Impure Hydrogen Valorization for Chemicals
Production in a Tubular Reactor
Dissertation presented for the Doctor of Philosophy degree in
Refining, Petrochemical and Chemical Engineering.
by
Clara Sofia Rodrigues Sá Couto
Supervison: Professor Luís Miguel Madeira
Professor Clemente Pedro Nunes
Doutor Paulo Araújo
Trabalho financiado pela Fundação para a Ciência e Tecnologia e
pela CUF - Químicos Industriais no âmbito do Programa Doutoral
em Engenharia da Refinação, Petroquímica e Química
(SFRH/BDE/51794/2012)
Ao concluir mais uma etapa do meu percurso académico e pessoal, gostaria de escrever umas palavras de agradecimento a todos os que me ensinaram, guiaram, apoiaram e partilharam comigo esta experiência. Tendo em conta tudo o que vivi nesta fase, as palavras que escreverei serão sempre poucas para demonstrar a minha gratidão e apreço.
Aos meus orientadores, ao Professor Luís Miguel Madeira, ao Professor Clemente Pedro Nunes e ao Doutor Paulo Araújo, em primeiro lugar, por terem acreditado em mim e por terem aceitado orientar-me nesta jornada. Obrigada por partilharem comigo os vossos conhecimentos, o vosso tempo e por me ensinarem a ser melhor profissional e a encarar as coisas de prespetivas diferentes. Obrigada pelo apoio, dedicação, paciência, empenho e por me terem sempre feito acreditar que seria possível levar este projecto até ao fim com sucesso.
À CUF – Químicos Industriais, nomeadamente ao Eng.º Mário Jorge, por ter dado a possibilidade de este doutoramento fosse concretizado. Uma ideia diferente, com desafios novos e uma instalação por construir requer investimento e empenho, em algo que apenas na teoria se tem a certeza que funciona. Agradeço a confiança da CUF e principalmente, o empenho do Doutor Paulo Araújo, por me ajudar a levar este doutoramento a bom porto.
À Fundação para a Ciência e Tecnologia – FCT, pelo apoio financeiro com uma bolsa de doutoramento em meio empresarial, ao abrigo do Programa Doutoral em Engenharia da Refinação, Petroquímica e Química (SFRH/BDE/51794/2012). Ao Laboratório de Engenharia de Processos, Ambiente, Biotecnologia e Energia (POCI-01-0145-FEDER-006939) – LEPABE – financiado pelo Fundo Europeu de Desenvolvimento Regional (FEDER), através do COMPETE2020 – Programa Operacional Competitividade e Internacionalização (POCI) e por fundos nacionais através da FCT I.P.
A todos os colegas da CUF, principalmente: Fernando Mendes, Hugo Pedreiras, Marco Prior, Rui Andrade e Susana Caldas, por me terem recebido tão bem e por estarem
Alejandro Ribeiro e à Dulce Silva pelo apoio, ajuda e disponibilidade.
À Professora Filipa Ribeiro, pelo apoio, por me incentivar a aceitar este desafio e por me abrir sempre as portas do Laboratório para fazer análises e para aprender como funciona o CataTest.
Aos amigos que fui guardando ao longo dos anos: Filipa Henriques, André Neves, Miguel Pinto, Rita Sousa, Inês Leal, Telmo Duarte, Diana Fernandes, Margarida Vilhena, que estiveram tão presentes nesta fase final. À Leonor Alves, Marta Silva e ao Pedro Brântuas.
À Raquel Bértolo, a pessoa que (quase) se adequa ao meu perfil melhor do que eu mesma…uma amiga sempre presente, que sempre me apoiou e com a qual tive a sorte de partilhar as mesmas experiências, apesar de distantes geograficamente.
À Família do Palacete, que quer tendo vivido nele ou não, são parte integrante: Daniel Marcos, Diogo Afonso, Joana Azevedo, João Dionísio Sousa, José Gomez, Mariana Cardoso, Rita Tavares, Sérgio Terras, Sofia Vilaça, Tiago Couchinho, pelas horas de distração, pela animação e pelos bons momentos partilhados. Um agradecimento especial ao João Martins (Escravo) e ao João Silva (Jonas) pelo apoio e ajuda, pela enorme paciência que tiveram e pelos momentos de discussões e gargalhadas no contentor / laboratório. À Joana Duarte pelo apoio constante, principalmente nesta fase final (e mais difícil) e pela companhia (quase) constante nas longas viagens entre Estarreja – Lisboa – Estarreja.
Anabela Nogueira…Sem sabermos crescemos na mesma zona, estudámos e acabámos por nos encontrar no IST. A partir daí tornámo-nos quase inseparáveis, Lisboa, Lyon, Estarreja e quem sabe o futuro? Ajudaste a tornar a decisão de vir para Estarreja muito mais fácil e estiveste sempre presente, apoiaste, chamaste à razão e acreditaste em mim, principalmente quando eu duvidei.
À Cristina Rodrigues, João Sáude, João Maria, Vitor Rodrigues, Ana Castro, Carolina Rodrigues, Afonso Rodrigues, Fernanda Pimenta, Rui Pimenta, João Pimenta e Tiago Pimenta, obrigada pela motivação e apoio.
presente, que poderei contactar contigo incondicionalmente.
Aos meus pais, Maria Alice e José Sá Couto, por Tudo. Por me terem sempre ensinado que devemos lutar por aquilo em que acreditamos, respeitando sempre o próximo. Pelos valores que sempre me incutiram, pelo apoio incondicional e por sempre me motivarem a desafiar-me a mim mesma, por sempre me terem colocado à frente de tudo e por serem sempre o meu porto de abrigo. Aquilo que sou é o reflexo do que sempre me transmitiram. As palavras nunca serão suficientes para agradecer tudo o que fizeram e fazem por mim.
Ao Nuno Amorim, pela pessoa extraordinária que és, por sempre me teres apoiado, por teres estado sempre a meu lado ao longo de todos estes anos. Nesta longa caminhada, que implicou várias deslocações, nunca puseste em causa se eu seria capaz de ultrapassar os desafios a que me propunha e estiveste sempre lá a incentivar-me. Obrigada pelas muitas lágrimas que tiveste de limpar e alguma tristeza que tiveste de afugentar, pelas muitas alegrias que partilhámos, pelos inúmeros sorrisos, por nunca duvidares, por acreditares sempre em mim.
Aniline (ANL) is an aromatic amine mainly consumed in the production of methylene diphenyl diisocyanate (MDI). MDI is in turn a key raw material in the polyurethane industry for the automotive and construction sectors. Worldwide ANL capacity was around 5.4 million tons per annum in 2011, and between 75 to 85 % was consumed for the production of MDI. There are around 30 companies producing ANL of which 8 account for 66 % of the total production. Among them is CUF-QI that owns 4% of the ANL production worldwide. ANL production is mainly done through nitrobenzene (NB) hydrogenation. This reaction can be carried out either in liquid or in vapor-phase. For that reason, several technological processes were developed to perform this industrial production, which basically differ on the type of reactor; however, the most common are the fixed-bed or the fluidized-bed for vapor-phase and the slurry reactor for liquid phase.
Catalyst development is also a key aspect for the NB hydrogenation and several papers are available for both phases. In the NB hydrogenation into ANL, there is the formation of several secondary products that leads to a lower productivity. Trying to understand the formation of those compounds is very important and some information is available in the open literature, although consensus has not yet been reached; moreover, the species reported to be formed are different from work to work.
Catalysts to be later tested in a fixed-bed reactor were acquired and a multiphase continuous stirred tank reactor (CSTR) operating in batch mode was firstly used to test them. The first step was to study the mechanism of ANL and secondary products formation as well as analysing the effect of the main operating conditions in this multiphase reaction system. It was found that there are more by-products than those referred in the literature and both NB consumption and selectivity are extremely dependent on temperature. The first catalyst used, designated as I.1 (1 wt.% Pd/Al2O3) proved to be selective to ANL formation. Besides, a new reaction network was proposed for ANL and secondary products formation, where benzene (Bz) was included, since it was not considered in a quantitative manner by any other previous authors in the literature.
reaction, was also analized over catalyst I.1. It was found that using p-toluidine (p-tol) as solvent prevents the formation of secondary products when compared with ANL. The presence of secondary products (namely Bz and water) in the feed mixture leads to a decrease in the NB conversion.
