydrocyclization and hydrocracking of paraffins; and the catalyst deactivation reactions, namely coking on alumina sites and sintering of platinum crystallites. The rate expressions for the above reactions are formulated, and the effects of transport limitations on the overall reaction rates are discussed in the appendices. Moreover, various types of interaction between the metallic and acidic active centers of reforming catalysts are discussed as characterizing the different types of reforming reactions.

Part II: In catalytic reactor operation, the activity distribution along the reactor determines the kinetics of the main reaction and is needed for predicting the effect of changes in the feed state and the operating conditions on the reactor output. In the case of a monofunctional catalyst and of bifunctional catalysts in limiting conditions, the cumulative activity is sufficient for predicting steady reactor output. The estimation of this cumulative activity can be carried out easily from measurements at the reactor exit. For a general bifunctional catalytic system, the detailed activity distribution is needed for describing the reactor operation, and some approximation must be made to obtain practicable estimation schemes. This is accomplished by parametrization techniques using measurements at a few points along the reactor. Such parametrization techniques are illustrated numerically with a simplified model of naphtha reforming.

To determine long term catalyst utilization and regeneration policies, it is necessary to estimate catalyst deactivation parameters from the the current operating data. For a first order deactivation model with a monofunctional catalyst or with a bifunctional catalyst in special limiting circumstances, analytical techniques are presented to transform the partial differential equations to ordinary differential equations which admit more feasible estimation schemes. Numerical examples include the catalytic oxidation of butene to butadiene and a simplified model of naphtha reforming. For a general bifunctional system or in the case of a monofunctional catalyst subject to general power law deactivation, the estimation can only be accomplished approximately. The basic feature of an appropriate estimation scheme involves approximating the activity profile by certain polynomials and then estimating the deactivation parameters from the integrated form of the deactivation equation by regression techniques. Different bifunctional systems must be treated by different estimation algorithms, which are illustrated by several cases of naphtha reforming with different feed or catalyst composition.

Estudo termodinâmico da precipitação de parafinas em petróleos brasileiros

Um dos grandes desafios enfrentados pela indústria do petróleo é reduzir o impacto causado pela cristalização indesejável de hidrocarbonetos parafínicos de elevada massa molar em tubulações e equipamentos de produção. A cristalização de parafinas em petróleo é normalmente detectada através da determinação da temperatura inicial de aparecimento de cristais (TIAC), que pode ser estimada através de modelagem termodinâmica com base na composição do petróleo. Os objetivos deste trabalho são: estudar os principais modelos termodinâmicos adotados para descrever a precipitação de parafinas; verificar a validade desses modelos para os petróleos brasileiros e determinar qual modelo é o mais adequado para esses óleos. Para tanto, três formas de cálculo da razão entre as fugacidades das fases sólida e líquida e cinco modelos para calcular os coeficientes de atividade dos componentes em cada fase são aplicados aos dados de composição de vinte e três petróleos brasileiros. Os resultados mostram que o modelo ideal de múltiplas fases sólidas e o modelo de Escobar-Remolina geram valores bastante abaixo da TIAC experimental. Para os modelos de única fase sólida ideal, de Won e de Coutinho, foi possível observar que: a) a grande maioria dos erros é negativa; b) que estes se distribuem melhor em torno de zero quando se utiliza a correlação de Coutinho para o cálculo dos valores de i; c) os valores de erro médio para os modelos de Coutinho, de Won e ideal com única fase sólida se equivalem, qualquer que seja o modelo utilizado para o cálculo de i, exceto para o caso em que todos os compostos presentes na fase líquida podem precipitar; d) os valores obtidos através do modelo de Coutinho apresentam erro sistemático em relação ao modelo ideal de única fase sólida; e) as diferentes formas de se calcular a razão entre as fugacidades da fase sólida e líquida (i) influenciam fortemente a capacidade preditiva dos modelos, o que não era esperado; f) o perfil do primeiro cristal formado nos petróleos é influenciado pelas moléculas mais pesadas presentes nos resíduos, o que mostra a necessidade de se desenvolver metodologias precisas e robustas de caracterização de resíduos; g) a inclusão de uma estimativa para a composição dos resíduos efetivamente melhorou o desempenho dos modelos em petróleos médio; h) em petróleos pesados, houve um aumento do erro de previsão da TIAC devido à pouca ou nenhuma quantidade de parafinas nos resíduos desses óleos. A necessidade de uma melhor caracterização dos resíduos de petróleos é corroborada pelo fato da TIAC calculada pelos modelos ser, via de regra, mais baixa que a TIAC experimental e pela melhora no desempenho dos modelos quando se estimou a composição dos resíduos, em petróleos médios

