玉米秸秆连续氢解制备生物乙醇

doi:10.1016/S1872-2067(20)63709-3

摘要/Abstract

摘要：

目前由纤维素制生物乙醇的工艺主要由生物酶解法实现, 但酶解法的效率低且经济性差; 此外, 生物酶发酵每产生1 mol乙醇的同时副产1 mol CO₂, 导致原子经济性低. 本文开发了一种通过连续氢解玉米秸秆纤维素转化为高浓度生物乙醇(6.1%)的工艺. 首先使用绿色溶剂(80 wt% 1,4-丁二醇)在不破坏木质素结构的前提下, 提取玉米秸秆中的高纯度纤维素; 再在浆态床反应器中通过Ni-WO_x/SiO₂催化剂将10 wt%纤维素水悬浮液转化为多元醇混合物(其中乙二醇占比58%). 经过连续进样, 纤维素质量浓度累积达30 wt%, 乙二醇产物浓度达到17 wt%. 随后, 多元醇混合物被泵入固定床反应器进行选择性断C-O键反应, 在改进的水热稳定Cu催化剂上转化为乙醇(转化率75%, 选择性84%).

纤维素转化为生物乙醇的过程反应至少包含四步基元步骤. 首先, 在高温水热环境中纤维素水解为葡萄糖, 葡萄糖在WO_x表面经Retro-aldol反应C-C键断裂生成乙醇醛. 随后, Ni催化剂将乙醇醛加氢为乙二醇, 接着在固定床反应器上, 乙二醇在NiAu修饰的Cu⁺/Cu⁰活性位点上选择性断裂C-O键生成乙醇. 在乙二醇选择性氢解为乙醇过程中, 催化剂Au-Cu-Ni/SiO₂表现出优异的水热稳定性和活性. XRD结果表明, 金属Ni的引入有效地减小Cu纳米粒子的尺寸和增加Cu颗粒的分散, HRTEM图像更加直观的验证这一点. H₂-TPR结果发现, Ni的引入使CuO的还原温度提高了20 °C, 表明金属-载体的相互作用增强. 同时发现, 催化剂合成过程中氯金酸浸渍在还原后的CuNi/SiO₂催化剂的活性最高. 紫外吸收光谱表明, 溶液中的Au³⁺与催化剂表面的Cu发生置换反应, 而非单纯的附着于催化剂表面. CO-DRIFTS结果表明, 在Au修饰过的Cu-Ni/SiO₂表面使得Cu⁺-CO的红外吸收峰降低, 主要是由于Au部分覆盖催化剂表面Cu⁺吸附位点造成的. XPS结果表明, Au的引入使得催化剂表面的Cu⁺/Cu⁰不容易被空气氧化, 形成更为稳定的(Au-Cu⁺)-Cu⁰活性中心, 增强了催化剂Cu活性中心的水热耐受性. 本文提供了一条有竞争力的水相转化秸秆为高浓度生物乙醇的途径.

关键词: 玉米秸秆, 纤维素, 水相氢解, 生物乙醇, Ni-WO_x催化剂, Cu⁰-Cu⁺物种, C-C键断裂

Abstract:

Current bio-ethanol production entails the enzymatic depolymerization of cellulose, but this process shows low efficiency and poor economy. In this work, we developed a consecutive aqueous hydrogenolysis process for the conversion of corn-stalk cellulose to produce a relatively high concentration of bio-ethanol (6.1 wt%) without humin formation. A high yield of cellulose (ca. 50 wt%) is extracted from corn stalk using a green solvent (80 wt% 1,4-butanediol) without destroying the structure of the lignin. The first hydrothermal hydrogenolysis step uses a Ni-WO_x/SiO₂ catalyst to convert the high cumulative concentration of cellulose (30 wt%) into a polyol mixture with a 56.5 C% yield of ethylene glycol (EG). The original polyol mixture is then subjected to subsequent selective aqueous-phase hydrogenolysis of the C-O bond to produce bioethanol (75% conversion, 84 C% selectivity) over the modified hydrothermally stable Cu catalysts. The added Ni component favors the good dispersion of Cu nanoparticles, and the incorporated Au³⁺ helps to stabilize the active Cu⁰-Cu⁺ species. This multi-functional catalytic process provides an economically competitive route for the production of cellulosic ethanol from raw lignocellulose.