Afterwards, the four commercial catalysts supplied, three Pd-based and one Ni-based, were compared and it was found that they present different performances, particularly different activities in what concerns the NB conversion and ANL selectivity. Chemical and physical characterization of the catalysts used, namely catalyst I.1, catalyst I.2, catalyst I.3 and catalyst II.1, was crucial to better understand their quite distinct performances. Based on those results one of the catalysts was chosen, the one that presented the highest NB consumption rate with a low secondary products formation, catalyst I.2 (0.3 wt.% Pd/Al2O3).
One of the main objectives of this thesis was the design, construction and testing of a laboratorial unit comprising a tubular reactor for the hydrogenation of NB into ANL. The unit was designed and constructed and some preliminary tests were carried out to ensure its proper functioning, and to evaluate the adequate temperature control and the pressure drop in the catalytic bed.
Using the catalyst chosen before, several catalytic tests were performed in the laboratorial trickle-bed tubular reactor. A parametric study was carried out to analyse the effect of the operating conditions in the catalyst performance, namely on NB conversion and selectivity towards ANL and secondary products. It was found that catalyst age is extremely important as it changes the selectivity to the products formed along time-on-stream, although NB conversion remains stable. In what concerns the influence of the operating conditions, it was found that temperature and pressure are important and critical parameters.
Then, it was decided to focus on some issues that are of paramount importance from the perspective of industrial process implementation. In particular, it was decided to evaluate the influence of the solvent and also to test if the catalyst was still active at mild conditions of pressure and temperature. Cyclohexane (CH) seemed to be a good solvent, however it promotes the formation of heavy secondary products. Relatively to the operation under mild conditions, the Pd-based catalyst showed to be active but on the
were analysed to determine their influence on ANL selectivity and on secondary products formation. Neither H2O nor CHA seem to have a significant influence on NB conversion, although selectivity to ANL decreases.
To verify if it is possible to valorise the industrial stream of impure H2, some analysis to that stream were carried out, in order to define the methodology to be used when studying the effect of contaminants in the reaction. It was shown that the contaminants that are present in higher quantities are ammonia (NH3), carbon dioxide (CO2) as well as some organic compounds, mainly benzene (Bz). Among all, it was decided to use NH3 as contaminant (because it is present in larger quantities) and it was possible to conclude that NH3 concentrations up to 1 wt.% do not have a negative influence in NB hydrogenation.
The ultimate goal was to test the industrial H2 stream, available at low pressures and with the contaminants referred above. No major effect was detected in NB conversion at any of the temperatures used (120 ºC and 150 ºC), nor in selectivity towards ANL. It was also seen that heavy products formation is low.
Summarizing, it was proved that the industrial H2 stream available at CUF-QI can actually be valorized to produce ANL in the range of operating conditions studied. Nevertheless, some attention must be given to the composition of this stream, mainly to the organic compounds eventually present, which can have some impact in the results obtained namely in the composition of the outlet stream. More tests should be performed to validate these conclusions and further explore this topic; however, it was demonstrated that the trickle-bed tubular reactor can be used to produce ANL, by using an active Pd supported catalyst, with good selectivity and high levels of NB conversion.
A anilina (ANL) é uma amina aromática consumida principalmente na produção de metileno difenil diisocianato (MDI). O MDI é uma das principais matérias-primas da indústria dos poliuretanos para os sectores automóvel e da construção. Em 2011, a capacidade mundial de produção de ANL rondava os 5,4 milhões de toneladas por ano, sendo que entre 75 % a 85 % era consumida na produção de MDI. Existem cerca de 30 empresas a produzir ANL, das quais 8 totalizam 66 % da produção global. Entre elas encontra-se a CUF-QI que detém 4 % da cota de produção mundial de ANL. A produção de ANL é essencialmente realizada através da hidrogenação de nitrobenzeno (NB), a qual pode ocorrer quer em fase líquida, quer em fase gasosa. Assim, foram desenvolvidas diversas tecnologias para esta reação, essencialmente relacionadas com o tipo de reator mais adequado. Não obstante, os tipos de reatores mais comuns em fase gasosa são os de leito-fixo ou de leito fluidizado, enquanto em fase líquida são os reatores agitados de “lamas”.
O desenvolvimento de catalisadores é também um aspeto fundamental na reação de hidrogenação de NB, sendo que existem inúmeros documentos disponíveis onde esta temática é estudada, quer em fase gasosa, quer em fase líquida. Durante a hidrogenação de NB a ANL existe a formação de produtos secundários, que conduzem a uma menor produtividade. Compreender a formação desses compostos secundários é extremamente importante e verifica-se que existe alguma literatura disponível, apesar de não existir consenso sobre o esquema reacional. Além disso, também se constata que as espécies identificadas diferem de estudo para estudo.
No âmbito desta tese, foram adquiridos alguns catalisadores comerciais para hidrogenação de NB em leito-fixo, tendo-se recorrido numa primeira fase a um reator agitado (CSTR), a operar em modo descontínuo, para os testar. O primeiro passo consistiu no estudo do mecanismo de formação de ANL e produtos secundários, assim como na análise do efeito das principais condições operatórias neste sistema reacional multifásico. Constatou-se que existem mais compostos secundários do que os que são referidos na literatura e que quer a velocidade de consumo de NB, quer a formação de
primeiramente testado, designado I.1 (1 % m/m Pd/Al2O3) demonstrou ser seletivo relativamente à formação de ANL. Adicionalmente, foi proposto um novo esquema reacional para a formação de ANL e dos compostos secundários, onde o benzeno (Bz) foi incluído, uma vez que a sua formação não foi avaliada quantitativamente, por nenhum autor na literatura existente.
O efeito dos produtos de reação e o uso de diferentes solventes, nesta reação, foram também avaliados, usando o catalisador I.1. Verificou-se que o uso de p-toluidina (p-tol), como solvente, evita a formação de produtos secundários quando comparado com o solvente ANL. A presença de produtos secundários, na corrente de alimentação (nomeadamente Bz e água), conduz a uma menor conversão de NB.
Posteriormente, os quatro catalisadores adquiridos, três à base de Pd e um à base de Ni, foram comparados, tendo-se concluído que apresentam diferentes desempenhos, nomeadamente diferentes atividades no que se refere à conversão de NB e seletividade à ANL. A caracterização química e física dos catalisadores utilizados, catalisador I.1, catalisador I.2, catalisador I.3 e catalisador II.1, foi crucial no entendimento dos seus desempenhos tão distintos. Com base nestes resultados foi escolhido um dos catalisadores, tendo-se optado pelo catalisador que apresentou maior velocidade de consumo de NB e baixa formação de produtos secundários, ou seja, o catalisador I.2 (0.3 % m/m Pd/Al2O3).
Um dos principais objetivos desta tese consistiu no projecto, construção e validação de uma unidade laboratorial compreendendo um reator tubular para hidrogenação de NB a ANL. A unidade foi concebida e construída e alguns testes preliminares foram efetuados com o intuito de assegurar-se o bom funcionamento da instalação e avaliar-se o controlo de temperatura, assim como a queda de pressão no leito catalítico.