Catalisadores para hidroisomerização de n-hexadecano

No processo de hidrocraqueamento para a produção de lubrificantes ocorre a formação de uma corrente rica em compostos parafínicos que possuem alto ponto de fluidez, apesar dos mesmos apresentarem excelentes desempenhos em termos de estabilidade térmica e oxidativa. A transformação das n-parafinas obtidas nestas correntes em isoparafinas e compostos naftênicos, os quais possuem menores pontos de fluidez, se faz necessária a fim de enquadrar esta propriedade. Uma das rotas catalíticas mais importantes neste sentido é a hidroisodesparafinação ou HIDW (hydroisodewaxing) que consiste na conversão de n-parafinas nas respectivas isoparafinas, onde são empregados catalisadores bifuncionais zeolíticos com a ocorrência de seletividade de forma. No caso dos catalisadores industriais, se faz necessária a dispersão da fase metálica e da zeólita em uma matriz amorfa para viabilizar sua conformação e melhorar a resistência mecânica do catalisador final. Neste cenário, o objetivo deste trabalho foi preparar e analisar o desempenho de uma série de catalisadores à base de zeólita beta inseridos numa matriz de alumina, variando-se o teor de zeólita e o tipo de precursor de Pt utilizado. Os catalisadores foram avaliados na reação de hidroisomerização de um composto modelo, no caso, n-hexadecano. Os testes realizados para avaliação da atividade e seletividade foram conduzidos em um reator de fluxo contínuo em alta pressão e fase líquida em unidade de laboratório. Os catalisadores foram testados em condições operacionais que proporcionassem uma ampla faixa de conversões do n-C16. Verificou-se que as atividades dos catalisadores foram proporcionais ao teor de zeólita no catalisador, indicando que a função ácida, neste catalisador bifuncional, é a etapa limitante do processo. Quanto à natureza do precursor de Pt, o catalisador preparado com ácido cloroplatínico foi sensivelmente mais ativo que os preparados com o complexo aminplatina. No entanto, para todos os catalisadores, a distribuição de produtos em função da conversão foi similar, independente do teor de zeólita e da natureza do precursor de platina. Foi também determinado o ponto de fluidez de uma série de produtos de reação, obtendo-se valores entre 17,5 C (n-hexadecano) e - 41 C (produto com 98% de conversão). Obteve-se uma boa correlação entre o ponto de fluidez e a composição dos produtos, considerando-se a presença de isômeros mono, di e tri-substituídos e compostos de menor peso molecular que C16