Key words: Corn-stalk, Cellulose, Aqueous-phase hydrogenolysis, Bio-ethanol, Ni-WO_x catalyst, Cu⁰-Cu⁺ species, C-C bond cleavage

褚大旺, 辛莹莹, 赵晨. 玉米秸秆连续氢解制备生物乙醇[J]. 催化学报, 2021, 42(5): 844-854.

Dawang Chu, Yingying Xin, Chen Zhao. Production of bio-ethanol by consecutive hydrogenolysis of corn-stalk cellulose[J]. Chinese Journal of Catalysis, 2021, 42(5): 844-854.

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链接本文: https://www.cjcatal.com/CN/10.1016/S1872-2067(20)63709-3

https://www.cjcatal.com/CN/Y2021/V42/I5/844

图/表 12

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Feedstock	Catalyst	Yield (%)
Feedstock	Catalyst	Cellulose	Lignin	Hemicellulose
Corn stalk	Blank	49.8	8.7	Dissolved
Corn stalk	0.1% NaOH	49.2	Dissolved	Dissolved
Corn stalk	0.5 g HUSY	46.2	7.2	Dissolved
Corn stalk	0.5 g ZSM-5	51.4	9.2	Dissolved
Corn stalk	0.1% HCl	35.0	6.6	Dissolved
Sawdust	Blank	51.9	18.8	Dissolved
Sawdust	0.1% HCl	10.0	19.1	Dissolved
Corn cob	Blank	53.3	6.6	Dissolved
Corn cob	0.1% HCl	24.6	14.7	Dissolved

Feedstock	Catalyst	Yield (%)
Feedstock	Catalyst	Cellulose	Lignin	Hemicellulose
Corn stalk	Blank	49.8	8.7	Dissolved
Corn stalk	0.1% NaOH	49.2	Dissolved	Dissolved
Corn stalk	0.5 g HUSY	46.2	7.2	Dissolved
Corn stalk	0.5 g ZSM-5	51.4	9.2	Dissolved
Corn stalk	0.1% HCl	35.0	6.6	Dissolved
Sawdust	Blank	51.9	18.8	Dissolved
Sawdust	0.1% HCl	10.0	19.1	Dissolved
Corn cob	Blank	53.3	6.6	Dissolved
Corn cob	0.1% HCl	24.6	14.7	Dissolved

Entry	Feedstock	Catalyst	Conc. (wt%)	Conv. (C %)	Yield (C %)
Entry	Feedstock	Catalyst	Conc. (wt%)	Conv. (C %)	EG	1,2-PDO	1,2-BDO	Sorbitol	Others
1	Cellulose	5%Ni-50%WO_x/SiO₂	1	100	30.3	2.3	2.7	3.2	9.1
2	Cellulose	10%Ni-50%WO_x/SiO₂	1	100	70.6	5.2	1.8	3.3	5.3
3	Cellulose	15%Ni-50%WO_x/SiO₂	1	100	72.0	4.1	3.6	5.8	7.1
4	Cellulose	25%Ni-50%WO_x/SiO₂	1	100	47.1	1.8	2.0	19.9	10.8
5	Cellulose	50%Ni-50%WO_x/SiO₂	1	100	33.8	2.0	3.3	28.3	12.5
6	Cellulose	15%Ni-50%WO_x/SiO₂	0.5	100	71.8	4.1	3.3	7.2	6.6
7	Cellulose	15%Ni-50%WO_x/SiO₂	5	100	70.5	5.4	6.6	3.6	6.0
8	Cellulose	15%Ni-50%WO_x/SiO₂	10	100	55.2	8.6	10.6	11.3	7.1
9	Cellulose *	15%Ni-50%WO_x/SiO₂	1	100	72.4	1.5	2.6	8.0	7.5
10	Cellulose *	15%Ni-50%WO_x/SiO₂	1	100	52.4	18.1	10.5	7.1	4.9
11	Cellulose *	15%Ni-50%WO_x/SiO₂	1	100	37.0	2.3	8.6	4.5	20.9