Usando o catalisador escolhido anteriormente, catalisador I.2, foram realizados diversos testes catalíticos no reactor tubular. Foi efetuado um estudo paramétrico, de forma a analisar o efeito das condições operatórias no desempenho do catalisador, nomeadamente, na conversão de NB e seletividade à ANL e aos produtos secundários. Constatou-se que o tempo de uso do catalisador (idade) é extremamente importante, uma vez que ao longo do tempo há alterações na seletividade aos produtos secundários, apesar da conversão de NB se manter estável. Relativamente à influência das condições
Posteriormente, o foco do estudo foi direcionado para aspectos de elevada importância do ponto de vista da implementação do processo a nível industrial. Mais especificamente, decidiu-se avaliar a influência do solvente e também testar se o catalisador permanece ativo em condições mais suaves de pressão e temperatura. O ciclo-hexano (CH) demonstrou ser um bom solvente, contudo conduz a uma maior formação de produtos secundários. Quanto às condições de operação mais suaves, o catalisador de Pd demonstrou que é ativo, mas por outro lado conduz à formação de diciclo-hexilamina (DICHA). Além destes ensaios, também se estudou a efeito de alguns produtos de reação, nomeadamente água (H2O) e ciclo-hexilamina (CHA), com o objetivo de determinar a sua influência quer na seletividade à ANL, quer na formação de produtos secundários. Nenhum dos compostos, H2O ou CHA, parece exercer qualquer tipo de influência na conversão de NB apesar de se registar uma diminuição na seletividade à ANL.
Para verificar a possibilidade de valorizar a corrente industrial de H2 impuro, realizaram-se análises a essa mesma corrente, por forma a definir qual a metodologia a seguir no estudo do efeito dos contaminantes da corrente gasosa. Verificou-se que os principais contaminantes são o amoníaco (NH3), o dióxido de carbono (CO2) assim como alguns compostos orgânicos, nomeadamente o Bz. Optou-se por estudar o efeito do NH3 (uma vez que está presente em quantidades elevadas) e concluiu-se que com concentrações de NH3 até 1 % m/m não existe uma influência negativa na reação de hidrogenação de NB.
O objetivo central desta tese consistiu no teste de uma corrente industrial de H2, que está disponível a baixa pressão e com os contaminantes referidos anteriormente. Não foi detetado qualquer tipo de influência na conversão de NB, independentemente da temperatura utilizada (120 ºC ou 150 ºC), nem na seletividade à ANL. Além disso, também se observou que a formação de produtos secundários pesados é baixa.
Concluindo, foi demonstrado que a corrente industrial de H2 existente na CUF-QI pode efetivamente ser valorizada na produção de ANL, na gama de condições operatórias estudadas. Não obstante, é necessário ter especial cuidado com a composição desta corrente, nomeadamente, ter atenção aos compostos orgânicos presentes, que poderão ter impacto nos resultados obtidos, principalmente na composição da corrente de saída. Para
o reator tubular de leito fixo pode ser utilizado na produção de ANL, usando um catalisador de Pd suportado ativo, obtendo-se boas seletividades e elevados níveis de conversão de NB.
List of Figures ... xix
List of Tables ... xxvii
Nomenclature ... xxix
Part I - Introduction and State of Art Chapter 1 - Introduction ... 3
Chapter 2 - State of the Art ... 7
2.1 Aniline industrial production and applications ... 7
2.2 Technological aspects of the Industrial Production of Aniline ... 13
2.2.1 Aniline ... 13
2.2.2 Reaction mechanisms for aniline production and by-products formed ... 14
2.2.3 Hydrogenation in Gas-phase ... 28 2.2.4 Hydrogenation in Liquid-phase ... 30 2.2.4.1 DuPont Process ... 30 2.4.2.2 Huntsman Process ... 31 2.4.2.3 Mitsui Process ... 33 2.4.2.4 Chematur Process ... 33 2.4.2.5 CUF-QI Process ... 34 2.4.2.6 Bechamp Process ... 35
2.2.5 Catalysts for Aniline production... 37
2.2.5.1 Catalysts for vapor-phase processes ... 40
2.2.5.2 Catalysts for liquid-phase processes ... 42
2.2.6 Types of reactors ... 44
Chapter 3 - Hydrogenation of Nitrobenzene over a Pd/Al2O3 Catalyst –
Mechanism and Effect of the Main Operating Conditions. ... 63
Abstract ... 63
3.1 Introduction ... 64
3.2 Material and Methods ... 67
3.3 Results and Discussion ... 69
3.3.1 Influence of initial nitrobenzene concentration ... 69
3.3.2 Influence of Pressure ... 75
3.3.3 Influence of Temperature... 77
3.4 Conclusions ... 82
References ... 83
Chapter 4 – Study of Effects of the Solvent and Reaction Products in the Catalytic Hydrogenation of Nitrobenzene. ... 85
Abstract ... 85
4.1 Introduction ... 86
4.2 Material and Methods ... 90
4.3 Results and Discussion ... 93
4.3.1 Influence of the solvent ... 94
4.3.2 Influence of the presence of reaction products in the feed ... 97
4.3.2.1 Effect of H2O ... 98 4.3.2.2 Effect of Benzene ... 101 4.3.2.3 CHA hydrogenation ... 102 4.3.2.4 ANL hydrogenation ... 104 4.4 Conclusions ... 107 References ... 108
Chapter 5 - Commercial Catalysts Screening for Liquid Phase Nitrobenzene Hydrogenation... 111
Abstract ... 111
5.1 Introduction ... 112
5.2.2. Catalysts Characterization ... 114
5.2.3. Catalytic Reaction ... 115
5.3 Results and Discussion ... 118
5.3.1 Catalysts Characterization ... 118 5.3.2 Nitrobenzene Hydrogenation ... 122 5.3.2.1 Catalysts activity ... 124 5.3.2.2 Catalysts selectivity ... 128 5.4 Conclusions ... 134 References ... 136
Part III - Catalytic Tests in a Tubular Reactor Chapter 6 - Tubular Reactor Laboratorial Unit ... 141
6.1 - Introduction ... 141
6.2 - Unit conception... 142
6.2.1 - Unit purpose ... 143
6.2.2 - Unit description ... 143
6.2.2.1 – Liquid feed section ... 146
6.2.2.2 – Gas feed section ... 147
6.2.2.3 – Reaction section ... 148
6.2.2.4 – Separation section ... 151
6.3 – Preliminary tests... 152
6.3.1 - Test with catalyst support, H2O and H2 ... 153
6.3.2 - Test with catalyst support, ANL and H2 ... 155
References ... 157
Chapter 7 - Hydrogenation of Nitrobenzene in a Tubular Reactor: Parametric Study of the Operating Conditions Influence ... 159
Abstract ... 159
7.1 Introduction ... 160
7.3.1 Reproducibility tests ... 167
7.3.2 Influence of Total Pressure... 169
7.3.3 Influence of Temperature... 172
7.3.4 Influence of Liquid Feed Flow Rate ... 174
7.3.5 Influence of NB Concentration in the Feed ... 175
7.4 Conclusions ... 176
References ... 178
Chapter 8 - Industrial Perspective of Nitrobenzene Catalytic Hydrogenation in a Tubular Reactor – Impure H2 valorization... 181
Abstract ... 181
8.1 Introduction ... 182
8.2 Material and Methods ... 184
8.3 Results and Discussion ... 188
8.3.1 Influence of the solvent ... 189
8.3.2 Influence of H2O ... 191
8.3.3 Influence of CHA ... 193
8.3.4 Reaction at mild conditions (T and P) ... 195
8.3.5 Influence of impure H2 ... 196
8.3.5.1 Influence of NH3 ... 197
8.3.5.2 Industrial H2 ... 199
8.4 Conclusions ... 202
References ... 204
Part IV - General Conclusions and Future Work Chapter 9 - General Conclusions ... 209
Chapter 10 - Future Work ... 213
10.1 Catalysts ... 213
10.2 Tubular reactor ... 214
Appendix A – Supporting Information of Chapter 3. ... 217 Appendix B – Supporting Information of Chapter 5 ... 223 Appendix C - Resume of the operating conditions used in the catalytic tests with
the tubular reactor (Chapters 7 and 8). ... 229 Appendix D - Complementary results of the parametric study in Chapter 7... 231
Figure 2.1 - ANL market share for 2010 [2]. ... 8
Figure 2.2 - Global ANL capacity by producer in 2011, adapted from [1]. ... 9
Figure 2.3 – Network of chemical complex of Estarreja [3]. ... 11
Figure 2.4 – Main world Producers of ANL (2013) [3]. ... 12