莱州湾区域表层沉积物中多氯化萘、多溴联苯醚和氯化石蜡的研究

本研究建立了沉积物中氯化石蜡（CPs）的分析方法，对莱州湾和该区域主要河流的表层沉积物中多氯萘（PCNs），多溴联苯醚（PBDEs）和CPs进行了分析，获得了他们在研究区域的含量水平、空间分布和单体分布模式，并初步探讨了它们在环境中的来源和迁移规律，估算了这三类污染物在莱州湾表层沉积物中的储量，初步评估了莱州湾沿岸的工业排放与人类活动对海洋生态环境的影响。 莱州湾海洋和河流沉积物PCNs的含量分别为65-470 pg/g dw，52-5100 pg/g dw，平均值分别为260 pg/g dw，1100 pg/g dw。莱州湾沉积物中PCNs的含量较低，与发达国家的背景值相当，主要河流沉积物与其他地区的近海、海湾、湖泊沉积物的含量相当。该区域的PCNs主要以5-Cl和6-Cl为主，为工业来源，主要受化工行业的影响。石化工厂热过程产生的低氯组分可能也是该区域PCNs的一个重要来源。莱州湾的PCNs主要来自水体颗粒的输入，而大气沉降来源的贡献不明显。 河流沉积物ΣPBDEs（不包括BDE-209）的含量分别为0.01- 53 ng/g dw，BDE-209的含量为0.74- 280 ng/g dw，平均值分别为4.4 ng/g dw，51 ng/g dw。在组成上，BDE-209占绝对优势，比低溴代BDEs高1-2个数量级，这是由于我国市场上十溴联苯醚是最主要的溴代阻燃剂。ΣPBDEs与亚洲一些地区含量相当，比北美和欧洲一些地区要低；BDE-209含量含量高出北美和欧洲一些地区，处于较高的水平。河流沉积物中BDE-47与-99，BDE-183与-153、-154具有很好的相关性，而且这几种单体质量分数相当，说明莱州湾区域存在五溴和八溴两种工业BDE阻燃剂来源。海洋沉积物中ΣPBDEs的含量为nd- 0.66 ng/g dw，平均值为0.32 ng/g dw，处于较低水平，BDE-209的含量为0.66- 12 ng/g dw，平均值为5.1 ng/g dw，与欧美一些地区相当，主要来自水体颗粒的输入。 本研究用电子捕获低分辨质谱（ECNI-LRMS）建立了沉积物中CPs的分析方法。该方法基于ECNI质谱对SCCP的响应与其氯含量在一定范围内呈线性关系的特性，建立SCCP的总响应因子与氯含量的工作曲线，从而建立定量方法。重点改进了传统方法中由于SCCP标准品和样品中氯含量不同所造成的响应因子的差别，不再要求标准品的含氯量与样品一致，从而提高了SCCP的分析效率与方法准确性。实验发现，当SCCP的实际氯含量在51%-63%之间时，二者线性关系良好（r2>0.96）。用不同氯含量的标准参考品测试，误差为8%-43%。仪器检测限和方法检测限分别为25-400 μg/L，20 ng/g。类似地，建立了中链氯化石蜡（MCCP）的分析方法，工作曲线的实际氯含量范围为44-57%，仪器检测限40-600 μg/L，方法检测限为6 ng/g。通过对比样品与标准品的峰形特征，严格控制保留时间来辨别SCCP与MCCP，实验证明由于二者叠加导致的误差：SCCP为8%，MCCP为14%，总体来说，用该方法得到的CPs数据是可靠的。本文所使用的净化方法能实现CPs与大部分有机氯化合物的分离。 用该方法对莱州湾的沉积物的CPs进行定量，除了两个河流样品MCCP的计算含氯量低于工作曲线以外，其他样品的SCCP和MCCP的计算氯含量都在工作曲线的范围之内。河流沉积物中SCCP和MCCP的含量分别为1-1200 ng/g dw，1-3300 ng/g dw，MCCP/SCCP均值为1.2；含量分布变化较大，一些河段受到工业排放的影响，CPs浓度高出均值1-2个数量级，MCCP/SCCP值也显著高出平均值。莱州湾区域大部分河流的CPs含量与欧洲、北美和日本一些地区相当，而一些受到点源污染的河段则处于较高的水平。河流中SCCP的质量分布在不同的站位不一样，在受到点源影响的样品中，C13的质量分数明显增大，占优势地位，可能是由MCCP携带的SCCP组分所致。MCCP的质量分布在河流和海洋中没有区别，都是C14占绝对优势。从氯取代的组分来讲，所有样品都是以6-8氯取代为主。海洋沉积物中SCCP和MCCP的含量分别为3-18 ng/g dw，1-13 ng/g dw， MCCP/SCCP均值为0.68，显著低于河流沉积物；SCCP的质量分布较为一致，都是以C10和C11为主。研究发现莱州湾区域SCCP与MCCP来源相似，但迁移规律有的不同。海洋环境中的MCCP可能主要来自水体颗粒的输入，而溶解态输入也是海洋环境中SCCP的重要来源。 对这三类污染物在莱州湾表层沉积物中的储量估算得到PCNs、ΣPBDEs、BDE-209、SCCP和MCCP在莱州湾表层0-10 cm沉积物中的储量分别为0.20t，0.25t，3.95t，6.52t，4.30t。拥有10%的渤海海域面积的莱州湾ΣPBDEs和BDE-209的储量分别占渤海海区总量的18-23%，18-32%，远远超过渤海的平均值。

Autoignition of alcohols and ethers in a rapid compression machine

The autoignition characteristics of methanol, ethanol and MTBE (methyl tert-butyl ether) have been investigated in a rapid compression machine at pressures in the range 20-40 atm and temperatures within 750-1000 K. All three oxygenated fuels tested show higher autoignition temperatures than paraffins, a trend consistent with the high octane number of these fuels. The autoignition delay time for methanol was slightly lower than predicted values using reported reaction mechanisms. However, the experimental and measured values for the activation energy are in very good agreement around 44 kcal/mol. The measured activation energy for ethanol autoignition is in good agreement with previous shock tube results (31 kcal/mol), although ignition times predicted by the shock tube correlation are a factor of three lower than the measured values. The measured activation energy for MTBE, 41.4 kcal/mol, was significantly higher than the value previously observed in shock tubes (28.1 kcal/mol). The onset of preignition, characterized by a slow energy release prior to early ignition was observed in some instances. Possible reasons for these ocurrences are discussed. © Copyright 1993 Society of Automotive engineers, Inc.

A new route to control product selectivity in the oxidative dehydrogenation of cyclohexane and cyclohexene

The product selectivity can be controlled by adding acetic acid in feed over vanadium phosphate (VPO) in gas phase oxidative dehydrogenation (ODH), in which cyclohexane and cyclohexene are oxidized to cyclohexene and 1,3-cyclohexadiene (1,3-CHD), respectively, at almost 100% selectivity. This approach is also an efficient method to capture the very unstable intermediates in the mechanism study.