Entry	Feedstock	Catalyst	Conc. (wt%)	Conv. (C %)	Yield (C %)
Entry	Feedstock	Catalyst	Conc. (wt%)	Conv. (C %)	EG	1,2-PDO	1,2-BDO	Sorbitol	Others
1	Cellulose	5%Ni-50%WO_x/SiO₂	1	100	30.3	2.3	2.7	3.2	9.1
2	Cellulose	10%Ni-50%WO_x/SiO₂	1	100	70.6	5.2	1.8	3.3	5.3
3	Cellulose	15%Ni-50%WO_x/SiO₂	1	100	72.0	4.1	3.6	5.8	7.1
4	Cellulose	25%Ni-50%WO_x/SiO₂	1	100	47.1	1.8	2.0	19.9	10.8
5	Cellulose	50%Ni-50%WO_x/SiO₂	1	100	33.8	2.0	3.3	28.3	12.5
6	Cellulose	15%Ni-50%WO_x/SiO₂	0.5	100	71.8	4.1	3.3	7.2	6.6
7	Cellulose	15%Ni-50%WO_x/SiO₂	5	100	70.5	5.4	6.6	3.6	6.0
8	Cellulose	15%Ni-50%WO_x/SiO₂	10	100	55.2	8.6	10.6	11.3	7.1
9	Cellulose *	15%Ni-50%WO_x/SiO₂	1	100	72.4	1.5	2.6	8.0	7.5
10	Cellulose *	15%Ni-50%WO_x/SiO₂	1	100	52.4	18.1	10.5	7.1	4.9
11	Cellulose *	15%Ni-50%WO_x/SiO₂	1	100	37.0	2.3	8.6	4.5	20.9

Entry	Catalyst	Preparation method	Reaction time (h)	Conv. (C%)	Selectivity (C%)		Ethanol yield (C%)
Entry	Catalyst	Preparation method	Reaction time (h)	Conv. (C%)	Acetaldehyde	Ethanol	Ethanol yield (C%)
1	20%Cu/SiO₂	AE	3	13.4	24.6	34.3	4.6
2	20%Cu-2%Ni/SiO₂	AE	3	35.3	5.7	73.4	25.9
3	20%Cu-2%Ni/SiO₂	AE	10	62.3	7.1	76.1	47.4
4	20%Cu-2%Ni/SiO₂	HT	3	26.6	10.2	60.2	16.0
5	20%Cu-2%Ni/SiO₂	HT	10	55.2	3.4	77.4	42.7
6	20%Cu-2%Co/SiO₂	AE	3	30.7	7.2	67.1	20.6
7	20%Cu-2%Co/SiO₂	AE	10	49.8	5.0	65.3	32.5
8	20%Cu-2%Co/SiO₂	HT	3	24.7	8.1	59.1	14.6
9	20%Cu-2%Co/SiO₂	HT	10	55.0	6.0	72.4	39.8
10	20%Cu-2%Mo/SiO₂	HT	3	30.1	6.0	68.4	20.6
11	20%Cu-2%Mo/SiO₂	HT	10	60.7	7.6	74.3	45.1
12	20%Cu-2%B/SiO₂	HT	3	24.0	1.3	74.2	17.8
13	20%Cu-2%B/SiO₂	HT	10	47.4	2.1	78.1	37.0
14	1%Ag-20%Cu/SiO₂	AE^*	3	13.3	11.3	56.4	7.5
15	1%Au-20%Cu/SiO₂	AE^*	3	28.7	8.7	64.5	18.5
16	1%Ru-20%Cu/SiO₂	AE^*	3	21.2	23.6	51.4	10.9
17	1%Au-(20%Cu-2%Co)/SiO₂	AE^*	3	29.7	6.7	69.4	20.6
18	1%Au-(20%Cu-2%Ni)/SiO₂	AE^*	3	39.7	4.3	74.1	29.4
19	1%Au-(20%Cu-2%Ni)/SiO₂	AE^*	10	73.1	5.0	85.1	62.2