Figure 2.5 – Schematic diagram of CUF-QI plant [3]. ... 12
Figure 2.6– Reaction network involved in nitrobenzene hydrogenation, Haber mechanism [9]. ... 15
Figure 2.7 – Reaction network of nitrobenzene hydrogenation, as proposed by Wisniak and Klein [13]. ... 16
Figure 2.8 – Scheme of components transformation on catalytic surface, proposed by Makaryan [14]. ... 16
Figure 2.6 - Reaction network of nitrobenzene hydrogenation proposed by Gelder et al. [7]. ... 17
Figure 2.10 – Proposed reaction pathway for the hydrogenation of aromatic nitro compound to aniline [15]. ... 18
Figure 2.11 - Scheme of NB catalytic hydrogenation in the presence of Pd-containing heterogeneous catalyst, [19]. ... 19
Figure 2.12 – Supplemented reaction mechanism for NB hydrogenation considering Haber’s and Gelder’s reaction mechanism, proposed by Turáková et al. [20]. ... 20
Figure 2.13 – Reaction network for the formation of ANL and secondary products proposed by Nagata [21]. ... 21
Figure 2.14 - Reaction network proposed by Narayanan et al. [23]. ... 22
Figure 2.15 – Reaction network proposed for ANL and secondary products formation by Relvas [24]. ... 23
Figure 2.16 – Reaction network proposed for secondary products formation from ANL hydrogenation by Králik et al. [25]. ... 24
Figure 2.17 – Reaction network proposed in liquid phase hydrogenation of NB by Králik et al. [24] ... 25
Figure 2.18 – Reaction network proposed for the Pd/C catalyzed hydrogenation of NB by Rubio-Marqués et al. [26] ... 26
[27]. ... 27 Figure 2.20 – Fluidized-bed ANL process in vapour-phase [1]. ... 28 Figure 2.21 – DuPont ANL Process via liquid-phase [1]. ... 31 Figure 2.22 – Huntsman ANL Process via liquid-phase [1]. ... 32 Figure 2.23 – Chematur ANL Process [1]. ... 34 Figure 2.24 – CUF-QI ANL process... 35 Figure 2.25 – Typical concentration profiles during hydrogenation of NB [4]. ... 38 Figure 2.26 – The two modes of reactants introduction in a catalytic membrane
reactor [59]. ... 46 Figure 2.27 – Catalytic wall reactor configuration [75]. ... 47 Figure 2.28 – Configuration proposed in US 2000/6040481 [43]. ... 49 Figure 2.29 – Process flow by Huntsman [76]. ... 50
Figure 3.1 – Reaction network for the formation of ANL and secondary products
as proposed by a) Nagata et al. [22]; b) Narayanan and Unnikrishnan [23]. ... 66 Figure 3.2 –Relvas [24] (*very reactive and unstable compounds)... 67 Figure 3.3– Influence of initial nitrobenzene concentration in the secondary
products formation (Bz, CHA, CHOL, CHONA, NB and DICHA) vs. time, runs
B4, B7 and B11. ... 70 Figure 3.4– Influence of initial nitrobenzene concentration in the secondary
products formation (CHENO and CHANIL) vs. time, runs B4, B7 and B11. ... 71 Figure 3.5 – Influence of initial nitrobenzene concentration in the ANL formation
a) and NB conversion b) vs. time, runs B4, B7 and B11. ... 72 Figure 3.6 – Comparison between total secondary products formation (closed
symbols) and NB consumption (open symbols) as a function of reaction time for
different initial NB concentrations; runs B4, B7 and B11. ... 73 Figure 3.7 - Influence of nitrobenzene initial concentration in the secondary
products formation for NB dimensionless concentration, runs B4, B7 and B11. ... 74 Figure 3.8 - Influence of nitrobenzene initial concentration in the secondary
products formation for NB dimensionless concentration, runs B4, B7 and B11. ... 75 Figure 3.9 - Influence of reaction pressure in the secondary products (Bz, CHA,
CHOL, CHONA, ANL, DICHA, CHENO and CHANIL) vs. time, runs B2, B3
function of reaction time; runs B2, B4 and B5. ... 77 Figure 3.11 - Influence of reaction temperature in the ANL and by-products
formation (Bz, CHA, CHOL, CHONA and DICHA) vs. reaction time, runs B4,
B5, B9 and B10. ... 78 Figure 3.12 - Influence of reaction temperature in the ANL and by-products
formation (CHENO and CHANIL) vs. reaction time, runs B4, B5, B9 and B10. ... 79 Figure 3.13 – Comparison between a) NB conversion and b) total secondary
products formation (closed symbols) and NB consumption (open symbols) as a function of reaction time for different reaction temperatures; runs B4, B5, B9 and
B10. ... 80 Figure 3.14 – Reaction network proposed for ANL and secondary products
formation including Bz (*very reactive and unstable compounds). ... 81
Figure 4.1 - Reaction network involved in nitrobenzene hydrogenation illustrating
intermediary species proposed by a) Haber [8] and b) Turáková et al. [14]. ... 87 Figure 4.2 - Reaction network involved in nitrobenzene hydrogenation illustrating
secondary products formation proposed by Relvas [18]... 88 Figure 4.3 - Reaction network involved in nitrobenzene hydrogenation illustrating
secondary products formation proposed by Sousa [21]. ... 89 Figure 4.4 – Scheme of the reactor and set-up used in the experiments. ... 91 Figure 4.5 – Evolution of a) NB and b) ANL as a function of reaction time for
different solvents - ANL and ANL + 28 wt. % P-tol (runs TB7 and TB8). ... 94 Figure 4.6 – Evolution of secondary products concentration as a function of
reaction time for different solvents - ANL and ANL + 28 wt. % P-tol (runs TB7
and TB8). ... 95 Figure 4.7 – Evolution of the concentration of a) light products and b) heavy
products, c) secondary products with ANL as solvent and d) secondary products with ANL + 28 wt.% p-tol as solvent, along reaction time for different solvents
(runs TB7 and TB8). ... 96 Figure 4.8 – Reaction network proposed for ANL and secondary products
formation including Bz (*very reactive and unstable compounds). ... 97 Figure 4.9 – Evolution of a) ANL concentration, b) secondary products
concentration, c) light products concentration, d) heavy products concentration, e) secondary products concentration distribution for ANL in the reactor feed and f) secondary products concentration distribution for ANL+ 1 wt.% H2O in the
Figure 4.11 – Evolution of a) secondary products concentration, b) light products concentration, c) heavy products concentration, along reaction time (runs TC1 and
TC5). ... 103 Figure 4.12– Evolution of a) ANL concentration, b) secondary products
concentration c) light products concentration and d) heavy products concentration,
along reaction time (runs TC1 and TC2). ... 104 Figure 4.13– Evolution of a) secondary products concentration distribution for 150
ºC and 14 barg and b) secondary products concentration distribution for 200 ºC
and 20 barg, along reaction time (runs TC1 and TC2). ... 105 Figure 4.14– Evolution of a) CHONA concentration, b) CHENO concentration
along reaction time (runs TC1 and TC2). ... 106
Figure 5.1– X-ray diffraction patterns of the fresh catalysts studied: a) catalyst I.1,
b) catalyst I.2, c) catalyst I.3 and d) catalyst II.1. ... 119 Figure 5.2 – Particle size distribution of fresh group I catalysts determined by
HRTEM... 120 Figure 5.3 – Temperature programmed reduction profiles for the fresh Pd-based
(a) catalyst I.1, b) catalyst I.2, c) catalyst I.3) and Ni-based (d) catalyst II.1)
materials studied. ... 121 Figure 5.4 – Reproducibility tests, showing NB consumption as a function of
reaction time at 150 ºC, 14 barg and 10% NB for each catalyst. ... 122 Figure 5.5 – Reproducibility tests, showing NB consumption as a function of
reaction time at 150 ºC, 14 barg and 10% NB for each catalyst. ... 123 Figure 5.6– Reaction network proposed for formation of ANL and secondary
products [10]. *very reactive and unstable compound. ... 124 Figure 5.7– Effect of reaction total pressure on NB consumption as a function of
reaction time for the different catalysts: a) P = 6 barg, b) P = 14 barg and c) P = 30
