Upgrading Cracking Waste to Rubber Precursors via Oxidative Dehydrogenation

Abstract

As the result of process changes within an ethylene cracking plant, the amount of a C4 byproduct waste stream has significantly increased (Fabiano, Nedwick 1999). A system of extractive distillation and catalytic oxidative dehydrogenation can be used to add value to this C4 waste stream by producing high purity 1,3-Butadiene, an important rubber precursor. 1,3-Butadiene is a critical component of multiple consumer goods, including automobile tires and synthetic rubber, and has a steadily increasing demand, reaching 10 million metric tons in 2012 (Biddy, Scarlata, Kinchin, 2016). The simulation assumes a feed flow rate of 30,000 lb/hr of mixed low-grade fuel containing the composition provided in Table 1, with outputs of 16,900 lb/hr of 99% pure 1,3-Butadiene and 10,800 lb/hr of fuel byproduct. The fuel byproduct is mixed and sold under the same low-grade fuel rating the mixed feed was previously sold by.

Experimentation and Findings

There are many cost considerations when designing a new plant, or an addition to an existing process as is the case for this project. First, the cost and availability of raw materials must be evaluated. First, the annual cost for catalysts in this process would be $35,468. This value is an annual average since the catalyst is only replaced every five years. It also includes the cost of disposal for the catalyst. The cost of the feed is included even though it is a byproduct of ethylene cracking. The value of the feed is based on if it were sold as a low-grade fuel for $194/MT (EIA.gov, n.d.). DMF, used as the extragent for extractive rectification, is recycled but must be replenished over time. Based on a price of $740/MT, the annual cost of DMF was determined and is displayed in Table 27 (China, 2020).

Table 27: Annual raw material costs 

                                       Catalyst               FEED               DMF           

Annual Cost ($/yr):      35,468                 23,149,800     7,111,000 

The total raw material cost is $30,296,268/year. Next, the annual revenue from the product and byproduct streams is calculated. Table 28 shows the estimated annual revenue from each of the product streams. 99% 1,3-Butadiene is the primary product with a value of $496/MT (Echemi, n.d.). The three byproduct streams, PROPYNE, HEAVIES, and ISOBUTYL are assumed to be blended and sold as a low-grade fuel with a value of $194/MT (EIA.gov, n.d.). Hydrogen gas, mixed with air, is produced in the catalytic oxidative dehydrogenation reactor. The value of hydrogen was calculated assuming that it is burned to produce electricity. This process was not included in the PFD. 

Table 28: Annual revenue from product streams 

                                           PROPYNE         HEAVIES        ISOBUTYL         H2+AIR          1,3-BD 

Annual Revenue ($/yr):   159,728            611,932           7,594,677          1,351,983        33,261,755

The total annual revenue is $42,980,075/year. As stated in the assumptions, an interest rate of 7%, a tax rate of 35%, and a project life of 15 years is assumed. Other assumptions including the cost of land, working capital and cost of labor were made based on heuristics and can be found in Appendix A-4 (Demirel, 2019).

Publications, Papers, and Presentations

Upgrading Cracking Waste to Rubber Precursors via Oxidative Dehydrogenation 

(Senior Engineering Design Project)