Creation of a continuous process for bio-ethanol to butadiene conversion via the use of a process initiator

doi:10.1016/j.catcom.2013.10.015

Catalysis Communications

Volume 43, 5 January 2014, Pages 207-212

https://doi.org/10.1016/j.catcom.2013.10.015 Get rights and content

Highlights

•
Bio-ethanol feedstock for butadiene production
•
The use of a process initiator to achieve a continuous process
•
Catalyst synthesis method comparism

Abstract

One of the major constraints to the efficiency of Lebedev's process for butadiene production is the deposition of soot on the active sites of the catalyst which results to the reduction of catalyst activity and the periodic regeneration of catalyst thereby increasing time and energy spent on the process and subsequently, cost. The use of a process initiator has been found to be a possible solution to the above mentioned challenges. A synergetic effect was observed during the initiation of the catalytic process. Furthermore, the interdependence between the efficiency of the process initiator and the morphology of Al₂O₃, linear velocity of the feed stream and other process parameters was observed.

Introduction

Butadiene, which is an important building block for the chemical industry is produced by (1) pyrolysis of butane–butylene fraction of petroleum [1], (2) as a byproduct of ethylene production from steam crackers [2] and (3) combined process of ethanol dehydrogenation and dehydration (Fig. 1) [1].

Butadiene in the 1930s was produced by a one-step catalytic process of both dehydrogenation and dehydration in the Soviet Union [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14]. During the Second World War, about 60% of butadiene produced in the United States was via a two-step process commonly known as Ostromislensky process [15], in which ethanol is oxidized to acetaldehyde which then reacts with additional ethanol over a tantala-promoted silica catalyst to yield butadiene [16]

One-step process:T = 430–450 °C, ZnO/Al₂O₃2C₂H₅OH → CH₂ CH–CH = CH₂ + H₂ + 2H₂O.
Two-step process:C₂H₅OH → CH₃CHO + H₂C₂H₅OH + CH₃CHO → CH₂ = CH–CH = CH₂ + 2H₂O.

The mechanism of the ethanol to BD transformation is extremely complicated and is still a subject of debate. However, one generally accepts the involvement of the following principal steps [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30]:

Step 1
Production of acetaldehyde from ethanol under the influence of the dehydrogenating centers of the catalyst.C₂H₅OH → CH₃CHO + H₂
Step 2
Condensation of acetaldehyde to form aldol under the influence of the dehydrating sites of the catalyst.
Step 3
Dehydration of aldol to form crotonaldehyde
Step 4
Meerwein–Ponndorf–Verley reaction between crotonaldehyde and ethanol to obtain Crotyl alcohol and acetaldehyde.
Step 5
Formation of butadiene from Crotyl alcohol on the dehydrating sites of the catalyst.

Soot formation is one of the numerous side reactions that take place in the process of butadiene formation. It forms on the surface of the catalyst there by blocking the access to active sites. This process of soot formation results to the periodic regeneration of the catalyst in a stream of hot air as shown below:C + O₂ → CO₂ + Q2C + O₂ → 2CO + Q2CO + O₂ → 2CO₂ + Q.

The aim of this study was to achieve a continuous process void of catalyst regeneration and to show the correlation between the efficiency of the process initiator and the morphology of Al₂O₃, linear velocity of the feed stream, temperature and selectivity of the process.

Section snippets

Catalyst preparation

Catalysts were prepared mainly by mechanical mixing and impregnation based on the different morphologies of aluminium oxide i.e. gamma and alpha. Sample A was prepared by mechanical mixing of zinc oxide with γ-Al₂O₃, B by impregnation of γ-Al₂O₃ with mixed aqueous solution of aluminium and zinc nitrate and C by mechanical mixing zinc oxide with α-Al₂O₃.

Impregnation of γ-Al₂O₃ was carried out using mixed aqueous solution of aluminium and zinc nitrates at 80 °C for 2 h. The precursor samples were

Kinetic study of butadiene production process

For the purpose of convenience, the reaction routes presented below were used for the calculation of material balance and molar concentration.

1.
2C₂H₅OH = C₄H₆ + 2H₂O + H₂ (X₁)
2.
2C₂H₅OH = C₄H₈ + 2H₂O (X₂)
3.
C₂H₅OH = C₂H₄ + H₂O (X₃)
4.
C₂H₅OH = CH₃CHO + H₂ (X₄)
5.
2C₂H₅OH = C₄H₈O + H₂O + H₂ (X₅)

where X₁, X₂, X₃, X₄, and X₅ are the molar percents of the main products of the above reactions.

The main stoichiometric routes of the reaction process considered, in order to study the selectivity of the process are as follows:

I.
C₂H₅OH → C₂H₄ + H₂O
II.
C₂H

Results and discussions

It was observed that among the catalysts prepared by the above described methods, those prepared by impregnation with zinc nitrate showed the highest activity. The yield (based on reacted ethanol) and selectivity at optimal conditions for maximum activity of industrial samples of A, B and C are presented in the table below.

As shown in the table, it could be seen that the most effective is B. The addition of 1–1.5 % of the initiator in relation to the quantity of ethanol has a complex modifying,

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Short CommunicationCreation of a continuous process for bio-ethanol to butadiene conversion via the use of a process initiator

Highlights

Abstract

Introduction

Section snippets

Catalyst preparation

Kinetic study of butadiene production process

Results and discussions

Catal. today

Appl. Catal.

J. Catal.

Catal. Today

Energy Convers. Manage.

J. Catal.

Chem.-Biol. Interact.

Catal. Sci. Technol.

Zh. Org. Khim.

J. Gen. Chem.

Chem. Ztg.

J. Appl. Chem.

J. Appl. Chem.

Ind. Eng. Chem. Process. Des. Dev.

Ind. Eng. Chem.

Short Communication
Creation of a continuous process for bio-ethanol to butadiene conversion via the use of a process initiator