barg. ... 125 Figure 5.8- Effect of reaction temperature on NB consumption as a function of
reaction time for the different catalysts: a) T = 150 ºC, b) T = 180 ºC and c) T =
240 ºC. ... 126 Figure 5.9 – Comparison of NB consumption rate for all operating condition used
a) per gram of catalyst and b) per gram of metal. ... 127 Figure 5.10 - Light products and Heavy products concentration at Tref as a
d) 30 barg. ... 130 Figure 5.12 – Total secondary products concentration at Tref as a function of
reaction time a) P = 6 barg, b) P = 14barg and c) 30 barg. ... 131 Figure 5.13 – Light products and Heavy products concentration at Pref as a
function of reaction time at: a) and d) T = 150 ºC, b) and e) T = 180 ºC and c) and
f) 240 ºC. ... 132 Figure 5.14 – Total secondary products concentration at Pref as a function of
reaction time a) 150 ºC Tref and b) 180 ºC. ... 133 Figure 5.15 – Total secondary products concentration at Pref as function of
reaction time: 240 ºC... 134
Figure 6.1 – Tubular reactor unit P&ID... 145 Figure 6.2 – Photos of the liquid feed section. ... 147 Figure 6.3 – Photos of the gas section. ... 148 Figure 6.4 – Photos of the reaction section, with closed (left) and open (right)
views of the oven. ... 149 Figure 6.5 – Tubular reactor: a) reactor bed distribution and b) thermocouples
positions. ... 150 Figure 6.6 – Photos of the separation section. ... 151 Figure 6.7– Tubular reactor unit overview. ... 152 Figure 6.8 – Oven program for preliminary test1. ... 154 Figure 6.9 – Results obtained for: a) Reactor and oven temperatures, b) Reactor
temperatures, c) Pressure and d) Gas flow rate in test1. ... 154 Figure 6.10 – Oven program for preliminary test2. ... 155 Figure 6.11 – Results obtained for a) Reactor and oven temperatures, b) Reactor
temperatures, c) Pressure and d) Gas flow rate in test2. ... 156
Figure 7.1 – Scheme of the tubular reactor used for the catalytic tests. ... 162 Figure 7.2 – Evolution of a) NB conversion and b) Selectivity to ANL and
secondary products, as a function of reaction time for all tests of the parametric
study. ... 166 Figure 7.3 - Evolution of NB conversion as a function of reaction time for the
TR5a) and TR10a). ... 168 Figure 7.5 - Evolution of a) NB conversion and b) selectivity to ANL for different
total pressures... 169 Figure 7.6 - Evolution of a) selectivity to secondary products and b) Secondary
products selectivity distribution for different total pressures. ... 170 Figure 7.7 - Reaction network proposed for ANL and secondary products
formation including Bz (*very reactive and unstable compounds). ... 171 Figure 7.8 - Evolution of a) NB conversion and b) selectivity to ANL for different
temperatures at 14 barg. ... 172 Figure 7.9 - Evolution of a) selectivity to secondary products and b) Secondary
products selectivity distribution for different temperatures at 14 barg. ... 173 Figure 7.10 - Evolution of a) NB conversion, b) selectivity to ANL, c) selectivity
to secondary products and d) secondary products selectivity distribution, for
different feed flows rates at 150ºC and 14 barg. ... 174 Figure 7.11 - Evolution of a) NB conversion and b) selectivity to ANL for
different NB concentrations at 120 ºC and 14barg. ... 175 Figure 7.12 - Evolution of a) selectivity to secondary products and d) Secondary
products selectivity distribution, for different NB concentrations at 120 ºC and
14barg. ... 176
Figure 8.1 – Scheme of the set-up and tubular reactor used for the catalytic tests. ... 185 Figure 8.2 – Evolution of a) NB conversion, b) selectivity to ANL at 120ºC and 14
barg. ... 189 Figure 8.3 – Evolution of a) selectivity to secondary products and b) secondary
products selectivity distribution for different solvents (ANL and CH) at 120ºC and
14 barg. ... 190 Figure 8.4 – Reaction network proposed for ANL and secondary products
formation including Bz (*very reactive and unstable compounds). ... 191 Figure 8.5 - Evolution of a) NB conversion, b) selectivity to ANL, c) selectivity to
secondary products and d) secondary products selectivity distribution for different
H2O concentrations at 120ºC and 14 barg. ... 192 Figure 8.6 - Evolution of a) NB conversion, b) selectivity to ANL in the presence
of CHA c) selectivity to secondary products and d) secondary products selectivity
distribution in the presence of CHA at 120ºC and 14 barg. ... 194 Figure 8.7 - Evolution of a) NB conversion and b) selectivity to ANL for different
Figure 8.9 - Evolution of a) NB conversion, b) selectivity to ANL, c) selectivity to secondary products and d) secondary products selectivity distribution for different
NH3 concentrations at 120ºC and 14 barg. ... 198 Figure 8.10 - Comparison of a) NB conversion, b) selectivity to ANL, c)
selectivity to secondary products, at 120 º C and 150 ºC, as a function of pressure
with pure hydrogen and impure industrial hydrogen grade. ... 200 Figure 8.11 - Comparison of a) selectivity to light products, b) selectivity to heavy
products at 120 and 150 ºC and c) secondary products selectivity distribution at 120 ºC and d) Secondary products selectivity distribution at 150 ºC as a function
Table 2.1– West Europe ANL capacity by producer in 2011 [1] ... 10 Table 2.2– Main chemicals produced at CUF-QI in 2014 and their applications [3]. ... 10 Table 2.3 – ANL properties [1]... 13 Table 2.4 – Typical ANL sales specification [1]. ... 14 Table 2.5 – Main ANL Vapour-phase Processes. ... 30 Table 2.6 – Summary of ANL liquid-phase processes. ... 36 Table 2.7 – Industrial ANL applications [41]. ... 39 Table 2.8 – Experimental conditions used in the several tests of the Hunstman patent [76]. 52 Table 2.9 – Experimental results of the tests described in Table 2.7 [76]. ... 53
Table 3.1– Main catalysts studied for NB hydrogenation. ... 64 Table 3.2 - Initial conditions of the experiments performed. ... 68
Table 4.1 - Initial conditions of the experiments performed. ... 92 Table 4.2 – ANL/H2O system solubility [31] ... 98
Table 5.1– Catalysts main physical characteristics. ... 114 Table 5.2 - Initial conditions of the experiments performed. ... 117 Table 5.3 – Textural parameters for the catalysts samples studied... 122
Table 6.1 – Main instruments characteristics. ... 146 Table 6.2 – Main equipment characteristics. ... 146
Table 8.1 – ANL/H2O system solubility [27] ... 192 Table 8.2 – Composition of industrial H2. ... 197
The nomenclature used in the manuscript will vary since it depends on the different authors.
Aniline ANL / Ar-NH2
Arylhydroxylamine Ar-NHOH / PHA
Azobenzene Ar-N=N-Ar / AZB
Azoxybenzene Ar-NO=N-Ar / AZXB
Benzene Bz
Catalytic wall reactor CWR
Coke oven light oil COLO
Cyclohexane CH
Cyclohexanol CHOL
Cyclohexanone CHONA
Cyclohexylamine CHA
Cyclohexyldeneaniline CHANIL
Dicyclohexylamine DICHA / DCHA
Diphenylamine DPA
Diphenylmethane diamine MDA
Direct methanol fuel cells DMFC
Hydrazobenzene Ar-NH=NH-Ar / HB
Hydroxyapatite HAP
kilotons per annum Kta
Methylene diphenyl diisocyanate MDI
N-cyclohexylaniline CHENO
Nitrobenzene NB
Nitrosobenzene Ar-NO / Ph-NO / NSB
N-phenylcyclohexylamine NPCHA
Supercritical carbon dioxide ScCO2
Toluidine TLD / p-tol
Part I
Chapter 1 - Introduction
The catalytic hydrogenation of nitrobenzene (NB) is an important industrial reaction used in the commercial production of aniline (ANL), for subsequent use mainly in the polyurethane industry. A mechanism for the reaction was first proposed by Haber in 1898 and has been widely accepted despite never being fully delineated. This reaction can be carried out in gas or in liquid-phase, and both alternatives are widely used by world producers.
In this work, a review of the ANL industry, as well as of the technologies available for its production, will be firstly done with the purpose of contextualizing the objective of this PhD thesis. The main goal of the thesis is to valorize an industrial stream of hydrogen that is available at CUF-QI at low pressures and has some contaminants. In this way, very active catalysts must be used (e.g. consisting in supported noble metals). If the catalyst is not in powder form, the most suitable reactors are those with a fixed-bed. Consequently, a tubular reactor with a fixed-bed configuration was chosen to perform the catalytic hydrogenation of NB into ANL.
Chapter 2 is dedicated to the presentation of the ANL market, the CUF-QI position, the technological aspects of the ANL production, such as the formation of intermediary compounds and of secondary products, and the type of reactors used in this process (either for vapor as for liquid-phase). Most used and appropriated catalysts for this reaction will be also discussed and it will be carried out a description of some new reactor configurations that have been proposed.
Chapter 3 is related with the first results obtained with a commercial catalyst for the NB hydrogenation in liquid-phase. The catalyst used was a 1 wt.% Pd/Al2O3 in pellets form and it was tested in a batch reactor. The main goal is to evaluate the performance of this type of catalysts in this multiphase reaction and also to understand the mechanism behind ANL and secondary products formation. The influence of the main operating conditions is also analyzed, namely of temperature, pressure and NB concentration.
In Chapter 4 will be analyzed the effect of the solvent as well as of the presence of reaction products in the reaction mixture, for the hydrogenation of NB into ANL using the same catalyst as in Chapter 3 (1 wt.% Pd/Al2O3). Besides, direct ANL and CHA hydrogenation studies will also be presented. The main goal is to evaluate the influence of those parameters in the catalyst performance, activity and selectivity to both ANL and secondary products.
Chapter 5 shows the catalytic behavior of several commercial catalysts that were supplied by different manufacturers. In order to have a better know-how about the performance of those catalysts and select the most active one, with low formation of secondary products, catalytic tests are performed in the batch reactor unit. Operating conditions, like temperature and pressure, are varied and a catalyst screening is done with the purpose of selecting the best on for further works. Moreover, all the catalysts are characterized by different chemical and physical techniques and their relationship with the hydrogenation performance is discussed.
Chapter 6 presents the design and construction of the tubular reactor aimed at testing the possibility of producing ANL using the impure H2 stream that is available in the plant. In this section, a detailed presentation of the unit design and construction is done: unit conception, unit purpose and unit description, as well as technical and operational details. It will be also presented some preliminary tests that were performed with the objective of evaluating the temperature control and pressure drop issues in the trickle-bed reactor.
In Chapter 7, the chosen catalyst of Chapter 5 is tested in the tubular reactor that was built. The influence of several parameters is analyzed, like temperature, pressure, liquid feed flow rate and NB concentration in the feed. Catalyst performance and selectivity towards ANL and secondary products are important questions that are discussed and analysed in detail.
Chapter 8 presents the results obtained on the trickle-bed tubular reactor with the industrial H2 stream. In this section, the same catalyst sample that was tested on Chapter 7 is used to study the hydrogenation reaction; some keys factors are analyzed from an industrial perspective. The effect of the solvent, the presence of some reaction products in the liquid feed stream as well as of some contaminants present on the industrial H2 is
discussed. The feasibility of using the industrial stream, that is available at low pressures, is also investigated.
Chapter 9 presents the main conclusions that were achieved with this work in terms of commercial catalysts performance and understanding of the mechanism behind ANL and secondary products formation, using this type of catalysts. Conclusions related with the use of a tubular fixed-bed reactor in the NB hydrogenation into ANL are also presented. Finally, response is given to the main objective of this thesis: the possible valorization of an industrial H2 stream, which results from other industrial processes and is available at low pressures.
Chapter 2 - State of the Art
2.1 Aniline industrial production and applications
Aniline (ANL) is mainly consumed in the production of methylene diphenyl diisocyanate (MDI), which is a raw material for polyurethanes, that are mainly used in the automotive and construction sectors. Polyurethanes have very different formulations and can thus be used in the form of flexible or rigid-foams, elastomers, coatings, adhesives and low molecular weight additives.
Legislation for energy-efficient buildings is pushing up the use of polyurethane-based building materials as they are more insulating than the competitor products (mineral fiber and polyester). Therefore, more extensive use of MDI in building insulation will provide additional drivers for market growth. This is particularly the case of Europe where the energy usage in buildings accounts for almost half of all energy consumption [1], and so legislation is being implemented to meet EU targets for energy efficiency of new buildings. Use of insulation is estimated to reduce energy usage by 30 to 50% when retrofitted into existing buildings and by as much as 90 to 95% in new buildings, offering the possibility of significantly lower utility bills to the domestic consumer at a time of inflationary pressures and economic instability [1].
Worldwide ANL capacity reached about 5.4 million tons in 2011. Depending on the geographical location, around 75 to 85% is consumed for the production of MDI via condensation of ANL with formaldehyde to give diphenylmethane diamine (MDA) that is then reacted with phosgene. Other uses of ANL are predominantly in rubber processing chemicals, such as vulcanization accelerators, antioxidants, antiozonates, and stabilizers. Smaller uses include agrochemical intermediates and chemicals, pesticides (fungicides) and herbicides. Miscellaneous uses for ANL include cyclohexylamine (CHA) for boiler treatment, rubber chemicals, pharmaceuticals, textile chemicals, photographic developers, amino resins, explosives, and specialty fibers (Kevlar, Nomex) [1]. Azo-dyes were once a substantial consumer of ANL but now only account for a small fraction of demand. A new interesting area for ANL consumption is the preparation of fuel cell membranes as in
the direct methanol fuel cells (DMFC). Oxidative polymerization of ANL adsorbed on a perfluorosulfonic acid membrane gives a polyaniline layer which acts as a barrier towards methanol without loss of proton conductivity.
In 2010, global ANL market distribution was the one shown in Figure 2.1 [2].
Figure 2.1 - ANL market share for 2010 [2].
In China, integrated coal to ANL facilities are under construction including those of
Jilin Connell and Shanxi Tianji Coal Chemical. Raw material hydrogen will be produced
from coal gasification and the benzene (from refining of the Coke Oven Light Oil - COLO), as a by-product from coke production, since COLO production increased dramatically (in line with the growth of coke demand for the burgeoning iron and steel industry in China). Then, hydrogen will be used in ammonia manufacture, which is the raw material for nitric acid manufacture. Sulphur from coal is also used to make sulphuric acid. Nitrobenzene (NB) is produced from the nitration of benzene with a mixture of nitric and sulphuric acid and is then hydrogenated to make ANL. In this case, all the feedstocks for NB and ANL can be derived from coal, however outside China, on a global basis the majority of the feedstocks still come from natural gas and oil.
The global capacity for ANL in 2011 was estimated at 5357 kilotons per annum (kta). There are around 39 companies producing ANL of which 8 account for 66% of the production, as shown in Figure 2.2. By 2016, it is estimated that the global capacity for
MDI 75% Others, 7%
Rubbers, 11%
ANL will increase to 6647 kta, a growth between 2012 and 2016 of about 4.4% per year [1].
Figure 2.2 - Global ANL capacity by producer in 2011, adapted from [1].
In North America DuPont is the largest manufacturer with 41% of the capacity, while Rubicon has the largest single plant (420 kta) and owns 37% of the installed capacity.
In West Europe, ANL capacity in 2011 amounted to 1574 kta. Analyzing Table 2.1 it is possible to conclude that Bayer is the largest producer with 38% of the capacity.
BASF has 22%, Huntsman 19%, CUF-QI 13% and Dow 8%. CUF, 4% Other , 34% Bayer, 17% BASF, 11% DuPont, 9% Rubicon, 8% Yantai Wanhua Polyurethane, 7% Hunstman, 5% Tosoh Corporation, 5%
Table 2.1– West Europe ANL capacity by producer in 2011 [1]
Company Location Capacity (thousand tons per annum)
BASF Antwerp 342 (22%) Bayer Antwerp 165 (10%) Bayer Antwerp 185 (12%) Bayer Brunsbuettel 100 (6%) Bayer Krefeld-Uerdingen 152 (10%) Dow Bohlen 130 (8%) CUF Estarreja 200 (13%) Huntsman Wilton 300 (19%)
In China the estimation for ANL capacity was 1767 kta in 2011, spread by 19 suppliers being Yantai Wanhua the largest producer with 20% of the capacity. Japan has only 5 producers, with a total capacity of 448 kta (2011), being Tosoh Corporation the largest manufacturer with 67% of the capacity. Companies in the rest of the world are estimated to have accounted for 534 kta of capacity in 2011. The largest single supplier is
Yantai Wanhua via its Borsodchem subsidiary’s plants in Ostrava, which has a total
capacity of 190 kta [1]
CUF-QI, SA is one of the companies owned by José de Mello, SGPS group
developing its activities in the chemical industry area. CUF-QI is located at the chemical complex of Estarreja, Portugal. The chemicals produced at Estarreja are nitric acid, NB, ANL, sulphanilic acid, CHA, hydrochloric acid, among others (Table 2.2).
Table 2.2– Main chemicals produced at CUF-QI in 2014 and their applications [3].
Compound Sales Volume Application
ANL 69.5% MDI production, rubber industry, paints and pigments, special fibers
NB 7.5% ANL production, chemical and pharmaceutical industry
Liquid Chlorine 6.7% PVC production, polyurethanes, water treatment
Sodium
Hydroxide 8.5%
Chemical, textile, cellulose, food, detergents and soap industry.
Hypochlorite 3.3% Water treatment, hygiene and cleaning products,
In CUF-QI in Estarreja, the organic compounds are exclusively destined to external markets, either directly or indirectly through DOW, and a considerable amount of the inorganic compounds is also for exportation. In Figure 2.3 is presented the network of the chemical complex of Estarreja:
Figure 2.3 – Network of chemical complex of Estarreja [3].
CUF-QI is the leader in terms of sales of ANL for the “open” market in Europe,
being the 4th producer. Currently, CUF-QI is one of the main non-integrated ANL producers, with a quota of approximately 3% of the global production capacity, as illustrated in Figure 2.4.
1 The only flows represented here are those in Estarreja where CUF participates (there are other entities and flows at the site)
LEGEND: Key Suppliers Key Customers CUF Operations in Estarreja ORGANICS INORGANICS HCL H2SO4 Hydrogen Salt Chlor., NaOH HCL Other Suppliers (“Market”) Other Customers (“Market”) • Aveiro Port • SGPAMAG NOVA AP QUIMITÉCNICA • Aveiro Port • SGPAMAG Aniline Ammonia Benzene Aniline, MNB Steam Electri-city Aniline, MNB, Nitric Acid, Sulphanilic Hypochlor. Chlorine, NaOH, HCL NaOH MDI DCP Aluminium Salts Hydrogen Chlor., NaOH HCL Over-the-Fence
Inputs CUF Estarreja Outputs CUF Estarreja Other flows
Figure 2.4 – Main world Producers of ANL (2013) [3].
ANL produced at CUF-QI is mostly sold to DOW for MDI production. The process begins in the plant of nitric acid, the 1st plant. Then the nitric acid is sent to the NB plant, 2nd plant, where it reacts with benzene (Bz). The NB formed goes to the 3rd plant, where it is hydrogenated in the presence of a catalyst and ANL is formed, Figure 2.5.
Figure 2.5 – Schematic diagram of CUF-QI plant [3].
Global capacity share (%)
Integrated with MDI Non-integrated with MDI
Nitric Acid Plant NH3 Nitrobenzene Plant Benzene Nitrobenzene Nitrobenzene Aniline Plant H2 Aniline Sulphanilic Acid Plant Aniline H2SO4 Sulphanilic Acid Nitric Acid Nitric Acid
2.2 Technological aspects of the Industrial Production of Aniline
2.2.1 Aniline
Aniline (C6H7N) when freshly distilled is a colorless, oily liquid with a characteristic “fishly” amine-like odor. It is manufactured by gas and liquid phase hydrogenation of NB using base or noble metal catalysts. If exposed to air and light, gains a brown color. In industrial use, color formation can be minimized by storage and processing under an inert atmosphere. The color might be removed by distillation just prior to use in color-critical applications. It is miscible with a large number of organic solvents, and forms soluble salts in the presence of strong acids in water. The main properties of ANL are shown in Table 2.3.
Table 2.3 – ANL properties [1].
Property Value
Molar Mass (g/mol) 93.1
Boiling Point (ºC) 184
Flash Point (ºC) 70
Auto Ignition Temperature (ºC) 615
Densityliquid 20ºC (g/cm3) 1.02
Viscosity 20ºC (cP) 4.4
Solubility20ºC
ANL in water 3.6 wt %
water in ANL 5.5 wt %
ANL is slightly corrosive to some types of metal, particularly amphoteric materials such as aluminium, copper, tin, zinc, and alloys containing any of these metals. These materials should be excluded from ANL service. For normal applications, carbon steel or cast iron are satisfactory materials for ANL storage and handling. If product discoloration must be kept to a minimum, then ANL should be stored and handled in 400-series stainless steel equipment with proper nitrogen blanketing.
Typical aniline sale specifications are shown in Table 2.4. For some special applications, the concentrations of trace impurities like CHA, cyclohexanol (CHOL),
cyclohexanone (CHONA), phenol, toluidine (TLD) and dicyclohexylamine (DICHA) may be specified.
Table 2.4 – Typical ANL sales specification [1].
Color maximum (APHA) 100
Freezing point, minimumdry (ºC) -6.2
Purity, minimum 99.9%
NB content, maximum (ppm) 2
Water content, maximum 0.15 wt %
2.2.2 Reaction mechanisms for aniline production and by-products formed
Traditional method for ANL production involves multiple reactions, as it happens in processes for preparing other aromatic amines. Typically, ANL is produced through the Bz conversion into a derivative, such as NB, phenol or chlorobenzene, which is then converted to ANL [4]. In the CUF – QI, SA unit, at Estarreja, the production is realized in three different plants. In the 1st plant occurs the HNO3 formation, then in the 2nd plant, takes place the Bz nitration with nitric acid in the presence of sulphuric acid (which is the catalyst and dehydrating agent) to produce NB, equation 2.1:
𝐵𝑒𝑛𝑧𝑒𝑛𝑒 + 𝐻𝑁𝑂3 → 𝑁𝐵 + 𝐻2𝑂…….. (2.1)
In the 3th plant occurs the NB hydrogenation in the presence of a Ni catalyst, at mild conditions (equation 2.2):
𝑁𝐵 + 3𝐻2 → 𝐴𝑛𝑖𝑙𝑖𝑛𝑒 + 2𝐻2𝑂……….. (2.2)
The reaction for ANL production is conducted at temperatures between 120-200ºC and pressures between 10-20 bar, with yields higher than 99% [5]. The highly exothermic catalytic hydrogenation of NB, with a heat of reaction of about 544 kJ/mol, is carried out commercially in the presence of excess hydrogen in either the vapor or in the liquid phase [6].
Commercially, ANL production is done through NB hydrogenation, however a route involving phenol amination was previously used by Sunoco Chemical but is no longer employed.
The catalytic hydrogenation of nitrobenzene is commonly employed as a standard reference reaction for testing and comparing the activity of hydrogenation catalysts for a range of applications, because its transformation is extremely easy and is carried out under relatively mild conditions [7, 8].
Although there is a large volume of literature references available studying and citing this reaction, there is not much information about the reaction mechanism. The first explicative mechanism for ANL formation through NB hydrogenation was proposed by Haber, in 1898 [9], and is widely accepted. The first step is a hydrogenolysis of N-O bond giving a nitrosobenzene (NSB), followed by the formation of arylhydroxylamine (PHA) – Figure 2.6.
Figure 2.6–Reaction network involved in nitrobenzene hydrogenation, Haber mechanism [9].
However, this mechanism does not fully explain all the experimental results, although a number of studies had reported the identification of the suggested reaction intermediates during hydrogenation [10 – 12]. Consequently, more studies were done, and another mechanism was proposed by Wisniak and Klein [13] that is slightly more complicated than the Haber’s mechanism. They also consider that probably the real mechanism is even more complex and should consider the phenomena at the surface of the catalyst (Figure 2.7).
Ar - NO2 nitro / NB Ar - NO nitroso / NSB Ar - NHOH arylhydroxylamine / PHA Ar - NH2 ANL Ar - NO = N - Ar Ar - NHOH Ar - N = N - Ar Ar - NH = NH - Ar hydrazo / HZB azo / AZB azoxy / AZXB Direct route Condensation route
Figure 2.7 –Reaction network of nitrobenzene hydrogenation, as proposed by Wisniak and Klein [13].
Beyond that, it was concluded that hydrogenation of nitro compounds and disproportionation proceed on different sections of catalytic surface and so, a scheme for the process was suggested, as shown in Figure 2.8.
Figure 2.8 – Scheme of components transformation on catalytic surface, proposed by Makaryan
[14].
In 2005, Gelder et al. [7] suggested that the number of steps involved in ANL formation was higher and substantially different from those previously reported. Figure 2.9 shows the mechanism proposed by these authors, using a Pd on carbon catalyst. Analyzing the results obtained, they concluded that NSB is not an intermediate in aniline formation. They also concluded that the new understanding of the mechanism had
NO2 NH 2 NB NO NSB N O N N N N H N H AZXB AZB HZB PHA NHOH ANL k4 k1 k1' k5 k5' k3' k3 k2 k6 k8 k 7
centre I centre II centre I
ArNO2 ArNHOH ArNH2 ArNO M H H M N H H Ar O H + -N Ar O H + - M H H ArNHOH
implications for both catalyst and reactor design and that to obtain a high activity and selectivity it is essential that the hydrogen flux at the surface is maintained at a constant level, with good access to the reaction site and no diffusion limitations [7].
Figure 2.9 - Reaction network of nitrobenzene hydrogenation proposed by Gelder et al. [7].
Summarizing, when NB is hydrogenated to ANL, the reaction mechanism is complex and there are some common intermediates, not depending on the mechanism proposed, such as NSB, azoxybenzene (AZXB), azobenzene (AZB), PHA and hydrazobenzene (HZB).
Corma et al. [15] reported that Au on TiO2 or FeO3 catalyzes the selective reduction of a nitro group without the need to add metal salts and thus acts as a highly selective and environmentally friendly catalyst. Some experiments were carried out over Au/TiO2 catalyst and it was verified that under the reaction conditions the NSB and hydroxylamine compounds formed react before desorbing. That explanation was consistent with the fact that the NSB and PHA derivatives were not detected in the reaction media. Their proposed mechanism is shown in Figure 2.10.
Ph - NO2 Ph - NOH (a) Ph - NO + Ph - NOH (a) Ph - N(OH)H Ph - N(O) = N - Ph Ph - N = N - Ph Ph - NH - NH - Ph Ph - NH2 Ph - NH NB NSB PHA ANL HZB AZB AZXB
Figure 2.10 –Proposed reaction pathway for the hydrogenation of aromatic nitro compound to aniline [15].
Thus, on Au/TiO2 catalysts, PHA is formed as both a primary product (from NB) and a secondary product (via NSB) at the active sites. The gradual accumulation of this intermediate on the catalyst surface showed that the transformation of PHA into aniline is the rate-determining step of the whole process. Makosch et al. [16] also evaluated the influence of the support in the reaction route of NB hydrogenation, using Au/TiO2 and Au/CeO2 catalysts. Both catalysts rapidly convert NSB but while over Au/TiO2 hydrogenation proceeds through the direct route, over Au/CeO2 proceeds through the condensation route (Figure 2.6). For the condensation route to occur, a high surface NSB is necessary. In the case of Au/TiO2, PHA is rapidly formed from NSB, accumulates on the surface and is then transformed to ANL. With Au/CeO2, hydrogenation rate is considerably lower and the conversion NB NSB is slower, which leads to an accumulation of NSB and to the formation of condensation intermediates. These authors concluded that the support has a direct impact on the reaction mechanism and actively changes the reaction route.
Selective hydrogenation of NB over Ni/γ-Al2O3 was also studied, using different media (dense phase carbon dioxide, ethanol, n-hexane) [17]; it was found that conversion of NB was higher in CO2 than in ethanol and selectivity to ANL was almost 100%. This might be explained by the interactions of dense phase CO2 with reacting species (NB, NSB and PHA): NB reactivity is decreased while NSB is increased and the
NO2 + H2 - H2O NO + H2 NHOH Fast Step + 2 H2 - H2O - H2O + H2 Slowest Step NH2 NB NSB ANL PHA
transformation of PHA to ANL is likely promoted. Thus, hydrogenation of NB should occur through the direct hydrogenation route (NB NSB PHA ANL), being NB NSB the rate determining step. On the other hand, using a Pd based catalyst in supercritical carbon dioxide (scCO2), Chatterjee et al. [18] concluded that the most probable route to the ANL formation is (i) NB ANL (as no intermediate compounds was detected even in short reaction times) and (ii) NB PHA ANL (through some calculations of the initial rate of ANL formation from NSB and NB, NSB presented the slowest rate of hydrogenation indicating that it could not be the possible intermediate specie involved in the ANL formation).
In 2014, Rakitin et al. [19] investigated the catalytic hydrogenation of NB using Pd catalysts in a scCO2 medium and proposed a scheme for the catalytic process, shown in Figure 2.11, based on the analysis effectuated to the mixture of the hydrogenation reaction either using scCO2 or isopropanol.
Figure 2.11 - Scheme of NB catalytic hydrogenation in the presence of Pd-containing
heterogeneous catalyst, [19].
Pd/C catalyst was used as well to study the hydrogenation of NB in methanol [20]; according to the experimental results obtained and mechanistic considerations, an extended reaction scheme for NB hydrogenation to ANL was proposed, illustrated in Figure 2.12. NO2 NB [Cat] H2 NO NSB PHA ANL AZXB AZB [Cat] H2 NHOH [Cat] H2 NH2 [Cat] H2 N N O [Cat] H2 N N [Cat] H2 NH NH [Cat] H2 HZB
Figure 2.12 –Supplemented reaction mechanism for NB hydrogenation considering Haber’s and
Gelder’s reaction mechanism, proposed by Turáková et al. [20].
Turáková et al. through the analysis of catalytic results and taking into account both Figure 2.4 and Figure 2.8, concluded that the intermediate Ph-NOH condensates to AZXB, that is going to react with hydrogen chemisorbed on the metal surface and subsequently Ph-NOH and chemisorbed form of nitrene Ph-NH are formed. Ph-NH chemisorbs near a chemisorbed hydrogen atom and then is desorbed from the surface as ANL. Ph-NOH can again enter condensation reaction and therefore higher concentrations of AZXB, in comparison to AZB, were measured and its temporary accumulation in the reaction mixture was observed. Other way, PHA is not formed directly from NSB but is formed through Ph-NOH. Authors did not observed accumulation of HZB and so ANL formation via direct AZXB hydrogenolysis was hypothesized as the preferred reaction
NO2 NB NO NOH NHOH NH2 N N O NOH N N NH NOH NH2 NH2 NH + NSB PHA ANL AZXB AZB HZB NH NH ANL ANL
